Atmospheric Pressure Raman Investigation of Binary Clathrate Hydrates in Their Role in New Energy Applications

Clathrate hydrates are hydrogen-bonded water molecules that form cage-like structures at high pressures and low temperatures. These clathrate hydrates enclathrate guest molecules and have applications in flow assurance, hydrogen storage, desalination, carbon capture and storage, and natural gas resources. Cyclopentane (CP) and tetrahydrofuran (THF) are both structure II clathrate formers that occupy the large cages within the structure, and are of interest because they promote clathrate hydrate formation in addition to reducing the required formation pressure. Other studies have observed a synergistic effect between THF and CP clathrate hydrates when small gases like carbon dioxide occupy the small cages, however, no studies have been done to analyze the relationship between CP and THF clathrate hydrates on their own. In this study, Raman spectroscopy is used to analyze these binary clathrate hydrate mixtures at varying molar ratios of CP/THF/water to determine the dissociation temperature. Additionally, the role of promoters in increasing the speed of clathrate hydrate formation is examined to determine the impact and optimum composition for clathrate hydrate formation. Our findings include that 0.5CP:0.5THF:17H2O and 0.75CP:0.25THF:17H2O (molar ratio) mixtures form most quickly with the greatest clathrate hydrate conversion, and that the latter mixture has a higher dissociation temperature than CP clathrate hydrates alone. This optimum mixture is favorable both thermodynamically and kinetically. Because it is more stable and can be formed/maintained at atmospheric pressure and higher temperatures, it has major implications for new energy technologies. Preliminary findings also reveal the mechanism in which the binary clathrate hydrate dissociation occurs, leading us to believe that THF actually remains within the large clathrate cages longer than CP. Further investigation is required to understand this phenomenon.