Phase Transitions in Mixed Gas Hydrates: Experimental Observations versus Calculated Data
| Autor: | Carolyn A. Koh, Keith C. Hester, Rudolf Naumann, Judith Maria Schicks, E. Dendy Sloan, Jörg Erzinger |
|---|---|
| Rok vydání: | 2006 |
| Předmět: |
Phase transition
Clathrate hydrate Analytical chemistry 550 - Earth sciences Atmospheric temperature range Spectrum Analysis Raman Methane Surfaces Coatings and Films symbols.namesake chemistry.chemical_compound Crystallography chemistry X-Ray Diffraction Propane Phase (matter) Materials Chemistry symbols Thermodynamics Gases Physical and Theoretical Chemistry Hydrate Raman spectroscopy Hydrogen |
| Zdroj: | Journal of Physical Chemistry B |
| Popis: | This paper presents the phase behavior of multicomponent gas hydrate systems formed from primarily methane with small amounts of ethane and propane. Experimental conditions were typically in a pressure range between 1 and 6 MPa, and the temperature range was between 260 and 290 K. These multicomponent systems have been investigated using a variety of techniques including microscopic observations, Raman spectroscopy, and X-ray diffraction. These techniques, used in combination, allowed for measurement of the hydrate structure and composition, while observing the morphology of the hydrate crystals measured. The hydrate formed immediately below the three-phase line (V-L --V-L-H) and contained crystals that were both light and dark in appearance. The light crystals, which visually were a single solid phase, showed a spectroscopic indication for the presence of occluded free gas in the hydrate. In contrast, the dark crystals were measured to be structure II (sII) without the presence of these occluded phases. Along with hydrate measurements near the decomposition line, an unexpected transformation process was visually observed at P-T-conditions in the stability field of the hydrates. Larger crystallites transformed into a foamy solid upon cooling over this transition line (between 5 and 10 K below the decomposition temperature). Below the transition line, a mixture of sI and sII was detected. This is the first time that these multicomponent systems have been investigated at these pressure and temperature conditions using both visual and spectroscopic techniques. These techniques enabled us to observe and measure the unexpected transformation process showing coexistence of different gas hydrate phases. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|