Physicochemical and thermodynamic study on aqueous solutions of dicyanamide – based ionic liquids

•The [BMPIP][DCA], or [BMPYR][DCA] and its aqueous mixtures have been studied.•The density, viscosity, VLE, HE, Cp have been determined.•The NRTL and Redlich–Kister equations have been used to correlate the experimental data.

In this work, the {1-butyl-1-methylpiperidinium dicyanamide, [BMPIP][DCA], or 1-butyl-1-methylpyrrolidinium dicyanamide, [BMPYR][DCA] (1) + water (2)} binary systems were studied as an alternative working pair for the absorption heat pump cycle. The thermodynamic properties of the tested systems including: density, viscosity and (vapor + liquid) phase equilibria were measured as a function of temperature and composition at ambient pressure. The density and dynamic viscosity have been measured at temperature range from (298.15 to 343.15) K. From experimental data, excess molar volumes, VmE and dynamic viscosity deviations, Δη were calculated and correlated using Redlich–Kister equation. The isothermal (vapor + liquid) phase equilibria have been measured by an ebulliometric method within temperature range from (328.15 to 368.15) K and pressure range from (0 to 100) kPa. The excess enthalpies for the tested systems were determined at T = 298.15 K using isothermal titration calorimeter. NRTL equation was used to correlate (vapor + liquid) phase equilibria and excess enthalpy. The influence of the cation structure on the presented physicochemical and thermodynamic properties were discussed.