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][NTHf2] 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 NTf2 or OTf anions toward the aforementioned alcohols: although [C(2)mim][NTf2] constantly exhibited partial miscibility, [C(2)mim][OTf] was always completely miscible. This divergence is likely to be related to the distinct abilities of NTf2 and OTf anions toward hydrogen bonding. It was also found that the shorter cation alkyl chain in the [C(n)mim][NTf2] ionic liquids provided better solubility with both propanediols and glycerol. In addition, the solubility of 1,3-propanediol in both [C(2)mim][NTf2] and [C(10)mim][NTf2] 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][NTf2] 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.