Effective absorption of dichloromethane using deep eutectic solvents

Abstract

Chlorinated volatile organic compounds (VOCs), of which dichloromethane (DCM) has become one of the main components because of its extensive use and strong volatility, are recognized as extremely hazardous and refractory pollutants in the atmosphere. The efficient treatment of DCM is of great significance to the protection of environment and human health. In this work, the strategy of DCM capture with deep eutectic solvents (DESs) with different hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) was proposed and systematically investigated. The experimental results show that tetrabutylphosphonium chloride: levulinic acid ([P₄₄₄₄][Cl]-LEV) presents the most excellent DCM absorption capacity among all DESs studied and considerable capacity in [P₄₄₄₄][Cl]-LEV (1:2) with 899 mg DCM/g DES (5.58 mol DCM/mol DES) at 30 °C and DCM partial pressure of 0.3 bar can be achieved. The microscopic absorption mechanism is explored by ¹HNMR and FT-IR spectra as well as quantum chemistry calculations, indicating that the absorption is a physical process. The interaction energy analysis suggests that the greater the interaction energy between DES and DCM, the greater the saturated absorption capacity of DCM. The hydrogen bond (HB) contributes most to the weak interaction between DCM and HBA/HBD, and both HBA and HBD play an important role in the absorption of DCM.

Keywords: Absorption; Deep eutectic solvents; Dichloromethane; Microscopic mechanisms; Quantum chemistry calculations.