Coal structure and mass spectrometry: volatiles in peat and coals

Mass spectrometry has been used to examine volatiles released by a range of fuels on heating them to 300 °C in a helium gas stream. Components volatilize under these conditions and there is no significant pyrolysis. While data on seven of the coals have been presented before, new data on Swedish peat, East German brown coals, an American coal and three British coals, including an anthracite, are presented here. The loss of weight of the air dried samples in this experiment is shown to vary in proportion to both the %C (daf) and the %O (daf). The weight loss includes both moisture in the air dried sample and aliphatic and aromatic hydrocarbon material. This correlation indicates that the material detected is an integral part of the coal structure. Plots of log ion intensities versus 1 T ( K) for peat, brown coal and bituminous coals are linear, and energies of evaporation have been derived from their slopes. The values are similar for all the coals and confirm the evaporation mechanism. Oxygenates and inorganic volatiles have larger energies of evaporation for release, perhaps because of their polarity or mode of bonding to the coal structure. Temperatures of first appearance of volatile components in the vapour phase show no correlation with either total weight losses or energies of evaporation. The similarity of the evaporated material to petroleum suggests that coal may have been a source rock for oil as well as gas (CO 2 and methane) during its formation. Consideration of the polysaccharide and lignin structures typical of plant material does not indicate a simple or obvious route to the aliphatics and aromatics detected.