Experimental Study and Modeling of Bubble Point of Aqueous Mixtures of Deep Eutectic Solvents Based on Dicarboxylic Acids and Choline Chloride

Assessment of deep eutectic solvents (DESs) as a new generation of green solvent for different applications requires sufficient knowledge about their physical, chemical, and thermodynamic properties. Because of the lack of bubble pressure data of aqueous solutions of DESs, the bubble pressure of two natural DESs, choline chloride–malic acid and choline chloride–malonic acid, as well as the bubble pressure of malic acid–water and malonic acid–water, was measured at various concentrations and at a temperature range from 303.2 to 343.2 K. According to the results, all studied systems exhibit a negative deviation from Raoult's law. The order of the negative deviation was malic acid > malonic acid > DES of choline chloride–malic acid > DES of choline chloride–malonic acid. The experimental bubble points were used for estimation of the water activity coefficient and consequently for estimation of the parameters of the nonrandom two-liquid (NRTL) and van Laar models. Then, the models were employed to estimate the bubble point of the studied systems. According to the results, the overall average absolute relative deviation of the NRTL and van Laar models were obtained to be 2.3% and 2.4%, respectively, which shows that the experimental data correlate well with the models' results.