Extractive Desulfurization of Fuel Oil Using Alkylimidazole and Its Mixture with Dialkylphosphate Ionic Liquids

Abstract

The sulfur partition coefficient KN is usually used to characterize the ability of extractive desulfurization (EDS). In this work, several KN values are measured at 298.15 K, which are between straight-run fuel oil and N-ethylimidazole (EIM), N-methylimidazole (MIM), and its mixture with a dialkylphosphate ionic liquid (IL), viz. N-ethyl-N-methylimidazolium diethylphosphate ([EMIM][DEP]) or N-butyl-N-methylimidazolium dibutylphosphate ([BMIM][DBP]). KN values between the oil and solvent at varying water content are also measured at 298.15 K. The results indicate that both EIM and MIM have excellent EDS performance with KN above 3.1 for dibenzothiophene. They have some solubility in fuel oil, but their solubility decreases with addition of IL. The EDS ability of the solvents for a specified sulfur compound followed the order alkylimidazole (EIM > MIM) > mixed solvent (MIM + IL) > IL ([BMIM][DBP] > [EMIM][DEP]); the extractive selectivity of sulfur for a specified solvent followed the order dibenzothiophene (DBT) > benzothiophene (BT) > 3-methylthiophene (3-MT). The used sulfur-containing solvent can be regenerated via a water diluting process followed by a simple distillation process; therefore, the solvent can be reclaimed in a cost-effective way. This work shows that the alkylimidazole solvent and/or its mixture with an IL can be used as a potential extractant for the EDS of fuel oils.