Carbon dioxide absorption with aqueous potassium carbonate promoted by piperazine

Abstract

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 CO 2 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°C. The addition of 0.6 m piperazine to a 20 wt% potassium carbonate system decreases the CO 2 equilibrium partial pressure by approximately 85% at intermediate CO 2 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 CO 2 absorption by an order of magnitude at 60°C. The rate of CO 2 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-CO 2/ kg-H 2 O for PZ/K 2CO 3 solutions, comparing favorably with other amines.