Structural and Kinetic Studies of Structure I Gas Hydrates via Low Temperature X-Ray Diffraction and High Resolution Neutron Diffraction

Gas hydrates are materials of interest as sources for clean energy, carbon sequestration, greenhouse gas mitigation, and gas storage. This body of work presents two projects that each separately explore one aspect of the potential found in gas hydrates. Chapter 1 tackles the structural changes found to occur over the CO₂ [carbon dioxide] - CH₄ [methane] hydrate solid solution. The application here pertains to the sequestration of CO₂ in natural gas hydrates found in permafrost regions and ocean floors. As CO₂ is injected into the hydrate reservoir, CH₄ is released and recovered for energy use. Samples synthesized from liquid water were studied using high-resolution neutron diffraction. Static images of the nuclear scattering density of the free moving gas molecules were determined. Cage occupants and occupancies, the volume change of the unit cell and the individual cages based on composition were determined. Chapter 2 pertains to the decomposition of methane hydrate and a phenomenon termed anomalous preservation. Three samples were studied using in situ low temperature x-ray diffraction as they decomposed over a temperature range of 140 – 260 K and the kinetics were analyzed using the Avrami model. Activation energies and Avrami constants were determined for two temperature ranges within the overall range.