Deep Desulfurization of 4,6-Dimethyldienzothiophene by an Ionic Liquids Extraction Coupled with Catalytic Oxidation with a Molybdic Compound

A series of the imidazolium-based phosphoric ionic liquids, N -methyl- N -methylimidazolium dimethyl phosphate ([Mmim]DMP), N -ethyl- N -methylimidazolium diethyl phosphate ([Emim]DEP), and N -butyl- N -methylimidazolium dibutyl phosphate ([Bmim]DBP), were synthesized and employed in the extraction and catalytic oxidation desulfurization system (ECODS) for the removal of 4,6-dimethyldienzothiophene (4,6-DMDBT) from a model oil, with hexaammonium heptamolybdate tetrahydrate ((NH 4 ) 6 Mo 7 O 24 ·4H 2 O) as catalyst and 30 wt % hydrogen peroxide (H 2 O 2 ) solution as oxidant. The effects of the type of ionic liquid, amount of catalyst and H 2 O 2, ILs/oil mass ratio, reaction time, reaction temperature, and regeneration of ionic liquid on the 4,6-DMDBT removal of a model oil were investigated in detail. The results indicate that a sulfur system containing H 2 O 2, (NH 4 ) 6 Mo 7 O 24 ·4H 2 O, and [Bmim]DBP, exhibited such a high catalytic activity that the removal of 4,6-DMDBT could reach 89.2% at 50 °C in 3 h, which was markedly superior to mere solvent extraction with IL (9.29%) or catalytic oxidation without IL (5.34%). The desulfurization system for a model oil could be recycled six times with an unnoticeable decrease in activity. Meanwhile, (NH 4 ) 6 Mo 7 O 24 ·4H 2 O not only possessed good catalytic activity but hardly contaminated the oil. This work shows that ECODS containing (NH 4 ) 6 Mo 7 O 24 ·4H 2 O, [Bmim]DBP, and H 2 O 2 may be a new option for producing cleaning fuel.