281919 Biocatalytic Membranes for Carbon Dioxide Capture From Flue Gas
Absorptive capture of CO2 from flue gas includes a number of steps: dissolution in the aqueous phase, hydration, dissociation to form bicarbonate, and finally formation of carbonate. The rate-controlling step in this mechanism is usually the hydration of CO2; if a viable means to accelerate the hydration of CO2 could be found, it should be feasible to fix rapidly large quantities of CO2 into solution. Fortunately, a catalyst for the rapid and reversible hydration of CO2 exists in biological systems: carbonic anhydrase (CA) [1-4]. Recent studies have confirmed that the hydration of CO2can be improved using CA [5-7].
This paper presents preliminary results investigating the possibility of using a biocatalytic membrane incorporating CA to capture CO2. Poly(vinylidene fluoride) (PVDF) was used as a membrane material due to its high resistance to harsh environments, both acidic and basic conditions, its high thermal and UV stabilities, and its reasonable cost [8-13]. PVDF membranes were cast using wet phase inversion ; casting parameters were changed to modify the hydrophobicity of the membrane to permit use in biocatalytic CO2 capture. Bovine carbonic anhydrase (BCA) was physisorbed on the PVDF membranes and the effects of pH, temperature, substrate concentration, and enzyme loading on enzyme activity were studied. The stability of the enzyme was also studied. Measurement of enzyme activity using CO2 as the substrate is difficult due to the high reaction rate, so CA activity was measured using hydrolysis of p-nitrophenal as a model reaction. Immobilization improved the reactivity and stability of the immobilized enzyme. PVDF is a promising candidate for carbonic anhydrase immobilization for carbon dioxide capture using a biocatalytic membrane system.
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