| Global warming has become a serious challenge to human survival and socialdevelopment. The key response to global climate change is reducing greenhouse gasemission, especially carbon dioxide (CO2). Carbonic anhydrase (CA), currently, is akind of efficient catalysts for the reversible reaction of CO2hydration. Application ofcarbonic anhydrase in the field of CCS (carbon capture and storage) will makeabsorption process highly efficient, low energy consumption and no secondarypollution. However there are still some problems need to be solved, including singleuse of CA, instability of enzyme activity. Immobilization of carbonic anhydrase is abreakthrough to solve the problems. This paper mainly discussed how CAimmobilized on surface carboxyl-functioned Fe3O4magnetic microspheres (SCMM)and CO2hydration absorption catalyzed by the immobilized CA and free CA.The preparation of SCMM as the carrier of immobilization included three mainsteps: the preparation of ferroferric oxide (Fe3O4) by co-precipitation method, thensurface modification with oleic acid and last surface modification by potassiumpermanganate (KMnO4) oxidation. The carboxyl content of SCMM surface wasdetermined about3.409mmol/g by the conductivity method; the diameter of SCMMwas about10nm by transmission electron microscopy (TEM); the Fe3O4content ofSCMM was measured about90.4%by thermal gravimetric analysis (TGA); besides,both the specific saturation magnetization (of about35emu/g) and thesuper-paramagnetic property of SCMM.were proved by vibrating samplemagnetometer (VSM).CA enzyme molecules combined with carrier through adsorption and covalentbinding mode, and the activity recovery rate reached69.2%. FTIR testing proved thatthe covalent bonds between the carrier and the enzyme molecule were the amidebonds (–CO–NH–). XRD analysis showed that the crystal structure of theimmobilized CA (CA–SCMM) and their carrier was mainly of Fe3O4; which withoutbeing oxidized by KMnO4, and the diameter of SCMM remained unchanged afterimmobilization. And both the specific saturation magnetization of CA–SCMM (about 34emu/g) and the super-paramagnetic property were proved by VSM. Results ofp-NPA esterase enzymatic properties’ study revealed that CA–SCMM owned largerrange of the optimum temperature and pH than free CA, and the enzyme owned morestable molecular structure and vitality than free CA.A gas-liquid reactor was designed and produced for investigating the impact ofenzyme on absorption of CO2hydration. The gas concentration of inner hermeticspace, except for water vapor pressure, was determined in real time by measuringpressure, temperature, relative humidity in the reactor. The device can be usednormally for a period of at least12hours, with temperature not higher than60oC andair pressure not more than120kPa. What is more, the device showed high accuracyof0.5%, and excellent instrument stability (variation of less than0.2%).Effect of temperature on CO2absorption of enzyme catalytic hydration wasemphatically investigated in this paper. The effect of temperature on mass transfer ofCO2absorption process had the following four key points:(1) the solubility of CO2,(2) mass transfer from gas to liquid,(3) mass diffusion in liquid and (4) mass transferfrom liquid to immobilized enzyme or carrier. In addition, temperature can alsosignificantly affect enzyme activity and chemical reaction rate. CO2absorptionprocess could be divided into the linear absorption stage, the curve stage and theequilibrium stage. Fitting analysis of absorption process showed that the data of CO2concentration changed by nine polynomial relations over time, with multiplecorrelation coefficient (R2) not less than0.99987. When temperature remainedunchanged, whether the catalyst was free or immobilized enzyme, the absorptioncapacities of the enzyme groups were equaled to the control groups; the absorptionrate of enzyme groups was faster than those of the control groups. When temperaturechanged, the optimum temperatures for capacities of CO2absorption by theimmobilized CA and free CA absorbents were35oC and28oC, respectively; while theoptimum temperatures for both immobilized CA and free CA catalyzing CO2hydration were28oC. |
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