Concentrated potassium carbonate/piperazine mixtures for an improved carbon dioxide capture process

Abstract

This chapter discusses the CO2 absorption performance for blends of aqueous piperazine (PZ) and potassium carbonate (K2CO3) in traditional absorber/stripper processes. Various experiments were carried out at conditions representative of CO2 removal from flue gas with a broad range of solvent concentrations. Results show that concentrated K+/PZ mixtures increase the rate of absorption by as much as a factor of four over that of monoethanolamine (MEA). Ionic strength effects were also studied including non-reactive salts, such as NaCl and K2SO4. They enhanced the absorption rate significantly. To predict absorption rates in PZ/MEA solutions, Bishnoi developed a rigorous rate model. The model explains mass transfer across a boundary layer using the eddy diffusivity theory with the proposed kinetic mechanism to describe mass transfer and the reaction of CO2 with amines. Ionic strength has a considerable effect on the rate of CO2 absorption into aqueous PZ. At 25°C, the apparent rate constant increases by an order of magnitude at 3M ionic strength. At 60°C, a factor of two increase is observed at 2M ionic strength. Furthermore, the magnitude of the increase does not appear to be ion specific. This behavior has significant implications for existing processes.