Solubilities of ammonia in choline chloride plus urea at (298.2-353.2) K and (0-300) kPa

The solubilities of ammonia (NH3) in deep eutectic solvents (DESs) comprising of choline chloride (ChCl) and urea at the temperature ranging from (298.2 to 353.2) K and pressure ranging from (0 to 300.0) kPa were determined by a volumetric method. The molar ratios of ChCl to urea in selected DESs were 1:1.5, 1:2.0 and 1:2.5. It is found that the solubility of NH3 increases with the increase of pressure, but decreases with the increase of temperature. In addition, the solubilities of NH3 in ChCl + urea (1:2.0) are slightly higher than those in ChCl + urea (1:1.5) and ChCl + urea (1:2.5) at 313.2 K, while the difference in NH3 solubilities of ChCl + urea mixtures is negligible at 323.2-353.2 K. By fitting the experimental data with Henry's law equation, the Henry's law constants of NH3 in ChCl + urea mixtures were obtained. According to the relationship between Henry's law constant and temperature, the thermodynamic properties of NH3 absorption in ChCl + urea mixtures such as Gibbs free energy changes, enthalpy changes and entropy changes were also calculated. (C) 2018 Elsevier Ltd.