Abstract
In this study, the cage occupations of guest molecules in gas hydrates formed from methane-carbon dioxide, methane-ethane, and methane-propane mixtures are estimated using cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance (CP-MAS 13C NMR) technique. The 13C chemical shifts of the guest molecules depended on the type of hydrate cage. The cage occupations of two guest components were estimated from the integrated intensity ratio of the obtained NMR signals. In the methane and carbon dioxide system, the number of methane molecules in the large cages of structure I tended to decrease with an increase in the concentration of carbon dioxide as a second component. On the other hand, in the methane-ethane and methane-propane systems, the large cages were predominantly occupied by C2H6 or C3H8 rather than CH4 molecules. The cage occupancies of methane-ethane and methane-propane gas hydrates were almost full in the case of large cages, but a few small cages remained vacant.
