(506e) 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.