This work studies the absorption of carbon dioxide into aqueous solutions of piperazine in a wetted wall contactor. Absorption was studied from 298 to 333 K in solutions of 0.6 and 0.2 M aqueous piperazine. The apparent reaction rate is first order in both carbon dioxide and piperazine with a value of 53,700 m(3)/kmols at 25 degreesC. The apparent second-order rate constant follows an Arrhenius temperature dependence over the range studied with an activation energy of 3.36 x 10(4) k(3)/kmol. Solubility in 0.6 M PZ was measured by bracketing absorption and desorption in the wetted wall contactor at 313 and 343 K. Chemical and phase equilibrium was modeled by considering the following piperazine species: piperazine carbamate, dicarbamate, protonated carbamate, and protonated piperazine. Henry's law and the dissociation of carbon dioxide to form bicarbonate and carbonate were also considered. The carbamate stability constant and pK(a) for piperazine carbamate were regressed from the VLE data. Although shown to be present by NMR, the dicarbamate is not the dominant reaction product at any loading. The carbamate stability constant is comparable to other secondary amines such as diethanolamine (DEA) but the apparent second-order rate constant is an order of magnitude higher than primary amines such as monoethanolamine (MEA) or diglycolamine (DGA(R)). The second-order rate constant obtained in this work is much higher than previously published values for the piperazine/carbon dioxide reaction. These previous studies were limited by mass transfer limitation of products and reactants and were not a true measurement of the kinetics of carbon dioxide/piperazine. There is some evidence that the reactivity of piperazine is due to its cyclic and diamine characteristics.