Deep oxidative desulfurization of dibenzothiophene with molybdovanadophosphoric heteropolyacid-based catalysts

Three hydrophobic Keggin-type heteropolyacid catalysts, [C 3 H 3 N 2 (CH 3 )(C 2 H 4 )] 5 PMo 10 V 2 O 40 ([C 2 mim]PMoV), [C 3 H 3 N 2 (CH 3 )(C 4 H 8 )] 5 PMo 10 V 2 O 40 ([C 4 mim]PMoV) and [C 3 H 3 N 2 (CH 3 )(C 6 H 12 )] 5 PMo 10 V 2 O 40 ([C 6 mim]PMoV), were synthesized by reacting molybdovanadophosphoric acid with imidazolium bromides, and characterized by spectroscopic methods. Their use as catalysts in the extractive catalytic oxidative desulfurization process using hydrogen peroxide as the oxidant and acetonitrile as phase transfer agent was studied. The catalytic properties decreased in the order: [C 6 mim]PMoV > [C 4 mim]PMoV > [C 2 mim]PMoV. The main factors influencing the rate of removal of dibenzothiophene (DBT) were investigated, including reaction temperature, the amounts of catalyst, H 2 O 2 and acetonitrile. Nearly 100 % sulfur removal rate was achieved under optimal conditions. The catalyst could be recycled six times with only a slight decrease in activity. A reaction mechanism for DBT oxidation is proposed, in which the Keggin anions first obtain active oxygen from H 2 O 2 , then the DBT is oxidized to dibenzothiophene sulfones.