Commercially available molybdic compound-catalyzed ultra-deep desulfurization of fuels in ionic liquids

Abstract

A simple liquid–liquid extraction and catalytic oxidative desulfurization (ECODS) system composed of molybdic compound, 30% H₂O₂ and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF₄) has been found suitable for the ultra-deep removal of dibenzothiophene (DBT) in model oil. The precatalyst of molybdic compound was oxidized with H₂O₂ to form peroxomolybdic compound, which was soluble in ionic liquid and dissolved in oil. The sulfur-containing compounds, such as benzothiophene (BT), DBT and 4,6-dimethyldibenzothiophene (4,6-DMDBT), in model oil were extracted into ionic liquid phase and oxidized to their corresponding sulfones by peroxomolybdic compound. In the case of the system containing model oil (DBT), H₂O₂, Na₂MoO₄·2H₂O and [bmim]BF₄, extraction and catalytic oxidation increased the sulfur removal to 99.0%, which was remarkably superior to mere solvent extraction with IL (13.6%) or catalytic oxidation without IL (4.1%). The desulfurization system could be recycled five times with very little decrease in activity.