Energy & Fuels 2005, 19, 725-730
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Articles Catalytic Hydrocracking of Petroleum Residue over Carbon-Supported Nickel-Molybdenum Sulfides Masato Kouzu,* Yasunori Kuriki, and Kunio Uchida Institute for Materials and Chemical Process, National Institute for Advanced Industrial Science and Technology, 1-1-1, Higashi, Tsukuba, Ibaraki, 305-8565, Japan
Kinya Sakanishi, Yoshikazu Sugimoto, and Ikuo Saito Institute for Energy Utilization, National Institute for Advanced Industrial Science and, Technology, 16-3, Onogawa, Tsukuba, Ibaragi, 305-8569, Japan
Daisuke Fujii and Katsumi Hirano Department of Materials and Applied Chemical, Nihon University, 1-8, Kandasurugadai, Chiyoda, Tokyo, 101-8308, Japan Received April 26, 2004. Revised Manuscript Received December 28, 2004
Carbon-supported nickel-molybdenum sulfide (NMC) was prepared using an active carbon with a surface area of 3070 m2/g for the slurry-phase hydrocracking of petroleum residue. The hydrocracking catalysis was evaluated, in comparison with that for an alumina-supported nickelmolybdenum sulfide (NMA). The experimental hydrocracking was performed with the atmospheric residue of the Middle Eastern crude at 350-450 °C for 2 h in an autoclave initially pressurized with 5 MPa of hydrogen. NMC was more active in the radical quench reaction with the thermally decomposed residue than NMA, which was effective in reducing the residual fraction. NMC also provided less sulfur content for the liquid product than NMA. For the carbon-supported catalyst, it was evident that an increase in the surface area of the support caused enhancement of the hydrocracking catalysis. These results were verified through a reaction of the model compounds, 1-methylnaphthalene and dibenzothiophene. The higher activity was due to the better dispersion of the active component on the supporting material. The catalytic C-C bond scission was the minor reaction over any of the catalyst samples. Deterioration of NMC was measured through the experimental hydrocracking series that recycled the catalyst. In addition, the carbon deposit was discussed in relation to the adsorption of the residual fraction on the catalyst.
1. Introduction Slurry-phase hydrocracking is an efficacious technology to convert petroleum residue to fuel oil, because the hydrodynamics of the reactor causes enhancement of the mass-transfer rate.1 The enhanced mass-transfer rate is beneficial not only to the catalytic reaction, but also for the temperature control within the reactor. The hydrodynamics of the reactor have been studied on the basis of much data from the pilot plant, which causes improvement in the technique used to design the reactor.2-4 * Author to whom correspondence should be addressed. Currently with the Core Laboratory for Kyoto COE Project, Keihanna Co., Ltd., Keihanna Plaza (Laboratory Wing 4F), 1-7 Hikaridai, Seika, Kyoto, 619-0237, Japan. E-mail:
[email protected]. (1) Dautzenberg, F. M.; DeDeken, J. C. Catal. Rev.sSci. Eng. 1984, 26, 421-444. (2) Onozaki, M.; Namiki, Y.; Sakai, N.; Kobayashi, M.; Nakayama, Y.; Yamada, T.; Morooka, S. Chem. Eng. Sci. 2000, 55, 5099-5113. (3) Onozaki, M.; Namiki, Y.; Ishibashi, H.; Takagi, T.; Kobayashi, M.; Morooka, S. Energy Fuels 2000, 14, 355-363.
Currently, much attention is given to the hydrocracking catalyst for the purpose of improving the product yield. Quenching of the radical fragment with hydrogen is the major catalytic reaction with the hydrocracking, because petroleum residue can be thermally decomposed under the hydrocracking conditions. The enhanced radical quench reaction increases the yield of the fuel oil and reduces the fouling trouble due to the carbon deposit. Unsupported molybdenum sulfide and iron ore pulverized by mechanical milling have been investigated for use as the hydrocracking catalyst.5-8 Although these materials catalyze the radical quench reaction, their hydrogenating activity, which is responsible for en(4) Ishibashi, H.; Onozaki, M.; Kobayashi, M.; Hayashi, J.-I.; Itoh, H.; Chiba, T. Fuel 2001, 80, 655-664. (5) Song, C.; Saini, A. K.; Yoneyama, Y. Fuel 2000, 79, 249-262. (6) Patmore, D. J.; Khulbe, C. P.; Belinko, K. Prepr.sAm. Chem. Soc., Div. Pet. Chem. 1981, 26, 431-432. (7) Hirano, K.; Kouzu, M.; Okada, T.; Kobayashi, M.; Ikenaga, N.; Suzuki, T. Fuel 1999, 78, 1867-1873. (8) Kaneko, T.; Tazawa, T.; Okuyama, N.; Tamura, M.; Shimasaki, K. Fuel 2000, 79, 263-272.
10.1021/ef049895h CCC: $30.25 © 2005 American Chemical Society Published on Web 02/17/2005
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hancement of the radical quench reaction, was not so high that the product distribution reached a level that made the upgrading technology feasible. Carbon-supported catalysts are considered to be the best for the slurry-phase hydrocracking. The M-coke process yielded more fuel oil at the lower temperature, by means of carbon-supported molybdenum sulfide that was formed in situ.9 It was supposed that very fine particles of molybdenum sulfide on the carbon support enhanced the hydrogenating activity. The fine dispersion of the active component was possibly related to the properties of the carbon support. The weak polarity reduces the interaction between the active component and the support, and the large surface area provides the numerous impregnating sites.10 We believe that it is possible for the carbon-supported catalyst to increase the number of impregnating sites by enlarging the surface area. Also, the hydrogenating activity was improved, to promote molybdenum sulfide with nickel. It has been reported that a nickelmolybdenum (NiMo) sulfide on carbon black was more active in the hydrogenation of 1-methylnaphthalene (1-MN) than an alumina-supported nickel-molybdenum sulfide, which is the conventional catalyst for the hydrotreatment of heavy oil.11 Recently, an interest has been taken in the adsorptive nature of the carbon support.12,13 Because the residue adsorbed on the catalyst exits the reactor without the deposit, following the re-polymerization, the adsorptive ability for the residue is significant, in regard to reducing the fouling trouble. In the present paper, carbon-supported NiMo-sulfide (NMC) was prepared using active carbons of two types for the hydrocracking catalyst. The surface area of the carbon support was conditioned to control the dispersion of the active component. The hydrocracking catalysis was evaluated in comparison to that of an aluminasupported NiMo-sulfide (NMA), on the basis of the data from the reaction of the atmospheric residue using an autoclave. The experimental data indicated the activity for the radical quench reaction, the degree of catalytic deterioration, and the adsorptive ability of the residue. In addition, the hydrocracking catalysis was discussed in relation to the activity for a reaction of the model compounds. 2. Experiment Catalyst Preparation. For the supporting material of the catalyst sample, two types of active carbons were prepared by annealing petroleum pitch with potassium hydroxide in an atmospheric flow of nitrogen.14 The surface area of the active carbon was monitored by means of the mass ratio of potassium hydroxide to petroleum pitch. The surface area was 3070 m2/g for the carbon activated with a large amount of potassium hydroxide (active carbon A), and 860 m2/g for that with a small quantity of the activator (active carbon B). The pore volume was naturally larger for active carbon A (1.59 mL/g) than for (9) Bearden, R.; Aldridge, C. L. Energy Prog. 1981, 1, 44-48. (10) Rodriquez-Reinoso, F. Carbon 1998, 36, 159-175. (11) Sakanishi, K.; Hasuo, H.; Mochida, I.; Okuma, O. Energy Fuels 1995, 9, 995-998. (12) Terai, S.; Fukuyama, H.; Uehara, K.; Fujimoto, K. J. Jpn. Pet. Inst. 2000, 43, 17-24. (13) Segawa, A.; Watanabe, K.; Yoshimoto, M. J. Jpn. Pet. Inst. 2001, 44, 163-168. (14) Marsh, H.; Yan, D. S.; O’Grady, T. M.; Wennerberg, A. Carbon 1984, 23, 603-610.
Kouzu et al. Table 1. Porosity of Catalyst Samples in the Sulfide Form, as Measured by N2 Adsorption Carbon-Supported BET surface area pore volume mesopore volumea pore diameter a
Alumina-Supported
NMC-A
NMC-B
NMA
1856 m2/g 0.96 mL/g 0.71 mL/g 2.07 nm
335 m2/g 0.17 mL/g 0.05 mL/g 2.03 nm
179 m2/g 0.31 mL/g 0.31 mL/g 6.72 nm
Based on the Barrett-Joyner-Halenda (BJH) method.
active carbon B (0.45 mL/g), whereas the pore diameters for both of the active carbons were equivalent (ca. 2.1 nm) The aforementioned porosity was evaluated on the basis of data obtained from nitrogen adsorption at 77 K, using Micromeritics model ASAP-2010. Molybdenum and nickel were impregnated simultaneously on the active carbon via the incipient wetness procedure, using a methanol solution in which molybdenum dioxyacethylacetonate was dissolved with nickel acetate. The methanol solution was used to enhance its affinity against the hydrophobic surface of the active carbon. The amount impregnated was 15 wt % for molybdenum in the sulfide form used for the experimental reaction and 3 wt % for nickel. The impregnating operation was repeated to the prescribed amount of the metals, followed by atmospheric drying at 80 °C between each step. The prepared precursor of NMC was converted to the sulfide form offsite, at 400 °C under an atmospheric flow of a H2S (10 vol %)/H2 mixture. Table 1 lists the porosity of the catalyst samples in the sulfide form. As a reference, a conventional NMA for hydrotreatment of the heavy distillate was used in the present experiment. The NMA contained the active component and the promoter in the same amounts as those in the NMC samples. Model Reaction. The model reaction was performed at 350-410 °C, using an autoclave that was inserted into an electric furnace of the vertically shaking type, to measure the activity of the catalyst samples. 1-Methylnaphthalene (1-MN, 10%) was dissolved in decane with dibenzothiophene (DBT, 2%) and diphenylethane (DPE, 2%), which was used as the feedstock. Five milliliters of the feedstock was charged with 20 mg of the catalyst sample into the autoclave, the inner volume of which was 50 mL. The autoclave was pressurized under a hydrogen atmosphere of 5 MPa at ambient temperature and was then heated to the prescribed temperature. The reaction temperature was maintained for 1 h for every run. After the reaction, the fate of the model compounds was examined quantitatively, using a gas chromatography system, coupled with flame ionization detector (GC-FID) (Agilent, model 6890), and a gas chromatography system, coupled with mass spectroscopy (GC-MS) (Agilent, models 6890GC and 5973MSD, respectively), that was equipped with a fused silica column (model OV-101; 0.25 mm inner diameter (I.D.) and 50 m in length). The rate constant was calculated on the basis of the first-order kinetics. Hydrocracking Test. An atmospheric residue of the Middle Eastern crude was hydrocracked at 350-450 °C for 2 h, using the same autoclave as that previously mentioned. Properties of the atmospheric residue used as the feedstock are shown in Table 2. The feedstock contained 58.2 wt % of the residual fraction, the boiling point of which was >538 °C. The amount of hexane-insoluble fraction was 7.2 wt %, whereas no toluene-insoluble fraction was contained in the feedstock. Five grams of the feedstock was charged with 67200 mg of catalyst into the autoclave, and then the autoclave was pressurized with 5 MPa of hydrogen. The gaseous product was subjected to gas chromatography, coupled with thermal conductivity detection (GC-TCD) (Agilent, model 6890GC), to estimate its composition. The obtained chromatogram was analyzed using AC-RGA software. The liquid product was handled as shown in Figure 1. First, the
Hydrocracking of Petroleum Residue over NiMoS/C
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Table 2. Properties of Atmospheric Residue of the Middle Eastern Crude Used as a Feedstock for the Experimental Hydrocracking property distillable fraction 3000 m2/g for active carbon A, because of the distorted graphitic hexagonal structure. The crystalline distortion was accompanied by the various defects, dislocation, and discontinuities on the graphitic hexagonal structure, which possibly increased the number of impregnating sites for the active component. The better dispersion of the active component caused the enhancement of the desulfurizing activity. As shown in Table 4, NMC-A provided a higher desulfurizing percentage than that of the other catalyst samples. Also, NMC-A caused the highest yield of cyclohexylbenzene in the catalyst sample. The increase of cyclohexylbenzene indicated that the C-S bond scission followed hydrogenation of the neighboring aromatic ring.15 This desulfurizing reaction was effective for the polyaromatic sulfur species that was concentrated in the residue. The distribution of the converted DPE was examined to evaluate the activity for C-C bond scission.16,17 A trace of DPE (0.2%-0.4%) was converted to benzenes, as shown in Table 5. It was evident that the decomposition of DPE was the minor reaction at 350 °C, regardless of the catalyst sample. The major product was the hydrogenated DPE for both NMC samples, whereas the major product was phenanthrenes for NMA. (15) Daage, M.; Chianelli, R. R. J. Catal. 1994, 149, 414-427. (16) Suzuki, S.; Kan-nan, S.; Sakoda, T.; Ikenaga, N. J. Jpn. Inst. Energy 1995, 74, 280-286. (17) Li, D.; Nishijima, A.; Morris, D. E. J. Catal. 1999, 182, 339344.
H2 C1-C3a C4-220 °C 220-350 °C 350-538 °C residual fraction 538 °C+ HS b HIc total TId sulfur nitrogen
NMC-A catalyst
NMC-B catalyst
NMA catalyst
no catalyst
-2.0 4.5 25.4 35.0 29.2
-2.0 6.3 26.0 33.8 25.2
-1.9 4.3 26.5 31.9 29.1
-1.5 9.5 27.9 30.6 14.9
(0.8) (0.5) 1.3 2.1 0.38 0.08
(2.3) (2.5) 4.8 2.3 0.44 0.08
(3.1) (2.5) 5.6 1.0 0.59 0.08
(7.3) (3.5) 10.8 6.3 1.82 0.13
a Gaseous hydrocarbons, methane, ethane, and propane. b Hexane-soluble fraction in the residual fraction. c Hexane-insoluble and toluene-soluble fraction. d Toluene-insoluble fraction.
The decomposition of DPE was observed at 410 °C, because the yield of benzenes was >15% for any of the catalyst samples. NMC-A provided the highest yield of benzenes in this reaction series, which indicated that thermal cleavage of the C-C bond, followed by the catalytic radical quench, was the dominant reaction in the decomposition of DPE. It was supposed that the catalytic C-C bond scission was the minor reaction, even at 410 °C. Interestingly, the yield of phenanthrenes was the highest for NMA, independent of the reaction temperature. The acidity of the alumina support possibly was responsible for the cyclopolymerization of DPE. Hydrocracking Catalysis for the Atmospheric Residue. Table 6 shows the product yields in the hydrocracking of the atmospheric residue that was conducted at 450 °C for 2 h using the autoclave. The yield of the liquid 350 °C- fraction reached ∼60 wt % in this hydrocracking series. The residual fraction, the boiling point of which was >538 °C, decreased from 58.2 wt % to 1.3-5.6 wt % for the catalytic runs. The blank run, where no catalyst was used, provided a higher yield of the residual fractions than that of any of the catalytic runs. In addition, the yields of TI fraction and C1-C3 fraction were greater for the blank run than for any of the catalytic runs. These results indicated that the radical quench reaction was catalyzed over any of the supported NiMo-sulfide samples. In the series of catalytic runs, the yield of the residual fraction was the lowest for NMC-A. It was evident that hydrogenating activity was essential to the acceleration of the radical quench reaction in the hydrocracking. NMC-A also provided the lowest sulfur content with the
Hydrocracking of Petroleum Residue over NiMoS/C Table 7. Product Yields in the Experimental Hydrocracking of the Atmospheric Residue over 200 mg of Catalyst at 350 °C for 2 h, Using an Autoclave Initially Charged with 5 MPa of Hydrogen
Energy & Fuels, Vol. 19, No. 3, 2005 729 Table 8. Product Yields in a Series of the Experimental Hydrocracking of the Atmospheric Residue at 440 °C for 2 h, Where the Used Catalysts Were Recycleda NMC-A
Product Yield [wt %]
H2 C1-C3a C4-220 °C 220-350 °C 350-538 °C residual fraction 538 °C+ HSb HIc total TId sulfur nitrogen
NMC-A catalyst
NMC-B catalyst
NMA catalyst
no catalyst
-0.5 >0.1 0.0 5.3 51.4
-0.3 >0.1 0.0 6.0 49.5
-0.3 >0.1 0.0 5.0 47.5
0.0 0.0 0.0 4.5 38.2
36.6 4.7 41.3 1.9 2.32 0.12
35.6 7.1 42.7 2.0 2.61 0.13
40.3 6.2 47.5 1.0 2.66 0.13
49.4 7.6 57.0 0.0 3.08 0.23
a
Gaseous hydrocarbons, methane, ethane, and propane. b Hexane-soluble fraction in the residual fraction. c Hexane-insoluble and toluene-soluble fraction. d Toluene-insoluble fraction.
liquid product. The enhanced desulfurizing activity with the atmospheric residue reflected the result of the model reaction, as mentioned previously. On the other hand, it was unreasonable that the TI fraction yield was greater for NMC-A than for NMA, because NMC-A was more active in the radical quench reaction than NMA. NMC-A also yielded as much TI fraction as did NMC-B. These results indicated that the yield of TI fraction was independent of the degree of carbon deposit. Because carbon is a good adsorbent for petroleum residue,12,13 it was supposed that the yield of TI fraction reflected the amount of residue that was adsorbed on the catalyst. The adsorptive ability of the carbon-supported catalyst was investigated through the experimental hydrocracking at 350 °C. Table 7 shows product yields in this hydrocracking series. Thermal decomposition accompanied by re-polymerization was the imperceptible reaction for the residue at this temperature. The blank run did not yield any TI fraction, nor did it reduce the residual fraction. Although a TI fraction was yielded in every catalytic run, the residual fraction was reduced after the catalytic hydrocracking. The catalytic C-C bond scission was the minor reaction, as mentioned previously; therefore, it was reasonable that the yield of TI fraction was interpreted as the amount of residual fraction adsorbed on the catalyst. The decrease in the residual fraction after the catalytic hydrocracking was possibly due to the enhanced hydrogenation and desulfurization. The yield of TI fraction was the least for NMA, and NMC-A provided as much TI fraction as NMC-B did in this series of catalytic runs. Evidently, both of the carbon-supported catalysts were superior to the aluminasupported catalyst, in regard to the adsorption of the residual fraction. The carbon-supported catalyst undoubtedly functioned as the good adsorbent in the hydrocracking series at 450 °C. The volumetric amount of the adsorbed residual fraction, assuming that its density was 1 g/mL, was equal to 50% of the pore volume for NMC-A and 83% of that for NMA. This was consistent with the adsorptive capacity of the carbon support measured at 60 °C.18 However, the adsorptive capacity was not related to the pore volume for NMC
catalyst run H2 C1-C3a C4-220 °C 220-350 °C 350-538 °C residual fraction 538 °C+ HSb HIc total TId sulfur nitrogen
NMA
1st 2nd 1st 2nd virgin recycle recycle virgin recycle recycle -1.5 4.6 24.0 26.4 36.3 3.2 2.8 6.0 1.1 0.74 0.09
-1.4 5.5 23.6 28.2 31.9 4.9 4.2 9.1 0.8 0.87 0.09
-1.3 5.4 22.0 28.5 34.8 4.1 4.2 8.3 0.5 0.87 0.09
-1.5 4.8 25.0 31.5 29.1 4.3 3.4 7.7 0.7 0.85 0.10
-1.4 5.3 22.3 29.6 30.8
-1.4 6.1 23.7 28.4 29.4
5.8 4.4 10.2 1.0 1.12 0.10
6.3 4.3 10.6 1.3 1.09 0.10
a Gaseous hydrocarbons, methane, ethane, and propane. b Hexane-soluble fraction in the residual fraction. c Hexane-insoluble and toluene-soluble fraction. d Toluene-insoluble fraction.
samples. It was supposed that the residual fraction molecules were so bulky that they could not penetrate into the micropore of the carbon-supported catalyst. In fact, the pore diameter was ca. 2.1 nm for both NMC samples. The external surface possibly is the major adsorbing field with the residual fraction. Deterioration of the Carbon-Supported Catalyst in Slurry-Phase Hydrocracking. Recycling of the catalyst is very essential for the slurry-phase hydrocracking process; the catalytic deterioration has been evaluated for NMC-A, in comparison to NMA. The hydrocracking of the residue allows the catalyst to deteriorate, because of the serious carbon deposit. In addition to the carbon deposit, aggregation of the active component is a possible source of deterioration for the carbon-supported catalyst. It was supposed that the anchoring force to the active component was fragile over the carbon support, because of its weak polarity. Table 8 shows product yields in the experimental hydrocracking series for evaluation of the catalytic deterioration. The catalyst sample was recycled two times in this hydrocracking series, and the variation of the product distribution was traced from the virgin run to the final second recycle run. The first recycle run yielded a greater residual fraction than the virgin run, but the yield after the second recycle run was as much as that after the first recycle run. Through this hydrocracking series, NMC-A provided less residual fraction than NMA. Similar trends were obvious for the residual sulfur content of the liquid product. Evidently, NMC-A was more active than NMA, even after the deterioration. The deterioration pattern observed in this hydrocracking series indicated that the deposited carbon was the major pollutant for the both catalyst samples. Aggregation of the active component was not as serious for NMC-A, as mentioned previously. The hydrocracking series that recycled the catalyst gave significant data to verify the better adsorptive ability of NMC-A. The yield of TI fraction decreased with the recycling number for NMC-A, whereas that of the residual fraction increased. Because the catalyst deterioration was appreciable after the virgin run, it was (18) Sakanishi, K.; Manabe, T.; Watanabe, I.; Mochida, I. J. Jpn. Pet. Inst. 2001, 43, 10-16.
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unreasonable that the deposited carbonaceous material was reduced in the first recycle run. The decrease in TI fraction should be interpreted as the deterioration of the adsorptive capacity for the residual fraction. The adsorption of the residual fraction was appreciable, even in the first recycle run as well as the virgin run, because the secondary recycle run was accompanied by a decrease in TI fraction. Taking the amount of the adsorbed residual fraction into consideration, the amount of deposited carbonaceous material was
