Some Aspects of the Chemistry and Petrology of Coking Coals

Abstract

The chemistry of five British Carboniferous coals exhibiting different degrees of swelling capability has been investigated. The organic material of the coals was separated according to its density into microscopically distinct groups known as macerals. The maceral groups were characterised using physical and chemical techniques. Scanning electron microscopy revealed each maceral group to have characteristic morphological properties which were affected differently by solvent extraction. 13C NMR spectra, diffuse reflectance infrared spectra, and elemental analyses were obtained of each maceral group. It was found that chemical characterisation of the inertinite maceral group was not feasible and therefore only the vitrinite and exinite groups were investigated. The chemical composition of pyridine extracts of the vitrinite and exinite groups were examined by gas chromatography/mass spectrometry, the molecular species present in the extracts were found to vary with rank and also with petrography. 1H nuclear magnetic resonance spectroscopy confirmed the identity of many of the structures indicated by gas chromatography/mass spectrometry of the initial pyridine soluble material. Significant amounts of high molecular weight material present in the extracts were rendered soluble by selective oxidation. Ethereal solutions of these products were investigated by GC/MS. All residues remaining after pyridine extractions were treated with alkaline glycol at 300°C to yield soluble material which was extracted successively with toluene and pyridine. These solutions were again examined by GC/MS. The final residues were subjected to analysis by 13C NMR spectroscopy. An attempt was made to relate the swelling behaviour of the coals to the chemical structures they contained.