Effect of pKa on the kinetics of carbon dioxide absorption in aqueous alkanolamine solutions containing carbonic anhydrase at 298Â K

The absorption of carbon dioxide in various aqueous alkanolamine solutions have been studied with and without carbonic anhydrase respectively in a stirred cell reactor at 298 K. The examined alkanolamines were: N,N-diethylethanolamine (DEMEA), N,N-dimethylethanolamine (DMMEA), monoethanolamine (MEA), triethanolamine (TEA) and tri-isopropanolamine (TIPA). This work confirms that the CO2 hydration is catalysed by the enzyme in presence of alkanolamines. The differences in reaction rate between the tested alkanolamines are attributed to the enzyme regeneration step in the mechanism - that is, an acid base reaction. A Langmuir-Hinshelwood-like equation has been postulated to describe the observed overall rate constant of the enzymatic reaction as a function of the enzyme concentration. The two kinetic constants in the postulated equation both depend exponentially on the pKa value of the alkanolamine present in the solution.