Kinetics of CO2 Absorption Into Aqueous Potassium Carbonate Solution Promoted by Carbonic Anhydrase Enzyme

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A novel Integrated Vacuum Carbonate Absorption Process (IVCAP) for post-combustion CO2 capture is being developed at the University of Illinois at Urbana-Champaign. A key technical aspect of this process is to employ a biocatalyst, carbonic anhydrase (CA) enzyme, to enhance the rates of CO2 absorption into the potassium carbonate (PC) solutions. This work investigates the kinetics, catalytic activity, and chemical and thermal stability of the CA enzyme to promote the CO2 absorption into PC solutions.

The rates of CO2 absorption into 20 wt% PC solutions containing various amounts of the CA enzyme have been measured in a stirred cell reactor under the pseudo-first-order conditions, and the values of the first-order reaction rate constant of the CA enzyme, ke, for enhancing the CO2 hydration were determined using classical theory of gas absorption. The results showed that the values of ke were between 9.0 and 15.0 L/mg∙s in the 20% PC solutions with carbonate conversion rate ranged between 10 and 50% at a temperature range of 25-50oC. The rates of CO2 absorption into 20 wt% PC solutions were promoted by 3~6 times using 300 mg/L CA enzyme at a temperature between 40 and 50oC.

The CA enzyme demonstrated good chemical stability to several flue gas impurities as evidenced by the fact that the increase of ionic strength with anions of Cl-, NO3-, and SO42- in the solution did not significantly impact the ke values. The long-term thermal stability study revealed that the CA enzyme maintained about 90% activity at 40oC over the 6 month period, whereas about 50% of the activity was lost at 50oC within two months.

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