A New Habit for Deep Marine Resources
Professor Garrison Sposito, of the University of California, Berkeley, has investigated a new morphology for methane hydrate crystallization by computational modeling of
clay minerals. Methane hydrates are a major potential natural gas resource, but they are primarily found in very low temperature, high pressure environments in deep marine sediments. They usually form either as pore-fillings
within granular sediments, or as coatings on grain boundaries. New Monte Carlo and molecular dynamic simulations have been used to investigate methane hydrate crystallization and stabilization within the interlayers of hydrated
Na-montmorillionite, a 2:1 clay mineral observed in oceanic sediments with naturally occurring hydrates. Interlayer methane hydrate model structures are predicted to occur at pressures from 10-30 atmospheres and at temperatures
up to 300K. The hydrate can exist in a three-layer structure with Na-montmorillionite containing 0.5, 1.0, or 2.25 CH4 per clay mineral unit cell. The modeling strongly suggests that only the 0.5 CH4/clay mineral unit cell geometry is stable. The molecular dynamics simulations suggest that the mechanism for stabilizing the hydrate is a repulsive "guest-host" interaction.
|
Methane-22 oxygen coordination is observed involving methane-water
and methane-clay interactions. The methane molecule (gray) is surmounted by an umbrella-like water structure, while below it is a hexagonal ring of clay surface oxygens.
|
|
|
|
|
Closeup snapshot of "hydrate forming" methane-water
clathrate near the clay surface.
|
Side view of the 0.5 CH4 per unit cell system. Water molecules and cations are shown together with the clay structure. .
|
|
|
