Rational design of efficient deep eutectic solvents for HCl absorption through their competitive H-bonding interactions

Abstract

The design of an efficient absorbent is the premise for recovery and resource utilization of hydrogen chloride (HCl) from its industrial tail gases. Herein, a series of 1-butyl-3-methylimidazolium chloride (BmimCl) based-deep eutectic solvents (DESs) were designed and the solubility behavior for HCl was studied in terms of their structure, basicity, free volume, intermolecular interaction energy, and absorption enthalpy. The relationship between the interaction energy and the phase change in the HCl dissolution process was explored in detail. BmimCl-TAA (thioacetamide) (1 : 1) shows high reversible solubility due to its high free volume, suitable absorption enthalpy, and closer H-bonding (HB) interactions between BmimCl and TAA or HCl. The dissolution mechanism of HCl and the dynamic evolution of the HB network were verified by FT-IR and NMR spectra and quantum chemical calculations. The results show that it is the competitive HB interaction that promotes the dissolution of HCl, reduces the absorption enthalpy, and renders a reversible absorption. Compared with BmimCl, the absorption enthalpy of HCl in BmimCl-TAA (1 : 1) is reduced by 25% and the reversible solubility increased 150%. The reversible solubility of HCl in BmimCl-TAA (1 : 1) is as high as 0.51 g g⁻¹ (1.76 mol mol⁻¹) at 303.15 K and 101.3 kPa, and the absorbent can be regenerated facilely by heating under reduced pressure. This work provides new insights into the rational design of DES for efficient and reversible absorption of HCl and other polar gases.