On the phase behaviors of CH₄–CO₂ binary clathrate hydrates: Equilibrium with aqueous phase.

The article focuses on the solubilities and phase equilibria of methane (CH₄) and carbon dioxide (CO₂) in aqueous solutions coexisting with their respective clathrate hydrates, using a statistical mechanical theory based on pairwise intermolecular potentials. It extends the van der Waals–Platteeuw (vdWP) theory to rigorously calculate chemical potentials and occupancies of guest molecules in hydrates, accounting for their nonstoichiometric nature and finite solubility, particularly of CO₂ in water. The study finds that CO₂’s finite solubility affects the water/hydrate equilibrium and slightly lowers the dissociation temperature of CO₂ hydrate, while CH₄’s much lower solubility has negligible impact. Additionally, the work examines binary CH₄–CO₂ hydrates, revealing significant differences in guest compositions between hydrate, aqueous, and fluid phases, influenced by preferential cage occupancy and solubility disparities.