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Ind. Eng. Chem. Res. 2009, 48, 1190–1195
Carbon-Modified Alumina and Alumina-Carbon-Supported Hydrotreating Catalysts S. K. Maity,†,* L. Flores,† J. Ancheyta,† and H. Fukuyama‡ Instituto Mexicano del Petro´leo, Eje Central La´zaro Ca´rdenas Norte 152, Col. San Bartolo Atepehuacan, Me´xico D.F. 07730, and Toyo Engineering Corporation, 8-1 Akanehama 2-Chome, Narashino-shi, Chiba 275-0024, Japan
Two types of supports, carbon-modified alumina and alumina-carbon, were prepared in this investigation. These supports were used to prepare hydrotreating (HDT) catalysts for Maya heavy crude. It was found that, when carbon was added to the alumina matrix and the carbon was then burned, pores having larger diameter were generated. The average pore diameter of the support increased with increasing amount of carbon in the alumina. However, when the carbon was not burned, the pore size decreased with added carbon. The hydrotreating activity results show that, because of the larger pore diameter and higher pore volume, the modified-alumina-supported PCoMo catalysts have slightly higher activities than the alumina-carbon-supported catalysts. The effects of additives, boron and phosphorus, on the hydrotreating of heavy oil were also compared. It was found that P-containing catalysts have higher activities than B-containing catalysts. It was also found that, when boron-containing catalyst were prepared at higher pH, they had higher hydrodemetalation (HDM) activities. Deactivation studies showed that the presence of carbon in the support might hinder rate of deactivation during hydrotreating of heavy oil. 1. Introduction The world energy demand is increasing rapidly, whereas the sources of conventional oils are becoming depleted. On the other hand, there are vast deposits of heavy crude oils in several parts of the world. Therefore, upgrading of heavy crude oils is necessary to fulfill the increasing demand for light fractions. Hydroprocessing is one of the best options for upgrading heavy crude oils. However, it is not an easy task for the refineries to implement this process because of the presence of high levels of impurities. The use of carbon supports to prepare hydrotreating catalysts for the upgrading of heavy oils has shown some interesting results in recent years. The advantages of using carbon supports are the low cost, easy recovery of deposited metals from the catalyst, very high stability, and comparatively easily controlled pore structure.1 Several studies on the hydroprocessing activities of carbon and carbon-modified supported catalysts have been published. The hydrodesulfurization activities of model compounds [dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6DMDBT)] and a real feed (diesel) have been compared on carbon- and alumina-supported catalysts.2,3 It was observed that, in general, the carbon-supported catalyst showed a higher HDS activity than the alumina-supported catalyst, even by as much as a factor of 2. The most well-known refractory sulfur compound, 4,6-DMDBT, was also studied on a carbonsupported catalyst, and the results showed that the HDS activity of this compound was much lower than that of DBT. Nevertheless, the HDS activity of the carbon-based catalyst was still higher than that of the alumina-based catalyst. The lower HDS activity of 4,6-DMDBT suggests the inaccessibility of the sulfur molecule to the active sites. The effects of the pore size of two carbon supports (pore sizes of 12.5 and 9.9 Å) on the HDS activity were also compared. The two carbon supports with * To whom correspondence should be addressed. E-mail: skumar@ imp.mx. Fax: +(55) 91758429. † Instituto Mexicano del Petro´leo. ‡ Toyo Engineering Corporation.
different pore sizes did not show significant differences in HDS activity for DBT; however, the support with the larger pore diameter exhibited a higher HDS activity for 4,6-DMDBT. These results confirm the diffusional limitation of the larger molecules of 4,6-DMDBT. Even the smaller pore diameter (9.9 Å) might be sufficient for the smaller reactive molecule DBT to enter the pores, but it might be difficult for the larger molecule DMDBT to reach active sites in the pore cavity. Hence, the HDS activity of this larger molecule is lower. The hydrodesufurization activity of diesel feed also was found to be higher on carbon-supported catalysts than on alumina-based catalysts. Boehmite alumina and carbon black (16 nm) were used for the preparation of carbon-coated alumina.4 The powdered alumina was first mixed with 1.5 vol % acetic acid for several minutes. The appropriate amount of carbon black was added to the alumina paste, and the mixture was again mixed vigorously. The paste was extruded and dried at an appropriate temperature. Then, the extrudate was calcined in a mixture of oxygen and nitrogen for 2 h at 600 °C. The supports prepared by this method showed a bimodal type of structure: one part of the support porosity was in the mesopore range, and the other part was in the macropore range. Hydroprocessing activities for the vacuum residue of Maya crude were investigated on carbon-supported NiMo catalysts. The conversions of the catalysts were not greatly affected by the macropores in the carbon; however, it was observed that the HDS activity was more favorable on the catalysts that contained more macropores. The authors also investigated the hydrodenitrogenation (HDN) activities of these catalysts and found that the HDN activity was influenced more by mesopores than by macropores. It was stated that the interaction between the active metal and the support for the carbon-based catalyst was weak and, as a result, the formation of more active type II sites occurred. Higher sediment formation was observed for the alumina-based catalyst than for the neutral carbon-based catalyst. It was also noticed that, as the reaction proceeded and carbon from the feed was deposited on the alumina surface, the sediment formation decreased. This finding indirectly reveals that the present of carbon indeed suppresses
10.1021/ie800606p CCC: $40.75 2009 American Chemical Society Published on Web 08/13/2008
Ind. Eng. Chem. Res., Vol. 48, No. 3, 2009 1191
sediment formation. The production of a higher percentage of lighter fractions was also observed for the carbon-supported catalyst. The main cause of catalyst deactivation in the hydrotreating of heavy oils is deposition of carbon and metals. If the hydrotreating catalysts contain carbon, the deactivation becomes slower.5,6 The use of a carbon support for the hydrotreating catalyst has several advantages as discussed above. However, the disadvantage of using this support is its mechanical strength. For that reason, alumina with carbon was used as a support material for the present investigation of the hydroprocessing of Maya heavy crude. 2. Experimental Section Alumina supports having different amounts of carbon were prepared. The following procedure was used to prepare the supports: Boehmite (Sasol) was mixed vigorously with an aqueous solution of acetic acid (1.5 vol %). The required amount of carbon (Aldrich, Darco, 175KB-G, 60 mesh) was added to the alumina, and the paste was again mixed. The paste was kept overnight and then extruded in the size of 1-mm diameter. The dried extrudate was divided into two parts: one was calcined at 600 °C in air (support designated as A-X), and the other was calcined in nitrogen atmosphere at 400 °C (support designated as AC-X), where X is the percentage of carbon on the alumina. For both cases, the duration of the calcination was 5 h. In this method, carbon contents of 5-25 wt % were added to the alumina. The coimpregnation method was used for the preparation of catalysts having 10 wt % of MoO3, 3 wt % of CoO, and/or 0.8 wt % of P (or B). Appropriate amounts of ammonium heptamolybdate (AHM, Aldrich), cobalt nitrate (Baker), and phosphoric acid (Aldrich, or boric acid in the case of B impregnation) salts were dissolved in distilled water. The solution was impregnated on a dry support, and the impregnated samples were allowed to dry at room temperature. Samples were then dried for 7 h at 120 °C and calcined at 450 °C for 5 h. The catalysts having B were prepared with four different pH values. Ammonium hydroxide was used to increase the pH. The specific BET surface areas, pore volumes, and pore size distributions (PSDs) of the catalysts were measured by nitrogen adsorption at 77 K (Quantachrome Nova 2000). X-ray diffractograms were recorded on a Siemens D-500 model diffractometer using Cu KR radiation. The radial distributions of carbon and other elements were measured with a scanning electron microscope (SEM, model XL30 ESEM, Philips). The total metal contents in the feed and products were measured by atomic absorption spectroscopy (Thermo Electron model Solaar AA). Sulfur was analyzed by X-ray fluorescence (Horiba model SLFA-2100). The activities of the catalysts were studied in a batch reactor. Five grams of fresh catalyst was sulfided ex situ for each experiment. An atmospheric-pressure unit was used for sulfidation. In this unit, hydrogen was passed through a container containing CS2, and the saturated mixture of CS2 and hydrogen was passed through the reactor. The sulfiding conditions for the activation of the catalyst were as follows: temperature, 400 °C; pressure, atmospheric; duration of sulfidation, 3 h; and hydrogen flow rate, 40 mL/min. For this study, 200 g of Maya heavy crude was taken into the batch reactor (1 L capacity). The sulfided catalyst was transferred into a basket under nitrogen atmosphere very quickly so that the catalyst would not contact the air for a long time. The reactor was sealed properly and checked for leakage. The reactor was then purged two or three
Figure 1. Calibration curve for TGA experiments.
times with hydrogen gas so that there was no air left inside the reactor. Heating was started from room temperature to the required temperature at a rate of 3 °C/min. Stirring was started when the temperature reached the set point (380 °C), and the time at this point was noted as the beginning of the reaction. The experimental conditions of the batch reactor were as follows: temperature, 380 °C; total pressure, 100 kg/cm2; catalyst weight, 5 g; Maya crude, 200 g; duration of reaction, 6 h; and stirring speed, 750 rpm. Products were separated from the catalyst after the reaction, and the metals and sulfur contents of the products were analyzed. The spent catalysts were washed with hot toluene by the Soxhlet process and dried at 110 °C before analysis of textural properties. A continuous microflow reactor was also used to study the activities of the two types of catalysts. In this reactor, oxide catalysts were sulfided in situ before an actual run was started. Ten milliliters of oxide catalyst was loaded with an equal volume of diluent, namely, carborundum (0.2 mm size). Both catalyst and carborundum were mixed and divided into five parts. Each part of the mixture was loaded into the reactor at one time and with intermittent tapping. The catalyst was then dried for 2 h at atmospheric pressure and 120 °C. After drying, the catalyst was allowed to soak for 2 h at 150 °C. Light gas oil (LGO) was used for soaking. This light gas oil contained 1.7 wt % of sulfur. The actual sulfiding agent was introduced after soaking. The sulfiding agent was light gas oil with dimethyl disulfide (DMDS, 1 wt %). Sulfidation was performed at 28 kg/cm2 pressure at two different temperatures. The first sulfidation was done at 260 °C for 3 h, and the second was performed at 320 °C for 5 h. Catalytic tests were performed in a high-pressure fixed-bed microreactor in upflow mode. The experimental conditions were as follows: total pressure, 75 kg/cm2; reaction temperature, 380 °C; liquid hourly space velocity (LHSV), 1.0 h-1; and hydrogen-to-hydrocarbon ratio, 356 m3/m3. Maya heavy oil was used for the catalyst activity tests. The first balance was taken after a stabilization period of 9 h. Boling point distributions of the feed and products were determined by thermogravimetric analysis (TGA) for boroncontaining catalysts. For these experiments, a calibration curve was created as shown in Figure 1. In this figure, the TGA evaporation temperatures of pure compounds (naphthalene, 218 °C; fluorine, 294 °C; dibenzothiophene, 332 °C; fluoranthene, 384 °C; chrysene, 448 °C; dibenzo[a]anthracene, 518 °C) are plotted against their normal boiling temperatures. For an actual case, the TGA evaporation temperatures of the feed and products can be converted to their corresponding normal boiling temperatures from the calibration curve. More details about such experiments are provided elsewhere.7,8
1192 Ind. Eng. Chem. Res., Vol. 48, No. 3, 2009 Table 1. Properties of Maya Heavy Crude property
value
C (wt %) H (wt %) N (wt %) S (wt %) metals (wppm) Ni V API gravity Ramsbottom carbon (wt %) asphaltenes (in C7) (wt %) density 20/4 °C
86.9 5.3 0.3 3.52 49.5 273 20.99 11.01 11.2 0.9251
Table 2. Physical Properties of Modified Alumina (A-X) and Alumina-Carbon (AC-X) Supports
a
support
BET SAa (m2/g)
TPVb (mL/g)
APDc (Å)
A-0 A-5 A-10 A-15 A-20 A-25 AC-5 AC-10 AC-15 AC-20 AC-25
118 127 125 129 138 137 156 180 203 224 230
0.55 0.76 0.64 0.84 0.82 0.86 0.76 0.77 0.74 0.72 0.70
188 238 203 259 238 252 196 170 146 129 133
BET surface area. b Total pore volume. c Average pore diameter.
Figure 3. Pore size distribution of alumina-carbon supports. Table 3. Physical Properties of Modified-Alumina- and Alumina-Carbon-Supported Catalysts catalyst
TPVc (mL/g)
APDd (Å)
150 Å
PCoMo/A-0 PCoMo/A-5 PCoMo/A-10 PCoMo/A-15 PCoMo/A-20 PCoMo/A-25 PCoMo/AC-5 PCoMo/AC-10 PCoMo/AC-15 PCoMo/AC-20 PCoMo/AC-25
122 114 105 114 102 105 113 109 114 170 172
0.61 0.65 0.61 0.64 0.61 0.62 0.55 0.60 0.57 0.59 0.57
201 229 231 226 238 236 196 220 201 139 132
64.12 53.83 50.44 38.83 44.68 38.59 59.08 69.10 67.62 58.03 61.17
35.88 46.17 49.56 61.17 55.32 61.41 40.92 30.90 32.38 41.97 38.83
d
Figure 2. Pore size distribution of modified alumina supports.
3. Results and Discussion In this study, Maya heavy crude oil was used as the feedstock, and the properties of this crude are listed in Table 1. The physical properties of the carbon-modified alumina (AX) and alumina-carbon (AC-X) supports were measured by the nitrogen adsorption method, and the results are given in Table 2. It can be observed that the total pore volume and average pore diameter of the modified-alumina support increase upon addition of carbon. The pure support has total pore volume of 0.55 mL/g. When this support is modified by carbon (25 wt %), it increases to 0.86 mL/g. Average pore diameter also increases from 188 Å of pure alumina to 252 Å of A-25 support. However, when carbon is inside the support material (AC-X), i.e. carbon is not burned off, the total pore volume decreases in general. The average pore diameter slowly decreases with increasing amount of carbon. The pore size distributions of A-X and AC-X series of supports are presented in Figures 2 and 3 respectively. Figure 2 clearly shows how the pore size distribution changes with addition of carbon in A-X series. Figure 2
PSDa (vol %)
BET SAb (m2/g)
a Pore size distribution. Average pore diameter.
b
BET surface area.
c
Total pore volume.
shows that the increase of pore volume is mainly due to increase of pore in higher pore diameter region. It contributes to increase the average pore diameter of the support. However, from Figure 3, it is noticed that the pore size distribution is slightly reduced in addition of 20 wt % of carbon on to the alumina in the AC-X series. Onuma9 studied the effects of carbon on the alumina support in detail, using different kind of carbons and different amounts to study its effect on the alumina pore size. When carbon was added to the alumina and subsequently burned off, this process generated pores with greater pore diameters. The author observed that both the micropores and mesopores of alumina increased upon carbon addition. It was stated that the micropore volume reached a maximum at around 10-20 wt % of carbon and that more than 20-30 wt % of carbon was required to obtain a considerable mesopore volume. The degree of increase of the pore size distribution and total pore volume was found to depend on the type of carbon and its amount. It was noted that, as the quantity of carbon was increased, the mesopore volume increased, and the position of the mesopore shifted toward larger pore diameters. It was also observed that, if the carbon used had a highly linked structure, it gave better results in terms of generating mesopore volume. When carbon is mixed with alumina, fine carbon powder enters into the interparticle regions of the alumina. A pore is generated between alumina particles when this carbon is subsequently burned off. However, if this carbon is not burned off, it remains inside the alumina particles, and the fine carbon particles can block the alumina pores instead of making pores. The physical properties of A-X and AC-X supported catalysts are listed in Table 3. The pore size distribution of pores with diameters below 150 and above 150 Å is also given. It can be
Ind. Eng. Chem. Res., Vol. 48, No. 3, 2009 1193
Figure 7. HDS activities of A-15 and AC-15 supported catalysts.
Figure 4. SEM micrograph of a catalyst particle (PCoMo/AC-10).
Figure 8. HDS and HDM activities of modified-alumina-supported PCoMo catalysts.
Figure 5. SEM-EDAX analysis of a catalyst particle (PCoMo/AC-10).
Figure 6. XRD diagrams of three different catalysts.
seen from the table that the total pore volume above a pore diameter of 150 Å increases with the addition of carbon in the A-X series. However, the reverse trend is observed in the case of the AC-X series. The carbon mapping of PCoMo/AC-10 catalyst was studied by SEM. Figure 4 shows that the carbon is distributed homogeneously in the catalyst particle. The carbon distribution of this catalyst (PCoMo/AC-10) is also compared with that of the PCoMo/A-10 catalyst in Figure 5. This concentration was measured along the diameter of the catalyst particle. The XRD diagrams of three different supported catalysts are presented in Figure 6. Two broad peaks are observed that correspond to γ-alumina. One peak appearring at a 2θ value of 27° might be due to the presence of crystalline MoO3. This peak disappears in the case of AC-10-supported catalysts. This peak again appears for the PCoMo/AC-25 catalyst, but the peak
position is shifted to a lower 2θ value. This might be due to crystalline MoO3 as stated earlier, or it might be due to graphite. Dugulan et al.10 studied the presence of the active phase in alumina- and carbon-supported CoMo catalysts. They found that a Co-Mo-S type of phase was present in both catalysts and that Co-Mo-S was the only Co phase present in the aluminasupported catalyst sulfided at high pressure. However, the stability of this Co-Mo-S phase was low in the carbonsupported catalyst, particularly when the sulfidation temperature was increased from 300 to 400 °C. The formation of crystalline Co9O8 was noted. It was suggested that, in the neutral carbon support, where the active metal-support interaction is weak, the formation of large MoS2 slabs is favored. This leads to fewer edges of MoS2 that can accommodate Co atoms, and hence, the Co phases sinter to crystalline Co9O8 at a relatively in higher rate. From our study, it can be stated that, when carbon content is very high at 25 wt %, metal-support interaction might decrease to a certain extent so that crystalline MoO3 is formed during calcination at 450 °C. However more studies are necessary to provide a definitive explanation. The hydrotreating activities of the carbon-modified aluminaand alumina-carbon-supported catalysts were studied for Maya heavy crude. For this purpose, a continuous high-pressure microreactor and a batch reactor were used. The hydrodesulfurization activities of A-15- and AC-15supported CoMo catalysts, as determined in the continuousflow reactor, are compared in Figure 7. This figure indicates that the HDS activity of the modified-alumina-supported catalyst is higher than that of the alumina-carbon-supported one. In both cases, the HDS activity decreases with time-on-stream (TOS). In Figure 8, the HDS and hydrodemetalation (HDM) activities of different PCoMo/A-X catalysts are presented. These results were obtained in the batch reactor. The HDS activity does not change markedly with increasing concentration of carbon in the alumina but does decrease slightly with increasing concentration of carbon. However, the PCoMo/A-10 catalyst shows the highest HDM activity compared to the other catalysts in the same series. The HDS and HDM activities of PCoMo/AC-X catalysts are compared in Figure 9. In this case, no notable trend with the
1194 Ind. Eng. Chem. Res., Vol. 48, No. 3, 2009
Figure 9. HDS and HDM activities of alumina-carbon-supported PCoMo catalysts. Table 4. HDS and HDM Conversions (%) of Different Catalysts catalyst PCoMo/A-0 PCoMo/A-5 PCoMo/A-10 PCoMo/A-15 PCoMo/A-20 PCoMo/A-25 PCoMo/AC-5 PCoMo/AC-10 PCoMo/AC-15 PCoMo/AC-20 PCoMo/AC-25
HDS 54.45 55.57 54.17 52.76 50.32 51.54 53 49.03 51.33 52.89 52.29
Figure 10. HDS and HDM activities of B- and P-containing CoMo catalysts. Table 5. Hydrocracking Activities of Boron-Containing Catalysts product distribution (wt %)
HDM 57.12 59.29 61.54 54 55 56 52 53.17 50.35 51.28 53
concentration of carbon in the alumina is apparent. Compared with their modified-alumina-supported counterparts, the alumina-carbon-supported catalysts show slightly lower activities (Table 4). From the pore size distribution results, it can be seen that, when carbon is added to the alumina and subsequently burned off, pores with higher pore diameters are generated. However, when the added carbon remains inside the alumina matrix, the pore diameters decrease as a result of the blocking of the alumina pores by the fine particles of carbon. Therefore, modified-alumina-supported catalysts have larger-diameter pores. Their total pore volumes are also higher than those of the alumina-carbon-supported catalysts. The larger pore diameters and higher pore volumes might be the reasons for the higher HDS and HDM activities of the modified-alumina-supported catalysts. These results also indicate that, for HDS activity, pores with large pore diameters might not be necessary. It is evident from the literature that the average size of sulfur compounds in heavy feeds is lower than that of metal-containing compounds. The effect of boron on the hydrotreating of Maya heavy crude was also studied. For this study, 0.8 wt % of boron was impregnated at four different pH values. The HDS and HDM activities of boron-containing catalysts are presented in Figure 10. In this figure (pH values given in parentheses), the activities of PCoMo/A-10 are also compared. This figure shows that, with increasing pH, the HDM activity increases; however, the HDS activity does not show considerable change with pH. Compared to the phosphorus-containing catalyst, the boron-containing catalysts show lower HDS and HDM activities. A plausible explanation for the catalyst prepared at higher pH showing a higher HDM activity is that the active metal might be better dispersed at higher pH than for the catalyst prepared at lower pH. Thus, the catalyst prepared at higher pH might contain more dispersed molybdates, resulting in its higher activity. Muralidhar et al.11 reported that boron did not show any beneficial effects on HDS and hydrogenation (HYD) conversions, but that hydrocracking activity was higher on boron-containing catalyst.
538 °C
°C °C °C °C °C
feed
BCoMo/ A-10(2)
BCoMo/ A-10(3)
BCoMo/ A-10(4)
BCoMo/ A-10(9)
10.31 10.62 5.72 3.76 14.99 10.11 44.49
13.82 13.00 6.94 4.35 16.44 10.55 34.90
12.99 12.73 6.85 4.33 16.50 10.81 35.79
12.00 12.53 6.77 4.26 16.63 11.01 36.80
13.37 12.70 6.75 4.27 16.42 10.78 35.71
The hydrocracking activity of boron-containing catalysts was also studied by TGA. The activity results are reported in Table 5, which shows that, in general, the catalysts prepared at lower pH values exhibited higher cracking activities; i.e., lower amounts of material having boiling temperatures higher than 538 °C were produced. The catalysts prepared at lower pH might contain highly acidic sites and have higher cracking activities as a result. However, more detailed study is necessary. The physical properties of the spent catalysts were also measured. The spent catalysts obtained after 6 h of reaction were washed by a Soxhlet process as described in the Experimental Section. The pore size distributions of the fresh and spent catalysts are presented in Figures 11 and 12 for catalysts PCoMo/A-10 and PCoMo/AC-10, respectively. The figures show that the pore size distribution decreases on the spent catalyst compared to that on the respective fresh catalyst. Moreover, the decreasing trend in pore size is more pronounced for the A-10-supported catalyst. The percentages of deposits on the spent catalysts were also measured, and the results are reported in Table 6. These results also show that the ACsupported catalysts have comparatively fewer deposits. The reductions of total pore volume of the A-10- and AC-10supported catalysts caused by the deposits were also calculated. It was found that the reduction in pore volume was 51% for the A-10-supported catalyst and around 40% in the case of the
Figure 11. Comparison of PSDs of fresh and spent PCoMo/A-10 catalysts (f ) fresh, s ) spent).
Ind. Eng. Chem. Res., Vol. 48, No. 3, 2009 1195
4. Conclusions
Figure 12. Comparison of PSDs of fresh and spent PCoMo/AC-10 catalysts. Table 6. Weight Percentages of Deposits on Spent Catalysts catalyst
deposits (wt %)
PCoMo/A-0 PCoMo/A-5 PCoMo/A-10 PCoMo/A-15 PCoMo/A-20 PCoMo/A-25 PCoMo/AC-5 PCoMo/AC-10 PCoMo/AC-15 PCoMo/AC-20 PCoMo/AC-25
27.6 28.26 30.14 31.46 28.1 34.7 26.62 28.4 29.16 30.82 33.78
AC-10-supported catalyst, compared to the pore volumes of their respective fresh catalysts. This indicates that the presence of carbon might hinder rate of deposition. Carbon is a neutral material, whereas alumina has acid sites on its surface. When the alumina surface is covered by carbon, the acid sites are less exposed to reaction, and hence, less coke formation occurs. XRD diagrams of fresh and spent PCoMo/A-10 catalysts are compared in Figure 13. There are no dramatic changes in these two diffractograms, indicating that the metals (vanadium and nickel) deposited during the hydroprocessing reaction are below the XRD detection level. This is also in good agreement with the results of our earlier study.12
In this investigation, two series of supports, A-X and AC-X, were prepared. It was observed that, when carbon is added to alumina and subsequently burned off, larger-diameter pores are generated, whereas if the added carbon is not burned off, it can block the pores of the alumina. The activity results show that the modified-alumina-supported catalysts have higher HDS and HDM activities than their alumina-carbon-supported counterparts. In addition, the catalyst supported by A-10 has a slightly higher HDM activity than the other supports in the same series. The effect of boron on the hydrotreating (HDT) activities of these catalysts indicates that use of a higher pH during catalyst preparation has a beneficial effect on the HDM activity. However, synergic effect of boron on the HDT activities is lower than that of phosphorus. Literature Cited (1) Rankel, L. A. Hydroprocessing of heavy oil over CoMo/carbon supported catalysts. Energy Fuels 1993, 7, 937. (2) Farag, H.; Whitehurst, D. D.; Sakanishi, K.; Mochida, I. Carbon versus alumina as a support for Co-Mo catalysts reactivity towards HDS of dibenzothiophenes and diesel fuel. Catal. Today 1999, 50, 9. (3) Farag, H.; Mochida, I.; Sakanishi, K. Fundamental comparison studies on hydrodesulfurization of dibenzothiophenes over CoMo-based carbon and alumina catalysts. Appl. Catal. 2000, 194-195, 147. (4) Salinas, E. L.; Espinosa, J. G.; Cortez, J. G. H.; Valente, J. S.; Nagira, J. Long term evaluation of NiMo/alumina-carbon black composite catalysts in hydroconversion of Mexican 538 °C+ vacuum residue. Catal. Today 2005, 109, 69. (5) Ferrari, M.; Bosmans, S.; Maggi, R.; Delmon, B.; Grange, P. CoMo/ carbon hydrodeoxygenation catalysts: Influence of the hydrogen sulfide partial pressure and of the sulfidation temperature. Catal. Today 2001, 65, 257. (6) Fukuyama, H.; Terai, S.; Uchida, M.; Cano, J. L.; Ancheyta, J. Active carbon catalyst for heavy oil upgrading. Catal. Today 2004, 98, 207. (7) Zhang, S. F.; Xu, B.; Herod, A. A.; Kandiyoti, R. Hydrocracking reactivities of primary coal extracts prepared in a flowing solvent reactor. Energy Fuels 1996, 10, 733. (8) Millan, M.; Adell, C.; Hinojosa, C.; Herod, A. A.; Dugwell, D.; Kandiyoti, R. Effect of catalyst deactivation and reaction time on hydrocracking heavy hydrocarbon liquids. Energy Fuels 2007, 21 (3), 1370. (9) Onuma, K. Preparation of bimodal alumina and other refractory inorganic oxides-suitable support for hydrotreating catalysts. In Preparation of Catalysts IV; Delmon, B., Grange, P. A., Poncelet, G., Eds.; Elsevier Science Publishers: New York, 1987; p 543. (10) Dugulan, A. I.; Craje´, M. W. J.; Overweg, A. R.; Kearley, G. J. The evaluation of the active phase in CoMo/C hydrodesulfurization catalysts under industrial conditions: A high pressure Mossbauer emission spectroscopy study. J. Catal. 2005, 229, 276. (11) Muralidhar, G.; Srinivas, B. N.; Rana, M. S.; Manoj Kumar; Maity, S. K. Mixed oxide supported hydrodesulfurization catalystssA review. Catal. Today 2003, 86, 45. (12) Maity, S. K.; Ancheyta, J.; Rana, M. S.; Rayo, P. The effects of phosphorus on catalyst and on hydrotreating activity of Maya heavy crude. Catal. Today 2005, 109, 42.
ReceiVed for reView April 15, 2008 ReVised manuscript receiVed June 5, 2008 Accepted June 27, 2008 Figure 13. XRD diagrams of fresh and spent PCoMo/A-10 catalysts.
IE800606P
