Application of imidazole ionic liquids in extractive distillation of benzene-cyclohexane system: Experimental verification and mechanism analysis

Abstract

This study focused on the separation problem of benzene and cyclohexane. Given their similar boiling points and properties, ionic liquids (ILs) were employed as sustainable green separation solvents. Four imidazole-based ILs were used as extractants, and the optimal experimental conditions for the extractive distillation of the benzene-cyclohexane model liquid by ILs were determined through batch distillation experiments. The optimal conditions were a total reflux time of 20 min, a reflux ratio of 2, and a solvent ratio of 0.6. Under these optimal conditions, the separation performances of the four imidazole - based ILs were evaluated. Among them, 1-pentyl-3-methylimidazolium bromide ([C₅MIM][Br]) showed the best separation effect, and the mass purity of the obtained cyclohexane reached 82.54 %. Furthermore, based on quantum chemistry (QC) calculations and molecular dynamics (MD) simulations, the effects of different cations on the microscopic structure distribution and diffusion behavior of the benzene-cyclohexane system were investigated. The results indicated that the interactions between ILs and benzene were mainly van der Waals interactions, and the interactions between ILs and benzene were stronger than those with cyclohexane, which was highly beneficial for the separation of azeotropes. [C₅MIM][Br] had more significant advantages as an extractant. In conclusion, [C₅MIM][Br] had great application potential in the separation of benzene and cyclohexane and was a promising solvent.