Design rules of ionic liquids tasked for highly efficient fuel desulfurization by mild oxidative extraction

The deep desulfurization of petroleum-based fuels using oxidative extraction processes has been hampered by the lack of suitable solvent systems and by the poor availability of inexpensive and efficient catalysts. As a strategy to address this limitation, the present study evaluates a number of hydrophilic and hydrophobic ionic liquids (ILs) for the oxidative extraction of dibenzothiophene (DBT) and other aromatic sulfur compounds (e.g., thiophene, TS, benzothiophene, BT, and 4,6-dimethyldibenzothiophene, DMDBT) from n-octane using H₂O₂ as the oxidant and V₂O₅ as the catalyst. Our findings are significant for petroleum desulfurization and suggest that ILs for effective sulfur removal will typically comprise low basicity/nucleophilicity anions paired to cations possessing some hydrophilic character. Among a number of suitable ILs identified for this application, [Choline][Tf₂N] is particularly promising as a relatively low-cost solvent ideal for use in oxidative extraction to desulfurize fuel. The [Choline][Tf₂N]–V₂O₅ system afforded essentially quantitative removal of DBT, BT, and DMDBT at room temperature, even for initial sulfur levels as high as 3000 ppm. This advance enables a highly efficient and cost-effective desulfurization process that has a promising industrial application for producing ultra-low-sulfur fuel.