Molar heat capacities of choline chloride-based deep eutectic solvents and their binary mixtures with water

In this study, the molar heat capacities, CP, of three choline chloride-based deep eutectic solvents (DESs); Reline, Ethaline and Glyceline, and their binary mixtures with water were determined. Using a heat flow differential scanning calorimeter, the heat capacities were measured at standard pressure from (303.2 to 353.2) K and over the complete range of composition. Results showed that the molar heat capacity increased with increasing temperature and, for the binary systems, with increasing DES concentration. The temperature-dependence of the pure DESs were successfully represented by a second-order empirical correlation with an AAD% of 0.05. The excess molar heat capacities, image, of the binary mixtures also determined and found generally negative over the whole composition range while exhibiting negative temperature dependence. The image values were fitted to a Redlich–Kister type equation to correlate them to the temperature and DES mole fraction and the molar heat capacities of the binary mixtures were predicted. The applied models successfully correlated the experimental CP data as functions of both temperature and composition.