CO₂ Absorption by Ethanolamine-Based Ternary Deep Eutectic Solvents

Ternary deep eutectic solvents (DES) comprising choline chloride (ChCl), glycerol (Gly) and ethanolamine (MEA) with different molar ratios were prepared. The CO₂ absorption ability of the ternary DES was investigated at room temperature and under atmospheric pressure. Among four ternary DES samples prepared with different molar ratios, a ChCl-Gly-MEA (1:1:10) ternary DES was found to absorb the most CO₂ at a capacity of 0.18 g CO₂ (DES per gram) at 298 K and 101.3 kPa. The experimental results showed that the CO₂ absorption capacity of ChCl-Gly-MEA (1:1:10) ternary DES increased with an increase in gas flow rate and a decrease in water content. The gas flow rate improved the mass transfer efficiency of CO₂ in the ternary DES system, and shortened the time required for CO₂ absorption to reach equilibrium. However, the addition of water could weaken the hydrogen bonding interaction among the three components in the DES system. Results from Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy indicated that CO₂ interacted with the amino groups in DES to form carbamates. The absorption of CO₂ by ChCl-Gly-MEA underwent both physical and chemical absorption, and the chemical absorption was significantly enhanced by the addition of MEA. A recovery experiment showed that no obvious loss in CO₂ absorption was detected after five absorption/desorption cycles with an absorption rate of 97.3% being retained.