Evaluation of COSMO-RS model for the LLE prediction of benzene plus cyclohexane plus ionic liquid system

The screening of potential extractant from a set of ionic liquids (ILs) (formed by 45 cations and 32 anions) to extract benzene from cyclohexane with COSMO-RS model was conducted in this work. The ternary liquid–liquid equilibrium (LLE) of benzene plus cyclohexane plus [BMIM]I3 was also experimentally validated to investigate the feasibility of the model. The screening result shows that [BMIM]I3 is an optimal extractant. The comparison of predictive data and experimental data of the ternary phase equilibrium shows the reasonability of the model. Furthermore, the gap between them was carefully analyzed to expect a better agreement. It is finally found that the factors of different parameterization sets, the molecule conformation and the form of IL existing in the solution have effects on the prediction. The prediction calculated with the ion pair molecular model of IL, the multiple conformations of molecule with Boltzmann distribution and the parameterization sets of C30-1701 provides the best accuracy. The calculated RMSD is about 4.9%. Finally, the micro-mechanism of extractant was investigated to uncover the interaction in the extracting process with the help of quantum calculation, which is beneficial to the select and design of latter extractants.