Oxabicyclic Guest Compounds as sII Promoters: Spectroscopic Investigation and Equilibrium Measurements

Area of Science:

• Materials Science
• Chemical Engineering
• Physical Chemistry

Background:

• Gas hydrates are crystalline solids trapping gas molecules, with applications in energy storage and transport.
• Promoters are crucial for stabilizing gas hydrates, but conventional options have limitations.
• Oxabicyclic compounds are explored as potential novel promoters for gas hydrate systems.

Purpose of the Study:

• To investigate three oxabicyclic compounds (ETHF, 14ECH, 12ECH) as novel promoters for methane (CH4) and nitrogen (N2) gas hydrates.
• To characterize the structure and thermodynamic stability of gas hydrates formed with these promoters.
• To evaluate the potential of these compounds as alternatives to conventional gas hydrate promoters.

Main Methods:

• Powder X-ray diffraction (PXRD) and synchrotron high-resolution powder diffraction (HRPD) for structural analysis.
• Solid-state 13C Nuclear Magnetic Resonance (NMR) and Raman spectroscopy for molecular characterization.
• Differential Scanning Calorimetry (DSC) for thermodynamic stability assessment.

Main Results:

• All three oxabicyclic compounds (ETHF, 14ECH, 12ECH) formed sII (Fd-3m) methane hydrates with distinct lattice parameters.
• CH4 molecules were confirmed to occupy sII-S cages, while the promoters acted as large guest molecules (LGMs) in sII-L cages.
• 14ECH demonstrated exceptional stability, forming a simple sII hydrate without help gases and significantly increasing CH4 hydrate dissociation temperature (~18 K).

Conclusions:

• The investigated oxabicyclic compounds are effective LGMs that enhance the thermodynamic stability of gas hydrates.
• 14ECH exhibits superior promotion capabilities, comparable to tetrahydrofuran (THF), and forms stable hydrates under various conditions.
• These novel promoters, particularly 14ECH, hold significant potential for advancing hydrate-based technologies and applications.