(320b) Molecular Simulation of Clathrate Hydrates In Porous Media

Clathrate hydrates are co-crystals of water and gases which form under high pressure and low temperature conditions (e.g 3-10 MPa and 275-285K for methane hydrates). Hydrates are formed of hydrogen bonded polyhedral water cages which accommodate small hydrophobic guest molecules (< 0.9nm). Industrially, clathrate hydrates are important for several reasons. Huge amounts of methane is trapped in hydrates found in permafrost and the continental margins. Clathrate hydrates also obstruct gas flow in undersea pipelines, leading to economic loss and ecological risks. Finally, these materials have been suggested as possible storage media for hydrogen and for sequestrating greenhouse gases such as carbon dioxide.

The properties of clathrate hydrates confined in porous materials differ from those of bulk clathrate hydrates. Experimental studies show an enhancement of clathrate stability when confined in porous media. To understand this stabilization and the formation of the clathrate hydrates in porous media we perform Grand Canonical Ensemble Monte Carlo (GCMC) simulations of these compounds in slit-shaped pores of width approximately 2-3 nm. The fluid-wall interaction is modeled by the '10-4-3' (Steele) potential. Simulations are done using the Monte Carlo for complex chemical systems (MCCCS) Towhee package, generally under conditions of constant water density and varying methane chemical potential; temperature scanning curves at constant pressure are also simulated. sI type methane hydrate clathrates are simulated, with water and methane modeled by the SPC-E and OPLS-UA force fields respectively.