Behaviour of sulfur in high-sulfur coal in a superacidic medium without gaseous hydrogen

Abstract

A Brönsted superacid, trifluoromethanesulfonic acid (TFMS), was found to desulfurize a lignite in the presence of a hydrocarbon without gaseous hydrogen at 150–200°C under autogenous pressure of 2.6–6.6 MPa. Removal of sulfur from the coal depended on the solvent, TFMS concentration and reaction temperature. TFMS alone without solvent removed only 5.3% of sulfur as H 2S, increasing the thiophenic sulfur content of the coal. In contrast, TFMS in toluene achieved 35.4–41.3% desulfurization, mainly from sulfides. Toluene in the presence of TFMS behaves as hydrogen donor to eliminate sulfidic sulfur as H 2S, while preventing acidic cyclization of sulfides to thiophenes.