The reaction kinetics of the absorption Of CO2 into aqueous solutions of piperazine (PZ) and into mixed aqueous solutions of 2-amino-2-methyl-1-propanol (AMP) and PZ were investigated by wetted wall column at 30-40 degreesC. The physical properties such as density, viscosity, solubility, and diffusivity of the aqueous alkanolamine solutions were also measured. The N2O analogy was applied to estimate the solubilities and diffusivities Of CO2 in aqueous amine systems. Based on the pseudo-first-order for the CO2 absorption, the overall pseudo first-order reaction rate constants were determined from the kinetic measurements. For CO2 absorption into aqueous PZ solutions, the obtained second-order reaction rate constants for the reaction Of CO2 with PZ are in a good agreement with the results of Bishnoi and Rochelle (Chem. Eng. Sci. 55 (2000) 5531). For CO2 absorption into mixed aqueous solutions of AMP and PZ, it was found that the addition of small amounts of PZ to aqueous AMP solutions has significant effect on the enhancement of the CO2 absorption rate. For the CO2 absorption reaction rate model, a hybrid reaction rate model, a second-order reaction for the reaction Of CO2 with PZ and a zwitterion mechanism for the reaction Of CO2 with AMP was used to model the kinetic data. The overall absolute percentage deviation for the calculation of the apparent rate constant k(app) is 7.7% for the kinetics data measured. The model is satisfactory to represent the CO2 absorption into mixed aqueous solutions of AMP and PZ. (C) 2004 Elsevier Ltd. All rights reserved.