The Properties Research On New Working Pairs Of Dimethylimidazolium Dimethylphosphate And Water/Alcohol

Absorption heat pump is an effective equipment for recycling low temperature waste heat for reuse. It has characteristics of high efficiency, energy saving and environmental protection. The working pair has an important influence in the operational performance for heat pump. The existing working pairs have the problems of corrosion, crystallization, high working pressure, toxicity, et al. Therefore, many researchers have pay attention on the study of new working pairs of heat pump.Ionic Liquid (IL) is a kind of room temperature melted salt, which consists of organic cations and inorganic anions. IL is regarded as green solvent. They have many advantages, such as strong stability, a negligible vapor pressure, wide liquid range, strong solubility in many organic or inorganic substances. So, it could be used as absorbent in absorption heat pump.In this paper, the IL 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]) was chosen, prepared and characterizied. Vapor pressure, excess enthalpy, heat capacity, density and viscosity for the three binary systems [MMIM][DMP]+H2O/C2H5OH/CH3OH were measured at different temperatures with different IL concentrations. It will provide the basic information for the research of thermodynamic model, for calculating the performance of absorption heat pump.The IL was synthesized in the laboratory via one-step method. The preparation and purification process was simple and environment friendly, the yield was high, the cost was low. So, it could be used in industrial area.The Vapor pressures of the three binary systems were measured by using the bubble point method. The experimental data showed a considerable negative deviation from Raoult's Law. The Vapor pressure data were correlated by NRTL model. The average deviation between experimental data and correlated ones were 1.72%,1.63%and 1.08%, respectively. The mixing heat (excess enthalpy HE) for the three binary systems were measured at 25℃with different IL concentrations. The HE data were negative, which means exothermic when the IL and the three solvents were mixed together. Heat capacities for the three systems were also measured in this paper. The heat capacities decreased with increasing [MMIM][DMP] molar concentration at the same temperature and slightly increased when the temperature was increased at the same IL concentration. Densities and viscosities for the three binary systems were measured From 25℃to 50℃with different IL concentrations. The densities of the three systems increased with an increase in the [MMIM][DMP] molar concentration at the same temperature whilst decreased slightly with a temperature increase at the same IL concentration. The viscosities of pure [MMIM][DMP] is very high, about 300 times of H2O at 25℃. But, it would decrease sharply when the [MMIM][DMP] was heated or the water/ethanol/methanol were added. As the absorption and generation temperatures of an absorption heat pump or absorption heat transformer are usually high, the viscosity of the [MMIM][DMP]+water/ethanol/methanol pairs is expected to be low. Consequently, the high viscosity of the ionic liquid would not limit its use as a heat pump absorbent.To sum up, the three ionic liquid systems [MMIM][DMP]+H2O/C2H5OH/CH3OH could be used as working pairs of absorption heat pump.