Intensified CO₂ Capture in Structured Microreactors with Carbonic Anhydrase Enzyme Immobilized on Open-Cell Foam Packings

To mitigate climate change, it is of utmost importance to develop innovative, energy-efficient technologies to capture CO2. In this context, this study is envisioned as an exploration of opportunities by proposing an intensified CO2 capture process in a novel immobilized enzyme structured packed-bed microreactor (IE-SPBμR) with human carbonic anhydrase II (hCA II) enzyme attached on open-cell foam packings, which constitutes a promising alternative for mass-transfer-limited reactions. Enzyme-mediated CO2 uptake and fluid dynamics in IE-SPBμR were analyzed for different microreactor operating conditions and enzyme loadings, and using different buffer systems, via a 3D two-phase flow model coupled with governing equations of mass transport in gas/liquid phases and diffusion/reaction within the enzymatic catalyst layer. The results showed that IE-SPBμR generates a remarkable intensification of CO2 uptake at low hCA II enzyme loadings due to enhanced mass transfer over large interfacial areas that allow greater use of the large hCA II enzyme turnover while, at the same time, maintaining low pressure losses. The performance of IE-SPBμR is significantly enhanced by increasing liquid flow rate, decreasing pore diameter of foam packing, operating with buffers with low dissociation constant of protonated form and widening packed bed height while preserving pressure drop at low levels. An important advantage is that the pressure drop in IE-SPBμR with selected open-cell foam packings is 1–2 orders of magnitude lower, compared to packed-bed microreactors of similar specific surface area, thus allowing the process volume to be easily scaled-up by increasing the height of packed bed. The significant process intensification highlights the attractiveness of IE-SPBμRs, connected in modular units, especially for capturing CO2 from dispersed sources.