Iron-Catalyzed Coprocessing of Coals and Vacuum Residues Using

Energy & Fuels 1998, 12, 1181-1190

1181

Iron-Catalyzed Coprocessing of Coals and Vacuum Residues Using Syngas-Water as a Hydrogen Source Kazu-aki Hata, Kenji Wada, and Take-aki Mitsudo* Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan Received February 18, 1998

The effectiveness of alternative hydrogen sources compared to pressurized hydrogen gas toward the coprocessing of coals and vacuum residues was investigated in the presence of different kinds of iron-based catalyst precursors. The reactions in syngas-water using pentacarbonyliron or synthetic pyrite achieved high rates of conversion to THF solubles comparable to those in pressurized hydrogen gas, indicating the presence of the synergistic effects of the two hydrogen sources, hydrogen gas and carbon monoxide-water. Under hydrogen gas, addition of water greatly increased the yields of the desired fractions. The Fe(CO)5-catalyzed coprocessing of a vacuum residue of Arabian Heavy and Wandoan coal (2:1, 400 °C, 60 min, H2 3.0 MPa, CO 3.0 MPa, water 0.5 g) in combination with the pretreatment at lower temperature (200 °C, 30 min) afforded the high yields of THF-soluble (100%) and n-hexane-soluble (69.5%) matter. At higher reaction temperatures, 425-450 °C, the use of Fe(CO)5 with sulfur or synthetic pyrite afforded much better rates of conversion than Fe(CO)5 without sulfur. The XRD and XPS analyses revealed the formation of a mixture of magnetite and pyrrhotite from Fe(CO)5 without sulfur, and the surface of the used catalyst was mainly covered with iron species in a relatively high oxidation state. On the other hand, pyrrhotite was formed from Fe(CO)5 with sulfur or synthetic pyrite. The gas consumption, eventually the efficiency of the coprocessing, was estimated to be influenced by such changes in the state of the catalyst surface.

Introduction Coprocessing is a simultaneous reaction of solid fossil fuels, such as coals, plastic wastes, or tire, and heavy oils.1-7 In the hydroconversion of petroleum residues, powdered coal is sometimes used as an additive to prevent coking. Vacuum residue works as a solvent, and coal acts as a catalyst carrier and/or a hydrogen shuttler.8-12 In addition, impurities including transition-metal species in the vacuum residue are concentrated into the coal residue.13 A number of studies have (1) Gray, M. R. In Upgrading Petroleum Residues and Heavy Oils; Marcel Dekker: New York, 1994; p 229. (2) Gataia, J. G. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1986, 31 (4), 181. (3) Mochida, I.; Iwamoto, K.; Tahara, T.; Korai, Y.; Fujitsu, H.; Takeshita, K. Fuel 1982, 61, 603-609. (4) Monnier, J. Review of the Coprocessing of Coals and Heavy Oils of Petroleum Origin. CANMET Report 84-5E, March 1984. (5) Moschopedis, S. E.; Hawkins, R. W.; Fryer, J. F.; Speight, J. G. Fuel 1980, 59, 647-653. (6) Symposium on Co-Utilization of Coal and Wastes. Prepr. Pap.s Am. Chem. Soc., Div. Fuel Chem. 1993, 38, and bibliography there cited. (7) Symposium on Co-Utilization of Coal and Wastes. Prepr. Pap.s Am. Chem. Soc., Div. Fuel Chem. 1995, 40, and bibliography there cited. (8) Wallace, S.; Bartle, K. D.; Burke, M. P.; Egia, B.; Lu, S.; Taylor, N.; Flunn, T.; Kemp, W.; Steedman, W. Fuel 1989, 68, 961-967. (9) Bartle, K. D.; Bottrell, S.; Burke, M. P.; Jones, C.; Louie, P. K.; Lu, S.; Salvado, J.; Taylor, N.; Wallace, S. Int. J. Energy Res. 1984, 18, 309-315. (10) Fouda, S. A.; Kelly, J. F.; Rahimi, P. M. Energy Fuels 1989, 3, 154-160. (11) Miyake, M.; Takahashi, K.; Kigashine, J.; Nomura, M. Fuel Process. Technol. 1992, 30, 205-213. (12) Yoshida, T.; Nagaishi, H.; Sasaki, M.; Yamamoto, M.; Kotanigawa, T.; Sasaki, A.; Idogawa, K.; Fukuda, T.; Yoshida, R.; Maekawa, Y. Energy Fuels 1995, 9, 685-690.

reported that addition of coal, at a level of 5-33%, to residue feed produced a boost in the distillate yields.14-18 Although the coprocessing is one of the most expected ways for utilization of coals and heavy oils, the use of expensive molecular hydrogen has aggravated its cost. There have been a limited number of reports on processes using alternative hydrogen sources, such as syngas-water or carbon monoxide-water.19,20 Fu et al. reported the efficiency of binary catalysts, i.e., Ni-Mo + K2CO3, for the coprocessing using syngas-water as an alternative hydrogen source.20 However, the more economically favorable iron-based catalyst of high activity in the coprocessing using syngas-water systems is not been well-developed. On the other hand, there are several reports on the high activity of organic solvent-soluble Fe(CO)5 with or without sulfur toward both the direct coal liquefaction and coprocessing in hydrogen-donor solvents and/or pressurized hydrogen gas.21-24 Suzuki et al. reported that Fe3O4 was formed from Fe(CO)5 in the absence of (13) Miller, T. J.; Panvelker, S. V.; Wender, I.; Shah, Y. T.; Huffman, G. P. Fuel Process. Technol. 1989, 23, 23-38. (14) Curtis, C. W.; Cassell, F. N. Energy Fuels 1988, 2, 1-8. (15) Herrick, D. E.; Tierney, J. W.; Wender, I. Energy Fuels 1990, 4, 231-236. (16) Pradhan, V. R.; Herrick, D. E.; Tierney, J. W.; Wender, I. Energy Fuels 1991, 5, 712-720. (17) Ceylan, K.; Stock, L. M. Energy Fuels 1991, 5, 482-487. (18) Tomic, J.; Schobert, H. H. Energy Fuels 1997, 11, 116-125. (19) Fu, Y. C.; Illig, E. G. Ind. Eng. Chem. Process Des. Dev. 1976, 15, 392-396. (20) Batchelder, R. F.; Fu, Y. C. Ind. Eng. Chem. Process Des. Dev. 1979, 18, 594-599. (21) Suzuki, T.; Yamada, O.; Fujita, K.; Takegami, Y.; Watanabe, Y. Chem. Lett. 1982, 1467-1468.

10.1021/ef980032w CCC: $15.00 © 1998 American Chemical Society Published on Web 10/03/1998

1182 Energy & Fuels, Vol. 12, No. 6, 1998

Hata et al.

Table 1. Analysis of Coal Samples

coal Yallourn (YL) Wyoming (WY) Wandoan (WD) Illinois No. 6 (IL)

volatile C H S ash material (daf %) (daf %) (daf %) (dry %) (dry %) 68.2 71.9 76.8 77.9

4.5 6.1 6.7 5.7

0.1 0.6 0.2 3.3

1.1 7.0 7.7 12.2

51.4 43.9 43.0 39.8

sulfur, whereas in the presence of sulfur or organic sulfur compounds, the formation of pyrrhotite was observed.23 Herrick et al. reported that in the Fe(CO)5catalyzed coprocessing using pure hydrogen gas, the initial decomposition of Fe(CO)5 yielded not only pyrrhotite but also very highly dispersed Fe3C and iron oxide/oxyhydroxide. These species were eventually converted to Fe1-xS during the prolonged reactions.15 In addition, catalytic activities of various kinds of pyrite (FeS2) have been investigated on the direct coal liquefaction using both hydrogen and carbon monoxidewater systems.25 Recently, we reported the high activities of Fe(CO)5 with sulfur, synthetic pyrite, and FeSO4 with sulfur toward the direct coal liquefaction using syngas-water or carbon monoxide-water.26-28 In the present study, the applicability of our previous catalytic coal liquefaction process using syngas-water as an alternative hydrogen source to the coprocessing of coals and vacuum residues was examined in the presence of iron-based catalyst precursors, i.e., pentacarbonyliron or synthetic pyrite. The reaction using syngas-water afforded the desired products in high yields, almost comparable to those using pressurized hydrogen gas, indicating the presence of a synergistic effect of each component of syngas, hydrogen and carbon monoxide. In addition, the effects of both of the catalyst precursors and the reaction conditions upon the state of the catalytically active species were investigated in detail. Preliminary experiments using a model compound and an activated carbon support were also performed in order to clarify the role of externally added water. Experimental Section Materials. Yallourn coal (Australian brown coal), Wyoming coal (American subbituminous coal), Wandoan coal (Australian subbituminous), and Illinois No. 6 coal (American bituminous coal) were used for the reaction. The analytical data of these coals are summarized in Table 1. The coals, dried at 100 °C under vacuum (13 Pa) for 10 h, were ground to less than 150 µm and stored in an argon atmosphere. The characteristic features of the two vacuum residues, the vacuum residue of Arabian Heavy (cut point 523 °C, AH) and propane-deasphalting bottom (PDB), are summarized in Table 2. Pentacarbonyliron (Fe(CO)5, purity higher than 95.0%) was purchased from Kanto Chemical, and synthetic pyrite (FeS2 80.3%, S (22) Watanabe, Y.; Yamada, O.; Fujita, K.; Takegami, Y.; Suzuki, T. Fuel 1984, 63, 752-755. (23) Suzuki, T.; Yamada, O.; Takahashi, Y.; Watanabe, Y. Fuel Process. Technol. 1985, 10, 33-43. (24) Montano, P. A.; Stenberg, V. I.; Sweeny, P. J. Phys. Chem. 1986, 90, 156-159. (25) Sofianos, A. C.; Butler, A. C.; Lourens, H. B. Fuel Process. Technol. 1989, 22, 175-188. (26) Watanabe, Y.; Hata, K.; Kawasaki, N.; Wada, K.; Mitsudo, T. Energy Fuels 1994, 8, 806-807. (27) Watanabe, Y.; Yamada, H.; Kawasaki, N.; Wada, K.; Hata, K.; Mitsudo, T. Chem. Lett. 1993, 275-278. (28) Hata, K.; Watanabe, Y.; Wada, K.; Mitsudo, T. Fuel Process. Technol. 1998, 56, 291-304.

12.3%, Na2SO4 7.1%, F ) 3.5 - 4.0 g‚cm-3, surface area 20 m2‚g-1, pore volume 0.02-0.03 cm3‚g-1) was provided by NEDO (New Energy Development Organization, Japan). Other reagents and gases were commercially available and used without further purification. Procedure. Coal (1.0 g), vacuum residue (2.0 g), water (0.5 g), and catalyst precursor ([Fe] 1.5 mmol) were placed in a 50 cm3 microautoclave made of Hasteroy C together with a stainless steel ball (11 mm) to help mixing. The autoclave was charged with syngas (H2 3.0 MPa (47.6 mmol), CO 3.0 MPa (47.6 mmol) at room temperature) and placed in a heat block. Then the pretreatment was performed at 200 °C for 30 min using a mechanical shaker (110 strokes/min). After cooling to room temperature, the autoclave was again heated and shaken at the desired temperature for an appropriate period, usually 60 min (plus an additional 3 min for reactor heat-up time). In the two-stage reaction, it took about 3 min to elevate the reaction temperature from 400 to 425 °C. The typical operating pressure was ca. 15.0 MPa with 0.5 g of water at 400 °C. After the specified reaction period, the autoclave was cooled by air blowing for 60 min. Analysis. After the reaction, the mass of the produced gases was recovered into a gas buret and analyzed by gas chromatography using a Porapak-Q column at 80 °C with FID for C1-C4 hydrocarbons and an active-carbon column at 50 °C with TCD for hydrogen and carbon oxides. The apparent hydrogen and carbon monoxide consumption was estimated from the balance of the initial substrates and recovered products. The produced slurry was Soxhlet-extracted with tetrahydrofuran (THF) for 10 h. The conversion was calculated from the amount of THF-insoluble matter. The THFsoluble matter was evaporated to remove THF and then extracted with 200 cm3 of n-hexane (NH) by magnetically stirring for 1 h to precipitate asphaltene (As) and preasphaltene (PA). The NH-soluble matter was defined as maltene (including C1-C4 gases). Maltene was separated into naphtha + middle (N + M; bp < 343 °C at atmospheric pressure), heavy (343 °C < bp < 523 °C), and pitch (bp > 523 °C) by vacuum distillation. The NH-insoluble matter was separated into As and PA by Soxhlet-extraction with benzene for 17 h. The coal conversion and the yields of C1-C4 gases, N + M, heavy, pitch, As, and PA was calculated as follows:

conversion (wt %) ) 100 × [1 - {THF insolubles(g) ash(g) - catalyst residue(g)}/{daf coal(g) + vacuum residue(g)}] maltene yield (wt %) ) conversion (wt %) - 100 × NH insolubles(g)/{daf coal(g) + vacuum residue(g)} As yield (wt %) ) 100 × As(g)/{daf coal(g) + vacuum residue(g)} PA yield (wt %) ) 100 × PA(g)/{daf coal(g) + vacuum residue(g)} C1-C4 yield (wt %) ) 100 × {CH4(g) + C2H4(g) + C2H6(g) + C3H6(g) + C3H8(g) + C4H8(g) + C4H10(g)}/ {daf coal(g) + vacuum residue(g)} pitch yield (wt %) ) 100 × vacuum distillate fraction (bp > 523 °C, g)/{daf coal(g) + vacuum residue(g)} heavy yield (wt %) ) 100 × vacuum distillate fraction (343 °C < bp < 523 °C, g)/{daf coal(g) + vacuum residue(g)} N + M yield (wt %) ) maltene yield (wt %) - C1C4 yield (wt %) - pitch yield (wt %) - heavy yield (wt %)

Iron-Catalyzed Coprocessing of Coals and Vacuum Residues

Energy & Fuels, Vol. 12, No. 6, 1998 1183

Table 2. Analysis of Vacuum Residue Samples vacuum residue

C (%)

H (%)

S (%)

N (%)

Ni (ppm)

V (ppm)

n-hexane solubility

vacuum residue of Arabian Heavy (AH) propane-deasphalting bottom (PDB)

83.7 83.9

10.3 9.4

5.5 5.6

0.5 0.3

37 49

103 160

78.9 74.6

The weight of the catalyst residue was calculated on the assumption that all of the catalyst residue was left in the THFinsoluble matter, and its molecular weight was equal to that of FeS. Note that calculated N + M yields include both coalor vacuum residue-originated water and carbon oxides, since in the case using alternative hydrogen sources, the presence of a large excess of externally added water and carbon monoxide prevents a precise estimation of their amounts. Catalyst residues were analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS). The XRD study was performed using a Shimadzu XD-D1 diffractionmeter with Cu KR radiation in the range of 3° < 2θ < 70°. XPS were recorded with an ULVAC PHI 5500 MT system using Mg KR1,2 radiation (15 kV, 400 W) operating at room temperature, with a pressure below 1.3 × 10-6 Pa. The electron takeoff angle was set at 45°. The spectral accumulation time was ca. 30 min for both the S 2p and Fe 2p lines of the residue. The binding energy was referenced to both the C 1s and Si 1p levels. Sputtering was performed by a Xe ion beam (3.0 kV) with a laster size 1.1 mm × 2.1 mm. The aromatic carbon fraction (f(a)) and the carbon structure of the light fraction (bp > 173 °C of maltene) were analyzed by 13C NMR (JEOL-EX-400, 100 MHz, NNE-mode) in CDCl3 solutions.

Results and Discussion Effect of Hydrogen Sources. First, to estimate both the merits and demerits of the use of syngaswater, a comparative study between different kinds of hydrogen sources on the coprocessing of Wandoan coal and vacuum residue of Arabian Heavy was performed. Note that the vacuum residue itself is almost completely soluble in THF, including 78.9% of pitch and 21.1% of the asphaltene fractions. Consequently, the 2:1 mixture of vacuum residue and coal before the reaction is estimated to include 52.6% pitch and 14.1% asphaltene. Hereafter, the results in the tables and figures represent the distribution of all the products based on the sum of the amounts of both coals and heavy oils. Figure 1 parts a and b shows the results of the noncatalytic and ironcatalyzed reactions at 400 °C for 60 min. In the latter case, pentacarbonyliron, which is one of the most active catalyst precursors for direct coal liquefaction, was employed. Pretreatment at 200 °C for 30 min was also done just before the reaction, since this helps complete the mixing of the coal and vacuum residues, and markedly improved the yields. As shown in Figure 1a, in regard to the noncatalytic runs, the yields of THF solubles were in the following order: CO-H2O > syngas-H2O > H2-H2O > He-H2O > H2 only, but the differences were small. The reaction using carbon monoxide-water showed the maximum THF-soluble yield (88.2%). Interestingly, in the case using hydrogen gas, addition of water increased the yields of THF solubles. Note that the reaction with water in inert gas, He, showed a higher efficiency than that under pressurized hydrogen gas. This suggests the significance of chemical reactions between added water and the coal or vacuum residue species, i.e., an ionic process.29 Since (29) Katritzky, A. R.; Allin, S. M. Acc. Chem. Res. 1996, 29, 399.

there was no externally added carbon monoxide, actually the formation of carbon dioxide was negligible, the contribution of conventional water-gas shift reaction (WGSR) seems to be small in this case. Generally, the addition of Fe(CO)5 markedly improved the efficiency of coprocessing, but the trend with regard to hydrogen sources was partly changed. Whereas the addition of water in the case using hydrogen gas greatly improved the conversion to THF solubles, the reaction using carbon monoxide-water was less promoted. Although one can expect low conversions by the use of syngas-water because of low partial pressure of each of the component gases, the high THF-soluble yield almost comparable to the case with hydrogen-water was achieved, indicating the presence of synergistic effects of the two components, hydrogen gas and carbon monoxide-water. Figure 1c shows the effects of hydrogen sources in the catalytic runs at 425 °C. The increase in reaction temperature markedly improved the efficiency of both the hydrogen gas and the hydrogen gas-water system. Note that the addition of water to the hydrogen system still showed a positive effect on the conversion, even at 425 °C. On the other hand, promotion in the case using syngas-water or carbon monoxide-water was less significant. Figure 1d shows the results of another set of raw materials, Illinois No. 6 and propane-deasphalting bottom. The conversions to THF solubles were generally high, especially in hydrogen gas-water system, in which the products were completely soluble in THF. There were similarities in the product yields with respect to the hydrogen sources, as shown in Figure 1b. The use of syngas with water afforded a slightly lower conversion than that using hydrogen gas-water. The effects of the hydrogen sources on the apparent amount of consumption of hydrogen gas and carbon monoxide were investigated. Figure 2a shows the results of the coprocessing of Wandoan coal and vacuum residue at 400 °C. Note that 7.5 mmol of CO was produced from 1.5 mmol of Fe(CO)5. In addition to carbon oxides, hydrogen, and C1-C4 gases, a trace amount of H2S was detected in all cases. Under hydrogen gas, the addition of water increased the consumption of hydrogen gas. This seems to reflect the high yields of THF solubles and maltene in the hydrogen-water system. The formation of coal- or vacuum residue-originated carbon oxides was estimated to be negligible (less than 1 mmol) in both cases, with or without water. There was no significant influence on the formation of carbon dioxide by the addition of water. More than 30 mmol of carbon monoxide was consumed in the case using carbon monoxide with water together with the formation of hydrogen gas (7.3 mmol), probably generated by the water-gas shift reaction (WGSR). The coprocessing using syngas-water showed a behavior intermediate between hydrogen-water and carbon monoxide-water. The total amounts of the consumption of reducing gases were in the following


Hata et al.

Figure 1. Effects of hydrogen sources on the conversion and yields in the Fe(CO)5-catalyzed coprocessing. (a) Wandoan coal and vacuum residue without a catalyst precursor, at 400 °C. (b) Wandoan coal and vacuum residue with Fe(CO)5, at 400 °C. (c) Wandoan coal and vacuum residue with Fe(CO)5, at 425 °C. (d) Illinois No. 6 coal and propane-deasphalting bottom with Fe(CO)5, at 400 °C. Coal 1.0 g, vacuum residue 2.0 g, H2O 0.5 g, Fe(CO)5 1.5 mmol, for 60 min with pretreatment at 200 °C for 30 min. Hydrogen source H2 (6.0 MPa), CO (6.0 MPa), syngas (H2 3.0 MPa + CO 3.0 MPa).

order: H2-H2O . CO-H2O > syngas-H2O > H2, but this did not completely reflect the order of efficiency. Despite marked carbon monoxide consumption, the reaction using carbon monoxide-water generally resulted in low conversions. To evaluate on the degree of WGSR in the case using carbon monoxide and water, we preliminary performed a model compound study in the absence of coal and vacuum residue. In the reaction of diphenylmethane (7.5 mmol) in the presence of activated carbon (0.5 g), Fe(CO)5 (1.0 mmol), and water (0.5 g) under 6.0 MPa of CO at 400 °C for 60 min, 23.6 mmol of hydrogen was produced. The main products were benzene and toluene, and no significant hydrogenation of the aromatic rings was observed (see below). Since the conversion of diphenylmethane was 6.7% and about 1.0 mmol of hydrogen was estimated to be consumed for the hydrogenolysis of the substrates, the extent of hydrogen formation by WGSR in the present conditions is estimated to be ca. 25 mmol. This value is consistent with CO consumption in the coprocessing. Note that this amount of hydrogen corresponds to 1.6 MPa of partial pressure at most. In the case of Illinois No. 6 coal and propanedeasphalting bottom (Figure 2b), the marked hydrogen

consumption was observed in the hydrogen-water system. The reason for such inconsistency between the marked consumption of carbon monoxide and the relatively low efficiency in the catalytic runs under carbon monoxide-water is still unclear. The active hydrogen species formed in carbon monoxide-water seems to be less effective than that in molecular hydrogen in general. To clarify this problem, extensive study on reaction mechanism using appropriate model compounds is proceeding. The effects of the hydrogen sources on f(a) of the maltene fraction (bp > 173 °C) was investigated by 13C NMR (NNE mode). In the Fe(CO)5-catalyzed coprocessing of Wandoan coal and vacuum residue at 400 °C, f(a) decreased to 0.17 (hydrogen without water), 0.31 (hydrogen with water), 0.38 (syngas-water), and 0.37 (carbon monoxide-water) from a value of 0.55 for the vacuum residue before the reaction. Hydrogen gas without water greatly decreased f(a). In the case of Illinois No. 6 and propane-deasphalting bottom (f(a) ) 0.61), f(a) of maltene fraction using syngas-water was 0.42. Recently, Song and co-workers have demonstrated the strong positive effect of the addition of water in the catalytic hydroconversion of coals using molybdenum


Figure 2. Effects of hydrogen sources on the apparent H2, CO consumption and H2 production in the Fe(CO)5-catalyzed coprocessing. (a) Wandoan coal and vacuum residue. (b) Illinois No. 6 coal and propane-deasphalting bottom. Coal 1.0 g, vacuum residue 2.0 g, H2O 0.5 g, Fe(CO)5 1.5 mmol, for 60 min at 400 °C with pretreatment at 200 °C for 30 min. Hydrogen source H2 (6.0 MPa), CO (6.0 MPa), syngas (H2 3.0 MPa + CO 3.0 MPa).

catalyst precursors,30-36 whereas addition of water has often has been reported to have negative effects.37 Their recent study using model compounds concluded that addition of water is effective for the preparation of active catalysts from precursors.36 In their studies, the promotional effect of water is found to be predominant at relatively low temperatures as high as 350-375 °C. At temperature above 400 °C, adding water decreased coal conversions. In contrast to their results, the addition of water still showed a positive impact even at 425 °C (30) Song, C.; Saini, A. K.; Schobert, H. H. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1993, 38, 1031-1038. (31) Song, C.; Saini, A. K. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1994, 39, 1103-1107. (32) Song, C.; Saini, A. K. Energy Fuels 1995, 9, 188-189. (33) Byrne, R.; Song, C. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1995, 40, 537-541. (34) Song, C.; Saini, A. K.; McConnie, J. Coal Sci. Technol. 1995, 24, 1391-1394. (35) Song, C. S.; Saini, A. K.; Yoneyama, Y.; Schobert, H. H. DGMK Tagungsber., 9704 (Proceedings ICCS 1997, Vol. 3) 1997, 1413-1416. (36) Yoneyama, Y.; Song, C. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1997, 42 (1), 52-54. (37) Kamiya, Y.; Nobusawa, T.; Futamura, S. Fuel Process. Technol. 1988, 18, 1.


in our study, as shown in Figure 1c. In addition, an increase in the formation of carbon dioxide by the addition of water, which was reported to markedly occur in their studies,30-36 was not observed. Although at the present stage we do not have sufficient data to explain the differences between our work and Song’s, at a minimum, chemical reactions between water and the species of coal or vacuum residue would have a significant effect, since the reaction in the helium-water system in the absence of catalyst showed a relatively high efficiency (see above). Furthermore, preliminary model compound study was done to investigate the role of water. The reaction of diphenylmethane (7.5 mmol; activated carbon (0.5 g), Fe(CO)5 (1.0 mmol) with or without water (0.5 g), under 5.0 MPa of hydrogen at 375 °C for 60 min) was influenced markedly by the addition of water. In the absence of water, hydrogenation of the aromatic rings proceeded (the yields of benzylcyclohexane and dicyclohexylmethane were 40% and 5%, respectively) without significant hydrogenolysis of the carbon-carbon bond. On the other hand, addition of water almost completely suppresses the hydrogenation. Most of the reactant was recovered, and only trace amounts of benzene and toluene were detected as the products. This result is consistent with the NMR data mentioned above, where the maltene fraction produced under hydrogen gas without water exhibited a very low f(a) compared with those using other hydrogen sources. The most probable reason of such differences in the activities would be changes in the state of the catalysts. Therefore, a detailed investigation of the influence of water on the state of the catalytically active species is now in progress. Effect of Catalyst Precursors. As described above, syngas-water showed excellent efficiency, almost comparable to hydrogen-water. Therefore, the effects of diffeent kinds of iron-based catalyst precursors were examined. Table 3 shows the activities and effects of the amount of several iron-based catalyst precursors toward the coprocessing using Wandoan coal and vacuum residue (1:2, 400 °C, 60 min) in combination with the pretreatment at 200 °C for 30 min. In addition to pentacarbonyliron, synthetic pyrite (FeS2) showed a high activity toward the coprocessing. Addition of sulfur to Fe(CO)5 was found to improve the activities at a relatively high temperature. Compared with a control experiment without iron species, addition of 1.5 mmol of Fe(CO)5 (2.8 wt % as Fe based on the amount of coal plus vacuum residue) afforded higher conversion (97.6%) and a higher maltene yield (64.7%). Further addition of Fe(CO)5 up to 2.0 mmol (3.7 wt % as Fe) increased the THF-soluble yield to almost 100% and the maltene yield to 69.5%. Synthetic pyrite also showed a high THF-soluble yield that was comparable to Fe(CO)5 together with the formation of 0.9 mmol of hydrogen sulfide, but was low in the N + M yield. At 400 °C, addition of sulfur to Fe(CO)5 did not show any positive effects but only decreased the N + M yield. In this reaction, the generation of 1.2 mmol of hydrogen sulfide was observed. Table 3 also shows the results of several kinds of coals. The Fe(CO)5-catalyzed coprocessing using syngas-water gave the high conversion for all coals. In particular, using Illinois No. 6 coal, a conversion of


Hata et al.

Table 3. Iron-Catalyzed Coprocessing of Wandoan Coal and Arabian Heavy Vacuum Residues Using Syngas-Watera run

coal

cat.

temp. (°C)

time (min)

conv. (daf %)

C1-C4 (daf %)

Nap + Mid (daf %)

Heavy (daf %)

pitch (daf %)

Malteneb (daf %)

As (daf %)

PA (daf %)

1 2 3 4 5 6d 7 8 9 10 11 12 13 14 15

WD WD WD WD WD WD WD WD YL WY IL WD WD WD WD

none Fe(CO)5 Fe(CO)5c FeS2 R-Fe2O3 Fe(CO)5 Fe(CO)5 Fe(CO)5 Fe(CO)5 Fe(CO)5 Fe(CO)5 Fe(CO)5 Fe(CO)5c Fe(CO)5e FeS2

400 400 400 400 400 400 400 400+425 400 400 400 450 450 450 450

60 60 60 60 60 60 120 60+60 60 60 60 60 60 60 60

87.5 97.6 96.6 95.9 90.4 100.0 99.1 96.6 95.4 95.3 99.5 87.7 95.8 95.6 96.9

1.0 1.0 0.8 0.8 1.1 1.3 2.0 3.8 0.7 1.0 1.3 7.1 4.8 4.9 5.6

9.6 12.2 4.6 7.4 5.8 13.8 31.3 26.4 15.7 15.7 16.9 36.4 30.6 26.6 36.1

13.3 5.8 5.6 5.7 7.2 6.8 6.7 21.8 6.7 7.8 6.9 14.2 20.1 21.5 19.3

34.7 45.8 51.7 50.4 46.1 47.7 29.5 19.7 40.8 39.0 36.7 5.5 17.4 18.5 12.4

58.6 64.7 62.6 64.3 60.2 69.5 69.5 71.7 63.9 63.5 61.7 63.1 68.1 66.7 67.8

22.6 23.3 28.8 27.2 21.8 24.0 22.2 19.8 24.2 25.7 27.5 19.6 22.9 23.9 23.0

6.4 9.6 5.2 4.4 8.4 6.5 7.4 5.1 7.3 6.1 10.3 4.9 4.8 5.0 6.1

a Coal 1.0 g, vacuum residue 2.0 g, H O 0.5 g, CO 3.0 MPa, H 3.0 MPa, catalyst precursor (cat.) [Fe] 1.5 mmol. With pretreatment (200 2 2 °C, 30 min). b Maltene ) C1-C4 + Naphtha + Middle + Heavy + Pitch. c With 2.0 mmol of sulfur. d Fe(CO)5 2.0 mmol. e With 4.0 mmol of sulfur.

Figure 3. Effect of the concentration of coal on the coprocessing of Wandoan coal and vacuum residue using syngaswater. Coal + residue 3.0 g, Fe(CO)5 1.5 mmol, H2O 0.5 g, CO 3.0 MPa, H2 3.0 MPa at 400 °C for 60 min. With pretreatment at 200 °C for 30 min.

99.5% was achieved but the yield of maltene was relatively low. These results indicate the wide applicability of the combination of Fe(CO)5 and syngaswater. Figure 3 shows the effect of the ratio of coal and heavy oil on the coprocessing of Wandoan coal and vacuum residue using syngas-water in the presence of Fe(CO)5. Without the addition of coal, the products were almost completely soluble in THF but the yields of N + M and heavy was very low. The yields of N + M + heavy increased with the increasing coal-to-heavy oil ratio and were generally higher than the simple sum of the results of the reaction with 100% coal or 100% heavy oil. The conversions to THF solubles also showed positive synergistic effects of coal and vacuum residue, but there were no improvements in the maltene yields. These results suggest that the coexistence of coal and vacuum residue is important, probably due to the roles of coal as a support for active iron species and a source of naphthenes that can act as hydrogen-shuttling compounds.12

Figures 4 parts a and b shows the effects of the reaction temperature on the conversions and yields with (a) Fe(CO)5 and (b) synthetic pyrite (FeS2) using syngas-water. With Fe(CO)5, the maximum conversion was achieved at 400 °C. Further increases in the reaction temperature greatly enhanced the yields of the light fractions (C1-C4 gases + N + M + heavy), whereas the conversion into THF solubles was slightly decreased. On the other hand, in the presence of synthetic pyrite, the maximum conversion was achieved at 425 °C. Above 425 °C, conversions using synthetic pyrite were higher than those using Fe(CO)5. The addition of sulfur to the Fe(CO)5-catalyzed system improved the conversions at relatively higher temperatures, as well as synthetic pyrite. At 450 °C, increases in the conversion by the addition of sulfur with Fe(CO)5 were observed (see Table 3) whereas the yield of naphtha + middle decreased as the amount of added sulfur increased. However, large amounts of sulfur, more than 2.0 mmol, did not improve the yields, although addition of H2S was often reported to improve the conversions.38 Figure 5 (parts a and b) shows the effect of the reaction temperature on the apparent hydrogen-gas and carbon-monoxide consumption in the presence of (a) Fe(CO)5 and (b) synthetic pyrite (FeS2). In the case using Fe(CO)5, the apparent carbon monoxide consumption was generally larger than the hydrogen gas consumption below 425 °C. At 450 °C, the carbon monoxide consumption greatly decreased and the hydrogen gas consumption markedly increased, becoming larger than the carbon monoxide consumption. This drastic change seems to be responsible for the variation in the catalytically active species (see below). In the synthetic pyritecatalyzed coprocessing, the compositions of the resulting gas were very different from those in the case using Fe(CO)5. The hydrogen consumption was higher than the carbon monoxide consumption in the range of 375-450 °C. Both the hydrogen and carbon monoxide consumption increased with increasing temperature, then increased markedly at 400-425 °C, and leveled off above 425 °C. In the comparative discussions between the degree of reducing gas consumption and conversion efficiencies, (38) Stenberg, V. I.; Nowok, J. Chemtech 1987, 636-641.


Figure 4. Effect of the reaction temperature on the conversion and yields in the coprocessing of Wandoan coal and vacuum residue in syngas-water systems. Catalyst: (a) Fe(CO)5 and (b) synthetic pyrite (FeS2). Coal 1.0 g, vacuum residue 2.0 g, H2O 0.5 g, catalyst 1.5 mmol-atom-Fe, CO 3.0 MPa, H2 3.0 MPa for 60 min with pretreatment at 200 °C for 30 min.

care must be taken because the contribution of the competitive retrogressive reactions would be significant at higher temperatures. As shown in Figure 5b, in the synthetic pyrite-catalyzed reaction, the supply of active hydrogen species is considered to be markedly promoted by increasing the temperature from 400 to 425 °C. This would surmount the disadvantages of retrogressive reactions, resulting in the high conversion at 425 °C. On the other hand, in the case using Fe(CO)5, increases in reducing gas consumption with an increase in temperature were rather gradual. Therefore, disadvantageous coking would be predominant at above 400 °C. Figure 6 shows the time dependence on the coprocessing of Wandoan coal and vacuum residue using (a) Fe(CO)5 at 400 °C and (b) FeS2 at 425 °C, the temperatures at which the maximum conversions were achieved. In Fe(CO)5-catalyzed coprocessing, the conversion into THF solubles gradually increased in the prolonged run and was almost completely THF soluble after 120 min. On the other hand, the yields of the light fractions (C1C4 gases + N + M + heavy) markedly increased with reaction time. Using synthetic pyrite, both the conver-


Figure 5. Effect of the reaction temperature on the apparent H2 and CO consumption in the coprocessing of Wandoan coal and vacuum residue in syngas-water systems. Catalyst: (a) Fe(CO)5 and (b) synthetic pyrite (FeS2). Coal 1.0 g, vacuum residue 2.0 g, H2O 0.5 g, catalyst 1.5 mmol-atom-Fe, CO 3.0 MPa, H2 3.0 MPa for 60 min with pretreatment at 200 °C for 30 min.

sion and the yields of the light fractions at an early stage were fairly higher than those with Fe(CO)5. The conversion was 100% after 60 min. We also examined the effects of the two-step reaction, which was very effective in achieving higher yields of the light fractions in the direct coal liquefaction.27 As shown in Table 3 (run 8), however, considerable decreases in the conversion and N + M yield were observed together with a slight improvement in the maltene yield, suggesting that the two-step reaction in the coprocessing was not as effective as those in the coal liquefaction. Analysis of Used Catalyst. To investigate the reasons for very different consumption of carbon monoxide and hydrogen by two iron catalyst precursors, the spent catalysts in the reaction residue were analyzed in detail. Figure 7 shows the XRD patterns of the reaction residues of the catalytic coprocessing of Wandoan coal and vacuum residue at 400 or 450 °C for 60 min. As shown in Figure 7a, the formation of highly dispersed magnetite from Fe(CO)5 without sulfur (mean crystallite size ca. 19.7 nm) together with a small


Hata et al.

Figure 7. XRD patterns of the reaction residues from Wandoan coal and vacuum residue using syngas-water with various catalyst precursors. Coal 1.0 g, vacuum residue 2.0 g, H2O 0.5 g, H2 3.0 MPa, CO 3.0 MPa, reaction time 60 min with pretreatment at 200 °C for 30 min. Catalyst precursor: (a, d) Fe(CO)5 1.5 mmol, (b, e) Fe(CO)5 1.5 mmol, S 2.0 mmol, (c, f) FeS2 1.5 mmol. (a-c) Reaction temperature of 400 °C and (d-f) of 450 °C. The pattern of magnetite (Fe3O4) and pyrrhotite (Fe1-xS) were indicated 3 and 1, respectively. Figure 6. Time dependence on the conversion and yields in the coprocessing of Wandoan coal and vacuum residue in syngas-water systems. Catalyst: (a) Fe(CO)5 and (b) synthetic pyrite (FeS2). Coal 1.0 g, vacuum residue 2.0 g, H2O 0.5 g, catalyst 1.5 mmol-atom-Fe, CO 3.0 MPa, H2 3.0 MPa with pretreatment at 200 °C for 30 min. Reaction temperature: (a) at 400 °C and (b) 425 °C.

amount of pyrrhotite (Fe1-xS) was revealed. When sulfur was added (2.0 mmol, Figure 7b) only the peaks of pyrrhotite (ca. 19.4 nm), one of the most active catalytic species,39-42 were clearly observed, as expected. Similarly, pyrrhotite was formed from synthetic pyrite (Figure 7c, ca. 22.2 nm). At 450 °C, whereas only the formation of pyrrhotite from Fe(CO)5 with sulfur or synthetic pyrite was observed, the form of the iron species from Fe(CO)5 without sulfur was significantly changed. The strength of the peaks corresponding to pyrrhotite increased, whereas those of magnetite markedly decreased (Figure 7d), which would be caused by the sulfidation by coalor vacuum residue-originated organic sulfur. This variation in the composition seems to deeply relate the marked changes in the gas consumption (see above). When only the formation of pyrrhotite was observed by (39) Bommannavar, A. S.; Montano, P. A. Fuel 1982, 61, 1288-1290. (40) Baldwin, R. M.; Vincigurra, S. Fuel 1983, 62, 498-501. (41) Bommannavar, A. S.; Montano, P. A. Fuel 1983, 62, 932-935. (42) Ogawa, T.; Stenberg, V. I.; Montano, P. A. Fuel 1984, 63, 16601663.

XRD, both the hydrogen consumption and carbon monoxide consumption were predominant. In the case of dominant formation of magnetite, the consumption of hydrogen was less significant. From these results one can assume that pyrrhotite can activate both molecular hydrogen and carbon monoxide-water in high efficiency, whereas magnetite is more suitable for the activation of carbon monoxide-water. For a more detailed analysis of the surface catalytic species, depth profiles of the X-ray photoelectron spectra were acquired.43 Figure 8 shows the changes in the surface atomic ratio of iron-to-carbon (Fe/C) and sulfurto-carbon (S/C) of the reaction residues from the coprocessing of Wandoan coal and vacuum residue (syngaswater, at 400 °C for 60 min with pretreatment 200 °C, 30 min) with sputtering time. Although the precise sputtering rate has not been determined yet, the rate is estimated to be ca. 1.0 nm‚min-1. Without sputtering, both Fe/C and S/C were very low, probably because of the adsorption of carbonaceous species during the cooling after the reaction. In the case using Fe(CO)5 (Figure 8a), the Fe/C ratio gradually increased with increasing sputtering time whereas S/C was kept very low. In the case of Fe(CO)5 with sulfur (Figure 8b) or synthetic pyrite (Figure 8c), both Fe/C and S/C were higher than those using Fe(CO)5 only. (43) Kim, J. Y.; Reucroft, P. J.; Taghiei, M.; Pradhan, V. R.; Wender, I. Energy Fuels 1994, 8, 886-889



Figure 8. The atomic concentration of iron and sulfur of the residue from the coprocessing of Wandoan coal and vacuum residue using syngas-water by the XPS analysis. Coal 1.0 g, vacuum residue 2.0 g, H2O 0.5 g, CO 3.0 MPa, H2 3.0 MPa at 400 °C for 60 min with pretreatment at 200 °C for 30 min. Catalyst precursor, (a) Fe(CO)5 1.5 mmol, (b) Fe(CO)5 1.5 mmol, S 2.0 mmol, (c) FeS2 1.5 mmol.

Figure 9 shows the Fe(2p) and S(2p) spectra of the residues from the reaction using (a) Fe(CO)5, (b) Fe(CO)5 with sulfur, and (c) synthetic pyrite. Since air exposure of the samples would cause a significant oxidation of the surface, all of the samples were treated very carefully in an Ar atmosphere. In the case of Fe(CO)5 (Figure 9a), the spectrum of Fe(2p) without sputtering showed peaks at 711.5 and 725.0 eV. After sputtering for only 1 min, in addition to the two peaks, the significant peaks of a reduced iron species were observed at 709.0 and 722.5 eV. The concentration of the reduced iron species increased with increasing sputtering time. Blank experiments using magnetite ruled out the contribution of surface reduction during sputtering. According to the literature44 and blank experiments using different kinds of iron species, the former set of spectra are possibly assigned to magnetite, although it (44) Moulder, F.; Stickle, W. F.; Sobol, P. E.; Bomben, K. D. Handbook of X-ray Photoelectron Spectroscopy; Perkin-Elmer Co.: Eden Prairie, MN, 1992.

Figure 9. Effects of catalyst precursor on XPS spectra of the residue from Wandoan coal and vacuum residue using syngaswater. Coal 1.0 g, vacuum residue 2.0 g, H2O 0.5 g, CO 3.0 MPa, H2 3.0 MPa at 400 °C for 60 min with pretreatment at 200 °C for 30 min. Catalyst precursor: (a) Fe(CO)5 1.5 mmol, (b) Fe(CO)5 1.5 mmol, S 2.0 mmol, (c) FeS2 1.5 mmol. (i) Without sputtering, (ii) 1 min sputtered, (iii) 4 min sputtered.

is dangerous to conclude the kind of species only by the chemical shift in the XPS. Baltrus and Diehl have assigned similar spectra to a mixture of Fe2+ and Fe3+ from pyrite oxidation.45 On the other hand, the latter reduced species is considered to be pyrrhotite or troilite.44 The S(2p) spectra showed the peaks of elemental sulfur and sulfide on the outer surface, whereas in the inside of the residue, only the peaks of sulfide were observed.43-45 One of possible reasons why the depth (45) Baltrus, J. P.; Diehl, J. R. Surf. Interface Anal. 1997, 25, 6470.


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profile of the iron species was markedly changed is the oxidation of “surface” iron species into magnetite by water. On the other hand, both in the case of Fe(CO)5 with sulfur (Figure 9b) or synthetic pyrite (Figure 9c), the main composition of the residual catalyst was found to be a reduced iron species (at 709.0 and 722.5 eV). Since the XRD patterns indicated the formation of pyrrhotite, assignment of these peaks to pyrrhotite is quite adequate. Only in the case without sputtering, peaks at 713.5 and 726.5 eV, corresponding to Fe(III) species, were observed. But the surface concentration of this species is quite low (see Figure 8), suggesting that its contribution to the coprocessing can be ruled out. The spectra of S(2p) also showed that most of the sulfur was present as sulfide together with very small amounts of sulfate and elemental sulfur.

100% in the coprocessing of Wandoan coal and vacuum residue of Arabian Heavy. Although synthetic pyrite and Fe(CO)5 with sulfur was slightly less effective than Fe(CO)5 without sulfur at 400 °C, at higher temperatures than 425 °C they showed higher activities. The gas consumption in the synthetic pyrite-catalyzed coprocessing was found to be very different from that using Fe(CO)5 without sulfur. On the other hand, XRD and XPS analyses revealed the formation of a mixture of magnetite and pyrrhotite from Fe(CO)5 without sulfur, in which the surface of the used catalyst was covered with iron species in a relatively high oxidation state, probably magnetite, whereas only pyrrhotite was detected in the case using Fe(CO)5 with sulfur or synthetic pyrite. These differences in the state of the catalyst were assumed to be responsible for the very different gas consumption.

Conclusion

Acknowledgment. Part of this work was carried out as a research project of The Japan Petroleum Institute commissioned by the Petroleum Energy Center with a subsidy of the Ministry of International Trade and Industry, and another part of this work was supported in part by a Grant-in-aid for Scientific Research No. 00075192 from the Japanese Education, Science, and Culture. Authors also thank Jun-ichi Hayashi and Yasunobu Nakagawa for their help in the study using a model compound.

Coprocessing of various coals and vacuum residues using syngas-water as a hydrogen source smoothly proceeded in the presence of pentacarbonyliron or synthetic pyrite. Among the alternative hydrogen sources examined, syngas-water was highly efficient, almost comparable to pressurized hydrogen gas with water. Note that the addition of water in the case using hydrogen gas afforded an improved conversion to THF solubles. The addition of Fe(CO)5 up to 2.0 mmol (3.7 wt % as Fe) improved the THF-soluble yield to almost

EF980032W

Iron-Catalyzed Coprocessing of Coals and Vacuum Residues Using

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