Kinetics and Structural Changes in CO2 Capture of K2CO3 under a Moist Condition

The capacity and kinetics of CO 2 capture of K 2 CO 3 were studied to determine the mechanism for CO 2 sequestration under ambient conditions. Bicarbonate formation of K 2 CO 3 was examined by thermogravimetric analysis under various CO 2 concentrations in the presence of water vapor, and the accompanying structural changes of K 2 CO 3 were demonstrated by X-ray diffraction (XRD). Morphological variations were observed during the reaction in the presence of different CO 2 concentrations through scanning electron microscopy (SEM). Structural changes and morphological variations, which occurred during the course of the reaction, were then connected to the kinetic and exothermic properties of the CO 2 capture process from XRD and SEM measurements. The XRD results showed that the bicarbonate formation process of K 2 CO 3 could be divided into three reactions, such as the formation of K 2 CO 3 ·1.5H 2 O from K 2 CO 3, the subsequent formation of K 4 H 2 (CO 3 ) 3 ·1.5H 2 O from K 2 CO 3 ·1.5H 2 O, and the slow formation of KHCO 3 from K 4 H 2 (CO 3 ) 3 ·1.5H 2 O. The SEM observations showed that the morphology of the particles at all three stages played a crucial role in the kinetic behavior for CO 2 sorptivity of K 2 CO 3 . CO 2 capture of K 2 CO 3 was inhibited under a concentrated CO 2 atmosphere during the initial stage, consisting of the first and second reactions, but the formation of KHCO 3 from K 4 H 2 (CO 3 ) 3 ·1.5H 2 O was thermodynamically favorable upon the increase of the CO 2 concentration.