Research On 1-ethyl-3-methylimidazolium Dimethylphosphate+Water/Alcohol System As New Working Pairs

Heat pump is an effective energy-saving device use low-grade heat source to transfer heat from low temperature to high one. In the industrial waste heat recovery, heat pump improves energy efficiency and reduces greenhouse gas emissions. The application of absorption heat pump in the industry depends largely on the thermodynamic property of working pair.Current working pair of absorption heat pump has corrosion, crystallization, high work pressure and toxicity issues. Therefore, new woking pair has been the focus.Ionic liquid is the liquid composed of the ion at or near room temperature. Ionic liquid has many special properties, such as good thermal stability and chemical stability, wide liquid range, low vapor pressure, etc.In this paper, the solution containing ionic liquid is suggested to be working pair, which ionic liquid 1-ethyl-3-methylimidazolium dimethylphosphate ([EMIM][DMP]) as an absorbent to water, methanol, and ethanol as the refrigerant.One-step synthesis and characterization of the ionic liquid [EMIM][DMP] were in the laboratory.Vapor pressures for the three binary systems ([EMIM][DMP]+H2O/C2H5OH/CH3OH respectively) with different concentration of [EMIM][DMP] were measured at different temperatures. The vapor pressure were correlated by NRTL model. The result showed that the average relative error between experimental and calculated values are 1.44%,1.96%,1.54% respectively and the binary system are negative deviation to Raoult's law.Excess enthalpies at the temperature of 298.15K and the pressure of 1atm for these binary systems and ternary system were measured and corrected by RK model. The average relative errors between experimental and calculated values are 0.71%,3.41%,0.64% and 1.57% respectively. The results indicate that the mixing process of [EMIM][DMP] with water, ethanol and methanol is an exothermic process, which is a very important characteristic for working pair used in absorption heat pumps or in absorption refrigerators.The specific heat capacity of binary system were measured at different temperature and different concentrations and correlated well by the empirical polynomial. The average relative errors between experimental and calculated values are 0.47%,1.05% and 0.82% respectively. The result shows that the specific heat capacity of binary system in line with temperature, and specific heat capacity decreases with the ionic liquid concentration.