Apparatuses for two-phase equilibria

In two-phase (H-V or H-Lhc) equilibria, one less phase is present than in the more common three-phase measurements therefore, an additional intensive variable (in addition to temperature or pressure) must be measured. Typically the water concentration of the hydrocarbon fluid phase is determined the fluid phase contains very low concentrations of water, and a special means must be used to measure minute water concentrations, such as the special chromatograph developed by Ertl et al. (1976) in Kobayashi s laboratory. Alternatively, the hydrocarbon concentration of the aqueous phase in equilibrium with hydrates is determined these concentrations are also very low and require special techniques. 

The most productive two-phase (H-V or H-Lhc) equilibrium apparatus was developed by Kobayashi and coworkers. The same apparatus has been used for two-phase systems such as methane + water (Sloan et al., 1976 Aoyagi and Kobayashi, 1978), methane + propane + water (Song and Kobayashi, 1982), and carbon dioxide + water (Song and Kobayashi, 1987). The basic apparatus described in Section 6.1.1.2 was used in a unique way for two-phase studies. With two-phase measurements, excess gas was used to convert all of the water to hydrate at a three-phase (Lw-H-V) line before the conditions were changed to temperature and pressures in the two-phase region. This requires very careful conditioning of the hydrate phase to prevent metastability and occlusion. Kobayashi and coworkers equilibrated the hydrate phase by using the ball-mill apparatus to convert any excess water to hydrate. 

---