Carbonic Anhydrase Promotes the Absorption Rate of CO₂ in Post-Combustion Processes

Abstract

The rate of carbon dioxide (CO₂) absorption by monoethanol amine (MEA), diethanol amine (DEA), <i>N</i>-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 (−Δ<i>H</i>_abs) of CO₂ 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 (Δ<i>T</i>) under adiabatic conditions was determined based on the DRC analysis. Bicarbonate and carbamate species formation mechanisms were elucidated by ¹H and ¹³C NMR spectral analysis. The overall CO₂ absorption rate (flux) and rate constant (<i>k</i>_app) followed the order MEA > DEA > AMP > MDEA in the absence or presence of CA. Hydration of CO₂ 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 <i>k</i>_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 °C