Evaluation of intensified CO2 capture in packed-bed microreactors with immobilized carbonic anhydrase by combined theory and experiment

Abstract

For the first time, an intensified CO2 capture using human carbonic anhydrase II (hCA II) enzyme immobilized in a packed-bed microreactor (IE-PBMR) was proposed. hCA II enzyme was covalently immobilized on packing (polyethylene solid (S) particles) surface (priori amine-functionalized via polydopamine & polyethyleneimine co-deposition) through glutaraldehyde. Enzyme-mediated CO2 capture process was studied (i) experimentally at various operating conditions, hCA II loadings, using different buffers and buffer concentrations and (ii) theoretically via a 3-D model describing the two-phase flow (averaged continuity and momentum equations), mass transport in liquid (L) & gas (G), and diffusion–reaction in enzyme layer. IE-PBMR ensures an enhanced CO2 conversion due to increased interphase mass transfer across large interfacial areas, allowing for superior utilization of the high enzyme turnover number. Low enzyme loadings and buffers with (i) higher pKa2 constant (generation of higher CO2 hydration driving force) or (ii) higher concentration (acceleration of intermolecular proton-transfer stage of enzymatic hydration) favor CO2 capture, thus mitigating the impact of internal diffusion. High enzyme loadings can be better exploited by increasing the height of packed bed, but this involves a higher pressure drop. The performance of IE-PBMR is significantly superior to that of fixed-bed macroreactors and is amplified by increasing the liquid velocity. Overall, due to their ease of installation and operation, IE-PBMRs, integrated in flexible small modular units, are attractive for green CO2 capture, particularly for emissions from residential, commercial, agriculture, and transportation.