In Situ Raman Spectroscopic Studies on Small-Cage Occupancy of Methane in the Simple Methane and Methane + Deuterated Tetrahydrofuran Mixed Hydrates

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• 作者：Caroline T. Moryama ; Takeshi Sugahara ; Danilo Y. Yatabe Franco ; Hiroko Mimachi
• 刊名：Journal of Chemical & Engineering Data
• 出版年：2015
• 出版时间：December 10, 2015
• 年：2015
• 卷：60
• 期：12
• 页码：3581-3587
• 全文大小：382K
• ISSN：1520-5134

文摘

To investigate the small-cage occupancies of methane (CH₄) in the structure-I and structure-II hydrates, under the three-phase equilibrium conditions of clathrate hydrate, aqueous solution, and fluid CH₄ phases, in situ Raman spectra of the guest molecules in the simple CH₄ hydrate and the CH₄ + deuterated tetrahydrofuran (THF-d₈) mixed hydrate with the stoichiometric THF-d₈ composition were measured. The three-phase equilibrium conditions of CH₄ + THF-d₈ mixed hydrate phase, THF-d₈ aqueous solution phase, and fluid CH₄ phase were measured in a temperature range of (278 to 294) K and pressure range up to 2.6 MPa. The small-cage occupancy of CH₄ in the structure-II CH₄ + THF-d₈ hydrate increases with increasing pressure (and also temperature) up to 3 MPa. At pressures higher than 3 MPa, the small-cages of structure-II hydrate are mostly filled up with the CH₄ molecules. In the simple CH₄ hydrate, the small-cage occupancy is almost independent of the pressures of (5 to 60) MPa measured in the present study. The three-phase equilibrium pressures at which the small cages are filled up with the CH₄ molecules would be lower than ever expected by the statistic-thermodynamic model.