Desulfurization of diesel fuel by one-pot method with morpholinium-based Brønsted acidic ionic liquid

Abstract

Ionic liquids (ILs) are highly efficient green solvents for the removal of thiophene sulfides. Several acidic ionic liquids (ILs) were synthesized with N-formylmorpholine (NFM) as cation and formic acid (HCOOH), sulfuric acid (H2SO4), p-toluenesulfonic acid (Tos), trifluoroacetic acid (TFA) as anions. [NFM][TFA] was selected in one-pot extraction-oxidative desulfurization process. The initial sulfide concentrations, competition with olefins and aromatics and the desulfurization mechanism were explored. When VIL/Voil = 1:20, O/S = 3, 60 °C, the desulfurization efficiency of DMDBT and DBT were 99.82% and 99.67% in 30 min, respectively. After recycling five times, the desulfurization efficiency of [NFM][TFA] for DBT could maintain over 98%. When the initial real diesel concentration of 535 ppm and 298 ppm, the desulfurization efficiencies of real diesel were 44.42% and 56.46%, the values increased to 85.73% and 92.13% after extraction and re-extraction by [DBU][Pr]. The mechanism of desulfurization process was proposed that [NFM][TFA] reacted with H2O2 to form corresponding peroxyacid transition state, and DBT in IL phase was oxidized to the corresponding sulfones.