Methane Gas Hydrates Viewed through Unified Solid–Liquid–Vapor Equations of State

The phase behavior of methane gas hydrates (clathrates) has been investigated with unified equations of state for solid–liquid–vapor phases. This is a new way to look at the clathrate-containing system, being radically different from the traditional statistical thermodynamic model for clathrates. The present paper includes modifications and refinements of the previously published method with the unified equations of state. The univariant three-phase equilibrium lines containing clathrates have been successfully predicted with the present equation-of-state model for a wide temperature and pressure range. Particularly, the phase behavior in very high-pressure regions has been modeled for the first time by the present work. Although the present results at high pressures are still tentative, they will shed some light on the unsettled problem of high pressure phases as reported in the literature