Optimization of CO2 2 capturing performance of amino acid-based deep eutectic solvent phase change absorbents: Introducing DBN into HBA

Phase change absorbents are quite competitive in reducing energy consumption for CO2 2 capture. In this work, we investigated two distinct CO2 2 phase change absorbents consisting of deep eutectic solvents (DESs), specifically amino acid-ethanolamine/n-propanol/water (AA-MEA/NPA/water) and [1,5-diazabicyclo[4.3.0]non-5-ene] [amino acid]-ethanolamine/n-propanol/water ([DBNH][AA]-MEA/NPA/water). Here, AA and [DBNH][AA] functioned as the hydrogen bond acceptor (HBA) of DESs, while MEA served as the hydrogen bond donor (HBD). Our experimental results revealed that the L-proline-ethanolamine/n-propanol/water (L-Pro-MEA/NPA/water) presented promising CO2 2 absorption and regeneration performance, with the absorption loading reaching 2.34 mol CO2/mol 2 /mol DES. Remarkably, the introduction of DBN enhanced the performance of [DBNH][L-Pro]-MEA/ NPA/water through a proton masking effect, resulting in an absorbent loading of 3.11 mol CO2/mol 2 /mol DES and a regeneration efficiency of 93.7 % after five desorption cycles under optimal conditions. Utilizing 13 C NMR analysis and DFT calculations, we proposed a mechanism for CO2 2 capture. CO2 2 reacts with MEA and L-Pro anion to form two carbamates, where in the amino N in MEA exhibits greater CO2 2 reactivity compared to the N atom in L-Pro anion. These carbamates can further undergo hydrolysis to form HCO3- 3 - and CO32-. 3 2- . In addition, by calculating the molecular polarity index (MPI), the free energy of solvation (Delta Gsol) Delta G sol ) and ion pair reduced density gradient (RDG) of the reaction products, we identified the polarity and solubility differences as the primary factors contributing to the phase change.