The Enzymatic Capture Of CO₂and Its Transformation In Multi-enzyme System

Atmospheric "greenhouse effect" and the global warming is the biggestenvironmental problems facing humanity in the21st century. Elevated CO2has profoundinfluence on environment and society, and CO2is important industrial raw material, whichis widely used in food and chemical or other fields. This topic adopts the method ofenzyme catalysis for CO2conversion. It can not only alleviate “greenhouse effect”, toachieve targets of emission reduction, and CO2is converted into chemical products storedin form of carbon source. Carbonic anhydrase (CA) can accelerate hydration of CO2toHCO3-, and fixed in form of solid CaCO3,which is a very promising method of dealingwith CO2in atmosphere. But free CA is expensive, poor stability of enzyme activity, and itis difficult to recycle. This topic immobilized CA with hollow nanofibers study propertiesof free and immobilized enzyme also its role in transformation of CO2capture system, andfurther established multi-enzyme system that conversion of CO2into formic acid.Hollow nanofibers were produced by co-axial electrospinning, which polyurethanewere as external electrospinning solution, and95%glycerol as internal electrospinningsolution, then enzyme were in-situ encapsulated. As the process of immobilization doesnot involve the reaction of functional groups, the structure of enzyme will not change, andthe active center get good protection. As enzymes exist in free state, so whenimmobilizing enzymes using entrapping method, enzyme molecules could conductcascade reaction well, and almost does not exist influence of the mass transfer resistancein reaction process.One of the most promising biological sequestration technologies of CO2is theenzyme catalyzed CO2sequestration into solid CaCO3.The reaction conditions of CO2hydration by free carbonic anhydrase (CA) and in-situ encapsulation of enzymeimmobilized by hollow-nanofibers was investigated in this study. The effect ofimmobilized carbonic anhydrase on CO2hydration system was evaluated. The resultsshowed that the CA stability was improved significantly by immobilization. Catalyticefficiency of CO2is88%and57%for free and immobilized enzyme, respectively.Immobilized enzyme still retained50%activity after10cycles of use.CA and formate dehydrogenase (FDH) were immobilized in the same system byhollow nanofibers, and successfully established the multienzyme system which is used toconvert CO2into formic acid. The results showed that CA significantly promoted the generation of formic acid. In the same reaction time, amount of formate generated inmultienzyme system is2times more than that in single enzyme system. The stability ofthe enzyme has also been significantly enhanced, and the yield of conversion of CO2is7.3times that of free enzyme. we also found that the acidic conditions is conducive to theconversion of CO2.