Performance And Mechanism Of CO₂ Absorption Catalyzed By Carbonic Anhydrase Immobilized In Zeolitic Imidazolate Frameworks

In recent years,the greenhouse effect has gradually become a global climate issue,and carbon reduction cannot be delayed.The introduction of carbonic anhydrase into an amine solution for CO₂ absorption is a novel idea for promoting carbon dioxide capture technology.Considering of the sensitivity of enzymes to the catalytic environment,they must be immobilized before it can be applied to the actual operation.We prepared a series of immobilized carbonic anhydrase based on variety of ZIFs by in-situ synthesis and employed them to promote the absorption of CO₂ into amine solvent.There were the major outcomes:（1）The as-synthesized immobilized enzyme based on diverse ZIFs supporters exhibited high enzyme loading and excellent catalytic ability.The enzyme loading of immobilized CA based on ZIF-8 achieved 24%,and the catalytic activity of immobilized CA based on ZIF-L reach 150%compared with the free counter.Meanwhile,the immobilized enzyme possessed great long-term stability and reusability compared with free CA.It retained 73%of its initial activity after deposited in 40 ^oC MDEA solution for 20 days,and 89%after 6 repetitive operations.The enhancement of CO₂ absorption into tertiary amine by immobilized CA was remarkable.The absorption rate could achieve 90%of that of MEA solution in same consentration.（2）The enzyme loading capacity and catalytic activity of immobilized CA prepared in different conditions were examined and the synthesis condition was optimized.The results showed that the enzyme adding time was crucial to the enzyme loading and catalytic activity.When the time of enzyme adding was far away from the strat of the reaction,the as-sythesised immobilized CA possessed a lower loading,a higher catalytic activity and a poorer stability.（3）The materials were characterized by several of methods such as N₂ sorption test,TGA,LSCM and XRD.The interaction of supporters and CA was analyzed and the influence of the interaction to the performance of immobilized was interpretd.The synergistic interaction between the imidazole group,Zn²⁺of ZIFs and CA enzyme facilitate the mass transfer.In addition,the moderate preparing condition make few change in the secondary conformation of CA so that a high activity was preserved.Futhermore,mechanism of CO₂ absorption into the tertiary amine promoted by CA/ZIF composites was proposed according to the analysis of the above relationship:1)CO₂gas-liquid mass transfer,2)CO₂ liquid-solid mass transfer,and 3)CO₂ hydration by the CA enzyme in CA/ZIF-L-1.The MDEA acts as the proton sinker to activate the CA enzyme for CO₂ hydration.