Intensified CO2 capture in wall-coated microreactors with immobilized carbonic anhydrase: Experimental and modeling

Abstract

An intensified enzymatic CO2 capture process in a wall-coated enzyme-immobilized microreactor (WCEI_MR) was investigated experimentally and numerically under diverse flow conditions, at different human carbonic anhydrase II (hCA II) enzyme and buffer concentrations, and using different buffers. The motivation for using this type of microreactor for the CO2 capture process is to enhance the absorption rate by improving the flow and mass transfer through Taylor gas–liquid flow to efficiently accommodate the reduced time scales of CO2 absorption associated with the CA enzyme. hCA II enzyme was covalently immobilized on the internal surface of experimental microreactor (priori amine-functionalized via polydopamine & polyethyleneimine co-deposition) through glutaraldehyde. An unsteady-state two-scale model involving volume-averaged continuity and momentum balance equations, mass transport/reaction in bulk liquid & gas, and diffusion/enzymatic reaction equations in immobilized-enzyme layer was developed to simulate the wall-coated enzyme-loaded microreactor. Gas-liquid two phase Taylor flow in wall-coated microreactor generates an intensified gas–liquid/liquid–solid mass transfer which, coupled with the large surface area and small axial dispersion and backmixing, enhances the utilization of the enormous hCA II enzyme turnover number and ensures an enhanced enzyme-mediated CO2 absorption process at low pressure drop. WCEI_MR favors low enzyme concentrations, buffers with higher pKa2 constant that generates higher driving force for CO2 hydration or higher buffer concentration that improves enzymatic activity and the intermolecular proton-transfer step that stimulate the absorption process, all of which mitigate the impact of resistance to mass transfer. These findings suggest that WCEI_MR has a high potential for CO2 absorption and, when connected in flexible small-scale modular parallel systems, could represent a promising approach for large-scale green CO2 capture.