Selection of entrainers in the 1-hexene/ n-hexane system with a limited solubility

Abstract

Vapor-liquid equilibria (VLE) have been measured for five 1-hexene/ n-hexane/ionic liquid systems and 1-hexene/ n-hexane/NMP ( N-methyl-2-pyrrolidone) system with a headspace-gas chromatography (HSGC) apparatus at 333.15 K. The ionic liquids investigated were 1,3-dimethylimidazolium tetrafluoroborate [C 2MIM] +[BF 4] −, 1-butyl-3-methylimidazolium tetrafluoroborate [C 4MIM] +[BF 4] −, 1-methyl-3-octylimidazolium tetrafluoroborate [C 8MIM] +[BF 4] −, 1,3-dimethylimidazolium dicyanamide [C 2MIM] +[N(CN) 2] − and 1-octylquinolinium bis(trifluoromethylsulfonyl)amide [C 8Chin] +[BTA] −. It was found that at low feeding concentration of 1-hexene and n-hexane, the separation ability of ionic liquids is in the order of [C 2MIM] +[BF 4] − > [C 4MIM] +[BF 4] − ≈ [C 2MIM] +[N(CN) 2] − > [C 8MIM] +[BF 4] − > [C 8Chin] +[BTA] −, which is consistent with the priori prediction of the COSMO-RS (conductor-like screening model for real solvents) model. But at high feeding concentration, the separation ability of ionic liquids is in the order of [C 2MIM] +[BF 4] − < [C 4MIM] +[BF 4] − ≈ [C 2MIM] +[N(CN) 2] − < [C 8MIM] +[BF 4] − < [C 8Chin] +[BTA] −. The liquid demixing effect should be taken into account. The activity coefficients of 1-hexene and n-hexane at infinite dilution calculated with the COSMO-RS model were correlated using the NRTL, Wilson and UNIQUAC model. In this work the predictive results from the COSMO-RS model and UNIFAC model for the 1-hexene/ n-hexane and 1-hexene/ n-hexane/NMP systems were compared. The UNIFAC model is one of the most important academic contributions by Prof. Jürgen Gmehling.