Deep Desulfurization of Fuels by Heteropolyanion-Based Ionic Liquid

A new heteropolyanion-based ionic ( $[Hmim]_5PMo_{10}V_2O_{40}$ ) was synthesized by the reaction of molybdovanadophosphoric acid ( $H_5PMo_{10}O_{40}$ ) with N-methylimidazole. [ $[Hmim]_5PMo_{10}V_2O_{40}$ showed a high catalytic activity in the oxidative desulfurization of sulfur-containing compounds in 1-methylimidazolium tetrafluoroborate ( $[Hmim]BF_4$ ) ionic liquid using 30% aqueous $H_2O_2$ 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, $60^{\circ}C$ , 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.