EFFECT OF MILD OXIDATION OF BITUMINOUS COALS ON CAKING PROPERTIES

Changes in caking properties, extraction yield, and coal structure on mild oxidation (at 100 °C) were examined for four caking coals. Fluidity decreased with increase in oxidation time for all coals, while changes in free swelling index (FSI) differed among the coals. FSI for Shin-yubari and Zao Zhuang coals increased during the initial stage of oxidation, suggesting that optimum fluidity was obtained by lowering the high fluidity of such coals. Extraction yields for two PSOC coals, using CS2-N-methyl-2-pyrrolidinone mixed solvent, were constant during oxidation for 22 h, but the fluidity decreased drastically. This indicates that reduction of caking properties by oxidation cannot be explained only by the decrease in extractable low molecular weight substances. The i.r. spectra indicated formation of CO, OH and ether groups accompanied by a slight decrease in aliphatic CH. The e.s.r. measurement suggested not only the formation of cross-linking by oxidation but also the cleavage of cross-linkages for prolonged oxidation. © 1990.