Liquid–liquid equilibria for ternary mixtures of water + 2-propanol + 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids at 298.15 K

• LLE of three ternary systems of water + 2-propanol + ILs were measured.
• Influence of ILs with different length of alkyl chain on the LLE was discussed.
• The molecular structural parameters of ILs were calculated by quantum chemistry.
• The NRTL and UNIQUAC models were applied to correlate the studied systems.

Ternary liquid–liquid equilibria for three systems of water + 2-propanol + 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Hmim][NTf2]), 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Omim][NTf2]), and 1-decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Dmim][NTf2]) ionic liquids (ILs) have been determined at T = 298.15 K and atmospheric pressure. The solute distribution coefficient and the selectivity were calculated for all systems. Influence of ILs with different length of alkyl chain on the liquid–liquid equilibria was revealed. The nonrandom two liquid (NRTL) model was used to correlate ternary systems. Three ILs were studied to determine the parameters of structural volume (r) and surface area (q) by quantum chemistry approach. According to the calculated values of r and q, the universal quasichemical (UNIQUAC) model was also applied to correlate three ternary systems. The results show that both NRTL and UNIQUAC models are capable of correlating the studied systems with reasonable accuracy.