CO2 capture and utilization by enzymatic reactive absorption: available technologies and perspectives

Enzymatic reactive absorption has been investigated as novel environmental friendly technology for post-combustion CO2 capture. The process is based on CO2 absorption in aqueous solutions, the absorption rate is enhanced by the catalytic action of free or immobilized carbonic anhydrase (CA) (E.C. 4.2.1.1), that is the ubiquitous enzyme devoted to CO2 hydration catalysis in Nature. About 10-5 M CA is able to speed up CO2 hydration to bicarbonate so that first order rate constant results between 1 and 103 s-1 thus, close to the rate of reaction between CO2 and amines. In this study we report about three recently developed techniques for the use of CA. In particular, our studies focused on the development of CA covalently attached to paramagnetic nanoparticles, on CA made insoluble in the form of Cross-Linked Enzyme Aggregates, and on CA available as enzyme entrapped in the debris of periplasmic membrane from bacteria cell lysate. These forms of solid biocatalysts were characterized and compared in terms of their apparent kinetics so that a preliminary assessment of their performances in real CO2 capture units (absorption column) was done. Finally, we analyzed some perspectives on two alternative routes for CO2 utilization processes based on the exploitation of bicarbonate ions form enzymatic reactive CO2 absorption. First, bicarbonate ions can be supplemented to microalgae cultivation to overcome the issue of gaseous substrates supply to photo-bioreactors. The second alternative is based on the coupling of enzymatic capture enhanced by CA with carboxylation reactions in an enzyme cascade process.