Experimental Evaluation of CO2 Absorption Promoted by a Biocatalyst in a Vacuum Carbonate Absorption Process for Post-Combustion CO2 Capture

The current mono-ethanol-amine (MEA)-based absorption is considered as the best available option for the capture of CO₂ from post-combustion flue gases. However, the cost for CO₂ removal with MEA is expensive, mainly due to the intensive energy consumption in the process. A U.S. patent-pending process, Integrated Vacuum Carbonate Absorption Process (IVCAP), has been proposed to reduce the energy use during absorption. This process employs potassium carbonate as solvent. Due to the lower heat of absorption in the carbonate solution, the stripping of CO₂ can be operated at a lower pressure and temperature than MEA-based absorption processes. The combination of lower stripping pressure and temperature enables the use of a low-quality steam from the power plant steam cycle, thus lowering the energy usage and the capture cost.

The chemical reaction rate of the CO₂ with the carbonate solutions, however, is lower by up to several magnitudes than the primary amine solvents. This technical issue must be addressed before the technology is ready for scale up and potential industrial applications. In this presentation, the results from an ongoing study which employs a biological catalyst -carbonic anhydrase enzyme- to promote the rate of CO₂ absorption in the potassium carbonate solution is presented. The carbonic anhydrase is the most effective catalyst known to date for the CO₂ hydration reaction. Experimental data from the parametric tests will be presented to show the impact of concentration of the solvent, dosage of the enzyme_, CO₂ loading, temperature, pH, ion strength, and presence of impurities on the activity of the enzyme catalyst.

Process simulations are performed to analyze the technical performance of the IVCAP and the sizing of major equipment using the software package Chemcad. The kinetic data obtained from the parametric tests are incorporated into the simulations of the absorber and stripper. A preliminary techno-economic analysis, based on the results of process simulations, is being performed and will be presented to compare the energy use and the cost between the IVCAP and the MEA process. The initial results showed that the CO₂ avoidance cost of the IVCAP process is 25-40% less than the MEA process.