Investigation of protic NH4SCN-based deep eutectic solvents as highly efficient and reversible NH3 absorbents

Ammonia (NH3) is not only a harmful gas to environmental problem, but also a fundamental raw material in chemical industry. The effective separation and recovery of NH3 from exhaust gas at low cost still remains a challenge for a long time. In this study, a new strategy to construct protic deep eutectic solvents (DESs) by paring NH4SCN as hydrogen-bond acceptor with various hydrogen-bond donors [glycerol (G), ethylene glycol (EG), urea (U), acetamide (AT), and caprolactam (CL)] was proposed for efficient and reversible absorption of NH3. Results showed that all the DESs possessed exceptional NH3 absorption capacity and high NH3/CO2 selectivity. At 303 K and 0.10 MPa, the absorption capacity of NH3 in NH4SCN-glycerol (2:3) is as high as 0.223 g NH3 per g DES, which is much higher than all reported functional ILs and DESs up to date. The NH3 saturated DES was easily regenerated and recycled 25 times with persistent absorption performance. The influences of DES composition, temperature, NH3 partial pressure on NH3 absorption performance were also explored in detail. The absorption mechanism was analyzed using NMR spectroscopy and quantum calculation. These protic NH4SCN-based DESs presented as promising absorbents for NH3 because of their high absorption capacity and good reversibility.