Phase diagram methane

Barrer s discussion4 of his analog of Eq. 28 merits some comment. Equation 28 expresses the equilibrium condition between ice and hydrate. As such it is valid for all equilibria in which the two phases coexist and not only for univariant equilibria corresponding with a P—7" line in the phase diagram. (It holds, for instance, in the entire ice-hydratell-gas region of the ternary system water-methane-propane considered in Section III.C.(2).) In addition to Eq. 28 one has Clapeyron s equation... 

If the critical temperature of the solute is below room temperature, the phase diagram is similar to the one described for the system hydroquinone-argon. No temperature can then be indicated above which hydrates cannot exist. This situation arises for the following solutes argon,48 krypton,48 xenon,48 methane,3 and ethylene.10... 

Data for the hydrogen sulfide-water and the methane-n-hexane binary systems were considered. The first is a type III system in the binary phase diagram classification scheme of van Konynenburg and Scott. Experimental data from Selleck et al. (1952) were used. Carroll and Mather (1989a b) presented a new interpretation of these data and also new three phase data. In this work, only those VLE data from Selleck et al. (1952) that are consistent with the new data were used. Data for the methane-n-hexane system are available from Poston and McKetta (1966) and Lin et al. (1977). This is a type V system. 

VLE data and calculated phase diagram for the methane-n-hexane system [reprinted from Industrial Engineering Chemistry Research with permission from the American Chemical Society],... 

Figure 14.15 LE data and calculated phase diagram for the methane -n-hexane system.

Fig. 2-15. Phase diagrams of mixtures of methane and ethane. (Bloomer, et al., Institute of Gas Technology, Research Bulletin 22, 1953. Reproduced courtesy of Institute of Gas Technology, Chicago.)...

Fig. 2-27. Ternary phase diagram of mixtures of methane, propane, and n-pentane at 1500 psia and 160°F. (Data from Dourson et al., Trans. AIME, 151, 206.)...

Fig. 2-30. Pseudoternary phase diagram of mixtures of a synthetic oil with carbon dioxide. The oil is represented as a mixture of methane and ethane plus. (Data from Leach and Yellig, Trans., AIME, 271, 89.)...

A common use of three-component phase diagrams is in analysis of miscible displacement. For instance, Figure 2-30 gives the phase envelope of an oil mixed with carbon dioxide.6 The oil is plotted as an artificial two-component mixture, with methane as one component and all other constituents added together as the other component. 

Phase behavior of multicomponent reservoir fluids is similar. Reservoir gases, which are predominately methane, have relatively small phase diagrams with critical temperatures not much higher than the orSiranempnatiire of nietfiahe. The critical point is"fairdown the left slope of the envelope. 

See Section 4.1.5 for other examples of how Gibbs Phase Rule works in the methane + water phase diagram. Section 5.2 shows the application of the Gibbs Phase Rule for hydrate guests of methane, ethane, propane, and their mixtures. 

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. 

In Figure 4.2c for natural gases without a liquid hydrocarbon (or when liquid hydrocarbons exist below 273 K), the lower portion of the pressure-temperature phase diagram is very similar to that shown in Figure 4.2a. Two changes are (1) the Lw-H-V line would be for a fixed composition mixture of hydrocarbons rather than for pure methane (predictions methods for mixtures are given in Section 4.2 and in Chapter 5) and (2) quadruple point Qi would be at the intersection of the Lw-H-V line and 273 K, at a pressure lower than that for methane. The other three-phase lines of Figure 4.2a (for I-Lw-H and I-H-V) have almost the same slope at Qj. Otherwise, the same points in Section 4.1.1 apply. 

Section 5.2 shows the prediction method of phase diagrams of the major components of natural gas, namely methane, ethane, and propane hydrates and their mixtures at the common deep-ocean temperature of 277 K. Many of the commonly observed phenomena in natural gas systems are illustrated, while the power of the method is shown to go beyond that of Chapter 4, to illustrate future needs. 

Figure 5.12 is the pressure versus temperature phase diagram for the methane+ water system. Note that excess water is present so that, as hydrates form, all gas is incorporated into the hydrate phase. The phase equilibria of methane hydrates is well predicted as can be seen by a comparison of the prediction and data in Figure 5.12 note that the predicted hydrate formation pressure for methane hydrates at 277.6 K is 40.6 bar. 

To evaluate the phase equilibria of binary gas mixtures in contact with water, consider phase diagrams showing pressure versus pseudo-binary hydrocarbon composition. Water is present in excess throughout the phase diagrams and so the compositions of each phase is relative only to the hydrocarbon content. This type of analysis is particularly useful for hydrate phase equilibria since the distribution of the guests is of most importance. This section will discuss one diagram of each binary hydrate mixture of methane, ethane, and propane at a temperature of 277.6 K. 

Figure 5.20 is a pseudo-ternary phase diagram for the methane + ethane + propane + water system at a temperature and pressure of 277.6 K and 10.13 bar,... 

The methane+ethane+propane+water system is the simplest approximation of a natural gas mixture. As shown in Figure 5.20, the phase equilibria of such a simple mixture is quite complicated at pressures above incipient hydrate formation conditions. One of the most interesting phenomenon is the coexistence of si and sll hydrates which occurs in the interior of some pseudo-ternary phase diagrams. 

The depths of the pressure stimulation and thermal stimulation experiments are superimposed on the methane phase equilibria—geothermal gradient diagram shown in Figure 7.35 (Wright et al., 2005). Without a BSR, the geothermal gradient... 

Sub-steps, similar to those in Figure 9.7, have been observed with both methane and ethane (Bienfait, 1980, 1985). It has been possible to construct 2-D phase diagrams for several of these systems (Gay et al., 1986 Suzanne and Gay, 19%). LEED and neutron diffraction have provided information on the 2-D structures. For example, seven different 2-D phases have been reported for ethane on graphite over the temperature range 64-140 K. Thus, three solid commensurate phases were identified at temperatures <85 K, the S3 phase apparently having a close-packed hexagonal structure, with ofCjHj) = 0.157 nm2. 

One of the interesting features of the system hydrogen sulfide + methane is liquid-phase immiscibility. The H2S-rich and CH4-rich liquids are immiscible. However, this occurs at temperatures well below those of interest in acid gas injection. Unusual looking phase diagrams are often obtained for mixtures rich in H2S and CH4 because the algorithms typically are not designed for multiple... 

Figure 3A.1 Ternary phase diagram for two mixtures of hydrogen sulfide + carbon dioxide + methane [data from Robinson and Bailey (1957) and curves from the Peng-Robinson equation of state].

Matsumoto S., Sato Y., Tsutsumi M., Setaka N., Growth of diamond particles from methane-hydrogen gas. J. Mater. Sci. 17, (1982) pp.3106-3112. Nonequilibrium phase diagrams of ternary amorphous alloys (Springer, Heidelberg, 1997) 295 pages. 

Consider the notable example of hydrate researcher D.N. Glew, who first published on ethylene oxide hydrates with Dow of Canada in 1959. Upon his retirement, his interest increased, as did his productivity in hydrates. In 2003, Glew published his 19th hydrate article in a series that provided the foundation for many new advances, including the new methane-I-water phase diagram discussed in Section 4,... 

Kobayashi and Katz" provided the first methane-l-water phase diagram, as a major advance in fundamental thermodynamics understanding. However, because these two researchers knew neither the hydrate structure nor their non-stoichiomet-ric 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. 

In contrast, with two-phase formation, without a free water (or a free vapor) phase, an additional degree of fi edom, such as temperature, pressure, or phase composition, must be applied. In Figure 2, the two-phase areas (V+H, L +H, L +H, M+H, or H+1) indicate that two variables (temperature of the single-phase composition, in addition to the isobar of the diagram) must be specified to fix the system state. Hydrate formation from a water-saturated vapor counters the common myth that a free water phase must be present to have hydrates. That there is no thermodynamic necessity for a fi ee water phase is perhaps shown most clearly by a study of the methane-H water phase diagram. 

Also, in Figure 2, hydrate formation from the two-phase regions is clearly permitted, and in fact comprises a large portion of the phase diagram. However, due to the small concentrations of water in the methane phase, or even smaller concentrations of methane in the water phase, it may be unlikely that kinetics will allow sufficient hydrate formation, for example, to plug a flow channel. Therefore, the restriction on a free water phase to form a hydrate plug is a kinetic restriction rather than a thermodynamic one. 

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