Extractive Desulfurization of Gasoline Using Imidazolium-Based Phosphoric Ionic Liquids

Abstract

Sulfur partition coefficients for sulfur compounds 3-methylthiophene (3-MT), benzothiophene (BT), and dibenzothiophene (DBT) between phosphoric ionic liquids (ILs), namely, N-methyl-N-methylimidazolium dimethyl phosphate ([MMIM][DMP]), N-ethyl-N-methylimidazolium diethyl phosphate ([EMIM][DEP]), and N-butyl-N-methylimidazolium dibutyl phosphate (BMIM][DBP]), and gasoline were determined experimentally at 298.15 K over a wide range of sulfur content and compared with other IL extractants. The solubility of sulfur (as DBT, BT) in ILs aqueous solution at 298.15 K and varying water content was also measured. It was shown that the desulfurization ability of the ILs for each sulfur component (DBT, BT, 3-MT) followed the order of [BMIM][DBP] > [EMIM][DEP] ≫ [MMIM][DMP], and the sulfur removal selectivity for a specified IL followed the order of DBT > BT > 3-MT. The phosphoric ILs are insoluble in gasoline while the fuel solubility in ILs is noticeable and follows the order of [BMIM][DBP] ≫ [EMIM][DEP] > [MMIM][DMP]. Considering the relatively high sulfur removal ability, low fuel dissolvability, and small influence on the gasoline treated, [EMIM][DEP] might be used as a promising solvent for the desulfurization of gasoline via an extractive desulfurization (EDS) process. The sulfur components in the spent ILs could be conveniently separated via a water dilution process.