04/01719 Identification of chemical structures in barkinite, vitrinite and fusinite using pyrolysis gas spectrometry: Sun, X. et al. Dizhi Xuebao, 2003, 77, (1), 135–143. (In Chinese)

Abstract

The Permian Lepingian coal is known for its high content of , which is a unique liptinite macer-al located only in the Late Permian coals, South China. In this paper, Rock-Eval pyrolysis and pyrolysis gas chromatographic analyses were used to investigate the pyrolysate composition and the chemical structure of barkinite. At the same time, paralleled studies were also carried out on vitrinite and fusinite. The results show that at low temperatures, the pyrolyzates of and vitrinite are dominated by heteroatomic compounds, followed by aliphatic compounds, lower molecular (one- and two-ring) aromatic compounds (such as benzene and naphthalene), and alkyl aromatics (toluene and xylenes). However, the pyrolysis products of fusinite are mostly composed of aliphatic compounds. With increasing temperature, the proportion of aliphatic compounds from the three macerals increases, whereas the aromatic compounds and the heteroatomic compounds from barkinite and vitrinite decrease. At high temperatures, the pyrolysis products from these macerals sre dominated by low-chain aliphatic compounds. On the basis of these results, we can deduce that the chemical structures of these macerals are mainly composed of four kinds of function groups: (1) aliphatic compounds; (2) lower molecular (one- and two-ring) aromatic compounds, and alkyl aromatics; (3) heteroatomic function groups,- (4) multi-ring aromatics. The outlayers of the chemical structures of these coal macerals are mostly composed of heteroatomic compounds, lower molecular aromatic compounds and alkyl aromatics. The nucleus of the chemical structures of these coal macerals are dominated by multi-ring aromatic compounds. Between the outlayer and the nucleus, the chemical structures of these macerals are mainly composed of aliphatic compounds. The ways of hydrocarbon generation from coal macerals are based on the values of band energy. The smaller the bond energy function groups, the earlier they break off from coal macerals. Because heteroatomic compounds, benzene, naphthalene, toluene, xylenes, and long-chain aliphatic compounds have relatively low band energy, they were broken off from coal macerals first, then the higher-bond energy short-chain aliphatic compounds, and the remaining function groups in coal macerals are the multi-ring aromatic compounds of the highest bond energy.