Fundamentals in CO2 capture of Na2CO3 under a moist condition

Capacity and kinetics of CO2 capture of Na2CO3 were studied to determine the mechanism for CO2 sequestration under ambient conditions. Bicarbonate formation of Na2CO3 was examined by a thermogravimetric analysis (TGA) under various CO2 and water vapor concentrations and the accompanying structural changes of Na2CO3 were demonstrated by X-ray diffraction (XRD). Morphological variations were observed during the reaction of CO2 capture through scanning electron microscope (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 CO2 capture process from the XRD and SEM measurements. The results showed that the bicarbonate formation of Na2CO3 has two different pathways. For higher CO2 and H2O concentrations, the bicarbonate formation proceeded effectively. However, for lower CO2 and H2O concentrations, the reactions were more complicated. The formation of Na2CO3•H2O from Na2CO3 as the first step, followed by the subsequent formation of Na5H3(CO3)4, and then the bicarbonate formation proceeds. To understand such fundamental properties in CO2 capture of Na2CO3 is very important for utilization of Na2CO3 as a sorbent for CO2 capture.