4.1 The Hydrate Phase Diagram

One might think that a review of a single hydrocarbon+water phase diagram would be simplistic. Yet, discussion of such a diagram leads to both new and essential results to understanding of industrial gas mixture hydrate equilibria. In industry, the hydrocarbon or gas phase is almost always present in large excess for economic reasons, so that the hydrocarbon gas composition does not change on hydrate formation, but maintains a fixed composition, adding credibility to the study simpler diagrams. Here, we discuss the methane+water diagram ^[56] for structure I. The reader may wish to supplement this discussion with more phase diagram details. ^{[57] , [58]}

Kobayashi and Katz ^[11] provided the first methane+water phase diagram, as a major advance in fundamental thermodynamics understanding. However, because these two researchers knew neither the hydrate structure nor their non-stoichiometric 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.

Recently, Raman spectroscopy was...