Liquid–liquid phase transition in the ionic solutions of tetra-n-butylammonium chloride in o-xylene and ethylbenzene: Phase diagrams and corresponding state analysis

Abstract

The phase diagrams of the liquid–liquid phase transition of solutions of tetra-n-butyl ammonium chloride (N 4444Cl) in o-xylene and ethylbenzene are reported and compared with the phase diagrams of solutions of other ionic liquids (IL) with halide anions (tri-n-hexyl-n-tetradecyl phosphonium (P 666 14 +)) chloride and bromide and 1-n-alkyl-3-methyl imidazolium (R nmim +) chlorides) in non-polar solvents such as alkanes, arenes and CCl 4 and also with solutions of various 1-n-alkyl-3-methyl imidazolium tetrafluoroborates (R nmim + BF 4) in alcohols and water. All phase diagrams have an upper critical solution point (UCSP) and are consistent with the presumption of Ising criticality. For the corresponding state analysis different concentration variables (mole fraction, volume fraction, and density) are applied. Using the variables of the model fluid of charged hard spheres in a dielectric continuum, termed restricted primitive model (RPM) a systematic overview of the critical properties of the mixtures is obtained. The critical temperatures of the solutions in the non-polar solvents are in the region predicted by the RPM but somewhat smaller. They are very similar, and do not correlate with the dielectric constant of the solvents but show a weak correlation with the boiling temperatures of the solvents, indicating the influence of the cohesion of the solvents on the phase separation driven by Coulomb interactions. The critical concentrations, width of the phase diagrams and the slope of the diameter are noticeably different for the solutions in protic and aprotic solvents but show no further systematic trends.