Diversity in Crystal Growth Dynamics and Crystal Morphology of Structure-H Hydrate

This paper demonstrates the diversity in crystal growth dynamics and crystal morphology of structure-H hydrate formed with methane and methylcyclohexane (MCH) correlated to the driving force. ΔT_sub, which is the difference between the experimental temperature of the crystal growth and the phase equilibrium temperature, was used as an index of the driving force. At ΔT_sub = 1.6 and 3.2 K, hydrate crystals were initially formed at the water/MCH interface and grew into the hydrate film covering the interface. After the entire interface was covered by the hydrate film, the hydrate growth stopped. The shape of individual hydrate crystals was polygonal. The size of hydrate crystals was smaller with increasing ΔT_sub. At ΔT_sub = 5.3 K, the first hydrate crystals were observed at the water/MCH interface and crystals grew not only along the interface but also toward the interior of MCH phase, even after the water/MCH interface was completely covered by the hydrate film. The dendritic hydrate crystals were observed at the interface at ΔT_sub = 5.3 K. The implications of these observations on crystal morphology on determining the conditions for methane capture for the purpose of storage and transportation are discussed.