10.1021/jp500081t.s001
Anh Phan
Anh
Phan
David
R. Cole
David
R.
Cole
Alberto Striolo
Alberto
Striolo
Aqueous
Methane in Slit-Shaped Silica Nanopores: High
Solubility and Traces of Hydrates
American Chemical Society
2014
methane solubility
methane hydrates stability
width 1.0 nm
OH
nonbridging oxygen atoms
bulk systems
simulation
bulk methane pressure
methane hydrates
cage adsorption hypothesis
2014-03-06 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Aqueous_Methane_in_Slit_Shaped_Silica_Nanopores_High_Solubility_and_Traces_of_Hydrates/2317726
Equilibrium
molecular dynamic simulations were employed to investigate
the methane solubility in water confined between two parallel silica
surfaces. The solid substrate was obtained from β-cristobalite;
all nonbridging oxygen atoms were protonated. The resultant surface
density of OH groups was ∼4.54 sites per nm<sup>2</sup>. The
simulations were conducted at constant temperature, 300 K, and at
increasing bulk methane pressure for pores of width 1.0 nm. For bulk
systems, these thermodynamic conditions are outside the window of
methane hydrates stability. Methane solubility in confined water was
found to far exceed that in bulk systems. The increase in tangential
pressure, observed under confinement, cannot solely explain the marked
increase in solubility predicted by our simulations. Most likely,
the structure of confined water favors the sequestration of methane.
The excess chemical potential for methane was found to significantly
decrease within the confined water compared with that in the bulk
phase. On the basis of the cage adsorption hypothesis for hydrate
nucleation, the predicted solubility of methane in the confined water
(up to ∼0.05 mol fraction) is large enough to suggest the possible
formation of methane hydrates. Indeed, analysis of simulation data
shows the presence of amorphous cages of hydrogen-bonded water that
host a single methane molecule. Within the limits of our simulations,
these amorphous cages last for only short times. Perhaps the pores
considered are too narrow to allow the formation of stable methane
hydrates, and perhaps longer simulations would allow us to observe
the formation of a hydrate nucleus. The large methane solubility in
confined water predicted by our simulations might have consequences
for hydraulic fracturing and other technological processes.