Polyoxometalate-based ionic liquids as catalysts for deep desulfurization of fuels

In order to obtain the ultra low-sulfur diesel, deep desulfurization of diesel oil has become a vital subject of environmental catalysis studies. Extraction and catalytic oxidation desulfurization (ECODS) system is one of the most promising desulfurization processes. A series of Keggin-type POM-based ionic liquids hybrid materials [MIMPS]3PW12O40·2H2O (1-(3-sulfonic group) propyl-3-methyl imidazolium phosphotungstate), [Bmim]3PW12O40 (1-butyl 3-methyl imidazolium phosphotungstate), [Bmim]3PMo12O40 (1-butyl 3-methyl imidazolium phosphomolybdate) and [Bmim]4SiW12O40 (1-butyl-3-methyl imidazolium silicotungstate) have been developed in this study, and the reaction has performed using the POM-ILs materials as catalysts, H2O2 as oxidant, and ionic liquid (IL) as solvent. Through experimental evaluations, [MIMPS]3PW12O40·2H2O was found to be the best catalyst, with an S-removal of 100% at 30 °C for 1 h. The main factors affecting the process including temperature, catalyst dosage, and O/S (H2O2/DBT) molar ratio were investigated in detail. Under the optimal conditions, DBT (dibenzothiophene) and 4,6-DMDBT (4,6-dimethyl-dibenzothiophene) could achieve high desulfurization efficiency. Moreover, the reaction system also exhibited high activity in actual diesel oil, which could be reduced from 1113 ppm to 198 ppm. The reaction system could recycle 8-times with a slight decrease in activity.

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► Several POM-based ILs were synthesized and characterized.
► New attempt with POM-based ILs as catalysts in removing DBT in fuels.
► High desulfurization was achieved in water-immiscible IL.
► Desulfurization differences among different POM-ILs catalysts have been explained.