Liquid–liquid equilibria in the binary systems (1,3-dimethylimidazolium, or 1-butyl-3-methylimidazolium methylsulfate + hydrocarbons)

Abstract

Liquid–liquid equilibria in binary mixtures that contain a room-temperature ionic liquid and an organic solvent—namely, 1,3-dimethylimidazolium methylsulfate, [mmim][CH₃SO₄], or 1-butyl-3-methylimidazolium methylsulfate, [bmim][CH₃SO₄] with an aliphatic hydrocarbon (n-pentane, or n-hexane, or n-heptane, or n-octane, or n-decane), or a cyclohydrocarbon (cyclohexane, or cycloheptane), or an aromatic hydrocarbon (benzene, or toluene, or ethylbenzene, or propylbenzene, or o-xylene, or m-xylene, or p-xylene) have been measured at normal pressure by a dynamic method from 270 K to the boiling point of the solvent. Thermophysical basic characterization of pure ionic liquids are presented obtained via differential scanning calorimetry (TG/DSC), temperatures of decomposition and melting, enthalpies of fusion, and enthalpies of glass phase transition. The liquidus curves were predicted by the COSMO-RS method. For [bmim][CH₃SO₄] the COSMO-RS results correspond much better with experiment than those for [mmim][CH₃SO₄]. This can be explained partly by the stronger polarity of [mmim][CH₃SO₄]. The solubilities of [mmim][CH₃SO₄] and [bmim][CH₃SO₄] in alkanes, cycloalkanes and aromatic hydrocarbons decrease with an increase of the molecular weight of the solvent. The differences of the solubilities in o-, m-, and p-xylene are not significant. By increasing the alkyl chain length on the cation, the upper critical solution temperature, UCST decreased in all solvents except in n-alkanes.