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Energy & Fuels 1991,5, 708-711
Insolubilization of Coal Soluble Constituents in Some Bituminous Coals by Refluxing with Pyridine Toshimasa Takanohashi and Masashi Iino* Institute for Chemical Reaction Science, Tohoku University, Katahira 2-1 -1, Aoba-ku, Sendai 980, Japan Received April 9, 1991. Revised Manuscript Received May 28, 1991
The solventrtreated coals were extracted with CS2-N-methyl-2-pyrrolidinone (NMP) mixed solvent at room temperature to investigate the effect of the treatment on extractability. The refluxing with pyridine greatly decreased the extraction yield compared to that of the untreated coal. The treatment with pyridine at room temperature needed a longer time, i.e., 1 week, to detect the decrease in the extraction yields of coals. A similar treatment with CSz-pyridine mixed solvent at room temperature, which is a better solvent than pyridine for coal molecules, for 1day at room temperature, decreased the extraction yield to a great degree compared to that with pyridine. Fractionation of the soluble fractions by acetone and pyridine clarified that this decrease in the yields is due to the insolubilization of the heavy fraction, i.e., the pyridine-insoluble (E-PI) fraction in the extract. The swelling ratios of the E P I fraction in benzene and methanol were decreased by this treatment, indicating the increase of cross-linking density. Spin concentrations of ESR spectra of the E-PI fractions were increased by refluxing with pyridine. Insolubilization mechanisms are discussed for the formation of covalent and/or noncovalent bonds between the heavy E-PI molecule and other heavy molecules (E-PI or residue) during the treatment.
Introduction Coals have been considered to consist of covalently cross-linked network and relatively low molecular weight soluble constituents.l" The thermal cleavage of the covalent bonds is a key step in the coal liquefaction process. Recently attention, however, has been directed to the significance and importance of noncovalent intra- and intermolecular interactions. The importance of hydrogen bonds in the coal structure has been established by many researchers." As for other interactions, Mallya and Stock,' and Miyake and Stock* indicated that the diminution in stacking interactions between aromatic compounds for high-rank coals results in an increase in coal solubility. Quinga and LarsenO and Nishioka and Lamenlo suggested that the formation of adducts between maleic anhydride and coals increased the pyridine extractability, due to the blocking noncovalent interactions. We found1' that 4 0 4 5 % of the extraction yields were obtained for some bituminous coals from extraction at room temperature with CS2-N-methyl-2-pyrrolidinone(NMP) mixed solvent, which might cleave some noncovalent bonds between coal molecules, like other good solvents. Nishioka and Lamenlo reported a decrease in pyridine Soxhlet extraction yields after pretreatment in several (1)Given, P. H.; Marzec, A.; Bartle, W.A.; Lynch, L. J.; Gerstein, B. C. Fuel lSS6,66,166-163. (2) Lucht, L. M.;Peppas, N. A. Fuel 1987,66,803-809. (3)Green, T.; Kovac, J.; Brenner, D.; h n , J. W . In Coal Structure; Meyem, R. A., Ed.; Academic Prese: New York, 1982;pp 199-282. (4) Liotta, R.; Row,K.; Hippo, E. J. Org. Chem. 1981,46,277-283. (5) Patel, K. M.; Stenberg, V. 1.; Baltisberger, R. J.; Wooleey, N.F.; Klabunde, K.J. Fuel 1980,59,449460. (6) Lareen, J. W.;Baskar, A. J. Energy Fuels 1987,2,230-232. (7)Mallya, N.;Stock, L. M. Fuel 1986,66,736-738. (8)Miyake, M.; Stock,L. M. Energy Fueb 1988,2,815-818. (9)Quingn, E.M.Y.; Larsen, J. W . Energy Fuels 1987,1 , 300-304. (10)Niehioka, M.; Lareen, J. W.Energy Fueb 1990,4,100-106. (11)Iino, M.; Takanohashi, T.; Ohsuga, H.; Toda, K. Fuel 1988,67, 16391647.
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solvents at 25-115 "C. They concluded that the decrease can be attributed to new noncovalent interactions between coal constituents formed when the treated coal became conformationally more stable than the raw coal, after the removal of treatment solvent. We preliminarily reported the similar decrease in the extraction yields with the CS2-NMP mixed solvent by mild acetylation, methylation, and treatment with pyridine for some bituminous coals.12 Our result differs from the result of Nishioka et al. in the effect of the kind of solvent and the effect of solvent removal after treatment. In the present study, the behaviors of this insolubilizationof coals by treatment with solvents are studied and the mechanisms are discussed. Experimental Section Materials. The ultimate and proximate analyses of coals used are shown in Table I. Zao Zhuang (China), Shin-Yubari (Japan), and Miike (Japan) coals were ground
