Tuning behaviors of methane inclusion in isoxazole clathrate hydrates

In this study, the inclusion of methane (CH₄) gas in isoxazole (C₃H₃NO) clathrate hydrates was investigated through spectroscopic observations, such as powder X-ray diffraction (PXRD) and Raman spectroscopy. PXRD patterns of isoxazole clathrate hydrates having two different mole fractions of water were analyzed, and Raman spectroscopy was used to understand the CH₄ inclusion behaviors in the hydrate cavities. Raman spectra indicated that CH₄ can be captured in both small and large cavities of structure II hydrate in the C₃H₃NO with 34H₂O system, while CH₄ can be entrapped in only small cavities of structure II hydrate in the C₃H₃NO with 17H₂O system. The PXRD result showed both clathrate hydrate samples exhibit the same cubic Fd3m structure II hydrate as expected. However, the structure II hydrate in the C₃H₃NO with 34H₂O system includes a small amount of hexagonal ice and structure I CH₄ hydrate. The phase equilibrium conditions of the binary (isoxazole + CH₄) clathrate hydrate were also identified through high-pressure micro differential scanning calorimetry (MicroDSC), and the equilibrium temperatures of the binary (isoxazole + CH₄) clathrate hydrate at given pressures are higher than those of the structure I CH₄ hydrate.