Physicochemical properties of tri(butyl)ethylphosphonium diethylphosphate aqueous mixtures

This work presents the new experimental data on physical and thermodynamic properties of binary system composed of tri(butyl)ethylphosphonium diethylphosphate and water: solid-liquid equilibrium (SLE) and vapor-liquid equilibrium (VLE) phase diagrams as well as the excess enthalpy of mixing. SLE phase diagram has been determined at wide temperature and composition range using two techniques: dynamic method and differential scanning calorimetry (DSC). Interesting behavior with a solid compound formation was observed for the studied mixture. The isothermal VLE have been measured by an ebulliometric method within temperature range from T = (328.15 to 368.15) K and pressure up to 100 kPa. The excess enthalpy for the tested binary system was determined at T = 298.15 K using isothermal titration calorimeter. Liquid density for pure IL and the binary mixtures with water has been determined at temperature range from T = (298.15 to 348.15) K and from experimental data, the excess molar volumes were calculated. The influence of temperature and composition on measured properties is discussed in terms of IL-water molecular interactions. Furthermore, the binary mixture under study was discussed as an alternative working pair for the absorption heat pump cycle.