Biomimetic CCS process: kinetic assessment of carbonic anhydrase

In the framework of research on post-combustion CCS processes, the will to develop eco-friendly processes has recently inspired biomimetic solutions based on the adoption of Carbonic Anhydrase (CA) as industrial biocatalyst. This ubiquitous enzyme may be adopted to increase CO2 absorption rate in aqueous solutions as an alternative to conventional additives (e.g. alkanolamines), being it the natural catalyst of the CO2 hydration reaction. The present contribution concerns the development of a stirred cell apparatus aimed at the characterization of CO2 absorption rate in the presence of CA. To validate the experimental procedure, tests were carried out with CA from bovine erythrocytes (BCA) as reference enzyme. The experimental apparatus consisted of a 2•10-3 m3 jacketed reactor equipped with differential pressure transducers and data acquisition unit. The reactor was operated batch-wise with respect to both liquid and gas phases. Stirrers located in the reactor headspace and in the bottom-liquid region provided even mixing of both liquid and gas phases. Pure CO2 was pumped into the head section of the reactor and the absorption rate into the aqueous solutions was assessed by working out time-resolved measurements of gas pressure. Data were worked out to assess the effects of CA activity on the absorption rate in terms of mass transfer enhancement factor. The CA characterization was carried out under operating conditions reported in the literature for the assessment of first order kinetic parameter - namely for enzyme kinetics the ratio kcat/KM - verifying the occurrence of fast first order reversible reaction. The results were in agreement with data reported in literature. The apparatus and the procedure adopted may be considered for further investigations on different CA forms consistent with the adoption in capture units.