Liquid−Liquid Equilibrium of Mixtures of Imidazolium-Based Ionic Liquids with Propanediols or Glycerol

In this work, liquid−liquid equilibria (LLE) of solutions of imidazolium-based ionic liquids—with either bistriflamide ([C n mim][NTf 2 ], n = 2 and n = 10) or triflate anions ([C 2 mim][OTf]), with 1-propanol, 1,2-propanediol, 1,3-propanediol, and glycerol (1,2,3-propanetriol)—were studied. The obtained phase diagrams show a remarkable difference in solvation properties between ionic liquids with NTf 2 or OTf anions toward the aforementioned alcohols: although [C 2 mim][NTf 2 ] constantly exhibited partial miscibility, [C 2 mim][OTf] was always completely miscible. This divergence is likely to be related to the distinct abilities of NTf 2 and OTf anions toward hydrogen bonding. It was also found that the shorter cation alkyl chain in the [C n mim][NTf 2 ] ionic liquids provided better solubility with both propanediols and glycerol. In addition, the solubility of 1,3-propanediol in both [C 2 mim][NTf 2 ] and [C 10 mim][NTf 2 ] was much lower than that of 1,2-propanediol. From the application point of view, the present results show that mixtures of [C 2 mim][NTf 2 ] and [C 2 mim][OTf] ionic liquids may achieve the separation of 1,3-propanediol from glycerol. The LLE experimental results were correlated using a model based on the Peng−Robinson equation of state (PR EoS) combined with the Mathias−Klotz−Prausnitz (MKP) mixing rule.