(494c) Absorption of CO2 Into Aqueous Potassium Carbonate Solution Promoted by Carbonic Anhydrase Enzyme for Post-Combustion CO2 Capture

A novel Integrated Vacuum Carbonate Absorption Process
(IVCAP) for post-combustion CO₂ capture is being developed by the
Advanced Energy Technology Initiative of the Institute of Natural Resource Sustainability at the University of Illinois at Urbana-Champaign. The solvent
used in the process is potassium
carbonate (PC). A unique feature of this process is its ability to use either waste or low quality
steam from a power plant's low pressure turbine for CO₂ desorption.
As a result, electricity loss due to steam extraction is significantly lower
than that of mono-ethanol-amine (MEA) processes. However, a key technical issue
for the IVCAP is the slow absorption rate of CO₂ into the PC
solution. In this study, the carbonic
anhydrase (CA) enzyme was experimentally
evaluated as a biocatalyst to promote the rate of CO₂ absorption
into PC solutions.

The activity of the CA enzyme and its long-term
chemical and thermal stability were evaluated using a stirred cell reactor
under various conditions of temperature, enzyme dosage level, concentration of
PC solution, initial CO₂ loading in the solution, CO₂
partial pressure, and concentrations of various contaminants. It was found that
the rate of CO₂ absorption was promoted by 3-15 times at a dosage
level of 300 mg/L CA between 25°C and 50°C. The CA enzyme exhibited a stable activity over a two-month
period. Activity tests over a longer time are in progress. The effect of
typical impurities in a flue gas on the enzyme activity was simulated by
exposing the CA enzyme to a solution containing SO₄^2- (0.1-0.9M),
NO₃^2- (0.05-0.2M) and Cl^- (0.3-0.7M), either individually
or in a mixture. It was revealed that the enzyme lost only less than 11% of its
initially activity.  

Process engineering data collected to date indicate
that the CA enzyme is a promising catalyst for promoting the rate of CO₂
absorption into the PC solution. Ongoing research is focusing on testing
several CA enzymes obtained from different sources, developing a CA
immobilization method, and evaluating the potential application of the IVCAP
for simultaneous removal of SO₂ and capture of CO₂ from
coal combustion flue gases.