UNCORRECTED PROOF. Role of hydrotreating products in deposition of ne particles in reactors. S. Wang a, K. Chung b, M.R. Gray a, *

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1 JFUE1550 Fuel 00 (2000) 000±000 Role of hydrotreating products in deposition of ne particles in reactors S. Wang a, K. Chung b, M.R. Gray a, * a Department of Chemical & Materials Engineering, University of Alberta, Edmonton, Alta., Canada T6G 2G6 b Syncrude Research Centre, Edmonton, Alta., Canada T6N 1H4 Received 25 November 1999; revised 1 February 2000; accepted 3 February 2000 Abstract Hydrotreating reactions may affect the deposition of ne particles, which can eventually lead to reactor plugging. The deposition of ne particles from gas oil was measured in an internally recirculating reactor at 3758C under hydrogen. H 2 S from hydrodesulfurization would convert corrosion products to metal sul des. Iron sul de deposited rapidly in the packed bed because the mineral surface did not retain a stabilizing layer of asphaltenic material. Addition of water, to test the role of hydrodeoxygenation, doubled the deposition of clay particles by reducing the surface coating of organic material. Neither ammonia nor quinoline had any effect on particle deposition, therefore, hydrodenitrogenation did not affect particle behavior. q 2001 Elsevier Science Ltd. All rights reserved. Keywords: Hydrotreating; Particle deposition; Hydrodeoxygenation; Hydrodenitrogenation 1. Introduction Catalytic hydrotreating is widely used to enhance the quality of residue and distillate streams by selectively removing heteroatoms to form ammonia (NH 3 ), water (H 2 O) and hydrogen sul de (H 2 S) by hydrodenitrogenation (HDN), hydrodeoxygenation (HDO) and hydrodesulfurization (HDS) reactions. Although the main focus of hydrotreater operation is on heteroatom removal, feed streams can contain a variety of ne solid particles including clays entrained during distillation, coke particles from upstream delayed cokers and corrosion products [1,2]. These ne particles can deposit in the catalyst beds and lead to premature shut down due to high pressure drop. Clay particles are a particular concern in the processing of distillates from Athabasca bitumen [2]. The behavior of such ne particles in hydrocarbon media is dominated by surface composition and charge. For example, the stability of suspensions of kaolin clay was enhanced at hydrotreater conditions by a surface coating of asphaltenic material [3]. This coating reduced the tendency of the clay to occulate, and reduced deposition in a model packed bed at 3758C and a hydrogen pressure of 14 MPa. In the presence of active hydrotreating catalyst, the asphaltene coating was progressively removed, thereby destabilizing the particle suspension and increasing the deposition in the test packed bed. If coupling between hydrotreating and particle behavior is observed due to the removal of adsorbed surface layers, can the hydrogen sul de, water and ammonia that form during hydrotreating also in uence the stability of ne particles in the oil phase? The mineral solids in Athabasca bitumen have been extensively studied, and the characteristics of these materials indicate the nature of solids that will appear in hydrotreater feed streams. Toluene-insoluble organic material adheres strongly to individual mineral particles as a surface layer, so that it is practically impossible to physically separate the ultra- ne solids from bitumen [4]. Pyritic sulfur accounts for more than 60 wt% of total sulfur in the ne solids from Athabasca bitumen, and iron is present at a relatively large concentration (2.4±8.2 wt%), compared with such metals as magnesium, calcium and nickel [5]. Iron oxide is a well-known feature of Athabasca oil sands [6]. Most crude oils will contain iron oxide and iron salts from corrosion, and such solids are carried directly into residue hydrotreaters. In the hydrogen-sul de-rich environment of the hydrotreater, the iron oxides and salts such as sulfate, chloride or carbonate would be converted to iron sul de [7]. Iron oxide is easily converted to iron sul de even at low partial pressures of H 2 S, so that this reaction is used to clean gas streams [8]. Iron sul de has some activity for hydrogenation, but its activity is inferior to NiS±WS 2 or NiS±MoS 2 catalysts [9]. Similarly, iron sulfate supported on coal was a good catalyst for very heavy hydrocarbon * Corresponding author. Tel.: ; fax: address: murray.gray@ualberta.ca (M.R. Gray) /00/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII: S (00)

2 2 S. Wang, K. Chung / Fuel 00 (2000) 000±000 oil feed in suppressing coke formation reactions and reducing coke precursors [7,10]. Consequently, the surface of the iron sul de particles could be catalytically active at hydrotreater conditions, which could in turn alter the surface chemistry of the particles. The most abundant gas product from hydrotreating is hydrogen sul de. Also formed are the more polar compounds H 2 O and NH 3, which could alter the behavior of clay particles. Water can hydrate the surface of metal oxides, and both water and ammonia may change the surface properties of the organic coating on ne particles. The objective of this study was to understand the role of hydrotreating products in altering the deposition of ne particles in catalyst beds. One interaction of interest was between hydrogen sul de and iron compounds transforming iron salts into sul des. The second interaction of interest was between ne clays and the water produced during hydrotreating of oxygen compounds such as phenol and furan. The third interaction of interest was between ne clays and the ammonia formed from hydrotreating weak bases such as quinoline. Two model suspensions were used to study particle deposition in a 500 ml stirred autoclave under hydrogen atmosphere: asphaltene-treated kaolin and iron sul de (untreated and asphaltene-treated) in a hydrotreated light gas oil. A packed bed of glass beads served as the collectors for the ne particles. Water, ammonium hydroxide, quinoline were introduced into a batch reactor at a temperature representative of hydrotreating. Quinoline was used to represent those unconverted nitrogen compounds in the liquid phase. The deposition of the mineral particles in the packed bed was measured, to identify which compositional variables were signi cant. 2. Materials and method 2.1. Feed and packing materials The treated light gas oil was a hydrotreated product of Athabasca bitumen from the Syncrude plant at Fort McMurray, Alberta (Table 1). Solids were removed from the oil by ltering it through a 0.22 mm Millipore membrane lter. Kaolin was selected because it is the major component of clay minerals found in the Athabasca oil sands. Kaolin of two different sizes was used: 0.68 and 5 mm. Iron sul de particles were prepared by reacting a suspension of iron oxide (0.2 mm) in treated light gas oil with carbon disul de (CS 2 ) under a hydrogen atmosphere in a sealed vessel at 3758C. The product particles, consisting of iron oxide with an outer layer of iron sul de, were collected on a 0.22 mm millipore membrane lter, rinsed with excess methylene chloride, and then dried in an oven under vacuum at 708C for 24 h. De-ionized water, ammonium hydroxide, and quinoline were added to the reaction mixture, based on the concentrations of oxygen and nitrogen in the feeds for Table 1 Composition and properties of Athabasca hydrocarbons Elemental composition Treated light gas oil hydrotreaters. The typical ranges for nitrogen and oxygen concentration in bitumen residues are 0.2±0.7 and ca. 1 wt%, respectively [11]. The distillate feeds to hydrotreaters can also contain signi cant amounts of N, for example, the nitrogen contents are ca wppm in the gas oil and and 1300 wppm in the middle distillate feeds to hydrotreaters at the Syncrude plant. A packed bed of glass beads was used to collect the ne particles at reaction conditions, giving a measure of the tendency of the particles to deposit on surfaces. The beads were washed with chromic acid cleaning solution, rinsed with excess deionized water, and then dried in an oven at 1108C for 24 h. Kaolin, iron sul de, and glass beads were stored in a desiccator after preparation Asphaltene treatment of kaolin and iron sul de The kaolin and iron sul de were treated with asphaltenes to simulate the coating of organic material that is normally found on mineral surfaces [5]. An asphaltene-rich fraction of Athabasca bitumen (aromatics, 2.2 wt%; resins, 9.4 wt%; asphaltenes, 88.0 wt%) from supercritical uid extraction [12] was diluted 40 to 1 by volume with toluene and mixed for 24 h by a magnetic stirrer. The mixture was then centrifuged at 3100 rpm for 1 h to remove solids. The supernatant was recovered and the toluene removed in a rotary evaporator under reduced pressure. The residual liquid was then dried under vacuum at 708C for 24 h to evaporate any volatiles, then Soxhlet extracted with n- pentane for 24 h to remove any entrapped maltenes. The resulting solids-free asphaltenes were dried under vacuum at 708C for 24 h, and then stored in a desiccator. The composition of the resulting solids-free asphaltenes is given in Table 1. Kaolin and iron sul de particles were treated with solidsfree asphaltenes, following the method of Yan and Masliyah [13]. Solid-free asphaltene (0.05±1 g) was mixed with 250 ml toluene, and sonicated at room temperature for 20 min to dissolve. Heptane (250 ml) was added to the solution, and the mixture was sonicated for 20 min. Kaolin Solids-free asphaltenes C (wt%) H (wt%) S (wppm) ,600 N (wppm) ,400 Asphaltene (wt%) Density (kg/m 3 ) 880 ± at 158C Viscosity (mpa-s) 6.5 ± at 208C Solids concentration 140 ± (wppm) Boiling range (8C) 177±433 ±

3 S. Wang, K. Chung / Fuel 00 (2000) 000±000 3 Table 2 Properties of asphaltene-treated kaolin, iron sul de and asphaltene-treated iron sul de Properties Asphaltenetreated kaolin Iron sul de Element (wt%) C H O ± N S ± Density (kg/m 3 ) Asphaltene-treated iron sul de thermowell baffle Liquid addition system 15 ml micro-reactor Valve A 2 ml micro-reactor Valve B Mass median diameter (mm) or iron sul de (2.5 g) was added, and the mixture was stirred at 400 rpm for 24 h. The solid particles were recovered by ltration through a 0.22 mm millipore membrane lter, then dried under vacuum at 708C for 24 h. The properties of asphaltene-treated kaolin, iron sul de, and asphaltenetreated iron sul de are listed in Table Reactor apparatus and liquid addition system Although stirred tanks give complex ow patterns and shear, the particle deposition experiments maintained the same hydrodynamic condition in every case by keeping all operating parameters constant. Consequently, any changes in deposition of particles were due to changes in composition, not liquid ow. A 500 ml batch stirred reactor was used for particle deposition experiments (Fig. 1). Two pitched blade turbine impellers operating at 700 rpm were employed to suspend kaolin in treated light gas oil and circulate uid through the packed bed in the draft tube. Four evenly spaced baf es reduced vortex or swirl in the reactor. The glass beads were retained by stainless steel mesh (#32) at each end of the draft tube. A 2 ml micro-reactor was used to introduce liquid additives, such as water, into the batch reactor under high pressure. A designated amount of liquid was injected into this micro-reactor with a 2 ml syringe. A 15 ml microreactor was pressurized with hydrogen to 17.2 MPa, then connected to the 2 ml micro-reactor as illustrated in Fig. 1. A suspension of kaolin (0.98 g) or iron sul de (0.65 g) in treated light gas oil (ca. 240 g) was sonicated for 20 min and then poured into the 500 ml reactor. The standard reaction conditions were 3758C, 60 min of reaction time, 700 rpm impeller speed, 20 g of glass beads, 240 g of light gas oil, initial hydrogen pressure 6.2 MPa. When the reaction temperature reached the speci ed value, the timing of reaction began and the impeller was switched on. Liquid additives were introduced from the micro-reactor by opening valves A and B. The valves were closed again after 10 s to prevent condensation of vapor in the cold micro-reactors. The mass change of the 2 ml micro-reactor was measured to determine the amount of additive that entered the reactor. After 60 min, the impeller was turned off and the reactor was allowed to cool. The concentration of asphaltenes remaining on the kaolin and iron sul de particles was determined from the carbon contents of ne solids in the liquid product. With the assumption that residual asphaltenes on the particle surfaces possessed the same carbon content of 80.4 wt% as solidsfree asphaltenes (Table 1), the amount of asphaltene-treated solids was corrected to a hydrocarbon-free basis. If the composition of the asphaltenes changed due to hydrogenation reactions, the bias in the corrected mass of particles would be less than 0.5% since the carbon content would not exceed the treated light gas oil (Table 1). A microscopy video image system was used to observe the top layer of the bed of packing. Images were displayed on the monitor and analyzed using a personal computer. The packing of glass beads was cleaned by sonicating with 250 ml methylene chloride for 20 min, then the solids were recovered by ltration through a 0.22 mm Millipore H =16.8cm collectors Φ=6.4 cm impeller top layer of packing screen Fig. 1. Schematic diagram of batch reactor and its internals (all internals are shown to scale with respect to the dimensions of the batch reactor). draft tube screen

4 4 S. Wang, K. Chung / Fuel 00 (2000) 000±000 lter to determine the mass of kaolin that had deposited. The sonication and ltration were then repeated, following the method of Biran et al.[14]. The ltered solids were dried in vacuum at 708C for 24 h and then weighed. The speci c deposit, s, was de ned as the mass of solid particles deposited per unit volume of the packed bed of glass beads (kg/m 3 ) Analysis of samples Solids were dried in vacuum oven at 708C for 24 h before elemental analysis. 3. Results and discussion 3.1. Repeatability of particle deposition measurements The repeatability of particle deposition experiments was checked with 0.98 g asphaltene-treated kaolin (0.68 mm) under the standard reaction conditions of 3758C, 60 min of reaction time, 700 rpm of impeller speed, 20 g of glass beads, 240 g of treated light gas oil and initial cold hydrogen pressure of 6.2 MPa. The speci c deposit (s) for the ve repeated runs was 14.3 ^ 0.8 kg kaolin/m 3 packed bed (95% con dence interval). The carbon content of kaolin from the liquid product was 2.3 ^ 0.3 wt% (95% con dence interval). These results showed that repeatability of particle deposition experiments was satisfactory Deposition of iron sul de particles The standard experimental conditions used ca. 1 g of kaolin (0.68 mm), giving a concentration of 4000 ppm by weight. The mass of iron sul de was 0.65 g, selected to give the same amount of surface coverage of particles on the collector surface, on an area basis. The composition of the iron sul de particles is given in Table 2. Since iron (II) sul de should contain 36 wt% sulfur, the iron oxide in the particles was not completely converted to sul de. Only the surface of particles contacts the collector surfaces and liquid media, and consequently, the formation of an iron sul de exterior surface was most important. The particle size of the iron sul de did not change signi cantly from the initial size of 0.2 mm due to sul dation, based on examination under an optical microscope. The speci c deposits of iron sul de and asphaltenetreated iron sul de on packed beds of glass beads were 30.9 and 33.5 kg/m 3, respectively, based on two repeated runs for each sample. Consequently, asphaltene pretreatment had no signi cant in uence on the deposition of iron sul de. This result was the opposite of previous work on kaolin, which showed that a surface layer of asphaltenes hindered kaolin deposition on a bed packed with either glass beads or catalyst pellets [3]. However, the carbon content of asphaltene-treated iron sul de dropped dramatically from the initial value of 4.7±0.9 wt% after reaction, indicating that most of the asphaltenes were desorbed or thermally decomposed from the iron sul de surface. The iron sul de without asphaltenes gave a carbon content of 0.7 wt%. Therefore, the equivalent deposition of the asphaltenetreated and untreated iron sul des in the packed bed was consistent with the equivalent organic coating on the two sets of particles at reaction conditions, based on carbon content. The catalytic activity of iron sul de probably enhanced the desorption of asphaltenes from its surfaces by promoting hydrogenation reactions. For example, suspended metal sul des were used as the catalyst for destructive hydrogenation of heavy petroleum and tar materials, and the degree of decomposition of asphaltenes was used to judge the activity of the catalyst [9]. Although the experiments with asphaltene-treated kaolin used 50% more by weight of particles than asphaltenetreated iron sul de, the speci c deposit of kaolin was less than half of that of iron sul de (14.3 ^ 0.8 versus 30.9± 33.5 kg/m 3 ). After reaction, asphaltene-treated kaolin gave a much higher carbon content (2.3 wt%) than the asphaltene-treated iron sul de (0.9 wt%) in the liquid products. Only the surface layer of particles is important during deposition, therefore, the mineral material makes no difference in deposition when it is coated with an organic layer Effect of hydrodeoxygenation on kaolin deposition Water is produced at low concentrations in hydrotreaters for Athabasca distillates due to hydrogenation of oxygencontaining compounds. To study the role of water in particle deposition, water was added to the reactor after the nal operating temperature was reached. This approach avoided contact between the clay and liquid water during the time required to heat the reactor (ca. 60 min). Injection of 0.8 wt% water gave an immediate increase in reactor pressure of 1.9 MPa. In comparison, adding the same amount of water to the empty reactor, along with the incremental hydrogen from the liquid injection apparatus, would increase the total pressure by 1.7 MPa. Kaolin was deposited throughout the bed of glass beads when no water was added. The addition of water, however, gave a continuous cake of kaolin on top of the bed of glass beads (Fig. 2). No agglomerated kaolin was found at the bottom of the reactor. This cake formation was consistent with the increase in speci c deposit on glass beads from 14.3 ^ 0.8 kg/m 3 to a mean value of 47.9 kg kaolin/m 3 packed bed (from two repeat experiments) when water was added. The observed deposition of kaolin could have been in uenced by total reaction pressure and condensation of water after the reaction. Upon the addition of water at 3758C, the total reaction pressure increased immediately from 12.1 to 14.0 MPa. In order to investigate the effect of this pressure increase on particle deposition, the experiment was repeated at a higher initial hydrogen pressure of 7.6 Mpa. The resulting nal reaction pressure of 13.6 Mpa gave a lower speci c deposit

5 S. Wang, K. Chung / Fuel 00 (2000) 000±000 5 Fig. 2. Cake formation on top of the packed bed of glass beads (3758C, 1 h, 2 g water added before reaction, 700 rpm, 20 g glass beads). of 8.8 kg kaolin/m 3 packed bed. Consequently, pressure differences cannot account for the increase in deposition due to water. The water would condense after the reactor was removed from the heater and allowed to cool. To test the effect of condensing water on kaolin deposition, 2 ml water was injected after the 60-min reaction time when the impeller was turned off. The speci c deposit in this case was 18.8 kg kaolin/m 3 packed bed, slightly higher than 14.3 ^ 0.8 kg kaolin/m 3 packed bed at standard conditions but far below the level of deposition observed with addition of water at reaction conditions Mechanism of water±clay interactions The above experiments showed that the addition of water increased the deposition of asphaltene-treated clay by a factor of two, and that this process was not sensitive to variations in pressure or temperature. At room temperature, the hydrocarbon phase and the water phase can be treated as being completely immiscible, but the solubility of water in hydrocarbon liquids increases exponentially with temperature. For example, oils can contain up to 40 mol% of soluble water at 3008C, far in excess of the,1 wt% water in this experiment [15,16]. At 3758C, therefore, the water would be present at low concentration throughout the liquid and vapor phases in the apparatus. Previous work showed that the organic coating on the clay stabilized a suspension in gas oil at hydrotreating conditions [3]. Any removal of this coating due to the presence of water would destabilize the clay particles and promote occulation and cake ltration. If water hydrated the clay surface, and displaced the asphaltenes, then the resulting destabilized clays would deposit more readily, as illustrated in Fig. 3. The carbon content of asphaltene-treated kaolin Clay with adsorbed organics Supercritical Water Flocculated clay Hydrated clay Collector + Displaced organics Deposited clay Fig. 3. Potential mechanism for role of water in deposition of clay particles.

6 6 S. Wang, K. Chung / Fuel 00 (2000) 000±000 Table 3 Role of polar compounds in deposition of kaolin (3758C, 700 rpm, 20 g glass beads, 1 h of reaction time, 0.98 g of asphaltene-treated kaolin with a carbon content of 5.9 wt%) Reaction conditions Carbon in kaolin from liquid product (wt%) Kaolin deposited (wt%) Speci c deposit (kg kaolin/m 3 packed bed) Standard 2.3 ^ ^ ^ 0.8 (n ˆ 5) a (95% con dence) 0.36% Water % Water (n ˆ 2) a 0.4% NH 4 OH % Quinoline a n is the number of repeat experiments. decreased after reaction, and it decreased further in proportion to the amount of water added (Table 3). Kaolin with a lower level of asphaltene coating, due to the displacement of asphaltene molecules with water, would be more easily deposited on the surface of the glass beads. This factor alone was suf cient to explain the increased tendency for deposition, without any need to suggest additional interactions between water and clay. As illustrated in Fig. 4, the observed deposition of clays in the presence of water was consistent with data for dry clays [3], when compared on the basis of carbon content. The displacement of the asphaltene layer by water molecules was also checked with the toluene-insoluble solids ltered from Athabasca vacuum residue (5258C 1 ) under the same reaction conditions. The carbon content of these solids dropped from 18.5 to 12.5 wt% without water, and decreased further to 11.8 wt% with water addition. Consequently, the model suspension exhibited the same trend as the authentic solids from bitumen. Specific deposit (kg/m 3 ) g water 0.86 g water 3.5. Effect of hydrodenitrogenation on kaolin deposition Another polar component that accumulates in the vapor phase during hydrotreating is ammonia due to hydrogenation of nitrogen-containing compounds in oil streams. The role of ammonia in particle deposition was determined by injecting 0.4 wt% of a 30 wt% solution of ammonium hydroxide into the reactor at reaction conditions. The amount of ammonia added, corresponded to the removal of 500 wppm of organic nitrogen from the gas oil. As indicated by the data of Table 3, 34.6 wt% of the asphaltenetreated kaolin (0.98 g) was deposited on 20 g of glass beads. The corresponding speci c deposit was 25.8 kg kaolin/m 3 packed bed. At 3758C, the ammonium hydroxide solution (1 g) would give 0.86 g water at reaction conditions. The effect of this amount of water on kaolin deposition was determined by injecting 0.36 wt% water (0.86 g) at reaction temperature. The results were equivalent to the experiment with ammonium hydroxide (Table 3), with 32.8 wt% of asphaltene-treated kaolin (0.98 g) deposited on 20 g of Residual carbon content (%) no water added (Data of Wang et al. 3 ) water added Fig. 4. Dependence of speci c deposit of clay in a packed bed of glass beads on residual carbon content of kaolin from liquid product (3758C, 700 rpm, 60 min of reaction time).

7 S. Wang, K. Chung / Fuel 00 (2000) 000±000 7 glass beads with a speci c deposit of 24.4 kg kaolin/m 3 packed bed. Consequently, the addition of ammonia had no signi cant effect on deposition of asphaltene-treated kaolin. Nitrogen compounds are often more dif cult to remove than sulfur compounds, and the persistent nitrogen bases could interact with ne particles to promote stability. Quinoline was added to treated light gas oil to give a nitrogen concentration of 450 wppm (2 ml in 240 g) to represent these nitrogen bases. Deposition of asphaltenetreated kaolin was insensitive to the addition of quinoline, giving a speci c deposit of 14.3 kg kaolin/ m 3 packed bed (Table 3). This value was almost the same as 14.3 kg kaolin/m 3 packed bed in the absence of quinoline. Consequently, the removal of polar organic species such as quinoline by catalytic reactions in hydrotreaters would have no signi cant impact on deposition of ne clays. The results of these experiments clearly show that the behavior of ne mineral particles at hydrotreater conditions is controlled by the presence of a coating of asphaltenic material. If this material is removed, as in the case of iron sul des, then the resulting particles are less stable in suspension and deposition will increase. Similarly, water displaced asphaltenic material from clay surfaces and enhanced deposition. Neither ammonia nor a nitrogen base had any effect. The implications of this study are that particles may deposit in different zones of the reactor depending on their surface properties. The iron sul des formed from reaction of corrosion products and hydrogen sul de would deposit most rapidly. Hydrophobic clays with an asphaltene coating would be more stable until they reached a zone of higher water content, due to active HDO. At this point, the rate of deposition would increase. Wang et al. [3] also showed that the organic coating was progressively removed from clays in the presence of an active catalyst. Consequently, the rate of deposition of clays would tend to increase during passage through a hydrotreater. The nature of the interaction between water and clay under the reaction conditions is not clear, but the data from this study suggest that the presence of water could further destabilize suspensions of ne clay particles. The actual deposition of solids in a hydrotreating reactor would depend not only on the stability of the suspension, but also on the hydrodynamic conditions. This study implies that the most stable particles in suspension could be coke, due to the intrinsic hydrophobic character of the coke material and the lack of organic layers to remove at hydrotreater conditions. 4. Conclusions Asphaltene-coated iron sul de deposited more readily than asphaltene-coated kaolin at hydrotreater conditions. This difference in behavior was consistent with the carbon contents of the two types of particles. At supercritical conditions the water released by HDO may displace a portion of asphaltene molecules from the surface of asphaltene-treated kaolin particles, exposing more hydrophilic areas on the solid surface, and thereby increased the tendency for particles to deposit on collectors. Polar compounds such as quinoline and ammonia had no signi cant effect on deposition of ne particles. Acknowledgements The authors are grateful to Syncrude Canada Ltd for its nancial support to this project. Mr Bob Scott and Mr Ron Cooper provided invaluable assistance in the preparation and modi cation of the reactor internals. References [1] Koyama H, Nagai E, Torri H, Kumagai H. Oil Gas J 1995;93(46):82. [2] Chan EW, Chung KH, Veljkovic M, Liu JK. International Petroleum and Petrochemical Technology Symposium. Beijing, September 15± 17, [3] Wang S, Chung KH, Masliyah JH, Gray MR. Deposition of ne particles in packed beds at hydrotreating conditions: role of surface chemistry. Ind Engng Chem Res 2001 (in press). [4] Chung KH, Xu C, Gray MR, Zhao Y, Kotlyar L, Sparks B. Rev Proc Chem Engng 1998;1:41±79. [5] Kotlyar LS, Kodama H, Sparks BD, Grattan-Bellew PE. Appl Clay Sci 1987;2:253±71. [6] Ignasiak TM, Zhang Q, Kratochvil B, Maitra DS, Montgomery DS, Strausz OP. AOSTRA J Res 1985;2:21±35. [7] Ranganathan R, Denis, Jean-Marie D, Pruden BB. US Patent 4,214,977. July 29, [8] Goldberg AS. Proceedings in SPE Annual Technical Conference & Exhibition, Omega (Pt. 2) pp. 551±5. [9] Weisser O, Landa S. Sulphide catalysts. Their properties and applications. Oxford: Pergamon Press, 1973 (p. 294). [10] Kriz JF, Ternan M. In: Kaliaguine S, Mahay A, editors. Studies in surface science and catalysis: catalysis on the energy scene, vol. 19. Amsterdam: Elsevier, p. 545±52. [11] Gray M. Upgrading petroleum residues and heavy oils. New York: Marcel Dekker, [12] Chung KH, Xu C, Hu Y, Wang R. Oil Gas J 1997;95(3):66±69. [13] Yan N, Masliyah JH. J Colloid Interface Sci 1996;181:20. [14] Biran R, Tang YZ, Brook JR, Vincent R, Keeler GJ. Int J Environ Anal Chem 1996;63:315. [15] Hoot WF. Pet Re ner 1957;36(6):198. [16] Nelson WL. Petroleum re nery engineering. New York: McGraw- Hill, 1958.