Coal Desulfurization and Demineralization by Molten Caustic Mixtures

Several bituninous coals have been treated with molten mixtures of NaOH plus KOH at 350-370°C in a 1:10 coal- to-caustic ratio for 1 hour and then washed with water, dilute acid, and finally with water again. By this procedure, which is similar to that of the TRW Gravi-melt Process, 80-90% of the ash and 70-80% of the total sulfur have been removed with a recovery of 80-90% of the coal on a moisture- and ash-free basis. The desulfurization could be improved by using a finer grind of coal, better washing procedures, or a recleaning step. Samples of raw and cleaned coals produced at the Ames Laboratory and obtained from TRW have been characterized for the mineral matter content and distribution among various particle sizes. The sulfur forms before and after treatment have been determined by conventional ASTM techniques and a direct SEM method.