CO2 capture by membrane-based absorption Enhancement of mass transfer using carbonic anhydrase

The influence of anthropogenic (i.e. human-induced) greenhouse gas emissions on climate change is now evident. Capturing CO2 in plant fumes is one way to avoid these emissions. Due to the lack of reuse applications and, by extension, economic benefits, this technology is struggling to develop worldwide. This paper focuses on the first two steps of a new process to capture CO2 to produce sodium bicarbonate. This process has been developed by the CO2LIFE project and a patent has been filed on December 3, 2020. The CO2 is captured by chemical absorption in a membrane contactor. The solvent used is a sodium carbonate solution catalysed by an enzyme, the carbonic anhydrase. This step has been studied using an experimental setup with a solvent in a closed-loop circuit. For enzyme concentrations between 0mg/L and 100mg/L, the maximum overall mass transfer coefficient varies between 0.0019 and 0.0032 m/min. The optimum concentration of carbonic anhydrase retained is 30mg/L with a maximum mass transfer coefficient of 0.0030 m/min. The enzyme is then recovered by ultrafiltration of the used solvent. It can then be reused while the rest of the solvent is crystallized to produce sodium bicarbonate. A maximum transmembrane flux of 0.0034 m^3/m^2*s has been obtained for a minimum filtration time of 21 minutes. The percentage of carbonic anhydrase recovered varies from 45 to 82%. Carbonic anhydrase reuse cycles were finally studied. These showed a decrease in the mass transfer coefficient compared to a solution with a similar concentration of fresh enzyme.