(154c) Immobilization of Carbonic Anhydrase On Ordered Mesoporous Alumina for Use in Biocatalytic Carbon Dioxide Capture

Carbon dioxide is considered to be a major greenhouse gas involved in global climate change, and the CO₂ concentration in the atmosphere has increased from its pre-industrial value of 280 ppmv to 455 ppmv [1]. This increased CO₂ concentration could, in turn, cause the average temperature at the Earth's surface to increase 1.8-4.0 K above the 1990 levels by the end of this century [2]. This warming is anticipated to cause sea level rise, increased intensity and frequency of extreme weather events, ice shelf disruption, and changes in rainfall patterns. Thus, much research is focused on developing methods to reduce CO₂ production and release into the atmosphere. CO₂ production can be reduced by using less carbon-intensive energy sources (wind, solar, and nuclear energy) and by increasing  the efficiency of the energy production and use [3]. However, these strategies are not sufficient to meet CO₂ reduction targets.

Since combustion of carbon fuels will likely be a primary source of energy for the foreseeable future, it is critical to capture and sequester the resultant CO₂  [3, 4]. Capturing CO₂ from flue gas using absorption processes involves CO₂ dissolution in the aqueous phase, hydration, dissociation to form bicarbonate, and finally formation of carbonate; the hydration step is often rate-controlling. Fortunately, a catalyst for the rapid reversible hydration of CO₂ exists in biological systems: carbonic anhydrase (CA) [5-11]. This enzyme is so highly adapted to the hydration of CO₂ that reaction rates are almost diffusion limited [12].

CA functions by activating hydroxyl ions formed through ligation to a zinc atom bound within the enzyme [13]. The enzyme further holds CO₂ in the active site close to the activated hydroxyl group, while preventing water from gaining access to the hydroxyl group. The enzyme thus creates an extremely basic microenvironment that allows for the rapid formation of carbonate ions to occur without altering the pH of the bulk solution.

The broad objective of the research reported in this presentation to develop a biocatalytic membrane for the capture CO₂ from combustion flue gas; the membrane consists of an inert matrix in which carbonic anhydrase (CA) is immobilized. Specifically, previously presented work demonstrating the temperature tolerance, pH tolerance, and storage stability of CA adsorbed on ordered mesoporous alumina (OMPA) is extended to amine-functionalized alumina.  The implications for the performance of a biocatalytic membrane incorporating CA are also explored.

References

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