Molecular analysis of sulphur-rich brown coals by flash pyrolysis-gas chromatography-mass spectrometry: The type III-S kerogen

Abstract

The molecular composition of five brown coals from three different basins (Maestrazgo, Mequinenza and Rubielos) in Spain was investigated by flash pyrolysis-gas chromatography and flash pyrolysis-gas chromatography-mass spectrometry. In these techniques, the macromolecular material is thermally degraded in an inert atmosphere and the compounds formed are on-line separated, identified and quantified. This information provided insight into the macromolecular structure of the coals which was inaccesible by other means. The composition of the pyrolysates is described in detail with emphasis on the distributions and relative abundance of n-alkanes, n-1-alkanes, (alkyl)phenols, sulphur compounds [(alkyl)thiophenes and (alkyl)benzenes and (alkyl)naphthalenes. These compound classes represent the major pyrolysis products of the samples analysed and were used to assess the contributions of specific biomacromolecules mainly originating from higher plants. One of the five brown coal samples investigated is so rich in organic sulphur (one sulphur atom for every 9-15 carbon atoms as determined by elemental analysis) that a new kerogen type (Type III-S) describing the kerogen contained in this coal is defined. Type III-S kerogen is defined as a kerogen with high atomic S org./C (0.04) and O/C (0.20) ratios. Two of the five brown coals samples investigated contain a series of long-chain alkylbenzenes with an unprecedented carbon number distribution pattern with a second maximum at C18. This unusual distrubution pattern is thought to originate from the presence of long-chain alkylbenzene moieties bound via a heteroatom(presumably an ether bond) to the macromolecular coal matrix preferentially at position 12 in the alkyl side-chain of these moieties.