Sintering mechanism of CaO during carbonation reaction in the presence of water vapor

Abstract

In this paper, CaO sintering in the presence of water vapor for CO2 capture were carried out by ReaxFF(Reactive Force Field) molecular dynamics. The CaO sintering model was simulated at different temperatures (873 K-1273 K) and atmospheres (CO2, H2O), respectively. The results showed that water vapor could significantly promote the sintering process of CO2 capture by CaO. The Mean-square displacement (MSD) and Boltzmann–Arrhenius dependency were used to study the diffusion properties of CaO particles. The decreased diffusion activation Ea and increased pre-exponential factor D0 indicate that CaO particles have a stronger initial diffusivity and a lower diffusion barrier in the presence of CO2 and H2O. The inner and outer regions of CaO atoms were analyzed and it was found that the activation energy is the main factor to enhance the diffusion in the presence of CO2 for CaO sintering process, whereas the pre-exponential factor dominates with both CO2 and H2O. Water vapor enhanced the sintering pf CaO carbonation reaction is mainly achieved by promoting atoms in the inner layers of CaO particles. The types and numbers of sintering atoms during the sintering process were counted, and the distances between Ca and O atoms were calculated, which found that water vapor first dissociates into hydroxyl and H protons on the CaO surface, and the hydroxyl group will stay on the surface of CaO and combine with CO2, while the H proton will combine with O inside CaO to promote the sintering of CaO further.