Energy Fuels 2010, 24, 2383–2389 Published on Web 03/10/2010
: DOI:10.1021/ef9013407
Hydrocracking of Athabasca Bitumen Using Submicronic Multimetallic Catalysts at Near In-Reservoir Conditions Carmen E. Galarraga* and Pedro Pereira-Almao Department of Chemical and Petroleum Engineering, Schulich School of Engineering, University of Calgary, Calgary, Alberta T2N 1N4, Canada Received November 12, 2009. Revised Manuscript Received February 25, 2010
NiWMo submicronic catalysts from emulsified metallic aqueous solutions were tested for Athabasca bitumen upgrading. The experiments were performed in a batch reactor (100 mL capacity) at a total pressure of 3.45 MPa, a stirring speed of 500 rpm, reaction times of 3-70 h, and temperatures from 320 to 380 °C. Ultradispersed (UD) catalysts enhanced the upgrading of Athabasca bitumen by increasing the hydrogen/carbon ratio and reducing both viscosity and coke formation. The conversion of bitumen increased with both the temperature and reaction time, whereas viscosity, sulfur, and microcarbon residue (MCR) in the reaction products decreased. Catalytic particles tend to agglomerate and become incorporated within the incipient coke matrix that develops at a residue conversion beyond 50 wt %. Nevertheless, good properties of upgraded oil (API gravity, 16°; viscosity at 40 °C, 60 cP; and MCR, 11.1 wt %) are obtained during processing before the onset of solids precipitation.
Hydrocracking (HCK) is a very useful process in modern petroleum refineries to produce valuable fuels from low-quality hydrocarbon feedstocks.6-8 Generally speaking, conventional HCK (of model molecules or light oils) involves a bifunctional catalyst, whose process scheme pairs the chemistry of hydrogenation (by hydrogen addition) plus catalytic cracking (using an acid catalyst). However, for processing heavy feedstocks, such as heavy oils and bitumen, the mechanism is similar to thermal cracking but having hydrogen transfer/hydrogenation superimposed, which will help to improve the quality of the upgraded product while decreasing the coke production.9 It is very probable that a strongly acidic catalyst, e.g., a zeolitic type, would deactivate by coke deposition when processing heavy feedstocks; nevertheless, a moderate acidity might work when combined with a fast hydrogenation, most probable to occur under low-temperature conditions. HCK is favored from moderate to high temperatures aiming to produce light high-quality fuels by increasing the hydrogen/carbon ratio and diminishing the undesirable contaminants, such as sulfur, nitrogen, aromatics, etc. Thus, such a treatment requires high temperatures and high pressures of hydrogen,10-12 which imposes high investments upon conventional processing units, i.e., strong metallurgic installations.
1. Introduction Canada has the second largest proven oil reserves in the world, estimated to make up about 174.5 billion barrels contained in oil sands.1,2 Oil production from oil-sand reserves appoints important challenges for the related industry. First, the recovery of these energy sources is difficult, and only 10% of the total oil in place can be exploited using all current in situ and surface mining methods.3 Second, these resources contain a large amount of useless residue that must be converted into valuable products (about 50 wt % of Athabasca bitumen distills at temperatures above 545 °C or even higher).4 Third, bitumen has high levels of contaminants, such as sulfur, nitrogen, and metals, which must be removed from feedstock and products to comply with the recent and more rigorous environmental constraints. Additionally, to treat bitumen for producing highly valuable hydrocarbons requires large amounts of hydrogen because the higher the hydrocarbon molecular weight, the lower the hydrocarbon hydrogen/carbon ratio.5 Therefore, the development of new and more efficient technologies to overcome the aforementioned issues would be desirable. *To whom correspondence should be addressed: Department of Chemical and Petroleum Engineering, Schulich School of Engineering, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada. Telephone: þ1-403-210-95-90. Fax: þ1-403-210-3973. E-mail:
[email protected]. (1) Patel, S. Canadian oil sands: Opportunities, technologies and challenges. Hydrocarbon Processing 2007, 65–73. (2) Stelmach, E. Speech at the II World Heavy Oil Congress Edmonton, Alberta, Canada, 2008, http://www.premier.alberta.ca/speeches/ speeches-2008-mar-10-World_Oil.cfm (accessed on March 2009). (3) Pereira Almao, P. R.; Larter, S.; Lines, L.; Maini, B.; Moore, G. M. An Alberta Ingenuity Fund Proposal for the Establishment of the Alberta Ingenuity Centre for In Situ Energy, Calgary, Alberta, Canada, 2004. (4) Rahimi, P.; Gentzis, T.; Taylor, E.; Carson, D.; Nowlan, V.; Cotte, E. The impact of cut point on the processability of Athabasca bitumen. Fuel 2001, 80, 1147–1154. (5) Billon, A.; Bigeard, P. H. Hydrocracking. In Petroleum Refining; Institut Francais du Petrole (IFP) Publications, Technip Editions: Paris, France, 2001; Vol. 3 Conversion Processes, pp 333-364. r 2010 American Chemical Society
(6) Dufresne, P.; Bigeard, P. H.; Billon, A. New developments in hydrocracking: Low pressure high-conversion hydrocracking. Catal. Today. 1987, 1, 367–384. (7) Scherzer, J.; Gruia, A. J. Hydrocracking Science and Technology; Marcel Dekker, Inc.: New York, 1996. (8) Meyers, R. A. Handbook of Petroleum Refining Processes, 3rd ed.; McGraw-Hill: New York, 2004. (9) Mohanty, S.; Kunzru, D.; Saraf, D. N. Hydrocracking: A review. Fuel 1990, 69, 1467–1473. (10) Panariti, N.; Del Bianco, A.; del Piero, G.; Marchionna, M.; Carniti, P. Petroleum residue upgrading with dispersed catalysts. Part 2. Effect of operating conditions. Appl. Catal., A 2000, 204, 215–222. (11) Ayasse, A. R.; Nagaishi, H.; Chan, E. W.; Gray, M. R. Lumped kinetics of hydrocracking of bitumen. Fuel 1997, 76 (11), 1025–1033. (12) Del Bianco, A.; Panariti, N.; Anelli, M.; Beltrame, P. L.; Carniti, P. Thermal cracking of petroleum residues. 1. Kinetic analysis of the reaction. Fuel 1993, 72, 75–80.
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From the previous, one can say that the demand for superior conversion of heavy oils and bitumen and the production of high-quality petroleum products that will match future specifications are linked to developing more efficient upgrading technologies, in which current HCK processes and catalysts must be improved. One idea could be researching on active phases able to upgrade bitumen at less severe operating conditions than those conventionally used. According to Lee et al., supported conventional HCK catalysts suffer fast deactivation when processing heavy hydrocarbon feedstocks because these contain large amounts of contaminants, such as asphaltenes, sulfur, and metals, which promote the formation of deposits in the catalyst pores and, consequently, inhibit effective diffusivity of reactants through active sites.13 Dispersed unsupported catalysts have been widely studied for heavy oil and bitumen processing10,12,14-18 as a substitute of supported catalysts. Because the contact between reactants (hydrocarbon components and hydrogen) can be maximized by a high catalytic particle population in the reaction media,13 reduction of diffusional problems is typically observed when processing bitumen and heavy oils.19 Some previous developments include the use of oil-soluble compounds that decompose under reaction conditions and produce a very small particulate; this particulate is able to locally generate hydrogen spillover, thus increasing the upgrading of residual feedstocks.20 Also, these catalysts can activate the hydrogen required for stabilizing the free radicals normally produced in the thermal cracking of heavy petroleum feeds.16 With respect to deactivation problems because of coke poisoning, these can be reduced with dispersed catalysts because of their high intrinsic catalytic activity.19 Another advantage when comparing dispersed unsupported catalysts to supported ones is that the former can be finely divided and incorporated into the reaction media to flow together with the feedstock to be treated, in such a way that reaction times can be longer than those conventionally used for hydroprocessing.21
Table 1. Properties of Athabasca Bitumen property viscosity at 40 °C (cP) API gravity (°API) microcarbon residue (wt %) H/C (atomic ratio) sulfur (wt %) distillation cuts (wt %) naphtha: IBP-213 °C distillates: 213-343 °C VGO: 343-545 °C residue: >545 °C
7680a 9.5 12.0 1.522 ( 0.001 4.25 2.76 ( 0.29 14.89 ( 0.81 34.68 ( 1.81 47.95 ( 1.57
a The selected feedstock was produced by steam-assisted gravity drainage (SAGD); therefore, this relatively low-viscosity value was derived from the presence of light ends, i.e., naphtha fractions.
Novel catalysts for hydroprocessing reactions developed at the University of Calgary involved ultradispersed (UD) catalysts that are obtained from water-in-oil emulsions containing transition metals able to catalyze such reactions.22,23 With this being a novel development, there is still a great deal of research to produce in this area. The objective of this work is to present and discuss the results from evaluating NiWMo submicronic catalysts for the HCK of Athabasca bitumen in a batch reactor at moderate operating conditions not reported before for this type of catalysts or for processing whole bitumen feedstocks. These findings open the door to the use of submicronic unsupported catalysts for in situ upgrading, in which only low-severity conditions are currently attainable. However, the advent of new technologies, such as heat provided directly in the reservoir, may convert the previous statement into an old paradigm. 2. Experimental Section 2.1. Preparation of Catalytic Emulsions. Trimetallic UD catalysts containing Ni, W, and Mo were prepared by emulsifying Athabasca bitumen (main properties in Table 1) with aqueous solutions of transition-metal salts: (a) nickel acetate (98% Aldrich), (b) ammonium metatungstate (88% Aldrich), and (c) ammonium heptamolybdate (99% Stream Chemicals), respectively. The amount of metallic precursors made up to 1000 ppmw of metal with respect to the bitumen to produce atomic metallic ratios as follows: Ni/metalsatomic = 0.3 and Mo/Watomic = 3, where metals = Ni þ W þ Mo. Tipical hydroprocessing catalysts are bimetallic: NiMo, CoMo, or NiW.24,25 Standard applications for conventional hydroprocessing, e.g., hydrodesulfurization (HDS), use CoMo; however, Ni and W are incorporated when higher hydrogenation activity is desired,26 for instance, hydrodenitrogenation (HDN) reactions.27 In the present work, the catalyst metals are combined using the following atomic ratios: Ni/(Ni þ Mo), 0.36; Ni/(Ni þ W), 0.63; and Ni/(Ni þ W þ Mo), 0.3. These
(13) Lee, D. K.; Park, S. K.; Yoon, W. L.; Lee, I. C.; Woo, S. I. Residual oil hydrodesulfurization using dispersed catalysts in a carbonpacked trickle bed flow reactor. Energy Fuels 1995, 9, 2–9. (14) Okamoto, Y.; Odawara, M.; Onimatsu, H.; Imanaka, T. Preparation and catalytic properties of highly dispersed molybdenum and cobalt-molybdenum sulfide catalysts supported on alumina. Ind. Eng. Chem. Res. 1995, 34, 3703–3712. (15) Panariti, N.; Del Bianco, A.; del Piero, G.; Marchionna, M. Petroleum residue upgrading with dispersed catalysts. Part 1. Catalysts activity and selectivity. Appl. Catal., A 2000, 204, 203–213. (16) Del Bianco, A.; Panariti, N.; Di Carlo, S.; Elmouchnino, J.; Fixari, B.; Le Perchec, P. Thermocatalytic hydroconversion of heavy petroleum cuts with dispersed catalysts. Appl. Catal., A 1993, 94, 1–16. (17) Del Bianco, A.; Panariti, N.; Di Carlo, S.; Beltrame, P. L.; Carniti, P. New developments in deep hydroconversion of heavy oil residues with dispersed catalysts. 2. Kinetics aspects of reaction. Energy Fuels 1994, 8, 593–597. (18) Fixari, B.; Peureux, S.; Elmouchnino, J.; Le Perchec, P.; Vrinat, M.; Morel, F. New developments in deep hydroconversion of heavy oil residues with dispersed catalysts. 1. Effect of metals and experimental conditions. Energy Fuels 1994, 8, 588–592. (19) Koseoglu, R. O.; Phillips, C. R. Effect of reaction variables on the catalytic hydrocracking of Athabasca bitumen. Fuel 1988, 67, 1201–1204. (20) Le Perchec, P.; Fixari, B.; Elmouchnino, J.; Peureux, S.; Vrinat, M.; Morel, F. New developments in deep hydroconversion of heavy oil residues with dispersed catalysts. Part 1: Thermocatalytic analysis of the transformation with various catalysts precursors. Prepr.-Am. Chem. Soc., Div. Pet. Chem. 1993, 38 (2), 401–406. (21) Pereira-Almao, P. R. Fine tuning conventional hydrocarbon characterization to highlight catalytic upgrading pathways. Presented at the Variability of the Oil Sands Resource Workshop, Lake Louise, Alberta, Canada, May 1-4, 2007.
(22) Pereira-Almao, P. R.; Ali-Marcano, V.; Lopez-Linares, F.; Vasquez, A. Ultradispersed catalyst compositions and methods of preparation. Patent WO 2007/059621 A1, 2007. (23) Vasquez, A. Synthesis, characterization and model reactivity of ultradispersed catalysts for hydroprocessing. M.Sc. Thesis, Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, Alberta, Canada, Feb 2007. (24) Gates, B. C.; Katzer, J. R.; Schuit, G. C. A. Chemistry of Catalytic Processes; McGraw-Hill, Inc.: New York, 1979; p 464. (25) Scheffer, B.; van Oers, E. M.; Arnoldy, P.; de Beer, V. H. J.; Moulijn, J. A. Sulfidability and HDS activity of Co-Mo/Al2O3 catalysts. Appl. Catal. 1985, 25 (1-2), 303–311. (26) Heinrich, G.; Kasztelan, S. Hydrotreating. In Petroleum Refining; Institut Francais du Petrole (IFP) Publications, Technip Editions: Paris, France, 2001; Vol. 3 Conversion Processes, pp 533-573. (27) Satterfield, C. N.; Modell, M.; Mayer, J. F. Interactions between catalytic hydrodesulfurization of thiophene and hydrodenitrogenation of pyridine. AIChE J. 1975, 21 (6), 1100–1107.
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2.3. Sample Characterization. Gas samples were quantitatively analyzed to determine composition and estimate average molecular weight. Thus, the hydrogen content was determined in a gas chromatograph (GC) Agilent model micro-GC 3000, whereas light hydrocarbons (C1-C5) were quantified in a Hewlett-Packard GC model 6900 provided with a 50 m length capillary column for PONA characterization. Liquid (feed or product) samples were analyzed using standard characterization techniques, as follows: (a) water content was measured by the Karl Fischer titration method in a MettlerToledo model DL-32; (b) viscosity at 40 °C was determined using a Brookfield viscometer model DV-IIþ Pro; (c) hightemperature simulated distillation (HTSD) was carried out in a GC from Agilent modified by Separation Systems, Inc. to estimate the amount of residue 545 °Cþ using the procedure ASTM D7169-2005 described by Carbognani et al.;29 (d) microcarbon residue (MCR) was evaluated using the method developed by Hassan et al.;30 (e) standard analyses to determine C and H were performed in a LECO apparatus, while S was determined by UV fluorescence in an Antek model 9000NS; and (f) the presence of solid particles was assessed by observing a sample drop (after reaction) using a National digital microscope model DC3-163 combined with Motic Images Plus 2.0 software. Total solids after the reaction were quantified as the filtered non-soluble matter after contacting the liquid sample with CHCl3 (99%, Aldrich) in a ratio of 1:50 (w/w). The filtration device comprises a 47 mm filter holder from VWR with a nylon membrane filter (0.45 μm) Nylaflo from Pall Corporation. Coke was defined as the difference between the total solids amount minus the theoretical mass of the catalyst component (0.15 wt %). Selected samples of solids (obtained from the filtration cake, top of the filter) were analyzed by electron microscopy to evaluate their morphology, size, and elemental composition. Microphotographs and spectra were obtained using a scanning electron microscope ESEM Philips model XL-30 with energydispersive spectrometry (EDS) acquisition and analysis software EDAX Genesis Spectrum V5.2. The high magnification images were collected using a transmission electron microscope (TEM) Hitachi model H-7650 at 10 kV. HTSD was used to determine the distribution cuts for both feed and products, as follows: naphtha (IBP-216 °C), distillates (216-343 °C), vacuum gas oil (343-545 °C), and residue (545 °Cþ). Gases and coke quantification were incorporated into mass balances to recalculate the cuts distribution. Finally, the conversion of residue was calculated from eq 1, which discards coke (if formed during the reaction). The average mass balance calculation for all of the experiments was better than 97.8%.
Table 2. Experimental Conditions Used for Evaluating the HCK Reaction of Athabasca Bitumen at 3.45 MPa Total Pressure and 500 rpm Stirring Speed test group
temperature (°C)
time (h)
emulsion type
1
320 320 350 350 360 365 365 380 380
24, 38 48, 69 7, 22, 30,a 48 6, 48 7, 15 5 6 3, 5.8, 6, 14 8b
dry fresh dry fresh dry dry fresh dry fresh
2 3 4 5 a
Repeated 3 times. b Repeated 2 times.
values are close to those already proposed as optimum for each pair of metals. The combination Mo/W is the result of keeping Ni close to its optimum value. Reported atomic ratios for Ni/(Ni þ W) range from 0.3 to 0.8, while reported atomic ratios for Ni/(Ni þ Mo) range from about 0.30 to 0.35.23,26 With regard the emulsifying procedure, it involves the mixture of the organic component with the aqueous solutions under high mixing speed. The organic component was prepared by mixing 99 wt % bitumen þ 1 wt % surfactant at 700 rpm and 60 °C. The mixture was stirred for about 30 min to reach stability. The surfactant was formulated in house to give a hydrophilic-lipophilic balance (HLB) = 8 by combining two commercial surfactants, namely, SPAN 80 from Sigma and TWEEN-80 from Sigma-Aldrich (0.65:0.35, wt/wt). Two different types of catalytic emulsions were prepared: fresh and dry. The fresh catalytic emulsion implicated (a) forming the organic mixture, (b) adding the molybdenum aqueous solution and waiting for stabilization (15 min), (c) adding the tungsten aqueous solution and waiting for stabilization, (d) adding ammonium sulfide (AMS) to provide a sulfur-rich environment able to promote, during the catalyst generation (at a temperature such that the precursor salts decompose), the formation of Me-sulfide species, known as the active species for hydroprocessing reactions, (e) adding the nickel aqueous solution and allowing 15 min for stabilization, and (f) mixing them all together for 30 min. This fresh emulsion will contain a maximum amount of water of 5 wt %. The dry catalytic emulsion was obtained from a sample prepared as fresh catalytic emulsion and then kept during 8 h under low stirring (200 rpm) and at a temperature of 40 °C to evaporate the water down to at least 0.5 wt %. 2.2. HCK Experiments. Table 2 lists the five sets of HCK experiments performed in a Parr batch autoclave reactor model 4565 with 100 mL of capacity. A controlled furnace allows for isothermal operation within the reactor. For every experiment, about 30 g of catalytic emulsion was placed into the reactor. After the safety leak test was performed, the unit was purged several times with hydrogen gas (Praxair, 99%) and the reactor was pressurized up to 2.5 MPa. The stirring speed was set at 500 rpm; the temperature was raised to the target value; then hydrogen was fed into the reactor to adjust the total pressure to 3.45 MPa; and the operating conditions were maintained for a fixed time. At this low pressure (aiming to simulate conditions near in-reservoir operation), the solubility of hydrogen in Athabasca bitumen is ca. 0.4 g of H2/kg of bitumen,28 which is about 70% of the solubility at 7.2 MPa (typical pressure value for conventional HCK of heavy oils). After the reaction, the unit was allowed to cool before collecting gases and liquid samples. Liquid products from bitumen HCK plus solids from the reaction, which contain UD catalytic particles and coke when produced, constitutes the liquid sample.
conv545 °Cþ ¼
mass of 545 °Cþ feed - mass of 545 °Cþ product - coke mass of 545 °Cþ feed
100
ð1Þ
3. Results and Discussion 3.1. Preliminary Evaluation. Table 3 depicts the results from a trial first stage, where a preliminary study to provide evidence of the effect of catalyst incorporation was conducted at a total pressure of 3.45 MPa, a stirring speed of 500 rpm, and a temperature of 380 °C, during 8 h of reaction (29) Carbognani, L.; Lubkowitz, J.; Gonzalez, M. F.; Pereira-Almao, P. High temperature simulated distillation of Athabasca vacuum residue fractions. Bimodal distributions and evidence for secondary “on-column” cracking of heavy hydrocarbons. Energy Fuels 2007, 21 (5), 2831–2839. (30) Hassan, A.; Carbognani, L.; Pereira-Almao, P. Effect of O2 on microcarbon residue standards analysis. Energy Fuels 2008, 87, 4062– 4069.
(28) Lal, D.; Otto, F. D.; Mather, A. E. Solubility of hydrogen in Athabasca bitumen. Fuel 1999, 78, 1437–1441.
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Table 3. HCK of Athabasca Bitumen at 380 °C and 8 h of Reaction Time Using UD Catalyst Precursors from Metallic Aqueous Solutions experiment
emulsion
residue 545 °Cþ (wt %)
conv545 °Cþ (wt %)
coke (wt %)
MCR (wt %)
sulfur (wt %)
feed 1 2 3 4
blank experiment fresh, 4.4 wt % water fresh, 4.3 wt % water dry, 0.3 wt % water
47.0 28.7 25.9 26.3 20.1
39 45 44 56
0.0 7.6 1.4 1.3 0.2
12.3 15.6 14.7 14.5 11.1
4.0 3.2 3.4 3.3 2.5
time. Experiment 1 was carried out as a blank experiment using a fresh emulsion with no metallic precursors. Experiments 2 and 3 use a fresh catalytic emulsion, and experiment 4 includes a dry catalytic emulsion. The table includes for both feedstock and products the following parameters: the mass of the fraction 545 °Cþ and its conversion, the amount of coke produced during the reaction, the MCR, and the sulfur content. This set of results compares (a) the effect of the catalyst (1 versus 2-4), (b) the effect of water in the emulsion (2 or 3 versus 4), and (c) reproducibility (2 versus 3). In all cases, incorporating UD catalyst improves the extent of residue conversion. In addition, using a dry emulsion (experiment 4) produces a higher conversion than using fresh emulsion (experiment 2 or 3) for this particular set of experimental conditions. This outcome may be due to the fact that not only are light hydrocarbon gases released during the reaction but also the water contained in the fresh emulsion evaporates and consequently produces a lower hydrogen partial pressure in the reactor. However, a detrimental effect of water on the activity of the catalyst cannot be completely ruled out. The reproducibility for these experiments is evidenced when comparing results from experiments 2 and 3, in which the error for the five parameters tested was less than 5%. All of these reactivity experiments produced coke (insolubles in CHCl3), but it was significantly decreased from almost 8 wt % in the blank experiment down to 1.4 and 0.2 wt % when using fresh and dry catalysts, respectively. These results indicate that the active phases included as UD catalysts effectively favor the hydrogenation reactions and inhibit the massive formation of coke usually present during the thermal processing of heavy hydrocarbons.16 MCR increased from 12 wt % in the feed to about 16 wt % for the blank experiment, where no catalytic precursors were added. This result concurs with the value of coke encountered for that experiment, because the MCR value can be used as a measure for potential coke formation.30 The MCR value was also improved by incorporating the UD catalytic particles. From 16 wt % in the blank experiment, MCR reduces to about 14.6 wt % for fresh catalyst and 11 wt % when the dry emulsion was used, confirming the previous statement that UD catalysts are acting as hydrogenating phases. 3.2. HCK Activity. Figure 1 plots the conversion of the residue as a function of the reaction time for the different temperatures evaluated. As expected, the conversion increases with both the temperature and reaction time. For moderate to high temperatures (350-380 °C), the reaction increases very fast and then the rate slows, reaching a pseudo-state of equilibrium. Similar trends were observed
Figure 1. Conversion of the residue fraction 545 °Cþ as a function of the reaction time evaluated at 3.45 MPa of total pressure and different temperatures (320-380 °C). Full symbols, fresh emulsion; open symbols, dry emulsion. At 360 °C, only dry emulsion was tested.
by Sanchez et al. when evaluating the kinetics for the HCK of Maya heavy oil31 and also by Song et al. when studying the hydroprocessing of the Gudao residue.32 For these studies, however, they used reaction conditions typical of HCK with higher temperatures and pressures, 380-435 °C and 7.0 MPa, respectively. For the HCK of Maya heavy oil with a Ni/Mo commercial catalyst (175 m2/g), the conversion at 380 °C and 3 h was limited to 30 wt %.26 With the UD catalysts, although the conversion at these conditions was observed to be the same, this limitation was moved further away. In fact, at 380 °C, the slope change was encountered at conversions higher than 50 wt %, for which also a higher formation of coke was observed. At the lowest studied temperature of 320 °C, the reaction increases monotonously with time for both dry and wet catalytic emulsions, for which all of the data correlate in a single trend line. Indeed, the strong inhibition effect that water caused at 380 °C and 8 h (Table 3) is less noticeable as the temperature and conversion decrease. For instance, at 350 °C and 48 h, the conversion only dropped 3 points, while at 380 °C and 8 h, it diminished 12 points. For conversions lower than 20 wt %, no water inhibition effect was noted. 3.3. Product Quality. Figure 2 presents the correspondence between product viscosity and residue conversion. As expected, the viscosity decreases exponentially with conversion. For conversions higher than 10 wt %, the experimental data fit with a correlation index r2 =0.962. Thus, the viscosity measurement may serve as a confirmation of the extent of bitumen upgrading. Sulfur removal or HDS is another important parameter to examine when dealing with bitumen upgrading. Figure 3 includes the plots of HDS as a function of the reaction time for the different temperatures evaluated. Similar to that observed for residue conversion and as expected, the HDS increases with both time and temperature. Finally, a corroboration of bitumen improvement achieved via HCK is further evidenced in Figure 4, which presents
(31) Sanchez, S.; Rodriguez, M. A.; Ancheyta, J. Kinetic model for moderate hydrocracking of heavy oils. Ind. Eng. Chem. Res. 2005, 44, 9909–9413. (32) Song, F. M.; Liu, C. G.; Zhou, G. S.; Yang, G. J. Thermal hydrocracking kinetics of Chinese Gudao vacuum residue. Pet. Sci. Technol. 2004, 22 (5-6), 689–708.
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Figure 2. Viscosity of liquid products at 40 °C as a function of the residue conversion for the HCK of whole Athabasca bitumen at selected operating conditions while using UD NiWMo catalysts.
Figure 3. HDS of Athabasca bitumen as a function of the reaction time evaluated at 3.45 MPa of total pressure and different temperatures (320-380 °C).
Figure 5. Optical microphotographs (40) of a liquid drop for samples obtained at different conditions: (a) catalytic emulsion, (b) product from the reaction at 380 °C when no catalyst was added (blank), and (c, d, and e) products from the reaction at 320, 350, and 380 °C, respectively, for increasing reaction times.
how the hydrogen/carbon ratio increases with the conversion of residue (all samples are from the reaction at 380 °C and different reaction times). The liquid product homogeneity was tested by observing one drop of liquid product using optical microscopy (OM). It is a very simple and non-expensive technique; however, it helps to predict whether or not the product contains large amounts of solid and may become unstable, which is an undesirable condition to deal with when handling synthetic oil for blending or marketing. Commercial processes must be
operated at conditions in which solid (coke) production may be prevented.33 Figure 5 presents the OM micrographs (40) for selected samples. The images include dry catalytic emulsion (Figure 5a), liquid product from the blank experiment performed without a catalyst at 380 °C and 8 h (Figure 5b), and the images collected for samples at different reaction times at 320, 350, and 380 °C in panels c, d, and e of Figure 5, respectively. These images confirm the previous statement regarding the effectiveness of the UD catalysts to activate hydrogen and, consequently, decrease the rate of coke production (panel b versus panel e of Figure 5 at 8 h). However, the severity conditions during the reaction must be controlled to prevent unwanted solid deposition in the processing units. The mechanism for HCK of Athabasca bitumen using dispersed catalysts in the presence of hydrogen could proceed via hydrogenation of the residue, which is then thermally decomposed to produce gases and distillates.33,34 Hence, failing to incorporate hydrogen in an effective way will promote massive coke formation. The initial value of CHCl3 insolubles in the evaluated feedstock was found to be 0.07 wt %. Increasing both time and temperature produces
(33) Sanford, E. C. Conradson carbon residue conversion during hydrocracking of Athabasca bitumen: Catalyst mechanism and deactivation. Energy Fuels 1995, 9, 549–559.
(34) Kennepohl, D.; Sanford, E. Conversion of Athabasca bitumen with dispersed and supported Mo-based catalysts as a function of dispersed catalyst concentration. Energy Fuels 1996, 10, 229–234.
Figure 4. Hydrogen/carbon atomic ratio as a function of the residue conversion (HCK carried out at 380 °C, UD submicronic catalyst, and varying reaction times).
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Figure 6. Coke production as a function of the reaction severity. Coke was defined as insolubles in CHCl3 and corrected for metal catalyst contribution.
more solid material in the liquid product, but the effect of the temperature is the strongest, as evidenced in Figure 6. For low- to mid-severity HCK, the production of coke can be considered low and seems not to depend upon the reaction time. It is also important to mention that the presence of water seems to inhibit the formation of coke, as evidenced when comparing fresh and dry emulsions at 320 °C in Figure 6, allowing for longer reaction times. Also evident in Figure 5c, 24 and 38 h correspond to dry emulsion, while 48 and 69 h were found for fresh emulsion. As previously mentioned, not much inhibition in residue conversion was evidenced at low to mid-severity (320-350 °C) with the higher amount of water in the emulsion (Figure 1). Thus, one might indicate that a lower formation of coke represents an advantage for using these submicronic catalysts in-reservoir conditions, where water is usually used for production stimulation. At the highest temperature, a clear trend is developed, in which the coke productivity stepped up to 0.71 wt %. As the temperature increases, the rate of thermal cracking reactions become faster and overcome the hydrogenating reactions, which are thermodynamically hindered with temperature;35 consequently, a higher proportion of free radicals will form then, producing a higher amount of coke. However, as already discussed, good quality upgraded oil can be obtained by processing up to 45-48 wt % of residue conversion with a low productivity of coke. 3.4. Solid Characterization. Panels a and b of Figure 7 illustrate TEM microphotographs of Ni-W-Mo catalysts from two different methods: (a) particles prepared by direct decomposition, as described elsewhere23 and included as a reference, and (b) particles produced in situ from catalytic emulsion followed by the reaction (sample reacted at 380 °C and 5.8 h from this work). The image in Figure 7a presents aggregates formed by smaller particles of about 100-200 nm; these are evidenced as well in Figure 7b, which additionally shows the typical coke-like particles (large black particles) also found by Panariti et al. for Mo-dispersed catalysts.10 The smaller particles from both images show enough similarity that one can conclude that both preparation processes starting from water-in-oil catalytic emulsions successfully produce particles in the submicronic size range. Figure 8 includes the scanning electron microscopy (SEM) microphotographs of CHCl3 non-soluble filtered
Figure 7. TEM microphotographs of Ni-W-Mo UD catalysts: (a) particles obtained by direct decomposition and (b) particles obtained after the HCK reaction of Athabasca bitumen at 380 °C and 5.8 h.
material obtained from reaction products at three different severities: (a) low severity at 320 °C and 48 h with 10 wt % residue conversion, (b) mid-severity at 350 °C and 22 h with 27 wt % residue conversion, and (c) high severity at 380 °C and 14 h with 63 wt % residue conversion. Because CHCl3 would dissolve the unconverted asphaltenes that remain in the liquid product, the non-soluble material (bigger than 450 nm) should only contain a mixture of coke plus catalytic particles. Selected zones in which energy-dispersive X-ray analyses (EDAXs) were performed are also shown: squares for analysis in a section and circles for spot analysis in a particle. The chemical composition mainly evidenced C, O, Mo, S, Ni, and W, whose atomic percentages are summarized in Table 4. Small amounts of Fe and V as well as traces of N, Na, and Cl that possibly segregated from the bitumen matrix were observed for some samples. The main morphology observed at low severity (square zone in Figure 8a) is a large population of nanometer-sized particles (70-700 nm in diameter), which are forming agglomerates of bigger sizes (in the micrometer range). As severity increases (Figure 8b), the small nanoparticles forming the aggregates start to fuse together and form some bigger and more compact particles than those of the aggregates. However, the filtrated material is still populated with a considerable amount of dispersed submicronic particles, as evidenced by the appearance and the chemical analyses from the square zone and the round particle indicated in Figure 8b, for which both elemental compositions are very similar (Table 4). At the highest severity, the aggregates grow bigger and form a sponge-like material, as evidenced in the square area of Figure 8c. In this figure, also some round particles of the typical “shot coke” can be noted.
(35) Demirel, D.; Wiser, W. H. Thermodynamic probability of the conversion of multiring aromatics to isoparaffins and cycloparaffins. Fuel Proc. Technol. 1998, 55, 83–91.
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: DOI:10.1021/ef9013407
Galarraga and Pereira-Almao
Figure 8. SEM microphotographs of filtered solids after the reaction for three different severities: (a) 320 °C, (b) 350 °C, and (c) 380 °C. Areas shown indicate zones where EDAX analyses were performed. The square zone is for scanning analysis in the complete area, and the round zone is for spot analysis in the particle. Table 4. Chemical Composition (Atom %) by EDAX from Zones and Particles, as Indicated in Figure 8
coke-catalyst aggregates form around them, or if the thermal cracking processes rapidly induce the massive formation of coke as the temperature increases. Ongoing research is addressing these issues.
severity and zones description 320 °C and 48 h
350 °C and 22 h
element
zone
zone
particle
C O S Ni Mo W Ni/metals C/metals
79.42 5.49 4.16 1.30 2.02 0.61 0.32 20.21
76.10 6.95 9.06 1.89 4.56 1.00 0.25 10.21
73.54 8.92 9.65 1.78 4.74 0.98 0.24 9.80
380 °C and 14 h zone
4. Conclusions
particle
92.85 94.49 ( 0.60 2.49 2.12 ( 0.26 1.66 1.15 ( 0.29 2.25 1.70 ( 0.65 0.43 0.13 ( 0.03 0.32 0.08 ( 0.04 0.18 0.10 ( 0.00 30.95 49.47
Nowadays, the requirement for new and improved processes and catalysts for the upgrading of heavy oils and bitumen is not only a challenge but also an opportunity to present and develop novel ideas for this type of processing. In this work, UD catalysts were successfully obtained from catalytic precursors in the form of water-in-oil emulsions of transition metals. Submicronic catalytic particles were successfully produced by decomposing water-in-bitumen catalytic emulsion in the reaction media at moderate temperatures. The resultant trimetallic formulation NiWMo enhanced the HCK reactivity of Athabasca bitumen by effectively activating hydrogen and, thus, inhibiting the coke production when operating at low temperatures, low pressures, and long reaction times. At 380 °C, the extent of upgrading not only increased the conversion of the residue 545 °Cþ from 40 wt % (blank experiment) to 56 wt % (catalyst added) with a significant reduction of the coke produced at the same reaction time but also improved the product quality by a reduction of viscosity, sulfur removal, and a reduction of the MCR.
Increasing severity produced a carbonaceous material that also altered the elemental composition of the solids recovered from the reaction. The increasing C/metals ratio included in Table 4 suggests that, as the coke particles form and grow, they encapsulate the catalytic metals in the inner matrix. For the solids recovered from the reaction at 320 °C, the atomic ratios for Ni/metals and Mo/W were estimated to be 0.32 and 3.31, confirming that, when forming the submicronic catalyst (Figure 8a), the precursor solutions are combined in the particles as initially targeted. As previously mentioned, the industrial operator should limit the severity of the operating conditions to produce the minimum amount of coke. For the system studied herein, the achievable residue conversion without coke formation is close to 48 wt %, for which the amount of filtrate from the liquid products after the reaction is about 0.3 wt %. From published reports, it is known that, at high temperatures (400 °C), dispersed catalysts play a dual role in both promoting (because they act as seeds) and preventing the formation of coke during the HCK of Athabasca bitumen and this depends upon the catalyst concentration.34 This work only used a constant concentration of the NiWMo catalyst in a fixed formulation for all of the operating conditions evaluated. Thus, in this set of experiments, it is unclear if the catalyst hydrogenation phases deactivate, because
Acknowledgment. The authors thank the financial support from The Alberta Ingenuity Centre for In Situ Energy funded by the Alberta Ingenuity Fund and the industrial sponsors: Shell International, ConocoPhillips, Nexen, Inc., Total Canada, and Repsol YPF. The ESEM Philips XL-30 was available thanks to an equipment and infrastructure grant from the Canadian Foundation for Innovation (CFI) and the Alberta Science and Research Authority. C.E.G. appreciates the economical support granted by the Schulich School of Engineering at the University of Calgary, Canada. Analytical support from the Catalysts for Bitumen Upgrading and Hydrogen Production (CBUHyP) group at the University of Calgary is acknowledged. L. Carbognani is appreciated for improvement of the original manuscript.
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