Deep Desulfurization of Fuels by Heteropolyanion-Based Ionic Liquid

Abstract

A new heteropolyanion-based ionic (<TEX>$[Hmim]_5PMo_{10}V_2O_{40}$</TEX>) was synthesized by the reaction of molybdovanadophosphoric acid (<TEX>$H_5PMo_{10}O_{40}$</TEX>) with N-methylimidazole. [<TEX>$[Hmim]_5PMo_{10}V_2O_{40}$</TEX> showed a high catalytic activity in the oxidative desulfurization of sulfur-containing compounds in 1-methylimidazolium tetrafluoroborate (<TEX>$[Hmim]BF_4$</TEX>) ionic liquid using 30% aqueous <TEX>$H_2O_2$</TEX> as the oxidant. The catalytic system was of high activity, simplified workup and flexible recyclability. The catalytic oxidation reactivity of sulfur-containing compounds decreased in the order dibenzothiophene (DBT) > 4,6-dimethyldibenzothiophene (4,6-DMDBT) > benzothiophene (BT). The influences of various parameters including reaction time (t) and temperature (T), catalyst dosage, and oxidant to sulfur molar ratio n(O)/n(S) on the desulfurization of model oil were investigated in details. 99.1% of DBT conversion in the model oil was achieved at atmospheric pressure under the optimal conditions: n(O)/n(S) = 4:1, <TEX>$60^{\circ}C$</TEX>, 100 min and molar ratio of catalyst to sulfur of 0.062. The ionic liquid can be recycled six times without significant decrease in activity.