Absorptive separation of HCl gas by choline chloride-based deep eutectic solvents

Abstract Effective separation of HCl from industrial tail gas is of great importance for its reclaim and high value utilization. For this, absorption behavior of HCl gas in three choline chloride (ChCl)-based deep eutectic solvents (DESs), i.e. ChCl-urea, ChCl-glycerol (Gly), and ChCl-glycolic acid (GA), was studied, and the stability and absorption mechanism were analyzed by 1H NMR, 13C NMR, TG and FT-IR spectra, respectively. The gas solubility of HCl in ChCl-urea, ChCl-Gly and ChCl-GA is 0.457, 0.255, and 0.214 g-HCl/g-DESs, respectively at 303.15 K and 101.3 kPa, being consistent with their decreasing basicity. The H-bonding and pseudo chemical interaction between HCl and the basic groups with lone-pair electron (–NH2, C=O, Cl-, and –OH) of DESs is responsible for the high solubility of HCl. The absorption isotherm of HCl in ChCl-Urea follows the Langmuir equation with some irreversible desorption amount due to the pseudo chemical nature. In contrast, the absorption of HCl in ChCl-Gly and ChCl-GA is physical and reversible. Viscosity of the DESs was reduced and the density increased notably with HCl absorption. ChCl-Gly is more viable for adsorption of HCl-bearing gas considering its high thermal stability, lower viscosity, and reversible absorption/desorption characteristics.