Phenol-Based Ternary Deep Eutectic Solvents for Highly Efficient and Reversible Absorption of NH3

In this work, a class of deep eutectic solvents (DESs) formulated by choline chloride (ChCl), phenol (PhOH), and ethylene glycol (EG) were designed and synthesized for NH3 capture. The effects of temperature, pressure, and DES composition on NH3 capacities were investigated systematically. By utilizing the weak acidity of PhOH, highly efficient and reversible absorption of NH3 was realized in PhOH-based ternary DESs. The absorption capacities of NH3 in prepared DESs can reach as high as 9.619 mol/kg (0.162 g/g) at 298.2 K and 101.3 kPa, ranking one of the best reported to date. The captured NH3 could be easily stripped out at elevated temperature and reduced pressure, with negligible loss in NH3 capacities after 10 adsorption-desorption cycles. The thermodynamic properties of the NH3 absorption process, such as reaction equilibrium constants, Henry's constants, and absorption enthalpies, were also calculated with the assistance of thermodynamic modeling. It is found that the NH3 absorption process exhibits a moderate enthalpy change of -36.91 kJ/mol, indicating the potentially energy-efficient feature of a subsequent desorption process. The results obtained herein suggest that PhOH-based ternary DESs are promising media for the capture of NH3 from industrial gases.