Vapor–Liquid Phase Equilibria and Excess Thermal Properties of Binary Mixtures of Ethylsulfate-Based Ionic Liquids with Water: New Experimental Data, Correlations, and Predictions

Abstract

This work reports the measurements of the vapor pressure, excess enthalpy of mixing, and molar heat capacity for selected {ionic liquid + water} binary systems. The studied ionic liquids are 1-ethyl-1-methylpiperidinium ethylsulfate, 1-ethyl-1-methylpyrrolidinium ethylsulfate, and 1-ethyl-1-methylmorpholinium ethylsulfate. The isothermal vapor–liquid phase equilibria have been measured by an ebulliometric method within temperature range from 338.15 to 368.15 K and pressure up to the vapor pressure of pure water. Excess enthalpy was measured with an isothermal titration calorimeter at temperature 298.15 K. Heat capacities have been determined within the temperature range from 288.15 to 383.15 K. The influence of temperature and composition as well as the structure of cation of the studied ionic liquids on the measured properties was assessed. The Redlich–Kister correlation was used in order to reduce the huge number of data points collected. Finally, thermodynamic modeling with molecular-based PC-SAFT equation of state was performed in order to check predictive capabilities of this model as well as to provide some physical insight into mutual ionic liquid–water interactions.