Imidazole tailored deep eutectic solvents for CO2 capture enhanced by hydrogen bonds

Abstract

Deep eutectic solvents (DESs) have emerged as promising alternative candidates for CO₂ capture in recent years. In this work, several novel DESs were firstly prepared to enhance CO₂ absorption. Structural and physical properties of DESs were investigated, as well as their absorption performance of CO₂. A distinct depression in the melting point up to 80 K of DESs was observed compared with that of BMIMCl. The observed red shifts of the C₂H group in an imidazolium ring and its chemical shifts downfield in NMR spectra are indicative of a hydrogen bond interaction between BMIMCl and MEA. In particular, CO₂ uptake in MEA : ILs (4 : 1) at room temperature and atmospheric pressure is up to 21.4 wt%, which is higher than that of 30 wt% MEA (13%). A hydrogen bond related mechanism was proposed in which ILs act as a medium to improve CO₂ uptake through hydrogen bonds. Finally, the firstly reported overall heat of CO₂ absorption is slightly higher than that of 30 wt% MEA, implying that the hydrogen bonds of DESs contribute to the overall heat of CO₂ absorption. This study reveals that the heat of CO₂ absorption can be tailored by the proper molar ratio of MEA and ILs.