The resilience of carbonic anhydrase enzyme for membrane-based carbon capture applications

A microbial carbonic anhydrase was immobilized onto the surface of hollow fiber membranes to enhance the absorption rate of carbon dioxide into an aqueous 30 wt% potassium carbonate solvent at pH 10-12. The performance of the immobilized enzyme was investigated over long time frames to determine the suitability of this approach for post-combustion carbon capture. The immobilized enzyme was able to maintain activity for up to 80 days at 25 °C even when initially exposed to pH 12, however lost activity rapidly when exposed to such high pH at 50 °C and subsequently was completely deactivated within 4 days. The effect of sulfur dioxide and nitric oxide that are present in post-combustion flue gas streams was investigated by contacting enzyme immobilized onto flat planar membrane coupons directly with the dry gases and with solutions containing the anions associated with the gases, namely sulfate, sulfite, nitrate and nitrite. The immobilized enzyme maintained at least 80% of its activity even in the presence of 200 mM of these anions or 500 ppm of the dry gases. Our findings indicate that the enzyme is not significantly affected by these toxic gases or their associated anions. Rather, the combination of high pH and ionic strength of the solvent at a high absorption temperature causes a reduction in the enzyme activity and affects the performance of the absorption process.