A COMPARISON OF LSCF-6428 AND BYS FOR THE OXIDATIVE ... · A COMPARISON OF LSCF-6428 AND BYS FOR...

A COMPARISON OF LSCF-6428 AND BYS FOR THE OXIDATIVE

CONVERSION OF METHANE AND ETHANE

By

CODRUTA ELENA PLATON

A thesis submitted in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE IN CHEMICAL ENGINEERING

WASHINGTON STATE UNIVERSITY Department of Chemical Engineering

MAY 2002

ii

To the Faculty of Washington State University:

The members of the Committee appointed to examine the thesis of CODRUTA

ELENA PLATON find it satisfactory and recommend that it be accepted.

Chair

iii

ACKNOWLEDGMENTS

I would like to thank Dr. William J. Thomson for his support and guidance

through the duration of the study of this project. I would also like to thank Alex Platon,

Sekar Darujati, Dave LaMont, Chris Fischer, and Rakesh Radhakrishnan for technical

advice and support. I would also like to thank Matt Fountain, Anand Chellappa, Yuko

Hashimoto and Jim Mullin for initiating me in the experimental procedures.

iv

A COMPARISON OF LSCF-6428 AND BYS FOR THE OXIDATIVE

CONVERSION OF METHANE AND ETHANE

Abstract

by Codruta Elena Platon, M.S.

Washington State University

May 2002

Chair: William J. Thomson

Results are reported for a comparative study of two materials, which have been

proposed as catalytic, dense phase ion conducting membranes for the oxidative coupling

of methane (OCM). These two materials, Bi1.5Y0.3Sm0.2O3-δ (BYS) and

La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF-6428), have been evaluated for their respective OCM

activities, their interaction with ethane, and their stability in reducing environments. The

results show that BYS is a superior OCM catalyst, having rates that are nearly six times

greater and yields that are over twice as high as LSCF-6428. On the other hand, using in-

situ, dynamic XRD, BYS was observed to undergo a phase transformation at about

700°C. This transformation was absent in an inert environment, but occurred in the

presence of methane, even at methane pressures as low as 0.1atm. Higher methane

pressures resulted in more severe crystalline changes and could not be inhibited by the

addition of 3% oxygen. Since OCM occurs at temperatures above 700°C, the catalytically

active species appear to be related to the oxides of its constituent cations, all of which are

known OCM catalysts. LSCF-6428, on the other hand, is somewhat more resistant to

v

methane and can be stabilized at high methane pressures by the addition of 3% oxygen.

At OCM temperatures, neither material catalyzed ethane reactions. Instead, ethane

underwent gas phase oxidative dehydrogenation and thermal cracking reactions.

vi

TABLE OF CONTENTS

AKNOWLEDGEMENTS ................................................................................................. iii

ABSTRACT....................................................................................................................... iv

LIST OF FIGURES .......................................................................................................... vii

INTRODUCTION ...............................................................................................................1

EXPERIMENTAL...............................................................................................................5

Preparation of Catalysts ...........................................................................................5

Microreactor Setup ..................................................................................................5

Dynamic X-Ray Diffraction ....................................................................................8

RESULTS AND DISSCUSIONS........................................................................................9

OCM – Oxidative Coupling of Methane .................................................................9

EODH – Oxidative Dehydrogenation of Ethane ...................................................12

Dynamic X-Ray Diffraction ..................................................................................16

CONCLUSIONS ...............................................................................................................20

REFERENCES ..................................................................................................................22

APPENDIX A. EODH and OCM Summary Tables..........................................................26

APPENDIX B. Conversion, Selectivity and Yield Data for All Runs ..............................30

APPENDIX C. Calibration of Shimadzu 14A Gas Chromatograph .................................46

APPENDIX D. Dynamic X-Ray Diffraction Results ........................................................54

APPENDIX E. BYS Synthesis Procedure .........................................................................62

vii

LIST OF FIGURES

1. Micro-reactor setup

2. C2+ production rate as a function of time in OCM over LSCF-6428 and BYS at

850°C and CH4/O2 = 4/1

3. Effect of CH4/O2 ratio on the CH4 conversion, C2 yield and CO, CO2 mole

fractions for OCM over BYS (GHSV = 30,000h-1)

4. Effect of catalyst on the C2H4 yield for EODH (C2H6/O2 = 8/1)

5. Effect of C2H6/O2 ratio and catalyst on the C2H4 selectivity for EODH

6. Effect of catalyst and C2H6/O2 ratio on the CO, CO2 mole fractions for EODH

7. XRD patterns of BYS exposed to Helium/Argon = 13/1

8. XRD patterns of BYS powder exposed to 10% CH4, 100% CH4 and 97% CH4 +

3% O2

viii

Dedication

This thesis is dedicated to my husband and my son

who helped me with their love and moral support

1

INTRODUCTION

Because of its reasonable cost and abundance, methane (90%), is now generally

recognized as a long-term and cost-effective energy resource for the future. One of the

promising routes for the methane conversion into higher molecular mass hydrocarbons is

the Oxidative Coupling of Methane (OCM). However, due to the low yields obtained,

commercial OCM applications have not been realized to date.

Keller and Bhasin conducted the first OCM study in 1982 [1], in a fixed-bed

reactor. The reactor was operated cyclically, i.e., methane and air were fed one-at-a-time

across the catalyst with short purging flows of nitrogen in between. They observed that

feed cycling produced C2 products (primarily ethylene) in the presence of a number of

metal oxides. The most active catalysts for C2 formation were the oxides of Sn, Pb, Sb,

Bi, Tl, Cd and Mn. Otsuka et al. [2] reported that rare earth metal oxides also have high

catalytic selectivity for the production of C2-hydrocarbons in both the oxidative

dehydrogenation and coupling of methane. Among the rare earth oxides tested, Sm2O3

was the most active and selective catalyst, but the yield of C2-hydrocarbons was less than

12%. Since then, many metal oxides have been found to be effective for OCM [3, 4, 5].

Lunsford and his coworkers reported that lithium-doped magnesium oxide, Li/MgO, by

Achieved a C2 yield of 20% with C2 selectivities higher than 50% [6, 7].

Because of the secondary oxidation of C2 products, C2 yields for OCM on solid

oxide catalysts operated in conventional packed-bed reactor are generally limited to 25%

[3]. Consequently there has been a concentrated effort to developing new types of

reactors that control the availability of oxygen [8, 9, 10, 11]. One of the proposed

strategies to achieve high C2 selectivity at higher methane conversion is to use ceramic

2

membrane reactors instead of conventional packed-bed reactors. Porous ceramic and

dense ion-conducting membranes have both been investigated [12]. Porous membranes

have the advantage of high permeability, but their selectivity is relatively low, whereas

dense membranes have very high selectivity while the permeability is usually low.

Recently, the mixed-conducting oxygen-permeable membranes have received great

attention since they can be synthesized to be perm-selective for only oxygen. However,

the most promising reactor concept is the use of dense ceramic membranes, which are

also catalytic for the OCM reaction. Zirconia [13, 14, 15], substituted perovskites [16, 17,

18, 19], and Bi-based membranes [20-27] all fall into this category.

Elshof et al. [16] used a mixed conducting perovskite-type oxide membrane,

La0.6Sr0.4Co0.8Fe0.2O3 (LSCF-6482), for OCM and achieved C2 selectivities of up to 70%,

but the methane conversion was only 1-3%. Xu and Thomson [17] investigated OCM in a

La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF-6428) membrane reactor with C2 selectivities as high as

50% at methane conversions of less than 3%. C2 selectivity was found to be limited by

high oxygen-ion recombination rates, which not only competes with surface methane

activation, but also leads to the formation of gaseous oxygen and subsequent combustion

of C2 hydrocarbons at the methane side of the membrane. Membrane stability can be a

serious problem with these materials. Using in-situ dynamic X-ray diffraction, Xu and

Thomson showed that LSCF-6428 was stable up to 960°C when exposed to methane with

3% oxygen, but underwent surface etching when exposed to 100% methane at 850°C. Pei

et al. [28], using LSCF-2828 for methane partial oxidation reactions, also observed

membrane instability due to the occurrence of a phase transformation.

3

More recently, promoted bismuth oxides with fluorite-structures have been

extensively studied for use as an OCM catalytic membrane [22-27]. These materials

appear to have superior OCM catalytic activity, relatively good oxygen permeation

properties and have been found to be stable under methane pressures of 0.1atm. Initially

Zeng and Lin [22] performed comparison studies on Bi2O3, Y2O3, and Bi2O3 powders

doped with 25 or 30 mol% Y2O3 (BY25, BY30), and showed that doping yttrium in

Bi2O3 results in increased C2 yields and slightly decreased C2 selectivities. They also

showed that a decrease in the surface area of the bismuth oxide-based ceramics resulted

in higher C2 selectivities and a lower C2 yield. In subsequent studies [22, 23, 24] they

were able to obtain a C2 yield of 18% and a C2 selectivity close to 50% in a co-fed

packed-bed reactor. When the bed was operated in a cyclic mode (oxygen and methane

were fed alternatively), the C2 selectivity improved to 93%, but the C2 yield was less than

5%. In a more recent study [26, 27], Zeng and Lin improved the stability properties of

BY25 using samarium oxide doped into the BY oxide, and obtained an oxygen-ion

conducting material with a stoichiometry of Bi1.5Y0.3Sm0.2O3 (BYS). Using disk-shaped

membrane reactors, the highest C2 yield achieved was 20-27% with C2 selectivity of

about 50-60%. However, all experiments were carried out at relatively low methane

pressures (0.1atm) on the methane side of the membrane.

To date no one has addressed the fate of the ethane product produced by OCM in

a catalytic membrane reactor. If successful, high ethane concentrations would be

expected near the reactor exit and its interaction with the catalytic surfaces is largely

unknown. At these high temperatures, ethane is known to undergo gas-phase-cracking

reactions and catalysts similar to OCM catalysts are known to catalyze the oxidative

4

dehydrogenation of ethane [29]. Therefore we have undertaken a study to examine the

fate of ethane under OCM conditions and to compare the stability and activity of BYS

with that of a standard perovskite material, LSCF-6428.

5

EXPERIMENTAL

Preparation of catalysts

Bi1.5Y0.3Sm0.2O3-δ (BYS) was synthesized using the Glycine-Nitrate Process

described in detail by Chick et al. in 1992 [30]. Stoichiometric amounts of the

corresponding metal nitrates, Bi(NO3)3*5H2O (99.99% Aldrich), Y(NO3)3*6H2O (99.9%

Aldrich) and Sm(NO3)3*6H2O (99.9% Aldrich) were fully dissolved in a dilute nitric acid

solution (10% volume of concentrated HNO3), followed by the addition of Glycine

(98.5% Aldrich) as a combustion fuel. The mixture (3 parts glycine to 1 part metal

cation) was allowed to boil until it underwent autoignition. The yellow and yellow-green

powder ash produced during combustion was then calcinated in air for 4 hours at 900°C

to burn off residual carbon and other impurities. The perovskite material,

La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF-6428), 99.9% purity (surface area 6.0m2/g, d50 < 1 µ m)

was purchased from Praxair Specialty Chemicals.

Microreactor – Temperature Programmed Reaction (TPR)

Catalytic activity experiments, using LSCF-6428 and BYS powders were carried

out in a microreactor system, which behaved as a plug flow reactor (PFR). The micro-

reactor setup is shown in Figure 1. The reactor consisted of a ¼” inner quartz tube with a

gas inlet at the top and gas outlet at the bottom, surrounded by a furnace. Methane

(99.9%) or ethane (99.5%), oxygen (99.9%) and helium (chromatographic grade) were

used as feed gases. A small quantity of catalyst (0.2 grams) was packed in the middle

portion of a quartz wool plug and supported by quartz particles from the top and a

6

Product Gas Outlet to the GC

Reactant Gases

Quartz Packing

Quartz Wool

Furnace

Powder Sample

Thermocouple wire

Fig. 1. Microreactor setup

Quartz Sheath

7

thermocouple from the bottom. The reactor was pre-heated from room temperature to

400°C in flowing helium and the temperature was controlled by a Cole Palmer Digi-

Sense model 89000-00 controller. At 400°C gas mixtures of methane or ethane and

oxygen were diluted with helium and fed into the micro-reactor with the flows regulated

by a multiple mass flow controller (Matheson 8274). The microreactor pressure was

maintained at 1atm, using a high-pressure regulator while methane pressure was held

constant at 0.18atm and ethane pressure was constant at 0.25atm. Once reactant gases

were admitted to the reactor, Temperature Programmed Reaction (TPR) experiments

were conducted by ramping in 50°C increments from 400-900°C or until coking rates

became too high to maintain reactor pressure. The effluents from the micro-reactor were

analyzed by gas chromatography (Shimadzu 14A) using a Porapak N column, 80/100

(6ft*1/8” SS, Alltech Inc.). Helium UHP, with a flow rate of 25ml/min, was used as the

carrier gas. The total analysis time for one sample was about 20 minutes. Each

experimental point was repeated at least once and the typical standard deviation was

about 1-5%. The activity experiments were conducted at 1:0, 4:1 and 8:1 CH4 (C2H6):O2

ratios, for both the BYS and LSCF-6428 catalysts.

Methane (Ethane) conversion was defined as the percentage of methane (ethane)

converted to products and calculated by:

44 CHCHii

ii

YnYnYn

C+ΣΣ

=

where: in is the number of carbon atoms in molecule i and iY is the mole fraction of

species i .

8

The selectivity for the carbon containing product, j , is the percentage of reacted methane

or ethane that forms product j and was calculated by:

∑∑=

ii

jjj Yn

YnS

where: j corresponds to C2H4 in the OCM reaction and to both, C2H6 and C2H4 in the

EODH (Oxidative Dehydrogenation of Ethane) reaction.

The C2 yield is the percentage of total methane or ethane that forms C2 compounds (C2H6

and C2H4), and is the product of methane conversion and selectivity.

The C2+ production rate of C2+ hydrocarbons is defined as:

cat

jj m

YNR ∑

•

=*

where: •

N is the molar flow rate of the exit gas ( µ mol/min) and catm is the catalyst mass

(g).

Dynamic X-Ray Diffraction

In order to monitor the stability of BYS under the reducing conditions associated

with the OCM process, the powder was exposed to flowing methane, and crystalline

phase changes were monitored using in-situ Dynamic X-ray Diffraction (DXRD). The

diffractometer consisted of a Phillips X’Pert system, using Co Kα radiation, and

equipped with a position sensitive detector and an Anton-Parr hot stage. Dynamic XRD

scans were carried out as the temperature was ramped from 700°C to 900°C at 1°C/min,

in flows of 10% CH4 in He, 50% CH4 in He, 100% CH4, 97% CH4 and 3% O2, and an

inert gas consisting of 1/13 ratio argon in helium.

9

RESULTS AND DISCUSSIONS

OCM – Oxidative Coupling of Methane

Both BYS and LSCF-6428 have been successfully formed into oxygen selective

membranes and have comparable oxygen fluxes under similar conditions [27, 18]. Since

catalytic activity must balance oxygen delivery rate in order to maintain high OCM

selectivity, the two powders were compared for their OCM catalytic activity, using the

microreactor described earlier. Figure 2 shows these results in terms of the rate of C2+

products under conditions where conversions were less than 15%. As can be seen, the

OCM rate for BYS is nearly six times greater. This is undoubtedly due to the fact that the

oxides of yttrium and samarium of BYS are known OCM catalysts [31], whereas

lanthana is the only component of LSCF that has known OCM activity [32]. Figure 3

shows the effect of the CH4: O2 ratio on the conversion and yield of OCM over the BYS

powder during TPR, where the temperature was ramped in 50°C increments from 400 to

900°C. These experiments were carried out with a constant methane pressure of 0.18atm

and at a constant gas hourly space velocity (GHSV = volume of gaseous feed per

hour/volume of reactor) of 30,000h-1. As can be seen, the conversions and yield increase

at temperatures above 700°C and the maximum yield of 13% is obtained at 850°C and at

a CH4:O2 ratio of 4:1. These yields are more than twice as high as LSCF-6428 under

comparable conditions [17]. As expected, CO2 is the major carbon byproduct (above

750°C) due to the combustion of either methane or the C2 products, and it increases with

the CH4:O2 ratio. At temperatures below 600°C, there is significant methane conversion,

with CO as the primary product. This is attributed to the partial oxidation of methane to

10

0

50

100

150

200

250

300

350

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00

Time (hr)

C2+

Rat

e

BYS

LSCF

Fig. 2. C2+ production rate as a function of time in OCM over LSCF-6428 and BYS at

850°C and CH4/O2 = 4/1

11

400 500 600 700 800 900

0.00

0.05

0.10

0.15

0.20

0.25

YCO_4/1 YCO2_4/1 YCO_8/1 YCO2_8/1

YC

O, Y

CO

2

Temperature (°C)

400 500 600 700 800 900

0

5

10

15

20

25

30

Conv_4/1 Conv_8/1 Yield_4/1 Yield_8/1

mol

%

Fig. 3. Effect of CH4/O2 ratio on the CH4 conversion, C2 yield and CO, CO2 mole fractions for OCM over BYS (GHSV = 30,000h-1)

12

CO and H2, since water was not detected in the GC analysis. By contrast, LSCF-6428 has

negligible partial oxidation activity at these temperatures, but does catalyze methane

combustion to some small degree.

EODH – Oxidative Dehydrogenation of Ethane

The interaction of ethane with catalysts was examined by exposing the powders to

ethane under different C2H6:O2 ratios, using TPR. In all experiments, the only identifiable

carbon products were ethylene, CO and CO2; that is, there was no evidence of ethane

coupling to higher hydrocarbons. The ethylene yield is plotted as a function of

temperature in Figure 4, for experiments where a gas with a C2H6:O2 ratio of 8:1 (PC2H6 =

0.25atm) was passed over the blank reactor, LSCF-6428 and BYS. As can be seen, the

ethylene yields were essentially the same in all three cases, indicating that ethylene is

formed by the oxidative dehydrogenation of ethane in the gas phase. However, at very

low conversions (temperatures < 600°C), the catalysts have an effect on ethylene

selectivity, as can be seen from Figure 5. That is, LSCF-6428 has some activity for

oxidative dehydrogenation at low temperatures whereas BYS has no activity under these

conditions. But BYS does appear to inhibit the higher temperature gas phase reactions by

about 50°C. At these same low temperatures, LSCF-6428 and BYS also interact with

ethane in different manners (Figure 6). LSCF-6428 appears to promote ethane

combustion, producing almost 100% CO2 and minimal CO. On the other hand, complete

combustion is minimal over BYS and the primary product is CO. The carbon balances in

these runs indicate that, with BYS at temperatures below 600°C, methane also cracks to

13

0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2H

4Y

ield

(%

)

Yield_Blank

Yield_LSCF

Yield_BYS

Fig. 4. Effect of catalyst on the C2H4 yield for EODH (C2H6/O2 = 8/1)

14

0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2H

4 S

ele

ctiv

ity

(%)

Blank_8/1

LSCF_4/1

LSCF_8/1

BYS_4/1

BYS_8/1

Fig. 5. Effect of C2H6/O2 ratio and catalyst on the C2H4 selectivity for EODH

15

400 500 600 700 800 900

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

YCO (LSCF, 8/1) YCO (BYS, 8/1) YCO (LSCF, 4/1) YCO (BYS, 4/1)

YC

O

Temperature (°C)

400 500 600 700 800 900

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14 YCO2 (LSCF, 8/1) YCO2 (BYS, 8/1) YCO2 (LSCF, 4/1) YCO2 (BYS, 4/1)

YC

O2

Fig. 6. Effect of catalyst and C2H6/O2 ratio on the CO, CO2 mole fractions for EODH

16

form coke and hydrogen. This was corroborated by the observance of coke on the spent

catalysts, with the problem being more severe at the 8:1 ratio than the 4:1 ratio.

Dynamic X-Ray Diffraction

Since oxygen ion conducting membranes have been considered for both partial

oxidation and oxidative coupling reactions, the oxygen-lean side of the membrane will be

exposed to high concentrations of reducing hydrocarbons. Thus, there is always the

possibility that the oxide structures will lose oxygen, leading to pitting and/or the

eventual loss of structural stability. Zeng and Lin [27] have reported that BYS

membranes maintain stability in the presence of 0.10atm of methane, for as long as 15

hours. However, reduction of these dense membranes is a surface reaction and therefore

they do not exhibit signs of instability as quickly as powders. For example, Xu and

Thomson [18] reported that LSCF-6428 had stable behavior for over 60 hours when

exposed to 1.0atm of methane at 850°C, but surface pitting and desintering was observed

on the post-reacted membrane. They also reported [17] that exposure of the powder to

1.0atm of methane led to the destruction of the perovskite structure at about 800°C.

Consequently the BYS powder was placed in the DXRD apparatus and exposed to

various methane pressures while the temperature was ramped at 1oC/min. Figure 7 shows

the DXRD results when the BYS powder was exposed to an inert atmosphere and the

temperature was raised to 800°C. As can be seen, the room temperature diffraction

pattern, which was essentially identical to that reported by Zeng & Lin [27], remained the

same over the entire temperature range. The phase change at 730°C that was mentioned

by Zeng & Lin [26] was not observed. Figure 8 shows the results when BYS was exposed

to 0.1 and 1.0atm of methane, respectively. As can be seen there is a sudden crystalline

17

Fig. 7. XRD patterns of BYS exposed to Helium/Argon = 13/1

18

Fig. 8. XRD patterns of BYS powder exposed to 10% CH4, 100%CH4 and 97% CH4 + 3% O2

19

change between 700 and 725°C in both cases (peak at 33.2 °2-Theta). The effect of the

more severe reducing atmosphere (PCH4 = 1atm) is particularly evident at temperatures

above 775°C (i.e., peaks at about 42 °2-Theta). Thus, it is apparent that the reducing

atmosphere destabilizes the powder. However, in an actual membrane operation, oxygen

would be present and could be expected to increase stability. In fact, LSCF-6428 was

previously found to be stable at temperatures up to 900°C in an atmosphere of 97:3

CH4:O2 [17]. Figure 8 shows the results when BYS was exposed to this same atmosphere.

As can be seen, the presence of oxygen does not retard the crystalline change at 725°C,

but it does inhibit further deterioration of the structure at the higher temperatures. It is

interesting to note that OCM activity also begins at about 700°C over BYS. Thus the

BYS activity is due to the products of the phase reaction(s) with methane and not to the

BYS structure itself. As expected, the product peaks formed by the phase reaction at

700°C did not give a definitive match to any of the patterns in the JCPDS (Joint

Committee on Powder Diffraction Standards) database. However, all the peaks were

generally consistent with the oxides of Bi and Y, as well as with non-stoichiometric

phases composed of Bi-Y-O.

20

CONCLUSIONS

In a successful membrane oxidative process, the catalytic properties of the

membrane surface need to be in balance with its ability to deliver oxygen. In comparison

with LSCF-6428, the BYS powder has superior OCM catalytic activity. Under similar

conditions, it has nearly 6 times the rate of C2 production than LSCF-6428 and the

maximum C2+ yields over BYS were more than twice as high as over LSCF-6428. These

superior results can be attributed to the fact that two of the BYS components are known

OCM catalysts, whereas only one of the oxides present in LSCF is known to be active for

OCM.

On the other hand, LSCF-6428 appears to be more stable than BYS under

reducing conditions. Whereas, BYS powder was stable up to 800°C in either an inert or

air atmosphere, DXRD experiments identified a significant phase change between 700°C

and 725°C in the presence of as little as 0.1atm of methane. It is interesting that OCM

catalytic activity with BYS occurs above 725°C, implying that the BYS structure is not

the catalytically active species for OCM. Attempts to identify the products of these phase

changes, were not definitive although the XRD spectra were consistent with a number of

the oxides and binary oxides of the constituent cations. Whereas LSCF-6428 was also

unstable in 1.0atm of methane, it was stabilized to 900°C by the addition of 3% oxygen

in methane. However, when the identical experiment was conducted with BYS, the phase

change at 700-725°C still took place and there was only a slight inhibition of further

crystalline changes at higher temperatures.

21

The behavior of the two materials was also evaluated in the presence of

ethane/oxygen mixtures since ethane is a major product of the OCM reaction. It was

found that, at OCM temperatures (> 750°C), the catalysts had a negligible influence on

ethane activity. Rather, ethane was found to undergo gas phase reactions involving

thermal cracking, and to a lesser extent, oxidative dehydrogenation, with the primary

product being ethylene in both cases. There was no evidence of oxidative coupling of

ethane over either of the powders.

The two materials behaved somewhat different at temperatures below 600°C. In

the presence of methane/oxygen mixtures, BYS demonstrated activity for partial

oxidation yielding CO and H2 as opposed to LSCF-6428, which has been reported to

have negligible partial oxidation activity at these temperatures. In the presence of

ethane/oxygen, LSCF-6428 shows some selectivity for ethylene as well as for complete

combustion, whereas BYS had no ethylene selectivity but promoted partial combustion to

CO and H2O. In addition, when oxygen free ethane was passed over these materials,

LSCF-6428 tended to coke to a far greater extent than BYS.

22

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23

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[11] Jiang, Y.; Yentekakis, I.V.; Vayenas, C.G. Methane to ethylene with 85% yield in a

gas-recycle electrocatalytic reactor separator. Science 1995, 264, 1563.

[12] Julbe, A.; Farrusseng, D.; Guizard, C. Porous ceramic membranes for catalytic

reactors–overview and new ideas. J. of Membr. Sci. 2001, 181, 3.

[13] Otsuka, K.; Yokoyama, S.; Morikawa, A. Catalytic activity–and selectivity–control

for oxidative coupling of methane by oxygen–pumping through yttria–stabilized

zirconia. Chem. Lett. 1985, 319.

[14] Eng, D.; Stoukides, M. Catalytic and electrocatalytic methane oxidation with solid

membranes. Catal. Rev. Sci. Eng. 1991, 9, 47.

[15] Eng, D. The partial oxidation of methane in a solid electrolyte cell. Ph.D. Thesis

Tufts University 1990.

[16] Elshof, J.E.; Bouwmeester, H.J.M.; Verweij, H. Oxidative coupling of methane in a

mixed-conducting perovskite membrane reactor. Appl. Catal. A: General 1995, 130,

195.

[17] Xu, S.; Thomson, W. Ion-Conducting Perovskite Membranes for the Oxidative

Coupling of Methane. AIChE Journal 1997, 43, 2731.

[18] Xu, S.; Thomson, W. Stability of La0.6Sr0.4Co0.2Fe0.8O3-δ Perovskite Membranes in

Reducing and Nonreducing Environments. Ind. Eng. Chem. Res. 1998, 37, 1290.

[19] Xu, S.; Thomson, W. Oxygen permeation rates through ion-conducting perovskite

membranes. Chem. Eng. Sci. 1999, 54, 3839.

24

[20] Guo, X.M.; Hidajat, K.; Ching, C.B.; Chen, H.F. Oxidative coupling of methane in a

solid oxide membrane reactor. Ind. Eng. Chem. Res. 1997, 36, 3576.

[21] Hayakawa, T.; Orita, H.; Shimizu, M.; Takehira, K.; Anderson, A.G.; Nomura, K.;

Ujihira, Y. Oxidative coupling of methane over LaCoO3-δ . Catal. Lett. 1992, 16,

359.

[22] Zeng, Y.; Lin, Y.S. Catalytic properties of yttria doped bismuth oxide ceramics for

oxidative coupling of methane. Appl. Catal. 1997, 159, 101.

[23] Zeng, Y.; Lin, Y.S. Stability and surface catalytic properties of fluorite–structured

yttria–doped bismuth oxide under reducing environment. J. Catal. 1999, 182, 30.

[24] Zeng, Y.; Lin, Y.S. Oxygen permeation and oxidative coupling of methane in yttria

doped bismuth oxide membrane reactor. J. Catal. 2000, 193, 58.

[25] Zeng, Y.; Lin, Y.S. Synthesis and properties of copper and samarium doped yttria–

bismuth oxide powders and membranes. J. Mat. Sci. 2001, 1271.

[26] Zeng, Y.; Akin, F.T.; Lin, Y.S. Oxidative coupling of methane on fluorite–structured

samarium–yttrium–bismuth oxide. Appl. Catal. 2001, 213, 33.

[27] Zeng, Y.; Lin, Y.S. Oxidative coupling of methane on improved bismuth oxide

membrane reactors. AIChE. Journal 2001, 47, 436.

[28] Pei, S.; Kleefisch, M.S.; Kobylinski, T.P.; Faber, J.; Udovich, C.A.; Zhang-McCoy,

V.; Dabrowski, B.; Balachandran, U.; Mieiville, R.L.; Poeppel, R.B. Failure

mechanisms of ceramic membranes reactors in partial oxidation of methane to

synthesis gas. Catal. Lett. 1995, 30, 201.

25

[29] Choudhary, V.R.; Mulla, S.A.R. Energy efficient simultaneous oxidative conversion

and thermal cracking of ethane to ethylene using supported BaO/La2O3 catalyst in the

presence of limites O2. Appl. Energy 2001, 68, 377.

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Glycine–nitrate combustion synthesis of oxide ceramics powders. Mat. Lett. 1990, 10,

6.

[31] Buyeskaya, O. V.; Rothaemel, M.; Zanthoff, H.W.; Baerns, M. Transient studies on

the role of oxygen activation in the oxidative coupling of methane over Sm2O3,

Sm2O3/MgO and MgO catalytic surfaces. J. Catal. 1994, 150, 71.

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1995, 155, 106.

APPENDIX A

EODH AND OCM SUMMARY TABLES

Table A-1. OXIDATIVE DEHYDROGENATION OF ETHANE (EODH) RUN SUMMARY TABLE

Conversion C2H6 (%) Selectivity C2H4 (%) RUN Date

GAS Ratio

CAT. TEMP PGM (°C)

600°C 700°C Last

Max (°C)

600°C 700°C Last Max (°C)

COMMENTS

1 09/20/01

0.25 atm Ethane

LSCF-6248 400-850 0.0 10.89 100 100 (850)

- 100 89.61 100 (650)

Coke

2 09/25/01

0.25 atm Ethane

(C2/O2 = 8)

LSCF-6248 400-650 4.71 - 8.9 11.14 (650)

39.30 - 65.49 71.91 (650)

No coke, but catalyst deactivated

3 10/12/01

0.25 atm Ethane

(C2/O2 = 8)

LSCF-6248 400-800 5.25 29.98 77.23 77.23 (800)

31.19 88.11 72.41 88.11 (700)

Run terminated at 800°C, coke

4 11/20/01

0.25 atm Ethane

(C2/O2 = 8)

Blank 500-850 4.73 29.11 90.64 90.92 (850)

0 87.45 87.35 89.76 (750)

No coke

5 01/02/02

0.25 atm Ethane

Blank 400-850 0.0 6.75 87.96 88.18 (850)

- 100 94.79 100 (650-700)

Coke

6 01/04/02

0.25 atm Ethane

(C2/O2 = 8)

LSCF-6248 400-800 4.41 27.48 79.37 79.37 (800)

31.56 80.88 78.79 80.62 (750)


7 01/07/02

0.25 atm Ethane

(C2/O2 = 8)

LSCF-6248 400-800 4.81 29.33 75.16 75.16 (800)

33.73 84.39 76.40 84.39 (700)


8 01/09/02

0.25 atm Ethane

(C2/O2 = 4)

LSCF-6248 400-750 10.47 45.07 63.86 63.86 (750)

31.03 79.07 77.69 79.07 (700)

Run terminated at 750°C, less coke than for

8/1 9

01/15/02 0.25 atm Ethane

(C2/O2 = 8)

BYS 400-900 4.31 20.89 97.97 97.97 (900)

0 89.19 77.5 94.12 (750)

Water peak at 850C, pressure increase; BYS

melted by EOR 10

01/24/02 0.25 atm Ethane

(C2/O2 = 4)

BYS 400-900 8.39 12.20 95.54 95.66 (900)

0 35.68 78.24 87.06 (750)

Less coke, no pressure, at 800°C unknown peak,

at 900°C water peak

27

Table A-2. OXIDATIVE COUPLING OF METHANE (OCM) RUN SUMMARY TABLE

Conversion CH4 (%) Selectivity C2 (%) RUN Date

GAS Ratio

CAT. TEMP PGM

°C 600°C 700°C Last

Max (°C)

600°C 700°C Last Max (°C)

COMMENTS

11 02/05/02

0.18 atm Methane

BYS 400-900 0 0 0 0 - - - - Run terminated at 900°C, small amount of

coke, no pressure 12

02/07/02 0.18 atm Methane

(C/O2 = 4)

BYS 400-900 21.7 21.64 25.11 28.05 (800)

0 0 34.19 45.29 (850)

Run terminated at 900°C, the smallest quantity of coke, no

pressure 13


(C/O2 = 8)

BYS 400-900 12.22 11.74 13.64 17.52 (800)

0 0 31.8 57.64 (800)

Run terminated at 900°C, no pressure, less

coke 14


Blank 400-900 0 0 0 0 - - - - Run terminated at 900°C, no pressure, less

coke 15


(C/O2 = 8)

Blank 400-900 12.10 12.12 14.70 14.7 (900)

0 0 25.25 25.25 (900)

Run terminated at 900°C, no pressure, no

coke

28

Table A-3. EODH PERFORMANCE OVER BYS AND LSCF-6428 POWDERS

C2H6 Conversion (%) C2H4 Selectivity (%) Run C2H6/O2

Ratio

Catalyst Initial Reaction

Temp. (°C)

Coke

blockage

Temp. (°C)

650°C 750°C 850°C 650°C 750°C 850°C

1 1/0 Blank 650 850 1.00 28.28 88.10 100.00 98.85 94.76

2 8/1 Blank 500 850 7.92 51.60 90.78 46.24 89.57 87.23

3 1/0 LSCF-6428 650 850 3.11 35.44 100.00 100.00 100.00 89.37

4 8/1 LSCF-6428 400 800 8.36 53.29 - 63.57 80.26 -

5 4/1 LSCF-6428 400 750 16.53 63.43 - 58.89 77.77 -

6 8/1 BYS 400 900 5.73 41.99 91.64 31.75 94.05 88.38

7 4/1 BYS 400 900 8.89 35.85 85.48 5.52 86.70 77.26

Table A-4. OCM PERFORMANCE OVER BYS

CH4 Conversion (%) C2 Selectivity (%) Run CH4/O2

Ratio

Catalyst Initial Reaction

Temp. (°C)

Final Temp.

(°C) 650°C 750°C 850°C 650°C 750°C 850°C

8 1/0 Blank - 900 0.00 0.00 0.00 0.00 0.00 0.00

9 8/1 Blank 400 900 12.10 12.00 13.15 0.00 0.00 12.19

10 1/0 BYS - 900 0.00 0.00 0.00 0.00 0.00 0.00

11 8/1 BYS 400 900 12.11 14.48 15.42 0.00 28.97 45.09

12 4/1 BYS 400 900 21.73 24.03 27.59 0.00 18.24 45.02

29

APPENDIX B

CONVERSION, SELECTIVITY AND YIELD DATA FOR ALL RUNS

31

Experiment 1-09/20/2001

Reaction conditions:

- Catalyst = LSCF-6428

- Pressure = 1 atm

- Temperature range = 400-850°C

- C2H6/O2 = 1/0

cc/min C2H6 cc/min He

20.47 78.6

Temp. (°C)

C2H6 Conv. (%) C2 Sel. (%) C2 Yield (%)

400 0.00 - 0.00 425 0.00 - 0.00 450 0.00 - 0.00 475 0.00 - 0.00 500 0.00 - 0.00 600 0.00 - 0.00 650 3.11 100.00 3.11 700 11.80 100.00 11.80 750 35.44 100.00 35.44 800 73.16 95.51 69.88 850 100.00 89.37 89.37

C2H6 conversion - temperature

0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2H

6 C

on

vers

ion

(%

)

C2 selectivity - temperature

0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Sel

ecti

vity

(%

)

C2 yield - temperature

0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Yie

ld (

%)

32

Experiment 2-09/25/2001 Reaction conditions:


- Pressure = 1 atm


- C2H6/O2 = 8/1

cc/min O2 cc/min C2H6 cc/min He

5 39.5 177

Temp. (°C)


400 0.00 - 0.00 450 4.84 14.91 0.72 500 4.16 16.53 0.69 550 4.20 18.44 0.77 600 4.65 28.43 1.32 650 11.14 71.91 8.01 650 10.61 71.35 7.57 650 10.60 72.01 7.64 650 10.41 68.76 7.16 650 10.02 68.74 6.89 650 9.30 67.54 6.28 650 9.25 67.57 6.25 650 9.28 66.28 6.15 650 9.30 65.96 6.13 650 9.11 65.78 5.99 650 9.09 65.25 5.93 650 9.04 64.54 5.83 650 8.90 65.49 5.83


0

2

4

6

8

10

12

400 500 600 700 800 900 1000

Temperature (°C)

C2H

6 C

on

vers

ion

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Sel

ecti

vity

(%

)


0

1

2

3

4

5

6

7

8

9

10

400 500 600 700 800 900 1000

Temperature (°C)

C2

Yie

ld (

%)

33



- Pressure = 1 atm


- C2H6/O2 = 8/1


4.89 38.22 171.43

Temp (°C)


400 4.11 14.49 0.60 450 4.06 16.12 0.65 500 4.1 18.28 0.75 550 4.17 20.06 0.84 600 4.85 30.39 1.47 650 8.11 55.61 4.51 700 29.52 86.02 25.39 750 53.89 82.24 44.32 800 77.23 72.41 55.92


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Tempera ture (°C)

C2H

6 C

on

vers

ion

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Sel

ecti

vity

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Yie

ld (

%)

34


- Blank

- Pressure = 1 atm


- C2H6/O2 = 8/1


5.11 40.27 175.32

Temp (°C)

C2H6 Conv, (%) C2 Sel. (%) C2 Yield (%)

500 4.38 0.00 0.00 550 4.72 0.00 0.00 600 4.73 0.00 0.00 650 7.92 46.24 3.66 700 28.95 87.75 25.40 750 51.60 89.57 46.22 800 73.73 89.58 66.05 850 90.78 87.23 79.19


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2H

6 C

on

vers

ion

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Sel

ecti

vity

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Yie

ld (

%)

35


- Blank

- Pressure = 1 atm


- C2H6/O2 = 1/0

cc/min C2H6 cc/min He

38.96 171.43

Temp. (°C)

C2H6 Conv. (%) C2 Sel (%) C2 Yield (%)

400 0.00 - 0.00 450 0.00 - 0.00 500 0.00 - 0.00 550 0.00 - 0.00 600 0.00 - 0.00 650 1.00 100.00 1.00 700 6.25 100.00 6.25 750 28.28 98.85 27.95 800 63.01 97.54 61.46 850 88.10 94.76 83.48


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2H

6 C

on

vers

ion

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Sel

ecti

vity

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Yie

ld (

%)

36

Experiment 6-010402 Reaction conditions:


- Pressure = 1 atm


- C2H6/O2 = 8/1


4.6 38.22 171.43

Temp (°C)


400 3.67 16.71 0.61 450 3.6 17.35 0.62 500 3.63 18.42 0.67 550 3.82 22.33 0.85 600 4.31 31.54 1.36 650 7.62 62.46 4.76 700 27.29 80.48 21.96 750 50.58 80.52 40.73 800 79.37 78.79 62.54


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2H

6 C

on

vers

ion

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Sel

ecti

vity

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Yie

ld (

%)

37



- Pressure = 1 atm


- C2H6/O2 = 8/1


4.98 39.74 168.75

Temp. (°C)


400 3.88 15.45 0.60 450 3.92 16.78 0.66 500 4.00 18.44 0.74 550 4.16 21.97 0.91 600 4.79 33.64 1.61 650 8.36 63.57 5.31 700 29.07 84.21 24.48 750 53.29 80.26 42.77 800 75.16 76.40 57.42


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2H

6 C

on

vers

ion

(%

)

C2 selectivity- temperature

0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Sel

ecti

vity

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Yie

ld (

%)

38



- Pressure = 1 atm


- C2H6/O2 = 4/1


10 38.96 189.74

Temp (°C)


400 8.48 13.89 1.18 450 8.52 14.16 1.21 500 8.69 15.68 1.36 550 9.17 19.89 1.82 600 10.44 30.37 3.17 650 16.53 58.89 9.73 700 45.07 79.07 35.64 750 63.43 77.77 49.33


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2H

6 C

on

vers

ion

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Sel

ecti

vity

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Yie

ld (

%)

39


- Catalyst = BYS

- Pressure = 1 atm


- C2H6/O2 = 8/1


4.8 38.71 166.67

Temp (°C)

C2H6 Conv (%) C2 Sel. (%) C2 Yield (%)

400 4.15 0.00 0.00 450 4.09 0.00 0.00 500 4.15 0.00 0.00 550 4.16 0.00 0.00 600 4.02 0.00 0.00 650 5.73 31.75 1.82 700 20.78 88.44 18.38 750 41.99 94.05 39.49 800 70.75 89.54 63.35 850 91.64 88.38 80.99 900 97.97 77.50 75.93


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2H

6 C

on

vers

ion

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Sel

ecti

vity

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Yie

ld (

%)

40


- Catalyst = BYS

- Pressure = 1 atm


- C2H6/O2 = 4/1


9.97 38.22 193.55

Temp (°C)


400 8.84 0.00 0.00 450 8.55 0.00 0.00 500 8.53 0.00 0.00 550 8.47 0.00 0.00 600 8.39 0.00 0.00 650 8.89 5.52 0.49 700 12.15 35.68 4.34 750 35.85 86.70 31.08 800 68.32 80.85 55.24 850 85.48 77.26 66.04 900 95.60 78.40 74.95


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2H

6 C

on

vers

ion

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Sel

ecti

vity

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Yie

ld (

%)

41

Experiment 11_020502 Reaction conditions:

- Catalyst = BYS

- Pressure = 1 atm


- CH4/O2 = 1/0

cc/min CH4 cc/min He

49.59 50.94

Temp. (°C) CH4 Conv.

(%) C2 Sel. (%) C2 Yield (%) 400 0.00 0.00 0.00 450 0.00 0.00 0.00 500 0.00 0.00 0.00 550 0.00 0.00 0.00 600 0.00 0.00 0.00 650 0.00 0.00 0.00 700 0.00 0.00 0.00 750 0.00 0.00 0.00 800 0.00 0.00 0.00 850 0.00 0.00 0.00 900 0.00 0.00 0.00

CH4 conversion - temperature

0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

CH

4 C

on

vers

ion

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Sel

ecti

vity

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Yie

ld (

%)

42


- Catalyst = BYS

- Pressure = 1 atm


- CH4/O2 = 4/1

cc/min O2 cc/min CH4 cc/min He

10.07 40.54 50.94

Temp (°C)

CH4 Conv. (%) C2 Sel. (%) C2 Yield (%)

400 22.22 0.00 0.00 450 21.87 0.00 0.00 500 21.88 0.00 0.00 550 21.82 0.00 0.00 600 21.65 0.00 0.00 650 21.73 0.00 0.00 700 21.59 0.00 0.00 750 24.03 18.24 4.38 800 27.81 44.15 12.28 850 27.59 45.02 12.42 900 24.98 34.38 8.59


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

CH

4 C

on

vers

ion

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Sel

ecti

vity

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Yie

ld (

%)

43


- Catalyst = BYS

- Pressure = 1 atm


- CH4/O2 = 8/1

cc/min O2 cc/min CH4 cc/min He 4.98 40 46.51

Temp (°C)


400 12.75 0 0.00 450 12.3 0 0.00 500 12.17 0 0.00 550 12.15 0 0.00 600 12.16 0 0.00 650 12.11 0 0.00 700 11.67 0 0.00 750 14.48 28.97 4.19 800 17.44 57.58 10.04 850 15.42 45.09 6.95 900 13.64 31.8 4.34


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

CH

4 C

on

vers

ion

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Sel

ecti

vity

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Yie

ld (

%)

44


- Blank

- Pressure = 1 atm


- CH4/O2 = 1/0

cc/min CH4 cc/min He

40 40.54

Temp. (°C)


400 0.00 0.00 0.00 450 0.00 0.00 0.00 500 0.00 0.00 0.00 550 0.00 0.00 0.00 600 0.00 0.00 0.00 650 0.00 0.00 0.00 700 0.00 0.00 0.00 750 0.00 0.00 0.00 800 0.00 0.00 0.00 850 0.00 0.00 0.00 900 0.00 0.00 0.00


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

CH

4 C

on

vers

ion

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Sel

ecti

vity

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Yie

ld (

%)

45


- Blank

- Pressure = 1 atm


- CH4/O2 = 8/1

cc/min O2 cc/min CH4 cc/min He

5.01 40 46.51

Temp (°C)


400 12.46 0 0.00 450 12.19 0 0.00 500 12.1 0 0.00 550 12.16 0 0.00 600 12.07 0 0.00 650 12.1 0 0.00 700 12.03 0 0.00 750 12 0 0.00 800 11.94 0 0.00 850 13.15 12.19 1.60 900 14.66 25.17 3.69


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

CH

4 C

on

vers

ion

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Sel

ecti

vity

(%

)


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000

Temperature (°C)

C2

Yie

ld (

%)

APPENDIX C

CALIBRATION OF SHIMADZU 14A GAS CHROMATOGRAPH

47

The possible product gases in the EODH reaction are CO, CO2, C2H4, C2H6,

C3H6, C3H8, cis-transC4H8, and n-C4H10. The possible product gases in the OCM reaction

are CO, CO2, C2H4, C2H6, C3H6, and C3H8.

The purpose of calibration is to correlate the concentration with the GC peak area

for each gas.

The GC used a Porapak N column, 80/100 (6ft*1/8”” SS, Alltech Inc.) with the

flow rate of the carrier gas, Helium UHP set at 25cc/min. The gas chromatograph

column, which was ramped at 5°C/min from 30 to 80°C, separated all gases and the total

analysis time for one sample was about 20 minutes. Each experimental point was

repeated at least once.

Mixtures of C2H6 diluted in He with different proportions of O2, CO, CO2, C2H4,

C2H6, C3H6, C3H8, cis-transC4H8, n-C4H10 were measured in order to determine the K-

values. K-value for an i component is defined as:

i

ii areapeak

wtK

).(.%)(

= .

The C2H6 K-value was obtained from the average of all K-values measured in each of the

nine calibration experiments. A calibration experiment consisted of waiting until the

30°C initial temperature was reached and then opening the sample valve for 10 seconds.

Table C-1 shows the K-values of various gases and the individual K-values for

C2H6 calculated from K-values for C2H6 that correspond to each mixture. Another method

to calculate KC2H6 is to correlate by regression all data points available for C2H6.

48

Table C-1

Gas Kgas KC2H6 Residence time (s)

O2 4.9431E-04 4.1957 0.028-0.03

CO 3.9431E-04 4.0586 0.034-0.045

CO2 4.4201E-04 3.6797 0.78-1.01

CH4 3.8196E-04 4.5994 0.11-0.15

C2H4 3.5234E-04 3.7405 1.25-1.38

C3H6 3.8659E-04 3.9018 5.5-6.6

C3H8 6.2412E-04 4.1675 6.5-7.17

c-tC4H8 3.2890E-04 3.6230 14.5-15.5

nC4H10 4.3585E-04 3.1694 15.5-16.02

C2H6 Averages 3.9040 1.38-1.6 (C2H6)

The plots given below represent the correlation of concentration for each gas with

peak area.

49

O2

0

10

20

30

40

50

0 20000 40000 60000 80000 100000

Peak Area

wt.

%

CO

0

10

20

30

40

50

60

70

0 50000 100000 150000 200000

Peak Area

wt.

%

50

CO2

0

10

20

30

40

50

60

70

80

0 50000 100000 150000 200000

Area Peak

wt.

%

CH4

0

10

20

30

40

50

60

0 50000 100000 150000

Peak Area

wt.

%

51

C2H4

0

10

20

30

40

50

60

70

80

0 50000 100000 150000 200000 250000

Peak Area

wt.

%

C2H6

0

10

20

30

40

50

60

70

80

90

100

0 50000 100000 150000 200000

Peak Area

wt%

52

C3H6

0

10

20

30

40

50

0 20000 40000 60000 80000 100000

Peak Area

wt.

%

C3H8

0

10

20

30

40

50

0 20000 40000 60000 80000

Peak Area

wt.

%

53

cis-trans C4H8

0

10

20

30

40

50

0 5000 10000 15000

Peak Area

wt.

%

n C4H10

0

10

20

30

40

50

60

70

80

0 50000 100000 150000 200000

Peak Area

wt.

%

APPENDIX D

DYNAMIC X-RAY DIFFRACTION RESULTS

0

5

10

15

20

25

30

35

20 30 40 50 60 70 80 90

°2 Theta

cou

nts

/s

XRD patterns of BYS in house and literature data [27]

55

XRD patterns of BYS exposed to room atmosphere

56

XRD patterns of BYS powder exposed to 10% CH4 in He

57


58


59

XRD patterns of BYS exposed to 97% CH4 and 3% O2

60

XRD patterns of BYS exposed to Helium/Argon = 13/1

61

APPENDIX E

BYS SYNTHESIS PROCEDURE

63

BYS SYNTHESIS PROCEDURE

To synthesize the BYS powder, 25g of the corresponding metal nitrates,

Bi(NO3)3*5H2O, Y(NO3)3*6H2O, and Sm(NO3)3*6H2O, were fully dissolved in 10%

volume nitric acid. Stoichiometric quantities of the metals were then combined with

glycine at a ratio of 3 parts glycine to 1 part total metals, and added to a 4L beaker. The

beaker was covered with stainless steel 325 mesh and secured with a wire; to prevent

powder entrainment once the combustion synthesis reaction was initiated. The resulting

transparent solution was heated while stirring to a temperature of about 90-110°C. The

experiment was carried out in a fume hood due to the emission of hazardous chemicals.

After 20 minutes (set point of the hot plate = 7), autoignition of the sample occurred. The

yellow and black ash produced during combustion was collected and then calcinated with

air (130cc/min) by ramping the temperature at 5°C/min to 900°C and holding at 900°C

for 4 hours to obtain the dark yellow powder (BYS). Comparison of the XRD scans of

the powder with those previously reported for BYS, were in good agreement.

The BYS powder was formed into disks by a combination of pressing and

sintering, following the procedure used by Zeng’s group at the University of Cincinnati

[25]. First, 2.7 grams of BYS powder was poured into a stainless steel mold and pressed

into a disk with a uniaxially pressure of 15,000 psi. The formed BYS disk was then

sintered at different temperatures 800°C, 1000°C, 1050°C and 1200°C and for different

times, using heating and cooling rates of 5°C/min. The sintering temperature and time

were both found to have a significant effect on the properties of the final disks. In

addition, some experiments were performed where small quantities of water (2-20% wt

of dried powder) were added in an attempt to improve the initial pressed form of the

64

SSiinntteerriinngg TTeemmppeerraattuurree,, °°CC

SSiinntteerriinngg TTiimmee,, hhrr

880000// 11220000

11000000// 11220000 11220000

22

55

2244

SSiinntteerriinngg TTeemmppeerraattuurree,, °°CC

11005500 11220000

HH22OO%% AAddddeedd ttoo PPoowwddeerr

00%%

1155%%

65

powder, in hopes that the subsequent sintering step could achieve a crack-free disk.

Neither Zeng’s procedure or any of the other variations that were attempted produced a

disk with the desired properties. Most of the sintered disks either cracked or had

exfoliated surfaces.

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