Facile Route for Fuel Desulfurization Using Generated Superoxide Ion in Ionic Liquids

In this study, a novel desulfurization method was conducted using the superoxide ion (O₂^-) generated chemically in four ionic liquids (ILs): 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, N-methoxyethyl-N-methylmorpholinium bis(trifluoromethylsulfonyl)imide, 1-(2-methoxyethyl)-1-methylpiperidinium tris(pentafluoroethyl)trifluorophosphate, and 4-(2-methoxyethyl)-4-methylmorpholinium tris(pentafluoroethyl)trifluorophosphate. Remarkably, it was found that O₂^- can convert the sulfur compounds (i.e., thiophene and 2-methylthiophene) dissolved in these ILs. The products of the conversion were identified as H₂O, CO₂, and SO₃. The conversion percentage ranged from 35 to 99% for thiophene and 20 to 96% for 2-methylthiophene. In addition, a mechanism was proposed for this conversion. Furthermore, the effect of temperature on this reaction was studied and the solubility of sulfur compounds in these ILs was determined. The ILs did not only behave as media for the generation of O₂^-, but they also possessed catalytic activity to accelerate the reaction rate between O₂^- and substrates.