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 NH 3 capture. The effects of temperature, pressure, and DES composition on NH 3 capacities were investigated systematically. By utilizing the weak acidity of PhOH, highly efficient and reversible absorption of NH 3 was realized in PhOH-based ternary DESs. The absorption capacities of NH 3 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 NH 3 could be easily stripped out at elevated temperature and reduced pressure, with negligible loss in NH 3 capacities after 10 adsorption−desorption cycles. The thermodynamic properties of the NH 3 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 NH 3 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 NH 3 from industrial gases.

In this work, three azole-based ternary deep eutectic solvents (DESs) were designed for highly efficient absorption of NH3 by utilizing the weak acidity of azoles. Specifically, the DESs are composed of choline chloride (ChCl); a model azole compound such as imidazole (ImZ), triazole (TrZ), or tetrazole (TetrZ); and ethylene glycol (EG). The effects of liquid composition, pressure, and temperature on NH3 solubilities in DESs were examined systematically. It is found that ChCl + TetrZ + EG displays obvious chemical behavior for NH3 absorption owing to the relatively stronger acidity of TetrZ, and it exhibits the highest NH3 capacities among the three DESs. The NH3 capacities of ChCl + TetrZ + EG are superior to most absorbents/adsorbents previously reported, especially when compared at low pressures. Recycling experiments demonstrate that the chemical absorption of NH3 in ChCl + TetrZ + EG is reversible, with only partial loss in NH3 capacities during absorption–desorption cycles. Furthermore, theoretical calculations were performed to gain molecular insights into the absorption of NH3 in azole-based DESs.

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