Deep oxidative desulfurization of fuels in redox ionic liquids based on iron chloride

Abstract

Three redox ionic liquids based on iron chloride were synthesized and employed in extraction and catalytic oxidation desulfurization systems for removal of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in model oil. Sulfur removal selectivity for S-compounds followed the order of DBT > 4,6-DMDBT > BT. Due to the redox properties of 1-butyl-3-methylimidazolium chloride iron chloride ([bmim]Cl/FeCl₃) with addition of hydrogen peroxide, DBT removal can reach 99.2% under mild reaction conditions, which is not only higher than mere extraction with ionic liquid (IL), but also superior to two other ILs based on iron chloride under the same reaction conditions. Herein, [bmim]Cl/FeCl₃ played a dual role in the process of desulfurization, not only acting as catalyst but also acting as an extractant. [bmim]Cl/FeCl₃ is insoluble in n-octane, and the solubility in the model oil is also negligible. The used ionic liquid could be recycled for six times with a slight decrease in activity.