Because of the presence of one or more primary or secondary amino groups, solvents containing diamines have a good potential for CO2 capture. In the present work, the CO2 reactions with two diamines, viz. N-(2-aminoethyl)ethanolamine (AEEA) and piperazine (PZ). in aqueous solutions are investigated using a stirred-cell reactor. The reaction pathways are described using the zwitterion and the termolecular mechanism. Solution densities and viscosities are measured. The investigated reactions belong to the fast reaction regime systems. It is found that the CO2 reaction with AEEA is of the second order with respect to AEEA within the temperature range 298-308 K and amine concentration range 1.5-3 kmol/m(3). At 303 K. the reaction rate constant equals 8530 m(6)/(kmol(2) s). The value of the second-order rate constant for the CO2 reaction with PZ is found to be 25.800 m(3)/(kmol s) at 303 K. (C) 2011 Elsevier B.V. All rights reserved.