Crystal growth of clathrate hydrate in a flowing liquid water system with methane gas

This paper reports the visual observation of the growth and formation of clathrate hydrate crystals in a stream of flowing liquid water presaturated with methane gas. The experimental apparatus used in this study was devised by inserting a porous pipe inside the reactor, thereby allowing methane hydrate crystals to form and grow in the liquid water stream. The morphology of methane hydrate crystals grown in a liquid water stream varied depending on the system subcooling temperature, ΔT_sub. ΔT_sub is defined as the difference between the equilibrium temperature of the hydrate, T_eq, and the system temperature, T_ex. The crystal growth in the bulk of liquid water was observed when ΔT_sub > 4.5 K. When 4.5 K < ΔT_sub < 9.0 K, polygonal flat plate crystals were observed growing from the porous pipe surface. At 9.0-10.0 K, the crystal morphology enters the transition phase, where the polygonal flat plate crystals started to change into dendritic crystals. When the subcooling temperature, ΔT_sub, is greater than 10.0 K, only dendritic crystals were seen to grow into the liquid water. On the basis of these observations, a continuous supply of the guest substance will enhance the growth of methane hydrate as the particle size of the crystals formed in this study was larger than that of the crystals observed in the previous study.