Abstract:

To discuss the affects of the different gas compositions and environment media on the forming of the different complicated clathrate hydrates with the different structure types,and hydration numbers, this study analyzed the crystal filling process of the hydrate, the crystal construction type,and the dynamics characteristics in the singleness system(CH₄, CO₂, and C₃H₈,respectively)and in the duality system(CH₄+CO₂, CH₄+C₃H₈, and CH₄+N₂,respectively), and proceeded to analyse the results using Raman spectra. The results show that the methane fills the small cavities of 512 and the large cavities of 5¹²6² forming structure Ⅰ clathrate hydrate(ＳⅠ),CO₂ and C₃H₈ only occupy the large cavities of 5¹²6⁴ forming structure Ⅱ clathrate hydrate(ＳⅡ) in the singleness system,and that in the duality system the small cavities are only filled by CH₄,neither  CO₂ nor N₂ and C₃H₈ is found. Applying the deconvoluting v1 symmetric bands to measure the relative occupancy factors of CH₄ in the large cavities and in the small cavities of SⅠ, and according to the area ratio (corresponding to the small cavities and to the large cavities) of the bands, and computing the cavity occupancy factors and the coupling hydration numbers of methane hydrate under a few equilibrium terms,it is shown that the size of the gas molecule not only affects the appearance and the type of the  filling cavities , but also do the structure type and the hydration number of hydrates.

Key words: clathrate hydrate, Raman spectrum, hydration number, coupling relationship