CO2-CAO SURFACE AND BULK REACTIONS - THERMODYNAMIC AND KINETIC APPROACH

CaO-CO2 interactions have been studied by thermogravimetry-differential thermal analysis (TG-DTA), temperature-programmed desorption (TPD), and temperature-programmed reaction (TPR). A less classical technique termed intermittent temperature-programmed desorption (ITPD) has also been used. A mass spectrometer has been employed as a gas flow analyzer in all the temperature-programmed techniques. The temperature at which CO2-CaO interactions take place determines whether their nature is limited to CO2 chemisorption or involves bulk carbonate formation in CaO particles as well. While only chemisorption occurs at temperatures between 323 and 573 K, bulk carbonate formation is observed at higher temperatures; the higher the temperature, the deeper the carbonate formation of CaO particles. CO2 chemisorption is interpreted by applying models commonly used for heterogeneous surfaces, with variations in the heat of adsorption and in the desorption activation energy as functions of coverage. The interpretation of the thermodynamics and kinetics of the process in the temperature range 323-1173 K led to the proposal of a mechanism for the first steps of the reaction of CO2 with CaO particles.