The effects of biosurfactants on gas hydrate formation in ocean sediments.

摘要

Recent discoveries of extensive gas hydrates in ocean sediments around the world center attention of researchers on vast amounts of natural gases and greenhouse gases in those hydrates. The extent of the discoveries were unexpected and inexplicable. In response to the discoveries, this research investigated the possible effect of microbial activities in promoting gas hydrate formation.; The critical micellar concentration (CMC) of rhamnolipid in distilled water at ambient conditions was found to be 1000 ppm by capillary surface tension measurement, but the value dropped drastically to 89 ppm at hydrate forming conditions. In seawater at ambient conditions, rhamnolipid was found to have a CMC as low as 400 ppm; it was estimated that the CMC drops to 36 ppm at hydrate-forming conditions.; At the CMC, hydrate formation was found to be greatly enhanced, determined by reduced induction time. Induction time in a sandpack was reduced from more than 100 hours for distilled water to 2 hours at the rhamnolipid CMC. Rhamnolipid in seawater also demonstrated very low induction times. This finding helps explain the occurrence of vast amounts of hydrates in ocean sediments.; Sodium dodecyl sulfate (SDS) and rhamnolipid at concentrations at or above CMC were found to generate micelles, solubilize gas, and to cause gas-laden micelles to rapidly migrate through a sandpack. This finding helps explain the connection of hydrates in a hydrate zone with activity outside the zone. Hydrate formation rate in a sandpack saturated with seawater increased 51% at the rhamnolipid CMC.; The results show that hydrate formation can be enhanced in sandpacks at very low biosurfactant concentrations (9 ppm for 100% active solution), which suggest that minimal microbial activity in ocean sediments could catalyze hydrate formation.