Initial Correlation of Hydrate Phase Equilibria

When Hammerschmidt (1934) identified hydrates in pipelines, he published a correlation summary of over 100 hydrate formation data points. Shortly afterward, Professor D.L. Katz and his students at the University of Michigan began an experimental study. Because it was impractical to measure hydrate formation conditions for every gas composition, Katz determined two correlative methods. 

The initial predictive method by Wilcox et al. (1941) was based on distribution coefficients (sometimes called Kvsi values) for hydrates on a water-free basis. With a substantial degree of intuition, Katz determined that hydrates were solid solutions that might be treated similar to an ideal liquid solution. Establishment of the Kvsj value (defined as the component mole fraction ratio in the gas to the hydrate phase) for each of a number of components enabled the user to determine the pressure and temperature of hydrate formation from mixtures. These Kysi value charts were generated in advance of the determination of hydrate crystal structure. The method is discussed in detail in Section 4.2.2. 

Katz s two predictive techniques provided industry with acceptable predictions of mixture hydrate formation conditions, without the need for costly measurements. Subsequently, hydrate research centered on the determination of the hydrate crystal structure(s). Further refinements of the Kvsi values were determined by Katz and coworkers (especially Kobayashi) in Chapter 5 of the Handbook of Natural Gas Engineering (1959), by Robinson and coworkers (Jhaveri and Robinson, 1965 Robinson andNg, 1976), and by Poettmann (1984). 

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