Design of deep eutectic solvents with multiple-active-sites for HCl separation and storage

The exploiting of efficient, reversible and environmentally friendly hydrogen chloride (HCl) absorbent is of great significance for the recovery and high-value utilization of by-product HCl. Herein, we propose a new strategy to design deep eutectic solvents (DESs) with multiple-active-sites to effectively absorb HCl. Therefore, five new DESs were designed and prepared by pairing 1,3-dimethyl-2-imidazolidinone (DMI) with amide derivatives or LiCl. Among them, DMI + 1,3-dimethylurea (2:1) showed the unprecedented HCl capacity of 2.16 mol/mol at 303.2 K and 1 bar, surpassing that of water, DESs and ILs reported in literature. Spectroscopic characterization and quantum-chemical calculations showed that such high HCl capacity originates from multiple interaction sites between DESs and HCl. DMI + 1,3-dimethylurea (2:1) also exhibited the advantages of fast absorption of HCl, good recyclability, good selectivity and acceptable cost. A new reaction equilibrium thermodynamic model was developed to correlate HCl solubility data. The absorption rate of HCl in DESs was measured systematically for the first time. These DESs with multiple-active-sites offer improvements over commonly used absorbents, indicating the promise for industrial application in HCl separation and storage.