Raman Spectroscopic Studies on Microscopic Mechanism of CP - CH4 Mixture Hydrate

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The formation of methane hydrates which occur in extreme thermodynamic conditions can be considerably reduced by addition of cyclopentane (CP). To elucidate the structure, composition, cage occupancy and analyze the crystal filling process of the hydrate, Raman spectroscopy of intramolecular vibration mode for each guest species in CP- CH4 mixed-gas hydrates have been measured. The Raman spectra reveal that CP molecules occupy the large cavities (51264) and CH4 molecules only occupy the small cavities (512) sII hydrates. The hydrogen-bonded water molecules arrange around CP molecules in the same way as in clathrate hydrate, which enhances the intrinsic enclathrate rate. The cavity occupancy and hydration number are calculated based on Raman bands area ratio. The cage occupancies of CP and CH4 reach 0.9976 and 0.2044 at 3.5 MPa, respectively. At 12 MPa, they are 0.9958 and 0.4098, respectively.