(83e) Selection of Ionic Liquids for Acetonitrile/ Water Separations and Determination of VLE Data Supported By COSMO-RS

The separation of acetonitrile and water is challenging, due to formation of azeotrope. Conventional solvents for those separations are volatile solvents. In recent years, Ionic liquids (ILs) as a new kind of solvent have many unique attributes, e.g. negligible vapor pressure, good thermal stability and environment-friendly, which make them attractive and potential being used as a suitable solvent in separation processes.

Ionic liquids are molten salts composed of large organic cations and various anions. The prediction of the ideal IL for each separation process is nowadays impossible, Since there are about 10¹⁸ possible ionic liquids by combination of cation and anion. Hence, it is possible to tailor a specific ionic liquid with the desired properties. In order to be able to make a selection out of all possible combinations COSMO-RS was found to be a suitable screening tool. By comparing the σ-profiles of acetonitrile - water compounds and an ionic liquid, it is possible to make an assumption whether the ionic liquid is suitable for the separation of the mixture.

In order to select a suitable IL entrainer for extractive distillation, the infinite dilution activity coefficients of acetonitrile and water in hundreds of ILs using the COAMO-RS (Conductor-like Screening Model For Real Solvents) model was calculated in this work. Then selectivity and solubility were determined according the infinite dilution activity coefficients. 1-ethyl-3-metnylimidazolium acetate ([EMIM]OAc), N-butyl-4-methylpyridine acetate ([4MePy]OAc), and 1-hexyl-2,3-dimethylimidazolium acetate ([HDMIM]OAc) has high selectivity and good solubility by screening. The isobaric VLE data for the ternary system of acetonitrile + water containing ILs were measured at 101.3 kPa, and the effect of the ILs on the separation performance of the acetonitrile and water system was discussed. The results show that the three ILs could increase the relative volatility of acetonitrile and even made the azeotropic phenomenon eliminate. The separation ability of ILs is in the order [HDMIM]OAc > [4MePy]OAc > [EMIM]OAc. COSMO-RS can thus be very useful in the scanning of the growing number of known ILs to find suitable candidates, or help designing new ILs, for specific applications before extensive experimental measurements.