Extraction of Dibenzyl Disulfide from Transformer Oils by Acidic Ionic Liquid

In recent years, dibenzyl disulfide (DBDS) in transformer oils has caused many transformer failures around the world, and its removal has attracted more attention. In this work, nine imidazolium-based ionic liquids (ILs) were applied as effective, green desulfurization extractants for DBDS-containing transformer oil for the first time. The results show that the desulfurization ability of the ILs for DBDS followed the order of [BMIM]FeCl₄ > [BMIM]N(CN)₂ > [BMIM]SCN > [BMIM](C₄H₉O)₂PO₂ > [BMIM]MeSO₄ > [BMIM]NTf₂ > [BMIM]OTf > [BMIM]PF₆ > [BMIM]BF₄. Especially, [BMIM]FeCl₄ ionic liquid had excellent removal efficiency for DBDS, with its S partition coefficient K (S) being up to 2642, which was much higher than the other eight imidazolium-based ILs. Moreover, the extractive performance of [BMIM]FeCl₄ increased with an increasing molar ratio of FeCl₃ to [BMIM]Cl, which was attributed to its Lewis acidity and fluidity. [BMIM]FeCl₄ ionic liquid could also avail in the desulfurization of diphenyl sulfide (DPS) from model oils. The experimental results demonstrate that π-π action, π-complexation, and Lewis acid-base interaction played important roles in the desulfurization process. Finally, the ([BMIM]FeCl₄) ionic liquid could be recycled five times without a significant decrease in extractive ability.