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Thermodynamic stability of type-I and type-II clathrate hydrates depending on the chemical species of the guest substances
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10.1063/1.2746324
/content/aip/journal/jcp/126/23/10.1063/1.2746324
http://aip.metastore.ingenta.com/content/aip/journal/jcp/126/23/10.1063/1.2746324

Figures

Image of FIG. 1.
FIG. 1.

(a) Relationship between the hydrate equilibrium pressures and van der Waals diameter of the guest compounds. (b) Relationship between the hydrate equilibrium pressures and molar mass of the guest compounds. Squares and circles indicate the data for the type-I and type-II hydrates, respectively. Equilibrium-pressure data at the temperature of are used (Ref. 10). van der Waals diameters were calculated with Winmostar (Refs. 11 and 12) The chemical formulas in the figure indicate the guest compounds.

Image of FIG. 2.
FIG. 2.

Schematic illustration of the cages forming (a) type-I and (b) type-II hydrates.

Image of FIG. 3.
FIG. 3.

Contour map of the residual free energy for (a) type-I and (b) type-II hydrates. The and of the molecules in Table II are also plotted.

Image of FIG. 4.
FIG. 4.

Contour map of the residual free energy for each cavity; (a) large cavity and (b) small cavity of the type-I and (c) large cavity and (d) small cavity of the type-II hydrates.

Image of FIG. 5.
FIG. 5.

The dependency of the residual free energy on for each cage and the whole hydrate at .

Image of FIG. 6.
FIG. 6.

Arrangement of the guest-molecule sizes and optimal sizes of for each type of cage and hydrate.

Tables

Generic image for table
Table I.

Combinations of , , , and of the guest molecules used for the calculations of the free energy differences between systems and .

Generic image for table
Table II.

The Lennard-Jones parameters and of , , Xe, , , Kr, , Ar, Ne, and He. They were compared with the maximum van der Waals (vdW) diameters.

Generic image for table
Table III.

The calculated free energy differences between the hydrates formed with Xe, Kr, , , Ar, , , , Ne, and He and for the type-I and type-II hydrates. The hydrate is employed as a reference to calculate the free energy differences. The unit is .

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/content/aip/journal/jcp/126/23/10.1063/1.2746324
2007-06-19
2014-04-24
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Thermodynamic stability of type-I and type-II clathrate hydrates depending on the chemical species of the guest substances
http://aip.metastore.ingenta.com/content/aip/journal/jcp/126/23/10.1063/1.2746324
10.1063/1.2746324
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