Organic compounds in coal: Structure and origins

Abstract

Traditionally, coal structure has been studied by characterization of pyrolysis liquids and also by examining the solvent extracts from coal. We have combined these 2 techniques to characterize more fully Wyodak subbituminous coal. The organic compounds obtained by pyrolysis in a hydrogen atmosphere and by benzene-ethanol extraction of Wyodak coal were characterized using column chromatography, GC, GC-MS, 1H-NMR, and 13C-NMR. We have detected in the extract, ferruginol, a C20H30O naturally occurring diterpene phenol, which is closely related to abietic acid, as well as large amounts of long-chain fatty acids. Moreover, sclarene, a triene diterpene hydrocarbon related to sclareol was identified. To our knowledge this is the first time that sclarene has been reported in coal. The coal extracts contained only small amounts of normal alkanes (0.4% of coal on DMMF basis), whereas the pyrolysate contained significant amounts (2.4% of coal on DMMF) of these components. We suggest that these saturated hydrocarbons are produced by thermal decarboxylation of the long-chain fatty acids and also from cleavage of the long-chain alkyl moieties attached to the polymeric structures of the coal. The most interesting pyrolytic products are a series of C14C34 long-chain alkylbenzenes. These components were not detected in the extract. Prist-1-ene and prist-2-ene were identified in the coal pyrolysis liquid, indicating that pristane was chemically bound in the coal structure.