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Kinetic, equilibrium and morphology studies of hydrate forming systems Servio, Phillip


Gas hydrates are nonstoichiometric crystalline compounds that form naturally in certain environments on earth. Gas hydrates have been viewed as a nuisance in the oil and gas industry because they may impede oil and gas operations. On the other hand, hydrates are getting recognition as a potential future energy source. Furthermore, in situ methane hydrate is linked to global warming and carbon dioxide hydrate is linked to carbon dioxide sequestration. In this work, certain kinetic, equilibrium and morphological data were obtained. Such data is useful for the design of safe and economical technologies for gas transportation and storage and facilities to allow exploitation of gas hydrates. Specifically the following issues were addressed in this work. Measurements of the solubility of methane and carbon dioxide gas in liquid water in the presence of gas hydrates have been obtained. It is known that in the absence of gas hydrates the solubility of methane and carbon dioxide increases with decreasing temperature. It was found that the presence of hydrates changes this trend such that the solubility of methane and carbon dioxide decreases with decreasing temperature. The data agree well with theoretically calculated values. This information removes a controversy that existed in the literature. Equilibrium studies were performed on structure H hydrate forming system of methane-carbon dioxide-neohexane-water. It was found that the presence of neohexane greatly decreased the hydrate equilibrium pressure. It was also found that the composition of the gas phase affected the hydrate equilibrium conditions. The lowering of the equilibrium formation pressure favors the conditions for gas storage and transportation. A laser light scattering technique was employed in order to establish a new method to extract kinetic data. Hydrate growth experiments were performed using ethane-water as a model system for convenience. These experiments where conducted in the presence of monodispersed latex spheres of known size and charge. The study was inconclusive in ascertaining i f the presence of latex particles had any effect on the nucleation or growth of hydrate crystals. Morphological studies on structure I hydrates (methane and carbon dioxide) where performed on water droplets under different driving forces for hydrate nucleation in order to elucidate the mechanistic aspects of hydrate nucleation, growth, and decomposition. The driving force was defined as the deviation of the experimental pressure from the equilibrium hydrate formation pressure at the experimental temperature. Studies showed that higher driving forces gave smaller nucleation times along with jagged sharp surfaces. Lower driving forces gave larger nucleation times with smoother surfaces. Morphology studies were also performed on the structure H forming system of methane-neohexane-water. Observations concluded that the rate of growth of structure H hydrate crystals was much more rapid then those of structure I. The kinetics of growth were also found to depend on the amount of time methane was allowed to dissolve into neohexane and not the magnitude of the driving force present.

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