Molecular-Scale Mechanisms of CH₄ Hydrate Displacement Using Multi-Component CO₂-Rich Industrial Waste Gas: Impacts...

The CH₄/CO₂ displacement method is regarded as a highly promising approach for natural gas extraction, which can improve CH₄ recovery efficiency while achieving carbon sequestration. However, CO₂ purification is technologically complex and energy-intensive, and the replacement performance remains limited. Directly injecting CO₂-rich industrial waste gases can not only improve the CH₄ recovery efficiency but also achieve waste gas sealing, reducing the cost of gas separation and purification. In this study, a model for replacing CH₄ hydrate with CO₂-rich industrial waste gas is established based on the molecular dynamics method. The effects of temperature, pressure, concentration of industrial waste gas, and salinity on the molecular structure evolution and mass transfer behavior during the displacement process were comprehensively analyzed. The results indicate that an increase in temperature can significantly promote the release of CH₄ and the formation of CO₂ hydrates within the simulation range. The influence of pressure on the displacement process is relatively limited. Overall, the increase in pressure enhances the spatial correlation between CO₂ and the hydrate cage, promoting the displacement and sequestration of CO₂. Compared with pure CO₂, the introduction of an appropriate amount of N₂ and NO can promote the displacement process, indicating that a small amount of associated components have a synergistic regulatory effect in confined systems. Salinity exerts a significant inhibitory effect on the displacement process by weakening the hydrogen bond network of H₂O molecules and the intermolecular spatial correlation. This study offers a molecular-scale basis for mechanism analysis and operational condition evaluation of CO₂ participation in hydrate displacement within multicomponent industrial waste gas environments.