Thermodynamic properties of new heat pump working pairs: 1,3-Dimethylimidazolium dimethylphosphate and water, ethanol and methanol

Ionic liquid 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]) + water/ethanol/methanol mixtures exhibit properties which render them suitable as candidates for working pairs in industrial applications of absorption heat pumps or chillers. In this paper, the thermodynamic properties including vapor pressure, density, viscosity, heat capacity as well as excess enthalpy of these binary systems were measured at various temperatures with different ionic liquid concentrations. The thermodynamic properties were correlated by different equations, respectively. The correlated values were significantly consistent with the experimental ones. In conclusion, the vapor–liquid equilibrium (VLE) data indicated that the vapor pressures of the three solvents in [MMIM][DMP] displayed a considerable negative deviation from Raoultʹs law, and the excess enthalpies of the three binary systems are negative. These characteristics are necessary and important for an absorption working pair.