MEASUREMENT OF CLATHRATE HYDRATES VIA RAMAN-SPECTROSCOPY

Raman spectra of clathrate hydrate guest molecules are presented for t hree known structures (I (sI), II (sII), and H (sH)) in the following systems: CH4 (sI), CO2 (sI), C3H8 (sII), CH4 + CO2 (sI), CD4 + C3H8 (s II), CH4 + N-2 (sI), CH4 + THF-d(8) (sII), and CH4 + C7D14 (sH). Relat ive occupancy of CH4 in the large and small cavities of sI were determ ined by deconvoluting the nu(1) symmetric bands, resulting in hydratio n numbers of 6.04 +/- 0.03. The frequency of the nu(1) bands for CH4 i n structures I, II, and H differ statistically, so that Raman spectros copy is a potential tool to identify hydrate crystal structure. Hydrat e guest compositions were also measured for two vapor compositions of the CH4 + CO2 system, and they compared favorably with predictions. Th e large cavities were measured to be almost fully occupied by CH4 and CO2, whereas only a small fraction of the small cavities are occupied by CH4. No CO2 was found in the small cavities. Hydration numbers from 7.27 to 7.45 were calculated for the mixed hydrate.