It is well known that methane hydrate undergoes several phase transformations at high pressures.
At room temperature and low to moderate pressure, methane and water form a stable cubic
structure I (sI) hydrate that is also known as MH-I. The structure is transformed to a hexagonal
phase (sH/MH-II) above 1.0GPa. Another phase transformation occurs above 1.9GPa where the
filled ice structure (MH-III) is stable up to 40 GPa before a new high pressure phase transition
occurs. Experiments at such high pressures have to be performed in a diamond anvil cell (DAC).
Our main interest, though, is to form sH methane hydrate at a lower pressure than reported in
previous studies but with some methane in the large cages consequently increasing the methane
content. This can be accomplished by introducing the molecules of the large hydrate forming
substance (tert-butyl methyl ether/TBME) at a concentration slightly below the stoichiometric
amount as suggested by molecular dynamics simulations. In this study we have synthesized
mixed methane hydrate of sI and sH and loaded the clathrate with methane into several DACs.
Raman spectra were collected at room temperature and pressures in the range of 0.1 to 11.3 GPa.
The existence of sH methane hydrate was observed down to 0.2 GPa. However, the existence of
methane in the large cages was visible only at pressure higher than 1.0 GPa. The excess methane
in the system apparently destabilizes the sH clathrate at pressure below 1.0 GPa as it transforms
to sI clathrate.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/1025 |
| Date | 07 1900 |
| Creators | Englezos, Peter, Desgreniers, Serge, Ripmeester, John A., Klug, Dennis, Susilo, Robin |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | text |
| Rights | Englezos, Peter |
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