Vapor pressures, excess enthalpies, and specific heat capacities of the binary working pairs containing the ionic liquid 1-ethyl-3-methylimidazolium dimethylphosphate

In present research the binary solutions containing ionic liquid (IL), 1-ethyl-3-methylimidazolium dimethylphosphate ([EMIM] [DMP]), are considered as new working pairs for absorption heat pumps or absorption refrigerators. The IL was synthesized in the lab and mixed with water, ethanol, or methanol. Experimental (vapor + liquid) equilibrium (VLE) of these binary systems was measured at different mole fractions ranging from 0.1 to 0.5 and was correlated by the NRTL equation within the average relative deviation of 2%, which means that the (vapor + liquid) equilibrium of these binary solutions containing ionic liquid can be predicted by traditional non-electrolyte solution model. Meanwhile these binary solutions are a negative deviation from Raoult’s law. Excess enthalpy of these binary systems was measured at the temperature of T = 298.15 K and at the pressure of 1 atm. The results indicate that the mixing processes of [EMIM] [DMP] with water, ethanol, or methanol are exothermal, which is a very important characteristic for working pairs used in absorption heat pumps or in absorption refrigerators.

Research highlights
► Ionic liquid (IL), 1-ethyl-3-methylimidazolium dimethylphosphate ([EMIM] [DMP]), was synthesized and mixed with water, ethanol, or methanol.
► Experimental (vapor+liquid) equilibrium of these binary systems was measured at different mole faction and were correlated by the NRTL equation.
► These binary solutions are a negative deviation from Raoult’s law.
► Excess enthalpy of these binary systems was measured at the temperature of 298.15 K and at the pressure of 1 atm.
► These characteristic make them possible to be new working pairs in absorption heat pumps or absorption refrigerators.