Deep Desulfurization of Fuel Oils Using Low-Viscosity 1-Ethyl-3-methylimidazolium Dicyanamide Ionic Liquid

Abstract

In this work, the extractive and oxidative deep desulfurizations of model fuel oils using a low-viscosity ionic liquid, i.e., 1-ethyl-3-methylimidazolium dicyanamide ([C 2 mim][N(CN) 2 ]), are investigated. [C 2 mim][N(CN) 2 ] is capable of effectively extracting thiophene (TS) and dibenzothiophene (DBT) from oils. The sulfur content in the raffinate phases is only ∼10 ppm after a few extraction steps. A short extraction equilibrium time of <5 min is observed. The extraction operation is insensitive to temperature, and it can be effectively performed at or around room temperature. Unexpectedly, the oxidative removal of DBT by such a dicyanamide-based ionic liquid is not effective and is not as good as the corresponding extraction operation. Such an undesirable oxidative desulfurization is understood at a molecular level from ab initio calculations, and it may be ascribed to the strong intermolecular interaction between CH 3 COOH or CH 3 COOOH and [C 2 mim][N(CN) 2 ] phase. Therefore, such a dicyanamide-based ionic liquid is efficient for direct extractive desulfurization, while it is less efficient for oxidative desulfurization.