Molecular Insight into the Effects of NaCl Concentrations on CO2 Hydrate Formation on the Montmorillonite Surface

Carbon dioxide (CO2), as a typical greenhouse gas, has gradually attracted attention for its capture and storage. Storing CO2 in the form of hydrates in clay sedimentary layers has been considered a promising method for controlling greenhouse gases. Although relevant experiments have been conducted to study the formation of CO2 hydrate in clay minerals, the molecular mechanism of the influence of clay surface on the nucleation and growth of CO2 hydrates in different salt concentration solution environments still deserves further exploration. In this study, molecular dynamics (MD) simulations were used to investigate the effect of lattice substituted montmorillonite (Mnt) surfaces on the nucleation and growth of CO2 hydrate under different salt concentrations. The results indicate that the nucleation and growth of CO2 hydrates occur in areas far from the surface of Mnt minerals. Compared to pure solution systems, the presence of Mnt minerals results in a lower growth rate and final amount of CO2 hydrates. In addition, the nucleation and growth of CO2 hydrates are significantly inhibited by salt ion solutions. The formation probability of the cage structure of CO2 hydrates is significantly affected by the presence of clay mineral layers and salt ions, resulting in significant nucleation and growth barriers for CO2 hydrates. High concentrations of salt ion solutions can significantly affect the nucleation rate of hydrates. The results of this study clearly indicate the synergistic effects of clay mineral surface and salt ions on the CO2 hydrates formation, which has important reference value for CO2 storage in clay reservoir environments with different concentrations of salt ions.