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Kinetics and Stability of CH 4 –CO 2 Mixed Gas Hydrates during Formation and Long‐Term Storage
Author(s) -
Uchida Tsutomu,
Ikeda Ikuko Y.,
Takeya Satoshi,
Kamata Yasushi,
Ohmura Ryo,
Nagao Jiro,
Zatsepina Olga Y.,
Buffett Bruce A.
Publication year - 2005
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200400364
Subject(s) - hydrate , methane , clathrate hydrate , chemistry , raman spectroscopy , kinetics , molecule , natural gas , carbon dioxide , gas composition , thermodynamics , organic chemistry , physics , quantum mechanics , optics
The formation of CH 4 –CO 2 mixed gas hydrates was observed by measuring the change of vapor‐phase composition using gas chromatography and Raman spectroscopy. Preferential consumption of carbon dioxide molecules was found during hydrate formation, which agreed well with thermodynamic calculations. Both Raman spectroscopic analysis and the thermodynamic calculation indicated that the kinetics of this mixed gas hydrate system was controlled by the competition of both molecules to be enclathrated into the hydrate cages. However, the methane molecules were preferentially crystallized in the early stages of hydrate formation when the initial methane concentration was much less than that of carbon dioxide. According to the Raman spectra, pure methane hydrates first formed under this condition. This unique phenomenon suggested that methane molecules play important roles in the hydrate formation process. These mixed gas hydrates were stored at atmospheric pressure and 190 K for over two months to examine the stability of the encaged gases. During storage, CO 2 was preferentially released. According to our thermodynamic analysis, this CO 2 release was due to the instability of CO 2 in the hydrate structure under the storage conditions.