Ammonia Solubility, Density, and Viscosity of Choline Chloride–Dihydric Alcohol Deep Eutectic Solvents

In the present work, dihydric alcohols (including 1,4-butanediol, 2,3-butanediol, and 1,3-propanediol) were paired with choline chloride (ChCl) to form deep eutectic solvents (DESs) with the molar ratio of ChCl to dihydric alcohol fixed at 1:3 and 1:4. The solubility of NH3 in these DESs was systematically determined at 303.15, 313.15, 323.15, and 333.15 K under pressures up to 420.0 kPa using the isochoric saturation method and was correlated using the Krichevsky–Kasarnovsky (K–K) equation. The dissolution Gibbs free energy, enthalpy, and entropy changes of NH3 solvation were further calculated according to the temperature dependence of Henry’s constants. Based on the reported CO2 solubility data, the selectivities of NH3/CO2 in DESs used herein were calculated. The density and viscosity data of the DESs were also measured and fitted at a temperature range of 303.15–343.15 K. Overall, the dihydric alcohol-based DESs present quite promising NH3 absorption and separation performance, with a value of 3.0 mol NH3 per kg DES and an NH3/CO2 selectivity of 98 at 303.15 K and 100.0 kPa.