| The carbonic anhydrase(CA) can effectively catalyze the reversible hydration reaction of CO2 to HCO3-, which is one of the highest catalytic rates of all known CO2 hydration enzymes. Applying CA enzyme to CO2 catalytic absorption can effectively accelerate CO2 capture from fossil fuel and reduce the discharge of CO2, which is the promising technology of CO2 capture. The technology of immobilization not only can make the separation of enzyme easily, but also make it conductive to promote the stability of enzyme. Besides, the immobilized enzyme has a certain shape and mechanical strength, which can be loading in the reactor, making the continuous production and process control convenience. The biomimetic CO2 capture through CA provides a new way for CO2 sequestration.The carbonic anhydrase was embedded with sodium alginate and cross-linked with glutaraldehyde. The enzyme activity is tested by eletrometric and colorimetric determination. The enzymatic properties were compared between free enzyme and immobilized CA. It was studied such as the enzyme activity recovery, the optimum p H and temperature, p H stability and heat stability, the effect of metal ions on immobilized CA. The effect of temperature and enzyme loading on the CO2 catalytic absorption was studied in the reactor. The operation stability and micro-structure of immobilized CA was researched. The characteristics of CO2 catalytic absorption in the vertical reactor were investigated. The effect of gas flow and enzyme loading on characteristics of catalytic absorption of CO2 from the simulated flue gas were studied.The results show that the immobilized CA retains 56.3% of its original activity. The optimum p H of immobilized CA is 7, and the optimum temperature is 30 ℃. The p H value of immobilized CA is stable at the range of p H=5.0 ~ 12.0. The immobilization enhances space structure of enzyme, which improves the p H stability and thermal stability of immobilized CA. Different metal ions from fuel gas have different effect on the stability of immobilized CA. Pb2+ and Hg+ are the inhibitor preparation of immobilized CA, Ca2+ and Mn2+are the weak enzyme inhibitor, Zn2+ and Al3+ have no effect on the enzyme activity. Co2+,Cu2+ and Fe3+ can enhance the activity of immobilized CA.The immobilized CA shows significant effect on CO2 catalytic absorption at T=30 ℃. The 80.2% of catalytic reaction accounts for 10% of the whole reaction time, and the amount of CO2 catalytic absorption is 4.2×103 times than the blank experiment. The surface of immobilized CA appears a large number of irregular shapes of holes, and space structure becomes rich through scanning electron microscope(SEM) observation. Furthermore, the immobilized CA enhances storage stability and durability. The relative enzyme activity of immobilized CA can be improved after reforming in calcium chloride solution for 1 h.The characteristics of CO2 catalytic absorption in the vertical reactor were investigated. The results show that immobilized CA speeds up the CO2 absorption. The gas flow is the main factor affecting CO2 absorption with the less enzyme loading, and the enzyme loading becomes major factor while the gas flow is improving. The enzyme loading has a decrease influence on the p H of terminal reaction with the flow gas greater improvement, and the gas flow also has a decrease influence on it when the enzyme loading is increasing. The efficiency of CO2 absorption declines with the increase of the gas flow, while it rises with the increase of the enzyme loading. The CO2 catalytic absorption by immobilized CA is remarkable with the gas flow of 650 m L·min-1 and the enzyme loading of 1 mg. Furthermore, the immobilized CA still keeps 54.4% relative enzyme activity after 6 times of continuous operation in vertical reactor, the immobilization of CA enhances operation stability. |
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