Selection of ionic liquids for aromatic/aliphatic separations and determination of LLE data supported by COSMO-RS

The separation of aromatic and aliphatic hydrocarbons is challenging, due to overlapping boiling points and formation of several azeotropes. Conventional solvents for those separations are polar substances, e.g. sulfolane. Recently it could be shown that ionic liquids can perform considerably better than common extraction solvents. Hence, ionic liquids can be a promising alternative [1]. Ionic liquids (IL) are molten salts composed of large organic cations and various anions. Some of their properties are negligible vapour pressure, wide liquid range (~300K) and the ability to dissolve polar, non-polar, organic and inorganic compounds. Since the properties of an ionic liquid are defined by the combination of cation and anion a great number of combinations (> 10) is conceivable. 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 [2]. By comparing the σ-profiles of aromatic and aliphatic 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 this work several ionic liquids have been tested with a simplified naphtha feed consisting of toluene and n-heptane. Based on the preselection made with COSMORS, LLE data have been determined and for the ternary mixtures (toluene + n-heptane + [BMIM][DCA]), (toluene + n-heptane + [BMIM][SCN]) and (toluene + n-heptane + [Mebupy][DCA]) ternary diagrams have been derived. It could be shown that COSMORS is a useful tool for the selection of ionic liquids.