Understanding the side chain effect on regulation of CO2 capture by amino acid-based deep eutectic solvents

CO2 capture from post-combustion is essential for reducing CO2 emission and further turning waste CO2 into marketable industrial and commercial products. Herein, in this study, the effect of side chain on the CO2 absorption by deep eutectic solvents (DES) based on amino acid (AA) and monoethanolamine (MEA) was examined. The presence of functional group in AAs leads to an increase in the DES viscosity and a reduction in the reaction rate of DESs with CO2, further resulting in a decrease in the CO2 absorption in the order of –OH < –SH < –COOH < –CONH2. Moreover, the effect of the number of alkyl group on the activation energy barrier is associated with the functional group types. Experimental and DFT results reveal that in the initial absorption stage the CO2 absorption is mainly mediated by the reaction rate of DES with CO2, while with the absorption time increasing, the mass transfer rate becomes a predominant role due to a significant elevation in the viscosity caused by the carbamate formation. This study paves a way for DES development for CO2 capture.