Thermodynamic Calculations in the System CH₄-H₂O and Methane Hydrate Phase Equilibria

Using the Gibbs function of reaction, equilibrium pressure, temperature conditions for the formation of methane clathrate hydrate have been calculated from the thermodynamic properties of phases in the system CH₄−H₂O. The thermodynamic model accurately reproduces the published phase-equilibria data to within ±2 K of the observed equilibrium boundaries in the range 0.08−117 MPa and 190−307 K. The model also provides an estimate of the third-law entropy of methane hydrate at 273.15 K, 0.1 MPa of 56.2 J mol^-1 K^-1 for 1/n CH₄·H₂O, where n is the hydrate number. Agreement between the calculated and published phase-equilibria data is optimized when the hydrate composition is fixed and independent of the pressure and temperature for the conditions modeled.