XPS study of reductively and non-reductively modified coals

Two demineralised coals: Mequinenza and Illinois No. 6 have been subjected to reduction and reductive methylation in the potassium/liquid ammonia system and to non-reductive methylation by the Liotta method. The initial coals and the products obtained have been analysed by classical chemical methods and by the X-ray photoelectron spectroscopy (XPS) method. The coal surface has been found susceptible to oxidation by atmospheric oxygen, but the differences in the elemental composition between the surface and the bulk sample proved small. Deconvolution of the XPS spectrum has shown that the dominant form of oxygen in all samples is ether and hydroxyl oxygen and the dominant form of nitrogen is pyrrolic nitrogen. It has also been shown that the main sulphur species in the initial Mequinenza coal is sulphidic sulphur, while Illinois No. 6 is richer in thiophenic systems. The results have confirmed an earlier finding that modification of coals in the potassium/liquid ammonia system leads to elimination of sulphur from some thiophene compounds.