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RAMAN STUDY OF THE METHANE + TBME MIXED HYDRATE IN A DIAMOND ANVIL

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Title: RAMAN STUDY OF THE METHANE + TBME MIXED HYDRATE IN A DIAMOND ANVIL
Author: Englezos, Peter; Desgreniers, Serge; Ripmeester, John A.; Klug, Dennis; Susilo, Robin
Subject Keywords International Conference on Gas Hydrates;ICGH;TBME;methane;high pressure;hydrate;Structure H
Issue Date: 2008-07
Publicly Available in cIRcle 2008-07-18
Citation: Susilo, Robin; Klug, Dennis; Ripmeester, John; Desgreniers, Serge; Englezos, Peter. 2008. RAMAN STUDY OF THE METHANE + TBME MIXED HYDRATE IN A DIAMOND ANVIL CELL. Proceedings of the 6th International Conference on Gas Hydrates (ICGH 2008), Vancouver, British Columbia, CANADA, July 6-10, 2008.
Abstract: 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.
Affiliation: OtherChemical and Biological Engineering, Dept of
URI: http://hdl.handle.net/2429/1025
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