Effective ammonia separation by non-chloride deep eutectic solvents composed of dihydroxybenzoic acids and ethylene glycol through multiple-site interaction

Abstract

The effective separation of ammonia (NH3) has important implication for the conversion improvement and pollution control during the synthesis of NH3. In the present work, a novel kind of non-chloride deep eutectic solvents (DESs) were constructed from dihydroxybenzoic acids (DHBAs) and ethylene glycol (EG). The DHBA + EG DESs exhibit several weak acidic sites and hydrogen-bond sites, thus were proposed for NH3 separation. We found that the amounts of NH3 absorbed by DHBA + EG DESs are quite impressive, particularly at reduced pressures. The capacities can reach 5.64 and 11.69 mol/kg at 0.1 and 1 bar respectively, when the temperature of 298.2 K is considered. Besides, after five absorption–desorption cycles, the DHBA + EG DESs can preserve the excellent NH3 absorption performance. The DHAB + EG DESs can also selectively absorb NH3 from N2 and H2 in the mixed gas. The NH3 absorption mechanism of DHBA + EG DESs was further deeply illustrated by spectroscopic techniques and theoretical calculations.