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Methane Hydrate Crystallization on Sessile Water Droplets
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Pathways through Equilibrated States with Coexisting Phases for Gas Hydrate Formation
1Department of Chemistry, Boston University , Boston, Massachusetts 02215-2521, United States.
The Journal of Physical Chemistry. B
|December 2, 2015
Summary
Methane influences water
Area of Science:
- Thermodynamics and phase transitions
- Computational chemistry
- Materials science
Background:
- Water typically freezes into hexagonal or hexagonal/cubic ice.
- Hydrophobic guest molecules can form gas hydrates by trapping guests in clathrate cages.
- Understanding competing phase transition pathways is crucial.
Purpose of the Study:
- To investigate the phase transition pathways of water and methane under pressure.
- To elucidate the mechanism of gas hydrate formation.
- To determine the role of methane in ice formation.
Main Methods:
- Utilized a generalized replica exchange algorithm for equilibrium sampling.
- Simulated a dilute solution of methane in water at 200 atm.
- Analyzed sequences of states with coexisting phases.
Main Results:
- Initializing simulations with full replicas led to methane in hexagonal/cubic ice.
- Gradually adding replicas promoted initial hydrate growth.
- Formed hydrate induced water rearrangement into empty cages, forming metastable β ice.
- Methane was found to catalyze the formation of β ice over hexagonal/cubic ice.
Conclusions:
- Methane acts as a catalyst in the formation of β ice, a scaffold for hydrates.
- Empty cages are suggested as reaction intermediates in hydrate formation.
- The study provides insights into competing pathways in water-methane systems.
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