Hydrate Phase Diagrams for Water Hydrocarbon Systems

1 Hydrate Phase Diagrams for Water + Hydrocarbon Systems 

The phase behavior of hydrocarbon + water mixtures differs significantly from that of normal hydrocarbon mixtures. Differences arise from two effects, both of which have their basis in hydrogen bonding. First, the hydrate phase is a significant part of all hydrocarbon + water phase diagrams for hydrocarbons with a molecular size lower than 9 A. Second, water and hydrocarbon molecules are so different that, in the condensed state, two distinct liquid phases form, each with a very low solubility in the other. 

For a rigorous discussion of phase diagrams, the reader is referred to Harmens and Sloan (1990) or to Huo et al. (2003), which represent an extension and in some cases a correction to those published earlier by Kobayashi (1951), by Kobayashi in Katz et al. (1959), by Bourrie and Sloan (1986), or in the earlier editions of this 

While a first approach to phase diagrams is given here, Section 5.2 extends the phase diagrams in this portion of Chapter 4 to single, binary, and ternary mixtures of methane, ethane, and propane. The reader may wish to consult Section 5.2 for a more enlightening discussion that applies the van der Waals and Platteeuw method to the most common components of natural gases. 

The Lw-H-V line has pressure-temperature conditions of the most interest in natural gas systems. 

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Hydrate phase diagrams for water-hydrocarbon systems provide a convenient overview of the calculation types. These diagrams differ substantially from the normal hydrocarbon phase diagrams primarily due to hydrates and the hydrogen bonds inherent in aqueous systems. The phase diagrams of Section 4.1 provide an overview for the calculation methods in this chapter and the next. 

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