Oxidative desulfurization of fuels catalyzed by peroxotungsten and peroxomolybdenum complexes in ionic liquids

Peroxotungsten and peroxomolybdenum complexes such as [WO(O-2)(2)center dot Phen center dot H2O] and [MoO(O-2)(2)center dot Phen] (Phen: 1,10-phenanthroline) have been synthesized and characterized and were immobilized in 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4), 1-n-octyl-3-methylifnidazolium tetrafluoroborate ([O-mim]-BF4), 1-butyl-3-methyl-imidazolium hexafluorophosphate ([Bmim]PF6), and 1-n-octyl-3-methylimidazolium hexafluorophosphate ([Omim]PF6) for extraction and catalytic oxidation of dibenzothiophene (DBT) remaining in n-octane. The results demonstrated that ionic liquid (IL) was only used as an extractant for DBT-containing model oil and the removal of sulfur was only about 12.2-22.0%. After addition of 30 wt % H2O2 in IL, model oil with 30.0-63.0% sulfur removal was given via chemical oxidation. While H2O2 and catalyst were introduced together, the removal of sulfur increased sharply. In the case of the system containing H2O2, WO(O-2)(2)center dot Phen center dot H2O and [Bmim]BF4, extraction and catalytic oxidation increased the sulfur removal to 98.6%. However, the oxidative desulfurization systems containing WO(O-2)(2)center dot Phen center dot H2O and H202 only led to 50.3% sulfur removal in the absence of IL. This experiment demonstrated that a combination of catalytic oxidation and extraction in IL can deeply remove DBT from model oil. This result also indicated the remarkable advantage of this process over the desulfurization by mere solvent extraction with IL or catalytic oxidation without IL.