Deep removal of dichloromethane using ionic liquids: Thermodynamic and molecular insights

In this work, the efficient capture of dichloromethane (DCM) with ionic liquids (ILs) was proposed and systematically investigated. The carboxylic acid-based anion and quaternary phosphonium cation were screened out, and on this basis the designed tetrabutylphosphonium hexanoate ([P4444][C5COO]) and tetrabutylammonium hexanoate ([N4444][C5COO]) ILs were finally synthesized. The results demonstrate that [P4444][C5COO] exhibits the optimal absorption performance (1400 mg center dot g � 1 at 30 degrees C and 0.3 bar). Notably, the Henry's law constant for DCM in [P4444][C5COO] (3.02 Pa center dot m3 center dot mol- 1 at 25 degrees C) is the lowest among all solvents documented in the literature. The microscopic mechanism was explored by 1H NMR spectra, quantum chemical (QC) calculations and molecular dynamics (MD) simulations. The results suggest that anion plays a dominant role, while weak cation-anion interaction and large free volume of cations are conducive to the absorption of DCM. The proposed IL was considered as a promising alternative absorbent to achieve high absorption capacity, suitable physicochemical properties and excellent recyclability.