Carbonic Anhydrase Promotes the Absorption Rate of CO2 in PostCombustion Processes

The rate of carbon dioxide (CO2) absorption by monoethanol amine (MEA), diethanol amine (DEA), N-methyl-2,2'-iminodiethanol (MDEA), and 2-amino-2-methyl 1-propanol (AMP) solutions was found to be enhanced by the addition of bovine carbonic anhydrase (CA), has been investigated using a vapor-liquid equilibrium (VLE) device. The enthalpy (-Delta H-abs) of CO, absorption and the absorption capacities of aqueous amines were measured in the presence and/or absence of CA enzyme via differential reaction calorimeter (DRC). The reaction temperature (Delta T) under adiabatic conditions was determined based on the DRC analysis. Bicarbonate and carbamate species formation mechanisms were elucidated by H-1 and C-13 NMR spectral analysis. The overall CO2 absorption rate (flux) and rate constant (k(app)) followed the order MEA > DEA > AMP > MDEA in the absence or presence of CA. Hydration of CO, by MDEA in the presence of CA directly produced bicarbonate, whereas AMP produced unstable carbamate intermediate, then underwent hydrolytic reaction and converted to bicarbonate. The MDEA > AMP > DEA > MEA reverse ordering of the enhanced CO2 flux and k(app) in the presence of CA was due to bicarbonate formation by the tertiary and sterically hindered amines. Thus, CA increased the rate of CO2 absorption by MDEA by a factor of 3 relative to the rate of absorption by MDEA alone. The thermal effects suggested that CA yielded a higher activity at 40 degrees C.