Utilization of Metal-Fouled Spent Residue Hydroprocessing Catalysts

Feb 23, 2007 - A series of catalysts were prepared by mixing and kneading of spent catalysts with boehmite in different proportions followed by extrus...
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1968

Ind. Eng. Chem. Res. 2007, 46, 1968-1974

Utilization of Metal-Fouled Spent Residue Hydroprocessing Catalysts in the Preparation of an Active Hydrodemetallization Catalyst M. Marafi,* S. Al-Omani, H. Al-Sheeha, A. Al-Barood, and A. Stanislaus Petroleum Refining Department, Petroleum Research Center, Kuwait Institute for Scientific Research, P.O. Box 24885, Safat 13109, Kuwait

In the present work, studies were carried out with the objective of utilizing spent residue hydroprocessing catalysts, which contained coke and metal (V and Ni) deposits, in the preparation of active new catalysts that can be used for hydrodemetallization of residual oils. Three types of spent catalysts that contained different levels of vanadium, molybdenum, and nickel were used in the experiments. These catalysts were collected from different reactors (front, middle, and back-end) of an industrial atmospheric residue desulfurization unit. A series of catalysts were prepared by mixing and kneading of spent catalysts with boehmite in different proportions followed by extrusion of the resulting paste. All prepared catalysts were characterized by chemical analysis and by surface area, pore volume, and pore size measurements, and their hydrodesulfurization (HDS) and hydrodemetallization (HDM) activities were evaluated by hydrotreating tests in a fixed-bed reactor using Kuwait atmospheric residue as feed. A commercial HDM catalyst was also tested under the same operating conditions and its HDM and HDS activities were compared with that of the prepared catalysts. The results revealed that the catalysts prepared from spent catalyst/boehmite blends contained vanadium, molybdenum, and nickel. The relative concentrations of these metals (V, Mo and Ni) in the prepared catalysts and other key properties such as surface area, porosity, and crushing strength showed a strong dependence on the amount and the type of spent catalyst used in the preparation. Forty to 60 wt % of spent catalysts could be mixed with boehmite and extruded to produce active HDM catalysts. Catalysts prepared from the spent catalysts with low vanadium content such as those discarded from the back-end reactors of an atmospheric residue desulfurization unit were more active than a reference commercial HDM catalyst for promoting HDM and HDS reactions. The presence of some kind of new active sites involving a combination of the three metals Mo, Ni, and V together with the reasonably high surface area and porosity could be responsible for the high hydrotreating activity of the catalyst prepared by mixing spent catalyst with boehmite. Introduction Catalysts play a key role in the refining of petroleum to produce clean fuels and many other valuable products.1,2 Among the various catalytic processes in the petroleum refining industry, hydrotreating processes consume large quantities of catalysts for the purification of various petroleum streams, particularly for the upgrading of heavy oils and residues.3 In the residue hydrotreating process, the catalysts which consist of Mo with promoters such as Co or Ni on alumina support enhance the removal of undesirable impurities such as sulfur, nitrogen, and metals present in the feed by hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and hydrodemetallization (HDM) reactions.4-6 However, the catalysts used in this process deactivate rapidly by coke and metal (V and Ni) deposits7,8 and have a short life (10-12 months). Since the technology for regeneration and reactivation of the catalysts deactivated by metal-fouling is not available to the refiners, the spent catalysts are discarded as solid wastes.9-11 The amount of spent hydroprocessing catalysts discarded as solid wastes has increased significantly in recent years because of a steady increase in the processing of heavier feedstocks containing higher sulfur, nitrogen, and metal (V and Ni) contents together with a rapid growth in diesel hydrotreating capacity to meet the increasing demand for low sulfur fuels. At the same time, environmental laws concerning spent catalyst disposal have become increasingly more severe in recent years. Spent * To whom correspondence should be addressed. E-mail: mmarafi@ prsc.kisr.edu.kw.

hydroprocessing catalysts have been classified as hazardous wastes by the United States Environmental Protection Agency (USEPA).12,13 The hazardous nature of the spent catalysts is attracting the attention of environmental authorities in many countries, and the refiners are experiencing pressures from environmental authorities for safe handling of spent catalysts. Several alternative methods such as disposal in landfills, reclamation of metals, regeneration/rejuvenation and reuse, and utilization as raw materials to produce other useful products are available to the refiners to deal with the spent catalyst problem.11,14-16 The choice between these options depends on technical feasibility and economic considerations. In recent years, increasing emphasis has been placed on the development of processes for recycling the waste catalyst materials as much as possible. Recovery of metals and other components from the spent catalysts is possible, particularly for the catalysts which contain valuable metals in high concentrations, and research in this area is continuing worldwide.11,17-18 Utilization of spent catalysts as raw materials in the production of other valuable products is an attractive option for their recycling from environmental and economical points of view. Spent fluid catalytic cracking (FCC) catalysts have been successfully used in cement production.16,19 Recently, a process for making highly stabilized nonleachable ceramic materials from spent catalysts has been reported by Sun et al.20 A few studies on the preparation of active catalysts from spent catalysts for various applications have been reported in the literature. Lee et al.21 reported that active reforming catalysts can be prepared using the V, Ni, and Mo containing extract obtained by leaching spent catalysts with citric acid. Furimsky22

10.1021/ie061192v CCC: $37.00 © 2007 American Chemical Society Published on Web 02/23/2007

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found that spent Co-Mo/Al2O3 and Ni-Mo/Al2O3 catalysts, after regeneration, can catalyze the decomposition of H2S. In a recent patented process, Choi et al.23 used spent hydroprocessing catalysts to prepare active catalysts for reduction of nitrogen oxides. The use of spent catalysts in preparation of active hydrotreating catalysts has been reported in a few earlier studies.24,25 However, the spent catalysts used in these earlier works were from petroleum distillates hydrotreating units and contained Mo, Co, and Al2O3 without V. Spent catalysts containing high levels of vanadium, together with Mo and Ni, are discarded as solid wastes in large quantities in Kuwait refineries. Over 250 000 barrels/day of residues are upgraded and converted to high-quality products by catalytic hydroprocessing in the three refineries of Kuwait bringing substantial economic returns to the country. These operations, however, generate a substantial amount of spent catalysts as solid wastes every year. Currently, about 6000 tons/year of spent catalysts are discarded as solid wastes from the three refineries in Kuwait. This will increase further and exceed 10 000 tons/ yr when a fourth refinery is built to process heavy crudes and residues. Therefore, in our research work, utilization of spent residue hydroprocessing catalysts containing V and coke together with Mo, Ni, and Al2O3 in the preparation of active hydrometallization (HDM) catalysts has been considered. The results presented in this paper are part of a comprehensive study on recycling and utilization of spent residue hydroprocessing catalysts.26-32 Three types of spent catalysts that contained different levels (high, medium, and low) of vanadium together with molybdenum and nickel were used in the experiments. These catalysts were collected from the front, middle, and back-end reactors of an industrial atmospheric residue desulfurization unit. A series of catalysts were prepared by mixing and kneading of spent catalysts with boehmite in different proportions followed by extrusion of the resulting paste. All prepared catalysts were characterized by chemical analysis and by surface area, pore volume, and pore size measurements, and their HDS and HDM activities were evaluated by hydrotreating tests in a fixed-bed reactor using Kuwait atmospheric residue as feed. The purpose of this comparative study was to identify the type of spent catalyst that will produce highly active HDM catalyst without any appreciable adverse effect in these important properties when mixed with boehmite. A commercial HDM catalyst was also tested under the same operating conditions and its HDM and HDS activities were compared with that of the prepared catalysts.

Table 1. Physical and Chemical Characteristics of Spent Catalysts Chemical Composition (wt %) spent catalyst type

Mo

Ni

V

C

A B C

6.3 5.6 4.5

3.4 3.8 4.0

3.4 5.9 9.7

23.1 19.2 15.3

Physical Properties surface area pore volume (m2/g) (cm3/g) 50 73 18

0.15 0.16 0.10

KM 100) and then was sieved using a sieve shaker (Endecotts, model OCT Digital 4587-01) with appropriate sieves obtaining particle sizes in the range of 25-90 µm, similar to that of the boehmite powder. A laboratory kneading and extrusion machine (Type, LUK 2.5 AS), manufactured by Werner and Pfleiderer & Co., Germany, was used for the preparation of catalyst extrudates from spent catalyst/boehmite mixtures. It contained a mixing chamber, two blades for mixing, and a drive unit with two threephase motors and gears, and a discharge screw. Three hundred grams of spent catalyst-boehmite mixture in the desired ratio was taken in the mixing chamber for each experiment. Then, 185 mL of dilute nitric acid (e.g., 2%), as a peptizing reagent, was added in drops at a constant rate to the boehmite/spent catalyst mix and was kneaded. The blades in the mixing chamber were counter rotating and were turned at different speeds. They were designed and arranged for intensive mixing and kneading of the material with the nitric acid to form a good, extrudable paste. At the end of the mixing and kneading time (20-30 min), the product was extruded by means of the discharge screw through a die containing several holes (1.5 mm in diameter) to form catalyst extrudates. The extrudates were dried at 110 °C in an oven for 24 h. The dried extrudates were calcined under controlled temperature and oxygen concentration to burn off the coke. After calcinations, the prepared extrudates were cooled in desiccators and were characterized.

Experimental Section Spent Catalyst. Three types of spent catalysts (A, B, and C) with different concentrations of the metals were obtained from different reactors of an atmospheric residue desulfurization (ARDS) unit at the Kuwait National Petroleum Company (KNPC). They were first washed with naphtha and then were extracted with toluene in a Soxhlet apparatus to remove the residual oil and then were characterized. The chemical and physical properties of the oil-free spent catalysts are shown in Table 1. Catalyst Preparation from Spent Catalyst-Boehmite Mix. The sequence of operational steps used for the preparation of catalyst extrudates from spent catalyst-boehmite mix in the present work is shown in Figure 1. Boehmite used in the catalyst preparation experiments was obtained from Sasol, Germany. The oil-free-spent catalyst was ground to fine powder in a grinding machine (Christison Particle Technologies, Ltd., Model

Figure 1. Operational steps in the preparation of catalyst extrudates from spent catalyst.

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Catalyst Characterization. The concentrations of V, Mo, and Ni in the spent catalyst and in the prepared catalyst samples were determined by inductively coupled plasma atomic emission spectroscopy (Varian Liberty II ICP-AES). A scanning electron microprobe X-ray analyzer (JEOL, model EPMA JXA 8600MX) was used for measuring the distribution profiles of the metals across the catalyst pellets. Surface areas of the catalysts were determined by the Brunauer-Emmett-Teller (BET) method using an autosorb adsorption unit manufactured by Quantachrome Corporation (USA). A mercury porosimeter (Quantachrome, Poremaster-60) was used for pore volume and pore size distribution determination in catalyst samples. A side crushing strength measuring apparatus designed and manufactured by AKZO Nobel (Model 120794-108) was used to determine the side crushing strength of the catalyst pellets. Catalysts Activity Testing. Hydrotreating activities of the prepared catalysts were tested in a high-pressure fixed-bed microreactor unit using Kuwait atmospheric residue as feed. The feedstock contained 4.3 wt % sulfur, 0.27 wt % nitrogen, 69 ppm vanadium, 21 ppm nickel, 3.6 wt % asphaltenes, and 12.4 wt % CCR. Thirty milliliters of the catalyst diluted with an equal amount of carborundum was used for each run. The catalysts were presulfided before introducing the feed using 1% CS2 in straight run gas oil by a standard procedure. After presulfiding, the test conditions were adjusted to desired operating temperature, pressure, hydrogen-to-oil ratio, and liquid hourly space velocity (LHSV). All catalysts were tested under the following operating conditions: pressure ) 120 bar, LHSV ) l h-1, H2/oil ratio ) 1000, and temperature ) 370 °C. A commercial HDM catalyst was also tested under the same operational conditions. For each run, product samples were collected every 24 h for analysis of S and metal (Ni, V) content. Sulfur content was determined using an Oxford Model 3000 XRF instrument. The concentrations of V and Ni in the oil were determined without ashing using a Varian Liberty Series II, ICP spectrophotometer. The catalyst activity was calculated as relative volume activity (RVA) compared to the reference catalyst activity. A commercial HDM catalyst was considered as the reference standard with RVA ) 100. The RVAs for HDS and HDV reactions were defined as follows:

RVA(HDS) )

k(HDS-sample) k(HDS-standard)

RVA(HDV) )

k(HDV-sample) k(HDV-standard)

× RVA (HDS-standard) × RVA(HDV-standard)

where kHDS is the reaction rate constant for HDS, and kHDV is the reaction rate constant for HDV. kHDS and kHDV were calculated using the following nth order rate equation

k)

[

LHSV 1 1 n - 1 C n-1 C n-1 p f

]

where LHSV is the liquid hourly space velocity (mL mL-1 h-1), n is the reaction order, Cf is the concentration of S or V in feed (wt %), and Cp is the concentration of S or V in product (wt %). In our previous studies, the reaction order n was found to be 2 for both HDS and HDV reactions in Kuwait atmospheric residue hydrotreating.33,34 Therefore, the value of n ) 2 was used in the above equation for calculating the HDS and HDV constants.

Figure 2. Comparison of surface area of the catalysts prepared from different spent catalysts.

Figure 3. Comparison of pore volume of the catalysts prepared from different percentages of spent catalysts A-C.

Results and Discussion Physical and Chemical Properties of the Catalysts Prepared From Different Types of Spent Catalysts. Mixing spent catalysts with boehmite in different proportions in the range 10-60% did not cause any problem in the peptization and extrusion of the resulting mix. Extrusion was smooth and good extrudates were obtained from all mixes. The key physical properties such as surface area, pore volume, pore size, and crushing strength and the concentrations of the metals (i.e., Mo, Ni, and V) in the catalysts prepared from the three types of spent catalysts (A, B, C) are compared and discussed in this section. The surface areas of the catalysts prepared from the three types of spent catalysts are compared in Figure 2. In the catalysts prepared from the high-vanadium spent catalyst C, the surface area decreases drastically with increasing spent catalyst addition, whereas for the catalyst prepared from the low-vanadium spent catalyst A, the surface area does not change appreciably. It is evident that the catalysts prepared from the low-vanadium spent catalysts A have substantially higher surface area than the others at all levels of spent catalyst addition in the range 10-60%. The next higher surface area is found for the catalysts prepared from spent catalyst B having V content higher than that of A but lower than that of C. The lowest surface area is found for the catalysts prepared from the spent catalyst C that has the highest vanadium content among the three types of spent catalysts. The pore volume data presented in Figure 3 also show similar trends. Pore volume of the prepared catalysts decreases with increasing spent catalyst content in all cases, but the extent of

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Figure 5. Comparison between the vanadium content of catalyst prepared from different percentages of spent catalysts A-C. Figure 4. Comparison of side crushing strength of the catalysts prepared from different percentages of spent catalysts A-C.

pore volume loss depends on the vanadium content of the spent catalyst used in the catalyst preparation. The highest and lowest pore volumes are found for the catalyst prepared with spent catalyst A and C, respectively. In the case of the catalysts prepared by mixing high-vanadium spent catalyst C with boehmite, the pore volume decreases drastically from about 0.7 mL/g to 0.2 mL/g when the amount of spent catalyst increases to 40%. Conventional HDM catalysts usually have surface area in the range 150-180 m2/g and pore volume in the range 0.40.6 mL/g. From the results presented in Figures 1 and 2, it is evident that, up to 40% spent catalyst addition, the catalysts prepared from the low-vanadium spent catalysts A and B have surface area and pore volume values that are in the acceptable range for a HDM catalyst. Catalysts prepared from the highvanadium spent catalyst C have lower surface area and pore volume values than the acceptable values. The mean pore diameter of the prepared catalysts did not change appreciably with increasing spent catalyst addition to boehmite. Even in the catalyst samples prepared with the addition of large amounts (e.g., 40-60%) of spent catalysts, the mean pore diameter values were in the range 140-160 Å.32 The side crushing strengths of the catalyst extrudates prepared from the three types of spent catalysts also show significant differences (Figure 4). The catalyst extrudates prepared by mixing the high-vanadium-containing spent catalyst C with boehmite have higher crushing strength than those prepared from spent catalysts A and B. Interestingly, in all three cases a significant improvement in the crushing strength occurs when the amount of spent catalyst added to boehmite is increased above 30%. In other words, spent catalyst addition in larger amounts makes the extrudates stronger. In Figure 5, the effect of increasing the amount of different types of spent catalysts mixed with boehmite on the vanadium content of the prepared catalysts is illustrated. It is seen that the catalysts prepared from the high-vanadium spent catalyst C have substantially higher vanadium concentrations than those prepared from spent catalysts A and B. The catalysts prepared from the low-vanadium spent catalyst A have the lowest vanadium content at all levels of spent catalyst addition. The concentrations of Ni in the catalysts prepared from the three types of spent catalysts are compared in Figure 6. Here again the highest and lowest Ni contents are observed for the catalysts prepared with spent catalysts C and A, respectively. The Mo contents of the prepared catalysts show completely opposite trend (Figure 7). The highest and lowest Mo concentrations are found for the catalysts prepared from spent catalysts A and C, respectively.

Figure 6. Comparison between the nickel content of catalysts prepared from different percentages of spent catalysts A-C.

Figure 7. Comparison between the molybdenum content of catalysts prepared from different percentages of spent catalysts A-C.

The above trends in the concentrations of the metals (V, Mo, and Ni) in the catalysts prepared from the three types of spent catalysts can be explained on the basis of the differences in the amount of these metals present in the original spent catalysts. The spent catalyst C contained larger amount of V and Ni than the others, and as a result, the catalysts prepared by mixing it with boehmite have more V and Ni. The spent catalyst A contained more Mo and less V than the other two types of spent catalysts. Consequently, the catalysts prepared from it exhibit the highest Mo and lowest V concentrations. The distribution profiles of vanadium in the catalyst extrudates prepared by mixing different percentages of spent catalyst with boehmite were measured by electron microprobe analysis. The results for the catalysts prepared from the spent catalysts A and B are presented in Figure 8a and 8b. Vanadium distribution profiles in the corresponding spent catalyst pellets are also included in these figures for the purpose of comparison. In both spent catalysts, it is seen that the vanadium concentration is substantially higher near the outer edges than at the center of

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Figure 8. Vanadium distribution profiles in catalyst extrudates prepared by mixing different percentages of spent catalyst. (a) Prepared from spent catalyst A; (b) prepared from spent catalyst B.

Figure 9. Activity comparison of different catalysts. (a) HDS activity; (b) HDV activity.

the pellet. In the prepared catalyst extrudates, the high edge concentration of vanadium is not seen. Vanadium is more evenly distributed throughout the pellet cross section with some spots having higher concentration than others. The processes such as peptization with an acid, mixing, kneading, and extrusion that are used to prepare the extrudates from boehmite/spent catalyst mix appear to influence the distribution of the metals in the prepared catalysts. Comparison of the HDM and HDS Activities of the Catalysts Prepared from Different Types of Spent Catalysts. The prepared catalysts were tested in a microreactor to evaluate their activity for promoting HDS and HDM reactions in residual oil hydrotreating process. Kuwait atmospheric residue was used as feed for the tests. The test conditions and operating procedure are described in detail in the Experimental Section. Activity tests were also conducted on a reference commercial HDM catalyst. In Figure 9a and 9b, the HDS and HDV relative volume activities (RVAs) of three catalysts prepared by mixing 40% each of different spent catalysts A, B, and C with boehmite are compared with that of a reference HDM catalyst. The procedure used for calculating the RVA is presented in the Experimental Section. The results show that in all three cases, the prepared catalysts are more active than the reference catalyst for promoting HDS and HDM reactions in residual oil hydrotreat-

ing. Among the three catalysts, the one prepared from spent catalyst A is substantially more active than the others. In general, the catalysts prepared from different types of spent catalysts and the commercial catalyst rank in the following order for hydrodemetallization and hydrodesulfurization of Kuwait atmospheric residues.

cat. A > cat. B > cat. C > ref HDM cat The differences in the HDS and HDM activities of the catalysts prepared from different types of spent catalysts could be explained on the basis of the differences in their physical and chemical properties. The catalysts prepared by mixing spent catalyst A with boehmite have higher surface areas and pore volumes than those prepared from spent catalysts B and C. The lowest surface area and pore volume are found for the catalysts prepared from spent catalyst C. Furthermore, the catalysts prepared from spent catalyst A have higher concentrations of Mo than the others. It also has a reasonably good amount of Ni which can promote the hydrotreating activity of Mo by the formation of Ni-Mo-S type active phase.33,34 The concentration of V which has a very low activity for HDS is relatively low in this catalyst. All these factors, namely, high surface area, high pore volume, and high active metals (Mo and Ni) content,

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could contribute to the higher hydrotreating activity of the catalysts prepared from spent catalyst A. On the other hand, the catalysts prepared from spent catalyst C have low surface area, pore volume, and Mo content, but high V content. High V concentrations in the catalyst could block the pores and reduce the surface area. Furthermore, V is catalytically less active than Mo for promoting hydrotreating reactions. All these factors could be responsible for the low HDS activity of the catalysts prepared from spent catalyst C. The results of the present studies show that highly active catalysts for residual oil hydrotreating could be prepared from spent catalysts containing V, Mo, and Ni and Al2O3 by mixing and extruding them with boehmite. Up to 40 wt % of spent catalyst could be mixed with boehmite in the case of lowvanadium spent catalysts from the back-end reactors of a multireactor ARDS unit for preparing catalysts with substantial HDS and HDM activities. The scientific basis for the high hydrotreating activities of these catalysts is explained below. Catalysts used for hydrotreating of petroleum distillates and residues normally consist of Mo supported on an alumina carrier with promoters such as Ni or Co.4,5,35 Mo alone can promote hydrotreating reactions such as HDS and HDM, but its activity is enhanced by the presence of Ni or Co. The synergy between Mo and Ni in promoting hydrotreating reactions has been explained on the basis of the formation of an active phase (NiMo-S) which contains both metals.35,36 Conventional HDM catalysts contain 4-6% MoO3 either alone or together with 0.5-1% NiO on a large pore (140-170 Å diameter) alumina support. These catalysts possess low intrinsic HDM activity and proper porosity to allow the large metal-bearing molecules to reach the active sites within the catalyst pores. In the catalysts prepared by mixing spent residue hydrotreating catalysts with boehmite, vanadium is present together with Mo and Ni. In the spent catalyst, the deposited vanadium is more concentrated near the outer surface of the catalyst pellet plugging the pores and reducing the catalyst’s surface area and porosity. In the prepared catalysts, vanadium is redistributed on the alumina support when they are mixed with boehmite, peptized with nitric acid, kneaded, and extruded. Close association between the three metals (V, Mo, and Ni) in different combinations could also occur in the spent and prepared catalysts. Dejonghe et al.37 found that in Ni-Mo-S/ Al2O3 catalysts Ni can be, at least, partly replaced by V coming from the feed during residual oil hydrotreating process. Smith and Wei38 speculated that in residual oil hydrotreating catalysts aged by the deposition of V and Ni, new active catalyst surface could be formed. Many other studies have shown that V either alone or in combination with Ni or Mo is very efficient for the HDM process.39-43 Therefore, there is a good reason to propose that some kind of new active sites formed from V, Mo, and Ni are responsible for the high activity of the catalyst prepared from spent catalyst. Furthermore, the prepared catalysts have high surface area and porosity. Thus, the presence of some new kind of active sites formed from V, Mo, and Ni in the catalysts prepared from the spent catalysts together with their high surface area and porosity could be responsible for their high hydrotreating activity. More research is needed to develop a fundamental understanding of the nature of active sites in catalysts containing mixed sulfides of V, Mo, and Ni. Conclusions Recycling of metal-fouled spent residue hydroprocessing catalysts in the preparation of active hydrodemetallization catalysts by mixing and extruding with boehmite was studied

in the present work. Three types of spent catalysts that contained different concentration of V together with Mo and Ni on γ-alumina support were used in the experiments. The following is the important results and conclusions of the studies. (1) Catalysts prepared from spent catalyst/boehmite blends contained vanadium, molybdenum, and nickel. The concentration of the three metals increased linearly with increasing amount of spent catalyst. (2) The relative concentrations of V, Mo, and Ni in the prepared catalysts and other key properties such as surface area, porosity, and crushing strength showed a strong dependence on the type of spent catalyst used in the preparation. In the catalyst samples prepared by mixing the high-vanadium spent catalyst with boehmite, the concentration of V was substantially larger than that of Mo, whereas in the catalyst prepared using the low-vanadium spent catalyst the level of Mo was more than that of V. (3) The catalysts prepared from the high-vanadium spent catalyst showed relatively low HDM and HDS activity because of their low surface area, pore volume, and high-vanadium content. (4) In the case of the spent catalysts with low-vanadium content such as those used in the back-end reactors of an atmospheric residue desulfurization unit, up to 40 wt % of the spent catalysts could be mixed with boehmite and extruded to produce highly active HDM catalysts. Acknowledgment The authors thank the management of the Kuwait Foundation for the Advancement of Sciences (KFAS) for their financial support of the project. The assistance of Mr. Inian and Ms. Navamani Rajasekaran in the catalyst preparation and characterization experiment is gratefully acknowledged. Literature Cited (1) Absi-Halabi, M.; Beshara, J.; Qabazard, H.; Stanislaus, A. Catalysts in Petroleum Refining and Petrochemical Industries; Elsevier: Amsterdam, 1996. (2) Absi-Halabi, M.; Stanislaus, A.; Qabazard, H. Trends in catalysis research to meet future refining needs. Hydrocarbon Process. 1997, 4555. (3) Silvy, R. P. Future trends in refining catalyst market. Appl. Catal. 2004, 261, 247-252. (4) Kressmann, S.; Morel, F.; Harle, V.; Kasztelan, S. Recent developments in fixed-bed residue upgrading. Catal. Today 1998, 43, 203-215. (5) Furimsky, E. Selection of catalysts and reactors for hydroprocessing. Appl. Catal., A 1998, 171, 177-206. (6) Oelderik, T. M.; Sie, S. T.; Bode, D. Progress in the catalysis of the upgrading of petroleum residues. Appl. Catal. 1990, 47, 1-24. (7) Al-Dalama, K.; Stanislaus, A. Comparison between deactivation patterns of catalyst in fixed bed and ebullating bed residue hydroprocessing units. Chem. Eng. J. 2006, 120, 33-42. (8) Furimsky, E.; Massoth, F. E. Deactivation of hydroprocessing catalysts. Catal. Today 1999, 52, 381-495. (9) Trimm, D. L. Deactivation, regeneration and disposal of hydroprocessing catalysts. Stud. Surf. Sci. Catal. 1990, 53, 41-60. (10) Trimm. The regeneration or disposal of deactivated heterogeneous catalysts. Appl. Catal., A 2001, 212, 153-160. (11) Furimsky, E. Spent refinery catalysts: Environment safety and utilization. Catal. Today 1996, 30, 223-286. (12) Rapaport, D. Spent hydroprocessing catalysts listed as hazardous wastes. Hydrocarbon Process. 2000, 79, 11-22. (13) Hazardous waste management system. Fed. Regist. 2003 68 (202), 59935-59940. (14) Marafi, M.; Stanislaus, A. Options and processes for spent catalyst handling and utilization. J. Hazard. Mater. B 2003, 101, 123-132. (15) Chang, T. Spent catalyst optionss1. Regeneration industry helps refiners control costs, limit liabilities. Oil Gas J. 1998, 96 (41), 49. (16) Clifford, R. K. Spent catalyst management. Pet. Technol. Q. 1997, (Spring), 33-39.

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ReceiVed for reView September 12, 2006 ReVised manuscript receiVed December 20, 2006 Accepted January 18, 2007 IE061192V