Synthesis and behaviour of hybrid polymer-silica membranes made by sol gel process with adsorbed carbonic anhydrase enzyme, in the capture of CO2

Thin nylon-SiO2 membranes made by sol–gel SiO2 coating of a nylon weaving were impregnated in a second step with an aqueous carbonic anhydrase solution. The biocatalytic hybrid membranes obtained were applied to the capture of CO2 from a N2–CO2 gas mixture containing 10% CO2, under a total pressure ≈ 1 atm. The CO2 permeance of these membranes was at least similar to those previously reported for liquid membranes. When impregnated with a 0.2 mg mL−1 enzyme solution in a pH ≈ 8 NaHCO3 buffer, the permeance of a nylon-SiO2 membrane was multiplied by a factor ≈ 3 when the buffer molarity was increased from 0.1 to 1 M. By comparison, this permeance only increased by a factor ≈ 1.3 without any enzyme in the same buffers. The permeance was also higher with the enzyme than without it: respectively ≈3.7 10−8 and ≈4.7 10−9 mol $$ {\text{m}}_{\text{membrane}}^{{ ^{- 2} }} $$ s−1 Pa−1 with and without enzyme, in a 1 M NaHCO3 buffer. A maximum permeance was observed for an enzyme concentration of ≈0.2 mg mL−1, possibly due to a competition between the H+ ions produced from CO2,aq by the enzyme and the H+ captured by the buffer. Besides, when the SiO2–CO2 contact was enhanced by the membrane architecture, SiO2 improved the CO2 permeance. The influence of an in situ CaCO3 deposit was also investigated and it improved the CO2 permeance when no enzyme was added.