Characterization of coal tar organics via gravity flow column chromatography

Changes in the polarity distribution of two types of coal tar during secondary pyrolysis have been examined by utilizing gravity flow column chromatography (GFCC). Trends in the polarity distributions are used to evaluate the predominance of various transformation mechanisms throughout secondary pyrolysis. In addition to observing neutralization and mass transformation during the early stages of secondary pyrolysis, a consistent increase in acetylene, methane and much longer aliphatic compounds with extent of sooting was observed midway through secondary pyrolysis, suggesting that aromatic ring structures were opening and decomposing. By the late stages of secondary pyrolysis, both tars from subbituminous and high volatile bituminous coals exhibit similar polarity compositions, indicating that thermal conditions rather than original coal structure determine the ultimate polarity distributions for both types of coal tar. Preferred pathways for soot formation can be identified based on the polarity distributions observed during various stages of secondary pyrolysis; the toluene fraction appears to contain the predominant precursors for soot. (C) 1998 Elsevier Science Ltd. All rights reserved.