Energy & Fuels 1993, 7, 328-330
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Antiliquefaction: Model Systems for Enhanced Retrogressive Cross-Linking Reactions under Coal Liquefaction Conditions Ajay K. Saini,? Michael M. Coleman,$ Chunshan Song,*’?and Harold H. Schobertt Fuel Science Program and Polymer Science Program, Department of Materials Science and Engineering, 209 Academic Projects Building, The Pennsylvania State University, University Park, Pennsylvania 16802 Received August 20,1992. Revised Manuscript Received November 23, 1992
It has been recognized that low-rank coals are more reactive than had been thought, and their conversion in high-severity processes is accompanied by significant retrogressive rea~tions.l-~Consequently, studies on the nature of retrogressive reactions, and the clarification of the structures responsible for retrogressive reactions, have become very important and have begun to receive increased a t t e n t i ~ n . ’ *Low-rank ~?~ coals are characterized by higher oxygen functionality than bituminous coals. Studies with model compounds such as benzyl phenyl ether and dibenzyl ether have provided some insights into both progressive and retrogressive reactions.g-12However, little is known about the details of retrogressive reactions involving coal, rather than pure model compounds alone. Apart from the difficult challenge of simulating the real coal molecules by model compounds, another major problem originates because reactions of low-rank coals largely involve “immobilized molecular structures”, whereas “mobile” molecules are encountered in most model reactions. In this Communication, we report two reaction systems leading to enhanced cross-linking under coal liquefaction conditions, which could serve as models of retrogressive reactions and are also related to the abovementioned studies with pure model compounds. The term cross-linking used in this paper refers to chemical linking of molecular fragments (reactive radicals from decomposition of coal or solvents, or thermally unstable compounds, etc) to coal through covalent bonds. Wyodak subbituminous coal from the DOE/Penn State Coal Sample Bank (DECS-8) was used after drying in a vacuum oven at 95 “C for 2 h. The characteristics of this coal are as follows: 32.4% volatile matter, 29.3% fixed * Author to whom correspondence should be addressed.
+ Fuel Science Program.
Polymer Science Program. (1)DOE COLIRN Panel. ‘Coal Liquefaction”, Final Report, DOEER-0400,1989,Vol. I and 11. (2)Suuberg, E.M.; Lee, D.; Larsen, J. W. Fuel 1986,64,1668-1671. (3)Suuberg, E. M.; Unger, P. E.; Larsen, J. W. Energy Fuels 1987.1, 305-308. (4)Song, C.; Hanaoka, K.; Nomura, M. Fuel 1989,68, 287-292. (5)Serio, M. A.; Solomon, P. R.;Kroo, E.; Bassilakis, R.; Malhotra, R.; McMillen, D. Proc. 1991 Znt. Conf. Coal Sci. 1991,656-659. (6)Song, C.; Schobert, H. H.; Hatcher, P. G. Energy Fuels 1992,6, 326-328. (7) Song,C.;Schobert,H. H.Prepr.Pap.-Am. Chem. Soc.,Diu. Chem. 1992,37 (2),976-983. (8)Solomon, P. R.;Serio, M. A.; Despande, G. V.; Kroo, E. Energy Fuels 1990,4,42-54. (9)McMillen, D. F.; Malhotra, R. Prepr. Pap.-Am. Chem. SOC., Diu. Fuel Chem. 1992,37 (l),385-392. (10)Song, C.; Nomura, M.; Ono, T. Prepr. Pap.-Am. Chem. SOC., Diu. Fuel Chem. 1991,36 (2),586-596. (11)Stohl, F. V.; Kottenstette, R. J. Prepr. Pap.-Am. Chem. Soc., Diu. Fuel Chem. 1992,37 (2),984-991. (12)Britt,P. F.;Buchanan,A. C.,III;Hitaman,V. M.Prepr.Pap.-Am. Chem. SOC.,Diu. Fuel Chem. 1991,36(2),529-535. 8
carbon, 9.9% ash, 28.4% moisture, on an as-receivedbasis; 75.8% C, 5.2% H, 1.0% N, 0.5% organic sulfur, 17.5% 0 (by difference), on a dmmf basis. The solvents used were reagentgradetetralin, l-methylnaphthalene (1-MN), benzyl alcohol (PhCHzOH), and 1,4-benzenedimethanol (Ph(CHZ0H)z). Liquefaction was carried out at 400 OC for 30 min in 25-mL microautoclaves using 4 g of coal (
