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Applied Catalysis A: General 441– 442 (2012) 99– 107
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
j ourna l ho me page: www.elsev ier .com/ locate /apcata
reparation and evaluation of hydrotreating catalysts based on activated carbonerived from oil sand petroleum coke
u Shia,∗, Jinwen Chena, Jian Chenb, Robb A. Macleodb, Marek Malacb
Natural Resources Canada, CanmetENERGY-Devon, One Oil Patch Drive, Devon, AB, T9G 1A8, CanadaNational Institute for Nanotechnology, National Research Council Canada, 11421 Saskatchewan Drive, Edmonton, AB, T6G 2M9, Canada
r t i c l e i n f o
rticle history:eceived 19 May 2012eceived in revised form 13 July 2012ccepted 14 July 2012vailable online 20 July 2012
eywords:il sand petroleum (OSP) cokectivated carbon (AC)ydrotreatingeavy vacuum gas oil (HVGO)
a b s t r a c t
Novel Ni–Mo/activated carbon (AC) hydrotreating catalysts were prepared and evaluated for upgradingheavy vacuum gas oil (HVGO). The AC supports were derived from Alberta oil sand petroleum coke, i.e.fluid coke and/or delayed coke, hereafter referred to as OSP coke, through a chemical process. The BETsurface area was as high as 2194 m2/g for the fluid coke derived AC and 2357 m2/g for the delayed cokederived AC. Both ACs contained a large number of micropores with pore volume as high as 1.2 cm3/g. Niand Mo based active component precursors could be easily loaded on the activated carbon supports bychemical impregnation of nickel nitrate and ammonium molybdate followed by calcination in nitrogenat 773 K without further modification or oxidation treatment to the activated carbons. Scanning electronmicroscopy (SEM) observation showed highly porous surface structure of the bare activated carbon sup-ports and well dispersed metal (oxide) precursor nanoparticles of 30–50 nm loaded on the AC supports.For comparison, two reference catalysts were also prepared by the same procedure but using commercialactivated carbon and porous alumina as supports. After catalyst activation by sulfiding, the hydrotreatingperformance of the prepared catalysts was evaluated in a magnetically stirred autoclave with a HVGOfeedstock to examine their hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities. Twocommercial hydrotreating catalysts were also tested and compared under similar conditions with thesame feed. The results showed that the catalysts based on the activated carbon supports prepared fromOSP coke had better hydrotreating performance than the other catalysts. Scanning transmission elec-tron microscopy (STEM) characterization of the catalysts after activation showed that small particles of
nanostructure (2–5 nm in size) were evenly embedded in the carbon matrix except for some bigger par-ticles that were located on the catalyst surface. Energy dispersive X-ray (EDX) spectroscopy revealed thatthese particles were composed of Ni, Mo and S elements. The dispersed nanoparticles formed the activesites and were responsible for the observed high HDS and HDN activity. Elemental analysis and surfacecharacterization of the spent catalysts showed that the formation of coke precursors was favored on thest, w
alumina supported cataly. Introduction
As the world remaining accessible crude oil become heaviernd more sour, there is an urgent need for improved technolo-ies to process such crudes to produce clean transportation fuels1]. Catalytic hydroprocessing technology is well established inonventional refineries worldwide. Due to the high contents ofulfur, nitrogen, asphaltenes and heavy metals (nickel and vana-
ium) in heavy feedstocks [2], existing catalysts and technologiesave to be modified or new ones have to be developed to keepace with more stringent environmental regulations, including∗ Corresponding author. Tel.: +1 780 987 8703; fax: +1 780 987 5349.E-mail address: [email protected] (Y. Shi).
926-860X/$ – see front matter Crown Copyright © 2012 Published by Elsevier B.V. All rittp://dx.doi.org/10.1016/j.apcata.2012.07.014
hich resulted in catalyst deactivation.Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
emissions from hydrocarbon fuel use, such as SOx, NOx, and CO2[3,4]. Hydrotreating catalysts are used in refineries to catalyticallyremove S, N and metals, and to saturate aromatic compounds. Cur-rently, alumina-supported hydrotreating catalysts are commonlyused because of the good mechanical and textural specifics of alu-mina [5,6]. However, sulfidation of alumina supported metal oxidesis always incomplete due to the strong metal–support interactions(SMSI) present in the catalyst sulfidation step, which is a signif-icant drawback of alumina [7–9]. In addition, alumina supportedcatalysts suffer from deactivation caused by coking and nitrogencompounds, and heavy metal deposition when heavy oil is treated[2,10–14]. In the past decades much effort has been paid either
to modify existing catalysts by developing new synthesis meth-ods through addition of new promoting species, or to develop newsupports based catalysts to improve hydrotreating performance forheavy feedstocks [15–20].ghts reserved.
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00 Y. Shi et al. / Applied Catalysis
Activated carbon (AC) possesses high microporosity and sur-ace area. It has attracted considerable attention recently as aossible candidate for replacing conventional alumina support forpgrading heavy gas oil [2,21–23]. Activated carbon supportedydrotreating catalysts also have less sensitivity to nitrogen com-ounds, good resistance to coke deposition and easy recovery ofetal components from spent catalysts, giving it advantages over
-Al2O3 for processing heavy petroleum feedstocks [13,23–25].revious studies have demonstrated good hydrotreatment activ-ties toward sulfur removal with AC supported Mo, Ni–Mo oro–Mo hydrotreating catalysts [24–26]. However they have noteen widely applied in commercial operations. Other promis-
ng hydrodesulfurization (HDS) results were also reported eithery applying activated carbon (or mesoporous carbon) throughybridization with alumina support or by using activated carbonolely as catalyst support [19,26–28]. Since activated carbon con-ains much less polar oxygen containing species than alumina,uring sulfidation, the much weaker interaction between the sup-ort surface and metals favors the formation of the Type II highctive sites (Ni–Mo–S II) [29–31]. Furthermore, since cost is anmportant factor in catalyst selection for refineries, the relativelyow production cost of activated carbon as hydrotreating catalystupport and easy recovery of metals by burning off the spent cata-yst provide additional advantages.
Recently, although activation of petroleum coke has beeneported by several research groups with different activationrocesses, no efficient method has yet been demonstrated foronverting Alberta OSP coke (both fluid coke and delayed coke)nto porous carbon materials with relatively high surface area andorosity [32–36]. Since OSP coke contains more impurities, such as
(>6 wt%) and heavy metals, than conventional coke, the activationnd application of it are more challenging [10,37]. Sulfur content inhe AC can potentially limit its application as a hydrogenation cata-yst support for supporting active metal components, especially forrecious metals. On the contrary, transition metal sulfide Ni(Co)S oro(W)S hydroprocessing catalysts usually require pre-sulfidationith sulfur containing compounds (such as H2S) to activate the cat-
lyst precursor. Therefore, sulfur is helpful, rather than harmful, inhe activation process of this type of hydrotreating catalysts.
Although activated carbon has a number of properties whichre favorable for hydrotreating heavy petroleum feedstocks, itsow mechanical strength and weak surface functionality might behe potential hurdles for industrial/commercial application. In the
ean time alumina, due to its high mechanical strength and sur-ace functionality, and mature commercial production technology,ill continue to be the dominating commercial hydrotreating cat-
lyst support in the foreseeable future. This paper explores theeasibility of developing low cost hydrotreating catalysts based onctivated carbon derived from Alberta OSP coke and examines theirydroprocessing performance using heavy vacuum gas oil (HVGO)s the testing feed. The catalytic activity of the prepared cata-ysts and the effects of catalyst support have been evaluated byonducting comparative performance tests with a commercial ACupported catalyst, an alumina supported catalyst, and two com-ercial hydrotreating catalysts supported on �-Al2O3.
. Experimental
.1. Materials
Dry fluid coke (F-coke) and delayed coke (D-coke) were used
irectly without further pretreatment. A reference mesoporousommercial AC (CAC) was purchased from Aldrich Chemical Com-any, Inc. and ground into similar particle size range (60–200esh) as that of AC samples converted from the OSP coke. Aneral 441– 442 (2012) 99– 107
mesoporous commercial �-Al2O3 (PURALOX HP 14/150) pow-der was provided by Sasol Germany GmbH and used as anotherreference catalyst support without any treatment. Since HVGOwas used as feed in this study to evaluate catalyst activity, themesoporous CAC and �-Al2O3 were expected to provide gooddiffusivity for large hydrocarbon molecules in the feed. In addi-tion, two reference commercial Ni–Mo/�-Al2O3 catalysts wereobtained from two different catalyst vendors. Potassium hydrox-ide (ACS grade) and hydrochloric acid (ACS grade) used for cokeactivation and the product washing were purchased from FisherScientific Canada. Other chemicals used for catalyst preparationand activation, Ni(NO3)2·6H2O, (NH4)6Mo7O24·4H2O and dimethyldisulfide (DMDS), were from Sigma–Aldrich with >99.9% purity(99% for DMDS). The HVGO feed was provided by a North Americanpetroleum refinery.
2.2. Activation of OSP coke
Both coke samples were activated through a chemical activa-tion process with KOH as activation agent. The raw delayed cokesample was ground and screened to a particle size range of 60–200mesh to match that of the fluid coke as it was received withoutgrinding. The coke sample was mixed with KOH powder with spec-ified KOH/coke mass ratios of 2/1, 3/1 and 4/1. The mixture wastransferred into a stainless steel combustion boat, which was thenput into a quartz tube furnace with nitrogen gas flow at a rate of50 ml/min. Thereafter, the mixture was heated to 673 K at a ramp-ing rate of 10 K/min. After pre-activation for 1 h, the sample washeated again to a desired temperature of 923–1123 K at a ramp-ing rate of 5 K/min, and maintained at this temperature for 1–5 h.After activation and cooling down to room temperature, the prod-uct was washed with 1 M diluted hydrochloric acid and deionized(DI) water through filtration until the pH value of the filtrate wasconstant at 7. The obtained activated carbon was dried in an oven at393 K overnight. In this paper, the activated carbon prepared fromdelayed coke is denoted as DAC and the one prepared from fluidcoke is denoted as FAC.
2.3. Catalyst preparation
Ni–Mo/AC supported catalysts were synthesized by incipientwetness metal impregnation of the prepared ACs. It is noted thatboth FAC and DAC were directly used for loading metals with-out any pretreatment for functionalization of the carbon surface.Ammonium hepta-molybdate and nickel nitrate aqueous solutionswith specified metal concentrations were used to sequentiallyimpregnate the AC supports. Mo was first impregnated at a temper-ature of 353 K. After overnight drying and subsequent calcinationat 723 K for 4 h with N2 purging, Ni was impregnated followedby drying and calcination under the same conditions. The metalconcentrations of the solutions were so determined that the oxidemetal concentrations in the calcined catalysts reached 15 wt% forMoO3 and 5 wt% for NiO. Similarly, 15 wt% of MoO3 and 5 wt% ofNiO over the commercial AC and Al2O3 supports were also loadedfor comparison purpose.
2.4. Catalyst characterization
The C/H/S/N/O elemental composition and metal contents of theraw coke samples, the prepared AC samples and the spent cata-lysts were analyzed according to ASTM standard methods (ASTMD5291 and ASTM D5708). Specific surface area and porosity analy-
ses of the samples were performed with a Micromeritic ASAP 2020instrument. The BET surface area was obtained from N2 adsorptionisotherm at 77 K. The pore size was analyzed from the desorptionisotherm following the BJH method. The total pore volume was
Y. Shi et al. / Applied Catalysis A: General 441– 442 (2012) 99– 107 101
Table 1Main properties of the HVGO feed.
Density (g/cm3, ASTM D4052) 0.9336Carbon (wt%, ASTM 5291M) 86.26Hydrogen (wt%, ASTM 5291M) 11.60Sulfur (wt%, ASTM 4294) 2.06Nitrogen (wppm, ASTM 4629) 1359Conradson carbon residue (CCR, wt%, ASTM D4530) 0.16Hydrocarbon type composition (ASTM D2786/D3239)
Saturate (wt%) 44.4Aromatic (wt%) 49.8Polars (wt%) 5.78
Simulated distillation (◦C, ASTM 7169)IBP 182.610 295.030 372.850 415.070 455.0
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Table 2Element and ash analyses of the coke and AC samples.
Element F-coke D-coke FAC DAC
Carbon (wt%, ASTM 5373M) 76.73 83.98 87.22 93.61Hydrogen (wt%, ASTM 5373M) 1.82 3.90 0.51 0.20Oxygen (wt%) 1.56 0.88 2.76 1.95Nitrogen (wt%, ASTM 5373M) 1.98 1.67 0.10 0.10Sulfur (wt%, ASTM 4239M) 6.90 6.33 <0.30 <0.30Nickel (wppm, ICP-MS) 601 398 320 172
90 509.6FBP 590.0
erived from the amount of N2 adsorbed at a relative pressure of/P0 = 0.9677 (desorption branch).
The morphology and structure characterization of the sup-orts and Ni–Mo oxide loaded catalyst precursors were carriedut by scanning electron microscopy (SEM), transmission electronicroscopy (TEM), and X-ray diffraction. SEM images of the sam-
les were recorded on Hitachi S-4800 high resolution field emissionnstrument. A thin layer of the powder sample was uniformly dis-ributed onto a piece of adhesive conductive carbon tape that wasubsequently mounted on alumina stubs for observation underEM. Scanning transmission electron microscopy (STEM) and highesolution micrographs were acquired using JOEL 2200S field emis-ion TEM with an accelerating voltage of 200 kV. Energy dispersive-ray (EDX) elemental analysis was also recorded from the TEM as
ollows: a small amount of powder sample, ground in an agate mor-ar, was dispersed into ethanol by ultrasonication to get a mixtureuspension, which was placed over a lacy carbon coated copper gridor TEM imaging. XRD analysis was conducted on Rigaku Ultima IViffractometer with Co K� radiation (� = 0.1789 nm) and graphiteonochromator. The XRD patterns of the samples were scanned in
he 2� range 20–90◦ with a scanning step of 0.05◦.
.5. Catalyst activity evaluation
.5.1. Pre-sulfidationAll the catalyst samples, including the commercial ones, were
re-activated by sulfiding with DMDS. Typically, 5 g of catalyst and ml of DMDS were charged into a 300 ml magnetically stirred auto-lave (Autoclave Engineers) at ambient temperature. The reactoras purged with 0.5 MPa H2 to remove air and then pressurizedith 3.45 MPa H2 at ambient temperature prior to heating up forre-sulfidation. The pre-sulfidation of the catalysts was conducted
n two steps at 503 K and 613 K respectively, with each step lastingor 1 h.
.5.2. Catalytic activity testA HVGO feed was used to evaluate the hydrotreating activ-
ty of the catalysts using the same magnetically stirred autoclaveight after completion of pre-sulfidation. The main characteristicroperties of the HVGO are given in Table 1. 100 g of HVGO feedas charged under nitrogen gas protection at ambient temper-
ture into the autoclave containing the sulfided catalyst. All thevaluation tests were carried out at 643 K under a hydrogen pres-
ure of 3.45–5.50 MPa, with magnetic stirring speed at 400 rmp.fter 2 h of reaction period at 643 K, the autoclave reactor wasooled down naturally. Before releasing the autoclave pressure aas sample was taken and analyzed with Agilent 3000 micro gasMolybdenum (wppm, ICP-MS) 99.1 89.5 27.4 30.7Ash (wt%, ASTM D5142) 9.52 3.49 5.22 0.23
chromatograph (GC) equipped with a thermal conductivity detec-tor. The liquid product was collected and analyzed after separatingthe spent catalyst from the hydrogenated oil.
2.5.3. Treatment and characterization of spent catalystsSince the prepared catalysts were used for hydroprocessing
of HVGO, coking on catalyst surface and pore structure changesmight have occurred, which could lead to catalyst deactivation. Toinvestigate the changes of the catalyst samples before and afterthe hydroprocessing tests, the spent catalysts were treated withrefluxing toluene to extract any residue oil and other contami-nants deposited on catalyst surface. The extraction process (soxhletextraction) was performed over a 5-h time period. The treated cat-alysts were dried at 423 K in N2 for 5 h. Elemental analysis andsurface characterization were then performed with the catalystsamples.
3. Results and discussion
3.1. Activation of OSP coke
The yield of AC based on raw coke was calculated as the per-centage of total mass of AC product over the total mass of the rawcoke. The element and ash analyses of the raw cokes and the ACs(activated at typical conditions and used as supports for prepara-tion of the Ni–Mo/AC catalysts) were listed in Table 2. As Ni, Mo andS are desired constituents for hydrotreating catalyst [39], particu-lar attention was paid to determine their contents in cokes and theprepared ACs. Both of the fluid and delayed cokes contain as high as6.3 wt% of sulfur, but relatively low amounts of Ni (<0.01 wt%) andMo (<0.001 wt%). After activation and the subsequent washing, lessthan half of the original metals were removed, whereas more than95% of the S was removed. Considering that the Ni–Mo hydrotreat-ing catalysts to be prepared is aimed at containing 15 wt% of MoO3and 5 wt% of NiO, the metal contents left in the activated carbonafter the activation of coke are considerably low and their contribu-tion to the catalytic performance is negligible. The concentrationsof the other elements and ashes were also reduced after activa-tion except for those of oxygen and carbon. The oxygen contentwas increased by over 1 wt% in the activated carbons comparedto the raw cokes, the reason for which will be discussed in thenext section. The carbon content was increased by 10 wt% after theactivation, which is expected since much of the heteroatoms andinorganic substances have been removed. It should be mentionedthat the yields of the activated carbon obtained at all of the testedactivation conditions were in the range of 67–70 wt%.
3.2. Selection of activation conditions
The catalytic activity of hydrotreating catalysts for heavy gas
oil conversion depends on the surface texture and porosity ofthe catalyst support. Therefore, various activation conditions wereinvestigated to achieve better AC textural properties. The BET sur-face characteristics of the ACs obtained at different conditions are
102 Y. Shi et al. / Applied Catalysis A: General 441– 442 (2012) 99– 107
Table 3Surface characterization of the coke and AC samples obtained at different activation conditions.
Sample Temperature (K) Time (h) Mass ratio ofKOH/coke
BET surfacearea (m2/g)
Pore volume(cm3/g)
Average porediameter (nm)
F-coke – – – 8.8 0 –FAC 923 1.5 3:1 1686 0.95 2.1FAC 923 5 3:1 1566 0.73 1.9FAC 973 1.5 3:1 1926 1.11 2.1FAC 1023 1 3:1 1987 1.15 2.1FAC 1023 1.5 3:1 2194 1.21 2.1FAC 1023 2 3:1 2133 1.20 2.1FAC 1023 4 3:1 2030 1.13 2.1FAC 1073 1.5 3:1 1827 0.99 2.2FAC 1123 1.5 3:1 1689 0.93 2.2FAC 1023 1.5 2:1 1174 0.65 2.2FAC 1023 1.5 4:1 1878 1.03 2.2D-coke – – – 0.17 0 –DAC 973 1.5 3:1 1716 0.91 2.1DAC 1023 1.5 3:1 2357 1.24 2.2DAC 1073 1.5 3:1 2257 1.19 2.1CAC – – – 559 0.76 5.3�-Al2O3 – – – 143 1.04 27.0Ni–Mo/FAC – – – 1681 0.88 2.1
simtseAauc
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Ni–Mo/DAC – – –
Ni–Mo/CAC – – –
Ni–Mo/Al2O3 – – –
hown in Table 3. For comparison, the BET surface area and poros-ty characteristics of the raw cokes, CAC, and �-Al2O3 were also
easured and are listed in Table 3. At most of the tested condi-ions, both F-coke and D-coke were successfully activated with highurface area (>1600 m2/g) and large pore volume (>0.93 cm3/g),xcept for KOH/coke mass ratio of 2. Compared with CAC and �-l2O3, although the average pore diameters of the prepared ACsre around 2 nm, their extremely high surface area and pore vol-me would still make them good catalyst support to achieve highatalyst activity.
Fig. 1 shows the surface characteristics of the FACs obtainedt different activation temperatures and activation times. The sur-ace area and pore volume of the FACs increased from 1686 m2/gnd 0.95 cm3/g to 2194 m2/g and 1.21 cm3/g, respectively, whenhe activation temperature was increased from 900 to 1023 KFig. 1A) with activation time fixed at 1.5 h. When the temper-ture was increased further from 1023 K, the surface area andore volume decreased sharply since extremely high tempera-ure might have caused texture sintering. Fig. 1B shows the BETurface areas and pore volumes at different activation times atxed activation temperature of 1023 K. The highest surface area
nd pore volume were achieved with activation time of 1.5 h.imilar observations were made for DACs (not shown here). DACith the highest surface area of 2357 m2/g and pore volume of.24 cm3/g was obtained at 1023 K from D-coke. In addition to
11501100105010009509001600
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1830 0.92 2.0323 0.48 6.1108 0.76 28.6
activation temperature and time, mass ratio of KOH/coke alsoaffected the textural properties of the prepared AC. Under the sameactivation conditions, KOH/F-coke mass ratio of 3/1 resulted inhigher surface area and pore volume than 2/1 and 4/1. In the meantime, another batch of F-coke was chemically processed at 923 Kfor 5 h to cover a wider range of operation conditions. The surfacemeasurement shows that neither BET surface area nor pore vol-ume is higher than the one treated at the same temperature for ashort activation time (1.5 h). Therefore, KOH/coke mass ratio of 3/1,activation temperature of 1023 K, and activation time of 1.5 h wereidentified as the best activation conditions for converting the OSPcoke into activated carbon.
3.3. Characterization of OSP coke and activated carbon
Fig. 2 shows the representative high resolution SEM imagingcharacterization of F-coke and D-coke (Fig. 2A and B, respectively)and their corresponding activated carbon after activation (Fig. 2Cand D, respectively). The insets are the corresponding low mag-nification SEM images. The high magnification images show flator rough surface of the raw cokes (Fig. 2A and B), while the
corresponding activated carbons show highly porous structure(Fig. 2C and D). In addition to micro-sized pores, meso-pores andmacro-pores are also seen in both ACs, indicating good structuralcharacteristics as catalyst supports for hydrotreating heavy gas oil.4.03.53.02.52.01.51.01950
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tivation temperatures (A) and activation times (B).
Y. Shi et al. / Applied Catalysis A: General 441– 442 (2012) 99– 107 103
(D) (i
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Fig. 2. SEM images of F-coke (A), D-coke (B), FAC (C) and DAC
The structure and crystallinity of the obtained ACs were alsonalyzed with XRD. The typical XRD patterns presented in Fig. 3curves a and b) reveals that the prepared ACs are almost amor-hous. Only two weak peaks are observed and no obvious impurityan be detected. The two diffraction peaks corresponding to (0 0 2)nd (1 0 1) are those of graphitic carbon, indicating the disorderedC structure. Since activated carbon is normally composed of ran-omly stacked graphite planes, such a disordered structure leadso a high porosity of the carbon materials, which is also confirmedy SEM characterization.
.4. Characterization of Ni–Mo/AC catalyst precursors
The XRD patterns of the calcined Ni–Mo/AC precursors are alsohown in Fig. 3 (curves c and d). In comparison with curves a and bor the AC supports, other than the two weak peaks originated from
806040200
200
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600
800
d
c
b
Inte
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ty (
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ig. 3. XRD patterns of the AC supports (a, DAC; b, FAC) and their correspondingalcined Ni–Mo/AC catalyst precursors (c, Ni–Mo/DAC; d, Ni–Mo/FAC).
nsets are the corresponding low magnification SEM images).
carbon, no additional diffraction peaks are observed from the XRDpatterns. Although the metal loading contents are 15 wt% for MoO3and 5 wt% for NiO for the calcined samples, neither MoO3 and NiO,nor NiMoOx diffraction peaks were recorded. Therefore, the XRDpatterns suggest that very good dispersions of both MoO3 and NiOon the AC supports are achieved.
Fig. 4A and B shows the SEM characterization of the calcined cat-alyst precursors Ni–Mo/FAC and Ni–Mo/DAC, respectively. Highlydispersed nanoparticles (white dots) of 30–50 nm in size can beclearly seen on both of the porous AC supports. Compared with thebare AC supports (Fig. 2C and D), these nanoparticles should be theloaded metal oxides. Such a very good distribution of metal oxidesaccounts for the related XRD patterns with an indication of goodcatalytic activity for hydrotreatment. As mentioned earlier that theoxygen content was increased by more than 1 wt% after activation.The addition of oxygen to the activated carbon during chemicaltreatment is attributed to the use of KOH as active agent for convert-ing the coke. Normally, the presence of various oxygenated groupsof either acidic or basic nature on the carbon surface is of greatimportance for metal adsorption and catalyst dispersion [40–42],since the surfaces of carbon supports are nearly neutral and het-eroatoms can modify the surface properties of carbon [43,44]. Theoxygen containing functional groups generated in situ on carbonsurface during the activation process lead to an effective and uni-form dispersion/distribution of active metals during impregnation[38].
To examine the differences in surface properties of the AC sup-ports and the prepared catalyst precursors, BET surface area andpore volume were also measured with the latter. The results areshown in Table 3 as well. It was observed that both the surfacearea and pore volume of the catalyst precursors were about 25%lower than those of their corresponding AC and alumina supports.The drop with the CAC catalyst precursor was even higher (∼40%).
This indicates that no matter which catalyst support is used, con-siderable decease in surface area is expected after metal loadingand calcination. However, little differences were observed with thepore size distribution as seen in Table 3.
104 Y. Shi et al. / Applied Catalysis A: General 441– 442 (2012) 99– 107
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NM/DAC
NM/CAC
NM/Al2O3
Com1
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0.91
0.92
0.93
0.94
De
nsity (
mg
/l)
Fig. 5. Density (ASTM D4052) of the feed and hydrogenated liquid products obtainedwith different catalysts (temperature: 643 K; pressure: 3.45 MPa; reaction time: 2 h).
NM/FAC
NM/DAC
NM/CAC
NM/Al2O3
Com1
Com2
0
20
40
60
80
Su
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r co
nve
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Fig. 6. HDS activity obtained with different catalysts (temperature: 643 K; pressure:3.45 MPa; reaction time: 2 h).
NM/FAC
NM/DAC
NM/CAC
NM/Al2O3
Com1
Com2
0
5
10
15
20
25
30
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ge
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ig. 4. SEM images of the calcined Ni–Mo/AC catalyst precursors (A: Ni–Mo/DAC;: Ni–Mo/FAC).
.5. Hydrotreating activities of the Ni–Mo/AC catalysts
All the hydrotreating evaluation experiments were carried outn a 300 ml autoclave reactor with a magnetic stirrer under theimilar operating conditions. The catalysts, including the preparedi–Mo/FAC, Ni–Mo/DAC, Ni–Mo/CAC, Ni–Mo/�-Al2O3, and the twoommercial reference hydrotreating catalysts were activated usingMDS with the same pre-sulfiding procedure under the similaronditions before activity tests. Since the two commercial Ni–Moydrotreating catalysts were in extruded form, for comparison theyere ground into the same size range as the prepared AC catalysts.
able 4 lists the main properties of the hydrotreated liquid productsbtained with different catalysts. It is observed that all the catalystshow some extent of hydrotreating activity indicated by lower oilensity, and lower contents of S, N and Conradson carbon residueCCR) than those of the HVGO feed.
The specific hydrotreating performance, in terms of densityhange, HDS, HDN, and CCR conversion are demonstrated inigs. 5–8, respectively. Fig. 5 presents the densities of the hydro-enated HVGO with the 6 different catalysts. The hydrogenatedroducts obtained with Ni–Mo/FAC and Ni–Mo/DAC have lowerensity than those obtained with other catalysts. Fig. 6 shows theDS conversions obtained with different catalysts. Over 70 wt%f the sulfur in the HVGO feed was removed after hydrotreat-ng with either FAC or DAC supported Ni–Mo catalyst, suggesting
higher HDS activity of the developed AC catalysts. It is worthoting that in agreement with S content of the hydrotreated liq-
id products, gas analysis showed that the AC-supported catalystsave both higher hydrogen consumption and hydrogen sulfide pro-uction than other catalysts, which are also indications of HDSFig. 7. HDN activity obtained with different catalysts (temperature: 643 K; pressure:3.45 MPa; reaction time: 2 h).
Y. Shi et al. / Applied Catalysis A: General 441– 442 (2012) 99– 107 105
Table 4Main properties of the HVGO feed and liquid products with different catalysts.
Density (g/ml, ASTM D4052) S (wt%, ASTM 4294) N (wppm, ASTM 4629) CCR (wt%, ASTM D4530)
Feed 0.9336 2.06 1359 0.16Ni–Mo/FAC 0.918 0.56 1036 0.01Ni–Mo/DAC 0.9159 0.45 954.3 <0.01Ni–Mo/CAC 0.9226 0.76 1324 0.08
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shltnfii
Fs
At low magnification (Fig. 10A), particles of 30–50 nm in size can
Ni–Mo/Al2O3 0.9228 0.71
COM1 0.9232 0.74
COM2 0.9205 1.16
ctivity. Although the HDN conversions shown in Fig. 7 for all ofhe catalysts are low (<30 wt%), Ni–Mo/FAC and Ni–Mo/DAC per-ormed better than the other four reference catalysts. Fig. 8 exhibitshe CCR conversions obtained with different catalysts. Again, thei–Mo catalysts supported on activated carbon derived from OSPoke (Ni–Mo/FAC and Ni–Mo/DAC) yielded higher CCR conversion>92 wt%). It is also noted that between the two catalysts basedn OSP coke derived activated carbon, Ni–Mo/DAC showed higherydrotreating activity than Ni–Mo/FAC in terms of density reduc-ion, HDS, HDN and CCR conversion, indicating that the delayedoke used in this study is more suitable for making activated carbonatalyst support. The higher hydrotreating activity of Ni–Mo/DACs attributed to the higher BET surface area and pore volume of thectivated carbon support (Table 3).
Note that the CAC and the �-Al2O3 used for catalyst preparationn this study are mesoporous supports, which favour the diffusionf large hydrocarbon molecules, such as those in HVGO. There-ore the corresponding catalysts should have demonstrated higherydrotreating activity than the FAC and DAC based microporousatalysts. However, experimental observations as discussed abovehow the opposite trend. Therefore the surface properties of FACnd DAC, which allow uniform distribution of well-dispersed smalletal oxide particles might have had significant contribution to the
bserved high hydrotreating activity.It should be pointed out that the activity tests conducted in this
tudy with all the catalyst samples lasted only a few hours and theydrotreating activity data represent their initial values. Due to the
imitation of the autoclave batch reactor, catalyst stability and deac-ivation over a long time period could not be evaluated. The large
umber of micropores in the DAC and FAC supports might sufferrom the deposition of coke and contaminants over time, result-ng in catalyst deactivation. The testing of the prepared catalystsn a continuous flow reactor system is undergoing to evaluate the
NM/FAC
NM/DAC
NM/CAC
NM/Al2O3
Com1Com2
0
20
40
60
80
100
CC
R c
on
ve
rsio
n (
wt%
)
ig. 8. CCR conversion obtained with different catalysts (temperature: 643 K; pres-ure: 3.45 MPa; reaction time: 2 h).
1255.5 0.051257 0.111140 0.06
catalyst stability and deactivation. The results will be published inthe future.
3.6. Aromatics conversion
In addition to HDS and HDN activities, the conversion of aro-matic molecules is another important indication of catalyst activityfor hydrotreating heavy feeds. Fig. 9 presents the contents of dif-ferent types of hydrocarbons in the feed and in the hydrotreatedliquid products. All the liquid products show at least 10 wt% highercontent of saturates and 10 wt% lower content of aromatics thanthe feed, indicating their hydrogenation activity for large aro-matic molecules. As seen in Fig. 9, the prepared Ni–Mo/FAC andNi–Mo/DAC do not show any advantage in aromatics hydrogena-tion over other catalysts. Instead, the catalysts prepared withmesoporous CAC and alumina show slightly higher aromaticshydrogenation activity than others. The lowest contents of polarsin the liquid products obtained with Ni–Mo/FAC and Ni–Mo/DACcatalysts confirm the superior HDS and HDN activities.
3.7. Structure characterization of Ni–Mo/DAC
In order to understand the observed higher hydrotreating activ-ity of the two catalysts prepared with activated carbon supportsderived from OSP coke, further study on metal distribution andmicrostructure of the Ni–Mo/DAC catalyst after sulfidation (withDMDS in H2 atmosphere) was conducted with STEM. Fig. 10 showshigh-resolution STEM images of the sulfided Ni–Mo/DAC catalyst.
be clearly seen dispersed on the AC support from the typical brightfield STEM image, which is similar to the SEM observation. Highangle annular dark field (HAADF) STEM imaging technique was
Feed
NM/FAC
NM/DAC
NM/CAC
NM/Al2O3
Com1Com2
0
10
20
30
40
50
60
70
Co
nte
nt (w
t%)
Saturates
Aromatics
Polars
Fig. 9. Hydrocarbon type composition (ASTM D2786/D3239) of the feed andhydrotreated liquid products obtained with different catalysts (temperature: 643 K;pressure: 3.45 MPa; reaction time: 2 h).
106 Y. Shi et al. / Applied Catalysis A: General 441– 442 (2012) 99– 107
F catalyH lected
atdctHmisacSp
aiatlfisst
TE
ig. 10. STEM images (A and B) and EDX elemental analysis (C) of the Mo–Ni/AC
AADF view of the marked edge area in image A; C: EDX elemental analysis of a se
pplied to explore the nanostructure feature of the fine oxide par-icles on the catalyst support. Since the contrast in HAADF-STEMepends on the Z-number of the constituent atoms with brighterontrast for heavier constituents, it is a powerful tool for charac-erization of supported catalyst. Fig. 10B shows the high resolutionAADF-STEM image taken from the circled area in Fig. 10A. Theagnified image acquired from the selected thin edge of the spec-
men exhibits large numbers of small particles embedded in theupport matrix with size ranging from 2 to 5 nm. EDX elementnalysis performed with the nanoparticles, as shown in Fig. 10C,onfirms that the composition of the nanostructures is Ni, Mo and. The carbon peak comes from the background of the AC sup-ort.
With respect to the hydrotreating activity of the prepared FACnd DAC catalysts, the high surface area and porous structure def-nitely have a positive effect on HDS and HDN. Further study onctivation of OSP coke is underway to enlarge the micropores inhe activated carbon, thereby further enhancing its supported cata-yst activity for conversion of large hydrocarbon molecules in heavyeeds. Meanwhile, because of the absence of strong metal–support
nteractions in activated carbon supported Ni–Mo catalysts, metal-ulfides particles tend to be dispersed more uniformly in a smallerize on the porous surface, which is another important factor forheir observed higher hydrotreating activity.able 5lemental analysis and surface characterization of the spent catalysts.
Sample Carbon content(wt%)
BET surfaarea (m2/
Spent Ni–Mo/FAC 72.2 781
Spent Ni–Mo/DAC 75.6 866
Spent Ni–Mo/Al2O3 8.1 115
st after sulfidation. A: low-magnification bright field view; B: high-magnification nanoparticle imaged in B.
3.8. Catalyst deactivation
As mentioned earlier, to better understand the deactivationmechanism and its effect on catalyst life, three spent catalysts,i.e. Ni–Mo/FAC, Ni–Mo/DAC and Ni–Mo/Al2O3 were analyzed aftersoxhlet extraction. Table 5 shows the carbon contents and surfaceproperties of the spent catalyst samples. After hydroprocessing,8.1 wt% of carbon was found on the alumina catalyst while car-bon content increase was much lower for the two AC-basedcatalysts, 3 wt% for Ni–Mo/FAC and <1 wt% for Ni–Mo/DAC, incomparison with the calculated values for the fresh ones. Evi-dently, coke precursor was formed during the hydroprocessingtests and the alumina support was more favorable for cokedeposition than the two AC supports. Surface characterizationshows that the AC supported catalysts lost more than halfof the surface area and pore volume after the hydroprocess-ing tests, while the alumina supported one retained almost allthe surface area and 90% of the pore volume, compared withtheir counterparts (fresh catalysts before sulfidation). However,after the hydroprocessing tests, the two AC supported catalysts
still had similar average pore size as the fresh catalysts whileaverage pore size of the alumina supported catalyst droppedfrom 28.6 nm to 22.2 nm. Indicatively, although the mesoporesin alumina were not blocked as much as the micropores inceg)
Pore volume(cm3/g)
Average porediameter (nm)
0.40 2.00.42 1.90.62 22.2
A: Ge
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4
cafaptsidfulvutcOmhtwwiaafl
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[[[[[[
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[[[[[[[41] B.R. Puri, Chemistry and Physics of Carbon, Marcel Dekker, New York, 1970.
Y. Shi et al. / Applied Catalysis
he AC supports after the hydroprocessing tests, they shrankonsiderably due to coke deposition. In combination with thearbon elemental analysis data, it is suggested that coke precur-or particles were formed on the walls/surface of the mesoporesn the alumina support during the hydroprocessing tests, whichrevented the active sites on the catalyst surface from contact-
ng hydrocarbon molecules. This might partially account for thebserved lower hydrotreating activity of the alumina supportedatalyst compared with the AC supported catalysts.
. Conclusions
Two types of OSP coke were successfully activated through ahemical process with an average yield of 68.5 wt%. The obtainedctivated carbons have high BET surface areas, over 2194 m2/gor the fluid coke and over 2357 m2/g for the delayed coke. Thectivated carbons contain a large number of micropores withore volumes as high as 1.2 cm3/g. High resolution SEM charac-erization was performed with the AC samples to confirm theirtructure and morphological features. Two Ni–Mo hydrotreat-ng catalysts were prepared by using the AC as supports. Goodispersion of the metal oxides was observed on the catalyst sur-ace. Both XRD and SEM analyses consistently confirmed theniform distribution of the metal particles. The prepared cata-
ysts were evaluated in a batch autoclave for hydrotreating heavyacuum gas oil and were compared with catalysts prepared bysing a commercial AC and an alumina as supports, and withwo reference commercial hydrotreating catalysts. Among all theatalysts evaluated, the two prepared with ACs derived fromSP coke showed significantly improved hydrotreating perfor-ance in terms of HDS, HDN and CCR conversion for HVGO
ydrotreating. High resolution HAADF-STEM imaging indicatedhat 2–5 nm fine nanostructures are embedded in the AC matrixith a composition of Ni–Mo–S after sulfidation of the catalysts,hich is the essential constituent of active site for hydrotreat-
ng. Therefore, the high surface area and porous structure, thebility for resistance to coke deposition of the AC supports,nd the highly dispersed small metal–sulfide particles accountor the observed hydrotreating activity of the prepared cata-ysts.
cknowledgements
Partial funding for this study was provided by the Canadiannterdepartmental Program of Energy Research and DevelopmentPERD 1.1.3). The authors are grateful to the CanmetENERGY-Devonilot plant staff for conducting the experiments and to the ana-
ytical lab staff for performing the analyses. Analytical support
rom the National Institute for Nanotechnology (National Researchouncil, Canada) is greatly appreciated. Dr. Edward Little’s valuablenputs and suggestions on revising this paper are greatly appreci-ted.
[[
[
neral 441– 442 (2012) 99– 107 107
References
[1] J.G. Speight, The Chemistry and Technology of Petroleum, fourth ed., Taylor andFrancis Group, Florida, 2007.
[2] H. Fukuyama, S. Terai, M. Uchida, J.L. Cano, J. Ancheyta, Catal. Today 98 (2004)207–215.
[3] J.H. Gary, G.E. Handwerk, Petroleum Refining Technology and Economic, fourthed., Marcel Dekker, New York, 2001.
[4] C. Song, Catal. Today 86 (2003) 211–263.[5] H. Topsøe, B.S. Clausen, Appl. Catal. 25 (1–2) (1986) 273–293.[6] H. Shimada, T. Sato, Y. Yoshimura, J. Hiraishi, A. Nishijima, J. Catal. 110 (1988)
275–284.[7] J.C. Duchet, E.M. van Oers, V.H.J. de Beer, R. Prins, J. Catal. 80 (1983) 386–402.[8] J.P.R. Vissers, B. Scheffer, V.H.J. de Beer, J.A. Moulijn, R. Prins, J. Catal. 105 (1987)
277–284.[9] B. Scheffer, P. Arnoldy, J.A. Moulijn, J. Catal. 112 (1988) 516–527.10] M.R. Gray, Upgrading Petroleum Residues and Heavy Oils, Marcel Dekker, New
York, 1994.11] F. Diez, B.C. Gates, J.T. Miller, D.J. Sajkowski, S.G. Kukes, Ind. Eng. Chem. Res. 29
(1990) 1999–2004.12] S.C. Korre, M.T. Klein, R.J. Quann, Ind. Eng. Chem. Res. 34 (1995) 101–117.13] H. Fukuyama, S. Terai, Petrol. Sci. Technol. 25 (2007) 231–240.14] M. Absi-Halabi, A. Stanislaus, D.L. Trimm, Appl. Catal. 72 (1991) 193–215.15] M.S. Rana, V. Sámano, J. Ancheyta, J.A.I. Diaz, Fuel 86 (2007) 1216–1231.16] Y.D. Liu, L. Gao, L.Y. Wen, B.N. Zong, Recent Pat. Chem. Eng. 2 (2009) 22–36.17] M. Breysse, C. Geantet, P. Afanasiev, J. Blanchard, M. Vrinat, Catal. Today 130
(2008) 3–13.18] E. Puello-Polo, J.L. Brito, J. Mol. Catal. A 281 (2008) 85–92.19] F. Liu, S.P. Xu, Y.W. Chi, D.F. Xue, Catal. Commun. 12 (2011) 521–524.20] H.L. Yin, T.N. Zhou, Y.Q. Liu, Y.M. Chai, C.G. Liu, Reac. Kinet. Mech. Cat. 102 (2011)
405–416.21] C.B. Xu, S. Hamilton, A. Malik, M. Ghosh, Energy Fuels 21 (2007) 3490–3498.22] P. Serp, J.L. Figueiredo, Carbon Materials for Catalysis, John Wiley & Sons, New
Jersey, 2009.23] L.A. Rankel, Energy Fuel 7 (1993) 937–942.24] Y. Sugimoto, 16th Saudi Arabia–Japan Joint Symposium, Dhahran, Saudi Arabia,
November 5–6, 2006, 2006.25] C. Glasson, C. Geantet, M. Lacroix, F. Labruyere, P. Dufresne, J. Catal. 212 (2002)
76–85.26] P. Vazquez, L. Pizzio, M. Blanco, C. Caceres, H. Thomas, R. Arriagada, S. Bendezu,
R. Cid, R. Garcia, Appl. Catal. A 184 (1999) 303–313.27] I. Eswaramoorthi, V. Sundaramurthy, Nikhil Das, A.K. Dalai, J. Adjaye, Appl.
Catal. A 339 (2008) 187–195.28] E.J.M. Hensen, H.J.A. Brans, G.M.H.J. Lardinois, V.H.J. de Beer, J.A.R. van Veen,
R.A. van Santen, J. Catal. 192 (2000) 98–107.29] H. Topsøe, B.S. Clausen, F.E. Massoth, Hydrotreating Catalysis, Springer, Berlin,
1996.30] J.A.R. van Veen, H.A. Colijn, P.A.J.M. Hendriks, A.J. van Welsenes, Fuel Process.
Technol. 35 (1993) 137–157.31] S.M.A.M. Bouwens, F.B.M. Vanzon, M.P. Vandijk, A.M. Vanderkraan, V.H.J.
Debeer, J.A.R. Vanveen, D.C. Koningsberger, J. Catal. 146 (1994) 375–393.32] R. DiPanfilo, N.O. Egiebor, Fuel Process.Technol. 46 (1996) 157–169.33] S. Mitani, S.I. Lee, S.H. Yoon, Y. Korai, I. Mochida, J. Power Sources 133 (2004)
298–301.34] S. Koutcheiko, T. McCracken, J. Kung, L. Kotlyar, Petrol. Sci. Technol. 25 (2007)
1215–1224.35] C.L. Lu, S.P. Xu, Y.X. Gan, S.Q. Liu, C.H. Liu, Carbon 43 (2005) 2295–2301.36] M. Kubota, A. Hata, H. Matsuda, Carbon 47 (2009) 2805–2811.37] L.F. Jia, E.J. Anthony, I. Lau, J.S. Wang, Fuel 85 (2006) 635–642.38] C. Moreno-Castilla, Carbon 42 (2004) 83–94.39] M. Brorson, A. Carlsson, H. Topsøe, Catal. Today 123 (2007) 31–36.40] G. de la Puente, J.A. Menendez, Solid State Ionics 112 (1998) 103–111.
42] J.P. Donnet, Carbon 6 (1968) 161–176.43] F. Rodriguez-Reinoso, C. Salinas-Martinez de Lecea, A. Sepulveda-Escribano,
J.D. Lopez-Gonzalez, Catal. Today 7 (1990) 287–298.44] H.P. Bohem, Carbon 32 (1994) 759–769.
