Kinetic characterization of carbonic anhydrase immobilized on magnetic nanoparticles as biocatalyst for CO2 capture

Carbon dioxide absorption into carbonate solutions promoted by the enzyme carbonic anhydrase (CA, E.C. 4.2.1.1) has been proposed as a potential technology for CO2 capture. The use of solid CA-based biocatalysts allows the enzyme recovery and reuse under continuous operating conditions typical of industrial applications. The present study regards the development and the kinetic characterization of a solid CAbased biocatalyst to be used in CO2 capture processes based on reactive absorption. A technical grade thermostable CA was immobilized by covalent bonding on aminated paramagnetic Fe3O4 nanoparticles via carbodiimide activation of the enzyme. The effective covalent binding of the enzyme on the support was verified in the alkaline carbonate solution used as solvent for CO2 absorption tests. The kinetics of the biocatalyst were assessed by means of CO2 absorption tests in a stirred cell reactor. The liquid solvents used in the CO2 absorption tests were 0.5 M Na2CO3/NaHCO3 buffer (pH 9.6) at 298 and 313o K and 10% wt/wt K2CO3 solutions at different carbonate conversion degrees (0-40%). The Danckwerts' theory for gas-liquid reactive absorption was applied to assess the intrinsic second order kinetic constant kcat/KM for the CO2 hydration reaction catalyzed by the immobilized CA. Results pointed out that kcat/KM ranged between 102 and 103m3·kg-1·s-1 and that it increased with the temperature and with the decrease of carbonate conversion degree.