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With the catalytic induction of ethylene glycol (EG), anhydrous N,N-dimethylethanolamine (DMEA) shows CO 2 absorption performance via chemical binding and physical storage under normal pressure. Among the absorbents, pure DMEA and EG can hardly absorb CO 2 directly, but when the zwitterionic alkylcarbonates are formed between CO 2 and DMEA-EG, which can be characterized by 13 C NMR and FTIR spectroscopy, the absorption rate of CO 2 is improved. With the increase in the CO 2 loading as the mass fraction of EG in DMEA−EG, 80 wt % EG captures up to 0.72 mol/mol at 293 K and 101 kPa via chemical binding and physical storage. The amount that is chemically bound and physically stored is directly dependent on temperature; within the range of 293−323 K, an absorption− regeneration cycle can be formed in a closed vessel because the zwitterion DMEA−EG−CO 2 is unstable at higher temperatures. In other words, DMEA−EG−CO 2 can be easily regenerated upon appropriate depressurization or heating. The corresponding thermodynamic calculations prove that the regenerative energy of DMEA−EG−CO 2 is −27.33 kJ/mol, far less than that of other absorbent systems.

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Amino acid ionic liquids (AAILs) exhibit prominent merits for CO2 capture including biocompatibility and good stability, but they still suffer from several demerits, such as high viscosity and low molecular utilization. Therefore, it is critical to construct proper systems that can address these problems to enhance CO2 absorption of AAILs. In this work, three types of AAIL absorbent systems, DMEE (2-[2-(dimethylamino) ethoxy] ethanol)–AAIL, H2O–AAIL, and EG (ethylene glycol)–AAIL, are prepared with six AAILs that have different amino acids. The absorption performance of these absorbents is characterized to investigate the reinforcing effects of the additives on the absorption properties of AAILs. With temperatures ranging from 293 to 313 K, the CO2 capture studies on the binary systems reveal that AAILs present better absorption efficiency when their concentrations are 40 or 50 wt %. Based on the zwitterion reaction mechanism model and a thermodynamic model, the interactions of AAILs with H2O, DMEE, and EG systems for absorbing CO2 are discussed, respectively. The results obtained in this work indicate that AAIL–DMEE systems are promising candidates for CO2 capture since the interaction between AAILs and DMEE increases the capacity of AAILs and promotes kinetics.

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