Thermodynamic study on CO2 separation by diamine functionalized aqueous deep eutectic solvents

CO 2 separation is critically important for mitigating CO 2 emissions, while traditional solvents used in the available absorption technologies suffer from high energy demand and low chemical stability. Deep eutectic solvents (DESs) have gained attention as a promising class of solvents, but their study and performance are still insufficient. To develop DES-based solvents for CO 2 capture, in this work, based on one promising DES [ImCl][EDA] identified in our previous work, a systematic study of its aqueous solutions was conducted from the properties (density, viscosity) to absorption capacity, regeneration, and thermal stability, covering experimental measurements and theoretical modeling. In the study, the effects of temperatures (288.15 to 328.15 K), pressures (up to 1.8 MPa), and water contents (60–80 wt%) were considered, and the studied gases include pure CO 2 , N 2 , and CH 4 as well as two simulated gas mixtures (simulated flue gas, 75 v% N 2 + 25 v% CO 2 ; simulated biogas, 60 v% CH 4 + 40 v% CO 2 ). The results indicate that the CO 2 absorption capacity of aqueous [ImCl][EDA] reaches 3.43 mol-CO 2 /kg-solvent, which is 21.6 % higher than that of aqueous MEA (2.82 mol-CO 2 /kg-solvent), its selectivity for CO 2 over N 2 is up to 842 and that for CO 2 over CH 4 is up to 601, and the viscosity of the CO 2 -saturated [ImCl][EDA] solution remains below 5 mPa·s. Further, recyclability tests demonstrated its excellent regeneration performance, and TGA analysis confirmed the thermal stability of the DES. The theoretical model was used to represent the determined gas solubilities reliably. This study highlights the potential of aqueous [ImCl][EDA] and provides theoretical and experimental data to support its industrial CO 2 capture applications.