(377q) Rapid Methane Hydrate Formation with Cyclopentane Hydrate Seed Crystals

Gas hydrates are one of prominent gas storage materials because they retain a high volumetric storage capacity up to 170 vol./vol., mild storage conditions, and less environmental risk. However, the kinetic rate of hydrate formation is too low to scale up due to diffusion limitations of guest molecules in the gas-liquid interface, and thus many chemical promoters have been suggested to accelerate the hydrate crystal growth in an unstirred reactor. We used cyclopentane hydrate crystals as seeds for methane hydrate formation to induce rapid hydrate nucleation and continuous crystal growth because cyclopentane hydrates can be easily prepared without any pressurization. In order to analyze the variation of structure and guest distributions, powder X-ray diffraction and Raman spectroscopy were utilized with various cyclopentane seed hydrate contents. The inclusion of cyclopentane cannot induce the tuning effect to occupy methane molecules in sII hydrate structure, and thus the amount of cyclopetane in binary sII cyclopentane + CH₄ hydrates can be controlled with the dosage of cyclopentane. With 0.0556 mol% cyclopentane (correspond to 1 mol% of stoichiometric amount of cyclopentane hydrate), hydrate nucleation simultaneously occurred with CH₄ hydrate growth. Moreover, the volumetric efficiency was maintained over 90 % of the theoretical value with the addition of SDS within an hour, and thus cyclopentane hydrate seeds, which have the sII structure, can accelerate sI methane hydrate formation with good efficiency in an unstirred reactor system.