Thermal expansivity for sI and sII clathrate hydrates

Area of Science:

• Materials Science
• Thermodynamics
• Crystallography

Background:

• Clathrate hydrates exhibit significant volume changes with temperature, impacting their macroscopic behavior.
• Accurate prediction of hydrate formation pressure is sensitive to minor changes in hydrate volume.
• Understanding thermal expansivity is key to quantifying lattice distortions and ensuring accurate phase equilibria predictions.

Purpose of the Study:

• To measure the thermal expansivity of Structure I and II clathrate hydrates with various guest molecules.
• To develop new correlations for hydrate lattice parameters as a function of temperature.
• To investigate the influence of guest molecules on hydrate thermal expansion.

Main Methods:

• Diffraction studies were used to measure hydrate lattice parameters at varying temperatures.
• Lattice parameter data were combined with existing literature values.
• Development of structure-dependent correlations for normalized lattice parameters.

Main Results:

• Structure I and II hydrates generally exhibit common thermal expansivity, largely independent of the guest molecule.
• Two novel guest-independent, structure-dependent correlations for sI and sII lattices were established.
• These correlations express normalized lattice parameters and volume as a function of temperature.

Conclusions:

• Thermal expansivity of clathrate hydrates is primarily structure-dependent, not guest-dependent.
• The developed correlations provide a more accurate method for predicting hydrate volume changes with temperature.
• This research enhances the understanding of hydrate phase equilibria and guest-host interactions.