Atomistic mechanisms study of the carbonation reaction of CaO for high-temperature CO2 capture

Ca-Looping is a promising technology for capturing CO2. Here, ReaxFF molecular dynamics simulations combined with thermogravimetric analysis (TGA) were employed to provide atomic-level insights into the carbonation reaction of CaO with CO2. Results showed that two fast kinetic stages appear when the temperature increases. To understand this phenomenon, the diffusion, structural evolution as well as the carbonates accumulation were analyzed. It was found that the recovery of the initial fast reaction rate largely stems from the formations of pyrocarbonate anion. On CO2-CaCO3 interface, the solid product molecules are continuously propagated and joined in the existing C2O52- phase with multiple instances of formation and dissociation. Furthermore, surface carbonates can combine with crystal oxygen in the form of metastable corner-linked CO44- tetrahedron to diffuse inward the CaO particle. The increase of temperature greatly accelerates the formation of outer polymeric phases of CO2-CO32- and diffusion of inner CO32-, causing more CO2 molecules to be adsorbed and the carbonation reaction rate rises sharply.