Catalytic hydrodesulfurization of a high organic sulfur turkish lignite: Amount, form, and mechanism of sulfur removal

Abstract

The removal of sulfur from Çayirhan (Turkish) lignite by catalytic hydrodesulfurization has been investigated. Ammonium tetrathiotungstate, ammonium tetrathiomolybdate and nickel sulfate salts were used as catalyst precursors impregnated into the lignite. The experiments were carried out in microautoclave reactors in a hydrogen atmosphere but without added solvent. The effects of the temperature and type of catalyst on the total sulfur removed were studied. In most of the experiments, the sulfur removed from the lignite appeared in two products, hydrogen sulfide and organosulfur compounds present in the extract. Catalyst impregnation of the lignite promotes the removal of sulfur as hydrogen sulfide. The highest total sulfur removed was about 42 wt.%, achieved at 325°C for lignite impregnated with ammonium tetrathiotungstate. In this experiment, 72% of the sulfur removed was eliminated as hydrogen sulfide. The variations of hydrogen sulfide and organosulfur compounds with total sulfur removed suggested a sequential mechanism for catalytic hydrodesulfurization of this lignite.