Kinetics, Thermodynamics, and Mechanism of a Novel Biphasic Solvent for CO2 Capture from Flue Gas.

The main issue related to the deployment of the amine-based absorption process for CO2 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 CO2 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 CO2 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. 13C NMR analysis revealed that the CO2 absorption into TETA-DMCA was initiated by the reaction between CO2 and TETA via the zwitterion mechanism, and DMCA served as a CO2 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 CO2 capture.

Carbonic Anhydrase Enzyme-MOFs Composite with a Superior Catalytic Performance to Promote CO2 Absorption into Tertiary Amine Solution.

Carbonic anhydrase (CA) enzyme-based absorption technology for CO2 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 CO2 absorption compared with their free counterparts, which was due to the synergistic enhancement of CO2 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 CO2 capture in industrial application.