[M-IS32] ガスハイドレートと地球環境・資源科学

[MIS32-12] メタン＋プロパン混合ガスハイドレートの分解挙動観察

*竹谷 敏¹、鎌田 諒也²、八久保 晶弘² (1.産業技術総合研究所、2.北見工業大学)

キーワード：クラスレートハイドレート、自己保存、天然ガスハイドレート、ホスト－ゲスト相互作用

The existence of enhanced preservation phenomena for structure I methane (CH₄) hydrate in the temperature region below ice point (273 K) is one remaining puzzle. This phenomenon has been termed “self-preservation” of gas hydrate. So far, this phenomenon has been observed for CH₄ hydrate upon dissociation by rapid pressure-release from high pressures at which CH₄ hydrate is stable (Stern et al., 2001). It is also reported that reduction of dissociation rates of gas hydrates by temperature ramping depends on neither the thermodynamic stability nor the crystal structure, but the nature of the guest molecules (Takeya & Ripmeester, 2008). The reduction of dissociation rates of gas hydrates was observed for gas hydrates such as oxygen hydrate, argon hydrate and carbon dioxide hydrate as well as CH₄ hydrate. However, the rate reduction was not observed for ethane (C₂H₆) hydrate, propane (C₃H₈) hydrate, and mixed gas hydrates of CH₄ and C₂H₆ (Takeya & Ripmeester, 2010)_.

In this study, powder X-ray diffraction (PXRD) studies of structure II mixed gas hydrates of CH₄ and C₃H₈ as guest with different compositions were performed. Kinetic stability of these mixed gas hydrate was examined by temperature ramping method by means of PXRD. It was revealed that none of them do not show of reduction of dissociation rates. These results may be useful for further understanding of natural gas hydrates.

References
Stern, L. A., Circone, S., Kirby, S. H., Durham, W. B., J. Phys. Chem. B., 2001, 105, 1756.
Takeya, S., Ripmeester, J.A., Angew. Chem. Int. Ed., 2008, 47, 1276.
Takeya, S., Ripmeester, J.A., ChemPhysChem, 2010, 11, 70.