Selective oxidation pretreatments for the enhanced desulfurization of coal

Abstract The desulfurization of selectively oxidized coals and unoxidized control coals was investigated using mild pyrolysis and various base treatments. Both an Illinois No. 6 and an Indiana No. 5 coal were selectively oxidized with peroxyacetic acid in the pretreatment step and then treated with various hydroxide and carbonate bases, using either water, methanol or ethanol as the solvent. Reaction variables investigated include reaction temperature, reaction time, pyrolysis pressure, and the level of oxidation in the pretreatment step. In general, it was found that selective oxidation, when combined with subsequent desulfurization reactions, always led to greater sulfur removal. In addition, the reactivity of the sulfur in the coal towards desulfurization was apparently enhanced by the selective oxidation pretreatment. Thus, the severity of desulfurization conditions can be reduced by employing this pretreatment. Sulfur removals of up to 95% were obtained in some cases. Usually the most effective treatments involved carbonate bases under supercritical alcohol conditions. The desulfurization of some selectively oxidized, sulfur containing model compounds was also observed under similar reaction conditions.