COSMO-RS Based Screening Ionic Liquids for Separation of Benzene and Cyclohexane

Cyclohexane is mainly produced by catalytic hydrogenation of benzene and the removal of unreacted benzene is very important process. However, the two components have close boiling points and form azeotropic mixture which needs special separation processes, such as extractive distillation. However, the existing conventional solvents used foe extractive distillation has diverse limitation. Although, ionic liquids became promising solvents in separation process, the selection of appropriate ionic liquid for specific process is impossible without a prior screening. This paper presents the screening of potential ionic liquid entrainers in the distillative separation of benzene and cyclohexane using COSMO-RS model. The screening starts with the prediction of the activity coefficients at infinite dilution by tailoring 44 anions and 60 cations resulting in 2640 possible combinations. The predicted infinite activity coefficients were compared with experimental results to check the reliability of the prediction. A total of 424 experimental data point were used for this purpose. The root-mean-square deviations (rmsd) of infinite dilution activity coefficient for benzene and cyclohexane are 0.12 and 0.44 ln-units respectively. The selectivity and solvent capacity at infinite dilution were calculated from the predicted activity coefficients. It was found that structural variation ns of the ionic liquid entrainer cause converse changes in selectivity and capacity. The selectivity of benzene to cyclohexane increases with a shorter and unbranched alkyl substituent of the cation and with anions with sterical shielding. Moreover, imidazolium and thiazolium have selectivity higher and low solvent capacity where as higher capacities were observed for ionic liquids with ionic liquids consisting of phosphonium and guanidinium cations.