C-13 NMR analysis and gas uptake measurements of pure and mixed gas hydrates: Development of natural gas transport and storage method using gas hydrate

Abstract

C-13 NMR spectra were obtained for pure CH4, mixed CH4+THF, and mixed CH4+Neohexane hydrates in order to identify hydrate structure and cage occupancy of guest molecules. In contrast to the pure CH, hydrates, the NMR spectra of the mixed CH4+THF hydrate verified that methane molecules could occupy only the small portion of 5(12) cages because the addition of THF, water-soluble guest component, to aqueous solution prevents the complete filling of methane molecules into small cages. Furthermore, from these NMR results one important conclusion can be made that methane molecules can't be enclathrated at all in the large 5(12)6(4) cages of structure II. In addition, gas uptake measurements were carried out to determine methane amount consumed during pure and mixed hydrate formation process. The moles of methane captured into pure CH, hydrate per mole of water were found to be similar to the full occupancy value, while the moles of methane captured into the mixed CH4+THF hydrate per moles of water were much lower than the ideal value. The overall results drawn from this study can be usefully applied to storage and transportation of natural gas.