The main issue related to the deployment of the amine-based absorption process for CO capture from flue gas is its intensive energy penalty. Therefore, this study screened a novel biphasic solvent, comprising a primary amine e.g., triethylenetetramine (TETA) and a tertiary amine e.g., N, N-dimethylcyclohexylamine (DMCA), to reduce the energy consumption. The TETA-DMCA blend exhibited high cyclic capacity of CO absorption, favorable phase separation behavior, and low regeneration heat. Kinetic analysis showed that the gas- and liquid-side mass transfer resistances were comparable in the lean solution of TETA-DMCA at 40 °C, whereas the liquid-side mass transfer resistance became dominant in the rich solution. The rate of CO absorption into TETA-DMCA (4 M, 1:3) solution was comparable to 5 M benchmark monoethanolamine (MEA) solution. Based on a preliminary estimation, the regeneration heat with TETA-DMCA could be reduced by approximately 40% compared with that of MEA. C NMR analysis revealed that the CO absorption into TETA-DMCA was initiated by the reaction between CO and TETA via the zwitterion mechanism, and DMCA served as a CO sinker to regenerate TETA, resulting in the transfer of DMCA from the upper to lower phase. The proposed TETA-DMCA solvent may be a suitable candidate for CO capture.

Carbonic anhydrase (CA) enzyme-based absorption technology for CO 2 capture has been intensively investigated. The main issue related to this novel technology is the activity and stability of the CA enzyme under the typical flue gas conditions. To address this issue, CA enzymes were embedded into zeolitic imidazolate framework (ZIF-L) nanoparticles to synthesize a novel CA/ZIF-L-1 composite. The composite exhibited a superior apparent catalytic activity (1.5 times higher) for CO 2 absorption compared with their free counterparts, which was due to the synergistic enhancement of CO 2 adsorption by support ZIF-L and enzymatic catalysis. The analyses of Fourier transform infrared spectroscopy and circular dichroism revealed that the CA enzyme's secondary structure was not significantly varied during the CA/ZIF-L-1 preparation, resulting in a high enzyme activity retention. Moreover, the CA/ZIF-L-1 possessed a high thermal stability and reusability due to the structural rigidity and confinement of ZIF-L scaffolds. Compared with the free enzyme, its thermal stability was improved by approximately 100% at 40 °C. After six cycles of reuse, CA/ZIF-L-1 still retained a relative activity of 134%. Therefore, the CA/ZIF-L-1 can be a good candidate to promote the CO 2 capture in industrial application.

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In order to fulfill the application of carbonic anhydrase (CA) in the carbon dioxide capture process, immobilization technology will be used to enhance the stability of the enzyme. The structure of the support for the enzyme immobilization is important to determine the enzyme activity and stability. In this work, mesoporous molecular sieves with different dimensions and pore sizes were used as supports for the immobilization of CA. Characterization analysis indicated that the carrier material retained its integrity after enzyme immobilization. The half-life (t 1/2) of CA/KIT-6, CA/SBA-15, and CA/MCM-41 increased to 3.0, 2.8, and 2.0 times compared to the free CA enzyme. Additionally, the experimental results showed that when using SBA-15 with a two-dimensional structure and a large pore size as the carrier, the CA enzyme loading was high and retained 78% relative activity and 98% initial activity after 6 days at 40 °C. Comprehensively, CA/SBA-15 was more suitable for capturing CO2 in flue gas than CA/MCM-41 and CA/KIT-6.