Deep oxidative desulfurization of diesel fuels by Lewis acidic ionic liquids based on 1-n-butyl-3-methylimidazolium metal chloride

Abstract

A series of Lewis acidic ionic liquids (ILs) based on 1-n-butyl-3-methylimidazolium metal chloride, i.e., [C4mim]Cl/MCl2 (M=Zn, Fe, Cu, Mg, Sn, Co), are synthesized and used to investigate the oxidative removal of sulfur compounds (S-compounds) from diesel fuels, with ILs serving as both extractant and catalyst and 30wt% H2O2 solution as oxidant. It is observed that metal chloride species affect S-removal, as S-removal efficiency follows the order: [C4mim]Cl/ZnCl2>[C4mim]Cl/FeCl2>[C4mim]Cl/CoCl2>[C4mim]Cl/MgCl2>[C4mim]Cl/CuCl2>[C4mim]Cl/SnCl2. The highly efficient [C4mim]Cl/ZnCl2 is selected to investigate the effects of ZnCl2 content on desulfurization. It is interesting to find out that ZnCl2 content has a significant influence on desulfurization; specifically, 99.9% S-removal is observed for [C4mim]Cl/3ZnCl2 after 3h at 45°C, O/S molar ratio of 8, IL/oil mass ratio of 1/2. [C4mim]Cl/3ZnCl2 then undergoes series of parallel experiments to systematically investigate the influence of factors such as temperature, molar ratio of O/S, mass ratio of IL/oil, and ILs recycling. The incorporation of real diesel fuel into this study demonstrates the efficacy of this IL in desulfurization. This work shows that oxidative desulfurization using Lewis acidic ILs may be a new option for producing cleaner diesel fuels.