Ethane hydrates

The fact that both heats of formation and equilibrium pressures of the hydrates of spherical molecules correctly follow from one model must mean that the L-J-D theory gives a good account of the entropy associated with the motions of these solutes in the cavities of a clathrate. That the heat of formation of ethane hydrate is predicted correctly, whereas the theoretical value of its vapor pressure is too low, is a further indication that the latter discrepancy must be ascribed to hindered rotation of the ethane molecules in their cavities. 

Coexistence of si and sll carbon dioxide hydrate has been detected from x-ray diffraction measurements during hydrate growth (Staykova and Kuhs, 2003). Similarly, metastable sll hydrate phases were detected using NMR spectroscopy during si xenon hydrate formation (Moudrakovski et al., 2001a) and during si methane/ethane hydrate formation (Bowler et al., 2005 Takeya et al., 2003). 

FIGURE 3.36 Average rates for methane hydrate samples reaching 50% dissociation at 0.1 MPa, following destabilization by rapid release of P. The anomalous preservation regime is between 242 and 271 K. Square symbols experiments in which P is maintained at 2 MPa, Diamonds 0.1 MPa rapid depressurization tests on sll methane-ethane hydrate, showing no comparable preservation behavior at 268 K. (Reproduced from Stern, L.A., Circone, S., Kirby, S.H., Durhan, W., Can. J. Phys., 81, 271 (2003). With permission from the National Research Council.)... 

Figure 5.13 is the equivalent ethane + water pressure versus temperature phase diagram. Note that the Aq-sI-V line intersects the Aq-V-Lhc line at 287.8 K and 35 bar. Due to differences in the volume and enthalpy of the vapor and liquid hydrocarbon, the three-phase hydrate formation line changes slope at high temperature and pressure from Aq-sI-V to Aq-sI-Lhc, due to the intersectiion of Aq-sI-V line with the Aq-V-Lhc line (slightly higher than the ethane vapor pressure). Note that the hydrate formation pressure for ethane hydrates at 277.6 K is predicted to be 8.2 bar. 

Figure 6.45 Methanol inhibition of simple ethane hydrates.

Figure 6.53 Methanol inhibition of methane + ethane hydrates.

Figure 2. Dissociation pressure of ethane hydrate at 273.15 K. Solid, dashed, and dash-dot lines show the dissociation pressures for the nonspherical guest evaluated by anharmonic and harmonic free energy, for spherical guest molecule evaluated by only harmonic free energy, and for spherical guest according to the original vdWP theory, respectively. The horizontal lines show the chemical potential difference between ice and empty hydrate, dashed harmonic-t-anharmonic, dotted harmonic.

S. A system composed of ethane hydrate, water, and ethane is classed aa a two-component system when Gibbs phase rule is applied since it could be formed from water and ethane. What is the variance of this system when a solid, a liquid, and a vapor phase coexist in equilibrium If the temperature of this three-phase system is specified, would it be possible to alter the pressure without the disappaaranoe of a phase ... 

The GCMC simulations for propane (ethane) hydrate structures at five (four) pressures are performed. The pressure values of gas phase guest... 

Figure 12. Dissociation pressures of ethane hydrate at 273.15 K. Solid line nonspherical and anharmonic, dashed line spherical and harmonic, dash-dot line spherical vdWP. Horizontal lines free energy differences between ice and empty clathrate hydrate I heavy anharmonic, thin harmonic.

Morita, K. Nakano, S. Ohgaki, K. Structure and stability of ethane hydrate crystal. Fluid Phase Equilibria 2000, 169, 167-175. 

Servio. P. Englezos. P. Bishnoi. P.R. In Kinetics of Ethane Hydrate Growth on Latex Spheres Measured by a Light Scattering Technique. Proceedings of the New York Academy of Science, 2000 Vol. 912. 576-582. 

Table 10.5 Constant pressure heat capacity (J/g K) of ice, methane CO2 and ethane hydrates...

It is clear that the thermal conductivity of gas hydrates is much less than that of ice, but similar to hquid water. Furthermore, when it comes to hydrate/gas/water or hydrate/gas/water/sediment systems, the thermal properties are usually determined as the average values of the properties of the components by considering their saturation (volumetric fraction) in the sample. Because of the paucity of data of CO2 hydrates, the heat capacities of ice, methane and ethane hydrates are shown in Table 10.5. Considering the similarity between CO2 hydrates and other gas hydrates, the heat capacity of CO2 hydrates is certainly less than that of liquid water and may be similar to that of ice. 

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