Assessment of a novel carbon capture and storage process by carbonic anhydrase treatment of flue gases

The huge emissions of greenhouse gases from fossil-fuelled power plants is emphasizing the need for efficient carbon capture and storage (CCS) technologies. With reference to operating plants, the post-combustion CO2 capture option is attractive as it implies minimal intervention on the existing plants. The most typical options are: amine-based absorption, pressure or thermal swing adsorption, membrane separation. These processes may turn out to be fairly expensive and result in major efficiency penalties. On the other hand, there has been growing attention on the possibility to sequester CO2 by water absorption and conversion into stable bi/carbonates. One drawback of this process is represented by the slow apparent kinetics. It appears that the rate enhancement may be pursued by enzymatic catalysis of carbonic anhydrase (CA), a broad group of ubiquitous metalloenzymes. The fixation of gaseous CO2 into carbonate ions is controlled by the hydration reaction. The captured carbon can be safely sequestered by precipitation of carbonates. Providing that a proper metal ion source is available to the biomimetic capture system, a mild mineral sequestration may occur. Sea water and/or brines are typical Ca++ sources available at industrial scale. A theoretical model has been proposed to analyse the performances of an innovative CA-based CCS process. The enzymatic absorption unit (EAU) is a three-phase system: the solid phase is the carrier with immobilised CA; the liquid phase, the aqueous stream bearing Ca++; the gas phase, the exhausted flue gas. The liquid phase is further processed in a Carbonate Recovery unit (CRU). The aims of the study are: i) the general assessment of the process mass and energy balances; ii) the analysis of the role of the immobilised CA specific activity and stability on process performance; iii) the optimization of operating conditions for both the EAU and the CRU. Results are directed to provide guidelines for process optimization, including the development of a protocol for the production of the industrial biocatalyst.