Experimental Study On Catalytic Absorption Of CO₂ With The Immobilized Carbonic Anhydrase

At present,the greenhouse effect caused by CO₂ has gradually become a hot issue in the world.Coal fired power plant is the main emission source of CO₂.The biomimetic method with the carbonic anhydrase is one of the effective methods to capture CO₂.It has become a research hotspot in the field of CO₂ capture and sequestration,because it has many advantages,for example high efficiency,no pollution and so on.The mian contents of this paper are:the preparation and characterization of the carrier,the study of the enzyme immobilization,and the experiment of CO₂ catalytic absorption with the immobilized carbonic anhydrase.The special mangnetic material was selected in this paper as the carrier for the enzyme immobilization.The carboxyl Fe₃O₄ was prepared by the coprecipitation method.The characterization analysis of the carrier and the immobilized enzyme showed that the specific surface area of the carrier was 100.89 m2/g;the content of organic matter was 11.24%;Fourier transform infrared spectra indicated that the oleic acid on the surface of the carrier was oxidized into the azelaic acid.All characterization results showed the structure of the carrier did not change significantly after immobilization.In this paper,the immobilization test was carried out by single factor method,and the optimum immobilization conditions,such as the pH value of Tris-HCl,the immobilization temperature,the immobilization time,shaking speed,enzyme dose,crosslinker concentration,and crosslinking time,were 8.5,30 ?,4 h,250 rpm,1 mL enzyme solution?0.1 mg/mL?/30 mg carrier,0.4%,1 h,respectively.Under the optimum conditions,the activity of the immobilized carbonic anhydrase was 1672.5 units/mg,and the maximum recovery of the immobilized enzyme was up to 66.90%.Besided,the immobilized enzyme has better stability.On this basis,the performance of CO₂ catalytic absorption with the immobilized carbonic anhydrase was investigated through the packed tower reactor and the bubbling tower in the paper.In the packed tower reaction,the operating conditions of CO₂ catalytic absorption with immobilized enzyme was investigated.The the optimum operating conditions,such as the ratio of liquid to gas,the gas flow rate,enzyme dosage of the unit tower volume,and absorption liquid temperature,were 28 L/m3,25.5 cm/min,600 mg/L,and 35 ?,respectively.The CO₂ removal efficiency could still reach more than 30%,after catalytic absorption with the immobilized enzyme for 5 h.Besides,the existence of SO2 was not conducive for CO₂ catalytic absorption.In the bubbling tower in the paper,the effect of the emzyme dosage of the unit absorption liquid volume and the residence time on the pH value of the solution and the pH value of the end of the absorption reaction were investigated.When at the pH value of the end of the absorption reaction,the concentration of CO₂ at the outlet of gas was measured.The results showed that it was more conductive to catalyze and absorb CO₂,when the residence time decreased,and the more the enzyme dosage of the unit volume of the absorption liquid was,and the pH value of absorption liquid decreased more quickly.When the amout of enzyme was less,the amount of enzyme had a great influence on the pH value of the end of the absorption reaction.With the high amount of the enzyme,the residence time had a great influence on the pH value of the end of the absorption reaction.The concentration of CO₂ was lower and the absorption effect was better with the increase of enzyme dosage and the extending of residence time.