(33b) Deep Oxidative Desulfurization of Fuels Catalyzed by Peroxophosphomolybdate Compounds in Ionic Liquids

Three peroxophosphomolybdates [(C4H9)4N]3{PO4[MoO(O2)2]4}, [C16H33NC5H5]3- {PO4[MoO(O2)2]4} and [C14H29N(CH3)3]3{PO4[MoO(O2)2]4} have been synthesized and characterized. A combination of catalytic oxidation using hydrogen peroxide (O/S=2) as oxidant and extraction employing ionic liquid (IL) as extractant was used for removal of benzothiophene (BT),dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). Ionic liquids included 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4), 1-n-octyl-3-methylimidazolium tetrafluoroborate ([Omim]BF4), 1-butyl-3-methyl-imidazolium hexafluorophosphate ([Bmim]PF6), 1-n-octyl-3- methylimidazolium hexafluorophosphate ([Omim]PF6) and 1-octyl-3-methylimidazolium trifluoroacetate ([Omim]TA). When [Bmim]BF4 was only used as the extractant for removing DBT remaining in n-octane, the removal of sulfur was only about 16.3%. After addition of 30 wt% H2O2 in IL, the sulfur removal was increased to 31.5%. [(C4H9)4N]3{PO4[MoO(O2)2]4} and H2O2 were employed together in the absence of IL, the desulfurization yield was only 16.8%. However, in the case of the desulfurization system comprising [(C4H9)4N]3{PO4[MoO(O2)2]4}, H2O2 and [Bmim]BF4, catalytic oxidation combined with extraction remarkably increased the removal of sulfur from16.8% to 97.3%. The process is superior to the simple extraction with IL or catalytic oxidation without IL. Compared with short carbon chain catalyst, long carbon chain catalyst mixed with IL and H2O2, the removal of DBT was low. The results demonstrate that a combination of catalytic oxidation using short carbon chain catalyst and extraction can deeply remove DBT from the model oil. Moreover, the catalytic oxidation combined with extraction reactivity was found to be in the following order: DBT>4,6-DMDBT>BT. Finally, the catalysis-extraction system can be recycled four times with slight decrease in activity.