KINETICS AND MODELING OF CARBON-DIOXIDE ABSORPTION INTO AQUEOUS-SOLUTIONS OF N-METHYLDIETHANOLAMINE

A wetted-sphere absorber was used to acquire kinetic data for the aqueous phase reaction between CO2 and N-methyldiethanolamine (MDEA). Data were obtained over the temperature range of 293-342 K for partial pressures of CO2 near atmospheric and for 10-30 mass % MDEA. The data are consistent with a mechanism in which MDEA catalyzes the hydrolysis of CO2. Three different mathematical models which are based on Higbie's penetration theory were developed and used to estimate the forward rate coefficient of the MDEA-catalyzed hydrolysis of CO2 reaction. A comparison of the numerical results of the three models indicates that the effect of the reaction between hydroxide and CO2 is significant, especially when estimating the rate coefficient of the CO2/MDEA reaction for unloaded aqueous MDEA solutions. Neglecting the CO2/OH- reaction can result in large errors in the rate coefficient for the MDEA-catalyzed hydrolysis reaction, especially at the higher temperatures. The second-order rate coefficients of the MDEA-catalyzed hydrolysis reaction for 10 mass % MDEA, which were estimated according to the most general model, are approximated by the following Arrhenius equation: k(21)=2.91x10(7) exp (-4579/T).