New Reagents and Reactions for Desulfurization of Coal

Searching for new reagents and reactions for pre-combustion desulfurization of coal was the goal of this work. In this study, modifications of mild desulfurization reactions, which were found to work with organosulfur model compounds, have been investigated systemetically for improvements in sulfur removal and reduction of reagent cost. The screening of reagents and new reactions utilized substituted thiophenes plus aryl sulfides as the initial models for organosulfur compounds in coal. Tetrahydrofuran extracts of Illinois Basin Coals were also used as second generation targets for desulfurization reactions. Dibenzothiophene was converted to biphenyl using potassium metal/tetrahydrofuran without the addition of electron transfer agents. Similar desulfurization reactions of tetrahydrofuran extracts of Illinois Basin coals gave up to an 82.8% reduction in organosulfur content. A soluble chlorovinyl nickel complex added to the reaction increased the desulfurization to 85.6%. Attempts to produce active desulfurization reagents from iron pentacarbonyl with reducing agents in alcohol solvents (conditions for the production of [H-Fe(CO)4]-1) did not lead to useful desulfurization of dibenzothiophene, benzothiophene or benzyl sulfide. Tetrabutylammonium hydroxide in aprotic solvents is known to react with elemental sulfur to produce trisulfide anion radical by the single electron transfer pathway. Reaction of tetrabutylammonium hydroxide with dibenzothiophene in aprotic solvents led to large amounts of unreacted starting material and gave no evidence of hydrocarbon products. Desulfurized products bibenzyl, biphenyl, and 2-phenyl phenol were produced by reaction of benzyl phenyl sulfide using potassium hydroxide/n-butyl lithium/18-crown-6 in dimethyl sulfoxide. No desulfurization of dibenzothiophene was observed using the same reaction system