Experiment on Phase Equilibrium of Carbon Dioxide and Methane Mixed Hydrates

Replacing of CH₄ from hydrate with CO₂ as an integrated way of greenhouse gas storage and exploiting natrual gas hydrates attracted more and more attention. To replace CH₄ from hydrate with CO₂, the phase equilibrium data for CO₂-CH₄ mixed hydrates are needed. In this paper, the three-phase (H-V-L_W) line and upper quadruple(H-L_W-L_C-V)points (Q₂) phase equilibrium properties of the mixed hydrate with different composition were measured by using a visual experimental apparatus in range of 273.7K~284.2K. The results of increasing equilibrium pressure with methane composition and the upper quadruple phase coexist range were provided, and the upper quadruple states of start and end melting for the CO₂-CH₄ mixed hydrates were identified. It is found that the equilibrium temperature and pressure range of Q₂ four-phase coexistence are increased as the concentration of methane increases.