Many commercial processes for the removal of carbon dioxide from high-pressure gases use aqueous potassium carbonate systems promoted by secondary amines. This paper presents thermodynamic and kinetic data for aqueous potassium carbonate promoted by piperazine. Research has been performed at typical absorber conditions for the removal of CO2 from flue gas. Piperazine, used as an additive in 20-30 wt% potassium carbonate, was investigated in a wetted-wall column using a concentration of 0.6 m at 40-80 degreesC. The addition of 0.6 m piperazine to a 20 wt% potassium carbonate system decreases the CO2 equilibrium partial pressure by approximately 85% at intermediate CO2 loading. The distribution of piperazine species in the solution was determined by proton NMR. Using the speciation data and relevant equilibrium constants, a model was developed to predict system speciation and equilibrium. The addition of 0.6 m piperazine to 20 wt% potassium carbonate increases the rate of CO2 absorption by an order of magnitude at 60 C. The rate of CO2 absorption in the promoted solution compares favorably to that of 5.0 M MEA. The addition of 0.6 m piperazine to 20 wt% potassium carbonate increases the heat of absorption from 3.7 to 10 kcal/mol. The capacity ranges from 0.4 to 0.8 mol-CO2/kg-H2O for PZ/K2CO3 solutions, comparing favorably with other amines. (C) 2004 Elsevier Ltd. All rights reserved.