BIOSURFACTANT FROM MICROBIAL ACTIVITY IN OCEAN SEDIMENTS ENHANCES GAS HYDRATE FORMATION

Carbon stored in ocean-floor gas hydrates is estimated to exceed combined amounts in conventional natural gas, coal, and crude oil. The revelation is surprising because hydrates form very slowly in a quiescent laboratory-system, solubility of the hydrocarbon gases in water is low, and relatively long hydrate-induction times are required.

This paper presents laboratory findings that minimal microbial activity in sediments catalyze gas- hydrate formation. Affecting many physical properties of a solution, critical micellar concentration (CMC) of surfactant is found to greatly enhance hydrate formation. It is shown that CMC of a rhamnolipid biosurfactant at 25oC and 1 atm is reduced by a factor of 11.2 at hydrate-forming pressure and temperature, creating a very low threshold concentration for promotion of hydrate formation; concentrations of rhamnolipid as low as 9 ppm are determined to provide the hydrate catalyzing effect. Rhamnolipid biosurfactant micelles at the CMC solubilize hydrocarbon gas and serve as nucleation sites for hydrate formation; micelles laden with gas at the CMC reduce hydrate induction time 82% in a seawater-saturated sand pack; hydrate formation rate increases 53%. These micelles are shown to rapidly migrate through a sand pack. Therefore, minimal microbial activity that generates biosurfactant can increase gas solubility in the water, reduce hydrate induction time, increase hydrate formation rate, and transport gas into the ocean sediment's hydrate zone from distant originating sites. A mechanism of biosurfactant micellar nucleation, gas solubilization, water structuring, and biosurfactant micellar migration is presented.