**Surfactants and Biosurfactants Catalyze Gas Hydrate Formation**

*R.E. Rogers (Mississippi State University*)

Abstract Number: **Rogers91**

**Figure ** - Micellar solution increases gas hydrate formation rate.

**Introduction**: Gas hydrates have two extraordinary physical
properties-storage of natural gas in amounts of 180+ vol/vol and
selective occlusion of gases based on gas molecular size. These
properties are manifested in the vast occurrence of gas hydrates in
ocean sediments that contain natural gases and greenhouse gases. Also,
the properties signal a potential for storage and transport of natural
gas in synthetic gas hydrates. We have studied means to enhance
formation mechanisms for natural gas storage, which led to a study of
the mechanism of gas hydrate formation in ocean sediments. Specifically,
the effects that were found of micellar solutions, surfactants, and
bioagents on gas hydrate formation and how those results suggested other
uses of gas hydrates are reported.

**Figure ** - Storage capacities of natural gas in gas hydrates from
micellar solution.

**Methods and Materials**: Gas storage tests were conducted in a
high-pressure hydrate test cell of 3900 ml capacity which was cooled by
circulation from a constant-temperature refrigerated bath. Omega
software facilitated collection of data transmitted from a pressure
transducer, RTDs and mass flow meter that monitored test-cell press,
temperature and gas flow rates. Ports in the test cell accommodated
camera and fiber optics lighting; a constant-pressure regulator
maintained desired pressure. Gas volumetric flows, pressure,
temperature, and time traces in conjunction with visual observations
allowed interpretation of hydrate formation.

For tests related to ocean-floor sediments, hydrate formation in a
sand/clay pack was followed with an array of RTDs and a pressure
transducer in two, refrigerated, stainless steel test cells. Micellar
solutions were injected into the bottom of the pack with a piston
metering-pump. Pinpointing of hydrate formation was easily followed by
temperature-time traces from the RTDs.

**Results**: Fig. 1 shows the \>700 fold increase in gas-hydrate
formation rate of a non-stirred system using 284 ppm sodium dodecyl
sulfate micellar solution. As they formed, gas hydrates packed
symmetrically by adsorption on the test-cell walls, continuing until the
test cell was packed in less than 3 hours with 156 volumes of natural
gas at standard temperature and pressure per volume of hydrate. Fig. 2
shows the capacity-pressure-time relationship for gas hydrate formation
in a non-stirred micellar solution at 35EF. The results indicated the
overcoming of major obstacles toward utilizing unique gas-hydrate
properties for natural gas storage.

With biosurfactant present above its CMC, induction time for hydrate
formation in a sand pack saturated with sea water was reduced by 86%.
Additionally, hydrate formation rates in the sand pack saturated with
sea water increased 53% in the presence of biosurfactant. At
hydrate-forming conditions, the biosurfactant rhamnolipid's CMC was
estimated to be less than 36 ppm in sea water, suggesting that even
minimal microbial activity in ocean sediments may suffice to
substantially catalyze hydrate formation.

**Conclusions**: Micellar solutions make feasible industrial storage of
natural gas in synthetic gas hydrates. Biosurfactants from minimal
activity of bacteria in ocean sediments probably catalyze gas hydrate
formation.