Energy & Fuels 2006, 20, 1145-1149
1145
Atmospheric Residue Desulfurization Process for Residual Oil Upgrading: An Investigation of the Effect of Catalyst Type and Operating Severity on Product Oil Quality A. Marafi,*,† A. Hauser,‡ and A. Stanislaus† Petroleum Refining Department and Central Analytical Laboratory, Kuwait Institute for Scientific Research, P.O. Box 24885, Safat 13109, Kuwait
Energy Fuels 2006.20:1145-1149. Downloaded from pubs.acs.org by KAOHSIUNG MEDICAL UNIV on 07/28/18. For personal use only.
ReceiVed NoVember 25, 2005. ReVised Manuscript ReceiVed February 11, 2006
Atmospheric residue desulfurization (ARDS) process is extensively used in upgrading of heavy petroleum oils and residues to more valuable clean environmentally friendly transportation fuels and to partially convert the residues to produce low-sulfur fuel oil and hydrotreated feedstocks. Graded catalyst systems in multiple reactors are used in the process in order to achieve hydrodesulfurization (HDS), hydrodemetallization (HDM), hydrodenitrogenation (HDN), and conversion of residues to distillates at desired levels. The characteristics of the feedstocks processed in different reactors are significantly different. The quality of the feed entering the second reactor is strongly dependent on the operating severity in the first reactor and can have an important impact on the performance of the catalysts in the following reactor with regard to various conversions and deactivation rate. In the present work, a systematic study was conducted on the effect of two industrial catalyst types, namely, MoO3/Al2O3 (HDM) and Ni/MoO3/Al2O3 (HDS) catalysts, in the range of 360-420 °C operating temperature on product quality in hydrotreating straight run Kuwait atmospheric residue. The liquid products and their asphaltene fractions from different runs were characterized by various techniques including 13C NMR and elemental analysis, and the effect of catalyst and operating severity on product quality was assessed. Special attention was paid to the changes in the characteristics of asphaltenes as a function of operating temperature and catalyst type. The results revealed that, besides the usual heteroatoms removal reactions, such as HDS, HDM, and HDN, asphaltenes and resins in the residual oil feed were converted to saturates and aromatics during the hydrotreating process. The aromatic rings in the asphaltenes remaining in the product oil become more condensed and less alkyl-substituted with increasing operating severity disregarding the types of catalyst used. The aromaticity and degree of condensation in the product asphaltenes were higher for the HDM than for the HDS catalyst. The catalyst’s hydrogenation activity appears to play a dominant role in determining the nature of the asphaltenes in the product oil. Since the quality of the liquid products, particularly the quality of the residual asphaltenes in the product oil from different catalyst beds, plays a key role in catalyst deactivation and fuel oil stability, the results are considered to be very valuable for optimization of the operating conditions as well as on catalyst selection for hydroprocessing of residual oil in an ARDS process.
1. Introduction To meet the challenges facing the refining industry, a number of conventional processes were developed to refine and upgrade petroleum residues to more valuable transportation fuels or lowsulfur fuel oil.1,2 Two main routes, namely, carbon rejection and hydrogen addition, are commonly used for residual oil conversion and upgrading.1-4 The former one involves thermal treating of heavy oils in the absence of hydrogen. This causes large hydrocarbon molecules to crack into smaller molecules, resulting in the production of distillates and gas. A number of * To whom correspondence should be addressed. Fax: (+965)3980445. E-mail:
[email protected]. † Petroleum Refining Department. ‡ Central Analytical Laboratory. (1) Gray, M. R. Upgrading Petroleum Residues and HeaVy Oils; Marcel Dekker: New York, 1994. (2) Khan, M. R.; Patmore, D. J. Heavy oil upgrading processes. In Petroleum Chemistry and Refining; Speight, J. G., Ed.; Marcel Dekker: New York, 1998; pp 149-173. (3) Babich, I. V.; Moulijn, J. A. Science and technology of novel processes for deep desulfurization of oil refinery streams: a review. Fuel 2003, 82, 607-631. (4) Le Page, J. F. Resid and HeaVy Oil Processing; Editions Technip: Paris, 1992.
technologies such as delayed coking, resid FCC, etc., have been developed over the years for residual oil upgrading based on the carbon-rejection route. The second route, the hydrogen-addition route, involves contact of the residual oil with hydrogen at high temperatures and pressures. The high-molecular-weight residual oil feedstock is cracked and hydrogenated to yield distillate products with an increased H/C ratio and residual oil with reduced sulfur, nitrogen, and metals contents. The process can be catalytic or noncatalytic. In the catalytic hydrogen-addition processes, highactivity hydrotreating catalysts, such as Ni-Mo/Al2O3 or CoMo/Al2O3, are employed.5-8 These catalysts have functions (i) to enhance the removal of undesirable contaminants, such as (5) Furimsky, E. Selection of catalysts and reactors for hydroprocessing. Appl. Catal., A 1998, 171, 177-206. (6) Delmon, B. New technical challenges and recent advances in hydrotreatment catalysis. Catal. Lett. 1993, 22, 1-32. (7) Topsoe, H.; Clausen, B. S.; Topsoe, N. Y.; Zeuthen, P. Progress in the design of hydrotreating catalysts based on fundamental molecular insight. Stud. Surf. Sci. Catal. 1990, 53, 77-102. (8) Bartholdy, J.; Cooper, B. H. Optimizing hydrotreater catalyst loadings for the upgrading of atmospheric residues. Catalysts in Petroleum Refining and Petrochemical Industries 1995; Elsevier: Amsterdam, 1996; pp 117124.
10.1021/ef050395d CCC: $33.50 © 2006 American Chemical Society Published on Web 04/04/2006
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sulfur, nitrogen, and metals, present in the residual feed by promoting hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and hydrodemetallization (HDM) reactions, (ii) to accelerate the conversion of the high-molecular-weight components to lighter products, (iii) to promote hydrogenation of the cracked fragments, leading to an increase in the overall H/C ratio of the products, and (iv) to reduce the coke formation. The preference between the two routes depends on factors such as environmental constraints, feedstock flexibility, and product target. The hydrogen-addition route has the advantage to yield products of higher quality than the carbon-rejection route does. The distillates and residual oils produced by hydroconversion processes have low levels of aromatics, sulfur, nitrogen, and other contaminants, and they have better stability. The atmospheric residue desulfurization (ARDS) process has been developed for residual oil upgrading following the hydrogen-addition route. This process is used extensively in Kuwaiti refineries for the upgrading of petroleum residues.5,9,10 The process involves hydrotreatment of the residual oil feed in a series of fixed bed reactors loaded with different types of catalysts. Catalysts for such hydrotreating processes are selected on the basis of activity, selectivity, and life-on-stream. The catalyst life depends on the rate of deactivation by coke and metal deposits as well as on the sintering of the active phase. The performance of the overall ARDS process with regard to various reactions, such as HDM, HDS, HDN, asphaltenes cracking, feed conversion to distillates, and catalyst lifetime, is clearly linked to the performance of the catalysts in the different reactors.5,11 In the ARDS process, the characteristics of the feedstocks processed in different reactors are significantly different. For example, the feed that enters the front reactor is original atmospheric residue, whereas the feed to the second reactor is a demetallized and partially hydrotreated product from the first reactor. The quality of the feed entering the second reactor is strongly dependent on the operating severity in the first reactor and can have a significant influence on the performance of the catalysts in the following reactor with regard to various conversion reactions and the catalyst deactivation rate. Therefore, information about the product quality and the behavior of a multiple catalyst system under ARDS process conditions are highly desired to optimize the reactor loading and the operating conditions. To date, information about the effect of catalyst type and operating severity on the product oil quality, e.g., detailed characteristics of the maltene and asphaltene fractions are limited. In the present study, performance comparison tests were carried out on two types of industrial catalysts, namely, an HDM (MoO3/Al2O3) and an HDS (Ni/Mo/Al2O3) catalyst, that are loaded in the front and middle reactors of the commercial ARDS process, using atmospheric residue from Kuwait expot crude (KU-AR) as a feed in a fixed-bed pilot plant. The primary objective of the work was to carry out systematic studies to assess the quality of the liquid oil products obtained at various reaction temperatures using both types of catalysts. The product oils were fractionated into maltenes and asphaltenes, and the asphaltene fractions were characterized by various techniques (9) Al-Nasser, A.; Chaudhuri, S. R.; Bhattacharya, S. Mina Abdulla refinery experience with atmospheric residue desulfurization (ARDS). Stud. Surf. Sci. Catal. 1996, 100, 171-180. (10) Abbas, A. K.; Chaudhuri, S. R.; Bhattacharya, S. Performance optimization of atmospheric residue desulphurization units. Proceedings, 8th Annual Saudi-Japanese Symposium, Dhahran, Saudi Arabia, November 29-30, 1998; pp 175-189. (11) Adams, C. T.; Del Peggio, A. A.; Schaper, H.; Stork, W. H. J.; Shiflett, W. K. Hydroprocessing catalyst selection. Hydrocarbon Process. 1989, September, 57-61.
Marafi et al. Table 1. KU-AR Feed Characteristics feed property
unit
values
accuracy %
API S N CCR asphaltene Ni V density @15 °C kinematic viscosity @ 50 °C
wt % wt ppm wt % wt % wt ppm wt ppm mg/mL cSt
12.27 4.30 2670 12.20 3.60 21 69 0.9837 871.
2 3 3 2 2 1 2 0.1 0.5
Table 2. Characteristics of Catalysts Used in the Present Study catalyst characteristics
unit
HDM
HDS
bulk density surface area average pore diameter active metal metal content Mo Ni metal capacity
g/mL m2/g Å
0.4-0.5 150-200 150-200 Mo
0.6-0.7 200-250 80-100 Ni, Mo
wt % wt %
2-3 high
7-9 2-3 medium
including 13C NMR. Special attention was paid to structural changes in the asphaltenes as a function of operating temperature for the two types of catalysts. Since the quality of the residual asphaltenes in the product oil plays a key role in catalyst deactivation and fuel oil stability, the results of the study will be useful for catalyst selection and for optimization of the operating conditions in the ARDS process. The results presented in this paper are part of a broader study on the ARDS process optimization pursued in our laboratories.12-18 2. Experimental Section 2.1. Materials. The characteristics of the typical feed used in the refinery ARDS process and in this study, namely, KU-AR, are shown in Table 1. Two industrial ARDS hydroprocessing catalysts, namely, a MoO3/Al2O3 (HDM) catalyst dedicated for metal removal and a NiMo/Al2O3 (HDS) catalyst intended to remove sulfur, were used for conducting the comparison studies. The characteristics of both catalysts are presented in Table 2. 2.2. Hydrotreating Techniques. The hydrotreating experiments were conducted in a fixed-bed reactor unit (Vinci Technologies) using KU-AR as feed. Experiments were carried out for each catalyst individually. A 50 mL of catalyst charge diluted with an equal amount of carborundum was used for each run. The catalyst was presulfided by a standard procedure using straight run gas oil (12) Matsushita, K.; Hauser, A.; Marafi, A.; Stanislaus, A. Initial coke deposition on hydrotreating catalysts: Part I. Changes in coke properties as function of time on stream. Fuel 2004a, 83, 1031-1038. (13) Matsushita, K.; Marafi, A.; Hauser, A.; Stanislaus, A. Relation between relative solubility of asphaltenes in product oil and coke deposition in residue hydroprocessing. Fuel 2004b, 83, 1669-1674. (14) Marafi, A.; Al-Bazzazi, H.; Al-Marri, M.; Maruyama, F.; AbsiHalabi, M.; Stanislaus, A. Residual-oil hydrotreating kinetics for graded catalyst sustems: Effect of original and treated feedstocks. Energy Fuels 2003a, 17 (5) 1191-1197. (15) Marafi, A.; Fukase, S.; Al-Marri, M.; Stanislaus, A. A comparative study on the effect of catalyst type on hydrotreating kinetics of Kuwaiti atmospheric Residue. Energy Fuels 2003b, 17 (3), 661-668. (16) Marafi, A.; Stanislaus, A.; Absi-Halabi, M.; Hauser, A.; Matsishita, K. A comparative studies of an industrial Mo/Al2O3 and Ni-Mo/Al2O3 catalysts: Deactivation behavior in hydrotreating Kuwaiti atmospheric residue. Pet. Sci. Technol. 2005, 23, 385-408. (17) Hauser, A.; Stanislaus, A.; Marafi, A.; Al-Adhwani, A. Initial coke deposition on hydrotreating catalysts: Part II. Structural elucidation of initial coke on hydrodemetallation catalysts by selective suppression of 13C signals in solid-state NMR. Fuel. 2005a, 84, 259-269. (18) Hauser, A.; Marafi, A.; Stanislaus, A.; Al-Adwani, A. Relation between feed quality and coke formation in a three-stage atmospheric residue desulfirization (ARDS) process. Energy Fuels 2005b, 19, 544-553.
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Table 3. Run Conditions for Temperature Effect Studies process parameter
unit
range/value
temperature pressure LHSV H2/oil ratio time on stream
°C bar h-1 mL/mL h
360-420 120 1 570 120
containing 3 wt % dimethyl disulfide (DMDS) before injecting the feed. After the presulfiding, conditions for each run were adjusted to desired operating temperature, pressure, hydrogen flow rate and liquid Hourly Space Velocity (LHSV). Table 3 shows the various operating conditions for the studies. During the course of each run, product samples were collected after 120 h and analyzed for sulfur, metals (V and Ni), nitrogen, asphaltenes, Conradson carbon residue (CCR), viscosity, density, and distillate yield using standard methods for petroleum product evaluation.19,20 2.3. Product Analysis. The product oils from hydrotreating experiments at various temperatures were separated into maltenes and asphaltenes applying the IP-143.20 The carbon, hydrogen, sulfur, and nitrogen contents were determined using a CE elemental analyzer, model EA 1110. The 1H and 13C NMR were carried out on a Bruker AVANCE300 spectrometer operating at 7.05 T. CDCl3 (99.8%) and tetramethylsilane (TMS), both from WILMAD, were used as solvent and as internal standard for the 1H NMR measurements. The 13C chemical shift values were referenced to the central signal of the CDCl3 at 77.7 ppm. For 1H NMR, the sample concentration was approximately 15 wt % in 0.5 mL of CDCl3. The solution was filled into a 5 mm tube, and a drop of TMS was added. To obtain quantitative 13C NMR spectra, the solution was transferred to a 10 mm tube, and the concentration was increased to about 60 wt %. 1H NMR spectra were acquired with a spectral width of 5.5 kHz, a pulse angle of 90° (20 µs), and a delay time of 3 s. The settings for the quantitative 13C NMR measurements were as follows: inverse gated decoupling as pulse program, 25 kHz spectral width, 30° (3 µs) pulse angle, and 60 s delay time.
3. Results and Discussions 3.1. Bulk Properties of the Product Oil. Initial studies focused on the effect of reaction temperature on the overall product quality during hydrotreating of KU-AR. The characteristics of the product oils obtained from various runs at different temperatures for both catalysts are presented in Table 4. The results reveal that an increase in the reactor temperature from 360 °C to 420 °C enhances the removal of various hetroatoms present in KU-AR. In the tested range, temperature increase has a favorable effect on the purification of the product from S, N, V, Ni, and CCR. Moreover, the results show for both catalysts that the density of the product oils decreases with increasing temperature, indicating an acceleration of feed conversion to lighter products at higher temperature. In terms of S, N, V, Ni, and CCR removal, the HDS catalyst shows a better performance than the HDM catalyst (Figure 1). The asphaltene conversion, however, is more efficient over the HDM catalyst. This result is expected since the HDM catalyst possesses large pores, which facilitate the diffusion of bulky asphaltene molecules into the catalyst pellet.15,21 The HDS catalyst, on the other hand, due to its medium pore size and higher hydrogenation activity, is more appropriate to remove sulfur, CCR, and to a lesser extent nitrogen. (19) ASTM. Annual Book of ASTM Standards: Petroleum Products, Lubricants and Fossil Fuels; American Society for Testing and Materials: Philadelphia, PA, 1996; Vols. 5.01, 5.02, and 5.03. (20) The Institute of Petroleum. Standard Method for Analysis and Testing of Petroleum and Related Products; John Wiley & Sons: New York, 1995; pp 143.1-143.4. (21) Quan, R. J.; Ware, A.; Hang, C. W.; Wei, J. Hydrodemetallation of Petroleum. AdV. Chem. Eng. 1988, 14, 95-257.
Table 4. Reaction Temperature Effect on the Liquid Product Quality in Hydrotreating of KU-AR over HDM and HDS Catalysts temperature 380 °C
400 °C
420 °C
S N CCR asphaltenes V Ni density @ 15 °C
HDM Catalyst wt % 3.23 2.79 wt ppm 2600 2570 wt % 10.50 9.52 wt % 2.22 1.68 wt ppm 35 23 wt ppm 12 10 g/mL 0.9837 0.9655
2.62 2486 8.54 1.21 11 8 0.9609
1.55 2255 6.83 6 4 0.9225
S N CCR asphaltenes V Ni density @ 15 °C
wt % wt ppm wt % wt % wt ppm wt ppm gm/mL
HDS Catalyst 1.38 1.08 2510 2430 7.56 6.95 2.93 2.40 26 22 10 8 0.9737 0.9510
0.56 1960 4.76 1.75 12 6 0.9444
0.22 1780 3.66 1.32 5 4 0.9100
parameter
unit
360 °C
The results presented in Figure 1 indicate that as the reactor temperature increases, the products are more purified and become lighter, suggesting that they might be processed more easily in the following reactor of an ARDS unit with multiple reactors. However, besides the contaminant levels, the structural characteristics of the various fractions of the product oil, particularly that of the asphaltene fraction, could play a dominant role in the ease of its processibility as well as on catalyst deactivation in the subsequent reactors in series.16,22 Therefore, the liquid products collected after hydrotreating of KU-AR at various temperatures over both types of catalyst were separated into maltenes and asphaltenes (Table 5). The asphaltenes fraction was subjected to detailed characterization using elemental and 13C NMR analysis to examine the nature of changes in its characteristics. 3.2. Properties of Product Asphaltenes. 3.2.1. Elemental Analysis. The asphaltene fractions from KU-AR hydrotreating over both HDM and HDS catalysts were further subjected to elemental analysis to determine C, H, N, and S contents. The results of H/C, N/C, and S/C molar ratios for the asphaltene fractions as a function of temperature are given in Table 6. For both catalysts, the H/C in the asphaltene fractions decreases as the temperature increases, with a steeper decrease for the HDM catalyst (Table 6). The S/C and N/C molar ratios in the asphaltene fractions are higher for the HDM catalyst than the HDS catalyst at all temperatures. As for the hydroprocessing of asphaltenes, the elemental analysis indicates that the HDS catalyst is superior to the HDM catalyst. These results are consistent with the quality of the product oils obtained from hydrotreating KU-AR over both catalysts as discussed earlier. 3.2.2. 13C NMR Analysis. The aromaticity and structural characteristics of asphaltenes remaining in the product oil resulting from hydrotreatment of KU-AR over the two types of catalysts were further examined by 13C NMR analysis. The results presented in Figure 2 show that the aromaticity of the asphaltenic fraction increases with increasing temperature despite an appreciable decline in their concentrations in the product oils. Besides the overall reduction in the amounts of asphaltenes, significant changes in the average chemical structure of the asphaltenes were also noticed as the temperature was increased. Due to a higher hydrogenation activity of the HDS catalyst compared with the HDM catalyst, the asphaltenes in the products (22) Higashi, H.; Takashi, T.; Kai, T. The effect of start-up conditions of hydrotreating catalyst for heavy residue with high asphaltene content. Catal. SurV. Jpn. 2002, 5, 111-119.
1148 Energy & Fuels, Vol. 20, No. 3, 2006
Marafi et al.
Figure 1. Performance of HDM and HDS catalysts in S, N, V, Ni, CCR, and asphaltenes removal; normalized contaminant level in product oils (KU-AR feed ) 100%). Table 5. Yield Comparison between HDM and HDS Catalysts temperature fraction
unit
360 °C
380 °C
400 °C
420 °C
maltenes asphaltenes
wt % wt %
HDM Catalyst 97.80 98.32 2.2 1.68
98.79 1.21
99.46 0.54
maltenes asphaltenes
wt % wt %
HDS Catalyst 97.07 97.61 2.93 2.41
98.25 1.75
98.68 1.32
Table 6. H/C, N/C, and S/C Atomic Ratios in Asphaltenes Fraction in the Product Oil Obtained from Hydrotreating of KU-AR over HDM and HDS Catalysts as a Function of Reaction Temperature temperature ratio
360 °C
H/C N/C S/C
1.11 0.01 0.04
H/C N/C S/C
1.22 0.01 0.03
380 °C
400 °C
420 °C
HDM Catalyst 1.09 0.01 0.04
0.85 0.01 0.03
0.82 0.01 0.02
HDS Catalyst 1.15 0.01 0.03
1.20 0.01 0.02
1.19 0.01 0.01
hydrotreated over the HDS catalyst possess about 10% less aromatic carbon than the asphaltenes in the “HDM products” (Figure 3a). As for the types of aromatic carbon in the asphaltenes, the following observations have been made: (i) the “HDM asphaltenes” contain more tertiary and quaternary aromatic carbons than the “HDS asphaltenes” (Figure 3b) and (ii) the tertiary aromatic carbon increases faster with increasing
Figure 2. Asphaltene aromaticity and content of asphaltanes in the product oils from hydrotreating of KU-AR over an HDM and an HDS catalyst vs reactor temperature.
temperature in the “HDM asphaltenes” than in the “HDS asphaltenes” (Figure 3c). The degree of condensation, defined as the ratio between carbon in bridgehead positions of condensed aromatic rings and total aromatic carbon, increases progressively with increasing temperature (Figure 4). At low temperatures; the “HDS asphaltenes” are more condensed than the “HDM asphaltenes”. As the reactor temperature rises, the degree of condensation in the
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Energy & Fuels, Vol. 20, No. 3, 2006 1149
Figure 5. Degree of alkyl substitution of aromatic rings in the asphaltenes remaining in the product oils vs reactor temperature: comparison between the HDM and HDS processes.
which in turn can lead to rapid deactivation of the catalyst in the next reactor in series. Thus, mild temperatures in the first rector in series and high hydrogen pressure and an active hydrogenation catalyst in the reactors following the “HDM reactor” can improve hydrogenation of the asphaltenes and suppress conversion of coke precursors to coke on the catalysts. The results obtained from this study have demonstrated that the quality of the residual asphaltenes in the product oil plays a key role in predicting catalyst deactivation and fuel oil stability. The results obtained from this study will be useful for catalyst selection and for optimization of the operating conditions in the ARDS process. 4. Conclusions Figure 3. Distribution of (a) aromatic carbon, (b) tertiary aromatic carbon, and (c) quaternary aromatic carbon in the asphaltenes remaining in the product oils vs reactor temperature: comparison between the HDM and HDS processes.
Figure 4. Degree of condensation in the asphaltenes vs reactor temperature: comparison between the HDM and HDS processes.
“HDM asphaltenes” increases at a faster rate than in the “HDS asphaltenes”. Because of the lower hydrogenation activity of the unpromoted HDM catalyst, thermal cracking and condensation may occur predominantly at higher temperature; while in the presence of the HDS catalyst, progressive asphaltene condensation may be prevented at the same temperatures. The degree of alkyl substitution of aromatic rings, defined as ratio of alkyl-substituted carbon to peripheral carbon in aromatic rings, stays lower in the “HDM asphaltenes” than in “HDS asphaltenes” through the whole temperature range (Figure 5). This points to differences in the ability of hydrothermal cleavage of side chains from aromatic rings by both catalysts. In catalytic hydroprocessing, highly condensed aromatic asphaltenes are the least reactive feed constituents, and they have a high propensity to form coke that could foul the catalyst.18,23,24 High operating severity in the first reactor of the ARDS unit in the presence of an unpromoted Mo/A2O3 catalyst with relatively low hydrogenation activity appears to have resulted in the formation of coke precursors in the product,
In the present study, the effect of operating severity on the quality of liquid products obtained during catalytic hydrotreating of Kuwait atmospheric residue (KU-AR) was investigated. Two types of industrial hydrotreating catalysts, namely, Mo/Al2O3 (HDM) and Ni-Mo/Al2O3 (HDS) catalysts, were used in the study. The results indicated that the quality of the liquid products formed during catalytic hydrotreating of petroleum residues depends strongly on the operating severity and catalyst type used in the process. The product oil became more purified by the removal of the undesirable contaminants (S, N, V, and Ni) with increasing temperature. The asphaltenes and resins present in the residual oil were converted to saturates and resins during the hydrotreating process. However, the polynuclear aromatic rings in the asphaltenes remaining in the product oil became more condensed and less alkyl substituted with increasing operating temperature regardless of the types of catalysts used. The catalyst’s hydrogenation activity also played a dominant role in determining the nature of the asphaltenes in the product oil. The aromaticity and degree of condensation in the product asphaltenes were higher when a MO/Al2O3 catalyst with low hydrogenation activity was used for hydrotreating compared to that for a NiMo/Al2O3 catalyst with high hydrogenation function. Acknowledgment. This work is a joint project between the Japan Cooperation Center Petroleum, JCCP (funded by the Ministry of Economic, Trade and Industry, METI), Japan, and the Kuwait Institute for Scientific Research, KISR, Kuwait. It bears the KISR Project No. PF010C. EF050395D (23) Seki, H.; Yoshimito, M. Deactivation of HDS catalyst in two-stage RDS process. II. Effect of crude oil and deactivation mechanism. Fuel Process. Technol. 2001, 69, 229-238. (24) Absi-Halabi, M.; Stanislaus, A.; Trimm, D. L. Coke formation on catalysts during the hydroprocessing of heavy oil. Appl. Catal. 1991, 72, 193-215.
