Kinetics study of carbon dioxide absorption into aqueous solutions containing N-methyldiethanolamine + diethanolamine

Kinetics of the absorption of CO2 into N-methyldiethanolamine (MDEA) + diethanolamine (DEA) + water were investigated at 30, 35, and 40 °C using a wetted wall column apparatus. Eight systems of which 1.0 and 1.5 kmol/m3 MDEA mixed with various DEA concentrations (0.1, 0.2, 0.3, and 0.4) kmol/m3 were studied. Densities and viscosities of eight blended amine systems were measured. The solubilities and diffusivities of N2O in the studied amine systems were also measured. The N2O analogy was applied to estimate the solubilities and diffusivities of CO2 in the investigated amine systems. Based on the pseudo first-order for the CO2 absorption, the overall pseudo first-order reaction rate constants were determined from the measured kinetic data. The addition of small amounts of DEA to MDEA results in a significant enhancement of CO2 absorption rates. A hybrid reaction rate model, a zwitterion mechanism for DEA and a first-order reaction for MDEA was used to model the kinetic data. The model satisfactory represented the CO2 absorption rates in MDEA + DEA aqueous systems.