Efficient Absorption of CO₂ by Protic-Ionic-Liquid Based Deep Eutectic Solvents

Carbon capture, utilization, and storage (CCUS) are among the key technologies to achieve large-scale carbon emission reduction globally. Deep eutectic solvents (DESs) are considered as designable solvents, which has attracted intensive attention for CO₂ capture. Here, a series of binary DESs are synthesized through one-step mixing with the starting materials of protic ionic liquid (PIL) and amine. The eutectic behavior was investigated by measuring the melting point of PILs and amine. The saturated vapor of these DESs and industrial MDEA solution were measured and compared. These DESs are investigated to have high absorption capacity (0.1 g ⋅ g^-1 at 1.0 bar and 25 °C), superior apparent absorption rate constant (0.381 min^-1 vs 0.012 min^-1 of 70 wt.% MDEA), moderate interaction with CO₂ (the enthalpy change is as low as -34.8 kJ ⋅ mol^-1). The absorption mechanism is also investigated by NMR analysis. Eight absorption/desorption regeneration experiments are carried out to show their reversibility. Considering the advantages, including convenience of synthesis, large absorption capacity, fast absorption rate, and moderate interaction energy as well as good regeneration, these DESs are believed to be as potential CO₂ absorbent in practical applications.