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Energy & Fuels 1996, 10, 718-725
Effect of Coal Characteristics and Molybdenum Sulfide Catalyst on Conversions and Yields of Heavy Products from Liquefaction in Phenanthrene Caroline E. Burgess† and Harold H. Schobert* Fuel Science Program, Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 Received October 3, 1995X
Eight coals, ranging in rank from subbituminous B to high-volatile A bituminous, were reacted in microautoclave reactors in a hydrogen atmosphere and with the nondonor solvent phenanthrene. Reactions were conducted at 360 °C for 1 h. Both noncatalytic and catalytic reactions were investigated. The catalytic reactions employed ammonium tetrathiomolybdate as a catalyst precursor. In noncatalytic reactions, conversions ranged from 18 to 47% and showed a dependence on the oxygen contents of the coals. Addition of a catalyst increases conversions to 54-83%. In catalytic reactions there is no apparent dependence of conversion on oxygen content, but rather the hydrogen content, the net hydrogen (the total hydrogen corrected for oxygen, sulfur, and nitrogen), and its distribution in the coal structure are important. Segregation of the coals into groups originally defined by Given shows two different effects of added catalyst: for medium- to low-rank medium-sulfur coals the available hydrogen in the coal and that supplied by the catalyst act additively, while for high-rank medium-sulfur coals there is a synergistic effect of added catalyst. At these reaction conditions, use of the catalyst does not shift the product slate markedly; rather, the catalyst increases conversion by enhancing the yields of individual products in the same relative proportions as were formed in noncatalytic reactions.
Introduction That direct coal liquefaction and coprocessing are highly complicated processes needs little elaboration. They involve high-temperature, high-pressure, threephase reactions of substances often having ill-defined structures that lead to hundreds of individual compounds among the products. A series of useful reviews traces the development of understanding of liquefaction reactions over the past half-century.1-8 We and our coworkers have investigated some aspects of coal properties, reaction conditions, and catalysis that affect liquefaction over the range of conversions from ≈10 to >95%. The present paper is the second in a series that will document the results of this work. The first paper described an exploration of the conversion of five coals, of ranks from subbituminous B to high-volatile A bituminous, without added catalysts and in solvents † Present address: Department of Chemistry, University of Texas Permian Basin, Odessa, TX. X Abstract published in Advance ACS Abstracts, April 1, 1996. (1) Storch, H. H. In Chemistry of Coal Utilization; Lowry, H. H., Ed.; Wiley: New York, 1945; Chapter 38. (2) Donath, E. E. In Chemistry of Coal Utilization. Supplementary Volume; Lowry, H. H., Ed.; Wiley: New York, 1963. (3) Gorin, E. In Chemistry of Coal Utilization. Second Supplementary Volume; Elliott, M. A., Ed.; Wiley-Interscience: New York, 1981; Chapter 27. (4) Van Krevelen, D. W. Coal: TypologysChemistrysPhysicss Constitution. Elsevier: Amsterdam, 1981; Chapter XI. (5) Berkowitz, N. The Chemistry of Coal; Elsevier: Amsterdam, 1985; Chapter 12. (6) Van Krevelen, D. W. Coal: TypologysChemistrysPhysicss Constitution. Elsevier: Amsterdam, 1993; Chapter 22. (7) Mochida, I.; Sakanishi, K. In Advances in Catalysis. Volume 40; Eley, D. D., Pines, H., Haag, W. O., Eds.; Academic Press: San Diego, CA, 1994; pp 39-85. (8) Olcay, A.; O ¨ ner, M. In Coal: Resources, Properties, Utilization, Pollution; Kural, O., Ed.; Kural: Istanbul, Turkey, 1994; Chapter 28.
0887-0624/96/2510-0718$12.00/0
that were not hydrogen donors.9 There, we showed that thermal decomposition of the coal is more important in determining yields of tetrahydrofuran-solubles than is the dissolving power of the solvent. A comparison of reactions in nitrogen and hydrogen showed some role of gaseous hydrogen in enhancing conversions, even in the absence of a catalyst, and in intercepting retrogressive reactions. The present paper is an extension of the previous work in that we examine an additional eight coals, the fraction of the products into solubility classes, and the effects of using a sulfided molybdenum catalyst. In reactions with a nondonor solvent and no catalyst present, i.e., systems in which effective utilization of hydrogen is not likely, conversions and yields of asphaltenes and preasphaltenes are inversely related to the oxygen content of the coal, suggesting that retrogressive reactions among reactive sites formed by loss of oxygen functional groups may be important in determining the behavior of the coal. When a good hydrogenation catalyst is present, the apparent dependencies on oxygen are lost. Gorin discusses the decrease in yields of solvent extracts and distillate products with increasing oxygen content of coals.3 Both carboxylic and carbonylic (as well as etheric) oxygen are known to be removed from subbituminous coals rapidly at 400 °C.10 The effect of oxygen functional groups has been documented in the literature.11-15 In general, the loss of oxygen-containing groups from the coal structure creates reactive sites. If (9) Tomic, J.; Schobert, H. H. Energy Fuels, in press. (10) Ruberto, R. G.; Cronauer, D. C. In Organic Chemistry of Coal; Larsen, J. W., Ed.; American Chemical Society: Washington, DC, 1978; Chapter 3. (11) Suuberg, E. M.; Lee, D.; Larsen, J. W. Fuel 1985, 64, 1668.
© 1996 American Chemical Society
Effect of Coal Characteristics and MoS2 Catalyst on Conversions
Energy & Fuels, Vol. 10, No. 3, 1996 719
Table 1. Characteristics of the Coals Used in This Work sample
PSOC 487
PSOC 831
PSOC 1216
PSOC 1379
PSOC 1503
DECS 5
DECS 6
DECS 12
seam state ASTM rank moisture, as recd mineral matter, dry elemental, dmmf carbon hydrogen nitrogen sulfur (org) oxygen (diff) net hydrogena atomic H/C atomic O/C fa fCO fOH faaH faH total vitrinites total liptinites total inertinites semifusinite
Bed 53 Wyoming sub A 11.55 6.89
Brazil Block Indiana hvCb 13.02 4.16
Lower Kittaning Pennsylvania hvAb 1.94 4.99
Colorado F Colorado hvCb 11.99 5.09
Blind Canyon Utah hvCb 10.35 4.46
Hiawatha Utah hvCb 7.54 9.80
Blind Canyon Utah hvAb 4.70 6.67
Pittsburgh 8 Pennsylvania hvAb 2.40 11.88
75.91 4.78 1.21 0.42 17.67 3.00 0.757 0.175 0.65 NDb ND ND ND 89.6 2.5 7.9 3.9
83.28 4.97 1.61 0.94 8.64 4.16 0.712 0.077 0.72 0.01 0.06 0.31 0.22 79.2 4.9 15.9 8.6
83.30 5.26 1.63 0.97 8.84 4.49 0.759 0.080 0.73 ND ND ND ND 91.1 4.0 4.9 2.9
76.74 4.97 1.61 0.63 15.96 3.36 0.779 0.156 0.67 0.11 0.08 0.20 0.13 92.2 0.6 7.2 2.9
80.80 6.12 1.55 0.54 10.98 5.42 0.910 0.102 0.55 ND ND ND ND 91.1 1.2 7.7 3.7
80.27 5.37 1.26 0.31 12.78 4.34 0.804 0.120 0.58 ND ND ND ND 65.5 14.7 19.8 9.7
81.72 6.22 1.56 0.40 10.10 5.62 0.914 0.093 0.63 0.01 0.05 0.29 0.20 69.1 17.3 13.6 5.6
84.75 5.66 1.39 0.83 7.37 5.13 0.802 0.065 0.69 0 0.03 0.37 0.26 83.0 8.1 8.9 4.0
a
Following Donath.2
b
Not determined.
these sites are not effectively capped, they can react among themselves to produce chars or semicokes of low reactivity. Low liquefaction conversions, product yields, and rates are a consequence. Since there is an inverse relationship of oxygen content to rank, this retrogressive cross-linking following loss of oxygen groups is of greater concern for low-rank coals. However, the phenomenon has been demonstrated even for a Pittsburgh No. 8 bituminous coal in which carboxyl groups were induced by air oxidation.13 Several reviews on dispersed liquefaction catalysts have been published over the past 40 years. Weller and Pelipetz published seminal data in the 1950s on hydrogenation catalysts containing iron and molybdenum, and on the effect of dispersion.16 Further work at the U.S. Bureau of Mines by Wu and Storch17 and by Hawk and Hiteshue18 continued the study of catalytic liquefaction. Reviews by Gorin,3 Donath and Hoering,19 Derbyshire,20 and Mochida and Sakanishi7 provide good summaries of catalysis in direct coal liquefaction and of the importance of using catalysis. Weller has recently published a review article on dispersed catalysts in liquefaction.21 These articles generally share the view that the ability of dissociated hydrogen to be available as the coal pyrolyzes and as the product liquids are upgraded is essential, and that making the dissociated hydrogen available can be most efficiently accomplished by the addition of catalysts. (12) Deshpande, G. V.; Solomon, P. R.; Serio, M. A. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1988, 33, 310. (13) Solomon, P. R.; Deshpande, G. V.; Serio, M. A.; Kroo, E. U.S. Department of Energy Report DOE/PC/80910-T6, 1989. (14) Solomon, P. R.; Serio, M. A.; Deshpande, G. V.; Kroo, E. Energy Fuels 1990, 4, 42. (15) Solomon, P. R.; Serio, M. A.; Deshpande, G. V.; Kroo, E.; Schobert, H. H.; Burgess, C. E. In Coal Science II; Schobert, H. H., Bartle, K. D., Lynch, L. J., Eds.; American Chemical Society: Washington, DC, 1991; Chapter 15. (16) Weller, S.; Pelipetz, M. G. Ind. Eng. Chem. 1951, 43, 1243. (17) Wu, W. R. K.; Storch, H. H. U.S. Bureau Mines Report 633, 1968. (18) Hawk, C. O.; Hiteshue, R. W. U.S. Bureau Mines Report 622, 1965. (19) Donath, E. E.; Hoering, M. Fuel Process. Technol. 1977, 1, 3. (20) Derbyshire, F. J. International Energy Agency Report IEA CR/ 08, 1988. (21) Weller, S. Energy Fuels 1994, 8, 415.
Experimental Section Coals and Reagents. Eight coals, ranging in rank from subbituminous B to high-volatile A bituminous, were selected for this work. The coals and attendant analytical data were supplied by the Penn State Coal Sample Bank and Data Base. The principal characteristics of the coals are summarized in Table 1. The coals were ground to -60 mesh, dried in vacuum at 100 °C to
