Influence of Vacancy Defect of Calcium Oxide Surface on the Wettability of Molten Alkali Metal Salt in Calcium Looping Process

The influence of the vacancy defect of the CaO surface on the wettability of molten alkali metal salt was studied by molecular dynamics simulations. The results indicated that in the temperature range of 800–1100 K, the molten Na2SO4 on both VDcalcium and VDoxygen defect surfaces presented a poor wettability compared to that on the complete surface. Measurement of the density profile and the contact angle of the molten Na2SO4 showed that the higher the temperature and defect concentration, the worse the wettability. The micromechanism was revealed by calculating the polarization intensity that the vacancy defect surface led to the formation of the induced dipole moment in the molten Na2SO4. Induced polarization caused by defect surfaces reduces the wettability of Na2SO4. More importantly, as the temperature and defect concentration increase, various defect surfaces form loose and local weak liquidity structures. These structures are beneficial for the diffusion of carbon dioxide into the solid, but the reduction in the spreading area caused by poor wettability causes the efficiency of the CaL to decline. The vibration difference between Na2SO4 and CaO increases with the increased temperature and defect concentration. This means that the thermal energy transportability at the interface is suppressed by poor wettability.