Does Confinement Enable Methane Hydrate Growth at Low Pressures? Insights from Molecular Dynamics Simulations

Area of Science:

• * Geochemistry and Materials Science
• * Energy Resources and Hydrocarbon Fuels

Background:

• * Natural methane hydrates represent a significant untapped hydrocarbon fuel source.
• * Optimal conditions for hydrate formation are high pressure and low temperature.
• * Porous materials may enable hydrate formation under milder conditions, but consensus is lacking.

Purpose of the Study:

• * To investigate methane hydrate formation in confined nanopores at milder conditions using molecular simulations.
• * To elucidate the effects of confinement on methane hydrate growth.
• * To determine if hydrate formation is possible at pressures lower than those required in bulk.

Main Methods:

• * Employed molecular dynamics (MD) simulations with a direct phase coexistence approach.
• * Conducted microsecond-scale simulations in the isobaric-isothermal (NPT) ensemble.
• * Studied methane-water systems in bulk and hydroxylated silica nanopores at 1-100 bar and 2 °C.

Main Results:

• * Validated TIP4P/ice water and TraPPE-UA methane models for accurate phase equilibria prediction.
• * Observed methane hydrate growth primarily in the center of nanopores, not at surfaces.
• * Demonstrated methane hydrate growth in nanopores at pressures too low for bulk formation.

Conclusions:

• * Confinement effects in hydroxylated silica nanopores facilitate methane hydrate growth at lower pressures.
• * This finding supports the potential for accessing methane hydrates as an energy source under less extreme conditions.
• * Dispersion corrections were found to artificially induce hydrate growth and were excluded.