Using functional acidic ionic liquids as both extractant and catalyst in oxidative desulfurization of diesel fuel: An investigation of real feedstock

• Five functional Brønsted or Brønsted–Lewis acidic ILs are prepared.
• Such acidic ILs act as both extractive and catalytic solvents in desulfurization.
• S-content in diesel fuel is reduced to <10 ppm through coupled EDS–ODS.
• Desulfurization condition is mild with very low loss of desulfurization efficiency.
• Nature of S-compounds in diesel fuel is determined by GC-SCD.

Desulfurization of diesel fuel with ionic liquids (ILs), as alternative to traditional hydrodesulfurization (HDS), has been studied intensively for the latest years. Most works, however, were focused on the investigation of model diesel fuel. In this work, two acidic ILs ([(CH2)4SO3HMIm][Tos] and [(CH2)4SO3HMIm][ZnCl3]) were synthesized and studied their desulfurization performance for real diesel fuel in a coupled oxidative–extractive way, where 30 wt% H2O2 acted as oxidant and ILs served as both extractants and catalysts with adding no acidic catalysts that were usually used in traditional oxidative desulfurization. The influences, on desulfurization, of temperature, time, mass ratio of ILs/oil, molar ratio of O/S, multiple desulfurization and ILs recycle were investigated. It was observed that sulfur content (S-content) in the real diesel fuel was reduced to <10 ppm from original 225 ppm in a coupled oxidative–extractive way ([(CH2)4SO3HMIm][Tos]; mass ratio of ILs/oil 1/2; 3 h, 348.15 K and molar ratio of O/S 40/1 in oxidative step; 30 min and 333.15 K in extractive step). These results are more competitive than other previous results. After 5 cycles of oxidative desulfurization with used ILs, the loss of efficiency is less than 1% at a mild temperature. Distribution of S-compounds in diesel fuel before and after desulfurization were determined by gas chromatograph with sulfur chemiluminescence detector. This work shows that such acidic ILs are capable of removing S-compounds effectively from real diesel fuel with a coupled oxidative–extractive operation.