Methane Hydrate Crystal Growth At the Gas/Liquid Interface in the Presence of Sodium Dodecyl Sulfate

This study reports the visual observation made of the formation and growth of clathrate hydrate on the surface boundary of a Sodium Dodecyl Sulfate (SDS) aqueous solution droplet and surrounding methane gas. The experimental temperature range was from 276 K to 282 K, under the pressure of 7.8 MPa, at pure water, wSDS = 10 ppm and wSDS = 100 ppm, where wSDS denotes the mass fraction of SDS in the aqueous solution. At pure water and wSDS = 10 ppm, the hydrate crystals were initially observed at the droplet surface, and followed by lateral growth at the droplet surface. However, at wSDS = 100 ppm, it was observed that hydrate growth behavior greatly changed compared to pure water system. At wSDS = 100 ppm and ΔTsub < 6.0 K, the structure of the droplet was not maintained and hydrate crystals grew horizontally on to the stage. We defined the subcooling, ΔTsub, the difference between the system temperature and the equilibrium temperature of methane hydrate as driving force index for crystal growth. At wSDS = 100 ppm and ΔTsub ≥ 6.0 K, the hydrate grew perpendicularly to the stage. At wSDS = 100 ppm and each ΔTsub, the amount of hydrate produced increased compared to pure water system.