Liquid–liquid phase separation of ionic liquids in solutions: Ionic liquids with the triflat anion solved in aryl halides

Abstract

After a short review of the research concerning the nature of the critical point in ionic systems, the phase behavior is reported and analyzed for five solutions of ionic liquids with the 1-alkyl-3-methyl imidazolium cation (Cnmim, n=6,7,8) and the triflat anion (SO3CF3+, TFO) in aryl halides (C6H5 X, X=Cl, Br, J). The phase diagrams are determined by the synthetic method and visual observation of the cloud points. Depending on the length of the side chain and the dielectric permittivity of the solvent, partial miscibility with an upper critical solution point (UCSP) at ambient pressure conditions is observed in the polar aprotic solvents. The phase diagrams are analyzed presuming Ising behavior and taking into account the asymmetry of the phase diagrams. Corresponding state behavior is observed. Comparison with the predictions of the model system of charged hard spheres (CHS) is made using structural information from Monte Carlo simulations for C2mimTFO. The critical temperatures are in remarkable good agreement with the simulation results of the CHS-model, which cannot be said for solutions in alkanols and non-polar hydrocarbons, where the critical temperatures are either above or below that of the CHS model, respectively. The corresponding state phase diagrams in the variables of the CHS model show an UCSP and are in fair agreement with the results for this model. When taking into account the temperature dependence of the dielectric permittivity of the solvents in the CHS-corresponding state variables the critical points remain UCSPs, which is different to the phase diagrams of ionic solutions in alcohols.