Highly efficient and selective separation of ammonia by deep eutectic solvents through cooperative acid-base and strong hydrogen-bond interaction

Exploring absorbents showing low volatility, high efficiency and good reversibility for NH3 absorption is of great significance. In this work, a novel class of DESs with both weak acid site and strong hydrogen-bond donating site were designed by using imidazolium hydrogen chloride ([ImH]Cl) and glycerol (Gly) as the motifs. The densities, viscosities and thermal stabilities of DESs were measured first. Then, the solubility, reversibility and selectivity of DESs for NH3 absorption were investigated systematically. It is found that the absorption of NH3 in DESs is chemical type, and there is strong interaction existing between DESs and NH3. As a result, the NH3 solubilities of DESs are very attractive especially at low pressures, with the values of 12.934 mol/kg at 298.2 K and 101.3 kPa, and 4.450 mol/kg at 298.2 K and 10.0 kPa. The NH3 absorbed by DESs can be easily desorbed by heating and evacuating. Moreover, the absorption of N-2 and H-2 in DESs is negligible, and has little effect on the absorption of NH3. Finally, the underlying mechanism of NH3 absorption was examined by theoretical and spectroscopic technique. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study developed a novel class of deep eutectic solvents (DESs) with weak acid sites and strong hydrogen-bond donating sites for efficient and reversible NH3 absorption. NH3 absorption in DESs was found to be chemical in nature with strong interaction between NH3 and DESs, leading to attractive NH3 solubilities at low pressures. The absorption of NH3 in DESs is easy to reverse by heating and evacuating, with little interference from N-2 and H-2 absorption.