Mass Transfer-Reaction Modeling of CO₂ Capture Mediated by Immobilized Carbonic Anhydrase Enzyme on Multiscale Supporting Structures

Immobilized carbonic anhydrase (CA) enzyme enhances CO₂ absorption in potassium carbonate (PC) solutions, offering an attractive alternative to amine-based processes for postcombustion carbon capture. In this work, the cross-scale models of mass transfer coupled with absorption reactions were developed to evaluate the structural impacts of different enzyme immobilization supporting materials, including nonporous nanoparticle carriers (nano scale), porous microparticle carriers (micro scale), and fixed packing structures (macro scale), on the rate enhancement effect of the immobilized CA. Increasing enzyme activity was demonstrated to be an effective approach to promoting the CO₂ absorption rate; however, there was an upper limit due to the limitation of CO₂ diffusion in the liquid phase, either adjacent to the gas-liquid interface or the liquid-solid interface. The size of particle carriers is another critical factor affecting the CO₂ absorption rate. Only nanoscale particle carriers could directly enter the region within the liquid film of mass transfer, thus providing effective enzymatic enhancement. When the particle size was reduced to below 0.35 μm, the PC promoted with the immobilized CA outperformed the benchmark monoethanolamine solution. The solid-side mass transfer resistance became dominant as the particle size decreased. Modeling results also showed that using stagnant packing materials in a fixed bed as a supporting structure for CA immobilization would be impractical for accelerating CO₂ absorption.