Influence of imidazolium based ionic liquids with different anions on liquid–liquid phase behavior for separation of azeotropic mixture isopropyl alcohol + diisopropyl ether

During production of isopropyl alcohol (IPA) by propylene hydration, a mixture of diisopropyl ether (DIPE) and IPA is obtained as a byproduct. Because DIPE and IPA have similar boiling points, an azeotrope can be formed. It is not feasible to separate the mixture (DIPE + IPA) using conventional distillation technology. In this work, the mixture (DIPE + IPA) was separated by liquid–liquid extraction and three imidazolium based ionic liquids (ILs) with different anions including 1-butyl-3-methylimidazolium thiocyanate ([BMIM]SCN), 1-butyl-3-methylimidazolium dicyanamide ([BMIM]DCA) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM]NTf2) were selected as the extractants. The effect of the ILs on liquid–liquid phase behavior for the ternary systems (DIPE + IPA + ILs) was discussed. Partition ratio (P) and selectivity (S) were calculated to assess the extraction ability of the ILs. The NRTL thermodynamic model was used to correlate the experimental data. The interactions between the ILs and (DIPE / IPA) were explored by analyzing electrostatic potentials, hydrogen bond length and reduced density gradient, which can help to design the ILs with reasonable structures for separating such azeotropic mixtures.