Temperature-Composition Diagrams for Methane Water

In the first edition (1989) of this monograph the details of all isobaric temperature-composition (T-x) diagrams were discussed, in a synopsis of 

FIGURE 4.3 Temperature-composition diagrams for methane and water. (Reproduced from Huo, Z Hester, K Miller, K.T., Sloan, E.D., AIChE /., 49, 1300 (2003). With permission from the American Institute of Chemical Engineers.) 

Cooling the system is continued until the temperature of Point 2, where the hydrate phase (vertical area that begins at Point 7) forms from the vapor (Point 8) and liquid (Point 6). At Point 2 three phases (Lw-H-V) coexist for two components, so Gibbs Phase Rule (F = 2 — 3+2) indicates that only the isobaric pressure of the entire diagram is necessary to obtain the temperature and the concentrations of the three phases (Fw, H, and V) in equilibrium. 

At still lower temperatures of the original mixture, some of the vapor condenses to liquid methane at the three-phase (H-V-Lm ) boundary (Point 3). Again the three-phase temperature and phase compositions (Points 9, 10, and 11) are specified by the single variable of pressure (F = C - P + 2 = 2 - 3 + 2). Below this three-phase line the vapor phase is totally condensed to a liquid resulting in a two-phase (H-Lm) region between Points 3 and 4. 

Point 4 is at the temperature of the lowest three-phase line (H-Lm-M), which occurs just below the solidification point of pure methane (M). Below this line 

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