The Hydrate Phase Diagram

Kobayashi and Katz provided the first methane-l-water phase diagram, as a major advance in fundamental thermodynamics understanding. However, because these two researchers knew neither the hydrate structure nor their non-stoichiomet-ric nature, their diagram did not indicate a variable composition for hydrates. This early advance was in violation of the phase rule because it suggests that only the specification of temperature or pressure is required to fix the hydrate composition in a two-phase condition. 

The system is constrained to obey the Gibbs Phase Rule. In the most common application, with methane (or a fixed gas composition) and water, the two components will form the three phases of hydrates, vapor, and liquid with one degree of fi eedom. Fixing the temperature (or the pressure) determines the pressure (or the temperature) at the three-phase condition. 

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Chapter 4 provides phase diagrams and simple prediction schemes for each of the hydrate phase diagram regions. 

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