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, w_SDS = 10 ppm and w_SDS = 100 ppm, where w_SDS denotes the mass fraction of SDS in the aqueous solution. At pure water and w_SDS = 10 ppm, the hydrate crystals were initially observed at the droplet surface, and followed by lateral growth at the droplet surface. However, at w_SDS = 100 ppm, it was observed that hydrate growth behavior greatly changed compared to pure water system. At w_SDS = 100 ppm and ΔT_sub < 6.0 K, the structure of the droplet was not maintained and hydrate crystals grew horizontally on to the stage. We defined the subcooling, ΔT_sub, the difference between the system temperature and the equilibrium temperature of methane hydrate as driving force index for crystal growth. At w_SDS = 100 ppm and ΔT_sub ≥ 6.0 K, the hydrate grew perpendicularly to the stage. At w_SDS = 100 ppm and each ΔT_sub, the amount of hydrate produced increased compared to pure water system.