Separation of n-heptane and tert-butanol by ionic liquids based on COSMO-SAC model

In the process of liquid–liquid extraction, it is necessary to look for green solvents as extractants. Ionic liquids have been studied as extractants due to their green recyclability in recent years. The infinite dilution activity coefficients of 100 ionic liquids with a combination of 10 cations and 10 anions were calculated by COSMO-SAC model, and the σ-profiles were plotted. The distribution coefficient and separation coefficient of n-heptane + tert-butanol + ILs were determined. [OMIM][OTF], [HMIM][OTF] and [BMIM][OTF] were selected as solvents for this study. The interaction energy, bond length and charge density of ionic liquids with tert-butanol were calculated by quantum chemistry calculation method. According to these results, the rationality of selected ionic liquids as extractants could be analyzed from the molecular level. At 298.15 K and 101.325 kPa, the liquid–liquid equilibrium data of the ternary system {n-heptane + tert-butanol + [OMIM][OTF], n-heptane + tert-butanol + [BMIM][OTF], n-heptane + tert-butanol + [HMIM][OTF]}) were measured. The distribution coefficient and separation coefficient for judging the extraction effect were obtained. The NRTL model was used to correlate liquid–liquid equilibrium experimental data, and correlation result proved that the correlated and experimental data had a good correlation. The research on ionic liquids is of great significance to the development of green and sustainable chemical industry.