BIOLOGICALLY IIMPORTANT COMPOUNDS IN SYNFUELS PROCESSES

BIOLOGICALLY IIMPORTANT COf4POUNDS I14 SYNFUELS PROCESSES*. 8. R. C l a r k , C.-h. Ho, W. H. G r i e s t , and 14. R. Guer in . A n a l y t i c a l Chemis t ry D i v i s i o n , Oak Ridge N a t i o n a l Labora-

Crude products, by-produc ts and wastes f rom s y n f u e l processes c o n t a i n a broad spec-

t o r y , P . 0. Box X, Oak Ridge, Tennessee 37830.

t rum o f chemical compounds--many o f wh ich a r e a c t i v e i n b i o l o g i c a l systems. which compound c l a s s e s a r e most i m p o r t a n t i s necessary i n o r d e r t o e s t a b l i s h e f f e c t i v e c o n t r o l over r e l e a s e o r exposure. a t e d PAH, p r imary a romat ic amines and N - h e t e r o c y c l i c PAH a r e s i g n i f i c a n t c o n t r i b u t o r s t o t h e o v e r a l l mutagenic a c t i v i t i e s o f a l a r g e number o f m a t e r i a l s examined. show t h a t t h e b a s i c , p r i m a r y a romat ic amine f r a c t i o n i s t h e most a c t i v e . a l k y l a t e d PAHs and N - h e t e r o c y c l i c PAHs a r e a l l components o f t h e n e u t r a l f r a c t i o n . n e a r l y a l l cases, t h e n e u t r a l f r a c t i o n s c o n t r i b u t e t h e l a r g e s t p o r t i o n o f t h e mutagenic a c t i v i t y , w h i l e t h e b a s i c p r i m a r y a romat ic amine f r a c t i o n s have t h e h i g h e s t s p e c i f i c a c t i v i t y . Neut ra l f r a c t i o n s a r e u s u a l l y t h e l a r g e s t ( w t x ) whereas t h e t o t a l b a s i c f r a c - t i o n s a r e m a l ? by comparison; thus , t h e o v e r a l l g r e a t e r c o n t r i b u t i o n o f t h e n e u t r a l f r a c t i o n t o t h e mutagenic a c t i v i t y o f most samples. i s o l a t e d i n p r e p a r a t i v e s c a l e amounts f r o m complex m i x t u r e s u t i l i z i n g combina t ions o f l i q u i d - l i q u i d e x t r a c t i o n and v a r i o u s 1 i q u i d chromatographic co lumn-e luent combina t ions . F r a c t i o n s a r e c h a r a c t e r i z e d u s i n g a combina t ion o f s p e c t r o s c o p i c techn iques and gas chromatography/mass spec t ro r re t ry . (*Research sponsored by t h e O f f i c e o f H e a l t h and Environmental Research, Cepartment o f Energy, under c o n t r a c t 1.1-7405-eng-26 w i t h t h e Union Carbide Corpora t ion . )

D i s c e r n i n g

P o l y c y c l i c a romat ic hydrocarbons (PAH), mu1 t i - a 1 k y l -

Ames t e s t da ta PAHs, m u l t i -

In

B i o l o g i c a l l y a c t i v e c o n s t i t u e n t s a r e

1

THE ELEMENTAL COMPOSITION OF SHALE OILS. J. P. Fox. Energy and Environment Divisiob Lawrence Berkeley Labora tory , Univers i ty of C a l i f o r n i a , Berkeley, CA 94720.

The abundance of 47 e lements were measured i n 1 2 s h a l e o i l s from LETC's cont ro l led- state retort, 7 s h a l e o i l s from LLL'S 125-kg s imula ted i n - s i t u r e t o r t and i n o i l s from t h e Geokine t ics , Occidenta l , Equi ty and Paraho processes us ing neut ron a c t i v a t i o n a n a l y s i s , x-ray f luo rescence spec t romet ry and Zeeman atomic abso rp t ion spec t roscopy. The elements s tud ied i n c l u d e C , H , N , A s , Se, Co, N i , Fe, Mn, Zn, U, C 1 , N a and o the r s . The r e s u l t i n g d a t a were analyzed t o de ta rmine t h e e f f e c t of r e t o r t ope ra t ing condi t ions on measured e lementa l abundances.

T h i s paper compares t h e e lementa l abundances i n o i l s from s imula ted , su r f ace and i n s i t u processes i n the framework of r e t o r t ope ra t ing cond i t ions and d i scusses t h e poten- t i a l environmental i m p l i c a t i o n s of observed t r a c e element p a t t e r n s . This i n v e s t i g a t i o n i n d i c a t e s t h a t t h e major elements i n s h a l e o i l s ( > l o ppm) a r e C , H , N , S , Fe, A s , C 1 and Na. The elements A l , B a , Co, C r , Cu, Hg, Mg, Mn, Mo, N i , Se, V and Zn OCCUK a t concen- t r a t i o n s of from 0 .1 ppm t o less than 10 ppm. A l l o t h e r elements s tud ied occured a t less than 0 .1 ppm i n most o i l s . abundances o f Antrim, Moroccan and Green River s h a l e o i l s .

S t r i k i n g d i f f e r e n c e s were observed between t h e e lementa l

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ANALYSIS OF ENERGY WASTE EFFLUENTS FOR ORGANIC CHEMICALS U S I N G THE MASTER ANALYTICAL SCHEXE. Linda Sheldon, S h i r l e y Yung, Roger Wiseman, Larry Michael, and Edo Pe l l iZZar i

Ana ly t i ca l Sc iences Div is ion , Chemistry and L i f e Sc iences Group, Research Tr i ang le I n s t i t u t e , P. 0. Box 12194, Research Tr i ang le Park, NC 27709.

A v a r i e t y of a n a l y t i c a l methods were t e s t e d dur ing the development of a comprehen- s i v e scheme to i d e n t i f y and q u a n t i t a t e v o l a t i l e o rgan ic chemicals i n aqueous samples us ing high r e so lu t ion gas chromatographylmass spectrometrylcomputer (GCI?fS/CO?P) a s the major a n a l y t i c a l t oo l . V o l a t i l e o rgan ic s a r e def ined a s those compounds which w i l l ei- t h e r e l u t e from a GC column a t 3OO9C i n one hour or less o r which may be d e r i v a t i z e d to meet these c r i t e r i a .

purge and t r a p procedure. t h e less v o l a t i l e (bp ,175'C) hydrophobic compounds. by ion exchange, then chemically d e r i v a t i z e d p r i o r t o gas chromatography. Las t ly , v o l a t i l e po la r organics were concent ra ted by f r a c t i o n a l d i s t i l l a t i o n . t o d i r e c t aqueous i n j e c t i o n , t h e d i s t i l l a t e was i n j e c t e d onto a Tenax GC precolumn through a hea ted i n j e c t i o n p o r t , t h e water vented , and t h e o rgan ic s were thermal ly desorbed i n t o a gas chromatograph. For energy waste e f f l u e n t s , methods which gave a minimum de tec t ion l i m i t o f 1 0 ppb wi th 40% recovery were considered accep tab le .

Developed methods were t e s t e d on a v a r i e t y of sp iked and unspiked sample waters i nc lud ing energy waste e f f l u e n t s . r e s u l t s w i l l be presented . This r e sea rch w a s supported by EPA Cont rac t No. 68-03-2704.

Highly v o l a t i l e (bp <175'C), hydrophobic compounds were analyzed us ing a modified Solvent e x t r a c t i o n wi th pH adjus tment served t o concen t r a t e

I o n i c o rgan ic s were concent ra ted

A s an a l t e r n a t i v e

S p e c i f i c problems wi th t h i s sample ma t r ix and t e s t

3

TRACE ELEMENT BEHAVIOR IN THE SOLVENT REFINED COAL PROCESSES. R . H. F i l b S. R. Kha l i l , * and M. L. Hunt. Nuclear Rad ia t i on Center, Washington d k i t y ,

Pullman, Washington 991 64.

High s u l f u r coa ls c o n t a i n s i g n i f i c a n t q u a n t i t i e s o f t r a c e metals which may have un- des i rab le e f f e c t s on l i q u e f a c t i o n processes, on upgrading o f de r i ved syncrudes, o r on the environment. A s tudy o f t he f a t e of up t o 35 t r a c e elements i n the SRC I and SRC I 1 processes by neut ron a c t i v a t i o n a n a l y s i s (NAA) and atomic absorp t ion spectroscopy (AAS) shows t h a t s i g n i f i c a n t emissions o f t o x i c elements f rom the F o r t Lewis, Washington 50 ton per day p i l o t p l d n t (opera ted by P i t t s b u r g & Midway Coal Min ing Co.) occur and tha t , except f o r Hg i n the SRC I1 process s a t i s f a c t o r y ma te r ia l balances can be ob ta ined f o r SRC I and SRC I1 processes. I n the case o f Hg i n the SRC I 1 process, and to a l esse r ex ten t As, Se and Sb, t r a n s p o r t v ia gaseous streams has been demonstrated and can be r e l a t e d t o t he v o l a t i l i t y and reac t i ons o f HgO, HgS, H2Se, AsO, e t c . The NAA and AAS techniques and t h e i r a p p l i c a t i o n to the complex ma t r i ces e n c o h t e r e d i n coal l ique fac- t i o n processes a r e discussed.

Present ly a t U n i v e r s i t y o f Kentucky

4

CHARACTERIZATION AND MUTAGENICITY OF SHALE OIL FRACTIONS, Deborah S. Sklarew, Donald M. Schoengold, R ichard A. P e l r o y t , S y l v i a P. Downey, Barbara A . Vieux, James T. Crestot , Phys ica l Sciences Dept. and B i o l o g y Oept. t , P a c i f i c Northwest

Labora tory , opera ted f o r t h e Department o f Energy by B a t t e l l e Memorial I n s t i t u t e

Product o i l s f rom severa l s h a l e o i l o p e r a t i o n s have been analyzed f o r o r g a n i c compounds wh ich a r e p o t e n t i a l biological/environmental hazards. Two f r a c t i o n a t i o n schemes have been compared bo th f rom an a n a l y t i c a l and a b i o l o g i c a l p o i n t o f v iew. The f i r s t method i n v o l v e s ac id -base f r a c t i o n a t i o n ; t h e second uses p a r t i t i o n chromatography on Sephadex LH-20. F r a c t i o n s have been t e s t e d f o r m u t a g e n i c i t y i n the Ames assay and those which gave p o s i t i v e r e s u l t s were f u r t h e r subd iv ided and analyzed by gas chromatography-mass spec t romet ry . I n t h e case o f t h e Sephadex LH-20 method, m u t a g e n i c i t y i s concent ra ted i n t h e methanol f r a c t i o n s ; i n t h e acid-base separa t ion , m u t a g e n i c i t y i s f o u n d i n t h e b a s i c and t a r f r a c t i o n s .

5

COMPARISON AND CONTRAST OF TRACE ELOIENTS IN C R U D E SHALE OILS AND PETROLEUM C . L . Wilkerson, D . 5 . Sklarew, J . C . Evans and J . S. Fruchter ,Pacif ic Flortliwest

Laboratory, Richland, WA 99352

The abundances and chemical forms of a large group of elements including t h e t race metals A s , Co, Fe, Elo, Ni, Se, V and Zn were determined i n three whole and fract ionated shale o i l s obtained from Colorado and Utah o i l shale reserves. The crude shale o i l s were rep- resentat ive product o i l s from a n above-ground, a modified in-s i tu , and a t r u e in-s i tu re tor t ing process and were produced by p i l o t p lant or larger sized f a c i l i t i e s . t a l abundances were determined by several modern analyt ical techniques including instru- mental neutron ac t iva t ion ana lys i s , energy dispers ive X-ray fluorescence ana lys i s , prompt y-ray ac t iva t ion ana lys i s , and plasma emission spectrometry. compared to ident i fy major differences between elemental par t i t ioning y i e l d s of the various retor t ing technologies and were fur ther compared and contrasted with reported elemental concentrations i n petroleum. The elements As and Fe were found t o be the most prominent t race metals i n the shale o i l m a t r i x and As and Se leve ls were observed to be 1 to 2 orders of magnitude grea te r than those reported f o r petroleum.

Elemen-

The analyses were

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ENVIRONMENTAL ORGANIC CHEMISTRY: THE ISOLATION AND IDENTIFICATION OF ORGANIC AXD ORGANOMETALLIC COMPOUNDS FROM OIL SHALE RETORT WATERS.* J. Kland. Energy and Environment Division, Lawrence Berkeley Laboratory, University of California, Berkeley, CA 94720.

The complex nature of the inorganic, organic and organometallic contaminants found i n

Richard H. Fish and Mathilde

oil shale retort waters is important to elucidate in order to evaluate the potential problems connected with the release of these compounds to the environment.

Our efforts have focused on more clearly defining the organic and the organometallic species, either synth.xized o r released during the retorting process, that eventually end up in the retort waters. Retort waters from LLL and LETC simulated in situ retorts and from Occidental's Logan Wash experiments were extracted with methylene chloride and the components separated and analyzed by a combination of dry column, thin layer and high performance liquid chromatography as well as capillary gas chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy.

A discussion of the classes of organic and organometallic species identifed, together with some of their toxicological and environmental implications, will be presented.

C + . . r l l - ~ SuDDorted through the Department of Energy under contract no. W-7405-ENG-48.

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INTERLABORATORY COMPARISON OF ENVIRONMENTAL ANALYSES ASSOCIATED W I T H SYNFUEL PRODUCTION, W. E . Play, J. M. Brown, S . N . Ches le r , F. R . Guenther, H . S . Hertz ,

L. R. H i l p e r t , R. Pi. P a r r i s , K . L . R i t ch ie , and S . A . Wise, Center f o r Ana ly t i ca l Chemis- t r y , National Bureau of Standards , Washington, DC 20234

In order t o begin eva lua t ing t h e s t a t e -o f - the -a r t of t h e de te rmina t ion of p o l l u t a n t s a s soc ia t ed wi th t h e product ion of a l t e r n a t e f u e l s , seven c o l l a b o r a t i v e s t u d i e s have been conducted by NBS. The aim of the f i v e i n i t i a l s t u d i e s w a s t o a s c e r t a i n how we l l p a r t i c i p a t i n g l a b o r a t o r i e s could p e r f o m the f i n a l q u a n t i t a t i o n s t e p i n a t r a c e o rgan ic a n a l y t i c a l scheme. The m a t e r i a l s examined in t hese i n i t i a l s t u d i e s were two polynuclear a romat ic hydrocarbon in hexane samples, a phenols i n water sample, a phenols i n hexane sample and a N-heterocyclic compounds (azaarenes) i n hexane sample. Each of t hese samples conta ined between f i v e and e i g h t pure compounds, w i th each compound being p resen t a t t h e 1-100 pg/mL (ppm) l e v e l .

The l a s t two c o l l a b o r a t i v e s t u d i e s involved quan t i a t i ave ana lyses of s e l e c t e d phenols, polynuclear a romat ic hydrocarbons and N-heterocycl ics i n a s h a l e o i l and a so lven t r e f ined c o a l (SRC) material. t h r e e s t eps : (1) I s o l a t i o n of t h e a n a l y t e from t h e sample ma t r ix ; (2) Separa t ion of t h e ana ly t e from non-ana ly te i n t e r f e r e n c e ; (3 ) measurement of de t ec to r response f o r t h e ana ly t e and r e l a t i n g t h a t t o t h e concen t r a t ion of the a n a l y t e i n t h e o r i g i n a l sample. The r e s u l t s of t h e s e c o l l a b o r a t i v e s t u d i e s w i l l be repor ted and d iscussed a long wi th methodologies developed a t NBS f o r c e r t i f y i n g the concent ra t ion of s e l ec t ed phenols, PAH and N-heterocylces i n a l t e r n a t e f u e l s .

Such ana lyses usua l ly requi red a minimum of

ANALYSIS OF SULFUR HETEROCYCLES I N COAL-DERIVED PRODUCTS AND SHALE OILS? C. W i l l e l M. Iwao, T. A . Broadbent, R. N. Cast le, and M. L . Lee, Department o f Chemistry,

Brigham Young Un ive rs i t y , Provo, Utah 84602.

The carc inogen ic a c t i v i t y demonstrated by complex m ix tu res o f p o l y c y c l i c a romat ic compounds (PAC) has s t imu la ted much e f f o r t by researchers t o i d e n t i f y i n d i v i d u a l mixturc components. f rac t i ons from coa l -der ived products and sha le o i l s a re the s u l f u r he te rocyc les . t o t h e i r low concent ra t ions , an enr ichment o f t he he te rocyc l i c s u l f u r compounds i s necessary f o r i d e n t i f i c a t i o n . A r e c e n t l y developed method t o i s o l a t e the s u l f u r he terocyc le f r a c t i o n f rom a composite aromat ic f r a c t i o n has g r e a t l y a ided e f f o r t s t o separate and i d e n t i f y i n d i v i d u a l h e t e r o c y c l i c s u l f u r compounds by g lass c a p i l l a r y gas chromatographic mass spec t romet ry .

and i d e n t i f i c a t i o n o f s u l f u r he terocyc le f rac t i ons has been app l i ed t o se lec ted coa l g a s i f i c a t i o n t a r s , coa l l i q u i d s , and sha le o i l s . I d e n t i f i c a t i o n was accomplished through comparison o f mass spec t ra l and chromatographic r e t e n t i o n da ta o f m ix tu re components H i t h standard re fe rence compounds.

Since few standard re fe rence compounds o f s u l f u r he terocyc les a re commercial ly ava i l ab le , compounds p red ic ted by mass spectrometry t o be present i n enr iched s u l f u r he terocyc le f r a c t i o n s were synthesized. g raph ic r e t e n t i o n da ta and f o r b i o l o g i c a l t e s t i n g .

and Environmental Research, Cont rac t No. DE-ACOZ-79EV10237.

Found i n low concent ra t ions among the m ix tu re components o f most PAC Due

I n t h i s study, the developed methodology f o r t he enr ichment and subsequent separa t i on

These compounds were used t o o b t a i n chromato-

*This s tudy was supported by the U . S . Department o f Energy, D i v i s i o n o f Biomedical

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THE IIQR(Tp CF "NO A C I M " . J. G. Seay, - t i t U t e Of G3S T&lxlOkX~y, 3436 S. S t a t e St. Chicago IL 60616.

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1 5

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TRANSPORTATION FUEIS F R O M SYNTHESIS GAS. R. H . F i s c h e r and R . E . Hi ldebrand. U.S. Department of Energy O f f i c e of F o s s i l ElleKgy rograms, D i v i s i o n o f F o s s i l F u e l

ABSTRACT Process ing , Mail s t o p E - j 3 8 / G e n ~ n t o w n , Washington: 20545.

The Department of Energy (WE) h a s formulated a program t o deve lop improved p r o c e s s e s t o c o n v e r t s y n t h e s i s g a s f rom c o a l t o q u a l i t y t r a n s p o r t a t i o n f u e l s . f o u r e l emen t s .

The program i n v o l v e s

Improved i n t e g r a t i o n of g a s i f i c a t i o n with l i q u e f a c t i o n . T h i s i n v o l v e s the use of low r a t i o H2 t o CO s y n t h e s i s g a s i n t h e hydrocarbon fo rma t ion s t e p . can be conve r t ed t o hydroca rbon by means o f t h e Ko lbe l -Enge lha rd t r e a c t i o n . The n e t r e s u l t i s c o n s i d e r a b l e ene rgy s a v i n g s i n s t eam. Improved s e l e c t i v i t y b u s e of shape s e l e c t i v e c a t a l y s t . Normal F i sche r -Tropsch re- a c t i o n c h e m i s t r y i s s u g j e c t t o i n h e r e n t l i m i t a t i o n s due t o t h e c h a i n growthmechanisms. Use o f shape s e l e c t i v e c a t a l y s t s c a n r e s u l t i n c i r cumven t ion of t h i s l i m i t a t i o n by t h e u s e o f a n i n t e r m e d i a t e t h a t can be formed i n h i g h s e l e c t i v i t y (meihanol) or by i n h i b i -

Low r a t i o H2 t o CO

t i o i

The i n i t i a l c o n t r a c t s i n t h i s program a r e abou t t o be s i g n e d and o t h e r s are beginning n e g o t i a t i o n . The g o a l s o f t h e program and t h i s up coming work w i l l be d i s c u s s e d .

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EVIDENCE FOR ADSORBED HYDROCARBON INTERMEDIATES DURING THE INITIAL STAGES OF CO HYDROGENATION ON IRON

H.P. Bonze1 and H.J. Krebs

Institut fur Grenzfllchenforschung und Vakuumphysik, Kernforschungsanlage Julich, D-5170 Jiilich, Germany

1. Introduction Surface science techniques have been applied to the study of the surface

properties of the transition metals Fe, Co, Ni and Ru /1-12/ and it is natural to extend the same approach to the study of Fischer-Tropsch synthesis (FTS) reactions on the same metal surfaces. However, reaction products in the adsorbed or gaseous phase apparently cannot be detected under vacuum conditions. There- fore, in order to utilize surface analytical techniques for the study of FTS, a combination of a surface analysis ultra-high vacuum system and an atmospheric reaction chamber has to be used, such as pioneered by Somorjai and coworkers /13, 141.

In this paper we report on the use of such a combination apparatus of novel design with Auger electron (AES) and X-ray photoelectron spectroscopy (XPS) as analytical capabilities and a differential microreactor. The analysis of the reaction products is performed by gas chromatography (GC). Using this system we studied the hydrogenation of CO on polycrystalline iron foils and a Fe(ll0) single crystal at a total pressure of 100 kPa (= 1 bar 1 atm) / 15 / .

2. Experimental

ultra-high-vacuum (UHV) chamber pumped by an ion pump, and an attached sample transfer system containing a small micro-reactor. The UHV chamber shown on the left hand side of Fig. 1 operates at a base pressure of 1 x lo-' Pa. This system (Leybold-Heraeus) features an ion sputter gun for surface cleaning, an electron gun, X-ray sour.ce and high resolution electron spectrometer for Auger electron (AES) and photoelectron (XPS) spectroscopies, and a quadrupole mass spectrometer for residual gas analysis. The sample is either a polycrystalline iron foil about 0.1 nun thick, or a Fe(ll0) single crystal, with an active area of 0.35 cm2. It is situated at a cutout portion of a stainless steel rod of 2 cm diameter. This rod serves as a transfer mechanism between UHV chamber, micro-reactor and atmosphere. The Fe sample can be heated resistively up to 1400 K in vacuum and about 900 K in 100 kPa of a H,/CO mixture. The temperature of the sample is measured by a sheathed Chromel-Alumel thermocouple attached to the underside of the sample.

sample transfer system, Fig. 1. A mixture of CO and H, was passed continuously through this reactor at a rate of 50 cm3/min. The partial pressure ratio of CO to H, was fixed by adjusting the individual flow rates of these two gases before entering the mixing stage. Partial pressure ratios of CO to H, from 1:lOO to 1 : 4 could be easily chosen.

The transfer of the Fe-foil from the UHV system into the micro-reactor was accomplished by pulling the sample rod until the sample was located inside the reactor. The sample could be moved to the atmospheric loading position i n a similar way, and also back into the UHV chamber. The transfer time from the reactor into the UHV position including pump-down to Pa was 45 seconds. The sample rod itself is water cooled such that during heating of the Fe sample inside the micro-reactor no parts other than the sample and the tip of the thermocouple get hot. During the catalytic rate measurements the hydrocarbon products were analyzed by gas chromatography. A 0.5 cm3 sample (loop volume) of the gas mixture was taken by the GC sample valve and passed over a 8 ft. Porapak Q column. The separated products were analyzed by a flame ionization detector.

The experimental system, sketched in Fig. 1, consisted of a stainless steel

The micro-reactor of about 4 cm' total volume is a small section of the

The Fischer-Tropsch measurements were carried out in the following way: The

19

c leaned F e sample w a s t r a n s f e r e d from UHV i n t o t h e micro- reac tor where a s teady s t a t e gas f low was a l r e a d y e s t a b l i s h e d . As soon a s t h e sample came t o a h a l t , t h e tempera ture was r a i s e d t o t h e d e s i r e d v a l u e a s measured by t h e thermocouple. From t h i s p o i n t on t h e t i m e was measured and GC samples were taken p e r i o d i c a l l y . A t a l a te r time t h e r e a c t i o n was s topped by t u r n i n g o f f t h e h e a t i n g c u r r e n t . About 4 s e c l a t e r t h e sample was t r a n s f e r e d back t o UHV f o r s u r f a c e a n a l y s i s by AES o r XPS . 3 . R e s u l t s and D i s c u s s i o n

The measurements of FTS from CO and H, on Fe were c a r r i e d o u t a t a t o t a l p r e s s u r e of 100 kPa (=1 a t m ) and CO/H, r a t i o s of 1:100, 1:20 and 1:4. The tempe- r a t u r e range i n v e s t i g a t e d w a s 460-750 K. I n a l l c a s e s methane was t h e dominant product and i t s r a t e of f o r m a t i o n t i m e dependent . In o r d e r t o check t h i s time dependence, a s e r i e s of GC r e a c t i v i t y measurements wi th a c y c l e of approximately 100 s e c was c a r r i e d o u t at t h e same tempera ture . Three examples of such curves are shown i n Fig. 2 f o r a CO/H, r a t i o of 1:20 and d i f f e r e n t tempera tures where t h e l o g a r i t h m of t h e t u r n o v e r number f o r methane i s p l o t t e d as a f u n c t i o n of t ime. These curves e x h i b i t s e v e r a l i n t e r e s t i n g f e a t u r e s : F i r s t , t h e r e i s a s t r o n g r i se i n t h e methane rate of f o r m a t i o n w i t h i n t h e f i r s t 40-60 s e c a f t e r reaching t h e r e a c t i o n t e m p e r a t u r e . T h i s r i se s i g n a l s t h e start of t h e r e a c t i o n , and t h e appa- r e n t de lay of about 30 s e c p r i o r t o t h e r i s e (which i s more obvious i n a l i n e a r p l o t of r a t e v e r s u s t i m e ) r e p r e s e n t s t h e t ime i t t a k e s f o r t h e gas t o f low from t h e r e a c t o r t o t h e GC sampling v a l v e . Second, t h e r e i s a maximum i n t h e r a t e of methane f o r m a t i o n f o l l o w e d by a s teady d e c l i n e ; bo th t h e p o s i t i o n of t h e maximum and t h e s l o p e of t h e d e c l i n e depend on t h e tempera ture of t h e F e - f o i l and the CO/H, r a t i o .

The occurence of t h e maximum i n t h e s e curves of F i g . 2 is connected wi th t h e known pehnomenon of carbon accumulat ion on t h e Fe s u r f a c e a s a f u n c t i o n of t i m e / 1 4 , 1 5 / . The r a t e of carbon accumulat ion is f a s t e r , t h e h i g h e r t h e tempera ture o r t h e h i g h e r ‘ the r a t i o of CO/H,. However, t h e i n f l u e n c e of t h e r a t e of carbon accumula t ion o n t h e rate of CO hydrogenat ion i s complicated due to d i f f e r e n t kinds of chemica l ly bound carbon. We have measured t h e r e l a t i v e carbon c o n c e n t r a t i o n by XPS and p r e s e n t as a n example t h e d a t a i n Fig. 3. This f i g u r e shows t h e carbon ( I s ) s i g n a l at d i f f e r e n t r e a c t i o n times f o r s imilar exper imenta l c o n d i t i o n s a s t h o s e of F i g . 2 . In t h e s e experiments t h e Fe sample w a s moved i n t o t h e micro- r e a c t o r for r e a c t i o n f o r a s h o r t t ime, t h e n i n t o t h e UHV chamber f o r s u r f a c e (AES o r XPS) a n a l y s i s , and back i n t o t h e r e a c t o r f o r a c o n t i n u a t i o n of t h e r e a c t i o n .

The d a t a i n F i g . 3 i l l u s t r a t e t h e r a p i d i n c r e a s e i n s u r f a c e carbon concen- t r a t i o n a s a f u n c t i o n of t h e r e a c t i o n t ime and a l s o a s h i f t i n t h e b i n d i n g energy EB of the C l s l e v e l from about 283.9 eV t o 284.6 e V . F i g u r e 4a shows t h e s h i f t i n EB(CIS) v e r s u s t ime f o r a p a r t i c u l a r r u n a t 530 K and CO/H, = 1:20. F i g u r e 4b Shows the cor responding i n t e g r a t e d C I S peak a r e a v e r s u s time. Note i n F igs . 4a and 4b t h a t t h e i n i t i a l change i n t h e p l o t t e d q u a n t i t i e s , i .e . dur ing t h e f i r s t 50 sec, is very r a p i d fo l lowed by a s lower i n c r e a s e . It i s tempt ing t o a s s o c i a t e t h i s behaviour w i t h t h e p r e s e n c e of d i f f e r e n t chemical carbonaceous s p e c i e s on t h e i r o n s u r f a c e and w i t h t h e r a t e of CHr format ion .

i n g t h e chemical n a t u r e o f t h e carbonaceous s u r f a c e phases a f t e r t h e CO/H, reac- t i o n . The procedure c o n s i s t s e s s e n t i a l l y i n comparing t h e carbon Auger peak shapes and C l s b i n d i n g e n e r g i e s of carbonaceous s u r f a c e l a y e r s of known chemical o r i g i n (composi t ion) w i t h t h o s e of t h e s u r f a c e phases genera ted by t h e hydrogena- t i o n of CO.

Therefore we performed a number of exper iments which were aimed a t i d e n t i f y -

‘ I

A t o t a l of t h r e e s i g n i f i c a n t l y d i f f e r e n t carbonaceous l a y e r s were observed a f t e r t h e hydrogenat ion r e a c t i o n . F i g u r e 5 shows t h e carbon Auger s p e c t r a of t h e s e t h r e e l a y e r s which we c a l l t h e s u r f a c e phases I , I1 and 111, r e s p e c t i v e l y . These s p e c t r a were obta ined f o r CO/H, = 1:20. In comparing t h e Auger s p e c t r a of Fig. 5 o n e should i n p a r t i c u l a r pay a t t e n t i o n t o t h e r e l a t i v e h e i g h t s of t h e peaks la - b e l l e d A, B and c. Other d i f f e r e n c e s can be noted i n t h e n e g a t i v e peak excurs ion a t 2 7 0 - 285 e V . These, however, w i l l no t be r e f e r r e d t o i n t h i s paper .

20

The carbon 1s s p e c t r a cor responding t o t h e AES s p e c t r a i n F i g . 5 showed d i f - f e r e n t b inding e n e r g i e s s i m i l a r t o t h o s e of F i g . 3 . These measured Cls b i n d i n g e n e r g i e s are l i s t e d in Table I t o g e t h e r wi th t h e d a t a f o r adsorbed a c e t y l e n e , segrega ted c a r b i d i c and g r a p h i t i c carbon.

Table I Cls Binding Energ ies

I Species I Binding Energy (eV) I

i n UHV

g r a p h i t i c C 285.0

a f t e r r e a c t ion

Phase I-CHx 283.9

Phase I1 284.2

Phase 111 284.7

Surface phase I The Cls b inding e n e r g i e s of t h i s s u r f a c e phase and chemisorbed molecular

a c e t y l e n e a r e i d e n t i c a l w i t h i n experimental e r r o r . T h i s f a c t s u g g e s t s t h a t s u r - f a c e phase I i s a h e a v i l y hydrogenated carbon l a y e r . A comparison o f Auger d a t a , F i g . 6 , shows, however, a s u b s t a n t i a l d i f f e r e n c e f o r s u r f a c e phase I and ace ty- l e n e . On t h e o t h e r hand, a very good s i m u l a t i o n of t h e s u r f a c e phase I Auger spectrum i s obta ined when a c a r b i d i c s u r f a c e carbon produced i n UHV by h e a t i n g t h e sample t o 720 K f o r about 2 min i s exposed t o C,H, a t 400 K f o r 5 min ( 2 X

lo-’ Pa) . It is l i k e l y t h a t under t h e s e c o n d i t i o n s some decomposi t ion of C,H, in - t o CH s p e c i e s w i l l occur /16,17/ . We propose t h e r e f o r e t h a t t h e s u r f a c e phase I c o n s i s t s mainly of c a r b i d i c carbon and CH s p e c i e s .

S u r f a c e phase I1

be i d e n t i c a l t o t h e spectrum of c a r b i d i c carbon segrega ted under UHV c o n d i t i o n s . However, t h i s i s n o t t h e case. F i g u r e 7 shows both s p e c t r a f o r a d i r e c t comparison, and i t can be noted t h a t t h e peaks B and C of t h e s e two s p e c t r a a r e s h i f t e d a g a i n s t each o t h e r by about 2 e V . The reason f o r t h i s s h i f t i s presumably bonded hydrogen i n t h e c a s e of t h e s u r f a c e phase 11, a s expected from t h e s h i f t of 0 .9 e V f o r t h e C l s s p e c t r a of UHV c a r b i d i c carbon and s u r f a c e phase I1 carbon ( s e e Table I ) . The f a c t t h a t some hydrogen is necessary i n o r d e r t o g e n e r a t e t h e Auger peak of s u r f a c e phase I1 i s i l l u s t r a t e d by t h e fo l lowing experiment: F e ( l l 0 ) wi th segrega ted c a r b i d i c carbon was exposed t o C,H, a t 475 ( 2 x Auger spectrum taken subsequent ly i s shown a s t r a c e (c ) i n F i g . 7 and i t has fea- t u r e s i d e n t i c a l t o t h o s e of t h e s u r f a c e phase I1 spectrum.

The amount of bonded hydrogen i n t h e s u r f a c e phase I1 i s presumably l e s s t h a n i n t h e CHx l a y e r , mainly f o r two reasons : (1) There is no shape change i n t h e Auger peak r e l a t i v e t o c a r b i d i c carbon, o n l y an e n e r g e t i c s h i f t ; ( 2 ) t h e procedure of s i m u l a t i n g phase I1 i n v o l v e s a n C,H, exposure a t h i g h e r tempera tures (475 K compared t o 400 K f o r CHx s i m u l a t i o n ) f a c i l i t a t i n g t h e dehydrogenat ion of C,H,. The s u r f a c e phase I1 can thus be c h a r a c t e r i z e d a s a c a r b i d i c carbon l a y e r w i t h bonded hydrogen.

A t f i r s t s i g h t t h e Auger spectrum of s u r f a c e phase 11, Fig. 5, appears t o

P a , 5 min). The

Surface phase 111 The carbon Auger peak of t h e s u r f a c e phase 111 h a s a g r e a t s i m i l a r i t y w i t h - - -

t h a t of g r a p h i t i c carbon /18,19/ . F i g u r e 8 shows an Auger ’ t race of g r a p h i t i c

2 1

carbon on F e ( l l 0 ) which was segrega ted t o t h e s u r f a c e by h e a t t r e a t i n g t h e crys- t a l i n ,WV ( 6 2 5 K , 2 5 min). Looking a t t h e r e l a t i v e peak h e i g h t s A , B and C one can n o t i c e t h e same sequence a s i n t h e spectrum of phase 111. I n a procedure equi- v a l e n t to t h o s e d i s c u s s e d i n t h e prev ious s e c t i o n s we c a n a l s o produce a phase 111 t y p e carbonaceous l a y e r by exposing t h e Fe c r y s t a l wi th c a r b i d i c carbon t o C,H, a t about 580 K ( 2 X a s t r a c e (b) i n F ig . 8. For comparison t h e phase I11 peak i s inc luded a s t r a c e ( c ) . A l l t h r e e t r a c e s ( a ) - (c ) have v e r y s i m i l a r shapes but from a c l o s e r in- s p e c t i o n of t h e e n e r g e t i c p o s i t i o n s of t h e peaks it is apparent t h a t peak B f o r t h e t r a c e s (b) and ( c ) i s s h i f t e d t o lower k i n e t i c e n e r g i e s r e l a t i v e t o t h a t of trace (a) . S i n c e b o t h l a y e r s c h a r a c t e r i z e d by (b) and ( c ) a r e o r i g i n a t i n g from gas phase r e a c t i o n s i n v o l v i n g hydrogen, i t i s reasonable t o assume t h a t t h i s peak s h i f t i s i n d i c a t i v e of bonded hydrogen.

Hydrogenation behavior An i n t e r e s t i n g o b s e r v a t i o n was made when t h e v a r i o u s carbonaceous l a y e r s

were s u b j e c t e d to hydrogen atmosphere a t e l e v a t e d tempera ture . It was s e e n t h a t t h e CH, l a y e r and t h e hydrogen c o n t a i n i n g c a r b i d i c carbon l a y e r (phases I and 11, r e s p e c t i v e l y ) could be r e a d i l y removed by hydrogenat ion b u t t h a t t h e g r a p h i t i c l a y e r was q u i t e i n e r t towards H,. An example of a hydrogenat ion of a mixed phase I I / p h a s e I11 l a y e r i s p r e s e n t e d i n Fig. 9. The t o t a l amount of carbon i s seen t o d e c r e a s e b u t t h e b i n d i n g energy s h i f t from 284.4 e V t o 284.9 eV i n d i c a t e s t h a t c a r b i d i c carbon (phase 1 1 ) i s removed and g r a p h i t i c carbon l e f t behind on t h e s u r f ace.

The f a s t hydrogenat ion of s u r f a c e phases I and I1 r e l a t i v e t o the much slow- e r removal of small amounts of g r a p h i t i c carbon c r e a t e s a p o s s i b i l i t y t o s e p a r a t e t h e d i f f e r e n t phases i n a mixed l a y e r . Experiments of t h i s k ind showed t h a t t h e t o t a l amount of carbon p l o t t e d f o r example i n F i g . 4b could be broken up i n t o a p o r t i o n r e p r e s e n t i n g CH, and c a r b i d i c carbon and a p o r t i o n r e p r e s e n t i n g g r a p h i t i c carbon. The f i r s t p o r t i o n p l o t t e d v e r s u s t ime y i e l d s a maximum a t about 30-50 s e c similar t o t h e maximum i n F i g . 2 . The second p o r t i o n , g r a p h i t i c carbon, in- c r e a s e s s t e a d i l y w i t h t ime. We conclude t h a t t h e maximum i n r e a c t i v i t y i s l i n k e d t o t h e maximum i n CHx and c a r b i d i c carbon on t h e s u r f a c e whereas t h e g r a p h i t i c carbon a c t s as an i n h i b i t o r on t h e methanat ion a s w e l l a s t h e Fischer-Tropsch re- a c t i o n .

Pa, 20 m i d . The Auger peak of t h i s l a y e r i s shown

4 . Conclusions 1 . Layers of (UHV s e g r e g a t e d ) c a r b i d i c and g r a p h i t i c carbon, molecular ly ad-

sorbed CO and C,H, c a n b e f a i r l y w e l l c h a r a c t e r i z e d by t h e i r r e s p e c t i v e carbon Auger peak f i n e s t r u c t u r e and C ( l s ) b inding e n e r g i e s .

2 . Carbonaceous l a y e r s d e p o s i t e d by t h e CO hydrogenat ion r e a c t i o n a t 1 b a r were analyzed by AES and XPS and could be c l a s s i f i e d by a comparison of carbon Auger l i n e shapes and C ( t s ) binding e n e r g i e s wi th t h o s e of l a y e r s of known chemica l composi t ion.

3 . A carbonaceous l a y e r of p a r t i c u l a r i n t e r e s t formed i n t h e i n i t i a l phase of CO hydrogenat ion on F e ( l l 0 ) w a s found t o correspond t o h e a v i l y hydrogenated c a r b i d i c carbon, most l i k e l y a CHx phase. T h i s phase i s sugges ted t o c o n s i s t mos t ly of CH r a d i c a l s .

4 . The CHx phase and c a r b i d i c carbon can be e a s i l y removed from t h e s u r f a c e by hydrogenat ion; g r a p h i t i c carbon i s q u i t e s t a b l e towards hydrogen a t 1 b a r and e l e v a t e d tempera tures .

maximum i n CHx and c a r b i d i c carbon; t h e s e l a t t e r s p e c i e s a r e impor tan t interme- d i a t e s f o r t h e f o r m a t i o n of methane and probably h i g h e r molecular weight pro- d u c t s .

5. The maximum i n t h e t i m e dependent methanat ion r a t e c o r r e l a t e s wi th t h e

22

References

I l l K. Kish i and M.W. Rober t s , J. Chem. SOC. Faraday Trans. 1 2 ( 1 9 7 5 ) 17 / 2 / R.W. Joyner and M.W. Rober t s , J . Chem. SOC. Faraday Trans. I lo (1974) / 3 / K.Y. Yu, W.E. S p i c e r , I . Lindau, P. P i a n e t t a and S.F. L i n , S u r f a c e S c i

(1976) 157 141 151 161 I 7 1 181

I 9 1 I 1 0 1 I 1 1 1 1121 1131 I 1 4 1

I 1 5 1 I 1 6 1 1171 I 1 8 1 I 1 9 1

. . .. C.R. Brundle, I B M J. R e s . Develop 11 (1978) 235 G . BrodLn, G. Gafner and H.P. Bonzel, Appl. Phys. 13 (1977) 333 T.N. Rhodin and C.F. Brucker , S o l i d S t a t e Corn. 2 3 7 1 9 7 7 ) 275 W. E r l e y and H. Wagner, Sur face S c i . 7 4 (1978) 3m. G. Wedler, K.G. Colb, G. McElhiney andW. H e i n r i c h , Appl. S u r f a c e S c i . 2 ( 1 9 7 8 ) 30 K.A. P r i o r , K . Schwaha and R.M. Lambert, S u r f a c e S c i . 77 (1978) 193 R. Ku, N.A. G j o s t e i n and H.P. Bonzel , Sur face S c i . s f i 9 7 7 ) 465 H.P. Bonzel and T.E. F i s c h e r , S u r f a c e S c i . 51 (1975) 213 K . J . Singh and H. Grenga, J. Catal . 5 ( 1 9 7 7 328 B.A. Sexton and G.A. Somorjai , J. Catal. 46 ( 1 9 7 7 ) 167 D . J . D y e r and G.A. Somorjai , J. C a t a l . 52 ( 1 9 7 8 ) 291 and J. C a t a l . 56 (1979) 249 H . J . Krebs, H.P. Bonzel and G. Gafner , S u r f a c e S c i . ( t o be p u b l i s h e d ) C.F. Brucker and T.N. Rhodin, J . C a t a l . 47 ( 1 9 7 7 ) 214 T.N. Rhodin, C.F. Brucker and A.B. Anderson, J . C a t a l y s i s ( t o appear ) J .P. Coad and J . C . R i v i s r e , S u r f a c e S c i . -25 ( 1 9 7 1 ) 609 C.C. Chang, Sur face S c i . ( 1 9 7 1 ) 53

5 1819 57 -

23

ELECTRON SPECTROMETER

GAS MIXTURE

11-6 BAR1

1

I- loam i ION PUMP

PUMPING 1

Figure 1 : Schematic of UHV apparatus with attached sample transfer system and micro-reactor for catalytic rate measurements. The sample, located at the surface analysis position "C" in the center of the UHV chamber, can be moved by pulling the stainless steel rod, to the position "B" (reactor for chemical reaction) or position "A", the atmospheric loading position.

i / id ,

yx) 200 303 4w 5M) 600 t (sed

'Figure 2 : Semilog-plot of methane turnover number versus time for a CO/H, ratio of 1:20.

290 2 8 8 2 8 6 28L 282

E, leV l

Figure 3: Carbon,ls XPS data after reaction, CO/H, = 1:20, T = 530 K, reaction times a) 3 sec, b) 23 sec, c) 83 sec and d) 600 sec. Note shift in maxirrum.

24

200 LOO 600 - 2 1L - 5 1 2 L c e 10 a o 8 ?

% L a

- a 6 3

O A " ' . ' ' 200 LOO . 600 tlsec!

F i g u r e 4 : Same r e a c t i o n d a t a as i n F ig . 3 . (a ) C l s b inding energy as a f u n c t i o n of r e a c t i o n time. (b) I n t e g r a t e d C l s peak a r e a ( a s a measure of s u r f a c e car - bon c o n c e n t r a t i o n ) v e r s u s r e a c t i o n t i m e .

a dE

230 250 270 290 EAA4

F i g u r e 5: Carbon Auger s p e c t r a of t h e t h r e e carbonaceous s u r f a c e phases formed a f t e r t h e CO/H, r e a c t i o n a t 1 b a r and CO/H, = 1:20. Reac t ion c o n d i t i o n s : Sur- f a c e phase I - T = 565 K , t = 15 s e c ; s u r f a c e phase I1 - T = 615 K , t = 15 s e c ; s u r f a c e phase 111 - T = 615 K , t = 90 min .

F i g u r e 6: Carbon Auger s p e c t r a . ( a ) Af- ter h e a t i n g t h e Fe(l1O) c r y s t a l i n UHV a t 720 K f o r about 3 min; (b) a f t e r exposure of t h e c a r b i d i c carbon on Fe (110) t o 2~ Pa C,H, f o r 5 min a t 400 K ; ( c ) a f t e r r e a c t i o n a t 1 b a r ; (d) a f t e r exposing t h e c l e a n F e ( l l 0 ) c r y s t a l t o C,H, a t room tempera ture (2 x 1 0 - ~ Pa, 5 min) .

25

, , i d t , , 230 250 no 290 F i g u r e 7: Carbon Auger s p e c t r a . ( a ) F e ( l l 0 )

c r y s t a l was h e a t e d i n UHV t o 720 K f o r about 3 min; (b) a f t e r CO/H, r e a c t i o n a t 1 b a r ; (c) a f t e r expos ing t h e s u r f a c e produced under ( a ) t o C,H, a t 475 K ( 2 X

Pa, 5 min) .

I

NIE

I

1 1 1 1 1 1 I I I

Mixed Carbtdic ond Graphitic

la)

(b) - 202 270

- 290 286

E eldl

26

I " ' X B C " "

posure of t h e Fe s u r f a c e t o C,H, a t 580 K ( 2 X Pa, 2 0 m i d ; a f t e r CO/H, r e a c t i o n a t 1 b a r .

F i g u r e 9: Cls s p e c t r a . ( a ) A f t e r CO/H, r e a c t i o n a t 1 b a r and 630 K (CO/H, = 1:20, 10 min r e a c t i o n t i m e ) ; (b) a f t e r hydrogenat ion of t h e s u r f a c e under ( a ) a t 1 b a r , 630 K f o r 60 min.

CO HYDROGENATION OVER RHODIUM FOIL AND SINGLE CRYSTAL CATALYSTS:

CORREUTIONS OF CATALYST ACTIVITY, SELECTIVITY, AND SURFACE COMPOSITION

D. G. Castner,* R. L. Blackadar, and G. A. Somorjai

Materials and Molecular Research Division, Lawrence Berkeley Laboratory and Department of Chemistry, University of California,

Berkeley, California 94720

*Present address: Chevron Research Company, P.O. Box 1627, Richmond, California,94802

ABSTRACT

CO hydrogenation at 6 atm over polycrystalline Rh foil and single crys-

tal Rh (111) catalysts was investigated in a system where the surface struc-

ture and composition of the catalysts could be characterized both before and

after the reaction. The reaction conditions ( H :CO ratio, reaction tempera-

ture, and surface pretreatment) were systematically varied to determine the

optimum conditions for formation of oxygenated hydrocarbons. Initially clean

Rh catalysts showed no structure sensitivity, primarily produced methane

(90 wt%) at an initial rate of 0.15 molecules site-lsec-’ at 3OO0C, and did

not produce detectable amounts of oxygenated hydrocarbons. Preoxidation of

the Rh catalysts (800 Torr 02, 6OO0C, 30 min.) resulted in dramatically in-

creased initial rates, a larger fraction of higher molecular weight hydrocar-

bons, some structure sensitivity, and formation of methanol, ethanol, and

acetaldehyde.

dized foils indicate that the methanation mechanism is different on these two

surfaces.

C H to C H ratio and shifted the product distribution towards higher mole-

cular weight hydrocarbons.

2

The different Arrhenius parameters over the clean and preoxi-

Decreasing the reaction temperature or H2:C0 ratio increased the

2 4 2 6

27

INTRODUCTION

Reaction of H -CO mixtures over t he Group VI11 metals u sua l ly y i e l d s a 2

wide range of products , inc luding a lkanes , a lkenes , and oxygenated hydrocar-

bons. I n recent s t u d i e s ,

t i v i t y f o r production of t h e two-carbon oxygenated spec ie s acetaldehyde,

a c e t i c ac id , and e thanol . S imi l a r s e l e c t i v i t y was shown at 1 a t m on ca ta -

l y s t s prepared by depos i t i ng Rh c l u s t e r s on bas ic metal This

con t r a s t s with r e s u l t s f o r Rh and Rh supported on A 1 0 j , ( 6 ) over

which no oxygenated hydrocarbons were formed a t 1 atm. A need the re fo re

e x i s t s f o r s tudying CO hydrocarbons over wel l -charac te r ized Rh a t e leva ted

pressures , under a v a r i e t y of r eac t ion condi t ions and su r face pre t rea tments ,

t o determine t h e cond i t ions necessary f o r oxygenated product s e l e c t i v i t y .

We have measured r e a c t i o n r a t e s and product d i s t r i b u t i o n s over c l ean and pre-

oxidized Rh f o i l and Rh( l l1 ) c r y s t a l su r f aces at 6 atm and 250-4OO0C, with

H :CO r a t i o s of 3:l t o 1:3. Sur face s t r u c t u r e and chemical composition were

charac te r ized us ing low-energy e l e c t r o n d i f f r a c t i o n (LEED) and Auger e l ec t ron

spectroscopy (AFS).

Rh ca t a lys t s .

Rh supported on Si02 showed a unique se lec-

2

The r e s u l t s w i l l be compared t o previous r e s u l t s on

EXPERIMENTAL

The appara tus and technique employed i n these experiments a r e described c\

elsewhere.(j ' " B r i e f l y , t h e r eac t ion c e l l is loca ted i n s i d e a n u l t ra -h igh

vacuum (UHV) chamber t o a l low ion s p u t t e r c leaning and su r face cha rac t e r i za -

t i o n by LEED and AES immediately before and a f t e r reac t ion .

t he c e l l , f i r s t t he H2 (99.9995% p u r i t y ) and then t h e CO (99.99% p u r i t y ,

Af t e r c los ing

28

Fe and Ni carbonyls removed in a dry ice trap) were admitted and circulated

in the closed loop. Allowing a few minutes for mixing at room temperature,

the reaction was then started by heating the Rh sample resistively.

buildup of products was monitored by a gas chromatograph using a Chromasorb

102 column and flame ionization detector. The reaction was stopped after

times ranging up to 3 hr, by cooling to room temperature and pumping down to

UHV, to measure changes in surface composition.

The

2 For preoxidized samples, the surface was heated to 6OO0C in 1 atm 0

for 30 minutes inside the reaction cell. During this treatment, an epitaxial

oxide was formed, and oxygen also dissolved into the bulk. The oxide layer

was amorphous and had an 0 510/F&jo2 AES peak intensity ratio of 0.5 to 0.6,

although ratios up to 2.6 were obtained by oxidizing carbon-covered surfaces.

The initial turnover numbers ( T N ) were determined from a least squares

fit to the initial slope of the product concentration vs. time curves. In

the calculation, the atom density of the %(Ill) surface (1.6 x IOl5 atoms

was used as the active site density. The same figure was also used for pre-

oxidized samples, thus ignoring possible increases in surface area as well as

a reduced Rh surface density on the oxide.

RESULTS

Fig. 1 shows the-buildup of products during a typical run on clean Rh at

300°C and 3H2:1C0.

Under the above conditions, CH4 was the main product (90 wt%) with initial

TN 0.15 molecules site-'set- . C2 and C hydrocarbons were formed, but no

oxygenated hydrocarbons were detected. All rates of product formation, ex-

Results on the clean Rh foil and %(Ill) were identical.

1 3

29

cept C2H6, dec l ined over t h e course of t h ree hours.

and a f t e r r eac t ion , i n F ig . 2, show t h a t small amounts o f S and C1 and a mono-

l a y e r of C b u i l t up on t h e su r face during CO hydrogenation.

s i t ies f o r these impur i t i e s remained nea r ly cons tan t a f t e r t h e f i r s t 30 minute

minutes, a l though the r e a c t i o n r a t e s continued t o dec l ine .

t h e Rh and Rh302 peaks prevented A E S l ineshape a n a l y s i s t o determine

t h e r t he carbon s t a t e w a s changing dur ing t h i s time.

The AES s p e c t r a before

AFS peak in ten-

The proximity of

whe- 256

Preoxida t ion of t h e Rh(ll1) c r y s t a l ( s ee Figs. 3 and 4) g r e a t l y increased

t h e i n i t i a l T N ' s , s h i f t e d product d i s t r i b u t i o n s l i g h t l y t o h ighe r molecular

weight, and r e s u l t e d i n the appearance of t h e oxygenated products methanol,

e thano l , and acetaldehyde. The marked decrease i n TN's dur ing t h e f i r s t 30

minutes coincided with r a p i d l o s s of t h e e p i t a x i a l oxide.

t h e near-surface oxygen concent ra t ion reached a low s t eady- s t a t e va lue , as

shown i n Fig. 5. Methane w a s s t i l l formed at a h ighe r r a t e on t h e steady-

s t a t e su r face wi th oxygen than on the c lean sur face .

were formed during t h e e n t i r e t h r e e hours.

t o a f u r t h e r s h i f t toward h ighe r molecular weight and an inc rease i n the C H

t o C2H6 r a t i o , as shown i n F igs . 6 and 7.

aldehyde was t h e only oxygenated hydrocarbon produced. Also, two t o four

monolayers of carbon were depos i ted on the preoxid ized Rh dur ing CO-rich runs

a t 3OO0C, probably account ing f o r t he increased poisoning r a t e (Fig. 6 ) .

A f t e r t h i s pe r iod ,

Oxygenated products

Decreasing t h e temperature l e d

2 4

During t h e CO-rich r eac t ions a c e t -

Resuits f o r preoxidized Rh f o i l were s i m i l a r t o those fo r preoxidized

Rh(lll) except for a s m a l l s t r u c t u r e s e n s i t i v i t y shown i n a lower CH4 TN and

l a r g e r C2H4 t o C2H6 r a t i o .

oxygenated products.

ox id ized f o i l than on preoxid ized Rh(lll), giv ing a faster poisoning r a t e .

Also, e thanol formed a smaller f r a c t i o n of t he

In CO-rich runs , more carbon w a s depos i ted on t h e pre-

30

The activation energy for methanation was found to be 12 kcal/mole on preoxi-

dized foil, half the value (24 kcal/mole) found on clean Rh foil. (5)

DISCUSSION

Preoxidation of the Rh surfaces markedly changes their activity and selec-

tivity, indicating that the chemical environment of the Rh atoms is important

in determining their catalytic properties.

bility of supported Rh catalysts depending on their

CH4 formation rate depends directly on the oxygen concentration in the near-

surface region, as shown in Table I. The lowest initial CH4 production rate

is obtained during CO hydrogenation over clean catalysts and the highest over

the catalyststwith an epitaxial oxide.

oxidized surface which are flashed in vacuum prior to CO hydrogenation,

resulting in a low near-surface oxygen concentration. (lo) The fact that C02

hydrogenation gives a higher CH4 TN than CO hydrogenation under the same reac-

tion conditions suggests that C 0 2 oxidizes the catalysts during hydrogenation.

This is consistent with the varia-

The

An intermediate value is given by per-

( 5 )

C02 has been shown to dissociatively adsorb on Rh surfaces, (839,ll) and an

oxygen AES signal was detected in the early stages of C02 hydrogenation over

Fe . (12)

The changes in Arrhenius parameters, shown in Table 11, strongly indicate

that a change in mechanism is the cause of the increased CH4 TN on preoxidized

surfaces. In particular, a simple effect of surface area or active site den-

sity can be ruled out. The activation energy on the oxygen-treated surface

is 12kcal/mole, half that on the clean surface, 24 k~al/mole,(~) and within

experimental error of the value for C02 hydrogenation on clean Rh. This again

31

sugges ts ox ida t ion by t h e C02. Preexponential f a c t o r s show a similar trend.

The e f f e c t of i nc reas ing pressure from 1 a t m (5) t o 6 atm ( t h i s s tudy)

was minor. The C H t o C H r a t i o was smal le r , presumably the r e s u l t of the

h igher H p a r t i a l p re s sk re inc reas ing o l e f i n hydrogenation. Also, t h e poison-

ing observed i n t h i s s tudy at 6 atm w a s no t observed at 1 atm.

e f f ec t of S and C1 i m p u r i t i e s , or deac t iva t ion of C over layers , is enhanced a t

high pressure .

1 a t n ~ ' ~ ) and agrees we l l wi th f ind ings f o r supported Rh c a t a l y s t s which produce

hydrocarbons. (1 '2 '6 ) This i n d i c a t e s t h a t me ta l l i c Rh o r a complex of Rh and C

is ac t ive i n hydrocarbon formation, bu t t h a t t hese su r faces do not provide t h e

condi t ions necessary f o r oxygenated hydrocarbon formation, suggesting t h a t a

h igher Rh oxidation s t a t e may be c r u c i a l t o t h i s process. Production of oxy-

genated hydrocarbons a f t e r t h e near-surface oxygen concent ra t ion reaches steady-

s t a t e i nd ica t e s t h a t CO is t h e source of oxygen i n these products , bu t bulk

oxygen d i f fus ing i n t o the near-surface reagion is another poss ib l e source.

a r e undertaking i s o t o p i c l a b e l i n g s t u d i e s t o reso lve t h i s question.

2 4 2 6

2

Poss ib ly the

Behavior a t 6 atm is i n o the r r e s p e c t s similar t o t h a t at

We

Varying the temperature and H2:C0 r a t i o produces r e s u l t s t h a t fo l low the

t r ends pred ic ted f o r a mixture of products i n equilibrium,(13) t h a t is, higher

molecular weight and more unsa tura ted or oxygenated products a r e favored at

low temperature, and t h e hydrogen-poor spec ies C2H4 and CH CHO a r e favored

a t low H2:C0 r a t i o . Thus thermodynamicsseemsto have relevance even though

t h e o v e r a l l CO-H conversion t o any of t he products is f a r from equilibrium

i n o u r experiments. A p o s s i b l e explana t ion is t h a t an i n i t i a l slow s t e p i n

t h e mechanism is followed by r ap id combination and p a r t i a l e q u i l i b r a t i o n of

hydrocarbon fragments.

3

2

32

REFERENCES

1.

2.

3.

4.

5.

6.

7.

8.

9.

I O .

11.

12.

13.

M. Ichikawa, Bull . Chem. SOC. Japan 2, 2268 (1978).

M. Ichikawa, Bull. Chem. SOC. Japan 2, 2273 (1978).

M. M. Bhasin, W. J. Bar t l ey , P. C. E l lgen , and T. P. Wilson,

J. Catal. 2, 120 (1978).

P. C. E l lgen , W. J. Ba r t l ey , M. M. Bhasin, and T. P. Wilson, 175th ACS

Meeting, Los Angeles, C a l i f . , Div. Pe t ro l . Chem. P r e p r i n t s 3, 616 (1978).

B. A. Sexton and G. A. Somorjai , J. Catal. 5, 167 (1977).

M. A. Vannice, J. C a t a l . 7, 449 (1975).

D. W. B lake ly , E. I. Kozak, B. A. Sexton, and G. A. Somorjai , J. Vac. Sc i .

Technol. 2, 1091 (1976).

D. G. Cas tner , B. A. Sexton, and G. A. Somorjai , Sur face Sc i . Tl,

519 (1978).

D. G. Castner and G. A. Somorjai , Sur face S c i . B, 60 (1979).

D. G. Castner and G. A. Somorjai , LBL-9288.

L. H. Dubois and G. A. Somorjai , LBL-8976 and LBL-9280.

D. J. Dwyer and G. A. Somorjai , J. Catal. 2, 291 (1978).

D. J. Dwyer, K. Yoshida, and G. A. Somorjai , 175th ACS Meeting, Los

Angeles, C a l i f . , Div. Pe t ro l . Chem. P r e p r i n t s 3, 521 (1978).

33

Table I. Comparison of initial methanation TN for CO and C02 hydrogenation

in a batch reactor at 300OC over Rh and Fe catalysts.

in molecules site sec.

Methane TN is

-1 -1

Reaction Surface Initial CH4 Conditions Pretreatment TN at 30OoC Ref. Catalyst

Rh foil

Rh foil

Rh foil

Rh(ll1)

Fe foil

Fe foil

0.92 atm

3 ~ ~ : 1co

0.92 atm 3H2: 1C02

6 atm 3H2:1CO

6 atm 3H2: IC0

6 atm 3H2: IC0

6 atm 3H2: IC0 2

clean

preoxidized (a)

clean preoxidized (a)

clean

preoxidized (b)

clean

preoxidized (b)

clean preoxi dized (C)

clean

0.13

0.33

0.33 1.7

0.15

1.7

0.15

4.6

1.9 18.7

10.9

(5) (5)

(5) (5)

this

study

this

study

(12)

(12)

(12)

(a) 15 min at 3OO0C in 700 T o r r 02, then heated to 1000°C in vacuum.

(b) 30 min at 600Oc in 800 Torr 02.

(c) 20 min at 300°C in 4 atm 02.

34

Table 11. Comparison of the Arrhenius methanation parameters (TN = A

for CO and CO

TN and A are molecules site- sec

hydrogenation over polycrystalline Rh foils. Units for 2 1 -1 . Ea is in kcal/mole.

Reaction Surface CH4 TN Ref. Ea A Conditions Pretreatment at 3OO0C

0.92 atm 3H2:1C0 clean

0.92 atm 3H2: 1C02 clean

6 atm 3~~ : 1c02 preoxidized(b)

0.13 i 0.03 10 (a) 24 i 3 (5)

(a) determined from data in Ref. (5). (b) 30 min. at 6OO0C in 800 Torr 02.

35

1401 1 I I I I I I I I 1 I 1

3 H2: I CO, 6 atm

0 30 60 90 I20 150 Time (minutes)

X BL794- 6130

Fig. 1. Buildup of t h e GI t o C 3 t i o n over i n i t i a l l y c l ean Rh f o i l o r & ( I l l ) c a t a l y s t s at 6 atrn,

300°C, and 3H2:1C0.

hydrocarbon products during GO hydrogena-

36

NIE:

Rh

( a ) Clean rhodium

(b)

4fter 3 hr at 3OO0C 3 H,: I CO, 6 a t m

- 3 0 200 300 400 500 60(

Energy (eV) XBL 797- 66 55

Fig. 2. A B s p e c t r a of t h e i n i t i a l l y c lean Rh c a t a l y s t s (a) befo re and

(b ) a f t e r 3 h r of CO hydrogenation a t 6 atrn, 3OO0C, and 3H2:1C0.

37

I120 I 1 I I I I I I I I I I'

-

-

Preoxidized Rh ( 1 1 1 ) O,,,-,/Rh,,, 0.6

3 H,: ICO, 6 atm 960 -

300 "C C H ~ (x 1/10)

800-

-

.- 2640- v, \ v) al 3 0

- -

;w-- I

-

320-

-

I I I I 1 I I 1 0 30 60 90 120 I50 18

Time (minutes) XBL794-6136

Fig. 3 . Buildup of t he C1 t o C

t i o n ove r a preoxidized % ( I l l ) c a t a l y s t a t 6 atm, 3OO0C, and 3H2:1C0.

hydrocarbon products during CO hydrogena- 3

38

Q a, N

Q X 0 Q)

(L

.-

.-

L

-0 a, N

-0 x 0 a,

.-

.-

rt

I I I I I I ( \ I o

0 0 0 0 O c o CD e 0 -

39

N'(E

a 100 200 .

eoxidi zed Rh (111)

3 H2: I CO, 6 otm

# X l C - - . X 2

(C)

fter 3hr at 300°C I H2: 3 CO, 6otm

Energy ( e V ) XBL797-6654

Fig . 5. AES s p e c t r a of t h e preoxidized Rh(ll1) c a t a l y s t ( a ) before and

(b) a f t e r 3 h r of CO hydrogenation at 6 atm, 3OO0C, 3H2:1C0, o r

(c) a f t e r 3 hr of C O hydrogenation a t 6 atm, 3OO0C, 1H2:3C0.

Rh 011) 3 ti2: I CO, Gatm

3 0 0 ° C

40

20

0

100-

80

60

40

20

0-

r r 00- 5 6 0 - C .- n .- I-

E 40-

s 20-

0 c

U 0 L

O-

Preoxidized Rh(l l l ) 05K)/Rh302 =0.5 3 ti2: I CO, Gatm

25OoC

-

-

-

-

3l+lCO,6atm 3OO0C

Rh(l l l ) I Hi 3 CO, 6 atm

300°C

Preoxidized Rh (111) 0510/Rh302=0.6 I H2 3 CO, 6 atm

300 *c

Preoxidized Rh (111)

I H i 3 C O . 6 0 t m 250’C

% ~ 1 0 / ~ ~ 3 0 2 =0.5

XB L 79746 53

~ i ~ . 6. Buildup of C1 to C

Over a preoxidized Rh(ll1) catalyst at 6 atm, 25OoC, and 1H2:3C0.

hydrocarbon products during CO hydrogenation 4

41

I I I I I I I I I I I I

560-

-

480-

-

400 - a

v) \

c .- - m

3 0 a

-2 320-

- 2

-

240 -

160-

Preoxidized Rh (Ill)

I H2: 3 CO, 6atm.

0510/Rh302 = 0.5

250°C

P

I I I I I I I I

0 30 60 90 120 150 I80 Time (minutes)

XBL794- 6129

Fig. 7 . The product distributions in weight percent after 2 hr of CO hydro-

genation over pretreated Rh(ll1) catalysts at various reaction con-

ditions. See Fig. 4 for explanation of symbols.

42

CATALYTIC METHANATION OVER SINGLE CRYSTAL NICKEL AND RUTHENIUFI:

REACTION KINETICS ON DIFFERENT CRYSTAL PLANES

R. 0 . Kelley and D . Wayne Goodman

Surface Science Division

National Bureau o f Standards

Washington, D . C . 20234

in t roduct ion

A s p e c i a l l y designed u l t r ah igh vacuum system has been used t o s tudy the k ine t i c s of t h e hydrogenation of CO over low su r face a r e a , s i n g l e c rys t a l c a t a l y s t s . In a r ecen t publ ica t ion (11, we have repor ted r eac t ion r a t e measurenients f o r a Ni(100) c a t a l y s t and compared those r e s u l t s with k ine t i c da t a , derived from t h e l i t e r a t u r e , f o r small p a r t i c l e N i supported on A1203. There was remarkable agreement between the two c a t a l y s t systems i n regard t o s p e c i f i c r eac t ion r a t e s ( t h e r a t e normalized t o the number o f su r face metal atoms), t he a c t i v a t i o n energy, and t h e product d i s t r i b u - t i o n . In t h e present r e p o r t , we compare reac t ion r a t e s measured on two c rys t a l planes o f Ni--the (100) and the close-packed (111)--and two c rys t a l planes o f Ru--the zig-zag, open (110) and t h e c lose packed (001). We a l s o r epor t t h e v a r i a t i o n of t h e r eac t ion r a t e and the su r face carbon concent ra t ion w i t h t o t a l p ressure and w i t h t h e H2:C0 r a t i o . The su r face carbon concent ra t ion (an a c t i v e "ca rb id i c" carbon spec ie s ) v a r i e s w i t h the t o t a l pressure and w i t h t he r e a c t a n t gas r a t i o . A s t r i k i n g c o r r e l a - t i o n has been found between the su r face carb ide level and t h e c a t a l y t i c r eac t ion r a t e .

Experimental

The apparatus used f o r t hese s t u d i e s cons i s t s of two connected u l t r a - h i g h vacuum chambers--one f o r su r face a n a l y s i s (Auger Electron Spectroscopy (AES)) and the o the r s u i t a b l e f o r high pressure c a t a l y t i c r a t e s t u d i e s . A de t a i l ed desc r ip t ion o f t h e appara tus , t he c rys t a l cleaning procedure, and the techniques used t o obta in k i n e t i c r a t e data have been published ( 1 ) . I t should be noted t h a t t he number o f metal su r f ace atoms exposed t o t h e r e a c t a n t gas (used t o normalize r eac t ion r a t e da ta ) i s derived from the geometrical su r f ace a rea o f t he a ryea led c ry2ta l and the zppropri75e su r face a t 9 dens i ty [Ni(100): j 5 6 2 x 10 2atoms/cm ; N i ( l l 1 ) : ls86 x 10 -gtoms cm ; Ru(l l0) : 1 .00 x 10 atoms/cm ; Ru(001): 1 .55 x 10 atom5 cm 3 . The Ru samples were cleaned using h i g h temperature oxidation a t 10- followed by heating i n vacuum t o 1570K. ( 2 )

t o r r O2

Resul t s a n d Discussion

The observa t ion (1) t h a t t he r a t e of the r eac t ion

3 H2 t CO -t CHq + H 2 0

(expressed as CH4 molecules/surface s i t e / s e c ) measured over a low sur face a r e a , s ing le c r y s t a l c a t a l y s t i s near ly i d e n t i c a l t o t h a t measured over a supported small p a r t i c l e Ni c a t a l y s t (2) i s a s t rong ind ica t ion t h a t t he re i s l i t t l e r e a c t i v i t y d i f f e r e n c e between those c r y s t a l planes commonly found i n po lyc rys t a l l i ne mater ia l ( i . e . , t he low index p l anes ) . This expec ta t ion i s confirmed i n t he da t a presented in Fig. 1 , which i s a plot of t he s p e c i f i c r a t e (or turnover number) of C H 4 production versus the rec iproca l temperature. (111) c rys t a l planes o f Ni i s evident in b o t h !!e value of t he s p e c i f i c r a t e and the a c t i v a t i o n energy ( 2 4 . 7 kcal mole d a t a ) . c a t a l y s t s a r e r ep lo t t ed from t h e l i t e r a t u r e . over N i , t he re i s e s s e n t i a l l y no v a r i a t i o n i n t he reac t ion r a t e a s the c a t a l y s t changes from small metal p a r t i c l e s t o bulk s ing le c r y s t a l planes.

low level of a carbon spec ie s and the absence of oxygen ( 1 ) . t he r a t e o f production of t h i s su r f ace carbon spec ies ( i n pure CO) a n d the r a t e of reac t ion ( i n pure H2) have ind ica ted t h a t both processes ( i . e . , the production a n d t h e removal of t h e sur face carbon spec ie s ) proceed a t very s i m i l a r r a t e s . (3) k i n e t i c data and t h e f i n i t e sur face carbon level during reac t ion was developed which involves t h e hydrogenation of an a c t i v e carbon spec ies formed from the d i s soc ia t ion .o f CO. t h e pressure i s increased from 1-120 torr a t a f ixed H2:C0 r a t i o . temperatures t h e r a t e s f a l l on the same s t r a i g h t l i n e a t a l l p re s su res . As t h e temperature i s increased a devia t ion from l i n e a r i t y i s seen--the higher t h e pressure t h e h igher t h e devia t ion temperature. l i n e a r r a t e behavior i s an increase i n t h e a c t i v e carbon l eve l on the su r face of t h e c a t a l y s t c r y s t a l . depar ture from the l i n e a r i t y pf the r a t e in F i g . 2a and the accompanying inc rease i n t h e su r face carbon l e v e l ) i s due t o a decrease in the sur face coverage of hydrogen and thus a decrease i n the r a t e of hydrogenation o f su r face carbon. Fig. 2 b shows s imi l a r data f o r a Ru( l l0 ) c r y s t a l . The va r i a t ion of t he r e a c t i o n r a t e w i t h p ressure i s very s imi l a r t o t he Ni(100) c r y s t a l - - i . e . , a depa r tu re from l i n e a r i t y o f the r a t e and accompanying t h i s depar ture a n increase i n t h e sur face carbon level (see reference ( 4 ) fo r d e t a i l s of t h e AES measurement of c a r b o n on R u ) . We presume t h a t t he explanation of t h i s behavior i s the same of fered f o r t he Ni c r y s t a l . I n f a c t , since the binding energy of H on Ru i s lower t h a n on Ni ( 2 ) the devia t ion from l i n e a r i t y should be expected a t a lower temperature. This i s p a r t i c u l a r l y ev ident i n the 1 torr data of Fig. 2a and 2 b .

The s i m i l a r i t y between the open (100) and the close-packed

derived from the Ni(100) For comparison t h r e e s e t s o f data f o r nickel (supported on alumina)

Thus f o r the H 2 + C O reac t ion

Analysis of a n a c t i v e c rys t a l c a t a l y s t su r f ace with AES i n d i c a t e s a Measurements of

A mechanism f o r t h e H 2 + CO r eac t ion cons i s t en t w i t h the

F i g . 2a shows t h e changes in the r eac t ion r a t e a s A t low

Accompanying t h i s n o n -

\le have proposed t h a t t h i s behavior ( t h e

4 4

In addition t o the r a t e data f o r t he Ru( l l0) c r y s t a l , F i g . 2b a l s o contains l imited data f o r t h e basal plane of ruthenium, Ru(001). While the comparison i s l imi t ed , i t i s c l e a r t h a t t he H 2 + CO reac t ion i s quite s imi la r i n regard t o the spec i f i c reac t ion r a t e and the ac t iva t ion energy f o r these two c rys t a l planes of ruthenium.

The data of Fig. 2 i nd ica t e t h a t the e f f e c t of the t o t a l p ressure on the reaction r a t e i s dependent on the temperature a t which the measurements a r e made. function of pressure a t two temperatures over a Ni(100) c a t a l y s t w i t h the H /CO = 4. pgessure t o a power r a t e law of t he form

Fig. 3 shows the va r i a t ion o f t he spec i f i c r a t e a s a

Many au thors ( 5 ) have f i t t e d reac t ion r a t e va r i a t ion w i t h

The exponents, f i t t e d from experimental da t a , have been used t o der ive information about t h e reac t ion mechanism ( 6 ) . I t i s c l e a r from Fig. 3 t h a t , while power r a t e law exponents can be derived and used t o sca l e r a t e data a t f ixed reac t ion condi t ions , such exponents a r e very s e n s i t i v e t o t he reac t ion temperature. I t i s doubtful t h a t any fundamental s i g n i f i - cance can be attached t o values of t he exponents derived a t one temperature.

We have attempted t o determine t h e dependence o f the methanation r a t e on the pa r t i a l pressure of both H and C O . In conducting t h i s s tudy , we have measured the r a t e o f CH4 pro2uction w i t h H :CO r a t i o s which varied from 0.1 t o 1000 and w i t h a t o t a l pressure whic2 varied from 1 t o 1500 torr. The r e s u l t s o f this study ind ica t e t h a t even a t one temperature a power r a t e law such a s equation 1 i s not adequate t o describe the p a r t i a l pressure dependence o f the reac t ion r a t e . d a t a measured over a Ni(100) c a t a l y s t can be co r re l a t ed , o n a smooth curve, w i t h t he concentration of "ac t ive" carbon on the Ni sur face . Figure 4 i s a p lo t of t he measured carbon sur face coverage and t h e measured spec i f i c reac t ion r a t e f o r various H 2 : C 0 r a t i o s and t o t a l pressures a t a temperature of 625K. I t should be noted t h a t the reac t ion r a t e s are s teady-s ta te r a t e s with no evidence fo r deac t iva t ion and t h a t t h e carbon AES l ineshape i s always t h a t of a "carbide" w i t h no evidence f o r graphi te formation. i n t e n s i t y i s based on AES data obtained from a CO monolayer ( 4 ) .

measurements--in t h e r a t e of carb ide production from pure C O ( 3 ) and s ince

However, fl reac t ion r a t e

The es t imate o f carbon sur face coverage from the AES carbon

Since there i s no pressure e f fec t - - in the pressure range of t hese

45

a t any H2:C0 r a t i o an increase i n pressure r e s u l t s i n a decrease i n sur face carbon, we conclude t h a t t h e data of Figure 4 i s a manifestation of t h e change i n t h e hydrogenation r a t e of t he sur face carb ide with t o t a l pressure and w i t h t h e H2:C0 r a t i o . t i on reac t ion r a t e i s determined by a d e l i c a t e balance of the formation and removal of surface carb ide and t h a t ne i the r of these processes a r e r a t e determining in the usual sense. T h u s , a s ind ica ted i n Figure 4 under r eac t ion condi t ions unfavorable f o r t he hydrogenation r a t e (e .g . , low p a r t i a l presjure o f H 2 a t a high temperature) t he reac t ion r a t e should decrease and be accompanied by an increase in the sur face carbon l e v e l . A t lower temperatures the sur face concentration of hydrogen (and thus the hydrogenation r a t e ) becomes 1 ess s t rongly dependent on pressure. example, t h e r a t e o f CH production f o r a 4:l H2:C0 r a t i o a t 503K ( l o t t e d i n F i g . 3 ) i s only s l i g i t l y dependent on pressure (from 1-1500 torr!. The measured sur face carbon leve l under these condi t ions i s approximately 10% of a monolayer and does not change s i g n i f i c a n t l y over the e n t i r e pressure range.

Thus i t appears t h a t changes i n temperature, H /CO r a t i o , and t o t a l p ressure have a common e f f e c t on the methanation rage--namely, t o change t h e sur face concentration of hydrogen. Although these e f f e c t s have been observed predominately on the Ni(100) c r y s t a l , the s i m i l a r i t i e s between Ni and Ru w i t h regard to r eac t ion r a t e va r i a t ion w i t h pressure and w i t h su r f ace carbide level (F ig . 2 ) s t rongly suggest a s imi l a r explanation fo r ru theni urn.

We have previously concluded ( 1 ) t h a t t he methana-

For

The results o f t hese pressure s tud ie s suggest considerable caut ion i n drawing the conclusion t h a t c rys ta l lographic e f f e c t s a r e absent i n t h e methanation reac t ion over Ni o r R u . While this r e s u l t appears va l id under r eac t ion condi t ions i n which sur face carb ide level i s low, as reac t ion conditions change e f f e c t s due t o d i f fus ion of carbon, s t a b i l i t y o f the sur face carbide, hydrogen sur face concentation and o ther e f f e c t s which can have a strong c rys t a l log raph ic dependence can become dominant f ac to r s influencing the r e a c t i v i t y .

46

Figure 1.

Figure 2.

Figure 3 .

Figure 4 .

FIGURE CAPTIONS

Arrhenius plot comparing CH4 synthes is on Ni(100), N i ( l l l ) ,

and supported Ni c a t a l y s t s . Reaction condi t ions : 120 torr ,

H2/C0 = 4 .

supported Ni - r e f . 7 .

a . ) Arrhenius plot o f CH4 synthes is on a Ni(100) c a t a l y s t

N i ( l l 1 ) - t h i s work; Ni(100) - r e f . ( 1 ) ;

a t t o t a l reac tan t pressures of 1 , 10, 120 t o r r . H2C0 = 4.

b . ) Arrhenius plot of CH4 synthes is on a Ru(ll0) c a t a l y s t

a t t o t a l reac tan t pressures of 1 , 10, 120 torr.

Data a t two temperatures f o r a Ru(001) c a t a l y s t a t 120

t o w i s plotted w i t h the symbol, x .

H2C0 = 4.

Methane production r a t e (molecules/surface s i t e / s e c ) versus

pressure a t 503K a n d 625K over a Ni(100) c a t a l y s t .

Methane production r a t e (molecules/surface s i t e / s e c ) a t

625K over a Ni(100) c a t a l y s t versus sur face carbon concentra-

t i o n (under steady s t a t e reac t ion cond i t ions ) .

r a t i o and the t o t a l pressure ( t o r r ) f o r each point p lo t t ed

i s indicated in the i n s e r t .

The H2:C0

47

REFERENCES

1 . D. W . Goodman, R . D . Kelley, T. E . Madey, and J . T , Yates, J r . ,

2 . D. W . Goodman, T. E . Madey, M. Ono, and J . T. Yates, J r . , J . Cata l . ,

3 . 0. W . Goodman, R . D. Kelley, T . E . Madey, and J . M . White, accepted

4. D . W . Goodman and J. M . White, accepted f o r publ ica t ion i n Sur face

5.

6.

7 .

accepted f o r publ ica t ion i n J . Cata lys i s .

- 50 279 (1977).

fo r publ ica t ion i n J . Cata lys i s .

Sc 1 ente . For example, M . A . Vannice, J . Cat l . , 37, 449 (1975).

D. F. O l l i s and 14. A. Vannice, J . Cata l . , 38, 514 (1975).

M . A . Vannice, Cata l . Rev. Sc i . Eng. 1 4 ( 2 ) , 153 (1976).

48

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49

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51

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5 2

THE EFFECTS OF POTASSIIJM PROMOTION ON THE CHARACTERISTICS OF IRON FISCHER-TROPSCH CATALYSTS. H. Arakawa and A. T. Be l l . M a t e r i a l s and Molecular Research D i v i s i o n , Lawrence Berkeley Labora tory and Department of Chemical Engineer ing , U n i v e r s i t y of C a l i f o r n i a , Berkeley, CA 94720.

The a d d i t i o n of potassium i s w e l l known t o a l t e r t h e performance of i r o n c a t a l y s t s used f o r Fischer-Tropsch s y n t h e s i s . t e r i z e the deFendence of t h e a c : i v i t y , s e l e c t i v i t y , and s t a b i l i t y of alumina-supported i r o n c a t a l y s t s on t h e K/Fe r a t i o and t o seek e x p l a n a t i o n s f o r t h e , i n f l u e n c e o f p o t a s s i m on t h e ca:aiysts performance. c o n t a i n i n g 0 t o 1 2 of p o t a s s i u n . i:j' c e i r e a s e d , the o l e f i n t o p2;affin r a t i o of t h e p r ' s t u c t i n c r e a s e d sc!stantial:y, t?,e methane s e l e c t i v i t y d e c r e a s e d , and the c a t a l y s t s t a b i l i t y v a s ennanced. ;'ne interprc:a- t i o n of t h e s e r e s u l t s w i l l be d i s c u s s e d i n terms of t h e i n f l u e n c e of po tass ium on t h e a d s o r p t i o n of H,, CO, and C02, and i n f r a r e d o b s e r v a t i o n s o b t a i n e d under r e a c t i o n c o n d i t i o n s .

The o b j e c t i v e s of t h i s i n v e s t i g a t i o n were t o charac-

L s p e r i z e n t s were conducted wi th ?OL Fe/i.l,O, catz::-s-.s hYth i n c r e a s i n g potass ium concent rL6 f a t a l y s t a c t i v -

53

DEACTIVATION BY CARBON OF NICKEL AND NICKEL-MOLYBDENUM METHANATION CATALYSTS

A. Douglas M o e l l e r and C a l v i n H. Bartholomew

Brigham Young U n i v e r s i t y Department of Chemical Eng ineer ing

Provo, Utah 84602

INTRODUCTION

A s e r i o u s p r o b l e m i n t h e c a t a l y t i c m e t h a n a t i o n o f coa l s y n t h e s i s gas i s f o u l i n g of t he c a t a l y s t by carbon deposi t ion. This problem can be avoided by i n c r e a s i n g t h e hydrogen content o f t h e feed stream so tha t thermodynamic e q u i l i b r i u n i s un favorab le toward carbon d e p o s i t i o n (1); however, p rocess economics f a v o r m i n i m i z i n g hydrogen usage. S ince most g a s i f i e r s p roduce a hydrogen d e f i c i e n t gas t h e a p p l i c a t i o n o f a methanat ion c a t a l y s t wh ich d e p o s i t s carbon a t n e g l i g i b l e r a t e s would be h i g h l y desirable, s ince i t would e l im ina te t h e need f o r the s h i f t reac tor p r i o r t o methanat ion. Except f o r a few r e c e n t s t u d i e s i n t h i s l a b o r a t o r y ( 2 - 5 ) t h e r e has been v e r y l i t t l e r e s e a r c h t o d e t s r m i n e t h e e f f e c t s of carbon d e p o s i t i o n o n a c t i v i t y o r t h e k i n e t i c s and mechanism o f c a r b o n d e p o s i t i o n on v a r i o u s c a t a l y s t s d u r i n g methanat ion . Such i n f o r m a t i o n would be v a l u a b l e i n determining t h e b e s t c a t a l y s t s and optimum opera t ing c o n d i t i o n s f o r methanat ion o f hydrogen-poor s y n t h e s i s gas.

A p r e v i o u s s t u d y i n t h i s l a b o r a t o r y (6 ) showed t h a t Ni-Mo c a t a l y s t s a r e p r o m i s i n g f o r use i n t h e BI-GAS p r o c e s s s i n c e t h e y a re as a c t i v e as N i bu t more r e s i s t a n t t o s u l f u r p o i s o n i n g . The p r e s e n t s t u d y was u n d e r t a k e n t o de termine t h e behav io r o f N i and Ni-Mo c a t a l y s t s under r e a c t i o n c o n d i t i o n s which are c h a r a c t e r i s t i c o f combined sh i f t /methanat ion and which favo r massive carbon format ion. The ob jec t i ves o f t h i s s t u d y were t o :

1. D e t e r m i n e t h e e f f e c t s o f c a r b o n d e p o s i t i o n o n t h e a c t i v i t y o f t h e s e c a t a l y s t s under h i g h t e m p e r a t u r e c o n d i t i o n s ( b o t h l o w and h i g h pressures) which promote carbon f o r m a t i o n .

2. Determine i f the carbon fou led ca ta l ys ts cou ld be regenerated by t rea tment i n a i r o r O 2 a t h i g h temperatures.

The r e s u l t s o f a c t i v i t y , a d s o r p t i o n , c a r b o n d e p o s i t i o n and r e g e n e r a t i o n t e s t s t o a c c o m p l i s h t h e s e o b j e c t i v e s a r e p r e s e n t e d and d i s c u s s e d i n t h i s paper.

EXPERIMENTAL METHODS

M a t e r i a l s

Cata lys t composi t ion and suppl iers are l i s t e d i n Table 1. C a t a l y s t p r e p a r a t i o n and pre t rea tment was t h e same as descr ibed p r e v i o u s l y (6 ) .

Hydrogen gas (99.99% Whi tmore) was p u r i f i e d u s i n g a Pd c a t a l y s t f o l l o w e d b y a m o l e c u l a r s i e v e t r a p . Gases f o r t h e r e a c t i o n m i x t u r e s , N2 (99.99% Whitmore), CO (99.9% Matheson) CH4 (99.97% Matheson), O2 (99.8% Whitmore) were used as d e l i v e r e d . The r e a c t i o n m i x t u r e f o r t h e carbon d e p o s i t i o n runs was passed th rough an a c t i v a t e d c h a r c o a l t r a p h e a t e d t o 473 K and a ZnO/molecu la r s i e v e t r a p heated t o 353 K t o rBnOVe any i r o n carbonyl and s u l f u r impur i t i es before undergoing methanation. C a t a l y s t p r e s u l f i d i n g t r e a t m e n t s were c a r r i e d out u s i n g a 66 ppm H2S i n H 2 m i x t u r e prepared i n t h i s l a b o r a t o r y d i l u t e d t o 9 ppm w i t h hydrogen.

54

Procedure

-- H Chemisorption. P r i o r t o each t e s t s e r i e s , smal l samples (0 .2-0 .5 g ) of reduce2catalysts were rereduced a t 773 K as previously described (6 ) . H 2 adsorption isotherms were then measured a t 298 K fo l lowing procedures r epor t ed previous ly (7 -9 ) . H chemisorption measurements were a l so performed following each se r i e s of t e s t s Eo de tec t any changes in t h e c a t a l y s t su r f ace a rea , and in the case of catalysts analyzed fo r carbon content H 2 chenisorption measurements were made d i r ec t ly a f t e r carbon deposition.

Spec i f i c Rate Measurement. Except fo r t h e f l u i d i z e d bed t e s t s s p e c i f i c r a t e s were measured i n a Pyrex, f ixed-bed r eac to r a t 498 K before and a f t e r the steady s t a t e carbon deposit ion runs and a f t e r regenera t ion in the same manner as in our previous study ( 6 ) . Spec i f i c r a t e measurements f o r c a t a l y s t s deac t iva ted in the f lu id i zed bed r eac to r were performed only a f t e r regeneration. Except f o r the measurements before and a f t e r high pressure carbon deposit ion these t e s t s were performed with 0.2 t o 0 .6 gram samples and a r eac t an t mixture cons i s t ing o f 1% CO, 4% HE and 95% N . To avoid lengthy reduction and passivation steps, t he spec i f ic r a t e measurements Eefore and a f t e r the high pressure carbon deposit ion runs were car r ied o u t in the s t a i n l e s s s t e e l high pressure reac tor described previously ( 6 ) using 1 ml samples. The reac tan t mixture f o r these measurements was 4.3% CO, 5.6% H 2 and 90.1% N p .

Steady S t a t e (24 h ) Carbon Deposition R u n s . Af t e r i n i t i a l spec i f i c r a t e measurements, each c a t a l y s t was operated in a f ixed bed f o r approximately 24 hours under steady s t a t e cond i t ions a t 723 K and pressures of 138 kPa or 2600 kPa t o observe i t s behavior under severe carbon depos i t i on condi t ions . Two samples of each ca t a lys t were run a t the lower pressure. One was used f o r regeneration t e s t s and one was analyzed f o r carbon cont n t . The space ve loc i ty f o r a l l steady s t a t e

of the equilibrium diagram was ensured by using a 4.2% CO mixture ( i n a N di'luent) and a H /CO r a t i o of 1 .3 . F igure 1 shows t h i s composition on a carbon-5ydrogen- oxygen {riaxial p lo t along with our 1% CO mixture (H2/C0 = 4 ) and the 61-GAS nminal f eed gas composition ( H /CO - 1 . 4 ) . Sample s i z e s were again 0.2-0.6 g f o r low pressure runs and 1 ml ?or high pressure runs. Reactant and producr. sampling was performed in the same way as in our previous in s i t u deac t iva t ion measurements ( 6 ) .

Ni-Mo-Cu (0.57 g ) and Ni-Mo (0.51 g ) were operated in a fluidized bed reac tor ( 6 ) fo r 24 hours a t 723 K and 138 kPa. A f lu id ized bed was used in order t o simulate more c l o s e l y t h e 81-GAS process . The r e a c t i o n mixture was a d i lu t e BCR mixture of the following composition: 5.3% CO, 6.5% H 2 , 1.6% CHq, 3.6% CO , 83.0% N . These runs were repeated using f r e sh samples (0.5-0.6 g ) and a 4.2% EO, 5.5% tf2, 90.3% N 2 mixture t o obtain samples f o r carbon analysis.

Regenera t ion t e s t s were performed with a 1-3 a i r i n N 2 mixture at 138 k P a c a t a l y s t s deactivated a t low pressure and a 1-4% O 2 i n N mix ture a t 2600 kPa f o r t hose deac t iva t ed a t high pressure. In b o t h ca ses the Zemperature was 573 K . Cata lys t s deac t iva t ed in a f lu id i zed bed were a l so regenerated in a f lu id ized bed. During regeneration CO and C o g concentrations in the product strean were monitored continuously with the chromatograph fo r 15 t o 30 minutes. After 30 minutes the CO concentration was negligible indicating completion of carbon removal. The ca ta lys t s &ich had undergone e i t h e r high pressure regenera t ion or low p res su re f l u i d i z e d bed r egene ra t ion were pass iva ted with a d i l u t e air/N2 mixture and t r ans fe r r ed t o the f ixed bed r eac to r c e l l t o f a c i l i t a t e subsequent spec i f ic r a t e and H 2 chemisorption measurements.

carbon deposit ion runs was 100,000 h- P . Operation in t h e carbon deposition region

Re;eneration T e s t s and P a s s i v a t i o n .

55

R e g e n e r a t i o n o f t h e N i c a t a l y s t was a t t e m p t e d u s i n g a 50% H20/H2 m i x t u r e a t 723 K and 2600 kPa f o r 6.5 hours, bu t it r e s u l t e d i n severe a t t r i t i o n and t h e r e was n o t enough c a t a l y s t l e f t i n t h e r e a c t o r t o p e r f o r m any m e a n i n g f u l t e s t s . F o r t h i s reason a d i l u t e 0 /N2 m i x t u r e a t h i g h p r e s s u r e was used f o r r e g e n e r a t i o n o f c a t a l y s t s d e a c t i v a t e d a$ h igh pressure.

P r e - s u l f i d i n g Runs. 0.5 m l samples o f t h e N i and Ni-Mo-Cu c a t a l y s t s were loaded i n t o t h e Pyrex f l u i d i z e d bed r e a c t o r and re - reduced as d iscussed p rev ious l y . The f l u i d i z e d bed was used t o assure un i fo rm p o i s o n i n g o f t h e c a t a l y s t p a r t i c l e s . These c a t a l y s t s were t h e n exposed t o 375 ml/min o f a gas m i x t u r e o f 9 ppm H S i n H2 a t 725 K f o r s u f f i c i e n t t i m e t o s u l f i d e 50% o f t h e c a t a l y s t s u r f a c e ( 6 ) . i f t e r exposure f o r t h e r e q u i r e d t ime , t h e c a t a l y s t s were c o o l e d t o room tempera ture and pass iva ted . A c t i v i t y t e s t s were t h e n run as d e s c r i b e d below.

RESULTS

S p e c i f i c Rate and H2 Chemisorp t ion Measurements

R e a c t i o n r a t e s per a c t i v e s i t e o f c a t a l y s t , i . e . methane t u r n o v e r numbers (N ), and produc t y i e l d s ( f r a c t i o n s o f conver ted CO o c c u r r i n g as v a r i o u s produc ts ) ob!%ined i n d i f f e r e n t i a l r e a c t o r t e s t s o f N i , Ni-Mo, and Ni-Mo-Cu c a t a l y s t s a re presented i n Tab le 2 a l o n g w i t h H2 chemisorp t ive uptakes.

The d a t a i n T a b l e 2 show t h a t a l l t h r e e c a t a l y s t s s u f f e r e d s i g n i f i c a n t decreases i n m e t a l s u r f a c e a r e a measured by H2 a d s o r p t i o n a f t e r carbon d e p o s i t i o n a t e i t h e r l o w o r h i g h p r e s s u r e . However, t h e r e were s i g n i f i c a n t v a r i a t i o n s i n t h e magn i tude o f changes observed f o r t u r n o v e r numbers a f t e r c a r b o n d e p o s i t i o n a t low pressure. The CH t u r n o v e r numbers o f N i and Ni-Mo-Cu d i d n o t change s i g n i - f i c a n t l y w h i l e t h a t o f di-Mo dropped o v e r 90%. CH4 y i e l d d ropped f o r Ni and N i - Mo bu t remained unchanged f o r Ni-Mo-Cu. Ni-Mo-Cu and Ni-Mo e x h i b i t e d s i g n i f i c a n t i n c r e a s e s i n COP y i e l d a f t e r carbon d e p o s i t i o n , whereas N i showed no s i g n i f i c a n t COz y i e l d e i t h e r b e f o r e o r a f t e r carbon d e p o s i t i o n .

The c a t a l y s t s a l s o r e s p o n d e d d i f f e r e n t l y t o r e g e n e r a t i o n . N i and Ni-Mo r e g a i n e d a c t i v i t y a f t e r r e g e n e r a t i o n h a v i n g CH4 t u r n o v e r numbers near those f o r t h e f r e s h c a t a l y s t s ; CH4 y i e l d was a l m o s t c o m p l e t e l y r e s t o r e d f o r N i b u t on l y i n p a r t f o r Ni-Mo. Regenera t ion d i d n o t improve t h e a c t i v i t y o r s e l e c t i v i t y o f N i - Mo-Cu, bu t r a t h e r caused decreases i n CH4 and C02 y i e l d s . A l l o f t h e s u l f u r - f r e e c a t a l y s t s a p p a r e n t l y s u f f e r e d a decrease i n s u r f a c e area a f t e r regenera t ion .

a t h i g h p r e s s u r e d e m o n s t r a t e d s i m i l a r t r e n d s . w e l l as CH4 y i e l d s decreased f o r a l l c a t a l y s t s . o f 2 f o r N i and a f a c t o r o f 10 f o r Ni-Mo-Cu and Ni-Mo.

-

The r e s u l t s o f d i f f e r e n t i a l runs f o r c a t a l y s t s subjected t o carbon d e p o s i t i o n T h a t i s , CH4 t u r n o v e r numbers as

I n f a c t NCH4 decreased by a f a c t o r

Despite a decrease i n sur face area the regenerat ion t reatment a t h i g h pressure w i t h a d i l u t e 0 m i x t u r e seemed t o g r e a t l y jmprove c a t a l y s t performance f o r a l l c a t a l y s t s . CH4 {u rnover numbers f o r t h e t h r e e c a t a l y s t s ranged from 1.5 t o 8 t imes t h e va lue b e f o r e c a r b o n d e p o s i t i o n and CH4 y i e l d s were 37 t o 66 p e r c e n t h i g h e r than pre-carbon d e p o s i t i o n va lues . To de termine i f t h i s e f f e c t was permanent t h e N i c a t a l y s was t e s t e d f o r an a d d i t i o n a l 20 h o u r s a t 623 K and space v e l o c i t y o f 100,000 h- w i t h 1% C O and H2/C0 = 4, a f t e r w h i c h t h e t u r n o v e r number r e v e r t e d t a t h e pre-carbon d e p o s i t i o n va lue .

T a b l e 2 a l s o shows t h e r e s u l t s o f d i f f e r e n t i a l t e s t s on two ca ta l ys ts , Ni-Mo-Cu and N i , which were p r e - s u l f i d e d and exposed t o carbon d e p o s i t i n g environment a t low Pressure. These r e s u l t s show t h a t carbon d e p o s i t i o n i s ex t remely de t r imenta l t o Ni-Ma-Cu when i t has been p r e v i o u s l y exposed t o H2S. On t h e o t h e r hand N i i s

I .

56

r e l a t i v e l y u n a f f e c t e d showing s i m i l a r a c t i v i t y p e r f o r m a n c e t o t h e n o n - s u l f i d e d C a t a l y s t . Both c a t a l y s t s showed l i t t l e change i n H2 up take as a r e s u l t of ca rbon depos i t i on and/or regeneration. However, regenerat ion apparent ly caused a s i g n i f i c a n t i nc rease i n CH4 y i e l d f o r p r e - s u l f i d e d N i .

Steady S t a t e (24 h ) Carbon Depos i t i on Tests

Values of CO conversion, r a t e s o f methane p roduc t i on and normal ized a c t i v i t i e s a re l i s t e d i n T a b l e 3 f o r N i , Ni-Mo and Ni-Mo-C c a t a l y s t s b e f o r e and a f t e r 24

a c t i v i t y versus t ime are shown i n F i g u r e s 2 and 3. Normal ized a c t i v i t y i s d e f i n e d as t h e r a t i o o f t h e i ns tan taneous r a t e o f methane p r o d u c t i o n t o t h e i n i t i a l r a t e ; t h e h a l f l i f e corresponds t o a no rma l i zed a c t i v i t y o f 0.5.

Based o n t h e n o r m a l i z e d a c t i v i t y a f t e r 24 hours t h e o r d e r o f d e c r e a s i n g r e s i s t a n c e t o ca rbon d e p o s i t i o n a t l o w p r e s s u r e was N i , N i ( p r e - s u l f i d e d ) , N i - Mo-Cu, Ni-Mo, Ni-Mo-Cu ( p r e - s u l f i d e d ) . The o r d e r o f i n c r e a s i n g c o n t e n t o f ca rbon d e p o s i t e d a f t e r 24 h o u r s f o l l o w e d t h i s same t r e n d . However, when t h e Ni-Mo and Ni-Mo-Cu c a t a l y s t s were operated i n a f l u i d i z e d bed, Ni-Mo m a i n t a i n e d an a c t i v i t y o f 0.38 compared t o z e r o f o r Ni-Mo-Cu a f t e r t h e 24 h o u r c a r b o n d e p o s i t i o n t e s t , even though 10 t imes more carbon was d e p o s i t e d on Ni-Mo compared t o Ni-Mo-Cu. I n f a c t , t h e Ni-Mo-Cu c a t a l y s t l o s t a l l measurab le a c t i v i t y w i t h i n 15 hours i n the f l u i d i z e d bed. The p r e - s u l f i d e d Ni-Mo-Cu a l s o d e a c t i v a t e d v e r y r a p i d l y as shown i n F i g u r e 2. F i g u r e 3 shows f a i r l y s i g n i f i c a n t f l u c t u a t i o n s i n t h e d a t a a t 8 hours f o r t h e Ni-Mo f l u i d i z e d bed r u n . Ma in tenance o f a s teady f l o w d u r i n g t h i s run requ i red constant a t ten t i on , and t h i s f l u c t u a t i o n can be a t t r i b u t e d t o f l o w v a r i a t i o n s d u r i n g t h e evening and n i g h t hours when t h e r u n was unattended.

Data i n Table 3 o b t a i n e d at h i g h p ressu re show t h a t Ni-Mo l o s t no a c t i v i t y d u r i n g t h e 24 hour p e r i o d . O n l y a s l i g h t d e c r e a s e i n a c t i v i t y was obse rved f o r N i , whereas the a c t i v i t y f o r Ni-Mo-Cu decreased by a lmost 40%.

Fo r the low pressure f i x e d bed carbon & p o s i t i o n rtms t h e decrease i n normalized

h o u r s t e a d y s t a t e t e s t s a t 773 K and 100,000 h - Y . T y p i c a l p l o t s o f n o r m a l i z e d

a c t i v i t y w i t h t ime i s rep resen ted bes t by t h e f o l l o w i n g express ion:

a 0 a =

1 + e x d - kaor) [exp( kd[COo] t) -1 3 1)

where a = n o r m a l i z e d a c t i v . t y a t t i m e t , a, = n o r m a l i z e d c t i i t y a t t = 0, k =

[ C O O ] concen t ra t i on of CO a t bed ent rance (mol 1- ), and T = i nve rse space v e l o c i t y ( h ) . ) i s ob ta ined from Equat ion 1 b y s e t t i n g a/ao = 0.5 and rea r rang ing . The r e s u l t !L2

r r e a c t i o n r a t e c o n s t a n t ( h - 1 ), kd = decay c o n s t a t ( 1 mol- ' h- ' ) , t = t i m e ( h ) ,

An express ion f o r t h e h a l f l i f e ( t

Equations 1 and 2 were used to p l o t the s o l i d l i n e s i n Figures 2 and 3 and t o c a l c u l a t e t h e h a l f l i v e s shown i n Table 3.

The d a t a f r o m t h e f l u i d i z e d bed r u n s a r e c o r r e l a t e d f a i r l y w e l l b y t h e f o l l o w i n g exp ress ion a f t e r about 5 hours:

- k d t a = aoe 3 )

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where the symbols have t h e same meaning as b e f o r e . From Equat ion 3 t h e h a l f l i f e can be ob ta ined as f o l l o w s :

t1/2 = 0.693 ( k d ) - l 4)

T h i s e x p r e s s i o n was u s e d t o c a l c u l a t e t h e h a l f l i v e s o f N i -Mo and Ni-Mo-Cu i n a f l u i d i z e d bed wh ich a r e shown i n Table 3.

DISCUSSION

E f f e c t s o f Carbon Depos i t ion-on Methanat ion A c t i v i t y

E f f e c t s on I n t r i ns i c A c t i v i t y l Se l e c t i v it P r o p e r t i e s . S e v e r a1 recent i n ves ti g ~ % ~ ~ f i a ~ ~ ~ ~ n ~ a ~ s ~ ~ 2)m- pr ov i ded ev i dence t h a t adsorbed c a r b o n i s an a c t i v e r e a c t i o n i n t e r m e d i a t e . McCarty and Wise (11) r e p o r t e d f o u r t y p e s o f carbon which a re adsorbed on t h e N i s u r f a c e a f t e r exposure t o CO. Two s p e c i e s d e s i g n a t e d a ' - c a r b o n and a - c a r b o n ( b o t h atomic carbon) were e a s i l y removed b y H2 and another d e s i g n a t e d 5 -carbon (po lymer ized carbon) was about 1/100 as a c t i v e toward H2. G r a p h i t i c carbon, t h e f o u r t h type i s a p p a r e n t l y formed by h i g h t e m p e r a t u r e c o n v e r s i o n o f t h e B-form. McCar ty and Wise i n d i c a t e d t h a t a -carbon ( C ) i s s l o w l y t r a n s f o r m e d t o 5 - c a r b o n (C5) a t t e m p e r a t u r e s above 600 K . Thus, cafbon f o u l i n g of methanation c a t a l y s t s i s l i k e l y t h e r e s u l t o f Cg f o r m a t i o n from C,, t h e r a t e o f t r a n s f o r m a t i o n p r o b a b l y depending on t h e n a t u r e o f t h e a c t i v e s i t e . The more a c t i v e s i t e s a r e more l i k e l y t o promote b o t h r a p i d d e p o s i t i o n and g a s i f i c a t i o n o f &. I f d e p o s i t i o n o c c u r s more r a p i d l y t h a n g a s i f i c a t i o n , C, w i l l b u i l d up on the s u r f a c e and Cg f o r m a t i o n w i l l be favored.

Assuming c a r b o n i s an a c t i v e i n t e r m e d i a t e , t h e d e a c t i v a t i o n r a t e i s then d e t e r m i n e d b y t h e r e l a t i v e c o n t r i b u t i o n s o f t h e r a t e o f a c t i v e carbon fo rmat ion and t h e r a t e o f g a s i f i c a t i o n . The r e l a t i o n s h i p between r a t e s o f carbon f o r m a t i o n and g a s i f i c a t i o n forms t h e b a s i s o f t h e f o l l o w i n g d i s c u s s i o n o f i n d i v i d u a l c a t a l y s t b e h a v i o r under low p r e s s u r e c o n d i t i o n s . Apparent ly under t h e low pressure c o n d i t i o n s of t h i s s tudy N i shows v e r y l i t t l e d e a c t i v a t i o n and accumulates v e r y l i t t l e carbon. T h i s behavior suggests t h a t the r a t e o f g a s i f i c a t i o n equa l izes the r a t e o f depos i t ion f o r n i c k e l u n d e r t h e s e c o n d i t i o n s . The s m a l l amount o f c a r b o n f o u l i n g t h a t d i d occur appears t o be m a i n l y due t o blockage o r loss o f s i t e s s i n c e carbon d e p o s i t i o n d i d n o t change the t u r n o v e r number. The a d d i t i o n o f Mo t o N i a p p a r e n t l y f a v o r s the massive depos i t ion o f carbon as evidenced b y t h e very s i g n i f i c a n t loss o f s p e c i f i c a c t i v i t y and g r e a t e r carbon c o n t e n t o f Ni-Mo. Indeed, r e c e n t l y o b t a i n e d d a t a f rom a g r a v i m e t r i c s tudy i n t h i s l a b o r a t o r y ( 4 , 5 ) show t h a t the r a t e o f carbon d e p o s i t i o n a t 773 K on a 5.5% Ni-Mo/A1203 c a t a l y s t i s 5 t i m e s g r e a t e r t h a n f o r a 3% Ni/A1203 c a t a l y s t . The m a j o r d i f f e r e n c e i n b e h a v i o r o f these t w o c a t a l y s t s appears t o be t h e s i g n i f i c a n t l y h i g h e r r a t e o f g a s i f i c a t i o n o f carbon f o r t h e 3% Ni/A1203. Perhaps Mo be l ieved t o be present as Mooe d issoc ia tes CO bu t no t H2, t hus c a t a l y z i n g f o r m a t i o n b u t n o t removal o f C,.

The a d d i t i o n o f Cu t o Ni-Mo a p p e a r s t o cause a r e d u c t i o n i n t h e amount Of C a formed as i n d i c a t e d b y t h e s i g n i f i c a n t l y l o w e r t u r n o v e r number o f Ni-Cu- Mo. Consequent ly l i t t l e Cg i s formed, r e s u l t i n g i n t h e r e l a t i v e l y l o n g h a l f - l i f e Of Ni-Mo-Cu r e l a t i v e t o Ni-Mo. Ponec (10,12) suggests t h a t i n o r d e r t o d i s s o c i a t e adsorbed CO and fo rm t h e a c t i v e s u r f a c e c a r b o n s p e c i e s an.ensemble o f a c t i v e N i s i t e s i s necessary, and t h a t a d d i t i o n o f Cu, i t s e l f i n a c t i v e towards methanat ion, d i l u t e s the a c t i v e N i s i t e s caus ing lower methanat ion a c t i v i t y o f Ni-Cu c a t a l y s t s as compared t o N i c a t a l y s t s .

58

The change i n s e l e c t i v i t y obse rved f o r a l l c a t a l y s t s a f t e r low p r e s s u r e ca rbon d e p o s i t i o n sugges ts some t y p e o f m o d i f i c a t i o n o f t h e a c t i v e s i t e s . It i s a l s o reasonable t o expec t t h a t a carbon covered s u r f a c e w i l l behave c a t a l y t i c a l l y more l i k e a metal c a r b i d e than a c lean meta l sur face. Th is i s suppor ted by prev ious work of McCarty e t a l . (13,14) and Sexton e t a l . ( 1 5 ) . I n add i t i on , massive depos i t s O f ca rbon i n f i l a m e n t o u s fo rm have been shown b y p r e v i o u s worke rs t o separa te and encapsu la te m e t a l c r y s t a l l i t e s . Thus f o r m a t i o n o f l a r g e amounts o f Cg may p l a c e t h e meta l c r y s t a l l i t e s i n a new suppor t environment, t h e subsequent change i n meta l - suppor t i n t e r a c t i o n s i n d u c i n g changes i n a c t i v i t y / s e l e c t i v i t y p r o p e r t i e s . I n t h e case of b i m e t a l l i c c a t a l y s t s meta l -carbon i n t e r a c t i o n s may induce changes i n su r face c o m p o s i t i o n wh ich a f f e c t s e l e c t i v i t y . Ponec ( 1 2 ) , f o r example, p r e s e n t s ev idence f o r t h e su r face m o d i f i c a t i o n o f a Ni-Cu f i l m by repeated a d s o r p t i o n and temperature programmed desorp t i on o f CO.

The d a t a i n T a b l e 2 suggest t h a t c a r b o n d e p o s i t i o n a t h i g h p r e s s u r e may i n c r e a s e t h e amount o f Cg formed i n t h e case o f N i and Ni-Mo c a t a l y s t s . That i s , t h e percentage decrease i n CH4 t u r n o v e r number observed a f t e r h i g h p ressu re carbon d e p o s i t i o n i s e q u a l t o o r g r e a t e r t h a n t h a t o b s e r v e d i n t h e low p r e s s u r e runs . T h i s o b s e r v a t i o n can be e x p l a i n e d on t h e b a s i s o f C O p a r t i a l pressure. A t h i g h p r e s s u r e t h e minimum p a r t i a l p r e s s u r e o f CO was 10 kPa (assuming 90% c o n v e r s i o n ) whereas t h e maximum p a r t i a l p r e s s u r e o f CO i n t h e l ow p r e s s u r e carbon d e p o s i t i o n t e s t s was 6 kPa. A t a h ighe r p a r t i a l p ressu re o f CO t h e adso rp t i on and d i s s o c i a t i o n of CO on t h e c a t a l y s t s u r f a c e proceeds a t a much g r e a t e r r a t e (4,5). I f t h e carbon fo rma t ion r a t e i s g r e a t e r t han t h e g a s i f i c a t i o n r a t e more w i l l r e s u l t .

E f f e c t s o f Carbon D e a c t i v a t i o n on Apparent A c t i v i t y / S e l e c t i v i t y P r o p e r t i e s i n a F i x e d Bed a t High Temperature, Conversion Cond i t i ons . Even though cons ide rab le ca rbon f o u l i n s was e v i d e n t . r e l a t i v e l v l i t t l e d e a c t i v a t i o n was obse rved d u r i n a s teady s t a t e i e p o s i t i o n t e s t s f o r m o s t c a t a l y s t s excep t Ni-Mo-Cu (see F i g s . 2 a n i 3 ) . T h i s was p a r t i c u l a r l y t r u e a t h i g h p r e s s u r e . T h i s b e h a v i o r i n d i c a t e s t h a t o n l y a p o r t i o n o f t h e a c t i v e s i t e s are necessary t o m a i n t a i n a h i g h r e a c t i o n r a t e . I t i s t h e r e f o r e reasonable to assume t h a t i n a f i x e d bed r e a c t o r most o f t h e r e a c t i o n takes p lace i n a small zone at the entrance t o the bed, c r e a t i n g a l a r g e c o n c e n t r a t i o n g r a d i e n t over t h e r e a c t o r . In t h i s s m a l l zone, t h e CO p a r t i a l p r e s s u r e i s l a r g e and t h e r a t e o f f o rma t ion o f Cg i s high; f u r t h e r downstream the c a t a l y s t i s sub jec ted t o a l o w e r C O p a r t i a l p r e s s u r e and l e s s Q i s formed. Thus a r e a c t i o n zone i s c rea ted which g r a d u a l l y moves downstream as t h e c a t a l y s t becomes f o u l e d . Therefore, a t h i g h temperature, h i g h c o n v e r s i o n c o n d i t i o n s and e s p e c i a l l y a t h i g h pressure, we would expect t o observe ve ry l i t t l e d e a c t i v a t i o n u n t i l t h e r e a c t i o n zone reaches t h e end o f t he bed. The c a t a l y s t would then e x h i b i t an ext remely r a p i d d e a c t i v a t i o n s i m i l a r t o the d e p l e t i o n o f an ion-exchange column. Thus, t h e t r u e d e a c t i v a t i o n b e h a v i o r i n a f i x e d bed a t h i g h tempera tu res and e s p e c i a l l y a t h i g h p ressu res i s masked b y heat and mass t r a n s f e r l i m i t a t i o n s .

Ni-Mo-Cu e x h i b i t s a d i f f e r e n t type o f b e h a v i o r f r o m t h e o t h e r c a t a l y s t s a t h i g h p ressu re . D u r i n g t h e f i r s t t h r e e hours a v e r y r a p i d d e a c t i v a t i o n occu rs . A f t e r t h i s t ime t h e d e a c t i v a t i o n r a t e i s s i m i l a r t o t h a t obse rved d u r i n g t h e l o w p ressu re carbon d e p o s i t i o n run . The tu rnove r number da ta i n Tab le 2 and the l a r g e r amount o f c a r b o n f o r Ni-Mo-Cu r e l a t i v e t o N i ( T a b l e 3) sugges t t h a t t h e r a t e o f g a s i f i c a t i o n o f t h e d e p o s i t e d carbon i s s lower a t h i g h p r e s s u r e r e s u l t i n g i n more C f o r m a t i o n and more r a p i d d e a c t i v a t i o n . The p r e s e n c e o f Cu p robab ly i n h i b i t s t i e g a s i f i c a t i o n s t e p by l i m i t i n g t h e a r e a a v a i l a b l e f o r H2 t o adsorb and s ince h ighe r C O p a r t i a l p r e s s u r e i n c r e a s e s t h e r a t e of C, f o r m a t i o n , a n e t i n c r e a s e i n $, occurs. Ponec (12) showed t h a t f o r CO adso rp t i on on Ni-Cu/Si02 powder the su r face

1 c o n c e n t r a t i o n i n c r e a s e d w i t h t i m e . Assuming such a change i n Ni-Mo-Cu, the i nc reas ing concen t ra t i on o f N i on the sur face would i nc rease t h e r a t e o f g a s i f i c a t i o n w i t h t h e n e t e f f e c t of s l o w i n g down t h e r a t e of $ f o r m a t i o n , t h u s a c c o u n t i n g f o r t h e lower d e a c t i v a t i o n r a t e observed a f t e r t h r e e hours.

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Ef fec ts of P r e - s u l f i d i n . Separate g r a v i m e t r i c s t u d i e s i n t h i s l a b o r a t o r y (4,s) h a v m t h a t pre-su1fidi;g the c a t a l y s t s u b s t a n t i a l l y reduces t h e g a s i f i c a t i o n r a t e w i t h o u t s i g n i f i c a n t l y a f f e c t i n g t h e r a t e o f i n a c t i v e carbon d e p o s i t i o n . The r e s u l t i s inc reased Cg f o r m a t i o n (4,5) and more r a p i d d e a c t i v a t i o n o f p r e - s u l f i d e d Ni-Mo-Cu and N i r e l a t i v e t o t h e f r e s h c a t a l y s t s (see T a b l e 3).

Carbon D e p o s i t i o n i n a F l u i d i z e d Bed. As m i g h t be e x p e c t e d Ni-Mo-Cu and Ni-Mo d e a c t i v a t e d more r a p i d l y i n a f l u i d i z e d bed t h a n i n a f i x e d bed due t o more u n i f o r m exposure t o the r e a c t i o n mix tu re . However, Ni-Mo-Cu d e a c t i v a t e d more r a p i d l y t h a n Ni-Mo, a r e s u l t o p p o s i t e t o t h a t o b t a i n e d i n t h e f i x e d bed. Perhaps t h i s can be accounted f o r b y t h e l o w e r space v e l o c i t i e s and l o w e r convers ions assoc ia ted w i t h t h e f l u i d i z e d bed r e a c t o r . The r a t e o f c a r b o n f o r m a t i o n i s p r o p o r t i o n a l t o t h e p a r t i a l p r e s s u r e o f CO. The lower c o n v e r s i o n would t r a n s l a t e t o a h i g h e r C O p a r t i a l p ressure a t t he c a t a l y s t sur face which would a f f e c t each c a t a l y s t d i f f e r e n t l y because o f t h e i r d i f f e r e n t c o m p o s i t i o n s . C a r e f u l e x a m i n a t i o n o f t h e l o w p r e s s u r e f i x e d bed data o f Tables 2 and 3 revea ls t h a t Ni-Mo and Ni-Mo-Cu su f fe red approxi inately t h e same percentage l o s s o f s u r f a c e area, b u t t h a t Ni-Mo c o n t a i n e d t e n t i m e s more carbon a f t e r t h e s t e a d y - s t a t e carbon d e p o s i t i o n r u n . Thus u n d e r t h e h i g h e r CO p a r t i a l p r e s s u r e Ni-Mo-Cu m i g h t b e e x p e c t e d t o d e a c t i v a t e more r a p i d l y than N i - Mo s i n c e inc reased carbon d e p o s i t i o n would have more e f f e c t on Ni-Mo-Cu. A p o s s i b l e a d d i t i o n a l e f f e c t i s t h a t under u n i f o r m exposure t o t h e r e a c t a n t m i x t u r e a g r e a t e r m o d i f i c a t i o n o f t h e s u r f a c e o c c u r r e d f o r Ni-Mo-Cu t h a n f o r Ni-Mo. S i n c e l a r g e c o n c e n t r a t i o n and t e m p e r a t u r e g r a d i e n t s a r e absent i n t h e f l u i d i z e d bed, these r e s u l t s a r e much more i n d i c a t i v e o f t h e t r u e d e a c t i v a t i o n b e h a v i o r . Moreover, t h e y model b e t t e r t h e b e h a v i o r a n t i c i p a t e d i n t h e BI-GAS process.

Regenerat ion o f Carbon Fou led C a t a l y s t s i n Air/Oxygen

The r e s t o r a t i o n o f a c t i v i t y f o l l o w i n g r e g e n e r a t i o n prov ides s t r o n g evidence t h a t c a r b o n f o u l e d c a t a l y s t s c a n be r e g e n e r a t e d w i th d i l u t e m i x t u r e s o f a i r o r oxygen. I n f a c t , t h i s may be t he on ly p r a c t i c a l approach since i n i n d u s t r i a l equipment t h e r e g e n e r a t i o n tempera ture i s u s u a l l y l i m i t e d t o 700 K, and s i g n i f i c a n t carbon g a s i f i c a t i o n b y steam, H2 o r C02 does no t occur a t temperatures below 800 K (16,17). The increase i n CH4 t u r n o v e r number f o r t h e c a t a l y s t s a f t e r t h e h igh pressure d i l u t e O2 t rea tment was more t h a n c o u l d be accounted f o r b y s imp le removal o f t h e deposi ted carbon. T h i s c o u l d b e t h e r e s u l t o f a s u r f a c e m o d i f i c a t i o n b y t h e O2 t rea tment and/or a m o d i f i c a t i o n w h i c h o c c u r r e d d u r i n g r e a c t i o n as d i s c u s s e d p r e v i o u s l y .

Palmer and V r o m (18) showed t h a t t h e a c t i v i t y o f n i c k e l i s inc reased by h i g h tempera ture t r e a t m e n t w i t h 0 as a r e s u l t o f i n c o r p o r a t i n g d i s s o l v e d O2 j u s t below the surface. U n f o r t u n a t e l y t h i s e f f e c t appears t o b e o n l y temporary, s i n c e t h e s p e c i f i c a c t i v i t y o f regenerated Ni/A1 0 r e t u r n e d t o t h e same va lue as t h e f r e s h c a t a l y s t a f t e r 24 hours o f r e a c t i o n a t 625 ;i< H2/C0 = 4, a c o n d i t i o n chosen t o ensure t h a t f u r t h e r d e a c t i v a t i o n d i d n o t occur .

Regenerat ion o f methane a c t i v i t y by oxygen i s n o t w i t h o u t a p r i c e , however. The r e s u l t s show an o v e r a l l decrease i n s u r f a c e area a f t e r carbon d e p o s i t i o n and r e g e n e r a t i o n o f 18 t o 71%. T h i s s u r f a c e a r e a l o s s i s u n d o u b t e d l y a consequence of s i n t e r i n g and even l o s s o f t h e c a t a l y s t c r y s t a l l i t e s themselves. Rostrup-Nielsen (19) r e p o r t s t h a t d e p o s i t e d carbon grows i n l ong h o l l o w f i l a m e n t s w i t h t h e N i c r y - s t a l l i t e at t h e end. T r a n s m i s s i o n e l e c t r o n m i c r o s c o p y s t u d i e s i n t h i s l a b o r a t o r y (20) conf i rm t h i s o b s e r v a t i o n . The N i c r y s t a l l i t e i s thus removed f r o m t h e support b y t h e carbon f i l a m e n t and when t h e carbon i s removed by o x i d a t i o n t h e c r y s t a l l i t e i s p r o b a b l y c a r r i e d o u t o f t h e r e a c t o r w i t h t h e gas s t ream. I n f a c t , chemica l a n a l y s i s of f r e s h and r e g e n e r a t e d Ni/A1203 samples r e v e a l e d a 7% l o s s o f n i c k e l . It may be, t h e r e f o r e , i m p r a c t i c a l t o r e g e n e r a t e c a r b o n - f o u l e d c a t a l y s t s w i t h a i r o r oxygen s i n c e a f t e r a few c y c l e s o f d e a c t i v a t i o n and r e g e n e r a t i o n a l a r g e p a r t

60

Sexton and Somzrjai (15) r e p o r t e d s i m i l a r r e s u l t s .

of t h e a c t i v e s u r f a c e o f t h e c a t a l y s t w o u l d b e gone. how much N i i s removed p e r t r e a t m e n t and t h e f requency o f t rea tments .

It depends, o f course, o n

A Model f o r D e a c t i v a t i o n by Carbon

We propose a model t o account f o r d e a c t i v a t i o n o f n i c k e l by 6 -carbon i n a f i x e d bed d u r i n g methanat ion. The proposed model f o r d e a c t i v a t i o n i s a m o d i f i c a t i o n of t ha t proposed by Wise e t a l . (21) f o r i n t e r a c t i o n o f s u l f u r w i t h N i . A m o d i f i c a t i o n i n t h e r e a c t i o n mechanism i s a l s o made t o a c c o u n t f o r t h e t r a n s f o r m a t i o n of Ca t o Cg and t h e l o s s o f a c t i v i t y f o r s u r f a c e r e a c t i o n between C and H as t h e number of a v a i l a b l e n i c k e l s i t e s d imin ishes . Our proposed model i s

cos 4 cas + 0,

C, + H, -+ (CH4)g s tepwise 6)

2cas 3 C2BS 7 )

5 )

where t h e s u b s c r i p t "s " denotes an adsorbed spec ies . Since t h e a s t a t e r e p r e s e n t s s i n g l e c a r b o n atoms w h i c h a r e e a s i l y g a s i f i e d and t h e B s t a t e r e p r e s e n t s p o l y - a tan i c carbon lrhich i s nuch less a c t i v e it i s reasonable t o assume tha t t h e d i m e r i z a t i o n o f s i n g l e CCC atoms t o Cg causes the d e a c t i v a t i o n observed f o r N i and N i b i m e t a l l i c methanat ion c a t a l y s t s .

A c c o r d i n g t o o u r p r o p o s e d model t h e r a t e o f d e a c t i v a t i o n due t o carbon f o u l i n g i s p r o p o r t i o n a l t o t h e r a t e o f Cg f o r m a t i o n w h i c h i s p r o p o r t i o n a l t o t h e n e t r a t e o f CCC f o r m a t i o n . The r a t e o f &X f o r m a t i o n i s i n t u r n p r o p o r t i o n a l t o the p a r t i a l p ressure o f CO and t h e a c t i v i t y o f t h e c a t a l y s t . Assuming f i r s t o r d e r dependence o n b o t h o f t h e s e v a r i a b l e s , an e x p r e s s i o n f o r t h e d e a c t i v a t i o n r a t e can be w r i t t e n as d a / d t = -kd[CO]a where k d e a c t i v a t i o n r a t e c o n s t a n t , [ C O ] = c o n c e n t r a t i o n o f CO, a = n o r m a l i z e d a c t i v i $ y = a t t i m e t . The d e a c t i v a t i o n model proposed by Wise e t a l . f o r s u l f u r p o i s o n i n g ( 2 1 ) can be adapted by assuming t h e r e a c t i o n r a t e t o be f i r s t o r d e r i n CO c o n c e n t r a t i o n and t h a t t h e r e are no r a d i a l c o n c e n t r a t i o n g r a d i e n t s . Simultaneous s o l u t i o n o f t h e d e a c t i v a t i o n r a t e express ion and t h e equat ion o f c o n t i n u i t y i n the z d i r e c t i o n ( d i r e c t i o n o f f l ow) y i e l d s Equat ion 1. The f o l l o w i n g e x p r e s s i o n a l s o r e s u l t s i f z/V<<l, where V i s t h e v e l o c i t y i n t h e z d i r e c t i o n .

In[(---- ' )-13 = ln[exp(kaoz/V)-l]-kd[COo]t 8) -xco I n [(- By p l o t t i n g versus t i m e t, va lues f o r k and kd can be de termined

f r o m the i n t e r c e p t at!d s lope r e s p e c t i v e l y .

Equat ion 1 i s p l o t t e d as a s o l i d l i n e i n F i g u r e 2 u s i n g t h e s e parameters. I t f i t s the data very w e l l f o r t h e low pressure f i x e d bed runs. A s i m i l a r development assuming no c o n c e n t r a t i o n g r a d i e n t i n t h e z d i r e c t i o n l e a d s t o t h e e x p o n e n t i a l r e l a t i o n s h p o f Equat ion 3 f o r f l u i d i z e d beds. Us ing Equat ions 1 and 3 we e s t i m a t e t h a t h a l f o f t h e a c t i v e s i t e s f o r Ni-Mo wou ld be f o u l e d i n 37 days i n a f i x e d bed and o n l y 30 h o u r s i n a f l u i d i ed bed based on p r o c e s s c o n d i t i o n s o f H2/C0 = 1.4

The f a c t t h a t t h e p r o p o s e d model f o r d e a c t i v a t i o n by carbon d e p o s i t i o n p r e d i c t s e x p e r i m e n t a l b e h a v i o r q u i t e w e l l i n d i c a t e s t h a t i t i s c o n s i s t e n t w i t h t h e observed d e a c t i v a t i o n b e h a v i o r - - i . e . , t h e r a t e o f d e a c t i v a t i o n i n c r e a s e s as the p a r t i a l p r e s s u r e of CO i s i n c r e a s e d and decreases as t h e s u r f a c e o f t h e

61

l - X c o ' I-''

and a space v e l o c i t y o f 3000 h- I .

c a t a l y s t i s f o u l e d b y i n c r e a s i n g accumulat ions o f i n a c t i v e carbon.

CONCLUSIONS

1. A t 7 2 3 K a n d a t m o s p h e r i c p r e s s u r e d e a c t i v a t i o n o f n i c k e l c a t a l y s t s b y carbon e x h i b i t e d f i r s t order dependence on CO concent ra t ion (second o r d e r o v e r a l l ) . H a l f - l i v e s of N i and Ni-Mo c a t a l y s t s va r ied f rom 13-170 hours. Based on t h e s p e c i f i c i n t r i n s i c a c t i v i t i e s (CH t u r n o v e r numbers) a f t e r r e a c t i o n under carbon d e p o s i t i n g c o n d i t i o n s t h e o r d e r o f I e c r e a s i n g r e s i s t a n c e t o carbon d e p o s i t i o n a t low pressure was: N i , N i ( p r e - s u l f i d e d ) , Ni-Mo-Cu, Ni-Mo, Ni-Mo-Cu ( p r e - s u l f i d e d ) .

Dur ing r e a c t i o n i n a f i x e d bed a t h i g h temperatures and pressures l i t t l e a p p a r e n t d e a c t i v a t i o n was o b s e r v e d e x c e p t i n t h e case o f Ni-Mo-Cu. The e f f e c t s o f d e a c t i v a t i o n were masked by t h e f a s t r a t e o f r e a c t i o n o c c u r r i n g i n a p o r t i o n o f t h e bed. Thus t h e t u r n o v e r numbers de termined under r e a c t i o n l i m i t e d c o n d i t i o n s r e v e a l t he t r u e e f f e c t s o f d e a c t i v a t i o n .

2.

3. Ni-Mo i s more r e s i s t a n t t o carbon d e p o s i t i o n i n a f l u i d i z e d bed than Ni-Mo-Cu. The f l u i d i z e d bed exper iments p r o v i d e more r e a l i s t i c i n d i c a t i o n o f t h e t r u e d e a c t i v a t i o n b e h a v i o r because t e m p e r a t u r e and r e a c t a n t c o n c e n t r a t i o n s a re more un i fo rm than i n a f i x e d bed.

P r e - s u l f i d i n g t h e c a t a l y s t s does n o t improve t h e i r t o l e r a n c e t o carbon d e p o s i t i o n . I n f a c t , p r e - s u l f i d i ng Ni-Mo-Cu s e v e r e l y degraded i t s per fo rmance under severe c a r b o n d e p o s i t i o n c o n d i t i o n s . I t i s b e l i e v e d t h a t s u l f u r p o i s o n s t h e g a s i f i c a t i o n o f a c t i v e carbon leading t o a b u i l d up and t r a n s f o r m a t i o n t o i n a c t i v e carbon.

5. A l o w p r e s s u r e d i l u t e a i r m i x t u r e a t 573 K r e g e n e r a t e s most carbon f o u l e d ca ta l ys ts . Using a d i l u t e O2 m i x t u r e a t h i g h pressure r e s u l t s i n CH4 t u r n o v e r numbers and CH4 y i e l d s wh ich are t e m p o r a r i l y h i g h e r t h a n f o r f r e s h c a t a l y s t s . Regen- e r a t i o n u s i n g a i r o r O2 r e s u l t s i n a s i g n i f i c a n t l o s s o f s u r f a c e area, b u t i t may be t h e on ly p r a c t i c a l method due t o temperature l i m i t a t i o n s o f i n d u s t r i a l equipment.

ACKNOWLEDGEMENTS

4.

The a u t h o r s g r a t e f u l l y acknowledge f i n a n c i a l s u p p o r t f r o m B i tuminous Coal Research, I n c . u n d e r t h e i r C o n t r a c t No. EF-76-C-01-1207, U.S. Dept . o f Energy; permiss ion t o p u b l i s h c a t a l y s t d a t a f rom t h e C1 imax Molybdenum Company o f Mich igan and t h e Harshaw Chemica l Co.; and t e c h n i c a l a s s i s t a n c e f r o m D r . Rober t S t r e e t e r o f BCR.

62

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D.C Gardner and C.H. Bartholomew, paper i n p r e p a r a t i o n .

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C.H. Bartholomew, " A l l o y C a t a l y s t s w i t h M o n o l i t h Supports f o r D e r i v e d Gases," Q u a r t e r l y Techn ica l Progress Repor t t o ERDA, FE-1790-1, (Aug. 6, 1975).

C.H. Bartholomew and R.J. Far rau to , J. Ca ta l . 5, 4 1 (1976).

R.B. P a n n e l l , K . S . Chung, and C.H. Bartholomew, J. C a t a l . 46, 340 ( 1 9 7 7 ) .

M. A rak i and V. Ponec, J. Ca ta l . , 44, 439 (1976) .

J.G. McCarty and H. Wise, J. Cata l . , 57, 406 (1979).

V . Ponec, Ca ta l . Rev. - Sc i . Eng., E ( l ) , 151 (1978).

J.G. McCarty and R.J. Madix, J. Cata l . 3, 402 ( i 975 ) .

J.G. McCarty and R.J. Madix, Surface Sc i . , 54, 121 (1976).

B.A. Sexton and G.A. Somorjai , J. Cata l . , 5, 167 (1977).

J.L. F i g u e i r d o and D.L. Trim, J. C a t a l . , 40, 154 (1975).

D.L. T r i m , Ca ta l . Rev. - Sc i . Eng. E ( 2 ) , 155 (1977).

R.L. Palmer and D.A. Vroom, J. Cata l . 50, 244 (1977).

J.R. Rostrup-Nielsen, J. C a t a l . 27, 343 (1972).

D. Mustard and C.H. Bartholomew, paper i n p r e p a r a t i o n , (1979).

H. Wise, B.J. G i k i s , W.E. Isakson, J.G. McCarty, K.M. Sanc ie r , S. Schechter , P.R. Went rcek , and B.J . Wood, S R I , F i n a l R e p o r t PERC-0060-8 (ERDA), Sept. 30, 1977.

2240-10 ( J u l y 1976).

63

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Figure 1. Equilibrium Diagram a t 723 K and 138 kPa Showing BI-GAS and Test Feed Gas Compositions. B = Fluidized Bed Runs, C = High and Low Pressure Runs plus some Differen t ia l R u n s , D = Differen t ia l Runs. Curve 1 i s the equilibrium curve based on

A = BI-GAS,

graphite. a s reported by J.R. Rostrup-Nielsen in J . Cat. 27,

Curve 2 i s based on "non-ideal" carbon

343-356 (1 972).

68

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69

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( ' L I / H ) A11 A I 1 3 V 032 IlWWLION

70

Fur the r R e s u l t s on t h e React ion of H2/C0 on Fused I r o n

by t h e T r a n s i e n t Method

J. P. Reymond, P. Mgriaudeau, B. Pommier, and C . 0. Bennett*

Labora to i r e de Thermodynamique e t C ine t ique Chimiques U n i v e r s i t 6 Claude Bernard, Lyon I

69621 Vi l l eu rbanne , France

I n t r o d u c t i o n

Jn a p rev ious s t u d y (1) it has been proposed t h a t t h e s u r f a c e of a promoted fused i r o n c a t a l y s t i s l a r g e l y covered wi th carbon d u r i n g t h e s t e a d y - s t a t e r e a c t i o n o f hydrogen and carbon monoxide (90% H 2 . 10% CO) a t a tmospheric p r e s s u r e and 2 5 O O C . This same c a t a l y s t , a commercial ammonia s y n t h e s i s c a t a l y s t (CCI), w a s a l s o evalu- a t e d ( a t 2 . 0 MPa) i n a more a p p l i e d way i n connec t ion wi th t h e s tudy of a scheme f o r energy s t o r a g e i n a c e n t r a l power p l a n t ( 2 , 3) . necessa ry t o cons ide r t h a t each c a t a l y s t ( < . e . , even t h e same meta l on d i f f e r e n t suppor t s ) may o p e r a t e f o r r e a c t i o n s of H2/CO through a unique sequence of s t e p s , or a t l e a s t w i t h a p a r t i c u l a r r a t e -de te rmin ing s t e p . t i o n o f s u r f a c e carbon seems t o be r a t e - l i m i t i n g on i r o n (l), on ruthenium t h e d i s - s o c i a t i o n o f adsorbed CO h a s been proposed as r a t e l i m i t i n g ( 4 ) . i s a c o n t i n u a t i o n of t h a t of r e f e r e n c e (1); t h i s t ime t h e r o l e of C02 and H30 h a s been i n v e s t i g a t e d , and i n t e r e s t i n g in fo rma t ion has been ob ta ined on t h e cha in growth p rocess .

I t i s now c l e a r t h a t it is

Thus a l though t h e hydrogena-

The p r e s e n t work

Experimental

The r e a c t o r was made o f Ulr-inch s t a i n l e s s s t e e l t ube and f i l l e d wi th 1 0 0 mg Of c a t a l y s t ( p a r t i c l e s of 300 pm) mixed wi th 500 mg of g l a s s beads o f t h e same s i z e . The r e a c t o r and t h e g l a s s beads were confirmed t o produce no p roduc t s a t t h e r e a c - t i o n c o n d i t i o n s . Feed r a t e s of H2/CO ( 9 / 1 ) between 20 and 120 ml/min were explored b u t i f n o t o the rwise no ted , 40 ml/min was used; t h e conve r s ion was always less than 5% o f t h e CO f e d .

Hydrogen (99.99%, A i r L iqu ide ) was p u r i f i e d by a molecu la r s i e v e (SA) t r aD, followed by a deoxo r e a c t o r , fol lowed by a second molecular s i e v e 5 A . oxide (99 .9%, A i r Liquide) was passed through a g l a s s t u b e hea ted t o 22O0C t o decompose ca rbony l s and then through a t r a p of a c t i v a t e d carbon a t 25OC.

Carbon mon-

4 n a l y s i s of t h e r e a c t i o n p roduc t s was by gas chromatography. For t h e sepa ra - t i o n o f t h e hydrocarbons, a Poropak Q (80-100 mesh) 6-m, 1/8- inch s t a i n l e s s s t e e l column was used wi th a f lame i o n i z a t i o n d e t e c t o r . Column t empera tu re was 195OC, and t h e c a r r i e r gas (He) w a s used a t 30 ml/min. The C02 and H20 were measured by a second i d e n t i c a l Poropak 0 column a t 175OC, l e a d i n g t o a thermal c o n d u c t i v i t y d e t e c t o r . For t h e r e a c t i o n c o n d i t i o n s used, on ly a l k a n e s were found among t h e hydrocarbon p roduc t s .

Resu l t s

The Basic React ion

A f t e r an i n i t i a l r e d u c t i o n i n f lowing hydrogen a t 60 ml/min f o r 60 hours a t 500°C, t h e r e a c t o r is cooled t o 250°C, and t h e f eed is switched a t t ime ze ro t o 10% C O i n H2. product ion r a t e o f methane p a s s e s through a maximum.

The cu rve 1 of F i g . 1 r e s u l t s . The d e a c t i v a t i o n i s r a p i d and t h e A r e a c t i v a t i o n i n H 2 a t 5 0 0 O C

* Now a t Un ive r s i ty of Connec t i cu t , S t o r r s , Connect icut 06268.

7 1

f o r 1 5 hours i n c r e a s e s t h e a c t i v i t y of t h e c a t a l y s t t o a l e v e l above what it was a t t h e end of t h e first run, b u t below what it was a t its maximum. This p r o c e s s con- t i n u e s wi th f u r t h e r r e a c t i v a t i o n s , and Fig . 1 shows curves a f t e r 1 0 r e a c t i v a t i o n s and a f t e r 20 r e a c t i v a t i o n s . However, it was found t h a t a s h o r t ( 3 0 min) t r e a t m e n t by oxygen a t 5 O O O C and 1 a m before t h e u s u a l r e d u c t i o n by hydrogen produced a r e l - a t i v e l y s t a b l e c a t a l y s t , a s shown by t h e curve 02 of F i g . 1. The a c t i v i t y of t h e c a t a l y s t - i s obvious ly v e r y s e n s i t i v e t o i ts s t a t e of o x i d a t i o n and t o t h e concen- t r a t i o n of r e f r a c t o r y carbon a t or n e a r i t s s u r f a c e . Matsumoto and Bennett (1) found t h a t s h o r t t r e a t m e n t s i n helium a t 2 5 O O C conver ted t h e a c t i v e carbon i n t e r m e d i a t e t o a form i n a c t i v e a t t h i s tempera ture . S i m i l a r e f f e c t s a r e observed f o r n i c k e l ( 5 ) .

I t may be r e c a l l e d t h a t

F igure 2 shows t h e o t h e r hydrocarbons produced cor responding t o t h e c u r v e l a b e l l e d 02 on Fig . 1. The numbers by t h e curves a r e t h e s t e a d y - s t a t e r a t e s of p r o d u c t i o n d iv ided by t h a t for methane. a c t i v i t y l e v e l and a r e a b o u t t h e same f o r a l l t h e c a t a l v s t c o n d i t i o n s of F i g . 1. Water and carbon d i o x i d e a r e also produced, b u t t h e s e product ion r a t e s a r e l e s s r e p r o d u c i b l e . The c a t a l y s t has a f r a c t i o n exposed of o n l y about 5 p e r c e n t , and i t h a s been shown t h a t t h e e n t i r e mass of i r o n is c a r b u r i z e d (1). Thus small changes i n carbon c o n c e n t r a t i o n i n t h e bulk may produce C 0 2 and H 2 0 a t r a t e s a t l e a s t a s h i g h as t h e c a t a l y t i c r e a c t i o n . F i g u r e 3 shows t h e h i s t o r y of a f r e s h l y reduced c a t a l y s t a f t e r exposure t o CO/H2 a t 2 5 0 ° C , H2 a t 250°C, and f i n a l l y H2 programmed t o 5 0 0 O C . The first peak r e u r e s e n t s t h e removal of a s u r f a c e carbon i n t e r m e d i a t e as methane, and t h e second l a r g e peak comes from t h e d e c a r b u r i z a t i o n o f t h e b u l k of t h e c a t a l y s t . T h i s r e s u l t has a l r e a d y been d i s c u s s e d (1).

These s e l e c t i v i t i e s a r e i n s e n s i t i v e t o t h e

Another a s p e c t of t h e r e a c t i n g system can be seen i n F i g . 4 . Experiments were s t a r t e d wi th a f e e d r a t e o f 120 ml/min, b u t t h e convers ion (0 .003 t o CH4) was n o t s u f f i c i e n t t o o b t a i n r e l i a b l e a n a l y s e s f o r H20 and COP by chromatography ( t h e r m a l c o n d u c t i v i t y d e t e c t o r ) . The hydrocarbons, however, were ana lyzed c o r r e c t l y ( f lame ionization d e t e c t o r ) . When t h e convers ion was i n c r e a s e d ( 0 . 0 0 6 t o C H 4 ) by reducing t h e f e e d r a t e t o 20 ml/min, a much lower format ion r a t e of methane was observed . T h i s r e d u c t i o n i n a c t i v i t y c a n only b e expla ined by i n h i b i t i o n o f t h e r a t e s by pro- d u c t s of t h e r e a c t i o n ; t h e r e a c t a n t c o n c e n t r a t i o n s a r e of course a lmost unchanged. In o t h e r words, even a t t h e s e low convers ions t h e r e a c t o r i s not t r u l y d i f f e r e n t i a l .

We a r e t h u s l e d t o i n v e s t i g a t e t h e e f f e c t of t h e products of r e a c t i o n on t h e r e a c t i o n r a t e s , and t h e s e exper iments w i l l be d e s c r i b e d l a t e r . mis lead by s e c u l a r changes i n t h e c a t a l y s t , a s t e a d y s t a t e c o n d i t i o n i s first e s - t a b l i s h e d w i t h 10% CO t H 2 f e e d . The f e e d is t h e n changed to one c o n t a i n i n g H20, C O q . e t c . a s d e s i r e d , and f i n a l l y it is changed back t o 10% CO t Y2.

I n o r d e r n o t t o be

The base r e a c t i o n h a s been s t u d i e d a t s e v e r a l t empera tures ( 2 3 0 ° , 250° , 270°, and 3 O O 0 C ) , and an a c t i v a t i o n energy of 20 .4 kcal/mole i s observed, s imi la r t o t h e v a l u e found a t 2.0 MPa ( 2 ) .

I n f l u e n c e o f C02

To t h e r e a c t i o n m i x t u r e 10% CO t H2 was added 5% CO2. The CHq product ion d iminished by about E%, and when t h e C 0 2 was removed t h e methane format ion r a t e r e - g a i n e d i t s i n i t i a l v a l u e . T h i s e f f e c t i s n o t s u f f i c i e n t t o e x p l a i n F i g . 4 .

If t h e CO i n t h e feed gas i s rep laced by C 0 2 , t h e methanation r e a c t i o n con- t i n u e s a t a lower r a t e , as shown i n Table 1. The format ion of h igher hydrocarbons, however, 1s d r a s t i c a l l y reduced . face oxygen c o n c e n t r a t i o n i s i n c r e a s e d .

I h e C02 i s d i s s o c i a t i v e l y adsorbed , b u t t h e s u r -

7 2

I n f l u e n c e o f Water

A c o n c e n t r a t i o n of 0.6% water vapor was added t o t h e 10% CO t H2 f e e d mixture a t s t e a d y - s t a t e r e a c t i o n , and Fig . 5 shows t h e r e s u l t . The i n h i b i t i n g e f - f e c t Of water i s c l e a r , and i t i s probable t h a t t h e lower rates a t h i g h e r conversion shown i n F i g . 4 a r e expla ined by t h e increased water c o n c e n t r a t i o n a t h igher con- v e r s i o n .

I t i s a l s o i n t e r e s t i n g t o e v a l u a t e t h e c a p a b i l i t y of t h e s t e a d y - s t a t e c a t a l y s t s u r f a c e t o c a t a l y z e t h e s h i f t r e a c t i o n . t h e 10% CO t H2 mixture i s rep laced by 0.6% water, a l l product ion o f hydrocarbons s t o p s , and a l a r g e r a t e o f C02 format ion i s observed . ev idence of t h e power of t h e i r o n c a t a l y s t t o adsorb d i s s o c i a t i v e l y H 2 a s w e l l as co.

F igure 6 i n d i c a t e s t h a t when t h e H2 i n

These r e s u l t s a r e f u r t h e r

Inf luence of Ethane

The a d d i t i o n of 10% C2H6 to t h e r e a c t a n t s does not change t h e r a t e s of r e a c t i o n . However, i r o n has some a c t i v i t y for hydrogenolys is ( 6 ) . I f t h e 10% CO t H2 mixture is changed t o 10% C2H6 t H2. methane is formed a t 0.65 u mole/g min ( s e e F i g . 71, l e s s than 10% of a t y p i c a l methanat ion r a t e .

I n f l u e n c e of O l e f i n s

When 10% C2H4 t H 2 i s fed t o t h e r e a c t o r j u s t a f t e r t h e r e d u c t i o n o f t h e c a t a l y s t a t 5OO0C, t h e curves of F ig . 7 a r e o b t a i n e d . There is immediate product ion of methane, propane, n-butane, and n-pentane. Ethane is confounded wi th t h e l a r g e e t h y l e n e peak i n t h e a n a l y s i s by chromatography. z e r o as i n F i g . 2. A swi tch t o hydrogen ( n o t shown on F i g . 7 ) uroduces no methane peak a t 25OoC, and programming t h e tempera ture t o 5OOOC r e s u l t s i n t h e product ion of o n l y 4 u moles of CHq/g o f i r o n . Thus t h e C2H4/H2 mixture does n o t c a r b u r i z e t h e i r o n a t 25OOC. The r e a c t i o n r a t e s a f t e r 4 hours wi th e t h y l e n e a r e about twice t h o s e wi th C O , and t h e i n i t i a l r a t e s a r e an o r d e r of magnitude h i g h e r . F i g u r e 7 shows a l s o t h e swi tch from C ~ H L + / H ~ t o CO/H2 and t h e n t o C&/H2.

The r a t e s do not i n c r e a s e f r o m

F igure 8 shows t h e u s u a l curves f o r CO/H2 over a reduced c a t a l y s t , fo l lowed by a swi tch t o C ~ H I + / H ~ o v e r t h e now c a r b u r i z e d c a t a l y s t . These r e s u l t s a r e cons is - t e n t w i t h t h e i d e a t h a t t h e ra te -de termining s t e p wi th CO is t h e hydrogenation of s u r f a c e carbon. Subsequent c h a i n growth occurs through CH2 groups ( o r CH), and if t h e s e groups a r e formed d i r e c t l y from e t h y l e n e , t h e product ion r a t e s of t h e pro- d u c t s a r e h i g h e r ; t h e r a t e l i m i t i n g s t e p coming from CO is no longer r e l e v a n t . The C2H4/H2 r e a c t i o n o c c u r s on i r o n , and a f t e r exposure of t h e c a t a l y s t t o CO/H2, much of t h e s u r f a c e i s covered w i t h carbon, so t h e r a t e o f CH4 p r o d u c t i o n wi th C ~ H I + / H ~ of F ig . 8 is lower t h a n t h a t of Fig. 7.

F igure 9 shows t h e r e a c t i o n of 10% C3H6 + H~ o v e r t h e reduced c a t a l y s t . r e s u l t s a r e q u a l i t a t i v e l y t h e same a s w i t h e t h y l e n e . i n F i g . 1 0 , and butene-1/H2 (always 90% H2) g i v e s r a t e s t h a t a r e a l l a b i t lower t h a n for butene-2, as shown. A l l t h e s e r e s u l t s emphasize t h a t on t h e i r o n s u r f a c e t h e CH2 or CH fragments come r a p i d l y t o a s t e a d y s t a t e ; t h e r a t e s of p r o d u c t i o n of t h e a l k a n e products (no o l e f i n s were observed) are n o t a p p r e c i a b l y i n f l u e n c e d by t h e s o u r c e o f t h e CH2 groups on t h e s u r f a c e . However, t h e r e a r e some d i f f e r e n c e s , as shown i n Table 2 , which g i v e s t h e r a t i o s of t h e product ion r a t e s a f t e r 4 hours . S t a r t i n g from a g iven o l e f i n , t h e p r o d u c t s a r e most ly of s h o r t e r cha in l e n g t h , and c l o s e t o t h e cha in l e n g t h of t h e r e a c t a n t . I n any e v e n t , we a r e j u s t i f i e d i n sup- pos ing t h a t , s t a r t i n g from CO/H2, a l l t h e s t e p s a f t e r CH2 or CH format ion a r e r a p i d , and l i t t l e of t h e s u r f a c e is covered by c h a i n fragments a t 25OoC and 100 kPa.

The Butene-2/H2 r e a c t s as shown

7 3

Discussion

The n e w r e s u l t s of t h e p r e s e n t s tudy confirm most a s p e c t s o f t h e sequence o f CO is adsorbed a s C + 0 , and t h e s t e p s proposed by Matsumoto and Bennet t (1).

f r e s h l y formed s u r f a c e ca rbon i s t h e most abundant s u r f a c e i n t e r m e d i a t e ; i t s hydrogena t ion by adsorbed hydrogen p r e s e n t a s H is t h e r a t e -de te rmin ing p r o c e s s . Carbon d i o x i d e added t o CO/H:, i s n o t s t r o n g l y enough adsorbed t o a f f e c t t h e r a t e apprec i - a b l y . s u r f a c e i s more o x i d i z e d , and t h e a c t i v e C is p r e s e n t i n lower c o n c e n t r a t i o n than i n t h e presence of CO.

However, i n t h e absence o f C O , CO2/H2 makes methane a t a lower r a t e ; t h e

However, water can compete wi th CO f o r t h e s u r f a c e , and it o x i d i z e s t h e s u r - The h igh r e a c t i o n r a t e f a c e while reducing t h e a c t i v e C coverage by forming C02.

of CO/H20 t o C02 r a t h e r t han CHq shows t h e s t r o n g a f f i n i t y of t h e s u r f a c e of t h e i r o n c a t a l y s t f o r oxygen ( F i g s . 5-61.

We r e c a l l t h a t t h e r a t e of hydrocarbon p roduc t ion over a f r e s h l y reduced ca ta - l y s t rises from a n i n i t i a l va lue o f zero. The carbon formed from CO r e a c t s w i th t h e bu lk i r o n of t h e c a t a l y s t , and t h e s u r f a c e carbon necessa ry for hydrocarbon pro- d u c t i o n g r a d u a l l y i n c r e a s e s i n coverage a s t h e bulk of t h e i r o n i s ca rbur i zed t o Fe2 C a t 250OC. a c t i v e C i n t e rmed ia t e seems t o be necessa ry . and t h e i r o n i s n o t c a r b u r i z e d . Thus t h e observed formation of CHq and C3H8 shown in Fig . 7 a r i s e s through a CH, fragment. No oxygen i s p r e s e n t . I r o n t h u s behaves d i f f e r e n t l y from c o b a l t , for which oxygen is a p p a r e n t l y necessa ry f o r cha in growth

However, when C2H4/H2 is passed ove r t h e reduced c a t a l y s t , no The r a t e starts a t a maximum v a l u e ,

( 7 , 8 ) .

When a CO/H2 f eed i s changed t o C2Hq/H2 (Fig . E ) , t h e r a t e o f hydrocarhon pro- Methane is an important p roduc t from

This r e s u l t is n o t i n c o n s i s t a n t with t h e l a c k o f 14CHq formed when 14C2H4 d u c t i o n i s h ighe r from e t h y l e n e t h a n from CO. C2Hq/H2. i s added i n sma l l q u a n t i t y t o CO/H2 (9). o r i g i n a t e p r i n c i p a l l y from C O , so t h a t t h e added l ' + C w i l l be concen t r a t ed p r i n c i - p a l l y i n CxHy groups of x 2 2 .

s i n c e t h e r a t e dec reases as t h e i n e r t g r a p h i t i c carbon b u i l d s up ( F i g s . 7 and 8 ) . I t w a s shown p rev ious ly (1) t h a t t h e r e a c t i o n from CO a l s o occur s on t h e i r o n p a r t of t h e s u r f a c e ; a f t e r s t e a d y s t a t e under CO/H2, a b r i e f exposure t o H 2 a l o n e and then a swi t ch back to CO/H2 l e a d s t o a temporary i n c r e a s e i n t h e r a t e . If t h e exposure t o hydrogen is long enough t o deca rbur i ze some of t h e bu lk , t h e subsequent CO/H2 r e a c t i o n r a t e i s lowered a s r e c a r b u r i z a t i o n lowers t h e concen t r a t ion o f t h e a c t i v e s u r f a c e carbon.

With CO p r e s e n t t h e C I H n groups must

It i s c l e a r t h a t t h e r e a c t i o n of e t h y l e n e t a k e s p l a c e on t h e i r o n s u r f a c e ,

A f r e s h l y reduced c a t a l y s t is ca rbur i zed by t h e H2/CO mix tu re i n abou t an hour ( r e c a l l t h a t c a r b u r i z a t i o n i n CO a l o n e i s much s lower (1)). iod t h e hydrocarbon formation r a t e g r a d u a l l y i n c r e a s e s as t h e s u r f a c e carbon con- c e n t r a t i o n rises, as in f luenced by t h e bu lk carbon ( c a r b i d e ) c o n c e n t r a t i o n . swi t ch t o p u r e H2 g i v e s a methane peak, meaning t h a t hydrogen reacts a s H on t h e s u r f a c e and t h a t t h e s u r f a c e coverage by C is h igh . i s t h e formation o f CH, from t h e s u r f a c e C ; subsequent c h a i n growth i s r a p i d and occur s through t h e s e g roups , and t h e product d i s t r i b u t i o n i s determined by t h e r a t e of propagat ion and t e r m i n a t i o n ( d e s o r p t i o n ) of c h a i n s a r i s i n g from CH,. p r e sence of H20 and t o some e x t e n t C02 i n t h e g a s phase i n c r e a s e s s u r f a c e 0 a t t h e expense of C and/or H , i n h i b i t i n g t h e r e a c t i o n . bon i s g radua l ly conve r t ed t o i n e r t ( a t 250'C) g r a p h i t e , and a c t i v i t y s lowly de- c l i n e s a s t h e p a r t of t h e i r o n covered wi th l a b i l e C d e c r e a s e s . For a much re- gene ra t ed c a t a l y s t , oxygen fol lowed by hydrogen c l e a n s o f f a h ighe r f r a c t i o n of i n e r t g r a p h i t e than H 2 a l o n e .

During t h i s per -

A

The r a t e -de te rmin ing p rocess

The

However, a c t i v e s u r f a c e car -

74

References

1. Matsumoto, H . , and Bennet t , C . O . , J. C a t a l . 53, 331 (1978). 2. Atwood, H . E . , and Bennett , C . O . , Ind. Eng. Chem. Process Des. Dev. 18,

163 (1979) . 3. Borghard, W. G . , and Bennet t , C . O . , Ind. Eng. Chem. Product Res. Dev. 2,

18 (1979). 4 . Dal la B e t t a , R . A . , and S h e l e f , M . , J. Catal. 49, 383 (1977) . 5 . McCarty, J. G . , and Wise, H . , J. Catal. 57. 4 0 F ( 1 9 7 9 ) . 6 . Montarnel, R . , and Martino, G . , Rev. I n s t , FranSais du P Q t r o l e 32, 367 (1977) 7. Gibson, E. J., and Clarke , R . ! d . , J. Appl. Chem. 11 293 (1962). 8 . Eidus , YaT. , Z e l i n s k i i , N . D . , and Ershov, N . I . , Dokl. Akad. Nauk SSSR 60,

599 (1948). 9 . Hal l , W . K . , Kokes, R . J . , and E m m e t t , P . H . , J. Am. Chem. SOC. 82, 1027

(1960).

75

Table 1

Reaction of C02 a n d H:,

Feed Before After

7 .0 4.4 7 . 4

3 . 2 0 .52 3.5

1.5 0.065 1 . 5

Forma t ion Rate, 1-1 mole/g min.

CH4

‘ZH6

C3H8

T a b l e 2

R e l a t i v e P r o d u c t i o n Rates

( 4 h o u r s on s t r e a m )

c5

Feed M i x t u r e c1

10% CO + H2 0 .6 0.29 0.10 0 .02

10% C2Hq + H2 0.15 0.06 0.001

- c11 - c3 - C2 -

10% C3H6 + H 2 0 .49 0.087 0.002

10% b u t e n e - 1 + H

10% bu tene -2 + H

0 .19 0.76 0.08

0.20 0 .92 0 . 0 9

2

2

76

- 0 0 I VU

>

> -

>

>

>

9

N

L ? J = 2

Y

3

3 0

0 N

L .I=

'2

0

0 0 0 in -r N I I I

0 v . CJ L

t

m

"l

c .r( tJ m a e, c tJ C

79

b. L

d

N I

- + I -

L

X

Synthesis Gas Reactions Using Catalysts Formed by Oxidizing Ni-Containing Intermetallic Compounds

H. Imamura and W. E. Wallace

Department of Chemistry University of Pittsburgh Pittsburgh, PA. 15260

I. Introduction

Intermetallic compounds containing rare earths or actinides in chemical union with the transition metals Fe, Co or Ni are transformed when exposed to synthesis gas at elevated temperatures into mixtures of rare earth or actinide oxides and elemental Fe, Co or Ni. It has been found that these mixtures are exceptionally active for syngas conversion (1-12). The converted alloys have been characterized by Auger spectroscopy (1,13), x-ray diffraction, ESCA (14) and electron microscopy (7 ) . These studies showed that the surface regions consisted of transition metal nodules growing out of or dispersed on a substrate of rare earth or actinide oxide. The decomposed materials rather than the original alloy appear to be the catalytically active species for the reaction.

Additionally, it has been found that thorium-containing intermetallics such as ThNi5 readily reacted with elemental oxygen to form a mixture of metallic Ni and ThOp (12). The oxidation of ThNi5 occurred with a predominant formation of Tho2 because of the strong chemical affinity of thorium for oxygen. During the oxidation reaction metallic Ni aggregates precipitated out in a fashion similar to that observed when the intermetallic is exposed to syngas. The reaction of ThNi5 with a stoichiometric amount of oxygen required for the formation of thoria- supported Ni catalysts (Ni/ThOp) brought about complete transformation into a mixture of Ni and T h O p . This mixture had higher activity for methane formation by an order of magnitude than oxide-supported catalysts (15) prepared by conventional wet chemical procedures. Accordingly, it appears that the oxidation treatment of intermetallics constitutes a novel way for forming oxide-supported catalysts with high activity for syngas conversion.

In this work, the character of catalysts formed by the oxidation of several rare earth-nickel intermetallic compounds was studied in the manner used earlier to study the Th intermetallics. They were evaluated using x-ray diffraction, ESCA and CO chemisorption techniques. The resulting materials, which are probably new supported catalysts, were examined as syngas conversion catalysts.

11. Experimental

The intermetallic compounds (LaNiS, CeNi5, PrNi5, NdNi5, HoNi5, ErNi5 and ThNis) were prepared by induction melting the metal components in a water-cooled copper boat under an atmosphere of purified helium. These intermetallics were subjected to remelting several times or annealing at a prescribed temperature to insure homogeneity. The formation of the desired compounds was established by x-ray diffraction analysis.

The oxidation treatment of the intermetallics, which had been previously powdered in a porcelain mortar followed by outgassing, was conducted in the presence of oxygen at 610 d g . determined by the pressure drop in a closed system.

The amount of oxygen uptake by the compound was

TO establish the nature of the sample thus treated x-ray diffraction, x-ray photoelectron spectroscopy (ESCA) and CO chemisorption techniques were used.

8 2

Powder x-ray diffraction patterns were obtained using a Picker model 3488K diffractometer with Cu radiation. electron spectrometer using A1 Ka radiation (1486.6 eV). The spectrometer was operated at 1 2 KV and 25 mA with base pressure torr in the sample chamber. The binding energy was determined by reference to the contamination C Is line at 285.0 eV. The CO chemisorption measurements were made at room temperature by means of an adsorption flow method (16). The procedures used have been described in detail previously (12).

ESCA spectra were recorded on an AEI ES200

111. Results and Discussion

1. Characterization of Catalysts Formed by Oxidation

X-RAY DIFFRACTION

The previous work (12) on the oxidation of thorium-containing intermetallic compounds showed that the oxidation reaction occurred in a stepwise fashion. At first, thorium in the alloy was oxidized largely to form the oxide, during which process finely divided Ni aggregates precipitated out on the resulting oxide surface. area, by up to 200-fold. After completion of the oxidation of thorium further oxygen was taken up by the reaction of Ni to form NiO.

Accompanying this there was a remarkable enlargement in the surface

All the compounds studied in the present work readily reacted with consider- It was confirmed from x-ray diffraction studies able amounts of oxygen at 350°C.

that the oxidation steps approximated that of the thorium intermetallics just mentioned. For example, as depicted in Fig. 1, CeNi5 was completely transformed into a mixture of Ni phase and CeOp, i.e., Ni/CeOp, when reacted with the stoichiometric amount of oxygen required to oxidize the Ce present in the alloy. When the CeOp-Ni mixture was exposed to oxygen there was an additional uptake of oxygen. This occurred by the oxidation of Ni to form NiO. However, after reduction with hydrogen there was no evidence of NiO peaks in the pattern.

From x-ray line broadening measurements of the Ni (111) peak at 28 = 44.5 (Cu Ka radiation) it was possible to establish the Ni particle sizes dispersed on the resulting oxide using the Sherrer equation (18). As shown in Table 1, the particle sizes ranged from 90 to 350 1. showed an increase with increasing oxygen uptake for LaNi5, CeNi5 and ThNi5.

The particle sizes usually but not always

ESCA -

X-ray diffraction studies in the preceding section provided an overall image of the alloy transformed by the oxidation. ESCA measurements were made on the oxidized CeNi5 to examine the chemical state of the surface species participating in the reaction. ESCA spectra of the oxidized CeNi5 showed Ni, Ce, 0 and C signals within the probing depth of ESCA (several atomic layers). Confirming the results obtained by x-ray diffraction analysis, the Ce present in the surface region was found to exist largely in an oxide form. For Ni species the oxidized CeNi5 (C-4) exhibited the Ni 2~312 peaks at 853.9 and 856.6 eV. characteristic of Ni and NiO, respectively (19). Hence Ni is present in the surface region, consisting of several atomic layers, as metal and oxide. Since the ESCA peak intensity is directly correlated with the surface concentration, the composition of the surface can be roughly established from the ESCA information. The intensity ratio of Ni 2~312 to Ce 3d5/p, a7.5, indicates that the surface is largely metallic Ni.

These binding energies are

8 3

Table 1. Characterization of Catalysts Formed by Oxidation

Precursor Intermetallic O2 Uptake Surface Areaa) CO Chemisorption Partigle Size Compound (mmol/g) (m2/g) (umol/g) (A)

" (L-1) 1.71 0.55 1.2 90 " (L-2) 2.99 0.66 2.6 100

" (L-3) 6.57 3.5 7.1 100

LaNi5 - 0.10* 0.17*

* CeNi5 - 0.08* 0.13

" (C-1) 2.32 1.1 4.8 110

" (C-3) 4.47 25.4 45.7 200

" (C-2) 3.74 15.7 31.7 300

" (C-4) 5.14 23.7 51.8 350 * * PrNi5 - 0.15 0.10

" (P-1) 1.73 0.79 2.8 170

NdNi5 (N-1) 1.71 1.1 1.2 140

HoNi5 (H-1) 1.64 0.76 2.0 3 30

ErNi5 (E-1) 1.61 1.0 2.0 280 * ThNi5 - 0.09* 0.2

" (T-1) 1.91 12.0 19.0 200 " (T-2) 3.35 18.0 105.7 2 70

a) Surface areas were measured at liquid nitrogen temperature by means of argon

* These values were obtained for the original intermetallic compounds. adsorption (17).

CO CHEMISORPTION

Although ESCA studies revealed existence of metallic Ni in the surface region, to obtain the information about the amount of metallic surface area or the number of active sites present on the surface room temperature CO chemisorption measurements were made. The results obtained are summarized in Table 1. It is informa- tive to notice that the oxidized samples (L-l, C-l, P-l, N-l, H-l, E-l and T-l) contain elemental oxygen corresponding to the complete formation of Ni/oxide assuming a stoichiometric reaction. It is evident that the oxidation led to an increase in the number of active sites along with a rise in the surface area. The extent of the increase was observed to be dependent upon the particular rare earth or actinide involved in the original compound. CeNi5 and ThNi5 exhibited striking changes in chemisorption during the stages of oxidation. CO chemisorption increases by up to 500-fold compared t o the original compound were observed. contrast, increases for LaNi5 were much less pronounced. of CeNi5 and ThNi5 on the one hand and LaNi5 on the other undoubtedly reflects important physicochemical differences. The most significant difference between LaNi5 and the other two compounds is that La is tripositive and Ce and Th are quadripositive. This leads t o a different electron concentration and perhaps a difference in chemical stability.

In The differing behavior

This may be responsible for variation in 84

I

behavior of the systems produced by oxidation, but the precise factors and their operation are as yet unclear.

2. Reaction of CO and H2

The reaction was carried out in the range of 150 to 300°C over the alloys, which had been oxidized to varying extents. Table 2.

The data obtained are summarized in Activity for the present reaction was represented by the rate of CO

Table 2. Activity of Various Catalysts

3 Precursor Intermetallic CO Conversion Activity T .N. x10 Compound (%) (ml/sec.g) (sec-l)

LaNi5 (L-1) 1.2 1. S X ~ O - ~ 48 CeNi5 (C-1) 2.0 2. ~ x I O - ~ 18

" (C-2) 1.0* 1. 2x1~-3* " (C-3) " (C-4)

* * 2.6 3.7~10-~* 1.7 5.0" 6.1~10 3.8" -3"

PrNi5 (P-1) 1.8 2. 2x1~-3 26

HoNiS (H-1) 1.6 2.0~10-~ 31 NdNi5 (N-1) 0.5 6. l ~ l O - ~ 19

ErNi5 (E-1) 4.2 5. 2x1~-3 59

ThNi5 (T-1) 9.0 1.1x10- *

10.6"

5.6

2* -2" *

" (T-2) 7.0(at 190OC) 3.5~10 * The values correspond to the results measured at 205OC; the others were obtained at 275"C, except as noted.

consumption per gram-catalyst. This kind of comparison seems valid since the catalysts were used under very similar conditions. that the catalytically active species is metallic Ni dispersed on the surface, it is also of interest to specify the turnover number (T.N.), representing the specific activity per site. per second was determined from CO chemisorption measurements assuming a 1:l ratio of a CO molecule to surface Ni atom in the surface complex. studied the oxidized CeNiS and ThNi5 exhibited exceptional activity (Table 2) . oxidized CeNi5 and ThNis showed T.N. measured at 205°C about an order of magnitude higher than conventional silica- or alumina-supported Ni catalysts (15). It is therefore apparent that the supported catalysts derived using the oxidation treatment of intermetallics are exceptionally active for the conversion of CO and Hg to methane. T. Inui et al. (20) have reported that activity for methanation was sub- stantially enhanced when a3% rare earth oxide such as Lap03 or Ce2O3 was added t o Ni-supported catalysts. It was found (21) that Tho2 was also operative as a promoter for supported Ni catalysts.

Taking into account the fact

The turnover number as molecules CH4 produced per site

Among the catalysts The

It should be emphasized that the effectiveness of rare earth or actinide oxide-supported catalysts for syngas conversion is very dependent upon the preparation method. As noted in the Introduction, for example, a ThOg-supported catalyst (6) prepared using the conventional impregnation procedure followed by calcining and reducing processes exhibited very poor activity compared to that obtained by the oxidation technique. It thus appears that the oxidation treatment of intermetallics plays a decisive role in formation of active catalysts and this method constitutes a new way of producing superior oxide-supported catalysts.

85

A s shown i n Table 2, f o r t he oxidized C e N i g and ThNi5 inc rease i n t h e ex ten t of ox ida t ion r e s u l t s i n an inc rease i n the a c t i v i t y . There i s a good correspon- dence between t h e CO chemisorption and a c t i v i t y and i n t h i s respec t t h e present systems c lose ly resemble behavior observed earlier f o r oxidized Ni5Si2 (22).

Hydrocarbon products i n t h e r eac t ion were l a r g e l y methane. S m a l l amounts of Cp t o C,, hydrocarbons were a l s o observed. va r ious oxidized a l l o y s is l i s t e d i n Table 3. The s e l e c t i v i t y w a s determined i n

S e l e c t i v i t y of hydrocarbon products over

Table 3. S e l e c t i v i t y of Ca ta lys t s

Precursor

Compound I n t e r m e t a l l i c Conversion Composition ( X )

(%) c1 c2 c3 c4

L a N i 5 (L-1) 1.8 92.0 7.0 1 . 0 - C e N i 5 (C-1) 3.4 86 .3 7.0 5.3 -

" (C-4) 5.0 77.3 15.9 6.8 - PrNi5 (P-1) 3.1 88.4 6.6 5.0 - NdNi5 (N-1) 1.8 91.3 4.3 4.3 - HoNi5 (H-1) 2.5 82.4 8.1 9.5 - E r N i 5 (E-1) 4.2 74.0 10.9 15.0 - ThNi5 (T-1) 12.5 80.0 1 2 . 1 6.8 1 .4

t h e conversion range below 10%. It is unclear from t h i s study whether t h e se lec- t i v i t y is dependent upon ex ten t of t he t o t a l conversion. It is t o be noted t h a t t h e s e l e c t i v i t y depends upon t h e na tu re of t h e rare e a r t h o r a c t i n i d e i n t h e pre- cu r so r compound. Oxidized LaNi5 revealed very high s e l e c t i v i t y f o r methane forma- t i o n . This accords wi th t h e observa t ion of T. I n u i e t a l . (20) r e f e r r e d t o above.

1.

2.

3.

4. 5.

6. 7 . 8.

References

V. T. Coon, T. Takeshi ta , W. E. Wallace and R. S . Craig, J. Phys. Chem. E, 1878 (1976). A. Elattar, T. Takeshi ta , W . E. Wallace and R. S . C r a i g , Science 196, 1093 (1977). V. T. Coon, W. E. Wallace and R. S . Craig, i n "The Fare Ear ths i n Science and Technology," eds . G . J . McCarthy and 3 . J . Rhyne, Plenum Press, NY (1978),

A. E l a t t a r , W. E . Wallace and R. S . Craig, w., (1978), p . 87. W. E. Wallace, i n Hydrides f o r Energy Storage, A. F . Andressen and A. J . Maeland, eds . , Pergamon Press Inc. (1978), p. 33. A . E l a t t a r , W . E . Wallace and R. S . Craig, Advances i n Chemistry, i n press . V. T . Coon, Ph.D. Thes is , Univers i ty of P i t t sbu rgh , August, 1977. C . A . Luengo, A . L. Cabrera, H. B. MacKay and M. B. Maple, J. Cata l . 47, 1 (1977).

p. 93.

9. G. B. Atkinson and L. J . Nicks, J. Catal . 46, 417 (1977). 10. A. Elattar and W. E . Wallace, i n "The Rare Ear ths i n Modern Science and

11. A. E l a t t a r and W. E . Wallace, Science, submitted. 12. H. Imamura and W. E . Wallace, J. Ca ta l , submitted. 13. A. G . Moldovan, A. E l a t t a r , W. E . Wallace and R. S. Cra ig , J . So l id S t a t e

Technology" (1979), i n press .

Chem. 5, 2 3 (1978).

86

14. 15.

16. 17. 18.

19. 20.

21. 22.

R. Chin, A. E l a t t a r , W . E. Wallace and D. Hercules, J . Catal., submitted. M. A. Vannice, J. Cata l . 37, 449 and 462 (1975); 60, 129 (1975); fi, 152 (1976); so, 228 (1977). H . L . Gruber, Anal. Chem. 34, 1828 (1962). F. M. Nelsen and F. T. Eggertsen, E., 3, 1387 (1958). H. P . Klug and L. E . Alexander, i n s a y Di f f r ac t ion Procedures f o r Poly- c r y s t a l l i n e & Amorphous Mate r i a l s , 2nd ed.,p. 68, Wiley, NY (1974). K. S. K i m and N . Winograd, Surf. S c i . 43, 625 (1974). T. I n u i , M. Funabiki, M. Suehiro and T. Sezume, J . C . S . Faraday 175, 787 (1979). S. Medsforth, J . Chem. SOC. 123, 1452 (1923). H . Imamura and W . E. Wallace, J . Phys. Chem., i n p re s s .

87

N i (2001 CeO,( I I I) Oxidized

CeNi, C - I ) I I I 1 i

50 40 30 20 6 0 2 9

Fig . 1 Comparison of x-ray d i f f r a c t i o n (Cu Ka rad ia t ion ) of t he oxidized and o r i g i n a l C e N i 5 .

ss

CATALYTIC ASPECTS OF H I G H TEMPERATURE METHANATION

Kars ten Pedersen , A l l a n Skov and J . R . Ros t rup-Nie lsen

Haldor Topsgie Research L a b o r a t o r i e s NymGllevej 55 , DK-2800 Lyngby, Denmark

INTRODUCTION

Methanat ion o f s y n t h e s i s g a s m i x t u r e s i s an e s s e n t i a l s t e p i n t h e manufac ture o f s u b s t i t u t e n a t u r a l g a s (SNG):

CO + 2 H 2 = CH4 + H20 (-AHo298 = 206 kJ/mol) C 0 2 + 4 H 2 = CH4 + 2 H 2 0 AH^^^^ = 1 6 5 kJ/mol)

The r e a c t i o n s a re c a t a l y z e d by v a r i o u s metals of which s u p p o r t e d n i c k e l i s p r e f e r r e d .

Methanat ion f o r SNG p r o d u c t i o n i s complex because t h e h i g h con- c e n t r a t i o n s of CO and C02 involved r e s u l t i n l a r g e p o t e n t i a l t e m - p e r a t u r e i n c r e a s e s . T h i s may c a u s e s i n t e r i n g of t h e c a t a l y s t or f o r some cases a p o t e n t i a l f o r carbon format ion .

One s o l u t i o n i s t o i n c l u d e a r e c y c l e s t r e a m of p r o d u c t g a s a s a d i l u e n t . I t i s e v i d e n t t h a t t h i s s o l u t i o n i n v o l v e s a loss of energy i n t h e r e c y c l e o p e r a t i o n , and t h a t a n economic p r o c e s s s h o u l d al low minimum r e c y c l e . For a n a d i a b a t i c p r o c e s s , however, t h i s is equiva- l e n t t o a l a r g e t e m p r a t u r e i n c r e a s e .

Another s o l u t i o n i s t o c a r r y o u t the methanat ion i n a c o o l e d r e a c - t o r i n which t h e h e a t o f r e a c t i o n i s t r a n s f e r r e d from t h e r e a c t i o n zone i n t o a c o o l i n g m e d i u m , e .g . b o i l i n g water. For a c o o l e d reac- t o r , it a p p e a r s advantageous t o d e s i g n f o r h i g h " h o t zone" tempera- t u r e s , because t h i s g i v e s a b e t t e r h e a t t r a n s f e r .

When d e c r e a s i n g t h e o p e r a t i n g t e m p e r a t u r e , the need f o r h i g h e r ca- t a l y s t a c t i v i t y i n c r e a s e s . Below a c e r t a i n t e m p e r a t u r e t h e r e a c t i o n w i l l n o t " i g n i t e " . T h i s problem may be aggrava ted because t h e c a t a - l y s t having been exposed t o t h e h i g h tempera ture , may have t o oper - a t e a t t h e l o w t e m p e r a t u r e a f t e r age ing or p o i s o n i n g of t h e c a t a l y s t a t t h e r e a c t o r i n l e t .

Moreover, t h e s t e e p tempera ture p r o f i l e means t h a t o t h e o p e r a t i o n t e m p e r a t u r e of a c a t a l y s t p e l l e t may change 50-100 C w i t h i n seconds i n c a s e of v a r i a t i o n s i n l o a d , r e c y c l e r a t i o and p r e h e a t ternpera- t u r e . T h i s r e q u i r e s h i g h mechanical s t a b i l i t y of t h e c a t a l y s t .

Thus fo r a d i a b a t i c and f o r cooled r e a c t o r s a s w e l l , i n o r d e r t o meet t h e s e p r o c e s s r e q u i r e m e n t s , t h e c a t a l y s t should b e a c t i v e and s t a b l e b o t h a t h i g h and l o w t e m p e r a t u r e s . T h i s i s a key problem t o b e so lved when o p t i m i z i n g t h e methanat ion p r o c e s s f o r coa l -based S N G .

The paper summarizes c a t a l y s t s t u d i e s o f impor tan t phenomena t o be c o n t r o l l e d i n t h e development and u s e o f a n i n d u s t r i a l c a t a l y s t meet ing t h e s e r e q u i r e m e n t s .

89

EXPERIMENTAL

The c a t a l y s t s were s t u d i e d i n v a r i o u s t e s t u n i t s . S i n t e r i n g s t u d i e s were performed i n a t u b u l a r r e a c t o r (Di=32 mm) i n which v a r i o u s ca- t a l y s t samples were exposed s i m u l t a n e o u s l y t o s i n t e r i n g a t g i v e n t e m p e r a t u r e , p r e s s u r e and atmosphere. Low t e m p e r a t u r e d e a c t i v a t i o n phenomena were s t u d i e d i n d i f f e r e n t i a l f low r e a c t o r s (Di=0.8 mm) . The c a t a l y s t was u s e d as 0 . 3 - 0 . 5 mm par t ic les d i l u t e d w i t h i n e r t m a t e r i a l . S t a n d a r d a c t i v i t y tests, and d e t e r m i n a t i o n o f n i c k e l s u r - face areas were d e s c r i b e d e a r l i e r (1). The main p a r t o f the devel - opment work took p l a c e i n a p i l o t p l a n t w i t h a 5 l i t r e a d i a b a t i c reactor. The reactor had a f u l l bed l e n g t h ( u p t o 2m) and o p e r a t e d a t i n d u s t r i a l mass ve loc i t ies , l e a v i n g t h e reactor d i a m e t e r as t h e o n l y sca le -up parameter . C a t a l y s t samples from p i l o t tests were used f o r p h y s i c a l and c a t a l y t i c a l examinat ion .

RESULTS

S i n t e r i n q

The methanat ion r e a c t i o n on n i c k e l r e q u i r e s a l a r g e ensemble of n i c k e l atoms ( 2 ) , a n d t h e s p e c i f i c a c t i v i t y i s i n f l u e n c e d by n i c k e l c r y s t a l l i t e s i z e ( 3 ) , by the composi t ion o f t h e s u p p o r t (4,5,6), and by n o n - l i n e a r p o i s o n i n g e f f e c t s (1). T h e r e f o r e , t h e r e a c t i o n a p p e a r s s e n s i t i v e t o t h e s t r u c t u r e of t h e c a t a l y s t and t o i t s h i s - t o r y of o p e r a t i o n .

S i n t e r i n g of t h e n i c k e l c r y s t a l s r e s u l t s i n loss of s u r f a c e area, and i n p r i n c i p l e r e c r y s t a l l i z a t i o n may change the n i c k e l ensembles a v a i l a b l e , and hence c a u s e a d e c r e a s e o f t h e s p e c i f i c a c t i v i t y . We showed p r e v i o u s l y ( 4 , 7 ) t h a t h e a t t r e a t m e n t o f n i c k e l c r y s t a l s ono a s t a b l e l o w area ceramic s u p p o r t r e s u l t e d i n no s i n t e r i n g a t 550 C o v e r a p e r i o d of 1 0 0 0 h o u r s , whereas the n i c k e l s u r f a c e a r e a dropped t o around 40 t o 25% o v e r t h e same p e r i o d a t 7OO0C and 85OoC r e s p e c t - i v e l y , t h i s r e s u l t cor responds t o t h e r u l e of Tammann, accord ing t o which s i n t e r i n g i s e x p e c t e d above 0 . 5 t i m e s t h e m e l t i n g p o i n t ( K) ( 8 ) o f t h e m e t a l . The growth mechanism of suppor ted metal c r y s t a l s a p p e a r s v e r y complex (9,101. The growth r a t e might b e i n f l u e n c e d by t h e w e t t i n g p r o p e r t i e s of t h e metal t o t h e s u p p o r t , and by t h e micropores of t h e s u p p o r t m a t e r i a l . I t w a s i l l u s t r a t e d t h a t t h e d i f f u s i o n o f a m e t a l c r y s t a l l i t e i s impeded, when t h e s i z e of t h e m e t a l c r y s t a l l i t e i s of t h e o r d e r magni tude o f t h e d i a m e t e r o f t h e p o r e ( 1 1 , 1 2 ) . I n g e n e r a l , t h e m e t a l p a r t i c l e s may h a r d l y grow t o a s i z e l a r g e r t h a n t h e pore d i a m e t e r o f t h e s u p p o r t . T h i s means t h a t a s t a b i l i z e d micropore sys tem o f t h e s u p p o r t e f f e c t i v e l y pre- v e n t s s i n t e r i n g o f t h e n i c k e l c rys ta l s .

N i c k e l c a t a l y s t s d e s i g n e d f o r low t e m p e r a t u r e o p e r a t i o n a re normally based on h i g h a r e a s u p p o r t s such a s gamma a lumina , s i l i c a , chromia, etc. These s u p p o r t s s u f f e r from s i g n i f i c a n t s i n t e r i n g , which ma accompanied by weakening when exposed t o t e m p e r a t u r e s above 5 0 0 C (4 ,131. The s i n t e r i n g may b e a c c e l e r a t e d by h i g h steam p a r t i a l p r e s - s u r e ( 1 4 ) . F i g u r e 1 shows r e s u l t s from s i n t e r i n g tests a t c o n d i t i o n s f o r a c c e l e r a t e d s i n t e r i n g ( i . e . H O/H2=10, 30 a t m ) . Three c a t a l y s t s are compared: a l o w area steam rezorming c a t a l y s t , a h i g h a r e a low

8 be

90

t empera ture methanat ion c a t a l y s t (Ni/y A 1 0 ) , and t h e Topsge methanat ion c a t a l y s t MCR-type. The MCR c a z a j y s t m a i n t a i n s a h i g h t o t a l s u r f a c e area and mechanica l s t r e n g t h , whereas t h e y A l Z 0 3 based c a t a l y s t d e t e r i o r a t e s . ~ l l c a t a l y s t s show s i g n i f i c a n t loss i n n i c k e l s u r f a c e a r e a a t 800°C.

Carbon Formation

Thermodynamics p r e d i c t carbon f o r m a t i o n f o r methanat ion above a c e r t a i n tempera ture , depending on f e e d composi t ion and p r e s s u r e . T h i s may i n f l u e n c e t h e minimum r e c y c l e r a t i o a l lowed, a s i l l u s - t r a t e d i n F igure 2 . However, t h e thermodynamic d a t a a r e i n f l u - enced by t h e c a t a l y s t , because it m o d i f i e s t h e s t r u c t u r e o f t h e carbon. This a l l o w s o p e r a t i o n a t c o n d i t i o n s more c r i t i c a l t h a n t h o s e , which correspond t o t h e l i m i t p r e d i c t e d on t h e b a s i s of i d e a l g r a p h i t e . W e have shown p r e v i o u s l y (4,151 t h a t t h i s e f f e c t i s f a v o r e d by s m a l l n i c k e l c r y s t a l s i n t h e c a t a l y s t .

I n p r a c t i c e , t h i s means t h a t t h e s o - c a l l e d p r i n c i p l e o f e q u i l i b r a t e d g a s (1,4), ( i . e . carbon f o r m a t i o n when t h e g a s shows a f f i n i t y for carbon, a f t e r t h e e s t a b l i s h m e n t o f t h e methanat ion and s h i f t equi - l i b r i a ) p r e d i c t s no carbon f o r m a t i o n f o r methanat ion . The v a l i d i t y o f t h i s p r i n c i p l e i s i n d i c a t e d by t h e r e s u l t s i n Table 1, o b t a i n e d from thermogravimet r ic s t u d i e s (1). The c o n c l u s i o n h a s been f u r t h e r confirmed by t h e e x p e r i e n c e i n the p i l o t tests.

Low Temperature Problems

Low o p e r a t i n g t e m p e r a t u r e s f a v o r the a d s o r p t i o n of p o i s o n s , e .g . s u l f u r on t h e c a t a l y s t . W e have shown t h a t t h e e f f e c t o f s u l f u r i s s t r o n g l y non- l inear (1) r e f l e c t i n g t h a t t h e methanat ion reac- t i o n i s s t r u c t u r e s e n s i t i v e . T h i s , and o t h e r s t u d i e s (16 ,171 , show t h a t a s u l f u r c o n t e n t i n t h e f e e d stream o f less t h a n 1 0 ppb i s r e q u i r e d t o o b t a i n a r e a s o n a b l e methanat ion a c t i v i t y a f t e r e q u i l i - b r a t i o n o f t h e s u l f u r a d s o r p t i o n . T h e r e f o r e , t h e e f f e c t o f s u l f u r po isoning should ra ther b e a n a l y s e d i n t e r m s o f a dynamic model f o r f i x e d bed a d s o r p t i o n (18 ) .

The o p e r a t i o n a t a l o w r e c y c l e r a t i o or t h e s t r a i g h t - t h r o u g h o p e r a t i o n i n a c o o l e d r e a c t o r , i m p l i e s h i g h p a r t i a l p r e s s u r e s of carbon monoxide a t the r e a c t o r i n l e t . T h i s r e s u l t s i n t w o problems.

A t t empera tures below 23OoC, t h e r e i s a s u b s t a n t i a l r i s k t h a t carbon monoxide reacts w i t h n i c k e l , forming n i c k e l carbonyl . O p e r a t i o n i n t h i s tempera ture r a n g e , w i t h a p a r t i a l p r e s s u r e o f carbon monox- i d e of 2.5 atm r e s u l t e d i n t r a n s p o r t o f n i c k e l i n t h e c a t a l y s t bed. Moreover, t h e f o r m a t i o n o f n i c k e l c a r b o n y l r e s u l t e d i n a d r a s t i c growth o f t h e n i c k e l c r y s t a l s , u p t o p a r t i c l e s of 2 0 , 0 0 O f t , t h u s exceeding, by l a r g e , t h e p o r e s i z e o f t h e c a t a l y s t s u p p o r t . T h i s growth r e s u l t e d i n break-down of t h e c a t a l y s t . The f o r c e s involved appear much s t r o n g e r t h a n observed i n thermal s i n t e r i n g o f t h e n i c k e l c r y s t a l s , as d e s c r i b e d above.

Another r e s u l t from o p e r a t i n g w i t h h i g h p a r t i a l p r e s s u r e o f carbon monoxide, appears t o be a d e a c t i v a t i o n phenomenon, c a l l e d B-deactiv- v a t i o n developing s lowly i n some p i l o t t es t s , and b e i n g r e f l e c t e d by

91

t h e appearance o f an i n f l e c t i o n p o i n t i n t h e a x i a l t empera tu re pro- f i l e . F i g u r e 3 i l l u s t r a t e s t h e movement of t h e t empera tu re p r o f i l e , and t h a t t h e 8 - d e a c t i v a t i o n d i s a p p e a r s above a c e r t a i n i n l e t t e m - p e r a t u r e . The a c t i v i t y cou ld be r e s t o r e d by t r e a t m e n t i n hydrogen, as exp la ined below.

The low t empera tu re d e a c t i v a t i o n phenomena were f u r t h e r demonst ra ted b y l a b o r a t o r y tests on a N i / q A 1 O3 c a t a l y s t i n a d i f f e r e n t i a l re- a c t o r . A s shown i n F i g u r e 4 , no 3 e a c t i v a t i o n was observed i f CO was r e p l a c e d by C02. The d e a c t i v a t i o n r a t e i n c r e a s e s s i g n i f i c a n t l y wi th t h e CO/H2 r a t i o and by t h e p re sence of s u l f u r . The r o l e of s u l f u r on o t h e r d e a c t i v a t i o n phenomena w a s i n d i c a t e d i n o u r e a r l i e r s t u d i e s (1) - The MCR-2X c a t a l y s t shows much less d e a c t i v a t i o n than t h e N i / n A 1 O3 c a t a l y s t . of n i c k e l c r y s t a l s showed t h a t t h e N i / q A 1 O3 c a t a l y s t had also been exposed to ca rbony l fo rma t ion i n c o n t r a s t $0 t h e MCR-2X c a t a l y s t . The l a r g e i n f l u e n c e of c a t a l y s t composi t ion on d e a c t i v a t i o n r a t e and ca rbony l fo rma t ion w a s a l s o r e p o r t e d by Vannice and Gar t en ( 6 ) .

The 8 -deac t iva t ion i s probably due t o t h e fo rma t ion of a l e s s r e - a c t i v e carbon s ta te on t h e n i c k e l s u r f a c e , which might be t h e 6 - s t a t e i d e n t i f i e d by W i s e e t . a l . ( 1 9 , 2 0 ) .

The s i t u a t i o n co r re sponds t o t h e d e a c t i v a t i o n observed i n steam naphtha re forming a t low t empera tu res ( 2 1 ) , and t o a g e n e r a l model f o r carbon fo rma t ion on n i c k e l ( 2 2 ) . The adsorbed i n t e r m e d i a t e (a '-carbon)may e i t h e r be g a s i f i e d t o methane (2,19) o r be d i s - so lved i n n i c k e l a s carbon and form carbon whiskers (l), o r be t r a n s f e r r e d i n t o e n c a p s u l a t i n g carbon (6 -ca rbon) . For t h e p r e s e n t c a s e , a p p a r e n t l y t h e conve r s ion of a' i n t o is too s l o w a t ve ry low t empera tu res , e . g . 25OoC, whereas a t h i g h t empera tu res t h e r a t e o f hydrogenat ion of 6-carbon exceeds t h e t r a n s f o r m a t i o n ra te of a' i n t o 8-carbon ( 2 0 ) . These e f f e c t s a r e ove r l apped by t h e i n f l u e n c e o f t h e s u r f a c e c o n c e n t r a t i o n of a ' - ca rbon such as t h e hydrogenat ion r a t e of a ' - ca rbon and t h e pa rame te r s govern ing t h e chemisorp t ion of carbon monoxide. The CO chemiso rp t ion depends on t h e p a r t i a l p re s - s u r e of CO and t h e t empera tu re a t a g iven p o s i t i o n i n t h e r e a c t o r , and it i s a l s o a f f e c t e d by t h e composi t ion of t h e c a t a l y s t (5). .

Analys i s of t h e s p e n t c a t a l y s t s i n d i c a t e d by t h e g rowt i

MCR-2X C a t a l y s t

The development program f o r methanat ion c a t a l y s t s a t Tops0e ' s l abo ra - t o r i e s aimed s p e c i f i c a l l y a t s o l v i n g t h e problem of o p e r a t i n g over a wide tempera ture r ange . The work r e s u l t e d i n t h e MCR-2X c a t a l y s t . The suppor t has a s t a b i l i z e d micropore sys tem t h a t e f f e c t i v e l y pre- v e n t s s i n t e r i n g of t h e n i c k e l c r y s t a l s . The r e s u l t i n g h igh n i c k e l s u r f a c e a r e a and t h e absence of a l k a l i (sometimes added t o p reven t carbon format ion) l e d t o t h e d e s i r e d h igh methanat ion a c t i v i t y . The c a t a l y s t i s mechan ica l ly stable a t h igh as w e l l a s low tempera tures . The s t a b i l i t y was proven i n p i l o t tests w i t h a t o t a l run-time arnount- i n g t o 1 5 , 0 0 0 hours . T h i s i nc luded 8 , 0 0 0 hours o g e r a t i o n a t t h e same c a t a l y s t f i l l i n g a t a maximum tempera tu re of 600 C. Data i n Tab le 2 demons t r a t e s t h e t h e r m o - s t a b i l i t y of MCR-2X r e f l e c t e d by an a lmost unchanged mechanica l s t r e n g t h and t o t a l s u r f a c e a r e a . The a c t i v i t y s t a b i l i z e d a f t e r 1,000-2,000 hours .

9 2

The mechanical and chemical p r o p e r t i e s of MCR-2X a l s o o f f e r f l e x i - b i l i t y i n p rov id ing t h e c a p a b i l i t y f o r r e g e n e r a t i o n of s p e n t c a t a - l y s t s . Tab le 3 shows r e s u l t s from r e g e n e r a t i o n tests performed on samples t aken a f t e r 4700 hours o p e r a t i o n i n t h e p i l o t p l a n t . The carbonaceous f i l m r e s p o n s i b l e f o r t h e 8 - d e a c t i v a t i o n can be removed simply by t r e a t m e n t i n hydrogen, whereas s u l f u r i s more d i f f i c u l t t o remove. However, t h e c a t a l y s t e a s i l y w i t h s t a n d s a h igh tempera- t u r e o x i d a t i o n and r e - r educ t ion , which w i l l n o t o n l y remove s u l f u r , b u t a l s o r e s u l t i n r e d i s t r i b u t i o n of any s i n t e r e d n i c k e l c r y s t a l s . AS shown i n Table 3 , more than 50% o f t h e o r i g i n a l a c t i v i t y of a new c a t a l y s t can be rega ined by t h i s method.

The p r o p e r t i e s of MCR-2X can be u t i l i z e d i n d i f f e r e n t p r o c e s s schemes opt imized f o r t h e feedgas i n q u e s t i o n . The c r i t i c a l s t e p i s t h e f i r s t methanat ion s t a g e , where t h e f u l l p o t e n t i a l o f MCR-2X i s u t i l i z e d , MCR-2X a l lowing maximum p r a c t i c a b l e t empera tu re in - c r e a s e from c a . 3OO0C t o 70OoC.

The mechanica l s i n , t e r i n g problem could be so lved by u s i n g steam r e - forming c a t a l y s t s , which w i l l , o f c o u r s e , be a c t i v e a l s o f o r metha- n a t i o n . However, t h e n i c k e l s u r f a c e a r e a s i n most steam reforming c a t a l y s t s a r e t o o s m a l l t o p rov ide adequa te low t empera tu re a c t i v i - t y , t h u s d i c t a t i n g o p e r a t i n g a t h i g h e r r e a c t o r i n l e t t empera tu res . Th i s w i l l n o t n e c e s s a r i l y i n f l u e n c e t h e o v e r a l l conve r s ion i n t h e r e a c t o r , which i s f i x e d by t h e e x i t t empera tu re . However, f o r a d i a - b a t i c o p e r a t i o n , t h e reduced t empera tu re r ise means a h i g h e r r e c y c l e energy consumption. I n p r i n c i p l e t h i s can be overcomed by i n c r e a s i n g a l s o t h e e x i t t empera tu re , b u t t h i s means a g r e a t e r number of r eac - t o r s because of t h e s m a l l e r conve r s ion pe r reactor. Th i s s i t u a t i o n i s i l l u s t r a t e d i n F i g u r e 5 , i n which t h e o p e r a t i o n , based on MCR-ZX, i s shown ( s o l i d l i n e ) i n a s i m p l i f i e d example invo lv ing t h r e e a d i a - b a t i c r e a c t o r s , cor responding t o an o v e r a l l conve r s ion o f 95%.

The p r o c e s s p a t h , TREMP (Tops0e Recycle Methanation P rocess ) is compared wi th a l t e r n a t i v e r o u t e s of h igh t empera tu re methanat ion (dashed l i n e s ) based on a re forming t y p e c a t a l y s t . A t empera tu re of 45OoC is assumed a s t h e minimum i n l e t t empera tu re f o r t h e reforming type c a t a l y s t . To ach ieve t h e same conve r s ion of t h e f i r s t r e a c t o r a s ob ta ined i n TREMP, a r e c y c l e r a t i o 2 t i m e s h i g h e r a s i n TREMP i s r e q u i r e d . T h i s means h ighe r energy consumption. I f r e c y c l e i s exc luded , f o u r r e a c t o r s t a g e s a r e necessa ry w i t h re forming c a t a - l y s t s t o o b t a i n a conve r s ion e q u i v a l e n t t o t h a t o f t h e f i r s t TREMP r e a c t o r , Moreover, t h i s s o l u t i o n i s d o u b t f u l because of t h e excess- i v e l y h igh e x i t t empera tu re of t h e f i r s t r e a c t o r .

By t h e u s e of a combined bed of a non-n icke l g a t a l y s t w i t h MRC-2X, t h e i n l e t t empera tu re can bg dec reased t o 200 C , t h u s a l lowing a t empera tu re i n c r e a s e of 500 C a t a reduced r e c y c l e r a t e . The wide o p e r a t i n g range of MCR-2X may be u t i l i z e d i n t h e d e s i g n o f b o i l i n g water r e a c t o r s f o r z e t h a n a t i o n . With MCR-ZX, d e s i g n f o r " h o t zone" t empera tu res of 7 0 0 C i s r e a l i s t i c , s i n c e t h i s l e a v e s a good s a f e t y margin. An e x p l o r a t i v e tes t w a s made i n t h e p i l o t p l a n t i n which M c R - ~ X was exposed t o 78OoC i n t h e " h o t zone". For s i m p l i c i t y t h e t e s t was made i n an a i r - coo led r e a c t o r . The i n l e t t empera tu re was

93

3OO0C and a f t e r t h e h o t zone, t h e r e a c t i o n tempera ture w a s decreased t o about 25OoC. The t u b e w a l l t empera tu re i n t h e h o t zone w a s between 300 and 4OO0C, which i s c l o s e t o t h e expec ted v a l u e i n an i n d u s t r i a l b o i l i n g water r e a c t o r . Measured and c a l c u l a t e d tempera- t u r e p r o f i l e s a r e shown i n F i g u r e 6 . N o s i g n i f i c a n t d e a c t i v a t i o n of t h e c a t a l y s t was observed a t t h e tes t , which suppor t s t h e p o s s i b i l i - t y f o r des ign ing f o r h igh h o t s p o t t empera tu res , be ing impor t an t f o r optimum r e a c t i o n and h e a t t r a n s f e r c o n d i t i o n s .

A s p e c i a l a p p l i c a t i o n o f methanat ion i s r e l a t e d t o t h e Long Dis tance Energy Transpor t System NFE or ADAM/EVA system, which i s be ing deve loped a t t h e German Nuc lea r Research Cen te r KFA-Jclich, i n cooper- a t i o n wi th Rhe in i sche Braunkohlenwerke AG i n Cologne. I n t h i s system ( 2 3 , 2 4 ) , nuc lea r ene rgy released i n a helium-cooled h igh tempera ture r e a c t o r i s t r a n s f e r r e d t o steam re fo rmer (EVA) w i th a h o t he l ium as h e a t i n g medium. The p r o d u c t i s t r a n s p o r t e d by p i p e l i n e t o power p l a n t s i n which t h e h e a t i s r ecove red i n a methanat ion p l a n t (ADAM). The h igh e x i t t empera tu re which can be accep ted of MCR-2X makes it p o s s i b l e t o raise s u p e r h e a t e d h igh p r e s s u r e steam a t t h e d e s t i n a t i o n f o r e l e c t r i c i t y p r o d u c t i o n a s r e q u i r e d i n t h e NFE system. TopsQe has s u p p l i e d t h e semi-commercial demons t r a t ion p l a n t ADAM-1 t o KFA - J i i l i c h . The p l a n t i s based on t h r e e a d i a b a t i c methanat ion s t e p 3 , and i t i s p rocess ing s y n t h e s i s g a s manufactured from up t o 200 Nm pe r hour of n a t u r a l gas ( 2 3 ) . F i g u r e 7 shows t empera tu re p r o f i l e s from a n ADAM I run which was made by KFA i n coope ra t ion wi th Tops@e ( 2 5 ) . MCR-2X was i n s t a l l e d i n t h e f i r s t two methanat ion s t e p s , whereas t h e t h i r d methanator o p e r a t e d on MCR-4 which i s a h i g h l y a c t i v e l o w t e m - p e r a t u r e c a t a l y s t .

CONCLUSIONS

The u s e of a n i c k e l c a t a l y s t f o r methanat ion i s l i m i t e d t o a minimum o p e r a t i n g t empera tu re because of t h e r i s k of carbonyl fo rma t ion and d e a c t i v a t i o n , and t o a maximum o p e r a t i n g t empera tu re because of s i n - t e r i n g and i n c e r t a i n c a s e s t h e r i s k of carbon format ion . B e t w e e n t h e s e t empera tu re limits, t h e a c t i v i t y and s t a b i l i t y of t h e c a t a l y s t de t e rmines t h e optimum l a y o u t of t h e methanat ion p rocess . The TopsQe MCR-2X c a t a l y s t a l l o w s o p e r a t i o n i n t h e t empera tu re range 25OoC t o w e l l above 70OoC. By combina t ion w i t h a non-nickel c a t a l y s t , t h e o p e r a t i o n r ange can , f o r c e r t a i n c a s e s , be ex tended t o 200 t o 70OoC. T h i s c a p a b i l i t y o f h i g h t empera tu re methanat ion o f f e r s t h e p o s s i b i - l i t y of d e s i g n f o r l o w r e c y c l e , o r f o r optimum b o i l i n g wa te r r e a c t o r s .

REFERENCES

1.

2 .

3.

4 .

Ros t rup-Nie lsen , J . R . , and Pede r sen , K . , J .Cata1 . ( i n p r e s s ) .

Araki , M . , and Ponec, V . , J .Ca ta1 . 44, 439 ( 1 9 7 6 ) .

Coenen, J.W.E., S c h a t s , W . M . T . M . , and van Meerten, R . Z . C . Bull.Sco.Chim.Belg. (1979) ( i n p r e s s ) .

Ros t rup-Nie lsen , J . R . , "Steam Reforming C a t a l y s t s " , Teknisk F o r l a g , Copenhagen 1 9 7 5 .

94

5.

6.

7.

8 .

9.

10.

11.

1 2 .

13 .

1 4 .

15 .

16.

17.

18.

19 .

20

2 1

22.

23.

24.

25.

REFERENCES (Cont 'd )

Schoubye, P . , J . C a t a 1 . 2, 238 (1969) .

Vannice, M.A. , and Gar t en , R . L . , J .Cata1 . 56, 236 (1979) .

Ros t rup-Nie lsen , J . R . , J.Cata1. 2, 171 (1971)

Garner S.W., "Chemistry of t h e S o l i d S t a t e " , B u t t e r w o r t h s , London 1955, p 307.

Ruckens te in , E . , and Pulvermacker, B . , AIChE J o u r n a l 2, 356 (1973) .

Wynbla t t , P . , and Tae-Moon, Ahn, " S i n t e r i n g and C a t a l y s i s " , Materials Sc ience Research E, 83 (1975) .

Ruckens te in , E . , and Pulvermacker, B . , J .Cata1 . 3, 416 (1975) .

Bor isova , M.S., Fenelonov, V . B . , Dzisko , V . A . , Simonova, L . G . , Kinet.Kata1. 2, 653 (1976) .

Wi l l iams , W . , B u t l e r , G . A . , and Hammonds, J . , J .Ca ta1 . E, 352 (1972) .

Levy, R.M., Bauer, D . J . , Roth, J . F . , 1nd.Eng.Chem.Prod. R e s . Develop. 2, 217 (1968) .

Ros t rup-Nie lsen , J . R . , J .Cata1 . 21, 343 (1972) . McCarty, J . G . , Wentrcek, P.R., Wise, H . and Wood, B . J . DOE C o n t r a c t 76-C-03-115, Annual Repor t O c t . 26, 1978.

F i t z h a r r i s , W.D., PhD T h e s i s , U n i v e r s i t y of Delaware, 1978.

C h r i s t i a n s e n , L . J . , and Andersen, S . , P r o c . 6 t h I n t . Symp. on "Chemical Reac t ion Eng inee r ing" , N i c e 1980 ( i n p r e s s ) .

McCarty, J . G . , and Wise, H . , J .Cata1 . 57, 406 (1979) .

McCarty, J . G . , Wentrcek, P.R., and Wise, H . , i n "Proc.Amer. Chem.Soc.Symposium", Chicago, Aug. 28-Sept. 2 , 1977" , p 1315.

Moseley, F . , S t ephens , R.W. , S t e w a r t , K . D . , and Wood, J. , J . C a t a 1 . 24, 18 (1972) .

Ros t rup-Nie lsen , J . R . , and T r i m m , D . L . , J .Catal . 48, 155 (1977) .

H a r m s , H . G . , HGhlein, B . , and Skov, A . , Chem.Ing.Tech.(in p r e s s ) .

Bo l t endah l , V . , Niessen , H.F., T h e i s , K . A . , GWF-Gas/Erdgas, - 1 1 7 , 517 ( 1 9 7 6 ) .

H a r m s , H . G . , HGhlein, B . , and Skov, A . , O i l and Gas J . (sub- m i t t e d ) .

95

T a b l e - 1 Carbon F o r m a t i o n , T h e r m o g r a v i m e t r i c T e s t s

E x p e r i m e n t a l c o n d i t i o n s re ref (1) C a t a l y s t , 1 3 w t % N i , DNi= 300 - 3500 8,

C a r b o n l i m i t s c a l c u l a t e d f r o m " p r i n c i p l e o f e q u i l i b r a t e d g a s "

1 2

PCO atm

Temp. OC

C a l c . c a r b o n l i m i t s C a r b o n f o r (Temp.OC) :

G r a p h i t e C a t a l y s t (DNi=3 500A

0 , 3 3

o r 2 0 , 3 3

4 00- 47 0 400

415 c: T 4 8 0 0 T 4 1069

6 0 0 4 T 4 3 5 0 T c 684

1 C a r b o n F o r m a t i o n I NO Y e s

T a b l e - 2

High T e m p e r a t u r e S t a b i l i t y o f MCR2X R e s u l t s f rom P i l o t T e s t s

O p e r a t i o n Time a t Temp.

h OC

D N i BET Area n2 Area

m 2 / s A

New MCR2X

8127 600

1895 600 f o l l o w e d by 8 6 0 7 0 0

52 7 220

30 3 295

35 3 345

52 7 220

30 3 295

35 3 345

96

O p e r a t i n g t i m e a t temp. h OC

R e g e n e r a t i o n A c t i v a t i o n C o n d i t i o n s C o n d i t i o n s

H2,15h,5000C - H2,4h,7000C - H 2 0 , 16h, 7OO0C 80O-85O0C, Zh H20,16h,7000C 800-850°C,2h

4800 290-385

4800 290-385

3900 280-300 3900 600

I n t r i n s i c A c t i v i t y r e l a t i v e to u n u s e d

ca t . B e f o r e A f t e r

0 .006 0 .05

0 . 0 0 6 0.15

0 .025 0 .42 0 . 1 1 0.50

T a b l e - 3

R e g e n e r a t i o n of MCR2X C a t a l y s t

Samples f r o m HTAS-run 5

97

1

Figure 1

Sintering of catalysts

30 kg/an 2 q, H20/H2=10, 140-170 hours 2 m-type. BET-area = 33 m /q

Ni/yA1203. BET-area = 101 m /q Ni/Ceramic. BET-area = 1.2 in /q

2 2

UIO I 0 I 1 I 1 5 6 R l C I C L l RATIO

11 il IO I I CARBON MOUOXlOt A1 1W11 HOL'I. I W l l l

Figure 2

Carton L i m i t s

Recycle ra t io and out le t temperature of adiabatic equilibration of gas. The example refers to a feedgas containing 12 vol% CH . Correction for car- bA-structure on catalyst moves carton l i m i t s to 950-lO5O0C.

98

0 0 0

0

cg 0

Figure 3

B-deactivation i n Pi lot Test

McR-type catalyst .

O/C = l., H/C = 6., P = 30 kg/an2g, PCO = 2 kg/an2g.

Zg7 = axial distance f m top of

catalyst bed for 97% conversion of max. adiabatic A T obtained.

Figure 4

Low Temperature Deactivation

Laboratory Tests

3OO0C, 21.2 kg/an2g, MW=106h-’

Fedgas (~01%) :

H2Q (35)

co (0-11)

H2 (rest) co2 ( 5 )

99

\ High Temperature Methanation

Sinplified Fxample

Canparison of TREMP reaction steps (solid l ine) w i t h reaction routes based on a reforming type catalyst (dashed l ines) .

Figure 6

Explorative P i lo t T e s t w i t h Air-cooled Reactor

Measured and calculated temperature profiles. The calculation nxxlel did not consider axial radiation i n the bed, which explains the difference of the two pro- f i l e s .

Figure 7

ADAM-1 T e s t Unit

Temperature Profiles

100

?.pplied Fischer-Tropsch Kinetics for a F l m Spray63 Iron Catalyst

W. J. Thanson, J. 11. Amdt, and K. L. Wright

University of Idaho, Department of Chenical wineerirq, Ibscow, IdaAo, 93843

INTRODUCTION

There has been a g rea t deal o f previous work done of Fischer Tropsch Cata lys i s but un t i l r ecen t ly , very l i t t l e r a t e data have been obtained o the r than semi-quant i ta t ive r e s u l t s . A g r e a t deal of the previous l i t e r - a t u r e dea ls with the proposed and hypothetical mechanisms of Fischer Tropsch c a t a l y s i s and i t s similarities/dissimilarities t o SNG methanation. Despite t he voluminous amount of work i n t h i s a rea there i s s t i l l cont ro- versy as t o whether deposited carbon o r i ron carb ide ( i n the case o f i ron c a t a l y s t s ) i s the a c t i v e intermediate i n the mechanistic scheme.' addi t ion t o t h i s t he re was a g r e a t deal o f work accomplished a t the Bureau of Mines in the 1940 ' s and 50 ' s concerning the behavior o f Fischer Tropsch c a t a l y s i s under various condi t ions . ' Iron a s well as coba l t and ruthenium have been proposed and s tudied as poss ib le Fischer Tropsch catalyst^.^' There has a l s o been cons iderable i n t e r e s t in t he incorpora t ion o f various promoters in Fischer Tropsch c a t a l y s i s in order t o a l t e r o l e f in - to -pa ra f f in r a t i o s , minimize CO2 make, e t c . the University of Utah' i s seeking t o sys temat ica l ly a l t e r various promoters in order t o determine the bes t combination i n o rde r t o achieve a maximum of Cz-Cg hydrocarbons. ogy u p t o 1975 has been given by Shah and P e r r o t t a . 6

Tropsch a p p l i c a t i o n s . ' ~ in the pressure range of 10-20 atmospheres and a t temperatures from 240- 270C t o determine t h e reac t ion orders of t h e CO consumption r a t e with respec t t o both hydrogen and CO. He employed a d i f f e r e n t i a l r eac to r with H2-toCO r a t i o s varying from 1 t o 7. They found t h a t t he reac t ion order with respec t t o CO was e f f e c t i v e l y zero b u t t h e reac t ion order with r e spec t t o H2 was f i r s t o rde r . ac t iva t ion energy o f 16.8 Kcal/mole. by measurements of t he C O 2 and water-make in the e x i t stream. ing t h a t t he re was minimal oxygenated products (reasonable f o r i ron

I n

An i n t e r e s t i n g study being conducted a t

A sho r t review of Fischer Tropsch technol-

There have been two k ine t i c s tud ie s using i ron c a t a l y s t s f o r Fischer Dry e t . a l . 7 used a t r i p l e promoted i ron c a t a l y s t

Between 225 and 265C they a l s o determined an However a l l t h e i r da ta were obtained

By assulii-

101

c a t a l y s t s ) , then the summation of t he Cop and water-make should equal t he to t a l CO consumption r a t e . I n a l l cases the r a t i o of Cop-to-water was l e s s than 1 except a t the highest temperatures (265C, where i t equaled 1 .15 ) . decrease t h e COz/H20 r a t i o , they concluded t h a t CO2 was a secondary reac t ion produced by the water gas s h i f t reac t ion . was conducted by Atwood and Bennett .* a tubular flow r e a c t o r b u t a l s o a n i n t e r n a l l y r ec i r cu la t ed r eac to r (simi- l a r t o the r eac to r employed he re ) . was l i t t l e d i f f e rence in the reac t ion k ine t i c s whether the r ec i r cu la t ed re - a c t o r o r t h e tubu la r flow reac to r was employed.

i n excess) and a zero o rde r dependency of t h e reac t ion with respec t t o CO ( a s reported by Dry e t . a 1 . 7 ) . I n t h i s ca se they reported t h a t with t h e i ron c a t a l y s t , the C02/H20 r a t i o was s i q n i f i c a n t l y o r e a t e r t h a n one but i t should be pointed out t h a t the temperatures employed in t h i s study ranged from 250C t o 315C; t h a t i s , s i g n f i c a n t l y h iaher than the temperatures used by Dry e t . They proposed a k i n e t i c expression which i s based on the r a t e being dependent on the hydrogen concent ra t ion and the f r ac t ion of reduced iron present . ’

Since the e f f e c t o f increas inq space ve loc i ty was t o dramat ica l ly

A more r ecen t k i n e t i c study I n t h i s case they employed not only

They claimed in t h e i r paper t h a t t he re

Based on our experience I i t would appear t h a t t h i s was due t o t h e i r minimal H2 consumption ( H Z

A psuedo steady s t a t e balance between the oxida- t i on of iron by H20 and i t s reduction by CO l eads

.4 P H 2 ) rrn =

t o equation ( 1 ) .

( 1 )

Experimental da ta a t t h r e e temperatures were used t o determine the con- s t a n t s k a n d b a s a func t ion of temperature. However i t should be pointed ou t t h a t the term involv ing the r a t i o of water t o CO p a r t i a l p ressures in the denominator was only important f o r a very few data poin ts . a cons tan t feed mixture with a H2 t o CO r a t i o o f 2 . 0 was used and t h e authors r epor t t h a t t h e mole f r a c t i o n o f Hp i n the product stream was e s s e n t i a l l y

Also, s ince

102

independent of carbon monoxide conversion, the H p p a r t i a l p ressure was c lose t o a constant f o r a l l runs. f i t when equation ( 1 ) i s rearranged t o the l i n e a r form o f equation (2), note t h a t the e s s e n t i a l l y cons tan t hydrogen p a r t i a l p ressures and a small

Although the authors show an exce l l en t

e f f e c t of t he water-to-C0 p a r t i a l p ressure would produce a cons tan t r a t e a t any tetiiperature.

been p r o p ~ s e d . ~ t i a l p ressure of H2 ( f o r conversions l e s s t h a n 6 0 % ) and, i n the o t h e r an

adequate co r re l a t ion f o r coba l t was obtained by equation ( 3 ) .

Two o the r r a t e expressions based s o l e l y on observa t ion , havc a l s o I n one, the r a t e was observed t o depend only o n the par-

Fischer-Tropsch synthes is i s highly exothermic and consequently a good deal of a t t e n t i o n has been spent on r eac to r design cons ide ra t ions . Designs ranging from s l u r r y r eac to r s t o f lu id i zed beds have been proposed’ and, in the l a t t e r ca se , a c t u a l l y cons t ruc ted .” u t i l i z e recyc le r eac to r s i n o rde r t o r e s t r i c t the temperature r i s e across t h e c a t a l y s t bed, b u t a heavy p r i ce must be paid in terms o f compressor c o s t s . coated w i t h c a t a l y s t was f i r s t proposed by DOE f o r t he exothermic methana- t i o n r eac t ion” and a s i m i l a r design using i ron c a t a l y s t s f o r Fischer Tropsch has been discussed by Haynes, e t . a1.I’ w i t h a n applied k ine t i c s study u t i l i z i n g t h i s c a t a l y s t concept. blhile the scope o f the p ro jec t i s concerned with product d i s t r i b u t i o n s as well as reac t ion r a t e s , in t h i s paper we wi l l only focus on r eac t an t a n d make-gas r a t e s .

I t i s a l s o comrron t o

A low pressure drop r eac to r u t i l i z i n g pa ra l l e l p l a t e s and i n s e r t s

The work repor ted here dea ls

103

EXPERIMENTAL EQUIPMENT AN0 P R O C E D U R E S

Berty Reactor System

All of t h e experiments were conducted in an i n t e r n a l l y r e c i r c u l a t i n g r eac to r ("Berty" type ) and a schematic of t h i s equipment i s shown in Figure 1 . meters equipped with pressure drop t ransducers and the flows a r e ad- j u s t e d with the reac to r on by-pass t o obta in the des i red i n l e t H2-to-CO r a t i o and t o t a l flow. sen t f o r ana lys i s v ia gas chromotography using a Carle :,lode1 111 H gas chromotograph. The r e a c t o r i s then p u t on stream and the H2-CO mix i s fed t o t he r eac to r . The e x i t stream leaving the r e a c t o r passes f i r s t through a "hot t r a p " ( a condenser maintained a t 120C) in order t o condense waxes. a co ld trap ( a t O C ) where water and o i l a r e condensed. from t h i s condenser passes i n t o a knock-out p o t t o remove en t ra ined l i q u i d s and then proceeds v i a a wet t e s t meter t o vent. Provis ions a r e made t o sample this e x i t gas stream on l i n e and aga in , ana lys i s i s done via a Carle 111 H gas chromotograph. The r eac to r pressure i s adjus ted and maintained by means of a needle valve a t t he r eac to r e x i t . wi th in the r eac to r a r e measured jus t above and below the c a t a l y s t sample. The mass ve loc i ty ac ross t h e c a t a l y s t su r f ace can be ad jus ted by means of regula t ing the RPH o f t h e magnedrive un i t equipped with t h e Berty r eac to r . Typica l ly a t RPM's above 750 the temperature d i f fe renceacross the c a t a l y s t i s wi th in 2 C and a l l da ta repor ted here were obtained a t 1500 R P M .

Hydrogen and CO a r e monitored sepa ra t e ly v ia c a p i l l a r y flow

Once t h e des i red r a t i o i s ob ta ined ,a sample i s

The uncondensed portion of t he stream then passes through The gas e f f l u e n t

Temperatures

The Carle Analy t ica l Gas Chromatograph i s equipped with an on- l ine

A 2 .5 rn poropak Q column a t 105C was

hydrogen t r a n s f e r tube so t h a t reasonably accura te hydroaen peaks a r e obtained as pa r t o f t he a n a l y s i s . placed i n a se r ies -bypass mode with a 2.5 m molecular s i eve column main- t a ined a t 30C. With the columns connected i n s e r i e s , H2 , C O and CH4 pass through the por0pa.k column and i n t o the molecular s i eve column where they

a r e temporarily reta.ined,. A valve i s then switched so t h a t the molecular

104

s i eve i s bypassed and C02, H20 and C2-C4 compounds a r e separated and analyzed. C O a n d CH4 takes place.

The i ron c a t a l y s t , supplied by t h e P i t t sburgh Energy Technology Center ( P E T C ) of DOE, cons is ted of t acon i t e which was plasma-sprayed t o an average thickness o f 0.56 mm on f l a t p l a t e s of i ron subs t r a t e . h a d a BET area of 2 m2/gm and a poros i ty of 0.48. The c a t a l y s t assembly cons is ted of 5 p l a t e s , each 7 . 6 cm h i g h and o f varying widths so as t o be compatible w i t h t he d r a f t tube s i z e o f the Berty r eac to r . The p l a t e s were bolted toge ther with two threaded rods and the assembly and dimen- s ions a r e shown in Figure 2 . The c a t a l y s t was assembled, leak t e s t e d in He and then reduced by hea t ing t o 501)OC in flowing H2 over a 4-hour period and then holding a t 450°C f o r 24 hours. Attempts were made t o es t imate the water make during reduction in order t o deteri i ine the percentage reduction o f t he ava i l ab le i ron . rate and consequent low H20 concent ra t ions d id not allow f o r accu ra t e measurements.

Tropsch c a t a l y s t s has been t h e sub jec t o f a number of i nves t iga t ions . l 3

In t h i s case we u t i l i z e d a H2/CO feed of 1 . 5 a t 300°C and 1 .6 MPa and ran f o r a t o t a l o f 30 hours on-stream. This corresponded t o the time a t which the a c t i v i t y and product d i s t r i b u t i o n s t a b i l i z e d . I t should be pointed out however, t h a t the c a t a l y s t was id led in H2 a t 3OOOC and 1 .6 MPa a t the end o f each day ' s running. I n add i t ion the conversions var ied during t h i s pretreatment a n d , s i nce the r eac to r behaves a s a CSTR, t he c a t a l y s t was exposed t o varying H2/CO r a t i o s . below in more d e t a i l .

RESULTS

With the columns placed in s e r i e s once aga in , ana lys i s o f Hp,

I t

Unfortunately the slow reduction

The need f o r a ca rbur i za t ion pretreatment when usina i ron Fischer

This wi l l be discussed

P r io r t o en te r ing i n t o a d i scuss ion o f the r e s u l t s , i t i s important t o emphasize the behavior of a CSTR r eac to r such as the one used here ,

105

F i r s t of a l l , in d i scuss ing reac t ion r a t e s or product d i s t r i b u t i o n s , i t i s t he r eac to r exit condi t ions which a r e the independent va r i ab le s . These

a r e brought about by independent control of t h e i n l e t flow r a t e , i n l e t composition, r eac to r pressure , and temperature. Consequently, in t h e subsequent discussion only the e x i t condi t ions wi l l be r e fe r r ed t o .

important f a c t o r i s t h a t , s ince a f ixed bed c a t a l y t i c r eac to r (s p l u g f low) wi l l have c a t a l y s t exposed t o both i n l e t a n d o u t l e t cond i t ions , i t i s important t o ob ta in data over a wide range of conversions and i n l e t compos i t i ons . qenera l ly increase a s conversion increases . t h e conversion a s well a s t he i n l e t H 2 / C O r a t i o so t h a t a wide range of independent data a r e a v a i l a b l e f o r s t a t i s t i c a l ana lys i s . In t h i s work t h e CO conversions var ied from 15% t o 85% and the e x i t H2/CO r a t i o s were var ied independently from 0.8 t o 18. Total p ressures ranged from 0.77 t o 3.1 MPa and temperatures from 250C t o 300C.

Induction Period

Another

For example, i n Fischer-Tropsch syn thes i s the H z / C O r a t i o wi l l T h u s i t i s important t o vary

The f a c t t h a t Fischer-Tropsch c a t a l y s t s aene ra l ly r equ i r e an induc- t i o n ( o r "ca rbur i za t ion" ) period has a l ready been mentioned. ca rbur i za t ion i s thought t o increase t h e c a t a l y s t l i f e t i m e and of course t h i s i s exceedingly important f o r commercial success . I n our case , we wished t o obta in r a t e da t a corresponding t o the s t a b l e a c t i v i t y of t h e

c a t a l y s t a n d we were unable t o run continuously. r e s t r i c t i o n we followed a procedure of i d l i n q the c a t a l y s t i n Hp a t 1 .0 HPa whenever we were n o t running. u t i l i z e an a l t e r n a t e induct ion method which was more compatible with our day-to-day opera t ion and which appeared t o give the same s t a b l e a c t i v i t y ' " a s t he more typ ica l complex carbur iza t ion procedure.

The procedure employed during the f i r s t 24 hours of induction was t o expose the c a t a l y s t a t 300C and 1.6 MPa pressure t o a 1 . 5 H 2 / C O mixture a t an "exposure ve loc i ty" ( J , volumetric flow r a t e a t standard condi t ion per un i t supe r f i c i a l c a t a l y s t a r e a ) of 2 .6 m / h r . Some of the r e s u l t s obtained

Proper

Because of th i s l a t t e r

Because of these d i f f e rences we e l ec t ed t o

106

d u r i n g t h i s p e r i o d a r e shown i n F i g u r e 3.

t h a t t h e c o n v e r s i o n was v e r y h i g h d u r i n g t h e f i r s t f o u r hours on s t ream.

T h i s p o i n t s t o t h e i m p o r t a n c e o f c o n d u c t i n g F i s c h e r - T r o p s c h c a t a l y s t

s c r e e n i n g t e s t s o n l y a f t e r t h e c a t a l y s t s have been exposed t o s y n t h e s i s

gas f o r a t l e a s t f o u r hours . Note t h a t d u r i n g t h e f i r s t 20 hours o f i n d u c -

t i o n , t h e c o n v e r s i o n s t a r t s o f f l o w and b u i l d s u p d u r i n g t h e d a y ' s run . I t

was h y p o t h e s i z e d t h a t t h e H2 i d l i n g p r o c e d u r e was e f f e c t i n g r e d u c t i o n o f

t h e a c t i v e i r o n c a r b i d e so t h a t t h e f i r s t few hours o f t h e r u n a r e spent

r e f o r m i n g FeC a t t h e expense o f hydrocarbon p r o d u c t i o n . As a r e s u l t , t h e

i n l e t c o n d i t i o n s were changed a t 24 h o u r s t i m e - o n - s t r e a m (TOS) t o 3.1 MPa

and H2/CO = 2.0.

made, t h e v a r i a t i o n i n d a i l y c o n v e r s i o n s was m a r k e d l y reduced and t h e

c a t a l y s t reached a p p a r e n t s t a b i l i t y a f t e r a b o u t 35 h o u r s TOS. Whi le t h e r e s u l t s i n F i g u r e 3 show o n l y t h e t o t a l CO c o n v e r s i o n ,

some m e n t i o n ought t o be made o f t h e s e l e c t i v i t y t o C5' d u r i n g t h i s p e r i o d .

D u r i n g t h e 24 hours TOS, t h e C5' w e i g h t f r a c t i o n o f t o t a l hydrocarbon make

g r a d u a l l y i n c r e a s e d on a d a i l y b a s i s f r o m a b o u t 0.05 t o 0.20.

p e r i o d t h e f r a c t i o n remained e s s e n t i a l l y c o n s t a n t a t about 0 .25 .

P r o d u c t D i s t r i b u t i o n

F i r s t o f a l l i t s h o u l d be n o t e d

As can be seen f r o m F i g u r e 3, once t h i s change was

A f t e r t h i s

I n p r i n c i p l e e i t h e r GO2 o r H20 can be produced f r o m t h e c h a i n g r o w t h

w h i c h o c c u r s d u r i n g F i s c h e r - T r o p s c h s y n t h e s i s .

p roduced v i a t h e r e v e r s i b l e w a t e r gas s h i f t r e a c t i o n

However, CO2 can a l s o be

T y p i c a l l y t h e COP make was comparable t o t h e CH4 make a t 250C and was 50

t o 100% g r e a t e r t h a n CH4 a t 300C.

r e a c t i o n such as e q u a t i o n (41, t h e n one wou ld e x p e c t an i n c r e a s i n g CO/H2

r a t i o w i t h i n c r e a s e d c o n v e r s i o n . As T a b l e I shows, t h i s i s i n d e e d t h e case

a t b o t h tempera tures as l o n g as t h e H2/CO r a t i o i s a p p r o x i m a t e l y c o n s t a n t .

Also shown i n T a b l e I i s t h e e q u i l i b r i u m parameter , C$I, w h i c h i s d e f i n e d as

I f t h e C02 i s produced f r o m a s i d e

107

and wi l l o f course be equal t o 1 .0 a t equi l ibr ium (Keq i s t he equi l ibr ium cons tan t ) . I t i s apparent from the r e s u l t s shown in Table I t h a t t he water gas s h i f t reac t ion i s well removed from equi l ibr ium a t 250C b u t c l o s e r a t 30OC. Some measure o f t h e r eve r s ib l e na ture o f the reac t ion r a t e can a l s o be obtained from Table I . That i s , a t cons tan t conversion the C02/H20 r a t i o decreases a s t h e H2/CO r a t i o increases . i nd ica t e a n i nh ib i t i on o f the forward r eac t ion r a t e o f equation ( 4 ) by increased product - to- reac tan t r a t i o s .

t o -pa ra f f in r a t i o of t he hydrocarbon products. Table I 1 shows the C2Hq/C2Hg r a t i o as a function of t h e H2/C0 r a t i o and conversion a t two temperatures. Note t h a t t h i s r a t i o decreases a s conversion inc reases a t both temperatures in agreement with K ~ g l e r ' s ' ~ hypothesis t h a t t h e main elements i n chain growth a re o l e f i n s , not p a r a f f i n s . lower the C2Hq/CzHg r a t i o s ince these would tend t o proniote hydrogenation. Comparing the da ta a t two temperatures, i t can a l s o be seen t h a t higher C2Hq/CzHg r a t i o s a r e favored a t t he lower temperature.

The experiments conducted during t h i s por t ion of the inves t iga t ion were designed pr imar i ly t o ob ta in reac t ion r a t e data and s ince a l a rge number o f s epa ra t e runs were required t o accomplish t h i s goa l , t he r u n times were genera l ly r e s t r i c t e d t o 3 hours o r l e s s . Unfortunately t h i s i s not a s u f f i c i e n t length o f time t o ob ta in l a r g e enough q u a n t i t i e s of o i l f o r accura te measurements ( t h e o i l make varied from about 0.2 t o 4 .0 ml /hr ) . Nevertheless, some i n s i g h t i n t o t h e parameters which favor o i l make can be obtained from t h e da ta shown i n Figure 4. Here the weight f r a c t i o n o f C$ (Cg+/total hydrocarbon make) i s p lo t t ed a s a func t ion of conversion f o r d i f f e r e n t H 2 / C O r a t i o s a t 250C. As expected, increas ing conversions r e s u l t grow) and apparent ly higher H 2 / C O r a t i o s r e t a r d t h e formation o f higher carbon numbers. Within t h e accuracy l i m i t a t i o n s of the d a t a , t he Cg frac t ion d i d not appear t o be a func t ion o f pressure a t 2SOC.

This would

Another important a spec t of Fischer-Tropsch syn thes i s i s t he o l e f i n -

As expected, higher H 2 / C O r a t i o s a l s o

in h igher C5+ f r a c t i o n s ( t h e chain has a chance t o

However t h i s

108

was not t he case a t 300C where i t was found t h a t higher pressures tended t o increase the C$ f r a c t i o n . da ta a t s imi l a r condi t ions i n o rde r to obta in a good coniparison w i t h t h e da ta a t 250C. Nevertheless the r e s u l t s i n Table 111 show a d e f i n i t e decrease in the Cf f r a c t i o n a s the temperature increases from 250C t o 300C.

Another parameter of i n t e r e s t in Fischer-Tropsch syn thes i s i s t h e product d i s t r i b u t i o n of the hydrocarbon make. b u t de tec tab le wax was co l l ec t ed from t h e h o t t r a p (see Figure 1 ) b u t t he q u a n t i t i e s were too small f o r accura te ana lys i s . make samples were a l s o subjec ted t o GC-MS ana lys i s and carbon numbers u p t o about 18 were de tec ted with the highest weight f r a c t i o n a t C8 o r C9. The major cons t i t uen t s of t h e o i l were t h e normal pa ra f f in s with varying q u a n t i t i e s of o l e f i n s and branched compounds a t each carbon number. i n t he way of oxygenated compounds were de tec ted .

i s t h e so ca l l ed "Schulz-Flory" d i s t r i b u t i o n . 1 6 the mass f r ac t ion of each spec ies divided by i t s carbon number would p lo t l i n e a r l y as a func t ion of carbon number i f Fischer-Tropsch syn thes i s follows equal p robab i l i t y chain growth. here , i s shown in Figure 5. t a ined a t low and high carbon numbers, t he re i s a t r a n s i t i o n region between C4 and c8 which does not p lo t l i n e a r l y . Since t h e C1-c4 compounds essen- t i a l l y remain in the gas phase and the Cg compounds are co l l ec t ed i n t he l i qu id phase, i t was f i r s t t h o u g h t t h a t t he behavior in Figure 5 was due t o a material balance e r r o r . However when various a r b i t r a r y e r r o r s were added, e i t h e r t o t h e gas o r l i q u i d q u a n t i t i e s , t he same type o f p l o t r e su l t ed . Evidently the Schulz-Flory d i s t r i b u t i o n does n o t apply over t he complete carbon number range. r e s u l t s with t h i s c a t a l y s t have been obtained a t PETC using a tubu la r flow reac to r .

Because o f t h i s , t h e r e were n o t enough 300C

Ourinq most runs a small

A number o f o i l -

L i t t l e

A common ana lys i s t o which Fischer-Tropsch hydrocarbons a r e subjec ted I n t h i s case t h e log o f

Such a p l o t , t yp ica l o f t h e da t a co l l ec t ed As can be seen, while l i n e a r p l o t s a r e ob-

I t i s i n t e r e s t i n g t o note t h a t s i m i l a r

109

Reaction Rates

Idea l ly we would l i k e t o measure i n t r i n s i c reac t ion r a t e s ( t h a t i s , r a t e s i n the absence of a l l t r anspor t l i m i t a t i o n s ) under proposed commercial opera t ing cond i t ions such a s those used here . synthes is t h i s i s d i f f i c u l t t o do because of t he production of higher carbon number o i l s which could s a t u r a t e the c a t a l y s t pores and lead t o the necess i ty of gaseous r eac t an t s having t o d i f f u s e through l i q u i d f i l l e d pores. 0.56 mm, the very low d i f f u s i v i t i e s of gases in l i q u i d s (%

can s t i l l r e s u l t in pore d i f fus ion l imi ted r a t e s . This wi l l be discussed i n more de t a i l below. be l imited by gas-so l id t r a n s p o r t phenomena. This was avoided i n these experiments by inc reas ing t h e r eac to r impeller speed un t i l t he re was no s epa ra t e dependency o f t he r a t e on impeller speed. This was found t o occur a t 750 rpm and, a s mentioned e a r l i e r , a l l data were obtained a t 1500 rpm.

data were n o t subjec ted t o thorough eva lua t ions of various mechanistic k ine t i c expressions. I n a d d i t i o n , because of the complexity of Fischer- Tropsch syn thes i s , i t was decided t o f i r s t at tempt t o analyze t h e r a t e of consumption of C O , independent o f the spec ie s , produced. Consequently a simple power law model in terms o f CO and H2 p a r t i a l p ressures was evaluated but i t d id not provide f o r a s u f f i c i e n t l y accura te c o r r e l a t i o n . Although a number o f more complex models were found t o give adequate co r re l a t ions of t he data i t was found t h a t the r a t e expression oiven by

For Fischer-Tropsch

Although the th ickness of t he c a t a l y s t used here was only cmZ/sec)

For high reac t ion r a t e s i t i s a l s o poss ib le t o

Because of the p o s s i b i l i t y of pore d i f fus ion l i m i t a t i o n s , t h e r a t e

equation ( 1 ) gave as good a c o r r e l a t i o n a s any. Spec i f i ca l ly

k Pn2 r C O = 1 + b PH$PCO

-4

with k = 7 . 6 ~ 1 0 ~ exp

110

In these quations rCO i s expressed i n terms of the s u p e r f i c i a l a rea o f the c a t a l y s t , g moles/mZ-hr, pressure i s i n atmospheres and temperature i s in degrees Kelvin.

Bennett' f o r a potassium promoted fused iron c a t a l y s t , t he major d i f f e rence i s in the apparent ac t iva t ion enerqy f o r k . Atwood and Bennet repor ted a value of 20.3 Kcal/mole whereas we observe a much lower value o f 8.8 Kcal/mole. Again t h i s miqht be due t o strong pore d i f fus ion e f f e c t s s ince i t i s well known t h a t f o r near f i r s t order k ine t i c s ,po re d i f fus ion r a t e l i m i t a t i o n s wi l l produce a n apparent ac t iva t ion energy equal t o one-half i t s true value. I f t h i s were the case , one w o u l d expect t h a t equation ( 1 ) would not g ive a s good a f i t a t the hipher temperature. p red ic ted versus the measured values of rCO and, as can be seen , t h e data s c a t t e r i s d e f i n i t e l y l a r g e r a t 300C. 250C was approximately 10% whereas i t was 20% a t 300C.

I n comparing these values with those given previously by Atwood and

Figure 6 shows a p l o t of t h e

I n f a c t the averaqe devia t ion a t

As a l ready mentioned, CH4 was t h e most s i q n f i c a n t product under a l l condi t ions . pression which would descr ibe i t s r a t e of formation. Due t o the f a c t t h a t CH4 i s only one of many products, no attempt was made t o base the r a t e expression o n k ine t i c mechanisms. Instead a simple power low model was employed and the r e s u l t s a r e shown i n equation (8)

Consequently a separa te determination was made of a r a t e ex-

Here again the r a t e i s given i n moles/m2hr a n d t he pressure in atmospheres. As expected, an increased r a t e of CH4 production i s favored by higher ternpera tures and higher H 2 / C O r a t i o s .

A s i m i l a r attempt was made t o obta in a s u i t a b l e c o r r e l a t i o n f o r t he r a t e of CO2 production. via the water gas s h i f t r eac t ion , i t was an t i c ipa t ed t h a t t he r a t e here would depend on the p a r t i a l pressures of CO and H20.

Since i t i s hypothesized t h a t t he C02 i s produced

Surp r i s ing ly however,

111

the r a t e was found t o be independent of Pco b u t r a t h e r t o be dependent on t he H20/H2 r a t i o a s shown in equation ( 9 ) .

rCo2 = 6 . 5 8 ~ 1 0 ~ exp [-,,500 -- ] (F) 1 - 3 (9)

This could be explained i n two ways: t h e reverse reac t ion r a t e i s s i g n i f i - can t and s t rong ly dependent on P H ~ ; and CO i s i n excess ( s ince H20 i s a product o f t h e primary synthes is r eac t ions ) . explanation can not be proven b u t seems t o be reasonable ( s t rono H2 adsorption could produce the same e f f e c t ) . Although the da ta used i n ob ta in ing equation ( 9 ) covered a wide range of CO/H20 r a t i o s (0 .2-12) , t he re were only t h r e e runs (out of 62) with CO/H20 l e s s than one. t hese runs had very high COP production r a t e s and high CO conversions, i t i s conceivable t h a t the r a t e of CO2 production does depend on Pco when i t i s l e s s than o r equal t o PH20. Diffusion Limi ta t ions

The f i r s t por t ion of t h i s

Since

The p o s s i b i l i t y o f s t rong pore d i f fus ion e f f e c t s has a l ready been mentioned and the da t a f o r t he CO consumption r a t e g ives some evidence of i t s ex is tence . ac t iva t ion energy more typ ica l of k ine t i c r ea t ions and s ince i t was found t o depend on P H ~ o , the primary product of Fischer-Tropsch syn thes i s , i t i s somewhat su rp r i s inq t h a t i t d id not have a lower apparent a c t i v i a t i o n energy. A poss ib le explana t ion could be t h a t t h e dominant reac t ion i s methanation and, i f i t were much f a s t e r and in pa ra l l e l with t h e o t h e r slower r eac t ions , i t could be the only pore d i f fus ion l imi ted r eac t ion . Since equation ( 1 ) i s based on the t o t a l CO consumption r a t e and CH4 i s the major product, t h i s would explain the apparent discrepancy in the apparent a c t i v a t i o n energ ies in equations ( 6 ) and ( 9 ) . Some support of this argument i s given by the low a c t i v a t i o n energy assoc ia ted with CH4 production [equation (8)].

However t h e r a t e expression f o r C02 production had an

112

Whereas s e p a r a t e exper iments t o q u a n t i f y t h e r o l e o f p o r e d i f f u s i o n

were n o t conducted, e s t i m a t e s o f t h e e f f e c t i v e n e s s f a c t o r can be made

p r o v i d e d t h e r e i s some knowledge o f t h e v a l u e o f t h e e f f e c t i v e d i f f u s i v i t y .

Atwood and Bennet t , ' assuming t h a t CO d i f f u s i o n i n t h e l i q u i d f i l l e d p o r e s

was l i m i t i n g , used a v a l u e o f 1 . 6 ~ 1 0 - 5 cm'/sec f o r a f u s e d i r o n c a t a l y s t .

Us ing t h i s v a l u e and r e a r r a n g i n g e q u a t i o n ( 1 ) t o g i v e an e f f e c t i v e f i r s t

o r d e r r e a c t i o n , we e s t i m a t e t h e e f f e c t i v e n e s s f a c t o r be a b o u t 0.30 a t

300 C . Thus i t appears t h a t we have s t r o n g p o r e d i f f u s i o n e f f e c t s w i t h

r e s p e c t t o t h e CO consumpt ion r a t e .

o f f o r m a t i o n o f CH4 wh ich was t h e m a j o r p r o d u c t ( s e l e c t i v i t y % 60%).

ACKNOWLEDGE

T h i s i s p r o b a b l y due t o t h e h i g h r a t e

The f i n a n c i a l s u p p o r t o f t h i s work by DOE under c o n t r a c t No.

DE-AS22-78ET00260 i s g r a t e f u l l y acknowledged.

113

REFEREPJC ES

Ponec, \/., CATAL. R E V . - S C I . E N G . , s, p . 151 (1978) .

S to rch , H. H . , t i . Golunibic, and R . E . Anderson, "The F i s c h e r - T r o p s c h and R e l a t e d Syntheses," John W i l e y & Sons, New York (1951) .

Dent, A . L . and 1.1. L i n , A C S P r e p r i n t s , D i v . o f P e t r . Cheiii., Anaheim, C A . , - 23, No. 2, p . 502, March 1978.

1.

2.

3.

4.

5.

10.

11 .

12.

13 .

14 .

15.

16.

Everson, R . C . , E . T. Woodburn, and A. R . M. K i r k , J. CATAL., 2, p . 136 (1978) .

Yang, C . H. and A . G. Oblad, P r e p r i n t s , D i v . of P e t r . Cheni., Anaheim, C4., - 23, No. 2, p. 513, March 1978.

Shah, Y . T . ana A. J . P e r r o t t a , I A EC PROD R ?, D, is, p. 123 (1976) .

Dry, M. E. , T. S h i n g l e s , and L . J . E o s h o f f , J . CATAL., 5, p. 99 (1972) .

Atwood, H. E. and C . 0 . E e n n e t t , I & EC PROC. DES. D E V . , 18, p . 163 (1979)

Anderson, R . B . , i n " C a t a l y s i s " , p. 257, V o l . I V , Ed. by P . H. Eininett, Rhe inho ld Pub. Co., N . Y . , 1956.

C1iei;iical and E n g i n e e r i n g Plews, Sep t . 17, 11. 13, 1 9 7 9 .

Denieter, J . J . , Youngblood, A . J., F i e l d , J . H . , and B l e n s t o c k , D . , U. S. BUR. MI:.ILS REPT. I I V . 7033 (1967) .

Haynes, W . P . , B a i r d , i4. J . , Schehl , R . R . and Zarochak, M. F . , P r e p r i n t s , D i v . P e t r . Chem., A C S , 2, No. 2, p . 559, 1Y78.

Sanc ie r , K . M., I s a k s o n , 14. E. , Wise, H . , P r e p r i n t s , D i v . of P e t r . Chem., ACS, g, No. 2, p. 545, 1978.

Schehl , R . R . , P i t t s Energy Tech Ctr., p r i v a t e conimunicat ion.

Kug le r , E . L., paper p r e s e n t e d a t t h e ADVANCES I!( CATALYTIC CHEMISTRY. Snowbird, UT, O c t . 2-5, 1979.

H e n r i c i - O l i v e , G., O l i v e , S . , Angem. Chein. I n t . Ed. E n g l . , 15, p . 136, 1976.

114

TABLE 1

COZ/H20 IWKE AT TWO TEMPERATURES

- H2/COp xco CO- P 2 0 0

250 C 2.24 .26 .14 ,004 2.25 .34 .25 .01 2.16 .50 .37 .01 5 . 9 . 7 9 .42 ,016

9 . 9 .74 .27 .027

300 C 1.2 .60 1.9 ,057 2.a .59 1.1 ,077 5.5 .62 0.6 ,083 3.6 . 75 1 .o ,091 6.1 .79 1 .o ,153 7.3 .74 0.6 ,110 9.3 .76 0.45 .11

TA6LE 1 1

ETHYLEIIE/ETHAilE ilAKE AT TWO TEVPERATURES

HZ/CO xco C2H4/C2H6

250 C 1.5 .15 .14 1.2 .21 .13 2.24 .26 .092 2.25 .34 ,076 2.16 .50 ,050 5.9 .79 .020 8.9 .74 ,012

300 C 1.05 .26 . 0 9 6 1.20 .41 .079 1.20 .60 ,028 2.60 .59 .023 5.50 .62 ,012 9.30 .76 .005

--

TABLE 111

COMPARISOH OF C l FRACTION AT TWO TEMPERATURES

H2/C0 PT(MPa) C i Frac t i on T(C) xco

250 .50 2.5 1.47 .31 300 .51 1.7 1.47 .12

250 .55 4.0 2.15 .18 300 .58 3.3 2.02 .10

250 .65 6.7 2.84 .13 300 .76 8.3 2.84 .07

115

FIGURE 1: SCHEMATIC OF EXPERIMEP!TAL EQUIPI.1ENT

FIGURE 2 : CATALYST ASSEMBLY

F L O W

116

.80

.70

0 V

X .60

. 5 0

. 4 0

.3 0

+ r J u

+ 0 3

. 1 0

F1GUP.E 3: INDUCTIOtl PEEIOD: CGNVERSlCfl VERSUS T I G E

. T O S = 0 / _ _ _ - - _ -- . \

\ .

/ / . , \ / .

__c_c----~ , _. / - T O S = 3 5 ----

/----

I- / /

/' ;TOS = 2 0

1 I I 1 2 3

T I M E F R O M S T A R T OF D A I L Y R U N , h r

FIGURE 4: \!EIGHT iRACTION C5' VS. X,-o (250C)

0 H 2 / C O 2

Ed H 2 / C O = 2.8

A H 2 / C O = 3.9

A

I I I I I I I .10 .20 .30 . 4 0 .50 .60 .70

x c o 117

n . - x 0 0 -

0.

0 . I I I !

2 4 6 I I I

8 10 1 2 14

C A R B O N NO. ( P )

FIGURE 6: PREDICTED VS. MEASURED VALUES OF RCO

15

0 n

n W K

0 @ / ' h

0 v 0 2 5 0 C

@ 300 C

1 0 t/ . O

1/ I I I I I 10 1 5 2 0 2 5 30

A L S

ME A S U f? E 0 nc o . rn o I P 5 I m2 - h r

118

Synthesis Gas Conversion to Gasoline Range Hydrocarbons over Medium Pore Zeolite Catalysts Containing 3d-Metals and Bimetallics

V. U. S. Rao, R. J. Gormley, H. W. Pennline, L. C. Schneider and R. Obermyer*

Pittsburgh Energy Technology Center 4800 Forbes Avenue Pittsburgh, PA 15213

and

*Department of Physics Pennsylvania State University

McKeesport, PA 15132

Introduction

There is much current interest in the conversion of synthesis gas to gasoline range hydrocarbons using bifunctional zeolite catalysts (1,Z). The medium pore (dia 6A) zeolite ZSM-5 in combination with Fe was shown to yield a high fraction of aromatics in the product, resulting in a favorable octane number ( = 9 0 ) . The transition metal (TM) component catalyzed the hydrogenation of CO while the acid function of the zeolite led to an aromatic product. Owing to the medium size pores of ZSM-5 there was a fairly sharp cut-off, in the product distribution near the end of the gasoline range for the aromatic fraction.

I n order to explore further the role of the TM component and the acidity of the zeolite on the product composition, experiments were performed i n our laboratory on ZSM-5 impregnated with Fe and Fe-Co, and on Silicalite impregnated with Fe. Silicalite is a molecular sieve form (3) of Si0

A romparison of the crystallographic studies (4,5) on ZSM-5 and Silicalite, shows that the two zeolites possess very similar crystal structures. While the SifA1 ratio in ZSM-5 can be varied from 3 to 03, Silicalite has essentially no Al. Hence, it appears that Silicalite is the limiting form of ZSM-5 when the A1 concentration is vanishingly small. Owing to the lack of cations which can be exchanged with protons, Silicalite has no acidity, while HZSM-5 is a highly acidic zeolite. Our investigations sought to find the difference in selectivity for synthesis gas conversion by ZSM-5 (Fe) and Silicalite (Fe) catalysts resulting from the above mentioned difference in acidity.

A further aim of the investigation was to investigate possible difference in selectivity between ZSM-5 (Fe) and ZSM-5 (Fe-Co) catalysts, resulting from the different 3d-electron concentration of the M component. Magnetic studies (TMA) were performed to characterize the TM component and particularly to detect the formation of bimetallic Fe-Co clusters.

2 '

Experimental

The zeolites were prepared using methods described in the literature (3,6). The metal component was introduced by gradually adding the metal nitrate solution to the zeolite until incipient wetness was reached. The impregnation with the metal nitrate solution was carried out for an hour under vacuum in order to enable the nitrate solution to enter the pores o f the zeolite. The material is initially dried with constant stirring over a boiling water bath, and further dried in air at 110" C for 12 hours. It is then pelleted to yield tablets 3mm in diameter. about 10% by weight of an amorphous silica such as Ludox AS-40 was added as a binder before the pelletization step.

119

I n the case of the Silicalite based catalysts,

The c a t a l y s t s were t e s t e d f o r s y n t h e s i s g a s conve r s ion i n bo th a f i x e d bed m i c r o r e a c t o r and a Berty ( con t inuous f l o w s t i r r e d t ank) r e a c t o r (7). The l a t t e r i s shown i n F i g u r e 1. The c a t a l y s t p e l l e t s were loaded i n t o the 2-inch d i ame te r CFSTR chamber and r e t a i n e d by g l a s s wool w i t h a sc reen . I m p e l l e r speed was 1240 rpm. E x c e l l e n t bed t empera tu re c o n t r o l was ob ta ined by a m o d i f i c a t i o n which invo lved t h e i n s t a l l a t i o n o f a c o i l i n t h e head o f the r e a c t o r through which a i r could f low f o r f a s t e r h e a t removal.

A schematic diagram o f t h e r e a c t o r system is shown i n F i g u r e 2. S y n t h e s i s g a s w i t h a H fC0- ra t io of e i t h e r 2 1 1 o r 111 would pass through a carbon t r a p and e n t e r t h e r e a c t o r . Lgquid and s o l i d hydrocarbon p r o d u c t s a r e c o l l e c t e d i n a h o t t r a p u s u a l l y ma in ta ined a t 150" C and i n an i c e t r a p . Th i s s e r i e s of t r a p s a r e a l t e r n a t e d and d ra ined p e r i o d i c a l l y . P roduc t gases a r e metered and then f l a r e d .

The t a b l e t s of t h e z e o l i t e impregnated wi th TM were reduced i n f lowing H a t 2 1 b a r and L50° C f o r 24 h r s . f o r 24-48 h r s t o y i e l d t h e a c t i v e c a t a l y s t . The gas phase p roduc t (C -C hydrocarbons) was ana lyzed by g a s chromatography. o l e f i n s , a romat i c s and oxygena te s by column chromatography us ing FIA d e t e c t i o n .

They were then ca rb ided w i t h s y n t h e s i s g a s a t 7 t a r and 250' C

The l i q u i d p roduc t w a s s e p a r a t e d l i n ? o p a r a f f i n s ,

R e s u l t s and Di scuss ion

( a ) In f luence of Z e o l i t e A c i d i t y :

The r e s u l t s ob ta ined i n t h e Ber ty r e a c t o r on t h e c a t a l y s t s ZSM-5 (11.1 wt% Fe) and S i l i c a l i t e (13 .6 w t % Fe) a r e shown i n Table 1. I t is appa ren t t h a t a h igh pe rcen tage of a r o m a t i c s is o b t a i n e d from t h e ZSM-5 (11.1% Fe) c a t a l y s t , w h i l e t h e product from t h e S i l i c a l i t e (13.6% Fe) c a t a l y s t has a low a r o m a t i c f r a c t i o n b u t much h i g h e r o l e f i n and oxy- g e n a t e f r a c t i o n s . I t is t h u s a p p a r e n t t h a t t h e a c i d f u n c t i o n of ZSM-5 based c a t a l y s t is r e s p o n s i b l e f o r t h e c o n v e r s i o n of t h e o l e f i n s and oxygena te s t o a romat i c s . The a romat i c f r a c t i o n impar t s a h igh o c t a n e number t o t h e p roduc t .

(b ) High O l e f i n Y i e l d s from S i l i c a l i t e Based C a t a l y s t s :

The i n t e r e s t i n g a s p e c t o f t h e p roduc t s l a t e s from t h e S i l i c a l i t e based c a t a l y s t s was the h igh pe rcen tage of o l e f i n s i n bo th t h e gas and l i q u i d phase p roduc t s . When promoted w i t h potassium, t h e Fe c o n t a i n i n g S i l i c a l i t e c a t a l y s t y i e l d e d a l a r g e C2-C4 o l e f i n f r a c t i o n a s seen i n Tab le 2. The C -C o l e f i n f r a c t i o n from S i l i c a l i t e ( 7 . 8 % Fe, 0.9% K ) i n a f i x e d bed microreactor2is4compared w i t h t h a t from a p r e c i p i t a t e d Fe-Mn c a t a l y s t of Kolbel e t a 1 (8), known f o r i ts ve ry h i g h o l e f i n y i e l d . It is s e e n t h a t t h e o l e f i n y i e l d s f rom t h e two c a t a l y s t s a r e q u i t e Comparable. The S i l i c a l i t e (7 .8% Fe, 0.9% K) c a t a l y s t y i e l d s a much h i g h e r C -C p r e c i p i t a t e d Fe-Mn c a t a l y s t and hence i s of po teng ia f commercial i n t e r e s t . f o r t h e enhancement o f o l e f i n p roduc t ion on add ing K a s a promocer h a s been d i s c u s s e d by Dry e t a l . ( 9 ) .

o l e f i n f p a r a f f i n r a t i o than t h e The mechanism

( c ) I n f l u e n c e of T r a n s i t i o n Metal Component on P roduc t Composition:

The a d d i t i o n o f c o b a l t t o Fe con ta i r l i ny ZSM-5 c a t a l y s t w a s found t o r e s u l t i n a marked change i n product compos i t ion a s s e e n from t h e Berty r e a c t o r s t u d y r e s u l t s i n Table 3 . I t i s seen t h a t t h e i n c o r p o r a t i o n of c o b a l t i n t o t h e c a t a l y s t r e s u l t s i n ( a ) r e d u c t i o n i n t h e w a s t e f u l s h i f t conve r s ion a s s e e n from t h e d e c r e a s e +n Cog f" t h e p roduc t ( h ) lowering o f t h e a r o m a t i c f r a c t i o n t o abou t 10% o f t h e C5 f r a c t i o n . However, t h e Octane number remained a t a r e l a t i v e l y high v a l u e of 81, d e s p i t e t h e d e c r e a s e i n t h e a r o m a t i c f r a c t i o n . p r o v i d e s a Promising means o f a l t e r i n g the e x t e n t of s h i f t conve r s ion and t h e composi t ion o f t h e l i q u i d p r o d u c t . pec t ed r e s u l t s i n c e a r o m a t i z a t i o n i s normally a s s o c i a t e d w i t h the a c i d i t y of t h e z e o l i t e . It i s p o s s i b l e t h a t some of t h e c o b a l t is a t t a c h e d t o t h e A 1 s i t e s i n t h e z e o l i t e , r educ ing i t s a c i d i t y .

Hence, t h e impregnat ion of z e o l i t e s w i t h b i m e t a l l i c TM c l u s t e r s

Changes i n t h e a romat i c f r a c t i o n w i t h TM component was a n unex-

F u r t h e r s t u d i e s on t h i s s u b j e c t a r e n e c e s s a r y .

120

(d) Magnetic Studies:

The magnetic properties of TM impregnated zeolite catalysts have been investigated between 77K and 923K in applied fields up to 21 kOe. Samples of ZSM-5 (11.1% Fe), ZSM-5 (5.6% Fe, 4.5% co) and Silicalite (13.6% Fe) were magnetically analyzed after each of the impregnation, reduction and carburization steps and after use as a catalyst.

The reduced samples of ZSM-5 (11.1% Fe) and Silicalite (13.6% Fe) indicate that Fe IS in the metallic state with 86% and 85% reduction, respectively. Thermo-magnetic analysis (TMA) of carbided ZSM-5 (11.1% Fe), show it to be in the high Curie point form (10) Of the Hagg carbide. the hexagonal close packed (hcp) carbide form of Fe2C, and the used Silicalite (13.6% Fe) to be the high Curie point form of the Hagg carbide.

The TMA of ZSM-5 (5.6% Fe, 4.5% Co) shows that the reduced, carbided, and spent samples have large magnetic moments (1.94, 2 . 0 4 and 2.61p8per TM atom respectively, at room temperature) and high Curie points (> 900" C), which cannot be accounted for on the basis of individual Fe and Co particles. The magnetic data indicate the composition to be that of a Fe-Co alloy (11). Hence, we conclude that the difference in selectivity between ZSM-5 (11.1% Fe) and ZSM-5 (5.6% Fe, 4.5% Co) catalysts can be attributed to the presence of bimetallic TM clusters in the latter, with consequent changes in the average number of 3d-electrons per TM atom.

(e)

To determine TM particle size in the bifunctional catalysts CO adsorption studies were performed to determine the TM surface area. These studies showed that the TM clusters had an average diameter of 100-110 A. Owing t o the limitations connected with CO adsorption for estimating metal surface areas, the above may be considered to be approximate values of the TM cluster diameter. Hence, the majority of the TM clusters must reside outside of the pores of the zeolite. We believe that the bifunctional catalytic behavior of these catalysts results from high interparticle diffusivity relative to intracrystalline diffusivity (12).

TMA analysis reveals the used ZSM-5 (11.1% Fe) to be

TM Cluster Size and Bifunctional Catalysis:

Conclusions

Our experiments lead to the following conclusions:

(1) Zeolite acidity plays an important role in the formation of aromatics from synthesis gas by bifunctional catalysts as strikingly evidenced in a comparison of the product slates from ZSM-5 (11.1% Fe) and Silicalite (13.6% Fe).

( 2 ) The transition metal component impregnated into the zeolite plays an important role in selectivity as seen from the liquid phase products from ZSM-5 (11.1% Fe) and ZSM-5 (5.6% Fe, 4.5% Co). I n this context, zeolites containing bimetallic clusters are of special interest.

(3) Silicalite impregnated with Fe and promoted with K has an exceptionally high selectivity for the production of C2-C4 olefins from synthesis gas.

Acknowledgements

We wish to thank R. R. Schehl and B. D. Blaustein for useful discussions, S. S. Pollack for x-ray diffraction analyses, M. F. Ferrer for FIA chromatographic studies, A. Elattar of the University of Pittsburgh for CO adsorption measurements, and W. Picking of Gulf Research for measuring octane numbers.

121

T a b l e 1. - Comparison of P r o d u c t s f rom ZSM-5 (11.1% Fe) and S i l i c a l i t e (13.6% Fe) C a t a l y s t s w i t h H /C0=2, and P=21 b a r . 2

C a t a l y s t ZSM-5 (11.1% Fe) Temperature , O C 300 CO Conversion, % 68.2 H Conversion, % 38.7 Spa re V e l o c i t y (h - l )

P r o d u c t Composi t ion (%)

1500 2

52.0 19 .4 28.6

3 cHn + oxygena te s

Hydrocarbon and Oxygenate Composi t ion (%)

CH 54 .1 1.1, 15.0

:2k,4' :2:6 2 .1 , 6 .3

C4+';nd oxygena te s 16.9

Composi t lon o f C,+ and o x y g e n a t e s (%)

Aromat i c s 12 O l e f i n s 3 S a t u r a t e s 24 Oxygenates 1 % G a s o l i n e r a n g e (BP <204O C) 75 Resea rch o c t a n e No. 96

C3H6' C2H;o 0.0, 4 .5

5

S i l i c a l i t e (13.6% Fe) 280

39.4 16 .5

1350

51.1 2 2 . 1 26.9

26.5 2 . 5 , 15 .0

10.8, 7.2 4 . 8 , 4 .8

25.0

4 41 33 22 77 36

T a b l e 2 . - Conversion of S y n t h e s i s Gas t o O l e f i n s i n Fixed Bed Reac to r s , Using S i l i c a l i t e

C a t a l y s t of K o l b e l e t a1 (8). (7.8% Fe. 0.9% K) Compared w i t h Tha t Using a P r e c i p i t a t e d Fe-Mn

C a t a l y s t S i l i c a l i t e (7 .8% Fe, 0.9% (our )

P r e s s u r e ( b a r ) 21 Temperature ("C) 280 H /CO R a t i o 0.9 &ace V e l o c i t y (h - l ) 1300 P r o d u c t Composi t ion (CH + Oxygenates) %

CH 8.6 c f i 8 . 2 C2H4 0 . 4 C2H6 19 .3

C3H8 8 . 6

c4-Eo O l e f i n s 36 .1 c2-c4 P a r a f f i n s <0.8

55.1 C,+ and oxygena te s

C3H6 < 0 . 2

C4H8 < 0 . 2

2 4

P r e c i p . Fe-Mn (Kolbel e t a l )

14 290

353 0.8

12.1 7.6 4.9

1 7 . 3 2 . 1

1 5 . 2 3 . 1

40.1 10.1 47.8

4 .0 c;-c4 O l e f i n s

C -C P a r a f f i n s 2 4

>45.1

122

Table 3 . - Product Compositions from the Catalysts ZSM-5 (11.1% Fe) and ZSM-5 ( 5 . 6 % Fe, 4 . 5 % Co), in a Berty Reactor, Showing the Influence of cobalt addition to the Catalyst.

Process Condition: H2/C0 = 2 , P = 2 1 Bar and GHSV = 1000 hr-l

Catalyst ZSM-5 (11.1% Fe) Temperature 300 CO Conversion, % 6 8 . 2

S$ace Velocity 1500

Product Composition ( X )

H Conversion, X 3 8 . 7

5 2 . 0 19.4 2 8 . 6

3 ~ i ; ~ + Oxygenates

Hydrocarbon and Oxygenate Composition (%)

C -C hydrocarbons 83.1 C1+ 2nd Oxygenates 1 6 . 9 5

Composition of C,+ and Oxygenates (%)

Aromatics 7 2 Olefins 3 Saturates 24 Oxygenates 1 X Gasoline range (BP 204' C) 7 5 Research octane No. 9 6

ZSM-5 ( 5 . 6 % Fe, 4 . 5 % Co) 280

3 7 . 8 4 1 . 3

1400

9 . 8 5 1 . 8 3 8 . 4

7 4 . 3 2 5 . 7

10 4 6 37

7 9 4 81

123

Refe rences

1. C. D . Chang, W . H . Lang and A. J. S i l v e s t r i , J. C a t a l . 56, 268 (1979).

2. P. D. Caesar , J. A. Brennan, W . E. Garwood and J. C i r i c , 3. C a t a l . 56, 274 (1979) .

3. R. W . Crose and E. M. F l a n i g e n , U. S . P a t e n t 4 ,061,724 (1977) .

4 . G. T. Kokota i lo , S. L. Lawton, D. H . Olson and W . M. Meier, Na tu re 272, 437 (1978) .

5. E. M. F l an igen , J. M. B e n n e t t , R. W . Grose, J. P. Cohen, R. L. P a t t o n , R. M. Kirchner and J. W . Smith, Na tu re 271, 437 (1978) .

6 . R . J. Argauer and G . R. Lando t t , U. S. P a t e n t 3,702,886 (1972) .

7. J. M. Be r ty , Chem. Engr. Prog . z, 68 (1974) .

8. H. Kolbe l , M. Ra lek and K. D . T i l l m e t z , Proc . 1 3 t h I n t e r s o c . Energy Conv. Eng. Conf. , S o c i e t y o f Automot. Eng inee r s (1978) , p . 482.

9. M. E. Dry, T. S h i n g l e s , L. J. Boshoff and G . J. Oosthuizen, J. Catal. 2, 190 (1969) .

10. K . M. S a n c i e r , W. E. I s a k s o n and H. Wise, P r e p r i n t s , Div. of Petroleum Chemis t ry , ACS, 23 (2 ) . 545 (1978) .

11. R . M. Bozor th , "Ferromagnetism", Van Nost rand , New York, 1951, p p . 190-209.

12 . P. B. Weisz, Adv. C a t a l . 13, 137 (19G2).

124

Bed thermocouple

Figure 1. - Berty Reac tor (CFSTR)

1 2 5

h 0 U U m p:

N

THE HYD-ION OF CARBON bONOXIDE OVER UCJSUPPORTED I I O N 4 1 A N G F N E S E CATALYSTS FO3 THE PR~DUCTION OF Low-i.DLECLLAR WEIm OLEFINS. Y. S. T d , A. G. Oblad and F. V. liarson, Departrrwt of Fuels Engineering, 320 W. C. Br-ng Building, Universi ty of Utah, Salt Lake City, Utah 84112.

The hydrogenat ion of carbon monoxide f o r t h e p r o d u c t i o n o f low m o l e c u l a r w e i g h t (C - C o l e f i n s has been i n v e s t i g a t e d over unsupported iron-manganese c a t a l y s t s . A segies

Of f i f t e e n c a t a l y s t s o f d i f f e r e n t iron/manganese r a t i o were prepared and eva lua ted .

c a t a l y s t e v a l u a t i o n co d i t i o n s were 473-523 K, 500 p s i g , 2/1 H /CO r a t i o and a gas h o u r l y space v e l o c i t y 1.08 cmgg-ls- l . The most p romis ing c a t a l y s t wi?h r e g a r d t o t h e C2-C4 hydrocarbon y i e l d was composed o f 2 . 2 p a r t s o f manganese p e r 100 p a r t s o f i r o n .

f o r an extended process v a r i a b l e i n v e s t i g a t i o n . c reas ing r e a c t i o n temperatures, w i t h decreasing space v e l o c i t y and w i t h decreas ing H2/C0 r a t i o . was n o t observed i n t h i s i n v e s t i g a t i o n . The a c t i v a t i o n energy i n t h e temperature range 473-523 K was 20-30 kca l mol-1.

The screen ing t e s t s were conducted i n a f i xed-bed, bench-scale r e a c t o r . The s tandard

Four o f t h e c a t a l y s t s , Mn/Fe=2.2, Mn/Fe=8.4, Mn/Fe=63 and Mn/Fe=278 were s e l e c t e d The o l e f i n y i e l d inc reased w i t h i n -

The dependence o f t h e o l e f i n y i e l d on r e a c t o r p ressure r e p o r t e d i n t h e l i t e r a t u r e

127

A MODEL FOR THE ISOTHERMAL PLASTOMETRIC BEHAVIOR OF COALS

Wil l iam G. Lloyd, Henry E. F r a n c i s , Morgan R. Yewell, Jr.

I n s t i t u t e f o r Mining and Minerals Research, Un ive r s i ty of Kentucky, P. 0. Box 13015, Lexington, KY 40583

Raymond 0. Kushida and Vega D. Sankur

Jet P ropu l s ion Labora to ry , C a l i f o r n i a I n s t i t u t e of Technology Pasadena, CA 91103


The p l a s t i c i t y of bi tuminous coa ls i n t h e range 350-5OO0C i s of c r i t i c a l importance i n thermomechanical f l u i d i z a t i o n such a s i s r e q u i r e d f o r c o a l pump- i n g by heated screws (1-3) and i n hydrogeno lys i s i n t h e absence of added s o l v e n t ( 4 , s ) . The f a c t t h a t t h e optimum r e a c t i o n t empera tu res f o r t h r e e major c u r r e n t l i q u e f a c t i o n t e c h n o l o g i e s a r e n e a r l y i d e n t i c a l (6) and a r e c l o s e t o t h e f l u i d i t y maxima f o r many p l a s t i c c o a l s s u g g e s t s t h a t t h e p rocesses comprising c o a l "melting" are c r i t i c a l l y impor t an t t o h y d r o l i q u e f a c t i o n . More g e n e r a l l y , c o a l plas- t i c i t y i s obv ious ly invo lved i n caking problems (7-10).

The most w ide ly used method of measuring c o a l p l a s t i c i t y w a s developed by G i e s e l e r (11). With minor mod i f i ca t ions t h i s remains a s t a n d a r d procedure ( 1 2 ) ; i ts r e l a t i o n s h i p t o o t h e r measurements h a s been d i scussed elsewhere (13) . This method measures t h e r e s i s t a n c e of a mass of well-packed pu lve r i zed c o a l t o t h e r o t a t i o n o f a rabble-arm st irrer which is d r i v e n through a cons t an t - to rque c l u t c h . A t low t empera tu res t h e s o l i d mass completely immobil izes t h e st irrer s h a f t . I n t h e s t a n d a r d G i e s e l e r p rocedure t h e coa l is h e a t e d a t a uniform r a t e of 3"C/min. A s t h e c o a l b e g i n s t o s o f t e n -- t y p i c a l l y a t abou t 390'C -- t h e s t i r r e r s h a f t commences t o t u r n s lowly. A s t empera tu re i n c r e a s e s t h e c o a l becomes more f l u i d and t h e s h a f t t u r n s more r a p i d l y , e v e n t u a l l y a c h i e v i n g a maximum r a t e . The c o a l m e l t -- a c t u a l l y a he te rogeneous mixture of s o l i d s , molten phase and gaseous p y r o l y z a t e -- t h e n undergoes a th i cken ing o r "coking"; t h e st irrer s h a f t t u r n s p r o g r e s s i v e l y more s l o w l y , and e v e n t u a l l y s t o p s . Gieseler d a t a a r e recorded i n u n i t s of d i a l d i v i s i o n s per min (ddpm), where 100 ddpm = 1 s h a f t r o t a t i o n pe r min. For t h r e e bi tuminous c o a l s of v a r y i n g p l a s t i c i t y t h e s t anda rd G i e s e l e r d a t a a r e shown i n Table 1.

The I so the rma l bfodel

It i s o f t e n u s e f u l t o s tudy phenomena under i s o t h e r m a l cond i t ions . Gieseler p la s tome t ry l e n d s i t s e l f t o such s t u d i e s , s i n c e sample warmup t ime i n t h e s t anda rd c r u c i b l e (2-3 min.) is s h o r t i n comparison w i t h t h e u s u a l me l t ing /cok ing time s c a l e (20-120 min.). I so the rma l G i e s e l e r p l a s tome t ry h a s been explored by F i t z - g e r a l d (14,15) and by Van Krevelen and coworkers (16,17) . a g a i n s t time shows a l o n g l i n e a r coking r e g i o n (14,15) .

A p l o t of log(ddpm)

F igure 1 (open c i r c l e s ) shows t h e i s o t h e r m a l p l a s t o m e t r i c cu rves a t 410-2°C o b t a i n e d with t h e t h r e e c o a l s desc r ibed i n Table 1. Both t h e maximum f l u i d i t i e s

128

and t h e p e r i o d s of f l u i d i t y are seen to vary s u b s t a n t i a l l y among t h e s e c o a l s .

The l i n e a r i t y of t h e coking s l o p e s has been i n t e r p r e t e d t o imply a sequence of f i r s t - o r d e r r e a c t i o n s (14-17):

c + 11 k ( i n i t ) ( f i r s t - o r d e r mel t ing) (1)

M + S k(coke) ( f i r s t - o r d e r coking) ( 2 )

where C, M and S r e p r e s e n t t h e m e l t a b l e p o r t i o n of t h e o r i g i n a l c o a l , t h e f r a c - t i o n which is molten ( m e t a p l a s t ) , and t h e f r a c t i o n which i s r e s o l i d i f i e d (coked). This scheme g i v e s rise t o t h e r a t e l a w :

d[Ml/dt = ki[C] - kc[M] ( 3 )

There are two problems w i t h t h i s scheme. curves which resemble observed curves . S p e c i f i c a l l y , i t p r e d i c t s t h e r a t e of i n c r e a s e of f l u i d i t y d u r i n g t h e s o f t e n i n g process t o d e c e l e r a t e p r o g r e s s i v e l y , w h i l e i n f a c t t h i s i n c r e a s e i s e x p o n e n t i a l w i t h t ime over most of t h e m e l t i n g per iod . Second, t h i s scheme s p e c i f i c a l l y assumes t h a t Gieseler f l u i d i t y i s a l i n e a r measure of t h e molten f r a c t i o n o r m e t a p l a s t ; b u t t h a t assumption is m i s - t aken , as w e w i l l show.

F i r s t , i t does n o t g e n e r a t e model

For t h e purpose of more c l o s e l y modeling t h e a c t u a l i s o t h e r m a l c u r v e s we propose a second mel t ing p r o c e s s , such t h a t t h e rate of i n c r e a s e of f l u i d i t y i s dependent upon t h e c o n c e n t r a t i o n s of bo th m e t a p l a s t and unmelted f r a c t i o n :

C + M -+ 2 M k (me1 t ) (4)

The r a t e l a w now a c q u i r e s a t h i r d term:

dF/dt = ki[C] + km[C][M] - kc[Ml (5)

(We use F f o r f l u i d i t y , r a t h e r t h a n [MI f o r m e t a p l a s t , on t h e l e f t - h a n d s i d e ) . The v i r t u e of Equation 5 is t h a t , f o r most i s o t h e r m a l runs , i t can p r o v i d e a f a i r l y good f i t t o t h e exper imenta l d a t a , and t h e r e f o r e can d e f i n e t h e exper i - mental curves i n terms of numer ica l c o n s t a n t s a s s o c i a t e d w i t h t h e m e l t i n g and coking processes . t i o n 5 model, u s i n g t h e v a l u e s g iven i n Table 2. model t h a t t h e exper imenta l p o i n t s i n t h e v i c i n i t y of maximum f l u i d i t y tend t o b e h i g h e r t h a n t h o s e genera ted by t h e model. bubbles , which l e a d t o anomalously h igh exper imenta l readings .

The s o l i d p o i n t s i n F i g u r e 1 a r e v a l u e s genera ted by t h e Equa- It is a c h a r a c t e r i s t i c of t h i s

T h i s may r e f l e c t format ion o f gas

In apply ing t h i s model, t h e l e a s t - s q u a r e s m e l t i n g and coking slopes are c a l c u l a t e d from t h e exper imenta l d a t a ; w e use a l l d a t a between 1 ddpm and one f o u r t h t h e maximum observed f l u i d i t y . The e x t r a p o l a t e d maximum f l u i d i t y (emf) and t h e t i m e of maximum f l u i d i t y are taken from t h e i n t e r s e c t i o n of t h e s e s l o p e s .

From t h e s e d e t e r m i n a t i o n s , approximate v a l u e s f o r t h e m o d e l c o n s t a n t s can b e e s t i m a t e d e m p i r i c a l l y from t h e cubic equat ions :

129

- = m(melt) -0.3179 + .71507 x R - .15991 x R2 + .012348 x R3 k (me1 t )

(7)

(8)

- = m(coke) -0.6934 + 1.1504 x R - .26779 x R2 + .020826 x R3 k(coke)

P ,n[k( in i t ) ] = -16.127 + 2.8478 x P - .25098 x P2 + .005726 x P3

where m(me1t) and m(coke) denote t h e me l t ing and coking s l o p e s , R = m(melt) / m(coke), and P = [ (m(melt) + m(coke)) x t(max f l u ) ] . These equa t ions g ive f a i r l y good f i t s when k(me1t) is i n t h e r ange 0.5 t o 4 min.-l and kccoke) is i n t h e range 0.2 to 1.5 min.-l. T o r e l a t e t h e concep tua l molten f r a c t i o n [MI t o t h e observed ddpm, the emf from a model curve i s compared w i t h t h a t from t h e expe r imen ta l curve. For example, Ohio 1/9 seam c o a l a t 411a h a s an expe r imen ta l emf of 81.3 ddpm, and a c a l c u l a t e d emf ( u s i n g t h e k va lues of Table 2 ) of [MI = 0.683. When each datum i n t h e model cu rve i s m u l t i p l i e d by t h e f a c t o r 81.3/0.683, t h e model f l u i d i t i e s a r e converted t o u n i t s of ddpm. [ D e t a i l e d procedures and programs f o r t h e s e e s t i m a t e s a r e a v a i l a b l e from t h e a u t h o r s . ]

E f f e c t of Temperature

I so the rma l cu rves w e r e ob ta ined upon Kentucky 811 seam c o a l a t f i v e addi- t i o n a l temperatures , i n t h e r ange 400-460°C. Values of t h e model c o n s t a n t s a r e given i n Table 3. An Arrhenius p l o t of t h e model c o n s t a n t s k(me1t) and k(coke) is shown i n F i g u r e 2. ( b e s t 5 of 6 d a t a ) i s 173 f 13 k J ; t h a t f o r kccoke) ( a l s o b e s t 5 of 6 ) is 228 t. 6 kJ. (18,191. compared wi th those f o r a s p h a l t (120-150 k J ) and g l a s s (390-400 kJ) (20,211.

For t h i s c o a l the v a l u e of t h e appa ren t E, f o r k(me1t)

V i s c o s i t i e s commonly show an analogous " a c t i v a t i o n energy of v i s c o s i t y " The appa ren t Ea of maximum f l u i d i t y is approximately 600 k J , h igh when

When t h e temperature dependencies f o r t h e pa rame te r s of t h i s model have been e s t i m a t e d from t h e d a t a o f Table 3, i s o t h e r m a l cu rves may be c a l c u l a t e d f o r any i n t e r p o l a t e d t empera tu re , o r f o r any e x t r a p o l a t e d t empera tu re c l o s e t o t h e range of expe r imen ta l d a t a . Kentucky 811 seam c o a l , based upon d a t a c a l c u l a t e d f o r t h e range 392-468'C. curve is an " i s o f l u i d i t y " envelope, open a t t h e top. F igu re 3 i s read a long hori- z o n t a l ( i so the rma l ) l i n e s . g r e a t e r than 1 ddpm) from 2 t o 30 min., and h a s a f l u i d i t y exceeding 100 ddpm from 5 t o 20 min. d i f f e r e n t c o a l s , may f i n d use i n a p p l i c a t i o n s i n which t h e p l a s t i c p r o p e r t i e s of bi tuminous c o a l s are impor t an t .

D i scuss ion

F i g u r e 3 shows a f a m i l y of f l u i d i t y envelopes f o r t h e Each

A t 430" t h i s c o a l e x h i b i t s a p l a s t i c pe r iod ( f l u i d i t y

This p r o j e c t i o n , which w i l l a f f o r d markedly d i f f e r e n t envelopes f o r

The o rgan ic s t r u c t u r e s of c o a l s a r e numerous and va r i ed . Bonds which the rma l ly c l e a v e a t u s e f u l r a t e s a t 390-400°C ( d i s s o c i a t i o n e n e r g i e s o f 210-230 k J ) a r e no t t h e same a s t h o s e c l eaved a t 460" (240-260 k J ) . measurements i s t o c o n t r o l t h i s v a r i a b l e .

A major reason f o r i s o t h e r m a l

G i e s e l e r f l u i d i t y c a n be r e l a t e d t o v i s c o s i t y u n i t s by c a l i b r a t i n g w i t h s t a n d a r d f l u i d s . Measurements w i t h t h e p l a s tome te r used i n t h i s s tudy and wi th

130

a p p r o p r i a t e s t a n d a r d s (22) i n t h e range 500 - 10,000 p o i s e y i e l d a l i n e a r c a l i - b r a t i o n :

Iln(p0is.e) = 16.2789 - 0.96787 9.n (ddpm) (9)

wi th a c o r r e l a t i o n c o e f f i c i e n t of .9997. Actua l c o a l mel t s are heterogeneous (7,161, p s e u d o p l a s t i c (23) , and v i s c o e l a s t i c i n t h e i r l a t e r coking s t a g e s (24) . It is n e v e r t h e l e s s u s e f u l t o i n t e r p r e t G i e s e l e r f l u i d i t i e s as e s t i m a t e s of t r u e v i s c o s i t i e s .

Nicodemo and N i c o l a i s (25) and Fedors (26) have shown t h e v i s c o s i t y of Newtonian suspens ions of s o l i d s t o conform t o t h e express ion:

where n , no, and 4 are t h e suspens ion v i s c o s i t y , s o l v e n t v i s c o s i t y , and s o l i d s f r a c t i o n . Data obta ined by Lee (27) show t h e logar i thm of t h e maximum f l u i d i t y of coa l b lends t o vary l i n e a r l y w i t h composition. These o b s e r v a t i o n s a r e t e l l i n g us t h e same th ing: t h a t t h e l o g a r i t h m of f l u i d i t y , n o t f l u i d i t y i t s e l f , is a d i r e c t measure of t h e molten f r a c t i o n . I f w e assume t h a t a f l u i d i t y of 1 ddpm corresponds t o t h e maximum s o l i d f r a c t i o n Omax, we can p r o j e c t t h e r e l a t i o n s h i p :

(11) tJ !Ln(F) = & n ( F " ) . [ 1 - - 1 'max

To use Equation 11 we need e s t i m a t e s of tJmX and of t h e f l u i d i t y of pure metaplas t , FO. spheres is 0.63 (28,29). This f r a c t i o n is h i g h e r f o r p o l y d i s p e r s e s p h e r e s (30) and f o r some s i z e d i s t r i b u t i o n s may b e as h i g h as 0.9 (31). w i l l assume a v a l u e of $max of 0.80. P i t t s b u r g h 118 seam sample a t 412" (1.0 x lo6 ddpm) i s t a k e n as a rough e s t i m a t e of F a , we can e s t i m a t e s o l i d f r a c t i o n s i n o t h e r c o a l s from f l u i d i t i e s a t t h i s temperature. F l u i d i t i e s of 10, 100, 1,000 and 10,000 ddpm i n d i c a t e s o l i d f r a c - t i o n s of approximately .67, .53, .40 and .27. The minimum v a l u e s of @ f o r Ohio 119 and Kentucky 1\11 samples i n Table 2 are approximately 0.55 and 0.41.

The maximum s o l i d f r a c t i o n i n a random d i s p e r s i o n of monodisperse

For c o a l mel t s w e I f t h e e x t r a p o l a t e d maximum f l u i d i t y of t h e

The l i n e a r i t y of l o g ( F ) w i t h @ has mechanis t ic i m p l i c a t i o n s as w e l l . left-hand of Equation 3 i s more a c c u r a t e l y expressed as d Rn[M]/dt. of F igure 1 show l i n e a r i n c r e a s e s of m e t a p l a s t w i t h t i m e i n t h e e a r l y s t a g e s , and l i n e a r d e c r e a s e s of m e t a p l a s t wi th t i m e (zero t l t o r d e r k i n e t i c s ) i n t h e l a t e r coking s t a g e s .

The The curves

Ext rus ion pumping of c o a l s i n t h e p l a s t i c s t a t e e n t a i l s s u b s t a n t i a l l y i so thermal o p e r a t i o n s f o r r e s i d e n c e times of a few minutes i n t h e screw (1-3). Severa l c o a l s , i n c l u d i n g those of t h e p r e s e n t s t u d y , have been ex t ruded w i t h no d i f f i c u l t y i n JPL's 1.5-in. c o a l pump. t i c i t y ( l e s s than 2 ddpm) were not e x t r u d a b l e (3) . The i s o t h e r m a l p las tomet ry p r o f i l e s may prove t o b e a u s e f u l t o o l i n p r e d i c t i n g behavior i n c o a l pumps. Recent ev idence of t h e s u b s t a n t i a l e f f e c t of p r e s s u r e upon observed p l a s t i c i t y (10) i n d i c a t e s t h a t t h i s v a r i a b l e should be cons idered i n f u t u r e work.

Two c o a l s which showed very l i t t l e p l a s -

131

Acknowledgments

Chr is topher England ( J e t Propuls ion Labora tory) f i r s t sugges ted t h i s s t u d y . Propuls ion Laboratory, C a l i f o r n i a I n s t i t u t e of Technology, under Cont rac t no. 954920. The c o a l pump p r o j e c t is suppor ted by t h e Department of Energy through a n agreement wi th the N a t i o n a l Aeronaut ics and Space Adminis t ra t ion .

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L. Nicodemo and L. N i c o l a i s , Polymer, 15, 589 (1974).

R. F. Fedors, E., 16, 305 (1975).

H. C. Lee (Kaiser S t e e l Corp.), p r i v a t e communication.

6. D. S c o t t , Nature, 188, 908 (1960).

R. F. Fedors, J. C o l l o i d I n t e r f a c e Sci., 46, 545 (1974).

R. F. Fedors, Polymer, 0, 225 (1979).

S. F e i n s t e i n ( J e t Propuls ion Labora tory) , p r i v a t e communication.

133

Seam

s o u r c e

P rox ima te : m o i s t u r e a s h v o l . m a t t e r f i x e d c a r b o n

U l t i m a t e : ' c a rbon hydrogen n i t r o g e n s u l f u r oxygen

H e a t i n g v a l u e '

T a b l e 1

P r o p e r t i e s of Three B i tuminous Coals

Ohio 89

Noble Co.

2.15% 18.87 39.40 39.58

79.41 5.30 1.13 5.38 8.78

14,010 B t u / l b

F r e e s w e l l i n g i n d e x 3

P e t r o g r a p h i c a n a l y s i s ' e x i n o i d s 2.1% v i t r i n o i d s 70.1 o t h e r r e a c t i v e s 1.9 i n e r t m a c e r a l s 12.9

ASTM G i e s e l e r p l a s t o m e t r y s o f t e n i n g T 398°C cok ing T 462" max f l u T 435" max f l u i d i t y 114 ddpm

Kentucky 111

Webster Co.

1.97% 8.34

41.19 48.50

82.21 5.43 1.36 3.52 7.48

14,770 B t u / l b

7

5.1% 76.3

1.2 11.0

392'C 474O 435O

6240 ddpm

P i t t s b u r g h 88

( f rom M E T C )

0.79% 8.65

40.85 49.71

84.83 5.49 1.44 2.92 5.33

15,290 B t u / l b

7%

4.0% 75.3 0.9

13.7

372°C 485"

(414-459") >>25000 ddpm

_ _ _ _ _ _ _ _ - - _ _ _ _ _ _ _ _ _ _ - _ - - _ - _ - - - - - - - - - _ _ - As r e c e i v e d . M o i s t u r e - and a s h - f r e e b a s i s . By d i f f e r e n c e .

134

I 0 5

I o4

IO

I I I I I I

..

0

?

8. 0.0

.O

'8 '0 '0 * c 8

Time, m i n u t e s

F i o u r e 1. I s o t h e r m a l n l a s t o m e t r i c c u r v e s of t h r e e b i t u m i n o u s c o a l s . A - Ohio F9 seam (Noble Co.) a t 411OC. B - Kentucky b l l seam ( I l e b s t e r Co.) a t 410°C. C - P i t t s b u r K h h3 S e a n ( f rom ::ETC) a t 412°C. 07en c i r c l e s a r e e x p e r i m e n t a l d a t a ; s o l i d n o i n t s are c a l c u l a t e d by t h e three-Tarameter model ( v a l u e s g i v e n i n T a b l e 2).

1 ;5

F i g u r e 1

T a b l e 2

C h a r a c t e r i s t i c s of Three I s o t h s r m a l P l a s t i c Curves a t 410-412°C

Ohio #9 Kentucky #11 P i t t s b u r g h #8 411°C 410°C 412’C

M e l t i n g s l o p e 0.425 0.621 1.084 Coking s l o p e -0.216 -0.151 -0.125 Maximum f l u i d i t y ,

ddpm’ 81 896 6 1.0 x 10

T i m e o f maximum f l u i d i t y ’ 14.34 15.42 15.75

C a l c u l a t e d v a l u e s :

‘k ( i n i t ) 6.0 4.3 3.4 x k(me1t ) 0.77 0.79 1.24 k ( c o k e ) 0.35 0.16 0.125

’ By e x t r a p o l a t i o n o f m e l t i n g and c o k i n g s l o p e s . Using t h e t h r e e - p a r a m e t e r model d e s c r i b e d i n t e x t . Dimensions of k ( i n i t ) and k ( c o k e ) a r e min-l ; k (me1t ) is min-l mass f r a c t i o n - I .

T a b l e 3 E f f e c t of Tempera tu re upon the I s o t h e r m a l P l a s t i c Curves o f Kentucky

811 Seam Coal (40O-46O0C)

Temperature,’C - 400. 410. 425.5 440. 449.9 460. M e l t i n g s l o p e 0.172 0.621 1.35 1.60 2.57 5.3

Maximum f l u i d i t y ,

T i m e of maximum

Coking s l o p e -0.069 -0.151 -0.325 -0.679 -1.11 -1.56

ddpm’ 44 896 2.58E4 3.34E4 8.89E4 2.21E6

f l u i d i t y ’ , min. 25.82 15.42 11.14 8.12 6.30 4.13

C a l c u l a t e d v a l u e s : * k ( i n i t ) 1.2E-3 4.33-5 1.9E-6 3.OE-6 6.5E-7 4.3E-7 k(me1t ) 0.26 0.79 1.74 2.49 4.05 7.1 k ( c o k e ) 0.083 0.158 0.339 0.848 1.40 1.66

’ * By e x t r a p o l a t i o n of m e l t i n g and c o k i n g s l o p e s .

See T a b l e 2, f o o t n o t e 2.

136

5

2

h m

2 ' e 6.

5 0 5 I4 VI

1

v

02

01

05 I36 I 4 0 I44 I48

I O ~ / O K

F i n u r e 2. A r r h e n i u s deqendency of t h e model c o n s t a n t s k ( n e 1 t ) ( c i r c l e s ) and k ( c o k e ) (diamonds) f o r Kentucky 811 seam coal

480

460

u

440 a U m a, E' 420 k

400

0

C D E

I I I I I IO 20 30 40 50 60 70

Time, m i n u t e s

b\\ \

F i g u r e 3. I s o t h e r m a l f l u i d i t y e n v e l o n e s f o r Kentucky #ll seam c o a l A - l o 4 ddpm. B - lo3 ddpm. C - 10' ddqm. D - 1 0 dd?n. E - 1 d d y

137

PITCH RESIDUES FKON UPGRADING OF BITUMEN ANI) HEAVY OILS AS ADDITIVES I N COKEMAKIWG: INFLUENCE OF PITCH PROPERTIES

K . B e l i n k o , L.A. C i a v a g l i a , B . N . Nandi and J . M . Denis ,

Energy Research L a b o r a t o r i e s

Department of Energy, Mines and P e s o u r c e s , c / o 555 Booth S t r e e t , Ottawa, O n t a r i o K 1 A O G 1

Canada Centre f o r Minera l and Energy Technology,

INTRODUCTION

Impending s h o r t a g e s of good c o k i n g c o a l s th roughout t h e world have prompted a series of i n v e s t i g a t i o n s a t CANMET (Canada C e n t r e f o r Minera l a n d Energy Technology) i n t o t h e u t i l i z a t i o n o f w e s t e r n Canadian m a r g i n a l c o k i n g c o a l s i n t h e p r o d u c t i o n of m e t a l l u r g i c a l g r a d e coke . One p o s s i b l e way t o do t h i s i s t o add res iJual p i t c h from thermal h y d r o c r a r k i n g of b i tumen and heavy o i l s t o s u c h c o a l s ( 1 ) . T h i s p i t c h h a s been found t o b e an e x c e l l e n t a d d i t i v e f o r up-grading low f l u i d , low v o l a t i l e , i n e r t - m a c e r a l r i c h c o a l s . The p i t c h a c t s a s a f l u i d i t y - e n h a n c i n g a g e n t , and by i n t e r a c t i n g w i t h t h e v i t r i n i t e o f t h e c o a l , augments t h e s u p p l y o f r e a c t i v e c a r b o n n e c e s s a r y f o r bonding t o g e t h e r of i n e r t m a c e r a l s .

The p u r p o s e of t h i s p u b l i c a t i o n is t o add f u r t h e r i n s i g h t i n t o t h e r o l e of p i t c h i n c a r b o n i z a t i o n o f c o a l / p i t c h b l e n d s . P i t c h e s d e r i v e d from thermal h y d r o c r a c k i n g o f bitumen a t d i f f e r e n t d e g r e e s of s e v e r i t i e s were u t i l i z e d f o r t h i s p u r p o s e . T h i s p r o v i d e d a means o f a s s r s s i n g t h e p r o p e r t i e s of t h e p i t c h e s i n t h e c a r b o n i z a t i o n p r o c e s s w i t h o u t c h a n g i n g t h e b a s i c c h e m i c a l n a t u r e o f t h e p a r e n t m a t e r i a l .

EXPERIMENTAL

The p r o p e r t i e s o f t h e p i t c h e s d e r i v e d from thermal h y d r o c r a c k i n g o f Athabasca bitumen under v a r i o u s o p e r a t i n g c o n d i t i o n s a r e g iven i n Table 1. These four p i t c h e s were produced under d i f f e r e n t d e g r e e s of s e v e r i t y d u r i n g t h e p r o c e s s A b e i n g c h a r a c t e r i s t i c o f p i t c h o b t a i n e d under r e l a t i v e l y mi ld c o n d i t i o n s and D , o f p i t c h o b t a i n e d a t h i g h s e v e r i t i e s . A r r l a t i o n was found t o e x i s t betwcen t h e d e g r e e o f s e v e r i t y d u r i n g h y d r o c r a c k i n g and t h e v a r i o u s p r o p e r t i e s l i s t e d i n T a h l e 1 (e .g . CCR, a r o m a t i c i t y , s o f t e n i n g p o i n t ) .

TABLE 1

P h y s i c a l and Chemical P r o p e r t i e s o f P i t c h e s

Vola t i l e matter % Ash % S o f t e n i n g t e m p e r a t u r e O C

Conradson c a r b o n r e s i d u e % S p e c i f i c g r a v i t y Benzene- inso lubles* A s p h a l t e n e s % H / C S u l p h u r % Aromat ic i ty** % --

A

73.1 1.8

50 34.7 1.10 2.6

37.2 1 . 3 2 5 .58

-

3 8 . 2

- B

64.8 2 . 3

9 5 42.2 1.12 4.2

4 4 . 6 1 . 1 5 5.6:

-

49.4

tch C

53.5 3 .2

50.7

11 .6 48.1

105

1 . 1 6

1 . 0 9 6.33

56 .3

___ D

44.6 -

5 . 8 135

64.6

20.6 55.2

1 .24

0 .94 4 .85

69 .8 -_ * Ash-free b a s i s , ** 1% NMR a n a l y s i s

138

The c o a l used was a w e s t e r n Canadian, low f l u i d , h i g h rank b i t u m i n o u s c o a l h a v i n g a r e l a t i v e l y h i g h c o n c e n t r a t i o n o f i n e r t m a c e r a l s . and P e t r o g r a p h i c a n a l y s e s of t h i s c o a l a r e g i v e n i n T a b l e 2 .

Proximate , u l t i m a t e

TABLE 2

P r o p e r t i e s o f t h e Coal

Proximate A n a l y s i s ( d r y b a s i s )

Ash % 9.8 V o l a t i l e m a t t e r % 21.2 Fixed Carbon % 69.0

U l t i m a t e A n a l y s i s

Carbon % 78.9 Hydrogen % 4.3 Sulphur % 0.8 N i t r o g e n % 1 . 3 Oxygen (by d i f f . ) % 4.9 Ash % 9.8

P e t r o g r a p h i c A n a l y s i s

V i t r i n i t e v o l . % 51.8 Semi-f u s i n i t e v o l . % 34.2 F u s i n i te v o l . % 1 1 . 2 M i c r i n i t e v o l . % 2 . 6 E x i n i t e v o l . % 0 .2

1.17 RO Mean r e f l e c t a n c e i n o i l ,

C o a l f p i t c h b l e n d s w i t h v a r y i n g p i t c h c o n c e n t r a t i o n s were p r e p a r e d and t h e i r f l u i d i t i e s de te rmined by means of a G i e s e l e r p l a s t o m e t e r . The f l u i d i t i e s of t h e v a r i o u s b l e n d s a r e r e p o r t e d i n Table 3 . of p i t c h which can p o t e n t i a l l y i n t e r a c t w i t h t h e c o a l d u r i n g c a r b o n i z a t i o n , Cp, is a l s o g i v e n i n Table 3.

A v a l u e r e p r e s e n t i n g t h e c o n c e n t r a t i o n

Cp was c a l c u l a t e d on t h e f o l l o w i n g b a s i s :

where CCR i s t h e Conradson carbon r e s i d u e (2) and approximates t h e c o n t r i b u t i o n of carbonaceous m a t e r i a l made by t h e p i t c h t o t h e b lend d u r i n g c a r b o n i z a t i o n .

The v a r i o u s c o a l l p i t c h b l e n d s were c a r b o n i z e d u s i n g a c a n i s t e r c o k i n g techniqu developed a t CANMET ( 3 ) . The b l e n d s were packed t o a b u l k d e n s i t y o f 801 kg/m i n t o p e r f o r a t e d t i n p l a t e c a n i s t e r s 2 9 . 3 cm l o n g and 1 .6 cm i n d i a m e t e r . Twenty c a n s , each c o n t a i n i n g a d i f f e r e n t b l e n d were s ide-charged i n t o CANMET'S 250-kg moveable w a l l coke oven.

5 .

The r e l a t i v e s t r e n g t h s of t h e cokes produced from t h e c a n i s t e r test were de te rmined by a small sample tumbler t e s t deve loped by Bituminous Coal Research (BCR) (4) and a r e r e p o r t e d i n Table 3 . These s t r e n g t h i n d i c e s are a measure of s i z e r e d u c t i o n i n tumbled coke p a r t i c l e s and t h e r e f o r e a l a r g e i n d e x c o r r e s p o n d s t o a weak coke.

O p t i c a l e x a m i n a t i o n s of t h e v a r i o u s cokes were made w i t h a L e i t z r e f l e c - t e d l i g h t microscope u s i n g an o i l immersion l e n s . The micrographs were t a k e n a t 6OOX m a g n i f i c a t i o n u s i n g p a r t i a l l y c r o s s e d n i c o l s .

139

TABLE 3

C a r b o n i z a t i o n Data f o r Coal P i t c h B lends

3 7 0 39.0

9 . 1

P i t c h A

c o n t r i b u t i o n o f c a r b o n f r o m p i t c h . Cp

F l u i d i t y of b l e n d BCR* s t r e n g t h i n d e x

P i t c h B

C o n t r i b u t i o n o f c a r h o n from p i t c h , Cp

F l u i d i t y o f b l e n d BCR* s t r e n g t h i n d e x

P i t c h C

C o n t r i b u t i o n o f c a r b o n from p i t c h , C

F l u i d i t y o f b l egd BCR* s t r e n g t h i n d e x

P i t c h D

C o n t r i b u t i o n o f c a r b o n f r o m p i t c h , Cp

F l u i d i t y of b l e n d BCR* s t r e n g t h i n d e x

400 40 .3

10.4

%

ddlmin

%

ddlmin

%

ddlmin

%

ddlmin

Conc 0 -

N i l

N i l N/A**

N i 1

N i 1 N/A**

N i l

N i 1 N/A**

N i l

N i l M I A * *

__ t r a t : __

5 __

1 .5

1.9 49.0

2.1

1 . 5 53.8

2 .6

1.1 52.7

3 . 3

1.0 57.8

__

8 ~

2.4

6 . 1 36.4

3 . 3

5 . 7 35.3

4 . 1

5 .0 36.7

5.2

4 .o 53.1

__ i t c h

10 __ __

3 .1

6 . 4 38.2

4 . 1

7 . 1 34.5

5.0

1 3 . 0 36.9

6 .5

6 .8 35 .1

n Blend w t % 'x-pi-

7.1 I 8.2

* Bituminous Coal Kesea r rh I n c . , P i t t s b u r g h , P.A. ** A non-agglomerated c h a r was produced

RESULTS AND DISCUSSION

A pho tograph showing t w o r e p r e s e n t a t i v e cokes from t h e c a n i s t e r t e s t is shown i n F i g . 1. The coke shown a t t h e top was produced from c o a l w i t h no p i t c h a d d i t i v e and was p o o r l y agg lomera ted . The coke a t t h e bot tom was agg lomera ted and h a r d and was t y p i c a l o f cokes produced from c o a l l p i t c h b l e n d s . The former coke c o u l d n o t b e e v a l u a t e d by t h e BCR tumbler tes t because of i t s non-agglomerated c h a r a c t e r . The s t r e n g t h i n d i c e s of t h e cokes produced from c o a l l p i t c h b l e n d s a r e g i v e n i n Tah le 3 .

The s t r e n g t h s o f t h e cokes produced from b lends c o n t a i n i n g p i t c h A a n d p i t c h B were n o t f o u n d t o va ry s i g n i f i c a n t l y f o r p i t c h c o n c e n t r a t i o n s above 5 % . On the o t h e r hand . a d d i t i o n s of more than 10% p i t r h i n r o a l l p i t r h C and c o a l l p i t c h I) b l e n d s were found t o b e d e t r i m e n t a l t o coke s t r c n g t h . Thr i n f l u e n c e o f ? i t c t l c o n c e n t r a t i o n on coke s t r e n g t h was t h e r e f o r e more pronounced f o r p i t c h o b t a i n e d from h igh s e v e r i t y t h e r m a l hydroc rack ing r u n s . I t would h e d i f f i c u l t t o p r e d i c t an e x a c t optimum p i t c h c o n c e n t r a t i o n hascd s o l e l y o n t h e r e s u l t s r e p o r t e d i n T a b l e 4 f o r m a l l p i t c h D b l e n d s .

C n a l l p i t c h h l c n d s hav ing Cp v a l u p s i n e x c s s s o f a b o u t 7 % produced cokes of p r o g r r s s i v e l y weaker s t r p n g r h s . The Conradson carhon r e s i d u c ( C C R ) c o n t e n t s o f p i t c h e s A a n d H were s u f f i c i p n t l y l o w t o p e r m i t a d d i t i o n s o f up t o 1hX p i t c h to t h e Coal withot i t CP valut2s o f t he hlend e x c e d i n g 77,. T h i s Would accoun t f o r t h e l a c k of a minimum i n IlCR s t r e n g t h index f n r cokes produced from b lends c o n t a i n i n g p i t c h

140

A and p i t c h B w i t h i n t h e c o n c e n t r a t i o n r ange i n v e s t i g a t e d .

F l u i d i t y d a t a f o r t h e v a r i o u s b l e n d s a r e summarized i n Tab le 3. mlrked i n c r e a s e i n t h e f l u i d i t y o f t h e b l e n d s w a s obse rved f o r p i t c h c o n c e n t r a t i o n s g r e a t e r t h a n LO%. nounced f o r p i t c h o b t a i n e d f rom h i g h s e v e r i t y the rma l hydroc rack ing r u n s . perhaps s u g g e s t s t h a t t h e r e i s a b e t t e r i n t e r a c t i o n between p i t c h and t h e v i t r i n i t e of t h e c o a l i n c a s e s where t h e p i t c h was t r e a t e d under more s e v e r e c o n d i t i o n s du r ing the rma l hydrocracking. is d i r e c t l y r e l a t e d t o t h e d e g r e e of s e v e r i t y d u r i n g t h e r m a l hydroc rack ing . i n t e r a c t i o n between t h e p i t c h and t h e v i t r i n i t e may t h e r e f o r e b e r e l a t e d t o t h e a r o m a t i c i t y of t h e p i t c h :

A

The i n c r e a s e i n f l u i d i t y w a s g e n e r a l l y found t o be more pro- Th i s

It is e v i d e n t f rom Tab le 1 t h a t p i t c h a r o m a t i c i t y The

Based on some of t h e arguments p r e s e n t e d above , t h e f o l l o w i n g r e l a t i o n - s h i p was found t o be c o n s i s t e n t w i t h t h e d a t a i n Tab le 3:

0 . 9 7 BCR s t r e n g t h index = 26.47 + 1 .75 Cp exp -* A3,2F, 1.5 5 CP 5 10 .4 2)

Where Cp is d e f i n e d a c c o r d i n g t o Equa t ion l ) , A is t h e a r o m a t i c i t y of p i t c h d e t e r - mined by l 3 C NMR and F i s t h e f l u i d i t y of t h e c o a l / p i t c h b l end . p l o t t e d i n F i g . 2 and w a s found t o have a c o e f f i c i e n t of c o r r e l a t i o n of 0.89.

Equa t ion 2) i s

According t o Equa t ion 2 ) , t h e BCR s t r e n g t h i n d e x of a coke produced from a c o a l / p i t c h b l end i s n o t o n l y dependent on t h e v a l u e of Cp, b u t a l s o on t h e f l u i d i t y of t h e b l end . Low v a l u e s o f Cp i n t h e b l end appea r t o b e d e s i r a b l e i n a c h i e v i n g good coke s t r e n g t h p rov ided t h e f l u i d i t y o f t h e b l e n d is s u f f i c i e n t l y h i g h t o make t h e e x p o n e n t i a l term in t h e e q u a t i o n approach u n i t y . e n t i a l term h a s approached u n i t y , a d d i t i o n a l i n c r e a s e s i n Cp may o n l y c o n t r i b u t e t o a d e t e r i o r a t i o n i n coke s t r e n g t h . The i n t e r - r e l a t i o n s h i p between Cp and f l u i d i t y bo rne o u t by Equa t ion 2) emphasizes t h e need f o r c o n t r o l l e d f l u i d i t y i n e n s u r i n g a uniform and e f f i c i e n t d i s t r i b u t i o n o f t h e b i n d i n g material th roughou t t h e c o a l d u r i n g c a r b o n i z a t i o n . Th i s i s demons t r a t ed , f o r i n s t a n c e , i n t h e c a s e of 5% a d d i t i o n of p i t c h D t o t h e c o a l , Tab le 3. Although t h e Cp v a l u e was r e l a t i v e l y h igh , low f l u i d i t y p reven ted p r o p e r d i s t r i b u t i o n of t h e b i n d i n g material in t h e c o a l d u r i n g c a r b o n i z a t i o n ; consequen t ly , a weak coke w a s produced.

Once t h e expon-

I n o r d e r t o conf i rm t h i s dependence on f l u i d i t y , a series o f mic roscop ic The coke pro- examina t ions w a s made on t h e cokes produced from t h e c a n i s t e r test.

duced from t h e c o a l w i t h no p i t c h a d d i t i v e was found t o be p o o r l y bonded. mace ra l s were s e g r e g a t e d w i t h i n t h e coke s t r u c t u r e w i t h l i t t l e or no b i n d i n g m a t e r i a l su r round ing them ( F i g . 3). q u a l i t i e s depending on v a l u e s of Cp and f l u i d i t y . Three s p e c i f i c c a s e s w e r e chosen t o demons t r a t e t h i s dependence: ( i ) c o a l + 5% p i t c h D, ( i i ) c o a l + 10% p i t c h D and ( i i i ) c o a l + 16% p i t c h D.

I n e r t

C o a l / p i t c h b l e n d s produced cokes of v a r y i n g

I n c a s e ( i ) , c o a l + 5% p i t c h D, some degree of bonding was o b s e r v e d between i n e r t mace ra l s , b u t t h e bonding was g e n e r a l l y d i s c o n t i n u o u s and s p o r a d i c . Th i s i s e x e m p l i f i e d f o r i n s t a n c e i n F i g . 4 . It i s noteworthy t h a t f o r b l e n d s hav ing s i m i l a r Cp v a l u e s b u t h i g h e r f l u i d i t i e s , e .g . c o a l + 10% p i t c h A, bonding was found t o be c o n s i d e r a b l y more un i fo rm than t h a t shown i n F i g . 4. The d i f f e r - ence i n bonding can t h e r e f o r e b e a t t r i b u t e d t o t h e f l u i d i t y of t h e r e s p e c t i v e b l e n d s .

The coke produced from c a s e ( i i ) , c o a l + 10% p i t c h D, w a s found t o e x h i b i t e x c e l l e n t bonding. The b i n d i n g m a t e r i a l w a s un i fo rmly and c o n t i n u o u s l y d i s t r i b u t e d th roughou t t h e coke and t h e i n e r t mace ra l s were embedded w i t h i n t h e coke matrix, F ig . 5. These o b s e r v a t i o n s were c o n s i s t e n t w i t h t h e r e l a t i v e l y good BCR s t r e n g t h i n d e x o b t a i n e d f o r t h i s coke.

141

The d e t e r i o r a t i o n i n coke s t r e n g t h observed f o r c a s e ( i i i ) , c o a l + 16% p i t c h D, was a t t r i b u t e d t o t h e development of micro-cracks w i t h i n t h e coke s t r u c - t u r e , Fig. 6 . The mechanism by which t h e s e c r a c k s form is n o t w e l l unders tood , b u t could perhaps r e s u l t f rom a n e x c e s s of b i n d i n g m a t e r i a l between the i n e r t m a c e r a l s of t h e c o a l , t h e r e b y weakening the o v e r a l l s t r u c t u r e .

From t h e t h r e e c a s e s c o n s i d e r e d , i t i s e v i d e n t t h a t coke s t r e n g t h can be c o r r e l a t e d t o t h e mic . ro-s t ruc ture o f t h e cokes. The coke q u a l i t y a p p e a r s to b e a complex f u n c t i o n of t h e amount of p i t c h added, t h e physico-chemical p r o p e r t i e s of t h e p i t c h and t h e f l u i d i t y of t h e c o a l / p i t c h b l e n d .

It should be emphasized t h a t t h e arguments p r e s e n t e d i n t h i s paper apply s p e c i f i c a l l y to i n e r t - m a c e r a l r i c h , low f l u i d , h i g h rank c o a l s . Equat ion 2) h a s so f a r only heen t e s t e d f o r t h i s p a r t i c u l a r type of c o a l . I t is p o s s i b l e t h a t o t h e r c o a l s may y i e l d r e s u l t s t h a t do n o t conform e x a c t l y to t h i s e q u a t i o n . For i n s t a n c e , t h e c o a l used i n t h i s work had no i n h e r e n t f l u i d i t y , and c o n s e q u e n t l y a term f o r the f l u i d i t y of t h e c o a l i t s e l f does not a p p e a r i n t h e e q u a t i o n . However Equat ion 2 ) does d e m o n s t r a t e t h e s t r o n g i n t e r - r e l a t i o n s h i p between t h e c o n t r i b u t i o n of b i n d i n g m a t e r i a l made by t h e p i t c h and t h e f l u i d i t y of t h e b l e n d .

CONCLUSIONS

High rank c o a l s f rom w e s t e r n Canada which are r i c h i n i n e r t m a c e r a l s , g e n e r a l l y r e q u i r e a p i t c h a d d i t i v e t o produce m e t a l l u r g i c a l g r a d e coke . P i t c h c o n c e n t r a t i o n i n t h e c o a l l p i t c h b lend d i c t a t e s b o t h t h e amount of b i n d i n g m a t e r i a l made a v a i l a h l e t n t h e c o a l and the f l u i d i t y of t h e b lend . Both t h e s e p a r a m e t e r s depend on t h e phys ico-chemica l p r o p e r t i e s o f t h e p i t c h and on t h e e x t e n t of i n t e r - a c t i o n between t h e p i t c h and t h e c o a l .

I n o r d e r t o p r o d u c e good q u a l i t y coke f rom a c o a l / p i t c h b l e n d , t h e b lend must possess s u f f i c i e n t f l u i d i t y t o e n s u r e a uni form and c o n t i n u o u s d i s t r i b u t i o n of b i n d i n g m a t e r i a l th roughout t h e c o a l . I n e r t m a c e r a l s of t h e c a1 must be a d e q u a t e l y wet ted and bonded t o g e t h e r . p i t c h is added i n s u F f i c i e n t amount t o g e n e r a t e a c o n t r o l l e d f l u i d i t y w i t h enough b i n d i n g m a t e r i a l t o a g g l o m e r a t e t h e coke. I f added i n l a r g e amounts , t h e p i t c h can have d e l e t e r i o u s e f f e c t s on t h e r e s u l t a n t coke . The r e a s o n why too much p i t c h weakens the s t r u c t u r e i s n o t w e l l u n d e r s t o o d , b u t a p p e a r s t o be r e l a t e d t o t h e development of microcracks w i t h i n t h e coke m a t r i x .

9 . Optimum coke s t r e n g t h i s a c h i e v e d when

ACKNOWLEDGEMENTS

h i s

1.

I .

3 .

4 .

The a u t h o r s w i s h t o thank B . H . M o f f a t t and S.E. Nixon f o r t h e i r t e c h n i c a l a s s i s t a n c e d u r i n g t h e c o u r s e of t h i s work. Thanks a r e a l s o due t o W . Gard iner and

s t a f f f o r t h e i r a s s i s t a n c e i n c a r r y i n g n u t c a r b o n i z a t i o n t e s t s .

REFERENCES

Bclinko. K . . C i a v a g l i a , L . A . and Nandi. B . N . "Energy f o r i n d u s t r y " , Ed. P . W . O 'Cal laghan; Pergamon Press , (London); pp. 79-89 (1978) .

American S o c i e t y for T e s t i n g and M a t e r i a l s : P a r t 2 3 , D-189 (1975) .

Montgomery, D.S. and Nandi , R . N . Fue ls Research C e n t r e D i v i s i o n a l Report 731 11; Department o f Energy, Mines and Resources , O t t a w a , Canada (1'973).

Elosrs, R . C . Ri tllminous Coal Research I n c . , E lonroevi l le , Pennsylvania ; ['e r s o n a 1 Commun i c11 t ion .

14 2

NO ADDITIVE

60

x 5 5 W P

5 5 0

40

COAL -k 10% PITCH D

4 cm

FIGURE 1: High Temperature Cokes Produced From Canister T e s t s

0 . 9 r BINDING INDEX = C P e x p [ F F ]

/

I 3

BINDING INDEX, PER CENT FIGURE 2 : Relative Strength Indices for Various Coal/Pitch Blends

143

FLGUKE 3 : Opt ica l Micrograph o f Coke F I G U R E 4 : Opt ica l Micrograph of Coke Proauced from Coal With No Produced trom Coal + 5% P i t ch Additive Showing Poor bonding D .Showing Discontinuous Bonding Between Fused V i t r i n l t e (FV) of Fused Mass (FPI) With Fusini- and Oxidizcd V i t r i n i t e (OV) t i c S t ruc tu re (F)

FIGURE 5 : Optical Micrograph of Coke FIGURE h : Produced from Coal+ 10% P i t c h D Showing Excel lent Bonding of F u s i n i t i c S t r u c t u r e (F) by Fused Mass (FM)

144

Opt i ca l Micrograph of Coke Produced From Loa1 + 167, Pi t ch D Showing Development of Micro- cracks Within Fused Mass (FM)

SYIVXETIC FUELS - PITFALLS AND PROMISE. Fred Schulman. Energy Systems Technology Corp . , 927-15th S t . , N . W . , Washington, D.C . 2000.5

Technica l p r o c e s s improvements and p o l i c y r e s t r a i n t s on OPEC's a b i l i t y t o i n c r e a s e o i l p r i c e s a t w i l l a r e two e s s e n t i a l components o f a v i a b l e s y n t h e t i c f u e l s i n d u s t r y . One wi thou t t h e o t h e r s p e l l s f r u s t r a t i o n and f a i l u r e . The Arab o i l embargo o f 1973-74 and t h e subsequent f i v e - f o l d inc rease i n pe t ro leum p r i c e s l e d t o m u l t i b i l l i o n d o l l a r programs t o develop s y n t h e t i c f u e l s . Expec ta t ions o f a g r e a t new s y n t h e t i c f u e l s i n - dus t ry were u n f u l f i l l e d as p r i c e s 2nd c o s t s r o s e toward t h e i r equ iva len t - v a l u s - t o - o i l . Cost d i f f e r e n t i a l s i n f a v o r o f imported o i l c o n t i n u e t o inc rhase y e a r by y e a r d e s p i t e many chemical and e n g i n e e r i n g innova t ions . F o r example, e s t ima ted cos ts o f p roduc ing s h a l e o i l r o s e from $7 p e r b b l i n 1973 t o $3O/bbl t oday . When t n e OPEC c a r t e l r a i s e d o i l p r i c e s ano the r Sk$ l a s t June , it became even more impor t an t t o encourage domes t i c o i l s roduc t ion and t o deve lop energy a l t e r n a t i v e s . OPEC's new p r i c e s w i l l f o r c e t h e base p r i c e o f s y n t h e t i c f u e l s t o r i s e t o $46-50 by 1983. i i s i n g f eeds tock c o s t s i m p e r i l t h e domestic pe t rochemica l i n d u s t r y and ?ndanger chemica l e x p o r t s . This pape r d e t a i l s some o f t h e s e problems and sugges ts a number o f energy p o l i c y a c t i o n s aimed a t e s t a b l i s h m e n t o f t h e iones t i c f u e l s i n d u s t r y on a sound b a s i s .

145

Development o f a Simula ted C a t a l y s t Aging Technique

J . F . K r i z and M. Ternan

Energy Research Labol -a tor ies Canada C e n t r e f o r Minera l and Energy Technology

Department of Energy, Mines and Resources Canada Ottawa, Canada

K1A O G 1

INTRODUCTTON

Under h y d r o c r a c k i n g c o n d i t i o n s , heavy o i l s produce d e p o s i t s t h a t accumula te on t h e c a t a l y s t s u r f a c e . By p o i s o n i n g and by h i n d e r i n g a c c e s s i b i l i t y of t h e a c t i v e s i tes, t h e s e d e p o s i t s c a u s e f o u l i n g of t h e c a t a l y s t . M a t e r i a l that is so d e p o s i t e d i s e i t h e r o r i g i n a l l y p r e s e n t i n t h e f e e d , such as heavy m e t a l s and m i n e r a l s , or i s formed d u r i n g h y d r o c r a c k i n g . such as coke . Not a l l d e p o s i t s d e a c t i v a t e t h e s u r f a c e a t t h e same r a t e . I t was e s t a b l i s h e d by r e p e a t e d r e g e n e r a t i o n t h a t r a p i d f o u l i n g under t y p i c a l bi tumen hydrocracking c o n d i t i o n s i s caused p r i m a r i l y by coke f o r m a t i o n ( 1 ) . To o b t a i n a l o n g e r - l a s t i n g formu- l a t i o n , c a t a l y s t deve lopment should t h e r e f o r e f o c u s on t y p e s t h a t resist coke format ion . Such a n e f f o r t would i n v o l v e a s y s t e m a t i c approach t o c a t a l y s t p r o d u c t i o n based on i n f o r m a t i o n o b t a i n e d i n a g i n g t e s t s .

To d e t e r m i n e t h e t r u e ag ing c l i a r a c t e r i s l i c s , a c t u a l p r o c e s s i n g cond- i t i o n s m u s t be m a i n t a i n e d b e c a u s e they a f f e c t p r o d u c t f o r m a t i o n and t h e r e b y a l s o t h e p r o c e s s of d e a c t i v a t i o n . However, a s e r i o u s d i s a d v a n t a g e of a g i n g t e s t s under a c t u a l p r o c e s s i n g c o n d i t i o n s is t h a t they a r e s low and t h u s consume a g r e a t d e a l of t i m e and manpower. The t ime involved becomes c r i t i c a l i f a g i n g c h a r a c t e r i s t i c s a r e r e q u i r e d f o r a l a r g e number of c a t a l y s t s . It is t h e purpose of t h i s r e p o r t t o d e s c r i b e a t e c h n i q u e t h a t s i m u l a t e s c a t a l y s t a g i n g and pro- v i d e s p r e l i m i n a r y i n f o r m a t i o n i n a much s h o r t e r t ime.

EXPERIMENTAL EQUIPMENT AND MATERIALS

A bench-sca le f ixed-bed r e a c t i o n system was u s e d , i n which t h e

The equipment was bi tumen mixed w i t h hydrogen flowed up through t h e c a t a l y s t bed c o n t i n o u s l y . L i q u i d and vapour were s e p a r a t e d in r e c e i v e r v e s s e l s . p r e v i o u s l y d e s c r i b e d i n d e t a i l ( 2 ) bu t t h e f o l l o w i n g m o d i f i c a t i o n s were made t o accommodate t h e p a r t i c u l a r r e q u i r e m e n t s of t h e p r e s e n t s t u d y ( 3 ) :

1. Bitumen was s t o r e d i n a h e a t e d hopper from which i t c o u l d be f e d through t a p s i n t o t w o 1000-mL b u r e t t e s i n a hea ted p l a s t i c c a b i n e t . With a l i g h t p o s i t i o n e d behind t h e c a b i n e t a n d , t h e i n s i d e of t h e c a b i n e t hea ted t o about 75OC, i t w a s p o s s i b l e t o moni tor t h e feed l e v e l i n t h e b u r e t t e s . A Mil ton Roy "Cons tamct r ic" p u m p , model numbcr 'TCP 4 3 - 4 3 TJ. was used to f e e d t h e bi tumen through hea ted l i n e s i n t o tlic r e a c t o r . A p r e s s u r e gauge w a s p l a c e d a t t h e pump o u t l e t t o m o n i t o r p r e s s u r e a t t h e pump head.

TO r e d u c e t h e r e a c t o r volume, a s t a i n l e s s steel i n s e r t w a s machined t o f i t i t , r e d u c i n g t h e i n s i d e d i a m e t e r t o 1 .27 cm from 2 . 5 4 cm b u t m a i n t a i n i n g l e n g t h a t 30.5 c m .

2.

146

The c a t a l y s t s e l e c t e d f o r compara t ive r u n s was a commercial type Harshaw 0603T w i t h 3 w t Z COO and 1 2 w t % MOO s u p p o r t e d o n a l u m i n a . i n t h e form o f c y l i n d r i c a l 3.2-mm p e l l e t s . About 1 5 8 g of t h i s c a t a l y s t r e p r e s e n t e d a f u l l r e a c t o r l o a d b u t on ly about 30 g c o u l d be loaded w i t h t h e i n s e r t . The r a t e of a g i n g w a s e v a l u a t e d u s i n g Athasbasca bitumen o b t a i n e d from Grea t Canadian O i l Sands Limited a t F o r t McMurray, A l b e r t a . P r o p e r t i e s of t h e feed- s t o c k are l i s t e d i n T a b l e 1.

TABLE I

P r o p c r t ies of htliah;isca Uitumcn

S p e c i f i c g r a v i t y 1.009 (15/15OC) Benzene i n s o l u b l e s 0.72 w t % Sulphur 4 .48 w t X Carbon 86.36 w t % Ash 0.59 w t % Hydrogen 10.52 w t % Conradson Carbon Kesidue 13.3 w t Z Ni t rogen 0.45 w t %

1 5 . 5 w t Z l ' i t ch (525OC+) 51.5 w t 9 . Pentane i n s o l u h l e s

OPERATING CONDITIONS

The c o n d i t i o n s t h a t a f f e c t c a t a l y s t d e a c t i v a t i o n i n a cont inuous

The hydrocracking p r o c e s s c o n s i s t s of a number of complex f low system a r e t e m p e r a t u r e , hydrogen p r e s s u r e , hydrogen f low r a t e and l i q u i d s p a c e v e l o c i t y . r e a c t i o n s t e p s , i n i t i a l l y i n v o l v i n g v a r i o u s c o n s t i t u e n t s of bi tumen. C a t a l y t i c p r o c e s s e s on a c t i v e s u r f a c e s i tes p a r t i c i p a t e i n some o f t h e r e a c t i o n steps.

Although i t would be d i f f i c u l t , because of complexi ty of t h e react- i o n s , t o p r e d i c t a c c u r a t e l y t h c Lmpact of changes of any p r o c e s s i n g c o n d i t i o n . some o v e r a l l e f f e c t s c a n be d e r i v e d from t h e fundamenta ls o f r e a c t i o n k i n e t i c s . The r a t e of i n d i v i d u a l r e a c t i o n s t e p s v a r i e s w i t h t e m p e r a t u r e and c o n c e n t r a t i o n of r e a c t a n t s . i n g tempera ture , whereas hydrogenat ion r e a c t i o n s a c c e l e r a t e w i t h i n c r e a s i n g hydrogen p r e s s u r e . Coke [ormation depends on t h e r a t e s of c r a c k i n g and dehydro- g e n a t i o n , fol lowed by p o l y m e r i z a t i o n . T h e r e f o r e c o k e f o r m a t i o n accelerates w i t h i n c r e a s i n g tempera ture and d e c r e a s i n g hydrogen p r e s s u r e .

Cracking r e a c t i o n s a r e endothermic and a c c e l e r a t e w i t h i n c r e a s -

The c o n d i t i o n s f o r "s imula ted ag ing" were chosen by per forming a series of s c r e e n i n g e x p e r i m e n t s t o i n v e s t i g a t e t h e e f f e c t o f v a r i a t i o n s i n space v e l o c i t y and t e m p e r a t u r e . The e f f e c t of hydrogen p r e s s u r e on ca ta lys t a g i n g w a s s t u d i e d p r e v i o u s l y u s i n g a d i f f e r e n t e x p e r i m e n t a l sys tem ( 4 ) . t h e p r e s e n t s t u d y , t h e hydrogen p r e s s u r e was main ta ined c o n s t a n t a t 13.9 MPa f o r a l l t e s t s , which is w i t h i n t h e p r a c t i c a l r a n g e f o r hydrocracking . A sat- i s f a c t o r y e f f e c t c o u l d n o t have been a c h i e v e d by v a r y i n g o n l y s p a c e v e l o c i t y ; a n i n c r e a s e i n t e m p e r a t u r e w a s a l s o n e c e s s a r y t o r e d u c e a g i n g t ime s u f f i c i e n t l y . A f t e r some p r e l i m i n a r y e x p e r i m e n t a t i o n , o p t i m y d e a c t i v a t i o n c o n d i t i o n s were found t o p r e v a i l w i t h a s p a c e v e l o c i t y of 5 h

I n

and a t a t e m p e r a t u r e of 495OC.

The f o l l o w i n g series of tests under d i f f e r e n t o p e r a t i n g c o n d i t i o n s a r e documented i n t h e p r e s e n t r e p o r t :

S e r i e s 1

True o r base d e a c t i v a t i o n t a t ' s were measured a t 45OoC and a t a l i q u i d volumet- r i c s p a c e v e l o c i t y o f 1 h- based o n t h c r e a c t o r vo ume packed w i t h t h e c a t a l y s t p e l l e t s . The c o r r e s p o n d i n g feed ra te was 152 mL h as no i n s r t was p laced i n t h e r e a c t o r . The hydrogen f low rate w a s m a i n t a i n e d a t 35.6 cm's-l a t STP. T h i s test is r e f e r r e d t o a s t r u e a g i n g and was r u n c o n t i n u o u s l y f o r 56 h o u r s , and then p e r i o d i c a l l y in f i v e - to e i g h t - h o u r i n t e r v a l s , t o t a l l i n g a b o u t 200 hours i n a l l . Analyses were performed on samples of t h e l i q u i d p r o d u c t accumulated i n two t o f i v e hour's of o p e r a t i o n .

-i

147

S e r i e s 2

High s p a c e v e l o c i t y tests were performed under t h e same c o n d i t i o n s as f o r t r u e a g i n g - 1 3 . 9 m a , 450°C. and w i t h o u t i n s e r t - e x c e p t f o r a d i f f e r e n t a r rangement of space v e l o c i t i e s . C a t a l y s t a g i n g w a s c a r r i e d o t i n two 12-hour p e r i o d s d u r i n 5 YPich space v e l o c i t y w. ib m a i n t a i n e d :it 5 Ii

95 c m s a t STP. was d e t rm'ned by changing t h e s p a c e v e l o c i t y to 1 h- , t h e hydrogen f low t o 35.6 c>s-* a t STP f o r two hours and a n a l y z i n g t h c l i q u i d sample t h a t accumulated d u r i n g t h e s e two h o u r s .

S c r i c s 3

-Y , and t h e hydrogen f low a t The l e v e l of n c t i v i t y . i n i t i a l l y anf a f t e r e a c h 12-hour p e r i o d

Simulated d e a c t i v a t i o n rates were measured a t h igh tempera ture and h i g h space v e l o c i t l . of 5 h . was 181 mL.h . The hydrogen f low r a t e was main ta ined a t a b o u t 70 cm3s-' a t STP. The s e r i e s was r e f e r r e d t o as s i m u l a t e d a g i n g and was r u n c o n t i n o u s l y f o r 32 hours . The l i q u i d product t h a t accumula ted d u r i n g e a c h hour o f o p e r a t i o n was withdrawn f o r a n a l y s i s .

S e r i e s 4

A l i n k between s i m u l a t e d a g i n g and t r u e a g i n g w a s sought by a d d i t i o n a l tests i n t h e f o l l o w i n g manner. The s i m u l a t e d a g i n g c o n d i t i o n s were a p p l i e d f o r a p e r i o d of t i m e and were t h e n changed t o match t h e t r u e a g i n g c o n d i t i o n s f o r approximate ly two hours d u r i n g which two l i q u i d samples were o b t a i n e d . The r u n was then t e r m i n a t e d , thc r e a c t o r r c - lo ; idcd w i t h a frcssli c a t a l y s t , and t h e tes t was rep- e a t e d f o r a d i f f e r e n t t ime p e r i o d under s i m u l a t e d a g i n g c o n d i t i o n s . Three d i f f e r e n t time p e r i o d s - 2, 4 and 6 h o u r s , r e s p e c t i v e l y - under s i m u l a t e d a g i n g c o n d i t i o n s were examined. a g i p g t e s t w a s run a t 495OC w i t h t h e f e e d r a e of 760mL.h- , s p a c e v e l o c i t y of 5h , and t h e hydrogen f l o w r a t e a t 70 cm3s-' a t ST1'.

T h i s tes t was r u n a t 495OC and a l i q u i d v o l u m e t r i c s p a c e v e l o c i t y Thy i n s e r t w a s p laced i n t h e r e a c t o r and t h e c o r r e s p o n d i n g f e d rate

N o i n s e r t was p laced i n t h c r c a f t o r and t h e s i m u l a t e d

S e v e r a l p r o c e s s i n g c o n d i t i o n s were a p p l i e d d i f f e r e n t l y i n e a c h s e r i e s of t e s t s . For i n s t a n c e , i n S e r i e s 2. t h e s p a c e v e l o c i t y was f i v e times g r e a t e r t h a n i n S e r i e s 1, whereas t h e g a s f l o w r a t e was only a b o u t t h r e e times g r e a t e r . I n S e r i e s 1, t h e g a s f1ow:feed r a t i o w a s lower t h a n i n S e r i e s 3 , b u t h i g h e r than i n t h e s imula ted a g i n g i n S e r i e s 4 . I n a d d i t i o n , t h c 1 e n g t h : d i a m e t e r r a t i o was i n c r e a s e d i n S e r i e s 3 by p l a c i n g t h e i n s e r t i n t h e r e a c t o r , t h e r e b y i n c r e a s - ing t h e l i n e a r v e 1 o c i t y : s p a c e v e l o c i t y ra t io through t h e c a t a l y s t bed. The use of t h e i n s e r t and v a r y i n g f low reg ime r e s u l t e d from e x p e r i e n c e w i t h t h e exper imenta l system and f a c i l i t a t e d smooth o p e r a t i o n . The changes made were necessary t o prevent t h e r e a c t o r p l u g g i n g and to m a i n t a i n t e m p e r a t u r e p r o f i l e s w i t h i n t h e catalyst bed.

Thc impact 01 incrc ; i s ing t e m p e r a t u r e and s p a c e v c l o c i t y i s d i s c u s s e d i n t h e next s e c t i o n of t h i s r e p o r t . V a r i a t i o n s i n hydrogen f l o w a r e n o t con- s i d e r e d s i g n i f i c a n t f o r t h e p u r p o s c o f t h i s i n v e s t i g a t i o n , because a n e x c e s s of hydrogen was used i n a l l e x p o r i m e n t s and because hydrogen f l o w seemed t o e x h i b i t o n l y a small e f f e c t on p r o d u c t f o r m a t i o n ( 5 ) .


True Aging

The d e a c t i v a t i o n p a t t e r n is shown i n F ig .1 i n terms of a n i n c r e a s e i n t h e s p e c i f i c g r a v i t y of the l i q u i d product and an i n c r e a s e in its s u l p h u r c o n t e n t . I t can b e p r e d i c t e d by e x t r a p o l a t i o n t h a t f u r t h e r d e a c t i v a t i o n would

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be recorded beyond 200 h o u r s of o p e r a t i o n . However, i t c a n be seen t h a t de- a c t i v a t i o n is more r a p i d i n t h e e a r l y s t a g e s of t h e t es t t h a n i n t h e l a t e r s t a g e s . S i n c e d e a c t i v a t i o n d e c e l e r a t e s w i t h t i m e . t h e c u r v e s i n F i g . 3 may e v e n t u a l l y l e v e l o f f , i n d i c a t i n g a c o n s t a n t a c t i v i t y . The d e c e l e r a t i n g de- a c t i v a t i o n is i n agreement w i t h r e s u l t s of a p r e v i o u s s t u d y which a l s o showed t h a t t h i s l e v e l i n g - o f f is r e l a t i v e l y more pronounced and t a k e s p l a c e e a r l i e r w i t h i n c r e a s i n g hydrogen p r e s s u r e ( 4 ) . Whether a s t a t e o f c o n s t a n t a c t i v i t y i n f a c t e x i s t s is n o t known as t h e p a t t e r n s i n F i g . 1 c a n n o t be e x t r a p o l a t e d w i t h any p r e c i s i o n . Furthermore. t e s t s c a r r i e d o u t c o n t i n u o u s l y f o r l o n g e r than 200 h o u r s of o p e r a t i o n are n e c e s s a r y t o d e t e r m i n e d e a c t i v a t i o n p a t t e r n s t h a t a r e u n a f f e c t e d by s t a r t - u p and shut-down p r o c e d u r e s . These long-term t e s t s a r e to be performed on a s p e c i a l t e s t i n g system p r e s e n t l y under con- s t r u c t i o n .

High Space V e l o c i t y

The r e s u l t s of t h e h igh space v e l o c i t y tests i n c l u d e d a n a l y t i c a l d a t a on l i q u i d p r o d u c t samples o b t a i n e d f o r bo th h igh and b a s e s p a c e v e l o c i t i e s of t h i s s e r i e s . The r e s u l t s f o r t h e b a s e s p a c e v e l o c i t i e s s e r v e d a s a measure of d e a c t i v a t i o n a f t c r comple t ing a p e r i o d w i t l i h igh s p a c e v e l o c i t y . The de- a c t i v a t i o n i s i n d i c a t e d i n t h e l e f t - h a n d s i d e o f F i g . 1 ,

A f i v e - f o l d i n c r e a s e i n feed ra te had an i n s i g n i f i c a n t e f f e c t o n t h e r a t e of d e a c t i v a t i o n . One could r a t i o n a l i z e t h i s f i n d i n g by assuming t h a t lower c o n v e r s i o n s caused by reduced r e s i d e n c e t i m e would compensate f o r t h e g r e a t e r feed r a t e i n r e l a t i o n t o coke f o r m a t i o n . However. a more d e t a i l e d a n a l y s i s would r e v e a l t h a t t h e r e l a t i o n s h i p between t h e s p a c e v e l o c i t y and t h e r a t e of d e a c t i v a t i o n may be more complex, main ly because of t h e mult icomponent s t r u c t u r e of t h e r e a c t i o n system. The c o n c e n t r a t i o n of r e a c t i o n c o n s t i t u e n t s depends on t h e x a t e s of t h e i r format ion and d e p l e t i o n . Thus t h e to ta l y i e l d o f a component may n o t he a monotonic f u n c t i o n of t h e r e s i d e n c e t i m e . I f some coke p r e c u r s o r s react f a s t e r than o t h e r s , t h e n t h e i r p a r t i c i p a t i o n i n t o t a l cokc format ion depends on t h e s p a c e v e l o c i t y , a change i n which may c o n s e q u e n t l y be r e f l e c t e d i n both t h e q u a n t i t y and t h e q u a l i t y of t h e coke d e p o s i t s . I n a d d i t i o n t o chemical phenomena, mechanica l r e g e n e r a t i o n may t a k e p l a c e whereby p a r t i c l e s of coke are d e t a c h e d from t h e s u r f a c e by a b r a s i o n or by d i s s o l u t i o n o f t h e binding carbonaceous m a t e r i a l . Should n s imi l a r p r o c e s s t a k e p l a c e w h i l e bi tumen is used, i t would b e enhanced by i n c r e a s i n g t h e s p a c e v e l o c i t y .

The h igh space v e l o c i t y s e r i e s i n d i c a t e d t h a t t h e d e s i r e d e f f e c t could n o t be e s t a b l i s h e d by changing t h e s p a c e v e l o c i t y a t b a s e t e m p e r a t u r e . To a c c e l e r a t e a g i n g s u b s t a n t i a l l y , t h e c a t a l y s t f o u l i n g was s i m u l a t e d a t a h i g h e r r e a c t i o n t e m p e r a t u r e . The term s i m u l a t e d a g i n g is used t o emphasize t h e s e v e r e consequences of t h e change i n t e m p e r a t u r e .

Simulated Aging

The r e s u l t s of t h e s imula ted a g i n g tests a r e shown i n F i g . 2 . The a c t i v i t y dropped r a p i d l y i n t h e f i r s t p e r i o d of t h e r u n , l e v e l e d o f f , and remained approximate ly c o n s t a n t beyond 1 5 h o u r s of o p e r a t i o n .

The performance under s i m u l a t e d a g i n g r e f l e c t e d t h e e f f e c t of bo th h igh tempera ture and h igh space v c l o c i t y . The performance seemed t o he more s e n s i t i v e t o t e m p e r a t u r e , p a r t i c u l a r l y w i t l i r e s p e c t to’ the p i t c h f r a c t i o n of t h e bitumen. The i n i t i a l h igh p i t c h c o n v e r s i o n observed c o u l d r e s u l t f rom molecular weight r e d u c t i o n o r growth. Molecular growth would r e s u l t i n p r e c i p i t a t i o n of coke , most o f which would be r e t a i n e d on t h e c a t a l y s t s u r f a c e and r e a c t o r walls. The moleculor weight r c d u c t i o n by c r a c k i n g would g e n e r a t e compounds having a lower b o i l i n g p o i n t t h a n t h o s e c o n t a i n e d i n t h e p i t c h . It

149

is a p p a r e n t t h a t , whereas both of t h c l a t t e r p r o c e s s e s Iiavc taken p l a c e s imul- t a n e o u s l y , t h e growth r a t e was much s m a l l e r because t h e amount of coke formed a c c o u n t s f o r o n l y a f r a c t i o n of t h e p i t c h c o n v e r t e d . However, t h e h i g h temper- a t u r e of s i m u l a t e d a g i n g compared w i t h t r u e a g i n g s h i f t e d t h e b a l a n c e towards coke format ion a s r e f l e c t e d i n r a p i d c a t a l y s t d e a c t i v a t i o n .

L e s s e x t e n s i v e h y d r o g e n a t i o n under s i m u l a t e d a g i n g c o n d i t i o n s , i n d i c a t e d by a l o w H:C r a t i o , was presumably due t o a h i g h a r o m a t i c carbon c o n t e n t . An a n a l y s i s by F o u r i e r Transform C-13 N.M.R. i n d i c a t e d t h a t t h e u n s a t u r a t e d c a r b o n r e p r e s e n t e d a b o u t 30% of t h e t o t a l carbon i n t h e i n i t i a l p r o d u c t of s i m u l a t e d a g i n g com a r e d w i t h a b o u t 20% of t h a t o f t r u e a g i n g . The f o l l o w i n g r e a s o n s may be c o n s ' 1 c r c d to a c c o u n t f o r changes i n t h e a r o m a t i c c a r b o n c o n t e n t . More e x t e n s i v e s p l i t t i n g of s i d e c h a i n s from a r o m a t i c r l n g s caused by t h e h i g h e r t e m p e r a t u r e could liave y i e l d e d more g a s i n t h e product . A p a r t from h y d r o c r a c k i n g r e a c t i o n s , t h e h i g h e r t e m p e r a t u r e a l s o s h i f t s t h e naphthenes-aromat ics e q u i l i b r i a towards f o r m a t i o n of a r o m a t i c s (6) . I n add- i t i o n t o t h e t e m p e r a t u r e e f f e c t s , t h e h i g h s p a c e v e l o c i t y of s i m u l a t e d ag ing may have h i n d e r e d t h e e x t e n t of hydrogcnat ion hccausc of t h e s h o r t e r c o n t a c t t ime . Link between S i m u l a t e d and True Aging

S i n c e t h e r a t e of d e a c t i v a t i o n under s i m u l a t e d a g i n g c o n d i t i o n s c o u l d not e a s i l y be r e l a t e d t o t h e r a t e of d e a c t i v a t i o n under t r u e a g i n g c o n d i t i o n s , a s e r i e s of e x p e r i m e n t s was performed i n which a l i n k was sought between s i m u l a t e d and t r u e a g i n g . The purpose of t h e s e exper iments w a s t o measure t h e l e v e l of a c t i v i t y under t r u e a g i n g c o n d i t i o n s a f t e r t h e c a t a l y s t had been s u b j e c t e d to s i m u l a t c d a g i n g c o n d i t i o n s f o r a c c r t a i n p e r i o d of t ime, and t h e n t o g r a p h i c a l l y e s t i m a t e t h e t i m e i n which t h e c a t a l y s t would d e t e r i o r a t e enough t o r e a c h t h i s l e v e l of a c t i v i t y w h i l e being s u b j e c t e d t o t r u e ag ing c o n d i t i o n s .

The a c t i v i t y l e v e l s de te rmined f o r t h r e e d i f f e r e n t t i m e p e r i o d s under s i m u l a t e d a g i n g a r e marked on t h e r igh t -hand s i d e of t h e c u r v e s i n F i g . 1 . By a p p l y i n g t h e s e r e s u l t s i t was e s t i m a t e d t h a t 2 h o u r s of o p e r a t i o n under s i m u l - a t e d ag ing c o n d i t i o n s would cor respond t o about 50-70 hours under t r u e ag ing . and s i m i l a r l y , 4 h o u r s t o 100-150 h o u r s , and 6 h o u r s to 150-200 h o u r s . Hence, assuming t h a t s i m u l a t e d a g i n g is a p p r o x i m a t e l y 30 t i m e s f a s t e r t h a n t r u e a g i n g , one could e x t r a p o l a t e t h c p a t t c r n of t r u e a g i n g and s p c c u l a t e t h a t i t would l e v e l o f f i n a b o u t 400 h o u r s of o p e r a t i o n .

E s t i m a t i n g t h e l i n k hetwecn t r u e and s i m u l a t e d ag ing i n F i g . 1 i s an approximat ion o n l y . However, i t is a p p a r e n t t h a t by u s i n g s i m u l a t e d a g i n g c o n d i t i o n s , t h e d e a c t i v a t i o n was a c c e l e r a t e d s u f f i c i e n t l y t o proceed s u b s t a n t - i a l l y i n a v e r y s h o r t t i m e . I t i s expec ted t h a t by a p p l y i n g t h i s method t o a number of c a t a l y s t s , p r e l i m i n a r y i n f o r m a t i o n c a n be o b t a i n e d by comparing t h e i r d e a c t i v a t i o n p a t t e r n s such a s t h e one shown i n F i g . 2 . T h i s i n f o r m a t i o n would t h e n be a v a i l a b l e e i t h e r i n a d d i t i o n to t h e t r u e a g i n g d a t a , or f o r u s e w i t h c a t a l y s t s on which t r u e a g i n g tests a r e n o t w a r r a n t e d .

ACKNOWLEDGEMENTS

The a u t h o r s wich t o e x p r e s s t h e i r s i n c e r e a p p r e c i a t i o n t o R.W. Taylor f o r modi fy ing t h e e x p e r i m e n t a l system and t o L. G a l b r a i t h f o r t e c h n i c a l a s s i s t a n c e .

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4. Ranganathan, R . , Logie , R.B. and Denis , J.M. " C a t a l y t i c hydrocracking of Athabasca bi tumen i n a f l u i d i z e d bed r e a c t o r - e f f e c t o f p r e s s u r e o n c a t a - l y s t decay"; Energy, Mines and Resoutces , Canada, CANMET Repor t 77-40; 1976.

5. M e r r i l l , W.H., Logic, R . H . and Dcnis , J . M . "The e f f e c t of hydrogen r e c y c l e r a t e on t h e n o n - c a t a l y t i c hydrocracking of G.C.O.S. s e p a r a t e d bitumen"; Department of Energy, Mines and Resources , Mines Branch; D i v i s i o n a l Repor t FRC 72/115-PPE; 1972.

6 . Gully, A . J . and B a l l a r d , W.P. "Hydrogenat ion of c a t a l y t i c c r a c k i n g c h a r g e s tocks" ; Adv P e t Chcm R c f i n (Ncw York, I n t e r s c i e n c e . P u b l i s h e r s ) 7:240-282; 1963.

151

I (0

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Fig. 1

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. . . . . . . . . ’.-” * * *

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20 a0 bo tio 100 1x1 wo ~ G O lira 200 1 I

1IOUI~S

S p e c i f i c g r a v i t y (15/lS°C) and s u l p h u r conten t (wt X) i n t h e l i q u i d product v e r s u s t i m e on stream (h) d u r i n g t r u e ag ing . A c t i v i t y levels on right-hand s i d e r e l a t e to d i f f e r e n t t i m e p e r i o d s under s imula ted a g i n g .

0 i n d i c a t e s h igh space v e l o c i t y experiments .

- ........................ i 1 . . . . . . . . . . . . . . . . .

30 tIOUf(S 2o

10

Fig.2 S p e c i f i c g r a v i t y (15/lSoC) and s u l p h u r c o n t e n t (ut I) i n t h e l i q u i d product v e r s u s time on stream (h) d u r i n g s imulated ag ing .

152

REMOVAL O F ORGANIC SULFUR FROM COAL: THE USE OF LIQUID SULFUR DIOXIDE

Duane F. Burow and Boris M. Glavincevski

Department of Chemistry, University of Toledo, Toledo, Ohio 43606

ABSTRACT

The u t i l i t y of l iquid SO, for the removal of organic su l fur from several Eastern bituminous coals has been explored. Reactions were carried o u t in sealed f r i t t e d glass tubes a t elevated temperatures; a f t e r subsequent washing, the coal was analyzed for su l fur content. Approximately 40% of the organic su l fur could be removed in these simple exploratory experiments. portion of the coal was extracted. The extract from selected coals was characterized by thin-layer chromatography, by nmr ( ' H and 1 3 C ) and infrared spectroscopy, and by field-ionization mass spectrometry. For comparison, extractions with phenol a n d p c r e s o l , under s imilar conditions, were also examined. The resul ts of these preliminary investigations warrant fur ther research to es tabl ish optimum conditions f o r the removal of su l fur compounds from coal by treatment with l iquid SO2 and t o f a c i l i t a t e removal of residual SO2 from the coal.

In addition, comminution of most of the coals occurred and a

I NTRO DUCT1 ON

Sol vent extraction has been extensively used f o r compositional characterization of coals. 1'2 Several exis t ing coal refining p r o c e s s e ~ ~ - ~ use solvent treatment, along with pressurized hydrogen t o f a c i l i t a t e some degree of desulfurization. used t o remove organic su l fur compounds from petroleum on a commercial scale.6 The ab i l i ty of l iquid SO2 t o dis integrate various coals has been exploited to produce low-sulfur coal powders via release of pyri te .7 Utilization of l iquid SO2 treatment of coal for the removal of organic su l fur , however, has not been investigated. In th i s paper we report the resul ts of a se t of preliminary experiments in which the effectiveness of l iquid SO2 f o r removal of organic sulfur from bituminous coals PSOC 194, 267, 270, and 319 was investigated.

Treatment w i t h 1 i q u i d SO, has been successfully

EXPERIMENTAL

Procedures for the manipulation and preparation of the su l fur dioxide (Matheson, anhydrous) have been described previously. were obtained from the Coal Research Section, Pennsylvania State University. All other materials were of commercial or igin a n d used as received.

Coal samples

153

Reactions were c a r r i e d out i n b o r o s i l i c a t e glass tubes f i t t e d w i t h a mdium-poros i ty f r i t t e d glass f i l t e r t o p rov ide two chambers o f ca. 20 mL capac i ty each. l ass tub ing of- d i f f e r e n t s izes : one end pe rm i t ted i n t r o d u c t i o n o f lump f ~ . 1 cm) coal and t h e o the r end f a c i l i t a t e d easy sea l i ng under vacuum. For reac t i ons a t e leva ted temperatures, these tubes were placed i n a Par r model 4641 autoclave reac tor .

sample (G. 5 g) sealed on one end, and thoroughly evacuated. d i s t i l l a t i o n o f s u l f u r d iox ide (s. 8 mL) i n t o t h e tube a t -78"C, t h e reac t i on tube was cooled t o -196°C and sealed a t t h e o t h e r end. Upon warming to room temperature, t he tube, along w i t h o thers , was p laced i n the autoclave and t h e autoclave was evacuated. The autoclave was then charged w i t h g. 100 mL o f l i q u i d SO, t o p rov ide backing pressure f o r t he reac t i on tubes a t e leva ted temperatures, closed, and heated a t z. 4"C/min t o t h e reac t ion temperature. f o r 60 min, t h e autoclave was cooled, depressurized, and opened. reac t i on tube was then i n v e r t e d i n a c o l d bath a t -78°C t o separate the l i q u i d SO, from the coal by f i l t e r a t i o n v i a the i n t e r n a l frit. The red t o orange co lo red l i q u i d SO, s o l u t i o n was frozen, t h e tube was opened, the coal was t r a n s f e r r e d t o another conta iner , and a l l v o l a t i l e ma te r ia l s were a l lowed t o evaporate over a two hour per iod . The viscous, o i l y e x t r a c t remaining a f t e r evapora t ion o f the l i q u i d SO, was re ta ined f o r subsequent ana lys is . Buchner funnel w i t h sequent ia l a l i q u o t s o f d i s t i l l e d water, acetone, water, 3.8 M n i t r i c acid, water, and acetone u n t i l no ye l low c o l o r was observed i n each wash l i q u i d . I n separate washing experiments w i t h t h e raw coals, no ye l l ow c o l o r was observed i n the wash l i q u i d s ; subsequent s u l f u r analyses o f t he coal i nd i ca ted t h a t on l y i no rgan ic s u l f u r was removed from the raw coal by t h i s wash procedure.

For comparison o f t he r e s u l t s o f these c o a l / l i q u i d SO2 experiments, two o the r types o f experiments were a l s o run. Authent ic samples o f i r o n p y r i t e were t r e a t e d w i t h l i q u i d SO2 and l i q u i d S0,/H20 mix tu res a t 100°C us ing procedures analogous t o those descr ibed above; no apparent reac t i on occurred. and p-cresol i n s e a l x tubes a t 181" and 2OOoC, respec t i ve l y . subsequently washed i n a Buchner funnel w i t h d i s t i l l e d water and acetone, d r i e d a t l l O ° C , and analyzed f o r s u l f u r .

A l l s u l f u r analyses, a t l e a s t i n t r i p l i c a t e , were accomplished w i t h a , F isher m d e l 470 s u l f u r analyser.

on a Varian model MAT CH5 spectrometer w i t h sample temperatures from 120"- 280°C. The 'H and 1 3 C nmr spectra w e r e recorded on a JEOL FX9OQ Four ie r t rans form spectrometer f i t t e d w i t h a broadband probe and deuterium lock . Samples were i n CDCl, s o l u t i o n w i t h i n t e r n a l TMS reference. of t he e x t r a c t ( t h i n f i l m on NaCl p la tes ) were recorded on a Perkin E l m e r model 621 spectrometer. Th in - layer chromatography o f t h e e x t r a c t was c a r r i e d ou t w i t h the nmr sample so lu t i ons us ing s i l i c a gel (S i -30) p la tes . E l u t i o n was accomplished w i t h 10% acetone/hexane, 30% acetone/hexane, and absolute e thano l ; e i t h e r I, vapor o r phosphomolybdic a c i d ( 5 % w/v i n ethanol) was used t o develop t h e p la tes .

The chambers w e r e te rmina ted w i t h

I n a t y p i c a l experiment, t h e reac t i on tube was charged w i t h a coal A f t e r

A f t e r maintenance o f t he reac t i on temperature Each

The t r e a t e d coal was washed f o r a n a l y t i c a l purposes i n a

The coal was then d r i e d a t 110°C and analyzed f o r s u l f u r .

Samples (ca. 4 9) o f PSOC 267 were t r e a t e d w i t h 10 mL o f phenol The coal was

F i e l d - i o n i z a t i o n mass spectra were obtained

I n f r a r e d spectra

154


Precombustion d e s u l f u r i z a t i o n o f coal has been a t o p i c o f immense i n t e r e s t and importancelO*ll s ince i t o f f e r s an a l t e r n a t i v e t o i n s t a l l a t i o n and opera t ion o f expensive post-combustion scrubbers f o r conventional combustion systems. Although a v a r i e t y o f processes are ava i l ab le f o r precombustion removal o f inorgan ic s u l f u r compounds, p r a c t i c a l procedures f o r removal o f cova len t l y bound organic s u l f u r are r e l a t i v e l y uncommon. Thus, app l i ca t i on o f novel chemical approaches t o t h e problem would appear t o be appropr iate. Ea r l y reports12 o f t h e a b i l i t y o f l i q u i d SO2 t o d i s in teg ra te a v a r i e t y o f coals and t o e x t r a c t a p o r t i o n o f the coal a long w i t h our previous experience w i t h t h i s so l ven t suggested i n v e s t i g a t i o n o f t h e u t i l i t y o f l i q u i d SO2 as a means o f removing organic s u l f u r from coal . If successful , such a procedure would u t i l i z e a p o l l u t a n t t o remove t h e source o f t h a t p o l l u t a n t .

L i q u i d s u l f u r d iox ide i s recognized as an e x c e l l e n t so l ven t f o r aromatic, he te rocyc l i c , and a l k y l s u l f i d e s 8 which can be der ived from coa1.1,2y13 As a l i q u i d , SO2 i s n o t e a s i l y ox id i zed o r reduced and t h e adducts responsible f o r i t s so lvent p roper t i es are both thermal ly and h y d r o l y t i c a l l y l a b i l e ; 8 thus any contaminat ion o f t h e coal by res idua l s u l f u r d iox ide should be r e a d i l y e l im ina ted . Although o t h e r i n t e r a c t i o n s and reac t ions w i l l be considered i n f u t u r e repor ts , on l y reac t ions based on the m i l d Lewis a c i d c h a r a c t e r i s t i c s o f l i q u i d SO2 are o f importance here. Thus, the reac t i on o f s ign i f i cance i s summarized by Eq.1:

I I -s : .. f so2 -+ -?:SO2 ( 1 )

Products from t h i s reac t i on are usua l l y h i g h l y co lo red and h i g h l y so lub le i n l i q u i d SO,.8 Physical d i s i n t e g r a t i o n o f t h e coal by l i q u i d SO,, p robab ly v ia s i m i l a r donor-acceptor reac t ions w i t h aromat ic, amine, and oxygen conta in ing func t i ona l groups, would serve t o promote t h e reac t i on i n Eq.1. I t should be emphasized t h a t f requen t l y , t h e chemical p roper t i es o f l i q u i d SO2 can be s i g n i f i c a n t l y a l t e r e d by the presence o f cosolvents;8 o f ten , undesirable s ide reac t ions occur i n such mixed media.

The c h a r a c t e r i s t i c s o f t h e bituminous coa ls u t i l i z e d i n these p re l im ina ry i nves t i ga t i ons are given i n Table I; our s u l f u r analyses are given i n parentheses. s i g n i f i c a n t amounts o f o rgan ic s u l f u r b u t l i t t l e p y r i t i c s u l f u r which might confuse i n t e r p r e t a t i o n o f p re l im ina ry resu l t s . Our analyses o f PSOC 270 reveal t h a t , a l though the lumps i n our sample had t h e composi t ion i nd i ca ted i n Table I, t h e f i nes i n ou r sample had a s u l f u r content o f - ca. 6% w i t h the add i t i ona l s u l f u r being p y r i t i c . A l l r e s u l t s repor ted here concern the lump coal o f PSOC 270. For comparison, PSOC 194 which conta ins both p y r i t i c and organ ic s u l f u r and PSOC 319 which contains on ly p y r i t i c s u l f u r were a lso examined. Use o f t h e f r i t t e d glass reac t i on tubes f a c i l i t a t e d observat ion o f reac t ions , i s o l a t i o n o f the ex t rac ted ma te r ia l , and r a p i d examination o f several coals and reac t i on cond i t ions .

The r e s u l t s are summarized i n Table 11. A t room temperature, l i q u i d SO2 r e a d i l y wets each o f t h e coals and begins t o develop a ye l l ow c o l o r upon contac t . The ye l l ow c o l o r becomes more in tense upon s tand ing and changes t o intense orange o r red-orange a f t e r heat ing. i nd i ca tes the d i s s o l u t i o n o f donor-acceptor compounds formed between t h e so lvent and coal cons t i t uen ts ; t h e inc reas ing i n t e n s i t y accompanies

PSOC 267 and 270 were chosen since they conta in

The c o l o r

155

an increasing concentration of these adducts. Disintegration of coal lumps was observed f o r PSOC 267, 270, and 319; the extent of dis inte- gration increases progressively in the order l i s t e d . Although lumps of PSOC 194 were not dis integrated, close examination revealed appreciable swelling a n d expansion along f issures . only mechanical agi ta t ion used d u r i n g these experiments was a mild shaking of the tubes t o i n i t i a l l y mix the materials. appear t o be an obvious pattern which links maceral content t o degree of disintegration .

Inspection of Table I1 reveals t h a t s ignif icant amounts of SO, are retained on the coal (Exp. 1 ) . Effective removal of th i s residual SO2 i s essent ia l . solutions were less e f fec t ive t h a n the wash solution used in Exp. 2 . When used alone, organic solvents are more e f fec t ive than mineral acid o r base (compare Exp. 2 and 3 with Exp. 4 , 5, and 6 ) . The u t i l i t y of washing with the organic l iquids f o r removal of the yellow SO2 adducts increases in the order: hexane, benzenesCClpethano1, and acetone. A sequence of washes u s i n g acetone, water, and HN03 (Exp. 7) effect ively removes the residual SO, in most cases. Since the wash sequence was carr ied out during a f i l t e ra t ion operation contact time with the HNO, was insuff ic ient t o appreciably modify the coal material i t s e l f ; separate wash experiments using the acetone, water, HN03 sequence with the raw coal (PSOC 267 a n d 270) i t s e l f indicated t h a t no appreciable mass change occurred and t h a t no yellow materials were obtained under these wash conditions. Where pyrite i s n o t present, t h e su l fur content of the coal a f t e r t h i s wash sequence represents the organic su l fur remaining in the coal a f t e r the l iquid SO2 treatment. For PSOC 267 and 270, G. 37% and 25%, respectively, of the organic sulfur can be removed by simple treatment of the lump coal with l iquid Sop. Grinding the lump coal PSOC 270 (-60 mesh) improves the percentage organic s u l f u r removal t o g. 48%. Present resul ts with coals containing pyrite are less eas i ly interpreted since the wash sequence probably does n o t completely remove the pyri te . Furthermore, in separate experiments with authentic pyri te samples, i t was demonstrated t h a t neither l iquid SO2 nor l iqu id S02/H,0 mixtures react with pyrite. where vir tual ly a l l t h e su l fur i s pyr i t ic , the measured value of 1.6% sul fur a f t e r SO, treatment probably represents pyrite which i s not removed in the wash sequence. For PSOC 194, the measured value of 2.1% su l fur a f t e r l iquid SO2 treatment more t h a n l ikely represents both unreacted organic and pyr i t ic su l fur . the coal probably limited extraction o f the organic su l fur by the SO,.

Extraction o f powdered PSOC 267 with phenol and p-cresol resulted in 52% and 66%, respectively, remval of organic su l fur compared to 37% by l iquid SO,. The resu l t s of the extractions with phenol and p c r e s o l are similar to those reported elsewhere for other coals.

Although these resu l t s with l iquid SO, a r e n o t a s impressive as those with phenol and e-cresol , i t has been demonstrated t h a t organic Sulfur can be removed by extraction with l iqu id SO,. I t i s also important to note that optimum conditions for liquid SO2 extraction and f o r residual So2 removal have as y e t t o be established. Furthermore, these preliminary resul ts when compared with other worker's r e s u l t s l 0 f o r a variety of organic sol vents, are suf f ic ien t ly encouraging t o indicate t h a t treatment with l iquid So2 should be investigated further. Experiments t o define conditions

I t should be realized t h a t the

A t th i s stage, there does n o t

Mild heating (110°C) and washing with water or aqueous detergent

For PSOC 319,

With PSOC 194, the fa i lure of l iquid SO, to disintegrate

156

more c a r e f u l l y and t o i nves t i ga te t h e use o f appropr ia te reagents t h a t w i l l enhance t h e removal o f s u l f u r compounds f r o m coal by l i q u i d SO2 are underway.

comprises 5-10% o f the o r i g i n a l coal . i n chloroform, acetone, and concentrated HC1 ; t h i s mater ia l i s on l y p a r t i a l l y so lub le i n benzene and i s i nso lub le i n hexane. p a r t i c u l a t e matter, observed t o be i n suspension i n t h e ch lo ro fo rm and acetone so lu t i ons appears t o resemble h igh m l e c u l a r weight ma te r ia l ob ta ined by Larsen and Choudhury13 dur ing t h e i r i n v e s t i g a t i o n o f the ef fect iveness o f coal depolymerizat ion reac t ions . Although i t i s l i k e l y t h a t l i q u i d SOn under these cond i t ions merely e x t r a c t s lower mo lecu la r we igh t mater ia l a1 ready i n t h e coal , some small degree o f depolymerizat ion cou ld a1 so be occur r ing .

was c a r r i e d ou t us ing a ch lo ro fo rm s o l u t i o n f o r depos i t ion and e l u t e d w i t h Progress ive ly more p o l a r solvents; long-wavelength UV i l l u m i n a t i o n was used t o observe f luorescence i n the samples. Although no d i s t i n c t bands were developed upon e l u t i o n , three d e f i n i t e f r a c t i o n s t h a t d i f f e r by p o l a r i t y o f cons t i tuents were apparent on t h e p la tes . Several conclusions can be drawn from these TLC experiments. The complete sample contains e a s i l y ox id i zab le func t ions . A l l a l k y l f unc t i ons are at tached t o aromat ic residues. The l e s s conjugated (b lue f l uo rescen t ) f r a c t i o n i s l e s s p o l a r than the more conjugated (orange f l uo rescen t ) f r a c t i o n . A very p o l a r f r a c t i o n , n o t t ranspor ted by any e luen t used, i s even m r e h i g h l y conjugated ( r e d f luorescent ) . s t ruc tu res14 known t o e x i s t i n coa ls as we l l as w i t h the spectroscopic measurements t o be descr ibed nex t .

PSOC 267 i s i l l u s t r a t e d i n Fig. 1; t he corresponding spectrum o f t h e e x t r a c t f r o m PSOC 270 i s s i m i l a r i n several fea tures . The molecular weight d i s t r i b u t i o n i n these spectra are no t as broad nor i s t he average molecu la r weight as h igh as might have been expected.14 The presence o f very f i n e l y d i v ided p a r t i c u l a t e mat te r , which presumably has h ighe r molecular weight components t h a t are n o t v o l a t i l i z e d under t h e measurement condi t ions, cou ld be responsible f o r such observat ions. The spec t ra conta in s t r i k i n g pa t te rns i n which the mass d i f f e rence among major components i s 14 amu. These pa t te rns suggest t h e presence o f a v a r i e t y o f CH2 con ta in ing s t ruc tu res . I t i s tempt ing t o assign another p a t t e r n near m/e = 184 t o dibenzothiophene s ince i t s t rong ly resembles t h a t ob ta ined w i t h an au thent ic dibenzothiophene sample. The lack o f h igh reso lu t i on mass spec t ra l data, however, makes such an assignment pure specu la t ion a t t h i s stage.

The i n f r a r e d spectrum o f the l i q u i d SO2 e x t r a c t o f PSOC 267 (neat , t h i n f i l m ) i s shown i n Fig. 2. I t i s apparent t h a t t h e e x t r a c t con ta ins 0-H, N-H, aromat ic and a l i p h a t i c C-H groups, a v a r i e t y o f s u b s t i t u t e d aromatic s t ruc tu res , and probably ethers. There i s no evidence o f e i t h e r res idua l so2 o r o f o rgan ic s t ruc tu res con ta in ing SO2 s u b s t i t u t i o n ; no procedures o t h e r than evaporat ion o f the l i q u i d SOn under ambient cond i t ions were used t o process t h i s e x t r a c t .

The mater ia l ob ta ined by evaporat ion o f t he SO2 e x t r a c t i o n l i q u i d Fbs t o f t h i s o i l y e x t r a c t d isso lves

Very f i n e l y d i v ided

Th in - layer chromatography o f t he l i q u i d SOn e x t r a c t from PSOC 267

These observat ions are cons is ten t w i t h the types o f

The f i e l d i o n i z a t i o n mass spectrum o f t he l i q u i d SOn e x t r a c t f rom

157

Proton and l 3 C (p ro ton no ise decoupled) nmr spectra o f t he l i q u i d Q u a l i t a t i v e l y , t he pro ton SO2 e x t r a c t of PSOC 267 are shown i n Fig. 3.

spectrum resembles t h a t o f CS2 ex t rac ts o f o the r bi tuminous coals as repor ted by Retcofsky and Fr iede l ;15 ou r assignments fo l low those o f these workers. those with 2.0 <6<3.5 are assignable t o benzy l i c type protons and those w i t h 6.9 < 6 < 8.8 are assignable t o aromatic type protons; t h e s igna l a t 6 G. 4.8 i s a t t r i b u t e d t o pheno l ic and a l c o h o l i c type protons. I n teg ra ted i n t e n s i t i e s p rov ide the f o l l o w i n g d i s t r i b u t i o n o f protons: 20.9% aromat ic, 1.9% -OH, 32.1% benzy l i c , and 45.1% o the r a l k y l types. I t would appear t h a t t h e alkyl-H/aromatic-H r a t i o i s h ighe r f o r t h i s e x t r a c t than f o r CS2 e x t r a c t s o f bituminous coals w i t h s i m i l a r carbon conten t (84.6% C i n PSOC 267).

s t ruc tu res found i n t h e l i q u i d SO2 e x t r a c t o f PSOC 267 s ince assignments are r e a d i l y made by re fe rence t o the work o f F ischer e t a1.16 common w i t h bo th SRC e x t r a c t s and methylnaphthalene e x t r a c t s o f b i tuminous coal a re found i n t h e l i q u i d SO2 e x t r a c t . The sharp s igna l a t 14.1 ppm i s assigned t o te rmina l methyl groups on a l i p h a t i c s ide chains, t h a t a t 19.8 ppm t o unhindered a r y l i c methyl groups, and those a t 22.7 and 31.9 ppm t o a and 6 methylene carbons, respec t ive ly , on t e t r a l i n type s t ruc tu res . The sharp, dominant resonance a t 29.7 ppm i s r e a d i l y assigned t o methylene carbons i n Ar -CH2-CH2-Ar ' groups whereas t h e weaker s igna ls a t 32.6, 37.4, and 39.2 ppm are c h a r a c t e r i s t i c o f s i n g l e methylene carbons b r i d g i n g aromatic s t ruc tu res . The broad, low f i e l d band w i t h a h ighe r f i e l d asymmetry i s t y p i c a l o f a composite o f aromatic type carbons. I n d i v i d u a l sharp s igna ls w i t h i n t h i s band correspond t o a1 te rna te po lynuc lear aromatics t h a t are p a r t i a l l y subs t i t u ted .16 The apparent absence o f s igna ls a t even lower f i e l d s from carbon atoms w i t h o u t p ro ton subs t i t uen ts i s a t t r i b u t e d t o l ack o f NOE enhancement f o r these nuc le i .

Thus t h e l i q u i d SO2 e x t r a c t o f PSOC 267 has been shown t o conta in coal cons t i t uen ts s i m i l a r t o those ob ta ined by e x t r a c t i o n w i t h common organic solvents. Although an abundance o f a l k y l groups (methyl and e s p e c i a l l y methylene) i s found i n the carbon s t ruc tu res as i l l u s t r a t e d by the i n f ra red , 1 3 C nmr, and mass spectra, i t i s no t c l e a r whether t h i s i s representa t ive of PSOC 267 composi t ion o r i s a consequence o f t h e p roper t i es o f l i q u i d SO2. Less i s known about t h e composition o f heteroatom compounds i n t h e e x t r a c t : OH, NH and probably e t h e r groups are apparent b u t ava i l ab le spec t ra l data do n o t revea l o t h e r groups such as might be found i n organic s u l f u r compounds. s u l f u r con ta in ing organ ic s t ruc tu res and re1 i a b l e elemental analyses were precluded by 1 ack o f s u f f i c i e n t mater ia l . of t h i s e x t r a c t may e v e n t u a l l y provide clues concerning the a b i l i t y o f l i q u i d SO2 t o remove organ ic s u l f u r compounds, such e f f o r t s a re t o be ma de.

can be used t o remove organ ic type s u l f u r compounds from bituminous coals and t h a t t h e l i q u i d SO2 e x t r a c t contains coa l components s i m i l a r t o those found by e x t r a c t i o n w i t h o rgan ic solvents. The a b i l i t y o f l i q u i d SO2 t o d i s in teg ra te some coa ls and t o f r a c t u r e o thers has been confirmed. t o opt imize t h e removal o f s u l f u r compounds from coal and t o f a c i l i t a t e removal o f r es idua l SO2 f rom the coal a re under i nves t i ga t i on .

The s igna ls w i t h 6 ~ 1 . 8 are assignable t o a l k y l t ype protons,

The 1 3 C nmr spectrum revea ls f u r t h e r d e t a i l concerning the types o f

Features i n

Unfor tunate ly , t h e spectra ob ta ined a re no t s e n s i t i v e t o d i va len t

Since b e t t e r cha rac te r i za t i on

I n summary, p r e l i m i n a r y experiments have demonstrated t h a t l i q u i d SO2

Condi t ions

158

ACKNOWLEDGEMENTS

The support o f t h i s research by the Department o f Energy, under Contract No. ET-78-G-01-3316, i s g r a t e f u l l y acknowledged.

REFERENCES

1. D.W. van Krevelen, "Coal: Typology, Chemistry, Physics, and Cons t i t u t i on " ,

2. H.H. Lowry, "chemistry o f Coal U t i l i z a t i o n " , Wiley, New York, 1945, Vol. 1,

3. R.M. Baldwin, J.O. Golden, J.H. Gary, R.L. Bain, and R.J. Long, i n "Coal

E l sev ie r , Amsterdam, 1961.

Chapter 19.

Processing Technology", American I n s t i t u t e o f Chemical Engineers, New York, Vol. 2, p. 128 (1975).

4. R.P. Anderson, x., p. 130.

5. S. Morooka and C.E. Hamrin, Jr., Chem. Eng. Science, 8, 521 (1979).

6. L. F. Audr ieth and J. Kleinberg, "Non-Aqueous Solvents", Wiley, New York,

7. W.K.T. Gleim, U.S. Patent 4, 120, 664, 1978.

8. D.F. Burow, "Su l fu r Dioxide" i n The Chemistry o f Non-Aqueous Solvent

9. D.F. Burow, Inorg. Chem., 2, 573 (1972).

1953, Chapter 11.

Systems, J.J. Lagowski, Ed., Vol. 3, 1970, p. 138.

10. R.A. k y e r s , "Coal Desu l fu r i za t i on " , Marcel Dekker, New York, 1977.

11. "Coal Desu l fu r iza t ion" , T.D. Wheelock, Ed., ACS Symposium Ser ies No. 64,

12. F. Fischer and W . Gluud, Chem. Ber . , g, 147 (1916).

13. J.W. Larsen and P. Choudhury, J. Org. Chem., ~, 2856 (1979).

14. "Organic Chemistry o f Coal", J.W. Larsen, Ed., ACS Symposium Ser ies

15. H.L. Retcofsky and R.A. F r iede l i n "Spectrometry o f Fuels", Plenum,

16. P. F ischer, J.W. Stadelhofer, and M. Zander, H, 3, 345 (1978).

ACS, Washington, D.C., 1977.

No. 71, ACS, Washington, D.C., 1978.

New York, 1970, Chapter 6.

159

TABLE 1 . C h a r a c t e r i s t i c s of Bituminous Coals Treated w i t h L i q u i d SO2

COAL (PSOC NO.)

194 26 7 2 70 31 9

Type

O r i g i n

Macerals ( % / v ) V i t r i n i t e P. V i t r i n i t e

M i c r i n i t e

Fusi n i t e S. F u s i n i t e Res i n i t e

SDorini t e

Elemental Analys is (DAF) %C

%H %N %0( d i f f )

%S( t o t a l )

organic

p y r i t i c

s u l f a ti c

HVB

OH

73.3

12.6

3.3 2.2

2.3 3.6

1.8

78.23 5.56

1.72 10.97

3.51

1.26 2.19

0.07

H VA H VA

VA AL

60.9 68.1

5.3 3.2 15.6 9.1

8.7 8.6

3.4 4.6 1.5 0.8 3.2 5.0

84.63 83.34 5.58 5.55

2.53 1.74 5.18 6.59

2.08 2.77 (1 .967)a (2.682)a

2.01 2.70 0.02 0.02

0.05 0.05

LV

PA

85.5

4.2 1 .o 4 .3 4.0 0.0

0.5

86.49

4.57

1.61 0.16

7.17

0.10

7.00

0.07

aAnalyses done i n t h i s work.

160

TABLE 2. Experimental Results

Sample Exp. React i on Organic

Temp.( "C) Removed (PSOC No.) No. Wash %S S u l f u r

2 70

1 ump 1 ump

1 ump

1 ump

1 ump 1 ump 1 ump

1 ump

1 ump powder d

26 7

1 ump powder powder

d

d

194 1 ump

31 4 1 ump

150

150 150

150

100

100 150 100

100

75

75

180 200

100

100

1.5M NaOH,H20

3M HC1 ,H20

H20 .C6H6

CC14 ace tone mu1 t i p l e b

b

b mu1 t i p l e

mu1 t i p l e

b mu1 t i p l e

H20 ,acetone H20 ,acetone

b mu1 t i p l e

b mu1 t i p l e

5.756

3.802

3.522

2.682

2.602 2.316 2.005

3.089 1.992

1.397

1.241

0.9394 0.6580

2.134

1.584

25%

25%

4 8%

3 7%

52% 66%

a. Fo r l i q u i d SO2 reac t i ons , 60 min r e a c t i o n t ime was used and f o r o rgan ic so l ven t reac t i ons , 5 h r was used.

b. The m u l t i p l e wash cons is ted o f t he use o f sequen t ia l a l i q u o t s o f acetone, H20, 3.8 M HN03, H20, acetone (see t e x t ) .

c. The S02/benzene s o l u t i o n was s. 1: l ( v o l ) . d. Lump coal was crushed and ground t o -60 mesh.

161

h W N

V 0 v, LL

c m 0 U

4- 0 u u m L u x W

0 v,

-0

3 0-

N

.r

.r c

W .c u 4- 0

162

163

B ..

. . . . . .

I

I .. 6 9 PPm

FIGURE 3. Nuclear magnetic resonance spectra o f the l iquid SO2 extract o f coal PSOC 267 ( C D C 1 , ,solution, 5 mm tube). A . l 3 C nmr spectrum, proton noise decoupled, 2000 pulses 8. 'H nmr spectrum, 10 pulses.

164

Eva lua t i on o f Oxydesu l fu r i za t i on Processes f o r Coal I . The E f f e c t o f t he Ames Process on Model Organosul fur Compounds

L. W. Chang, W. F. Goure, T. G . Squi res, and T . J. Bar ton

Ames Laboratory , US DOE and Department o f Chemistry Iowa S ta te U n i v e r s i t y

Ames, Iowa 50011

I NTRODUCT I ON

One o f the main obs tac les t o the use of coa l as an a l t e r n a t e energy source i s t h a t i t con ta ins s u l f u r which c o n t r i b u t e s t o a i r p o l l u t i o n when the coa l i s burned. I t i s est imated t h a t o n l y few percent of c o a l s i n the Un i ted States w i l l be a b l e t o meet EPA SO emission s tandards ( I ) . A l t i o u g h some chemical procedures have been repo r ted t o be e f f e c t i v e f o r d e s u l f u r i z a t i o n o f coa ls , most, i f no t a l l , of the s u l - f u r t h a t i s removed i s inorganic . There i s l i t t l e i n fo rma t ion about what a c t u a l l y happens t o the o rgan ic s u l f u r when coals a r e subjected t o these process c o n d i t i o n s . A major reason f o r t h i s ignorance i s the l a c k o f i n f o r m a t i o n about t h e n a t u r e and d i s t r i b u t i o n o f t h e o rganosu l fu r f u n c t i o n a l groups i n the coal .

s u l f u r can be removed by o x i d a t i v e processes ( 2 - 6 ) . Wheelock, e t . a l . ( 2 ) repo r ted tha t under the f o l l o w i n g c o n d i t i o n s : 150OC, 200 p s i g 0 0 .2M aq. NaZC03, 1 hour; up t o 40% o f the o r g a n i c s u l f u r can be removed f rom coa j ’w i thou t significantly r e - duc ing the recovery o f combust ib le o rgan ic ma t te r .

process i n the d e s u l f u r i z a t i o n o f coa l . Instead o f us ing coa l , model o rganosu l fu r compounds were subjected t o Ames process c o n d i t i o n s . Our approach i s based on the assumption t h a t a d e f i n i t i v e knowledge o f t h e o rganosu l fu r f u n c t i o n a l groups and t h e i r d i s t r i b u t i o n i n coa l i s n o t a p r e r e q u i s i t e f o r i n v e s t i g a t i n g t h e v i a b i l i t y o f d e s u l f u r i z a t i o n processes. Thus, i t i s s u f f i c i e n t t o measure t h e p ropens i t y o f a rep resen ta t i ve spectrum o f o rganosu l fu r model m a t e r i a l s toward d e s u l f u r i z a t i o n under process cond i t i ons .

I n our study, t h e f o l l o w i n g o rganosu l fu r compounds have been subjected t o Ames process c o n d i t i o n s e i t h e r by themselves o r i n t h e presence of coal . For comparison, some model s u l f u r compounds were also run under t h e same c o n d i t i o n s except t h a t n i - trogen was used i n p lace o f oxygen. The r e s u l t s o f our s tudy a r e summarized i n Tables I and 1 1 .

2

Recent ly , severa l workers have repor ted t h a t o r g a n i c s u l f u r as w e l l a s i no rgan ic

I n t h i s paper we w ish t o r e p o r t our e v a l u a t i o n o f t h e e f f e c t i v e n e s s of t h i s Ames

m

E X P E R I MENTAL

Reactions i n t h e Absence o f Coal

The r e a c t i o n s were run e i t h e r i n an 1 l i t e r o r a 300 m l au toc lave . I n a t y p i c a l run, approx imate ly 5 g ( f o r the I l i t e r au toc lave) o r 1 gram ( f o r t h e 300 m l au to- c l a v e ) of o r g a n i c s u l f i d e was placed i n a g l a s s l i n e r o f an au toc lave . A f t e r adding 300 m l ( I 1 autoc lave) or 50 m l (300 m l au toc lave) o f 0 .2M aqueous sodium carbonate s o l u t i o n , t h e r e a c t o r was sealed, f l u s h e d w i t h N2, and heated as r a p i d l y as p o s s i b l e t o 150OC. A f t e r the r e a c t o r had e q u i l i b r a t e d a t 15OoC (10-15 minutes) , t h e system was pressur ized t o 200 p s i g w i t h oxygen and the r e a c t o r was f lushed w i t h a slow stream o f oxygen f o r 3 minutes. A c o l d t r a p was connected t o the vent tube o f the au toc lave t o c o l l e c t t h e s t a r t i n g s u l f i d e ( u s u a l l y a smal l amount) which escaped from t h e r e a c t o r d u r i n g the f l u s h i n g process ( t h e c o l l e c t e d s u l f i d e was combined w i t h t h e r e a c t i o n m i x t u r e i n t h e au toc lave a f t e r the r e a c t i o n ) . The r e a c t o r was then sealed, and temperature (I5O0C), s t i r r i n g (1500 rpm) and pressure (200 p s i g ) were maintained f o r one hour. Dur ing t h e i n i t i a l p r e s s u r i z a t i o n and t h e f i r s t 20- 30 minutes o f t h e r e a c t i o n , c o o l i n g o f the r e a c t o r w i t h water was sometimes requ i red .

p e r a t u r e and t h e conten ts werepoured i n t o a beaker. The r e a c t o r and t h e g l a s s l i n e r were washed w i t h benzene and w i t h water. The r e a c t i o n m i x t u r e and these washings were combined and e x t r a c t e d w i t h benzene, and t h e benzene e x t r a c t was d r i e d (Na SO4) and f i l t e r e d . To the r e a c t i o n s run i n the 300 m l au toc lave an i n t e r n a l standar8 was added d i r e c t l y t o the d r i e d benzene e x t r a c t and t h e s o l u t i o n was analyzed by gas chromatography ( G C ) t o de termine the q u a n t i t y o f s t a r t i n g s u l f i d e l e f t and v o l a t i l e compounds formed i n t h e r e a c t i o n . G C response f a c t o r s f o r the s u l f i d e s , p roduc ts and the standards were generated i n the form o f c a l i b r a t i o n t a b l e us ing standard so- l u t i o n s c o n t a i n i n g t h e s u l f i d e , products and the standard. For the r e a c t i o n s run i n t h e 1 l i t e r au toc lave , the volume o f d r i e d and f i l t e r e d benzene e x t r a c t was ad jus ted t o 500 rnl, and a 50 m l of a l i q u o t o f t h e benzene s o l u t i o n was withdrawn. An i n t e r - n a l standard was added t o t h e 50 m l s o l u t i o n ; t h e s o l u t i o n was analyzed w i t h GC.

s u l f i d e r e a c t i o n m i x t u r e was a c i d i f i e d w i t h concent ra ted h y d r o c h l o r i c a c i d , and washed w i t h benzene. a f f o r d a res idue wh ich NMR and I R a n a l y s i s showed t o 6e benzoic a c i d . aqueous layer was evaporated t o dryness, and the r e s i d u e was analyzed by NMR, IR, and UV spectroscopy.

React ion i n the Presence o f Coal Under Oxygen o r Under N i t r o g e n Atmosphere

A f t e r one hour, t h e heater was tu rned o f f ; t h e r e a c t o r was cooled t o room tem-

The e x t r a c t e d aqueous l a y e r of t h e benzyl phenyl s u l f i d e o r the benzyl methyl

The benzene washings were d r i e d (Na SO4) and f l a s h evaporated t o The remaining

The coal used was Iowa coal ( L o v i l i a , 200 mesh) and was d r i e d a t llO°C overn igh t . The r e a c t i o n s i n the presence o f coal were run in a 300 m l au toc lave . The r e a c t i o n procedures were t h e same as those mentioned above except t h a t E 4.0 g o f coal was added to the r e a c t i o n m i x t u r e f o r each run. A f t e r the r e a c t i o n , the r e a c t i o n m i x t u r e and washings were combined and f i l t e r e d , and the f i l t r a t e was e x t r a c t e d w i t h benzene. The coal c o l l e c t e d w i t h f i l t r a t i o n was washed w i t h acetone, then benzene several t imes. and analyzed w i t h GC u s i n g i n t e r n a l standards.

The benzene and the acetone-benzene e x t r a c t s were combined, d r i e d (Na2S04)


Tables I and I I demonstrate t h a t among the model compounds t h a t we s tud ied , o n l y

Thiophenol was converted t o phenyl d i s u l f i d e which was r e s i s t a n t th iopheno l and compounds c o n t a i n i n g a b e n z y l i c s u l f i d e l i n k a g e were o x i d i z e d t o an apprec iab le e x t e n t . t o f u r t h e r o x i d a t i o n . Benzyl phenyl s u l f i d e was o x i d i z e d and cleaved t o g i v e benzlde- hyde, benzoic a c i d and benzenesu l fon ic a c i d ; benzyl methyl s u l f i d e gave s i m i l a r r e - s u l t s . The o t h e r model compounds were u n r e a c t i v e under the Ames proces's c o n d i t i o n s e i t h e r by themselves or i n t h e presence of coa l . Even i n t h e presence o f c o a l , more than 70% of the s t a r t i n g s u l f i d e was recovered. The reduced r e c o v e r i e s o f s t a r t i n g

166

Table I . React ion Resu l ts o f Compounds Run Under the Ames Process Cond i t ions i n the Absence o f Coala

Compound Recovered Y i e l d (%) o f S t a r t i n g S u l f i d e Product

- - - - - - - Benzothiophene 87

Dibenzothiophene 96

Th iphenol 0

Phenyl s u l f i d e 98

Phenyl methyl s u l f i d e 89

- - - - - - -

Phenyl D i s u l f i d e

- - - - - - - - - - - - - -

Benzyl methyl s u l f i d e

Benzyl phenyl s u l f i d e

36

29

Benzoic a c i d

Benzaldehyde

Methanesu l fon ic a c i d

Benzoic a c i d

Ben za 1 de hyd e

Benzenesul fonic a c i d

- - - - - - - N-Octyl s u l f i d e 90

a Ames process c o n d i t i o n s : 150°C, 200 p s i g 02, 0.2M aqueous Na C O 1 hour. 2 3 ’

Table I I . React ion Resu l ts o f Compounds Run Under the Ames Processa Cond i t ion i n t h e Presence o f Coal b

Compound

Dibenzothiophene

Phenyl s u l f i d e

Benzyl methyl s u l f i d e

N-oc ty l s u l f i d e

Recovered Y i e l d (%) o f S t a r t i n g S u l f i d e

N,C 021! - - 83 76

76 74

75 13

a2 - _

a Ames process c o n d i t i o n s : 1 5 O o C , 200 p s i g 02, 0.2M aqueous Na2C0 , 1 hour. blows L o v i l i a Coal. CReact ion run under n i t r o g e n atmosJhere. React ion run under oxygen atmosphere.

167

m a t e r i a l s i n t h e presence o f coa l (see Tab le I I ) can be a t t r i b u t e d t o abso rp t i on o f the o rganosu l fu r compound by t h e microporous s t r u c t u r e of coal and the mechanical loss associated w i t h work ing up the r e a c t i o n m ix tu re . T h i s hypo thes i s was confirmed by the co r respond ing ly low recove r ies o f s t a r t i n g s u l f i d e s from r e a c t i o n s run i n the presence o f coal under n i t r o g e n atmosphere--an i n e r t atmosphere. Furthermore, no o x i d a t i o n p roduc ts were de tec ted i n the r e a c t i o n m ix tu res . C l e a r l y , o f the compounds inves t i ga ted thus f a r , o n l y benzyl s u l f i d e s and th iopheno l underwent any chemical r e a c t i o n , and ( t h e benzyl s u l f i d e s were the o n l y compounds i n which carbon s u l f u r bond c leavage occurred.

The base-cata lyzed r e a c t i o n of compounds c o n t a i n i n g a b e n z y l i c s u l f i d e l i nkage w i t h molecular oxygen has been s tud ied under a v a r i e t y o f c o n d i t i o n s . Wallace et. - a l . (7 ) r e p o r t e d t h a t benzyl phenyl s u l f i d e can be o x i d i z e d w i t h molecular oxygen i n 2M potassium t-butoxide-HMPA a t 80°C t o y i e l d benzoic ac id . t h a t the r e a c t i o n proceeded via the fo rma t ion o f an a-carbanion fo l l owed by reac t i on between the ion and oxygen.

The au tho rs proposed

@-CH -S-@ base > 0-?H-S-@ 2

> @-c-s-g 2 0

@-EH-s-Q I o-o-

The r e s u l t i n g a - p e r o x i d e anion can then decompose i n e i t h e r a s tepwise o r concerted manner t o form benzaldehyde and benzenesul fenate which a r e o x i d i z e d t o the corresponding c a r b o x y l i c and s u l f o n i c ac ids. I n t h e f i r s t s t e p of t h i s mechanism, the a-carbanion i s s t a b i l i z e d by t h e d - o r b i t a l o f t h e ad jacen t d i v a l e n t s u l f u r atom.

0-

168

We b e l i e v e t h a t a s i m i l a r mechanism i s invo lved i n the o x i d a t i o n o f benzyl phenyl s u l f i d e under Ames process c o n d i t i o n s .

O x y d e s u l f u r i z a t i o n o f the o r g a n i c s u l f i d e s i n coa l has been fo rmula ted as a two-step process (8) : I . S e l e c t i v e o x i d a t i o n o f the s u l f u r t o s u l f o x i d e s and S U I - fones w i t h the l a t t e r as the favorab le p roduc t ; and 2 . Thermal decomposi t ion o f the o x i d a t i o n produc ts , u s u a l l y under b a s i c c o n d i t i o n s .

Step 1 .

R 0 R \ '& R

R" 's - R'/s=o - R , / \ o

Step 2 .

or .A> Hydrocarbons + SOx

In t h i s fo rmula t ion , t h e r e a c t i o n i s i n i t i a t e d by o x i d a t i o n o f t h e s u l f u r and, i n f a c t , i s made p o s s i b l e by t h i s o x i d a t i o n wh ich r e s u l t s i n p o l a r i z a t i o n and weakening o f the carbon t o s u l f u r bonds ( 8 ) .

We f i n d no evidence to support t h i s hypothes is ; o x i d a t i o n o f t h e s u l f u r was de- t e c t e d o n l y in th iopheno l and i n t h e benzyl s u l f i d e s . I n the f i r s t case, o x i d a t i o n o f mercaptans t o d i s u l f i d e s i s a f a c i l e r e a c t i o n known t o occur under c o n d i t i o n s such as the Ames process. No f u r t h e r o x i d a t i o n o f the d i s u l f i d e was de tec ted . In the l a t t e r case, we submit t h a t c a r b o n - s u l f u r bond cleavage i s i n i t i a t e d by o x i d a - t i v e a t t a c k a t the benzyl p o s i t i o n ins tead o f a t s u l f u r . T h i s p o s t u l a t e i s supported by our recent d i s c o v e r y t h a t , under Ames process c o n d i t i o n s , f l u o r e n e was o x i d i z e d r a p i d l y and q u a n t i t a t i v e l y t o f luorenone w h i l e dibenzothiophene was removed unchanged from the same r e a c t i o n m i x t u r e .

a s u b s t a n t i a l impact on t h e development o f processes for t h e oxydesu l fu r c o a l . We intend t o i n v e s t i g a t e t h i s phenomenon and e x p l o r e methods f o r

Ox ida t ion o f b e n z y l i c carbon hydrogen bonds i n p re fe rence t o s u l f u r would have

r e v e r s i n g the r a t i o o f b e n z l i c t o s u l f u r o x i d a t i o n .

ACKNOWLEDGEMENTS

T h i s work was supported by t h e U . S. Department o f Energy, c o n t r a c t W-7405-Eng-82, D i v i s i o n o f F o s s i l Energy, budget code AA-10-03-03.

z a t i o n o f educing or

No.

169

REFERENCES

1 . J. A. Cava l la ro , M. T. Johnston, and A. W. Deurbrouck, " S u l f u r Reduction Po- t e n t i a l of the Coals o f t h e U n i t e d Sta tes ; A Rev is ion o f Report of I n v e s t i g a - - t i o n s 7633," R I 8118, U. S . Bureau o f Mines, 1976.

2 . T . D . Wheelock, R . T . Greer, R . Markuszewski, and R. W. F i s h e r , "Advanced Development of F i n e Coal D e s u l f u r i z a t i o n and Recovery Technology," Annual Technical Progress Report, Oct. 1977 - Sept. 1978. IS-4688 prepared f o r DOE-Fossil Energy, by Ames Labora tory , Iowa S t a t e U n i v e r s i t y , Arnes, Iowa. A p r i l , 1979.

R . A. Meyers, "Coal D e s u l f u r i z a t i o n , " Mercel Dekker, I n c . , New York (1977). 3.

4. P. S . Gangul i , G. C. Hus, G. R. Gavalas, and 5. H. Kal fayan, Am. Chem. SOC., D i v . Fuel Chem., P r e p r i n t , 3, 118 (1976) .

5. S . S . Sareen, R. A. G i b e r t i , P. F. I rm inger , and L . J . P e t r o v i c , AICHE Symp. - Ser., 2, 183 (1977) .

6.

7. T. J. Wallace, H . Pobiner , F. A. Baron, and A. Schr iesheim, J. Org. Chem., 0, S . Friedman and R . P . Warz insk i , J. Eng. f o r Power, 2, 361 (1977).

3147 (1965).

A. A t t a r and W. H. Corcoran, Ind. Eng. Chem., Prod. Res. Dev., 1, I D 2 (1978). 8.

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HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY SEPARATION OF OLEFIN, SATURATE, AND AROMATIC HYDROCARBONS I N HIGH-BOILING

DISTILLATES AND RESIDUES OF SHALE O I L

John F . ElcKay and D . R . Latham

Laramie Energy Technology C e n t e r , DOE, P . 0 . Box 3395, Laramie , Wyo. 82071

ABSTFXT

A h igh-per formance l i q u i d chromatography (HPLC) method has been deve loped f o r t h e s e p a r a t i o n of o l e f i n , s a t u r a t e , and a r o m a t i c hydrocarbons found i n h i g h - b o i l i n g d i s - t i l l a t e s and r e s i d u e s of s h a l e o i l and i n whole s h a l e o i l s . The dual-column chromatographic system uses s i l i c a g e l i n one column and s i l i c a g e l c o a t e d w i t h s i l v e r n i t r a t e i n a second column. Sepa ra t ed f r a c t i o n s a r e ana lyzed by i n f r a r e d and carbon-13 nuc lea r magnet ic resonance spec t romet ry t o demons t r a t e t h e v a l i d i t y o f t h e s e p a r a t i o n . The t ime r e q u i r e d f o r a s e p a r a t i o n i s a b o u t two hour s . The s e p a r a t i o n s a r e r e p r o d u c i b l e , and r ecove ry of m a t e r i a l a f t e r s e p a r a t i o n i s g e n e r a l l y b e t t e r t han 90 p e r c e n t . The o l e f i n , s a t u r a t e , and a r o m a t i c f r a c t i o n s ob ta ined from a s e p a r a t i o n a r e s u i t a b l e f o r f u r t h e r a n a l y s i s .

INTRODUCTION

A s i n c r e a s e d amounts o f s h a l e o i l a r e p rocessed t o g e t h e r w i t h p e t r o l e u m , i t becomes i n c r e a s i n g l y impor t an t t o have methods a v a i l a b l e f o r t h e a n a l y s e s of s h a l e o i l . A fundamenta l d i f f e r e n c e i n t h e composi t ion o f s h a l e o i l and pe t ro leum i s t h a t s h a l e o i l c o n t a i n s t h r e e major hydrocarbon compound t y p e s - - o l e f i n s , s a t u r a t e s , and a romat i c s - - w h i l e pe t ro leum c o n t a i n s o n l y s a t u r a t e s and a r o m a t i c s . O l e f i n s , because t h e y a r e hydrogen d e f i c i e n t and u n s t a b l e , cause problems i n t h e p r o c e s s i n g o f s h a l e o i l t h a t a r e n o t encountered i n t h e p r o c e s s i n g o f pe t ro l eum. They a r e a l s o of s p e c i a l i n t e r e s t because t h e amounts, and pe rhaps k i n d s , o f o l e f i n s i n s h a l e o i l a r e r e l a t e d t o t h e r e t o r t i n g c o n d i t i o n s t h a t p roduce t h e s h a l e o i l . Techniques f o r t h e a n a l y s i s of s a t u r a t e s and a romat i c s i n pe t ro leum a r e w e l l known; however, methods f o r de t e rmin ing o l e f i n , s a t u r a t e , and a romat i c hydrocarbons i n t h e heavy d i s t i l l a t e and r e s i d u e p o r - t i o n s of s h a l e o i l a r e needed.

Many t echn iques f o r t h e d e t e r m i n a t i o n of o l e f i n s , s a t u r a t e s , and a r o m a t i c s have been r e p o r t e d i n t h e l i t e r a t u r e (1-11) . The methods u s u a l l y invo lve l i q u i d chromatography w i t h s i l i c a g e l (3, 4 , 10) o r l i q u i d chromatography combined w i t h chemica l r e a c t i o n s ( 1 , 11, 1 2 ) . The methods work w e l l i n t h e a n a l y t i c a l a p p l i c a t i o n s f o r which t h e y were des igned- -p r imar i ly t h e d e t e r m i n a t i o n o f hydrocarbon types i n l i g h t d i s t i l l a t e s . D i f f i c u l t i e s , such a s incompleLe s e p a r a t i o n o f compound t y p e s , o f t e n a r i s e when t h e methods a r e a p p l i e d t o t h e a n a l y s e s of h e a v i e r hydrocarbon f r a c t i o n s . The purpose of t h e work d i scussed i n t h i s paper i s t o ex tend t h e a n a l y s i s of o l e f i n , s a t u r a t e , and a romat i c hydrocarbons t o t h e h i g h - b o i l i n g d i s t i l l a t e and r e s i d u e f r a c t i o n s of s h a l e o i l . Seve ra l requi rements were e s t a b l i s h e d f o r a s a t i s f a c t o r y a n a l y t i c a l method: 1 ) t h e de t e rmina t ion should be f a s t ; 2 ) t h e r e s u l t s shou ld be r e p r o d u c i b l e ; 3) t h e sam- p l e s should have minimum exposure t o a i r , l i g h t , and h e a t ; and 4 ) t h e s e p a r a t e d hydrocarbon Lypes should be chemica l ly u n a l t e r e d and t h e r e E o r e s u i t a b l e f o r f u r t h e r ann ly - s e s .

T h i s paper d e s c r i h e s a dun 1-column h igh-per formance l i q u i d chromatogcaphy (tipLC) method f o r t he s e p a r a t i o n and d e t e r m i n a t i o n o f o l e f i n , s a t u r a t e , and a r o m a t i c hydroca rbons i n h i g h - b o i l i n g d i s t i l l a t e and r e s i d u e f r a c t i o n s of sli:ile o i l . The method can a l s o he used t o separaLe hydrocnrbon t y p e s i n whole s h a l e o i l s . The dual-column t echn ique uses s i l i c a ge l t o s e p a r a t e a r o m a t i c hydrocarbons from o l e f i n and s a t u r a t e hydrocarbons and s i l i c a g e t coa ted w i t h s i l v e r n i t r a t e t o s e p a r a t e o l e f i n from s a t u -

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r a t e hydrocarbons . Cyclohexane i s used a s s o l v e n t f o r t h e hydrocarbon samples . The t i m e r e q u i r e d f o r a s e p a r a t i o n i s abou t two hour s .

EXPERIMENTAL

Appara tus

S h a l e o i l d i s t i l l a t e s and r e s i d u e s were o b t a i n e d u s i n g a n ASCO (Ar thu r F. Smith Co. ) 2 - i n . Rota-Film (wiped-wal l ) s t i l l . Ac ids , b a s e s , and n e u t r a l n i t r o g e n compounds were removed from t h e samples u s i n g a g r a v i t y - f l o w g l a s s column ( 2 . 5 cm x 90 cm) packed i n t h r e e s e c t i o n s w i t h a n i o n r e s i n , c a t i o n r e s i n , and f e r r i c c h l o r i d e / A t t a p u l g u s c l a y . The column was wet-packed u s i n g cyc lohexane .

Hydrocarbon s e p a r a t i o n s were made u s i n g a dual-column sys tem i n a Waters A s s o c i a t e s AGC/CPC-202 l i q u i d chromatograph equipped w i t h r e f r a c t i v e index and u l t r a v i o l e t de- t e c t i o n u n i t s . The f i r s t column c o n t a i n e d s i l i c a g e l , and t h e second column con ta ined s i l i c a g e l coa ted w i t h s i l v e r n i t r a t e . Both columns were s t a i n l e s s s t e e l (7 .8 mm i . d . x 6 1 cm) and were s u p p l i e d w i t h 5-micron f r i t t e d end f i t t i n g s . I n f r a r e d s p e c t r a were reco rded on a Perk in-Elmer model 621 s p e c t r o p h o t o m e t e r , and carbon-13 NMR s p e c t r a were o b t a i n e d u s i n g a V a r i a n CFT-20 s p e c t r o m e t e r .

M a t e r i a l s

Arnberlyst IRA-904 an ion-exchange r e s i n (Rohm and Haas) was used f o r removal of a c i d s , and Amberlyst A-15 ca t ion -exchange r e s i n (Rohm and Haas) was used f o r removal o f b a s e s . A t t apu lgus c l a y , 50 /80 mesh (Engelhard Mine ra l s and Chemical Corp . ) coa ted w i t h f e r r i c c h l o r i d e (Baker and Adamson) removed n e u t r a l n i t r o g e n compounds from t h e samples . The p r e p a r a t i o n of r e s i n s and f e r r i c c h l o r i d e / A t t a p u l g u s c l a y has been d e s c r i b e d (13 ) .

S i l i c a g e l 60G (E. Merck) f o r t h i n - l a y e r chromatography was used a s r ece ived t o s epa - r a t e a romat i c s from s a t u r a t e s and o l e f i n s . The same s i l i c a g e l c o a t e d w i t h 20 p e r c e n t s i l v e r n i t r a t e (Baker and Adamson) s e p a r a t e d s a t u r a t e s from o l e f i n s . The s i l v e r n i t r a t e - c o a t e d g e l was p repa red by d i s s o l v i n g t h e s i l v e r n i t r a t e i n w a t e r , mixing t h e s o l u t i o n w i t h s i l i c a g e l , and removing t h e w a t e r on a r o t a r y e v a p o r a t o r . The g e l was a c t i v a t e d a t 1 l O O C f o r 1 2 h o u r s . Cyclohexane, benzene , and methanol were commercial HPLC-grade s o l v e n t s f rom v a r i o u s s u p p l i e r s and were used a s r ece ived .

S h a l e O i l Samples

The s h a l e o i l s used i n t h i s s t u d y were produced by i n s i t u and aboveground r e t o r t i n g p r o c e s s e s (14 ) . The S i t e 9 o i l was o b t a i n e d from t h e Laramie Energy Technology Cen te r (LETC) i n s i t u expe r imen t n e a r Rock S p r i n g s , Wyo. The 150- ton r e t o r t o i l i s from t h e LETC s imula t ed i n s i t u 150- ton r e t o r t n e a r Laramie , Wyo. Paraho and S u p e r i o r o i l s a r e from aboveground r e t o r t s l o c a t e d a t Anv i l P o i n t s , C o l o . , C leve land , Ohio , respec- t i v e l y .

D i s t i l l a t i o n of S h a l e O i l s

Crude s h a l e o i l s t h a t had been c e n t r i f u g e d t o remove p a r t i c u l a t e m a t t e r and water were d i s t i l l e d u s i n g a wiped-wal l s t i l l . The s t i l l was o p e r a t e d a t 20 t o r r t o remove o i l b o i l i n g below 210'C ( c o r r e c t e d t o a tmosphe r i c p r e s s u r e ) . D i s t i l l a t e f r a c t i o n s b o i l i n g from c o r r e c t e d t e m p e r a t u r e s of 210 t o 370°C and 370 t o 535'C were o b t a i n e d a t lower p r e s s u r e s and i n c r e a s e d t empera tu res . The r e s i d u e was recovered m a t e r i a l t h a t d id n o t d i s t i l l aL 25OOC ( c o r r e c t e d ) and 0 . 2 t o r r . The r e s i d u e was a c t u a l l y exposed t o a t empera tu re o f 250'C f o r o n l y a tew seconds s o t h a t t he rma l d e g r a d a t i o n was minimal.

172

P r e p a r a t i o n o f Hydrocarbon Samples

A sample ( 1 g ) of d i s t i l l a t e , r e s i d u e , o r whole s h a l e o i l was d i s s o l v e d i n cyc lohexane (100 ml) and passed th rough a g r a v i t y - f l o w g l a s s column c o n t a i n i n g s u c c e s s i v e beds o f an ion ( 8 0 g ) and c a t i o n ( 8 0 g ) r e s i n s and f e r r i c c h l o r i d e / A t t a p u l g u s c l a y (100 9). The column was washed w i t h cyc lohexane (500 ml) t o r ecove r t h e hydrocarbons . The cyc lohexane was removed from t h e hydrocarbons u s i n g a r o t a r y e v a p o r a t o r .

P r e p a r a t i o n and Assembly of HPLC Columns

A r e s e r v o i r column was a t t a c h e d t o an empty HPLC column, and b o t h columns were f i l l e d wi th d r y s i l i c a g e l o r s i l v e r n i t r a t e / s i l i c a g e l ( abou t 20 9 ) . Cyclohexane was then pumped through t h e sys tem t o w e t and compress t h e pack ing m a t e r i a l i n t o t h e HPLC column. The r e s e r v o i r column was t h e n de tached . Columns packed u s i n g t h i s t echn ique con ta ined 15 g o f g e l we t t ed w i t h Cyclohexane , and t h e g e l was un i fo rmly d i s t r i b u t e d i n t h e column. A f t e r a s e p a r a t i o n , t h e s i l v e r n i t r a t e l s i l i c a g e l column cou ld be r e a c t i v a t e d by washing w i t h cyc lohexane (100 m l ) . The s i l i c a g e l column was n o t r e u s a b l e . F i g u r e 1 shows t h e dual-column as sembly , chromatograph , and d e t e c t o r s .

Column C a l i b r a t i o n

Dur ing r o u t i n e a n a l y s e s , t h e c u t p o i n t f o r t h e s e p a r a t i o n o f s a t u r a t e s and o l e f i n s from a romat i c s on t h e s i l i c a column was made a c c o r d i n g t o e l u t i o n volume. The p r o p e r e l u t i o n volume was e s t a b l i s h e d p r i o r t o t h e s e p a r a t i o n s by p a s s i n g samples th rough t h e s i l i c a g e l column and m o n i t o r i n g t h e s e p a r a t i o n w i t h u l t r a v i o l e t and r e f r a c t i v e index d e t e c t o r s . Once t h e p r o p e r e l u t i o n volume had been e s t a b l i s h e d , t h e d e t e c t o r s were removed from t h e chromatographic sys tem.

S e p a r a t i o n Procedure

A r o u t i n e s e p a r a t i o n was made i n t h e f o l l o w i n g manner. A s h a l e o i l hydrocarbon sample (200 mg), d i s s o l v e d i n cyc lohexane (1 ml), was p l a c e d on t h e s i l i c a g e l column, and cyc lohexane was pumped th rough t h e two columns f o r 40 minutes a t a r a t e o f 1 mlfmin and a p r e s s u r e o f a b o u t 350 p s i g . Under t h e s e e l u t i o n c o n d i t i o n s a r o m a t i c s a r e re- t a i n e d on column 1, w h i l e s a t u r a t e s and o l e f i n s p a s s th rough t o column 2 . Valves between t h e columns and a second s o l v e n t r e s e r v o i r a l lowed con t inued pumping cyc lo - hexane through t h e second column where o l e f i n s and s a t u r a t e s were s e p a r a t e d . Sa tu - r a t e s were e l u t e d w i t h cyc lohexane from t h e s i l v e r n i t r a t e column w i t h con t inued pumping f o r 30 minutes a t 1 ml lmin . O l e f i n s were t h e n e l u t e d from t h e s i l v e r n i t r a t e column by pumping benzene lcyc lohexane , 2 0 / 8 0 p e r c e n t , th rough t h e column f o r 30 min- u t e s a t 1 mllmin. S imul t aneous ly , benzene/methanol , 40 /60 p e r c e n t , was pumped through t h e f i r s t column f o r 60 minu tes t o e l u t e a r o m a t i c s . The t o t a l s e p a r a t i o n t i m e was a b o u t 2 hour s .

DISCUSSION

I d e n t i f i c a t i o n o f Hydrocarbon Types

I n f r a r e d and carbon-13 NEIR s p e c t r o m e t r y were used t o a n a l y z e t h e hydrocarbon f r a c t i o n s p repa red by t h e dual-column ch romatograph ic sys t em. The a n a l y s e s demons t r a t e t h e v a l i d i t y of t h e s e p a r a t i o n s . Both s p e c t r o m e t r i c t echn iques have s p e c i a l a n a l y t i c a l advan tages and l i m i t a t i o i l s ; when used t o g e t h e r t h e y p e r m i t a s a t i s f a c t o r y a n a l y s i s of t h e hydrocarbon f r a c t i o n s .

The f r a c t i o n s of s a t u r a t e s , o l e f i n s , and a r o m a t i c s were f i r s t examined u s i n g i n f r a r e d s p e c t r o m e t r y . Two a b s o r p t i o n b a n d s - r e r e used t o a n a l y z e t h e f r a c t i o n s : 1) t h e mono- o l e f i n s t r e t c h i n g band a t 1630 cm to - i d e n t i f y o l e f i n s and 2 ) t h e a r o m a t i c r i n g carbon-carbon s t r e t c h i n g band a t 1600 cm t o i d e n t i f y a r o m a t i c s . S a t u r a t e s have no a b s o r p t i o n bands i n t h e i n f r a r e d t h a t d i s t i n g u i s h t h e m from o t h e r hydrocarbon t y p e s .

An example o f t h e u s e of i n f r a r e d s p e c t r o m e t r y i n a n a l y z i n g hydrocarbon f r a c t i o n s p r e s e n t e d i n F igu re 2 , which shows t h e p a r t i a l i n f r a r e d spec t rum of t h e t o t a l hydroca rbons from a 21O-37O0C d i s t i l l a t e t o g e t h e r w i t h t h e p a r t i a l i n f r a r e d s p e c t r a of s e p a r a t e d f r a c t i o n s . I n F i g u r e Za, b o t h mono-olef in and a r o m a t i c a b s o r p t i o n may be seen i n t h e spec t rum of t h e t o t a l hydroca rbons . F i g u r e s 2b , Z C , and 2d show t h a t a s e p a r a t i o n of a r o m a t i c s , o l e f i n s , _a d s a t u r a t e s has been ach ieved . Only t r a c e amounts o f a romat i c s a b s o r b i n g a t 1600 cm can be obse rved i n t h e spec t rum o f t h e s a t u r a t e s ( F i g . 2d) and o l e f i n s ( F i g . 2 c ) . O l e f i n s a r e obse rved i n on ly t h e o l e f i n f r a c t i o n (F ig . 2 c ) .

I n g e n e r a l , i n f r a r e d s p e c t r o m e t r y i s a v e r y u s e f u l method f o r a n a l y z i n g t h e hydrocar - bon f r a c t i o n s because i t i s f a s t and s e n s i t i v e . I t d o e s , however, have l i m i t a t i o n s . F i r s t , i n a mix tu re o f hydrocarbon t y p e s , satu! tes canno t he d i s t i n g u i s h e d from o l e f i n s o r a r o m a t i c s , Second, u se of t h e 1630 cm band does no t a l l o w t h e d e t e c t i o n o f con juga ted d i - and t r i - o l e f i n s . T h i r d , i n f r a r e d a n a l y s e s of complex mix tu res of o l e f i n s cannot be q u a n t i t a t i v e because t h e molar a b s o r p t i v i t i e s o f i n d i v i d u a l o l e f i n i c compounds a r e q u i t e v a r i a b l e . The c o r r e c t v a l u e of molar a b s o r p t i v i t y t o u s e i n an i n f r a r e d c a l c u l a t i o n i n v o l v i n g B e e r ' s l a w i s n o t known.

Carbon-13 NNR s p e c t r o m e t r y was used t o complement i n f r a r e d s p e c t r o m e t r y i n t h e ana ly - s e s o f s e p a r a t e d f r a c t i o n s . These d a t a conf i rmed i n f r a r e d d a t a and provided add i - t i o n a l i n fo rma t ion a b o u t t he hydrocarbon t y p e s , e s p e c i a l l y t h e o l e f i n s .

F i g u r e 3 shows carbon-13 NMR s p e c t r a o f s a t u r a t e s ( F i g . 3 a ) , o l e f i n s ( F i g . 3 b ) , and a romat i c s ( F i g . 3c ) from a 370-535OC hydrocarbon c o n c e n t r a t e . For q u a n t i t a t i v e d e t e r - mina t ion of o l e f i n s , t h e s p e c t r a l r e g i o n o f i n t e r e s t i s between 110 and 140 ppm r e l a - t i v e t o t e t r a m e t h y l s i l a n e (TMS). S a t u r a t e s show no carbon-13 a b s o r p t i o n i n t h i s r e g i o n . O l e f i n s show a b s o r p t i o n bands between 114 and 138 ppm (15 , 1 6 ) ; t h e p o s i t i o n o f a b s o r p t i o n is dependent upon t h e t y p e o f o l e f i n . Alpha o l e f i n hands a r e observed a t 11'. and 138 ppm, w h i l e i n t e r n a l o l e f i n s have a b s o r p t i o n bands between 114 and 138 ppm. Aromatic ca rbons a r e s e e n a s a b r o a d , symmet r i ca l a b s o r p t i o n envelope c e n t e r e d a t abou t 128 ppm. F i g u r e 3a shows t h a t , i n t h i s p a r t i c u l a r s e p a r a t i o n run , t h e s a t u - r a t e s c o n t a i n 1 o r 2 p e r c e n t o f a n o t h e r hydrocarbon t y p e , p robab ly a r o m a t i c s . O l e f i n s a r e observed o n l y i n t h e o l e f i n f r a c t i o n , n o t i n t h e s a t u r a t e o r a r o m a t i c f r a c t i o n s . T race amounts of a r o m a t i c s appea r t o b e i n t h e o l e f i n f r a c t i o n , c o n f i r m i n g t h e i n f r a - r ed d a t a .

Carbon-13 NHR is u s e f u l n o t o n l y because it a i d s i n j u d g i n g t h e q u a l i t y o f s e p a r a t i o n t h a t has been ach ieved b u t a l s o because it p r o v i d e s d e t a i l e d i n f o r m a t i o n abou t molecu- l a r s t r u c t u r e . For example , i n an o l e f i n m i x t u r e , t h e number of doub le bonds of an ave rage o l e f i n molecule can be c a l c u l a t e d i f t h e a v e r a g e molecu la r weight of t h e o l e f i n mix tu re i s known and i f t h e r a t i o of a l i p h a t i c / o l e f i n i c carbons can be measured by carbon-13 NNR. However, carbon-13 NMR a l s o has l i m i t a t i o n s . F i r s t , i n a mixture o f hydrocarbons , s a t u r a t e s canno t be d i s L i n g u i s h e d from o l e f i n s and a r o m a t i c s . Sec- ond , o l e f i n s may n o t be o b s e r v a b l e i n a c o n c e n t r a t e o f s a t u r a t e s o r a r o m a t i c s i f t h e amount of o l e f i n s is lower t h a n abou t 3 o r 4 p e r c e n t . T h i r d , w i t h carbon-13 s p e c t r o - met ry a l o n e , i t may be d i f f i c u l t t o d i s t i n g u i s h between i n t e r n a l o l e f i n s and aroina- t i c s ; i n such a c a s e u l t r a v i o l e t a n a l y s e s a r e u s e f u l .

I n f r a r e d and NHR a n a l y s e s e s t a b l i s h e d t h a t s a t u r a t e , o l e f i n , and a r o m a t i c compound c l a s s e s were s e p a r a t e d i n t o t h r e e d i s c r e t e f r a c t i o n s by t h e dua l -co lumn sys tem. Th i s a l lowed t h e q u a n t i t a t i v e d e t e r m i n a t i o n o f each c l a s s t o h ) c iiiilcle g r a v i m e t r i c a l l y .

S e p a r a t i o n R e s u l t s

a . Hydrocarbons i n High-Ro i l ing D i s t i l l a t e s and Res idues . - The dual-column method was used t o s e p a r a t e hydrocarbons from t h r e e d i f f e r e n t b o i l i n g r anges of f o u r s h a l e o i l s . The r e s u l t s of t h e s e p a r a t i o n s a r e shown i n T a b l e 1. A l l d a t a were ob ta ined g r a v i m e t r i c a l l y . D u p l i c a t e d e t e r m i n a t i o n s were made t o show t h e r e p r o d u c i b i l i t y t h a t

174

can b e expec ted w i t h t h e s e p a r a t i o n t e c h n i q u e . I n most c a s e s t h e r e p r o d u c i b i l i t y i s s i m i l a r t o t h a t expe r i enced i n t h e s i l i c a g e l s e p a r a t i o n o f s a t u r a t e and a r o m a t i c hydrocarbons i n pe t ro leum. The c a u s e of t h e poor r e p r o d u c i b i l i t y e x p e r i e n c e d i n some runs i s n o t known. The r ecove ry o f s e p a r a t e d hydrocar,bon types was g e n e r a l l y b e t t e r t han 90 p e r c e n t .

From a c h a r a c t e r i z a t i o n p o i n t of v iew, t h e d a t a i n Tab le 1 show some i n t e r e s t i n g t r e n d s . F i r s t , d i s t i - l l a t e s and r e s i d u e s from t h e S i t e 9 i n s i t u o i l and t h e 150- ton r e t o r t o i l c o n t a i n s m a l l e r amounts of o l e f i n s and l a r g e r amounts o f s a t u r a t e s t h a n t h e o t h e r o i l s . Thus , it. a p p e a r s ' t h a t t h e S i t e 9 and 150- ton r e t o r t o i l s were produced under m i l d e r r e t o r t i n g c o n d i t i o n s t h a n t h e Paraho and S u p e r i o r o i l s . Second, t h e d i s t r i b u t i o n s o f hydrocarbon compound t y p e s a s r e l a t e d t o d i s t i l l a t i o n t e m p e r a t u r e c a n be seen . For example, i n t h e S i t e 9 o i l , t h e a r o m a t i c s i n c r e a s e a s t h e d i s t i l l a t i o n t empera tu re i n c r e a s e s . The o l e f i n s a r e c o n s t a n t i n t h e d i s t i l l a t e s and i n c r e a s e i n t h e r e s i d u e . These changes a r e a t t h e expense of s a t u r a t e s which d e c r e a s e a s t h e d i s t i l l a t i o n t empera tu re i n c r e a s e s .

b . Hydrocarbons from Whole S h a l e O i l s . - The dual-column method p e r m i t t e d t h e f a s t d e t e r m i n a t i o n o f s a t u r a t e s , o l e f i n s , and a r o m a t i c s i n whole s h a l e o i l s . The r e s u l t s of t h e s e p a r a t i o n s a r e shown i n Tab le 2 . Both r e p r o d u c i b i l i t y and r e c o v e r y v a l u e s a r e s i m i l a r t o those s e e n i n t h e s e p a r a t i o n of d i s t i l l a t e s and r e s i d u e s . Unknown amounts of l i g h t hydrocarbons from t h e whole s h a l e o i l s were l o s t d u r i n g t h e so lven t - r emova l p rocedure .

SUMMARY AND CONCLUSIONS

An HPLC method has been developed f o r t h e s e p a r a t i o n o f s a t u r a t e s , o l e f i n s , and a r o - ma t i c s i n h i g h - b o i l i n g d i s t i l l a t e s and r e s i d u e s of s h a l e o i l and i n whole s h a l e o i l s . The dual-column chromatographic sys tem uses s i l i c a g e l i n one column and s i l i c a g e l coa ted w i t h 20 p e r c e n t s i l v e r n i t r a t e i n a second column. The t i m e r e q u i r e d f o r a s e p a r a t i o n is abou t two hour s . The s e p a r a t i o n s a r e r e p r o d u c i b l e ; r ecove ry o f i i i a t e r i a l a f t e r s e p a r a t i o n i s g e n e r a l l y b e t t e r t h a n 90 p e r c e n t . The s a t u r a t e , o l e f i n , and a romat i c f r a c t i o n s o b t a i n e d from a s e p a r a t i o n a r e s u i t a b l e f o r f u r t h e r a n a l y s e s .

ACKNOWLEDGMENTS

The a u t h o r s thank Mr. Shawn C . Tap ley f o r t h e chromatography work, D r . Dan ie l A . N e t z e l f o r t he carbon-13 NMR a n a l y s e s , and Dr. Shuang-Ling Chong f o r h e l p f u l d i s c u s - s i o n s .

DISCLAIMER

Mention of s p e c i f i c models o r b rand names o f equipment i s made f o r i n f o r m a t i o n only and does n o t imply endorsement by t h e Department o f Energy .

LITERATURE CITED

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4 . E . L . S a i e r , A . Poze f sky , and N . D . Coggesha l l , Anal. Chem., 26, 1258 (L'354).

5 . t l . 6. Jensen , J. R . Horand i , and G . L . Cook, P r e p r i n t s , ACS Div. P e t r o l . Chem., 13 ( 2 1 , 698 (1968) . -

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7 .

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1 3 .

14 .

15 .

16 .

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R . E . Pou l son , H . B . J e n s e n , J . J . D u v a l l , F. L. H a r r i s , and J . R . Morandi, P roc . 1 8 t h Annual TSA A n a l y s i s I n s t r u m e n t a t i o n Symposium, San F r a n c i s c o , C a l i f . , May 1972, p . 193.

J . R . Morandi , D . G . Earnshaw, and H . B . J e n s e n , A b s t r a c t s , P i t t s b u r g h Conference on A n a l y t i c a l Chemis t ry and Appl ied Spec t roscopy , C leve land , Ohio , March 1972, p . 170 .

ASTM Book o f S t a n d a r d s , 1975, P a r t 24 , Method D 2003-64, p . 144 .

L . P . J a c k s o n , C . S . A l l b r i g h t , and R . E . Pou l son , Ana l . Chem., 5, 604 (1974) .

L. P . J ackson , C . S. A l l b r i g h t , and R . E . Poulson, " A n a l y t i c a l Chemis t ry o f Liquid Fue l Sources : T a r Sands , O i l S h a l e , C o a l , and Pe t ro leum," P e t e r C . Uden, Sidney S i g g i a , and Howard B . J e n s e n , E d . , Advances i n Chemis t ry S e r i e s 170 , American Chemica l S o c i e t y , Wash., D . C . 1978 , p. 232.

D . M . J e w e l l , J . H . Weber, J . W . Bunger, Henry P l a n c h e r , and D . R . Latham, Anal. Chem., +, 1391 (1972).

G . L. Baughman, S y n t h e t i c F u e l s Data Handbook, 2nd Ed . , Cameron Eng inee r s , I n c . , 1978, Denver , Co lo . , 80210.

R . A . F r i e d e l , and H. L . Re tco f sky , J . Amer. Chem. S O C . , 5, 1300 (1963) .

D. A . N e t z e l , D . R . McKay, R . A . Heppner, F. D. Guffey , S . D. Cooke, and D . L . Va r i e , P roc . EPA O i l S h a l e Symposium: Sampl ing , A n a l y s i s , and Q u a l i t y Assurance , Denver, Colo., March 26-28 , 1979.

176

TABLE 1. - Hydrocarbon s e p a r a t i o n r e s u l t s of d i s t i l l a t e s and r e s i d u e s

W t . Dercent of t o t a l hydrocarbon f r a c t i o n P e r c e n t

Sample S a t u r a t e O l e f i n Aromatic recovery 150- ton , 210-370°C d i s t . 64 5 1 9 88

11 63 7 20 90

370-535OC d i s t . 6 1 6 29 96 59 7 34 100 I t

>535OC r e s i d u e 45 11 43 99 45 11 38 94 11

S i t e 9 , 210-370°C d i s t . 70 5 1 7 92 72 6 23 101 I t

370-535OC d i s t . 64 6 24 94 59 5 29 93 11

>535OC r e s i d u e 48 8 40 96 40 10- 47 97 11

Paraho, 210-370°C d i s t . 25 27 30 82 36 23 26 85

370-535OC d i s t . 38 24 34 96 3 1 23 35 89

>535OC r e s i d u e 19 10 48 77 23 13 44 80

S u p e r i o r , 210-370°C d i s t . 25 29 30 84 27 36 28 91

370-535OC d i s t . 32 2 1 42 95 32 22 42 96

>535OC r e s i d u e 27 22 47 96 31 19 48 98

I t

II

I t

I t

I t

I ,

177

TABLE 2 . - Hydrocarbon s e p a r a t i o n r e su l t s o f whole s h a l e o i l s

W t . p e r c e n t of hydrocarbons from t o t a l o i l Percent

S h a l e o i l sample S a t u r a t e O l e f i n Aromatic recovery 150-ton r e t o r t 53 1 7 2 2 92

II 40 2 1 2 2 8 3

S i t e 9 r e t o r t I t

46 1 8 18 82 55 15 2 0 90

Paraho r e t o r t 41 27 2 4 92

Super ior r e t o r t 4 1 26 32 99 11 36 31 2 8 95

178

(Y

: , i! , ’3’ U

> ‘1- 4

v) 3 *

b) AROMATICS

c) OLEFINS

d) SATURATES

1800 1600 WAVELENGTH, cm-’

FIGURE 2. Partial infrared spectra of shale oil 210-370°C distillate total hydrocarbon and fractions

180

a) SATURATES

JlL

b) OLEFINS

I i I 1 5 0 0 loo PPM 150

FIGURE 3. Carbon-13 NMR spectra o f hydrocarbon fractions from Paraho 370-535OC distillate

181

LOW TEMPERATURE CLEAVAGE REACTIONS OF ILLINOIS NO. 6 COAL

Frank R . Mayo, David H. Buchanan,l and Lee A . Pavelka

S R I I n t e r n a t i o n a l , Menlo Park , C a l i f o r n i a 94025

T h i s paper p r e s e n t s a p r o g r e s s r e p o r t on our e f f o r t s t o de te rmine t h e k inds and p r o p o r t i o n s of s i n g l e bond i n I l l i n o i s No. 6 c o a l t h a t can b e broken below 100°C. The p r i n c i p a l o b s t a c l e t o t h e u s e of p r e s e n t l i q u e f a c t i o n processes i s t h e h igh c o s t of p l a n t s t h a t would employ t h e r e q u i r e d h igh tempera tures and p r e s s u r e s . Our work d e a l s o n l y w i t h low-temperature p r o c e s s e s near a tmospher ic p r e s s u r e . It h a s focused o n (1) t h e a s p h a l t o l f r a c t i o n of I l l i n o i s No. 6 c o a l , which i s t h e p y r i d i n e - s o l u b l e , toluene- i n s o l u b l e f r a c t i o n t h a t comprises about two- th i rds of t h e 15% of c o a l t h a t can be ex- t r a c t e d by p y r i d i n e , and (2) t h e p y r i d i n e - e x t r a c t e d c o a l , which i s about 85% of t h e i n i t i a l d ry c o a l , and which r e p r e s e n t s t h e e s s e n c e of t h e l i q u e f a c t i o n problem.

Oxida t ions

Previous work by Huntington e t a12 d e s c r i b e d t h e e f f e c t s on t h e same two sub- s t r a t e s of (1) AIBN-in i t ia ted o x i d a t i o n s i n p y r i d i n e s o l u t i o n a t 50°C, and (2) r e f l u x - i n g w i t h a l c o h o l i c KOH (781) w i t h o u t oxygen. a v e r a g e molecular weight (Mn, by vapor-phase osmometry) of t h e a s p h a l t o l by n e a r l y 50% b u t s e q u e n t i a l t r e a t m e n t w i t h both r e a g e n t s produced l i t t l e a d d i t i o n a l e f f e c t , as i f t h e two r e a g e n t s were a f f e c t i n g s i m i l a r bonds. Only about 10% of t h e e x t r a c t e d c o a l w a s made s o l u b l e i n p y r i d i n e , bu t some s u b s t r a t e became s o l u b l e i n a l c o h o l i c KOH.

E i t h e r r e a g e n t would reduce t h e number-

N a O C l o x i d a t i o n of very f i n e l y d iv ided e x t r a c t e d c o a l i n water suspens ion a t 30" and pH 1 3 h a s been much more e f f e c t i v e i n d i s s o l v i n g t h i s m a t e r i a l . 3 76% of t h e carbon i n t h e e x t r a c t e d c o a l has been converted t o b l a c k a c i d s (M, about 1000) s o l u b l e i n aqueous base , and 7% t o water -so luble acids; 4% of t h e i n i t i a l carbon w a s undis- so lved; t h e remaining 12% is presumably i n carbon oxides . Oxygen o x i d a t i o n of ex- t r a c t e d c o a l i n water suspens ion a t pH 13 and 50" is much s lower b u t has l e d t o 85% d i s s o l u t i o n of t h e c o a l and recovery of 66% of t h e o r i g i n a l c o a l i n b l a c k a c i d s . Oxi- d a t i o n s of a s p h a l t o l , w e l l d i s p e r s e d i n water a t pH 13 , gave b e t t e r r e s u l t s : wi th N a O C l a t 30°, 99% d i s s o l u t i o n and 93% of t h e carbon i n b l a c k a c i d s ; wi th oxygen a t 50°, 98% d i s s o l u t i o n and 80% of t h e carbon i n b l a c k a c i d s .

These o x i d a t i o n s i n w a t e r suspens ion a t pH 1 3 and o x i d a t i o n s w i t h A I B N and oxygen i n p y r i d i n e s o l u t i o n 2 a t 50°C appear t o proceed by d i f f e r e n t mechanisms. i n i t i a t e d o x i d a t i o n s of e x t r a c t e d c o a l , t h e H/C r a t i o d e c r e a s e s from . 7 3 t o .69, as i f b e n z y l i c hydrogen were be ing removed p r e f e r e n t i a l l y . However, i n bo th N a O C l and oxygen o x i d a t i o n s of bo th a s p h a l t o l and e x t r a c t e d c o a l i n w a t e r , H / C i n c r e a s e s somewhat, no twi ths tanding rep lacement of some H by 0 , s u g g e s t i n g p r e f e r e n t i a l removal of a r o m a t i c groups. P o s s i b l y some hydroxyla ted a romat ic r i n g s a r e s i tes of a t t a c k . The p r i n c i p a l p r o d u c t s , b l a c k a c i d s , from oxygen and NaOCl o x i d a t i o n s i n water a t pH 1 3 have similar composi t ions .

Cleavages of A s p h a l t o l s

I n r a d i c a l -

R e s u l t s of c l e a v a g e s of a s p h a l t o l s , p robably a t e t h e r l i n k s , a r e summarized i n F i g u r e s 1 and 2 . s l i g h t l y d i f f e r e n t Mn. I n g e n e r a l , r e a c t i o n s were r u n under n i t r o g e n , and a t room tempera ture e x c e p t a s no ted . Products were sometimes s e p a r a t e d by s o l u b i l i t y b u t always washed f r e e o f r e a g e n t s and s o l v e n t s and d r i e d i n an Abderhalden d r i e r a t <0.001 t o r r , u s u a l l y a t 14OoC i n F igure 1, u s u a l l y a t 76OC i n F i g u r e 2. need f o r 140' d r y i n g seems to-be w i t h samples t h a t c o n t a i n p y r i d i n e or amines and have n o t been acid-washed.) M n s were determined by VPO in p y r i d i n e , i n which a l l pro- d u c t s were s o l u b l e , a t c o n c e n t r a t i o n s of 0 .5 t o 3g/L. Keys t o a b b r e v i a t i o n s and

E_ach h a l f of each t a b l e s t a r t s from t h e c e n t e r w i t h a s p h a l t o l wi th

(The o n l y

182

arrangement of d a t a a r e given i n F igu re 2 . t h e middle of each second l i n e of each b lock of d a t a .

Thus, molecular weights of p roduc t s a r e i n

Experiments i n t h e upper l e f t q u a r t e r of F i g u r e 1 show t h a t e i g h t e x t r a c t i o n s of

23% of t h e o r i g i n a l C was l o s t , a t l e a s t p a r t l y a s wa te r - so lub le a s p h a l t o l with 5% KOH a t room temperature r e s u l t e d i n s o l u t i o n and r ecove ry of 9% of s o l u b l e carbon. and/or v o l a t i l e p roduc t s . a t 78O.2

Molecular weight r educ t ions without h e a t i n g p a r a l l e l t h o s e

React ions of a s p h a l t o l w i th benzylamine ( lower l e f t q u a r t e r i n F igu re l ) , and then drowning t h e r e a c t i o n i n e t h e r or methanol, r e s u l t e d i n p a r t of t h e a s p h a l t o l becoming so lub le i n t h e s e s o l v e n t s and a d e c r e a s e i n fin of about one-half . Treatment of the e t h e r - i n s o l u b l e product w i th a l c o h o l i c KOH r e s u l t e d i n f r a c t i o n a t i o n of t h e product b u t not f u r t h e r deg rada t ion . The butylamine-methanol combinat ion appea r s t o behave s i m i l a r l y .

Py r id ine hydroiodide i n p y r i d i n e a t room temperature dec reases t h e En of a s p h a l t o l t o one-half t o one - th i rd of t h e o r i g i n a l (upper r i g h t i n F igu re 1 ) . Th i s experiment w a s run on the premise t h a t p y r i d i n e hydroiodide would be an a c i d i n p y r i d i n e , which is an e x c e l l e n t s o l v e n t f o r a s p h a l t o l . a s H I . Asphal t01 was t r e a t e d wi th methyl i o d i d e a t room temperature i n t h e hope of making sulfonium as w e l l as pyridinium salts . reduced p res su re i n t h e e x p e c t a t i o n of s p l i t t i n g out methyl i o d i d e from pyr id in ium salts (without n e t c o a l bond c l eavage ) and conversion of t h e o r i g i n a l s u l f i d e s t o methyl s u l f i d e s and c o a l a l k y l i o d i d e s , w i t h n e t c l eavage of s u l f i d e bonds. However, t h e r educ t ion i n En from 1250 t o 660 i s s u r p r i s i n g l y h igh , s i n c e the 1 . 7 % S con ten t corresponds t o on ly 0.66 S / a s p h a l t o l molecule , of which most is expected t o be i n h e t e r o c y c l i c a romat i c r i n g s . d u p l i c a t e experiment i n F igu re 2 . I t i s t h e r e f o r e p o s s i b l e t h a t I a l o n e may be a b l e t o c l eave e t h e r l i n k s , a conc lus ion t o be supported i n d i s c u s s i o n of F i g u r e 2. Thus, a b i l i t i e s of Me.Si14 and of hexamethy ld i s i l azane p l u s MEsSiCl ( t h e l a t t e r i n t ended f o r t r i m e t h y l s i l y l a t i o n ? t o c l e a v e a s p h a l t o l s may be due a s much or more t o h a l i d e ions gene ra t ed a s t o t h e o r i g i n a l r eagen t .

However, methyl i o d i d e w a s n e a r l y as e f f e c t i v e

The product was then hea ted t o 140' a t

A somewhat g r e a t e r r educ t ion i n Mn is r e p o r t e d f o r a

We t r i e d sodium i n l i q u i d ammonia as an e the r -c l eav ing r e a g e n t , b u t found t h a t a d d i t i o n of sodium i n l i q u i d ammonia t o a co ld s o l u t i o n of a s p h a l t o l i n butylamine gave b e t t e r c o n t r o l , less r e d u c t i o n of t h e a s p h a l t o l , and a dec rease i n Mn by n e a r l y 50%. Treatment of t h i s product with p y r i d i n e hydroiodide ( r i g h t c e n t e r of F igu re 1) then gave f u r t h e r r e d u c t i o n i n molecular weight . However, our d a t a s u g g e s t t h a t com- b i n a t i o n of the sodium and H I r e a c t i o n s gave no more c l eavage than H I a l o n e .

F i g u r e 2 summarizes c l eavage r e a c t i o n s of two o t h e r a s p h a l t o l s w i t h H I (check of Figure 1 experiment) , H B r , t o luene s u l f o n i c a c i d , and some me ta l s a l t s , (except t h e Me1 experiment) i n p y r i d i n e s o l u t i o n . The o t h e r a c i d s , even a t 50°, are n o t a s e f f e c t i v e a s H I a t room temperature , b u t z i n c bromide, and e s p e c i a l l y z i n c c h l o r i d e and L i I*Hz0 ,6 have given more molecular weight r e d u c t i o n than any of t h e a c i d s . How- e v e r , a l l of t h e s e r e a c t i o n s have a p p a r e n t l y r e s u l t e d i n i n c o r p o r a t i o n of p y r i d i n e i n t h e p roduc t s , a s shown by t h e high r e c o v e r i e s and h igh n i t r o g e n con ten t s . Some pro- d u c t s a l s o l o s e weight s lowly and p e r s i s t e n t l y on h e a t i n g a t 140" i n vacuo. exp lana t ion is t h a t c l eavage of an a r y l a l k y l e t h e r by me ta l h a l i d e g i v e s metal pheno- l a t e and a l k y l h a l i d e ; some of the l a t t e r then r e a c t s w i t h p y r i d i n e s o l v e n t t o g i v e u n s t a b l e qua te rna ry pyridinium s a l t s . However, t h e remarkable r e a c t i v i t y of t h e s e re - agen t s a t low temperatures may be a s s o c i a t e d wi th t h e use of p y r i d i n e as s o l v e n t .

Conclusions

A p o s s i b l e

Th i s p rogres s r e p o r t shows t h a t a s p h a l t o l from I l l i n o i s No. 6 c o a l can be ex ten - s i v e l y degraded a t or nea r room temperature by s e v e r a l a c i d i c and b a s i c r e a g e n t s and by some o x i d i z i n g and r educ ing a g e n t s , w i t h good t o e x c e l l e n t recovery of o r i g i n a l

183

carbon. These a g e n t s appear t o a t t a c k e t h e r l i n k s , o r maybe aromat ic r i n g s i n oxida- t i o n s a t pH 1 3 , b u t a s y e t we know of no precedent f o r r e a c t i o n s of a l i p h a t i c amines o r a l c o h o l i c KOH wi th e t h e r s a t t h e s e tempera tures . To de te rmine t h e p r o p o r t i o n s of v a r i o u s kinds of b r e a k a b l e s i n g l e bonds i n I l l i n o i s No. 6 c o a l , we p l a n t o c a r r y out f u r t h e r degrada t ions on a s p h a l t 0 1 by combinations of r e a g e n t s , and t h e n ex tend t h e most promising of t h e s e r e a c t i o n s t o e x t r a c t e d c o a l . We expec t t h a t t h i s k ind of in format ion w i l l p r o v i d e t h e b a s i s f o r new and economical approaches t o c o a l l i q u e f a c - t i o n , which w i l l employ much m i l d e r c o n d i t i o n s and much less expens ive p r o c e s s e s and p l a n t s .

Acknowledgement

Most of t h e r e s e a r c h d e s c r i b e d h e r e was suppor ted by t h e U.S. Department of Energy under Cont rac t No. ET-78-C-01-3293.

References

(1) P r e s e n t a d d r e s s , Department of Chemistry, E a s t e r n I l l i n o i s U n i v e r s i t y , Char les ton , I L , 61920.

(2) J. G. Hunt ington , F. R . Mayo, and N. A . Kirshen , Fue l , 58, 24 (1979).

(3) F. R. Mayo and N. A . Kirshen, Fue l , i n p r e s s .

( 4 ) M. E. Jung and M. A . L y s t e r , J. Org. Chem., 42, 3761 (1977).

(5)

( 6 )

S . Friedman, M. L. Kaufman, W. A. S t e i n e r , and I . Wender, F u e l , 40, 33 (1961).

I . T. H a r r i s o n , Chem. Communications, 1969, 616.

184

7 In .-

I

3 P- 3 cn

A cn 0

3 -?

"$- E ?

w . - I

d

Y Z d

185

23-A 82 / .7T/ . lY 2 4 4 81/.790/.133

03.6/ 524/ - 03.4/ 616/ -

11-A 104/.784/ - Asph 100/.787/.125 104/ 555/ -

H I 6-8 84/.787/ - 9-A 99/.769/ - Li I 'H$ As@ 1Qd.782f.140 . 89/ 430/ -

1 7 4 100/ 980/ -

102/ 363/ - 28-A lOp/lW/ -

@-A 95/.804/ - I-A ios / .ns / - 42-A 96/.810/ - 108/ 379/ - r19/ 4281 - 102/ 392/ -

Key t o a-gement of data: Abbreviations :

Sanple Atom $ C/ H/C /.O/C A s = asphalt01 + Bn = benzyl Py = pyridine Yield Bu, Et, Me = n-butyl, ethyl, methyl 4 HbDS = hemethyldisilazme

d, h, rn = days, hours, minutes No. Vt. $ /-weq.OH/rnole

Figure 2. Cleavages of asphaltole in pyridine eolution (except with HeI) and at room temperature (except a8 noted othenise) .

186

OXYDESULFURIZATION OF COAL TREATED WITH METHYL IODIDE -- IMPLICATIONS FOR REMOVAL OF ORGANIC SULFUR

R. Warkuszewski, C.-K. Weia, and T. D . Wheelock

A m e s L a b o r a t o r y , USDOE, and Department of Chemical Engineer ing

Iowa S t a t e U n i v e r s i t y , A m e s , Iowa 50011


Zn t h e chemica l d e s u l f u r i z a t i o n p r o c e s s b e i n g developed a t t h e Ames Labora tory , c o a l i s leached w i t h a d i l u t e s o l u t i o n of sodium c a r b o n a t e c o n t a i n i n g d i s s o l v e d oxygen under p r e s s u r e and a t e l e v a t e d tempera ture . For many c o a l s , most of t h e i n o r g a n i c ' s u l f u r c a n be removed, and t h e o r g a n i c s u l f u r c o n t e n t can be reduced by 25-40% ( 1 , Z ) . I n some i n s t a n c e s , as much as 70% of t h e o r g a n i c s u l f u r h a s been removed. An e s s e n t i a l p i e c e of i n f o r m a t i o n i n e v a l u a t i n g t h e e f f e c t i v e n e s s of a p r o c e s s f o r t h e removal of o r g a n i c s u l f u r i s t h e i d e n t i . t y and r e a c t i v i t y of t h e v a r i o u s s u l f u r f u n c t i o n s grouped under t h e term "organic s u l f u r . "

Although much d a t a is a v a i l a b l e on t h e c o n t e n t and d i s t r i b u t i o n of the s o - c a l l e d p y r i t i c , s u l f a t i c , and o r g a n i c s u l f u r i n v a r i o u s c o a l s , rei-atively l i t t l e h a s been p u b l i s h e d on t h e n a t u r e and abundance of t h e o r g a n i c s u l f u r g r o u p s i n c o a l . E s s e n t i a l l y no d a t a a r e a v a i l a b l e on t h e r e a c t i v i t y of such f u n c t i o n a l groups under o x i d i z i n g c o n d i t i o n s , such a s t h o s e found d u r i n g o x y d e s u l f u r i z a t i o n . I n f a c t , no c o m p l e t e l y s a t i s f a c t o r y method e x i s t s as y e t f o r t h e d i r e c t d e t e r m i n a t i o n of or- g a n i c s u l f u r i n c o a l , a l t h o u g h a few methods a r e b e i n g developed . These methods are based e i t h e r on microprobe a n a l y s i s ( 3 , 4 ) , o r on low- k m p e r a t u r e a s h i n g of t h e o r g a n i c components of c o a l ( 5 ) , o r on t h e i r t h e r m o k i n e t i c r e d u c t i o n t o hydrogen s u l f i d e ( 6 ) . A s a r o u t i n e , however, o r g a n i c s u l f u r i s s t i l l b e i n g de termined as t h e d i f f e r e n c e between t h e t o t a l s u l f u r and t h e amount of t h e i n o r g a n i c ( i . e . , p y r i t i c p l u s s u l - f a t i c ) s u l f u r , a c c o r d i n g t o ASTM p r o c e d u r e s .

Attempts t o i d e n t i f y and q u a n t i t a t i v e l y d e t e r m i n e o r g a n i c s u l f u r f u n c t i o n s i n c o a l have been few. On t h e b a s i s o f v e r y s p a r s e d a t a , i t i s g e n e r a l l y assumed t h a t t h e o r g a n i c s u l f u r i n c o a l c a n be d e s c r i b e d a lmost comple te ly by t h e f o l l o w i n g c l a s s e s :

a P r e s e n t a d d r e s s : Dept . of Chemical E n g i n e e r i n g , U n i v e r s i t y of Minnesota , Minneapol i s , MN 55455

187

Class 1. A l i p h a t i c o r a r o m a t i c t h i o l s (mercaptans , t h i o p h e n o l s ) : R-SH, Ar-SH

Class 2 . A l i p h a t i c , a r o m a t i c , o r mixed s u l f i d e s ( t h i o e t h e r s ) : R-S-R, Ar-S-Ar, R-S-Ar

Class 3. A l i p h a t i c , a r o m a t i c , or mixed d i s u l f i d e s ( b i s t h i o e t h e r s ) : R-SS-R, Ar-SS-Ar, R-SS-Ax

Class 4 . H e t e r o c y c l i c compounds o f t h e t h i o p h e n e t y p e : e .g., d i b e n z o t h i o p h e n e

It i s g e n e r a l l y assumed t h a t any chemica l d e s u l f u r i z a t i o n p r o c e s s that can remove o r g a n i c s u l f u r w i l l do s o because of t h e r e a c t i v i t y of compounds i n C l a s s 1, 2 , and 3. H e t e r o c y c l i c compounds i n Class 4 are ext remely s t a b l e t o chemica l a t t a c k and h i g h t e m p e r a t u r e .

The fundamental approach i n t h i s s t u d y i s b a s e d on t h e d i f f e r e n t r e a c t i v i t y of methyl i o d i d e toward d i f f e r e n t o r g a n o s u l f u r f u n c t i o n s t o produce su l fonium compounds. The g e n e r a l scheme o f r e a c t i o n s f o r t h e v a r i o u s c l a s s e s o f s u l f u r groups can b e summarized a s f o l l o w s ( 7 ) :

1. H e r c a p t a n s :

R-SH + CH I ---t R-S-CH + H I 3 3 + -

R-S-CH3 + CH I *R-S -(CH ) 3 3 2 I

2. S u l f i d e s :

+ R-S-R + CH I - R2S -CH I- 3 3

3. D i s u l f i d y :

+ R-SS-R + 4 CH 1 - 2 R-S (CH3)2 I- + I2 3

4 . H e t e r o c y c l i c compounds:

Dibenzoth iophene + CH I + n o r e a c t i o n 3

3 )

4 )

The r e a c t i o n of c o a l w i t h methyl i o d i d e w a s used p r e v i o u s l y ( 8 ) t o de te rmine t h e t h i o e t h e r c o n t e n t of c o a l by measur ing t h e u p t a k e o f i o d i n e , presumably a s s o c i a t e d as i o d i d e w i t h t h e s u l f o n i u m compounds. But t h e i o d i n e u p t a k e is n o t a t r u e measure of t h e t h i o e t h e r c o n t e n t because o t h e r compounds, n o t a b l y h e t e r o c y c l i c n i t r o g e n compounds, can al.so r e a c t r e s u l t i n g i n u p t a k e o f i o d i n e . To overcome t h i s d i f f i c u l t y , t h e s u l f o n i u m compounds were washed o u t w i t h a s o l v e n t l i k e a c e t o n e , and t h e d e c r e a s e i n t h e s u l f u r c o n t e n t was t h e n t a k e n as t h e i n d i c a t o r of t h e t h i o e t h e r c o n t e n t ( 7 ) . A s i m i l a r p r o c e d u r e w a s adopted i n t h i s work.

Exper imenta l

Ma t er i a l s

The c o a l used i n t h i s s t u d y was a h i g h - v o l a t i l e b i tuminous c o a l from t h e Star mine i n Mahaska County, Iowa. The c o a l w a s p u l v e r i z e d , s c r e e n e d us ing U.S. S tandard sieves, d r i e d , and a n a l y z e d f o r a s h , h e a t - i n g v a l u e , and s u l f u r d i s t r i b u t i o n by ASTM p r o c e d u r e s .

F r e s h methyl i o d i d e was used d i r e c t l y from t h e r e a g e n t b o t t l e . I n some exper iments , t h e r e a g e n t was c l e a n e d by s h a k i n g w i t h mercury , b u t no s i g n i f i c a n t d i f f e r e n c e was n o t i c e d i n t h e r e s u l t s .

Methyl I o d i d e Reac t ion

A s l u r r y o f 20 g c o a l and 30 m l methyl i o d i d e was p laced i n a l a r g e test t u b e , covered w i t h f o i l , and a l lowed t o s t a n d f o r 3 days a t room t e m p e r a t u r e . The s l u r r y was then f i l t e r e d and washed w i t h a b o u t 2 1. a c e t o n e t o remove r e a c t i o n p r o d u c t s and u n r e a c t e d methyl i o d i d e , u n t i l t h e test f o r i o d i d e ( s i l v e r n i t r a t e ) was n e g a t i v e . The t r e a t e d c o a l was d r i e d and ana lyzed a g a i n . Q u a l i t a t i v e tests f o r r e s i d u a l i o d i d e i n t h e t r e a t e d c o a l (hydrogen p e r o x i d e t r e a t m e n t fo l lowed by e x t r a c t i o n of i o d i n e i n t o a benzene l a y e r ) showed o n l y t r a c e s o f i o d i d e . The methyl i o d i d e t r e a t m e n t s w e r e r e p e a t e d on enough c o a l samples t o p r o v i d e a s t o c k of t r e a t e d c o a l t o be used f o r t h e o x y d e s u l f u r i z a t i o n e x p e r i m e n t s .

O x y d e s u l f u r i z a t i o n of Coal i n Autoc lave

The c o a l ( 4 0 g) was leached f o r 1 h r w i t h 400 m l s o l u t i o n i n a I - l i t e r a u t o c l a v e d e s c r i b e d p r e v i o u s l y (1). The l e a c h i n g w a s done a t 1 5 O o C under 50 o r 200 p s i a oxygen p a r t i a l p r e s s u r e . For non-oxid iz ing c o n d i t i o n s , a p a r t i a l p r e s s u r e of 5 0 p s i a n i t r o g e n was used. Water o r 0 . 2 E sodium c a r b o n a t e was used as t h e l e a c h i n g s o l u t i o n . from t h e a1kal i ;e l e a c h i n g s t e p were l e a c h e d f o r a second t ime, a l s o f o r 1 h r a t 150 C , u s i n g w a t e r , 0 .1 E s u l f u r i c a c i d , 0 . l M p h o s p h o r i c a c i d , o r 0 . 2 M sodium c a r b o n a t e i n a n i t r o g e n atmosphere.

The r e s i d u e s

C a l c u l a t i o n s

I n o r d e r t o a c c o u n t f o r t h e d i f f e r e n t l e v e l s of a s h i n t h e v a r i o u s c o a l r e s i d u e s , t h e s u l f u r c o n t e n t was c o n v e r t e d from weight p e r c e n t t o pounds of s u l f u r p e r m i l l i o n Btu. T h i s c o n v e r s i o n , i n e f f e c t , a l lowed t h e com- p a r i s o n of t h e o r g a n i c s u l f u r c o n t e n t i n t h e o r g a n i c p o r t i o n of t h e c o a l .

( i . e . , c o m b u s t i b l e )

I n a few cases, t h e h e a t i n g v a l u e was n o t a c t u a l l y de te rmined b u t was c a l c u l a t e d u s i n g a formula (l), based on t h e assumpt ion t h a t t h e a s h - f r e e h e a t i n g v a l u e is r e l a t i v e l y c o n s t a n t f o r t h e same c o a l , r e g a r d - less of t h e t r e a t m e n t c o n d i t i o n s .

189

R e s u l t s and D i s c u s s i o n

Removal of S u l f u r b y t h e Methyl I o d i d e Trea tment

The r e s u l t s of t r e a t i n g c o a l w i t h methyl i o d i d e are p r e s e n t e d i n T a b l e 1. Based on t h e pounds o f s u l f u r p e r m i l l i o n Btu, t h e methyl i o d i d e t r e a t m e n t removed, on t h e a v e r a g e , 4 8 . 3 % of t h e o r g a n i c s u l f u r . T h i s seems t o i n d i c a t e t h a t a t l e a s t one-ha l f of t h e o r g a n i c s u l f u r i s i n t h e c l a s s t h a t i s reactive toward methyl i o d i d e . S ince t h i o p h e n i c compounds a r e u n r e a c t i v e and d i s u l f i d e groups r e a c t t o o s lowly a t room tempera tu re , t h e r e a c t i v e p o r t i o n of t h e o r g a n i c s u l f u r i s p robab ly of t h e s u l f i d e and mercap tan c l a s s e s .

F u r t h e r t e s t s were run by t r e a t i n g m i n e r a l p y r i t e w i t h methyl i o d i d e under s i m i l a r c o n d i t i o n s and then washing w i t h a c e t o n e . No r e a c t i o n was o b s e r v e d ; t h e s u l f u r c o n t e n t w a s u n a f f e c t e d . A l s o , s i m p l e washing of c o a l w i t h 2 1. of a c e t o n e (wi thou t p r i o r methyl i o d i d e t r e a t m e n t ) d i d n o t a l t e r s i g n i f i c a n t l y t h e a s h c o n t e n t , h e a t i n g v a l u e , and s u l f u r d i s t r i b u t i o n of t h e c o a l .

Another p o s s i b l e e x p l a n a t i o n f o r t h e r e d u c t i o n of t h e o r g a n i c s u l f u r may be o f f e r e d i f methyl i o d i d e s imply m e t h y l a t e s t h e c o a l , t h u s i n c r e a s i n g i t s o r g a n i c c o n t e n t and d e c r e a s i n g t h e s u l f u r c o n t e n t by " d i l u t i o n . " I f t h i s o b s e r v a t i o n were a r e f l e c t i o n of a m e t h y l a t i n g e f f e c t , then t h e h e a t i n g v a l u e should have i n c r e a s e d , t h e a s h c o n t e n t should have dec reased , and t h e " d i l u t i o n " shou ld a p p l y t o a l l t y p e s of s u l f u r i n c o a l . Yet t h e changes i n a s h c o n t e n t , h e a t i n g v a l u e , and weight r e c o v e r y were i n s i g n i f i c a n t ; and t h e p y r i t i c and s u l f a t i c s u l f u r v a l u e s w e r e f a i r l y c o n s t a n t . It seems, t h e r e f o r e , that o r g a n i c s u l f u r was r e a l l y removed by t h i s p rocedure . It i s n o t known, however, by what mechanism t h e s u l f o n i u m s a l t s are washed away.

Removal of S u l f u r by O x i d a t i v e Leach ing

The r e s u l t s o f l e a c h i n g t h e methyl i o d i d e - t r e a t e d c o a l are pre- s e n t e d i n Tab le 2 . The s u l f u r c o n t e n t should be compared n o t on ly t o t h a t of t h e i n i t i a l c o a l b u t a l s o t o t h a t o f t h e me thy l i od ide - t r e a t e d c o a l ir! Tab le 2 . It c a n be s e e n t h a t l e a c h i n g w i t h a l k a l i o n l y , (sample'No. 016D), i n t h e absence of oxygen, d i d n o t have any e f f e c t on t h e s u l f u r c o n t e n t . When l e a c h i n g i n t h e p r e s e n c e of oxygen, t h e t o t a l s u l f u r c o n t e n t d e c r e a s e d , l a r g e l y because of a d e c r e a s e i n t h e i n o r g a n i c s u l f u r c o n t e n t . The t o t a l s u l f u r c o n t e n t w a s lower when h i g h e r oxygen p a r t i a l p r e s s u r e s were used o r when t h e l e a c h i n g s o l u t i o n s were a l k a l i n e . The o r g a n i c s u l f u r c o n t e n t was r e l a t i v e l y c o n s t a n t , a l - though i t appea red s l i g h t l y h i g h e r under n o n - a l k a l i n e c o n d i t i o n s when water on ly w a s used as t h e l e a c h a n t .

190

In T a b l e 3 r e s u l t s are p r e s e n t e d f o r d e s u l f u r i z a r i o n e x p e r i m e n t s i n which a second l e a c h i n g s t e p was added a f t e r t h e f i r s t l e a c h i n g s t e p w i t h a n a l k a l i n e s o l u t i o n . The a d d i t i o n a l l e a c h i n g was done i n a non-oxid iz ing n i t r o g e n a tmosphere , u s i n g water, s u l f u r i c a c i d , phosphor ic a c i d , o r sodium c a r b o n a t e s o l u t i o n s . As ide from one r u n which a p p e a r s t o be anomalous, t h e t o t a l s u l f u r c o n t e n t d i d n o t seem to be reduced by t h e second l e a c h i n g s t e p .

The o r g a n i c s u l f u r c o n t e n t , however , a p p e a r s t o b e s l i g h t l y h i g h e r t h a n that o b t a i n e d a f t e r one l e a c h i n g s t e p , under a l k a l i n e c o n d i t i o n s and i n t h e p r e s e n c e of oxygen. I t may be p o s s i b l e t h a t under t h e n i t - rogen atmosphere o f t h e second s t e p , some of t h e p y r i t e may be c o n v e r t e d t o elemental s u l f u r . Such a c o n v e r s i o n would be c h a r a c t e r i z e d by a de- c r e a s e i n t h e p y r i t i c s u l f u r , an i n c r e a s e i n t h e o r g a n i c s u l f u r , b u t no change i n t h e t o t a l s u l f u r . Such a convers ion would a l s o be f a v o r e d by a c i d i c c o n d i t i o n s .

I M e t b l I o d i d e Trea tment of Oxydesul fur ized Coal

The r e s u l t s i n Table 4 show t h e e f f e c t of methyl i o d i d e t r e a t m e n t on S t a r c o a l t h a t had been p r e c l e a n e d by a f l o a t - s i n k t e c h n i q u e and s u b s e q u e n t l y l e a c h e d f o r 1 h r w i t h 0 .2 fl sodium c a r b o n a t e a t 15OoC under 50 o r 200 p s i a p a r t i a l p r e s s u r e of oxygen. s u l f u r v a l u e s i n T a b l e 1, t h e c l e a n i n g and l e a c h i n g a p p a r e n t l y removed o n l y t h e i n o r g a n i c s u l f u r , l e a v i n g t h e o r g a n i c s u l f u r c o n t e n t l a r g e l y u n a f f e c t e d . Leaching a t h i g h e r oxygen p a r t i a l p r e s s u r e seemed t o remove more t o t a l s u l f u r .

By comparison w i t h t h e

C u r i o u s l y , s u b s e q u e n t t r e a t m e n t of t h e leached c o a l w i t h methyl i o d i d e d i d n o t seem t o remove any o r g a n i c s u l f u r a s i t d i d when a p p l i e d t o t h e r a w , un leached c o a l ( s e e Tab1.e 1). T h i s l a c k o f r e a c t i v i t y may b e dueoto p h y s i c a l changes i n t h e c o a l caused by t h e h i g h t e m p e r a t u r e (150 C) of t h e l e a c h i n g . A l t e r n a t i v e l y , t h e chemica l l e a c h i n g may have caused a c o n v e r s i o n of r e a c t i v e o r g a n o s u l f u r g r o u p s i n t o u n r e a c t i v e groups . Perhaps a l s o t h e d i f f e r e n c e i n t h e p a r t i c l e s i z e (-200 mesh i n t h i s set of e x p e r i m e n t s compared t o -150/+200 mesh i n p r e v i o u s exper iments ) can be a c o n t r i b u t i n g f a c t o r .

Conclus ions

Treatment of c o a l w i t h methyl i o d i d e fo l lowed by e x t e n s i v e washing w i t h a s o l v e n t t o remove t h e r e a c t i o n p r o d u c t s h a s been used t o remove a p p r o x i m a t e l y one-half o f t h e o r g a n i c s u l f u r c o n t e n t i n a n Iowa h i g h v o l a t i l e b i t u m i n o u s c o a l . The p y r i t i c and s u l f a t i c s u l f u r c o n t e n t was n o t a f f e c t e d by t h e m e t h y l i o d i d e t r e a t m e n t . Washing t h e c o a l w i t h s o l v e n t o n l y d i d no t produce any e f f e c t e i t h e r . On t h e b a s i s of chemica l r e a c t i o n s r e p o r t e d i n t h e l i t e r a t u r e , i t is assumed t h a t t h e r e a c t i v e s u l f u r groups t h a t were removed by t h i s t r e a t m e n t may be o r g a n i c s u l f i d e s or mercaptans .

191

Subsequent l e a c h i n g s of t h e methyl i o d i d e - t r e a t e d c o a l under v a r i o u s c o n d i t i o n s o f o x y d e s u l f u r i z a t i o n d i d n o t r e d u c e f u r t h e r t h e o r g a n i c s u l f u r c o n t e n t . The i n o r g a n i c s u l f u r c o n t e n t , however, was reduced by t h e o x y d e s u l f u r i z a t i o n s t e p s . I t can b e assumed t h a t a l l t h e r e a c t i v e and a c c e s s i b l e o r g a n i c s u l f u r was removed by t h e methyl i o d i d e t r e a t m e n t , and f u r t h e r chemical d e s u l f u r i z a t i o n w a s d i r e c t e d o n l y a g a i n s t t h e i n o r g a n i c s u l f u r .

When t h e c o a l was f i r s t p r e c l e a n e d by a f l o a t - s i n k t e c h n i q u e and then leached by t h e o x y d e s u l f u r i z a t i o n p r o c e d u r e , t h e o r g a n i c s u l f u r c o n t e n t was n o t a f f e c t e d by subsequent t r e a t m e n t w i t h methyl i o d i d e . T h i s l a c k o f r e a c t i v i t y of t h e o r g a n i c s u l f u r toward methyl i o d i d e may be caused by p h y s i c a l o r chemica l changes i n t h e c o a l b r o u g h t a b o u t by the h igh t e m p e r a t u r e o r chemica l n a t u r e of t h e o x y d e s u l f u r i z a t i o n p r o c e s s .

Acknowledgment

T h i s work was per formed under C o n t r a c t No. W-7405-eng-82 w i t h the U.S. Department o f Energy, D i v i s i o n of F o s s i l Energy.

References

1 . Wheelock, T. D . , G r e e r , R. T. , Markuszewski, R . , and F i s h e r , R . W . , Annual T e c h n i c a l T r o g r e s s R e p o r t , O c t . 1, 1977 - S e p t . 30, 1978, LS-4668, Ames L a b o r a t o r y DOE, Iowa S t a t e U n i v e r s i t y , Ames, I A , ( A p r i l , 19 79)

2 . Markuszewski, R . , Chuang, K.-C. , and Wheelock, T. D . , P r o c e e d i n g s : Symposium on Coal Cleaning t o Achieve Energy and Envi ronmenta l Goals ( S e p t . 1978, Hollywood, FL), Vol. 11, p. 1039, EPA-600/7-79- 098b, A p r i l 1979.

3. Harris, L. A.. Yust, C. S . , and Crouse, R. S . , F u e l 3, 456 (1977) .

4. Raymond, R. and Gooley, R . , Scanning E l e c t r o n Microscopy, 1 9 7 8 / I , 0. J o h a r i , e d . , SEN, Lnc., AMF O'Hare, I L , 93 (1978) .

5. Paris, B . , Chap. 3 i n Coal D e s u l f u r i z a t i o n : Chemical and P h y s i c a l Methods, T. D. Wheelock ( e d . ) , ACS Symposium S e r i e s 64, Am. Chem. S O C . , Washington, D . C . , 1977.

6. Attar, A. and Dupuis , F. , Am. Chem. SOC. Div. of F u e l Chem. Pre- p r i n t s z ( 2 ) , 44 (1978) .

7. Angelova, G . K. a n d Syskov, K. I . , I z v . Akad. Nauk SSSR, M e t . Topl . , No. 5, 1 5 3 (1959) .

8. Postowsky, J. J . and Harlampovich, A. B . , F u e l 1 5 ( 8 ) , 229 (1936) .

192

Table 1. E f f e c t of methyl i o d i d e (MeI) t r e a t m e n t and a c e t o n e (Me2CO) washing on s u l f u r c o n t e n t of c o a l . a

6 Trea t - H . V . , Ash, S C o n t e n t , l b . / 1 0 Btu. S Redn. , % No. ment B t u . / l b . % Tot. Pyr . S u l f . Org. Org. T o t .

O O l D None 12579 8 .34 2.02 0 .98 0 .15 0 .89 -- -- 029D Me2C0 12495 8 . 9 5 2.06 1 . 0 8 0 .20 0.78 -- -- 003 Me1 + Me2C0 12552 8.29 1 . 6 8 1 . 0 8 0 .17 0 .43 50 .6 1 6 . 8

004 Me1 + Me2C0 12490 8.46 1 .62 1 . 1 8 0 .14 0 .30 6 6 . 3 1 9 . 8

005 Me1 + Me CO 12506 8 .57 1.78 -1.04 0 . 1 0 0.64 2 8 . 1 1 1 . 9

Ave (of 003 , 004, 005) 12516 8 . 4 4 1 .70 1.10 0.14 0.46 4 8 . 3 1 5 . 8 2

a s t a r c o a l (-150/+200 mesh) .

b'lD" d e n o t e s a v e r a g e of d u p l i c a t e a n a l y s i s .

T a b l e 2. One-step o x y d e s u l f u r i z a t i o n of Me1 - t r e a t e d c o a l . a

SampAe Leach 0 P r e s s . , H . V . , Ash, No. s o l n . p s i a B t u . / l b . %

O O l D -- None -- 12579 8 .34

M e 1 -- 12516 8.44 Ave. of 003, _ _ 004, 005

50 12046 6.75 013 H2° 006 Na2C03 50 10220 12.90

014D H2° 200 11818 6.68

012 Na2C03 200 11787 13 .02

016D Na2C03 OC 12245 7 . 4 1

6 S Content , l b . / 1 0 Btu. T o t . Pyr . S u l f . Org.

2.02 0 .98 0.15 0.89

1 .70 1.10 0.14 0.46

1 . 2 8 0.44 0.17 0.67

1 . 2 1 0 .52 0 .16 0 .53

1.06 0.20 0.12 0.75

0 .91 0.39 0 . 0 8 0.44

1 . 6 3 0.95 0 . 1 1 0.57

astar c o a l (-150/+200 mesh) , t r e a t e d w i t h Me1 and t h e n l e a c h e d 1 h r a t 150°C w i t h H20 o r 0 . 2 Na2C03 under 50 o r 200 p s i a 02.

b''D" d e n o t e s a v e r a g e of d u p l i c a t e a n a l y s i s .

%on-oxidizing a tmosphere of 50 p s i a N p a r t i a l p r e s s u r e . 2

193

T a b l e 3. Two-step d e s u l f u r i z a t i o n of Me1 - t r e a t e d c o a l . a -

6 Sarnphe 2nd s t e p H . V . , Ash, S C o n t e n t , l b . / 1 0 Btu. No. Leach Btu. /lb. % T o t . P y r . S u l f . Org.

1st Leach S t e p w i t h 0 . 2

11119 14 .28 1 .30 0.67 0.03 0 .60

6.72 1 . 2 4 0.46 0.05 0.73

018D

020D 0.1 H2S04 11529

023 0.1 H3P04 11479 12 .26 1 . 3 1 0 .53 0 .03 0 . 6 3

024D 0.2 5 Na2C03 9042 13.33 1.20 0.52 0.07 0 . 6 1

Na2C03 under 5 0 p s i a O2

HZO

2 1st Leach S t e p w i t h 0 .2 E Na2C03 under 200 p s i a 0

11763' 9 .32 0.86 0.21 0.05 0.60 02 7 D

035D 0.1 E H2S@4 11614' 6 . 0 3 1 . 0 3 0.30 0.08 0 . 6 5

0 3 i n 0.1 fi H3P04 11478' 1 2 . 2 7 1 .16 0.52 0.05 0.59

0 . 2 _M Na CO 9831 19 .65 1 .20 0.65 0.08 0 . 4 7 033D

H2°

2 3 __ -

aSta& coal (-150/+200 mesh) , t r e a t e d w i t h Me1 and then leached 1 h r a t 150 C wi th 0 .2 1 a d d i t i o n a l h r a t f 5 0 W under 50 p s i a N 2 w i t h i n d i c a t e d l e a c h s o l u t i o n .

Na CO3 under 50 o r 200 p s i a @?. For 2nd s t e p , l e a c h e d

b''D" d e n o t e s a v e r a g e o f d u p l i c a t e a n a l y s i s

"H.V. c a l c u l a t e d .

Table 4. Methyl i o d i d e (MeI) t r e a t m e n t of l e a c h e d c o a l . a ~~

SampAe No. Treatment

~~ ~~ ~ ~ ~~

6 H . V . , Ash, S C o n t e n t , lb./10 Btu.

B t u . / l b . % Tot. P y r . S u l f . Org.

06OD Leached u n d e r 50 p s i a O2 9162 9 .53 1 . 2 9 0.24 0 . 0 5 1.00

Sample 060D 11370 10 .63 1 .26 0.24 0 . 0 1 1.01

p s i a 0 10810 1 1 . 7 1 1 . 0 4 0 .11 0.02 0 . 9 1

Sample 064 11534 1 0 . 5 6 0 . 9 6 0.10 0.01 0.85

062D Me1 t r e a t m e n t of

@64 Leached under 200

065D Me1 t r e a t m e n t o f

a s t a r c o a l (-200 mesh) p r e c l e a n e d and l e a c h e d 1 h r a t 15OoC w i t h 0 . 2 E Na2C03

b*fD" d e n o t e s a v e r a g e of d u p l i c a t e a n a l y s i s . 2'

under 50 o r 200 p s i a 0

194

MOLECULAR COMPONENTS OF C U L AND COAL STXUCTUFG D. Bodzek and A. hlarzec. Departmect of petroleum and Coal Chemistry. Pol ish

Academy o f Sciences. 44-100 Gliwice, 1 Naja 62 St. Poland.

High v o l a t i l e bituminous coal was extracted a t room temperature by means o f 18 solvents having t L e i r electron-donor /DH/ end -acceptor /AN/ prope r t i e s quan t i t a t ive ly determined. Extracts were analysed by f i e l d ion iza t ion and h igh r e so lu t ion mass spectrometry. Extractable compounds havicg molecular masses i n 200-600 8.xn.u. range c o n s t i t u t e 30% wi;. o f coa l organic material . Hydrocarbons /CnH2n,6 up t o C,U2n-34/, n i t rogen comgounds /CHIT, CHN2, CH.N3/, oxxygen compounds /CHO, CH02/ and nitrogen- oxygen compounds /CEJO, C€!N20, CHN02, CIIIi202, CID130/ were i d e n t i f i e d i n the extracts . On the bas i s of ex t r ac t ion da ta / ex t r ac t y i e l & * solvent DN acd AB numbers/ end LS analysis the conclusion has been drawn t h a t ex t r ac t ab le compounds a r e bonded to coa l macromolecular network by electron-donor-acceptor bonds. These bonds a re destroyed during extrac- t i o n by s u b s t i t u t i o n a c t i v i t y of solveots. Solvent s u b s t i t u t i o n capabi- l i t i e s depend on t h e i r donor and acceptor ~ w b e r 3 .

135

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