Experimental Research On Catalytic Hydration And Mineralization Of CO₂ By Immobilized Carbonic Anhydrase

Carbon dioxide is the main component of greenhouse gas and the sharp increase of CO2 emission has caused escalate of greenhouse effect and problems such as global warming, desertification, increase in extreme weather, climate change and so on. Mineralization of CO2 is one of the most effective means of CO2 capture, and mineralization in the presence of carbonic anhydrase in the bio-catalyst-catalytic hydration of CO2 which effectively promote the mineralization reactions.Carbonic anhydrase was immobilized by using two-component polyurethane, and properties of the immobilized CA were investigated. After immobilization, there is partial loss of enzyme activity, and the activity recovery is 54.85%, but the storage stability has been greatly improved, relative activity of immobilized CA after 30 days is 85.80%. The heat-resistant and acid-resistant ability of immobilized enzyme have increased and the thermal stability, p H stability have also enhanced.CO2 catalytic absorption experiment has been taken in vertical reactor and absorption characteristics was studied by comparing variation of parameters such as solution p H, void fraction and decarburization rate caused by gas flow and enzyme amount, catalytic properties of free and immobilized enzyme have also been studied and compared. Absorption reaction has almost completed after 240 s, the presence of CA improves hydration rate of CO2, thus, the decline rate and the drop of solution p H increases, and decarburization rate has also raised. With the increase of gas flow and enzyme amount, the effect is more obviously, and decarburization rate can still keep a high level when gas flow increases under higher enzyme amount. In comparison with immobilized CA, free CA has better catalytic effect of CO2 hydration due to the higher activity of free enzyme and uniform distribution in reaction system.Variation of solution p H and Ca CO3 precipitation amount with enzyme amount, buffer p H and reaction temperature in the CO2 mineralization with free and immobilized enzyme was studied. CO2 mineralization nearly completes in 60 s, the presence of CA is conductive to Ca CO3 precipitation, the rate and amount of precipitation has improved, in the experiment with free enzyme, the effect of CA is more obviously. The increase of precipitation reduces when the enzyme amount increases. Buffer solution helps maintaining the p H of reaction system, which is conducive to CO2 hydration catalyzed by free CA, and the buffer with higher p H is more conducive to Ca CO3 precipitation.The amount of Ca CO3 precipitation and solution p H are lower in experiments with free CA at different temperatures. Solution p H decline rate and Ca CO3 precipitation reduce when reaction temperature increases. Compared with T=0℃, when T=30℃, solution p H after mineralization and its decline rate is almost the same, and Ca CO3 precipitation has reduced. When T=50℃, solution p H after mineralization raises, Ca CO3 precipitation drops significantly and is just around 50% of precipitation under lower temperature condition.