Absorption of Carbon Dioxide Using Ethanolamine-Based Deep Eutectic Solvents

The development of a new, green CO2 absorbent with high energy utilization and low solvent loss can replace CO2 capture by ethanolamine solution, which is currently a necessary and important issue. This work is devoted to the design and synthesis of DESs based on ethanolamine and the absorption of CO2, focusing on the systematic study of the effects of CO2 absorption and the effect of water on the deep eutectic solvents (DESs) of ChCl/MEA, TMAC/MEA, and TEAC/MEA (MEA = ethanolamine, TMAC = tetramethylammonium chloride, and TEAC = tetraethylammonium chloride). A series of DESs comprise various hydrogen-bonding donor–acceptor pairs as CO2-capturing solvents. The main factors that influence the absorption process, such as rotational speed, flow rate, temperature, absorption time, molar ratio, and water content on the absorption of CO2, are examined. Simultaneously, the influence on the DESs after absorption was analyzed, and the absorption mechanism was systematically studied. Furthermore, the use of three-component alkaline DESs (TMAC/MEA/MDEA) (MDEA = methyl diethanolamine) and the three components of TMAC/MEA/LiCl, TMAC/MEA/ZnCl2, and TMAC/MEA/NH4Cl were investigated by adding pure water to remove CO2 performance. The TMAC/MEA/LiCl solvent reaches a maximum absorption of 36.81 wt % at 50 °C, and for TMAC/MEA/LiCl + 10% H2O system, the absorption of CO2 decreases with increasing temperature. The TMAC/MEA/LiCl + 10% H2O system has the highest absorption at 30 °C and reaches 37.31 wt %. NMR was applied to investigate the absorption mechanisms. The hydrogen-bonding and electrostatic interactions were the main driving force for this specifically high CO2 absorption process.