Spectroscopic analysis of various gas hydrates and Reproduction of hydrate replacement phenomena

Abstract

Under low temperature and high pressure condition, various low molecular weight gas molecules like methane react with water, then clathrate hydrate is made. Clathrate hydrates called gas hydrates have some structures, sI, sII, sH etc. ‘Host’ water molecules make cage and then ‘guest’ gas molecules are entrapped. Gas hydrate is expected to replace petroleum energy. Because the amount of world gas hydrate is estimated more than twice as fossil fuel’s. Gas hydrates have infinite potential as the energy source of next generation. In this study, first, natural hydrate samples from East Sea are analyzed using various spectroscopic tools like NMR, Raman and PXRD. Hydration number and cage occupancy were identified by NMR and Raman spectroscopic data. Hydrate structure is revealed by PXRD pattern. Gas chromatography is also used to know the composition of hydrocarbons. Total five samples are analyzed, which are extracted all different spots. The result of analysis shows all natural samples are sI methane hydrates. Second, tuning pattern of tert-butyl alcohol hydrate is revealed. tert-upon the interaction of gaseous methane with the solid (TBA+$H_2O$), a clathrate host lattice is formed that can enclose both methane and TBA molecules. The complex structural and guest dynamic characteristics are examined by spectroscopic methods, including NMR, Raman and PXRD. The thermodynamic stability of the double hydrates is checked by direct gas release measurements. At low TBA concentrations a unique tuning pattern and a limiting critical guest concentration (CGC) are observed. The methane storage capacity of TBA appears to be much higher than that of THF, known to be one of the most powerful hydrate promoters. Last, at third, replacement ratio of $CH_4$ hydrate to $CO_2$ hydrate under seawater condition is analyzed. From methane peak area ratio of $^{13}C$ High Power Decoupling(HPDEC) NMR spectra, limiting substitution cage occupancy ratio is obtained. Limiting substitu...