An estimated 1000 trillion cubic meters of gas in the unconventional hydrocarbon resource of gas hydrates in the world?s ocean floors far exceeds the known hydrocarbons in conventional reserves like coal, petroleum, and natural gas. These hydrate deposits also contain massive amounts of the greenhouse gases like methane and carbon dioxide. As relatively little is known about the oceanloor natural gas hydrates, mechanisms leading to the formation of these hydrates in ocean sediments need to be investigated before the significant technical challenges of recovery and environmental hazards are addressed. The subject research focuses on possible catalytic effects of biosurfactants on the formation of natural gas hydrates in oceanloor sediments. Sand/clay packs were saturated with seawater containing 1000 ppm of biosurfactant and pressurized with natural gas of 90 mole% methane, 6 mole% ethane and 4 mole% propane. The experimental results showed that gas hydrates formation in porous media is catalyzed by biosurfactants at very low concentrations. Commercially available representatives from the five biosurfactant classifications that microbes produce were purchased and evaluated in sand/clay packs at hydrateorming conditions. The rate of formation and induction time differed in the presence of bentonite and kaolin. The surface activities of biosurfactants were either specific to sand or clay surfaces. While in the presence of bentonite, Surfactin decreased hydrate induction time by 71% over a reference test with no biosurfactant in the seawater; Surfactin lowered induction time by 25% in the presence of kaolin. Rhamnolipid reduced the induction time by 58% in the presence of bentonite and by 66% in the presence of kaolin. Snomax and Emulsan, belonging to the classification of polysaccharide lipid complexes, reduced induction time by 30 to 40% in the presence of both kaolin and bentonite. Fatty acids reduced the induction time by 55% in the presence of bentonite and by 20% in the presence of kaolin. Surfactin enhanced the rate of formation by 400% in the presence of bentonite, but it had minimal effect in the presence of kaolin. Emulsan and Snomax increased the rate of formation by 250%, while rhamnolipid and phospholipids doubled formation rate in the presence of bentonite. Emulsan increased the rate of formation by 800%. In seawater, at hydrateorming conditions, rhamnolipid was found to have a critical micellar concentration of 12 ppm. This very low value of CMC suggests that minimal bacterial activity in ocean sediments could greatly catalyze hydrate formation. The recent analysis by Lanoil et al. (2001) of sediments from around gas hydrate mounds in the Gulf of Mexico gives a direct association between microbes and gas hydrates and supports the conclusions of the subject work.
| Identifer | oai:union.ndltd.org:MSSTATE/oai:scholarsjunction.msstate.edu:td-1966 |
| Date | 03 August 2002 |
| Creators | Kothapalli, Chandrasekhar R |
| Publisher | Scholars Junction |
| Source Sets | Mississippi State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
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