A Steady-State Kinetic Investigation of Enzyme-Assisted Carbon Capture

Enzyme-assisted carbon capture is attracting massive interest, and absorbents composed of aqueous carbonate supplemented with carbonic anhydrase have proven particularly promising. Here, we study basic capture mechanisms using a novel approach grounded in comparative enzymology. We determined initial, steady-state capture rates in potassium carbonate under a range of conditions and observed a characteristic saturation behavior at high concentrations of either enzyme or CO2. These results could be rationalized by a modified Michaelis–Menten framework applied to a “reaction zone” near the liquid surface. Capture rates corresponded directly to enzyme reaction rates in the reaction zone as determined by KM and kcat, and this explained the observed saturation behavior. The kinetic data suggested a depth of the reaction zone of about 20 µm. This meant that equilibrium between CO2 and HCO3− was obtained within this shallow film and that enzymes deeper in the liquid had little or no influence on capture rates. This approach also allowed us to rationalize the effect of pH on enzyme-assisted capture rates. Overall, steady-state kinetics can be used in comparative and mechanistic analyses of enzyme-accelerated carbon capture. The approach is theoretically simple, requires limited experimental input, and offers key molecular insights.