Efficient Oxidative Desulfurization of Model Oil at Room Temperature with Ionic Liquid as Extraction Solvent

Abstract

The oxidative desulfurization of model oil (hexane solution of thiophene) was carried out at room temperature in a two-step method involving: 1) the acetic acid catalyzed oxidation of thiophene with hydrogen peroxide and 2) the subsequent extraction of the oxidized products with three 1-alkyl-3-methylimidazolium bromide [RMIM]Br ionic liquids of varying alkyl substituent R chain length (R: C2, C4, C6) and with acetonitrile as control. For purposes of comparison, a non-oxidative extractive desulfurization of model oil with the above ionic liquid and with acetonitrile was also performed. The thiophene extraction efficiencies of the ionic liquids and that of the control in both the oxidative and non-oxidative procedures were determined by means of gas chromatography. The ionic liquid of the shortest alkyl substituent chain length (R: C2), [EMIM] Br exhibited the highest extraction efficiency in the oxidative desulfurization of the model oil; the extraction efficiency of [EMIM] Br was also observed to exceed that of acetonitrile. In general, the oxidative desulfurization with the above [RMIM]Br's is apparently a more efficient method of thiophene removal from the model oil as compared to a non-oxidative procedure with the same extraction solvents. The extraction efficiency of [RMIM]Br's was observed to decrease with the lengthening of the alkyl substituent chain. The same trend is observed in the non-oxidative extractive desulfurization of the model oil. Recyclability analysis of [EMIM]Br showed that [EMIM]Br can be recycled thrice with no significant decrease in extraction efficiency.