A comparative study of the extractive desulfurization mechanism by Cu(II) and Zn-based imidazolium ionic liquids

A comparative study of the extractive desulfurization (EDS) mechanism by Cu(II) and Zn-based ILs ([C4mim]2[MCl4], M = Cu(II) or Zn) has been performed. It is found that the π–π interaction and C-H⋯π interaction play important roles in EDS for both Cu(II) and Zn-based ILs, which is different from Al, Fe-based ILs. In the gas phase models, the interaction energy between Zn-based ILs and dibenzothiophene (DBT) is stronger than the interaction energy of Cu(II)-based ILs. In order to consider the solvent effect, a generic ionic liquid of solvation model has been implemented, which is few considered in the previous calculations of EDS. It is interesting to find that the gap of interaction energies between Cu(II), Zn-based ILs and DBT are reduced when the solvent effect is considered. In addition, by combined discussion of currently theoretical and experimental evidences for metal-based ILs with different compositions, we firstly propose that the EDS performance should be influenced by the balance of the contribution of cation, metal-based anion, metal chlorides and the viscosity. Keywords: Extractive desulfurization, Metal-based ILs, Mechanism, Density functional theory