Enhanced enzyme-based CO2 capture in countercurrent packed-bed column reactors

Abstract

An enhanced CO2 hydration process with human carbonic anhydrase II (hCA II) enzyme immobilized on packing surface and micro-particles dispersed in the liquid phase was proposed. This innovative hybrid enzymatic process was simulated in a countercurrent packed-bed column reactor via an unsteady-state, isothermal, 3-D model including continuity, momentum and species (including the biocatalytic micro-particles) balance equations in the liquid and gas phases, filtration equation describing the accumulation of biocatalytic micro-particles in packed bed, chemical reaction and diffusion in hCA II enzyme washcoat and liquid film. In the hybrid enhanced immobilized enzyme CO2 capture system, hCA II enzyme supported on the surface of micro-particles works as a free solution-phase enzyme, which instantaneously catalyzes CO2 hydration reaction and upgrades significantly CO2 conversion, particularly in the region where the enzymatic process with immobilized hCA II enzyme on the packing surface is strongly limited by the diffusion. The impact of hCA II enzyme immobilized on the micro-particles surface is more important when the foremost amount of hCA II enzyme is immobilized on the packing via larger washcoat layers with enhanced mass transfer resistance, at larger feed buffer concentration and lower thermodynamic dissociation constant of the protonated acid form of buffer. Enhanced CO2 hydration process provide a reasonable CO2 conversion at a much lower liquid velocity and permits to significantly downgrade the height of the packed bed. These immobilized enzyme CO2 capture systems intend to maximize the mass transfer in packed-bed column reactors to expand the degree of utilization of the large hydration turnover of hCA II enzyme.