Insights into the effects of pore size and wettability on the stability of CO2 hydrate: A molecular dynamics simulation study

CO2 hydrate has attracted extensive attention as a promising storage medium due to its high gas storage density and excellent mechanical stability. Many studies have demonstrated that the stability of CO2 hydrate in confined space is crucial to the feasibility and safety of hydrate-based CO2 sequestration. In this study, molecular dynamics (MD) simulations were employed to investigate the influence of pore size and wettability on the morphology, melting point, and growth/dissociation behaviour of CO2 hydrate in pores using molecular number density analysis, cage growth rate analysis, and an independent gradient model based on the Hirshfeld partition (IGMH). The pore size significantly affects the stability of CO2 hydrate. Moreover, variations in pore wettability cause differences in both silica-hydrate interactions and the distribution of CO2 nanobubbles, which have minor and non-negligible effects on hydrate stability, respectively. In the hydrophilic system, CO2 hydrate exhibits a faster growth rate and a slower dissociation compared to the hydrophobic system. Nanobubbles can decrease the CO2 concentration around hydrates and reduce the CO2 chemical potential, which are responsible for the different dissociation processes and dissociation/growth rates.