Hydrophobic Functional Deep Eutectic Solvents Used for Efficient and Reversible Capture of CO₂

CO₂ emission from flue gas is an important issue threatening human survival. Deep eutectic solvents (DESs), which have many unique properties, have been studied for CO₂ capture. However, water can be absorbed by DESs during the absorption of CO₂, which may increase the energy cost during the desorption of CO₂. In this work, a new kind of hydrophobic functional DES formed by polyamine hydrochloride and thymol was synthesized and used for CO₂ capture. It had been found that these DESs could efficiently capture CO₂ even at low partial pressures. The CO₂ capacity of [TEPA]Cl-thymol (n _[TEPA]Cl/n _thymol = 1:3) was high up to 1.355 mol CO₂/mol DES at 40 °C and 101.3 kPa. Interestingly, these DESs were still hydrophobic after saturated with CO₂. The CO₂ absorption capacity increased with a decrease of temperature and an increase of CO₂ partial pressure. Regeneration results showed that no obvious loss in the capacity could be found after five absorption/desorption cycles of these DESs. The Fourier transform infrared (FT-IR) spectra indicated that CO₂ could interact with amino in the DESs by the formation of carboxylate. Moreover, the equilibrium constant and Henry's law constant in chemical absorption and physical absorption were studied.