Molecular Dynamics Study of Clathrate-like Ordering of Water in Supersaturated Methane Solution at Low Pressure

• Published in: Molecules (Basel, Switzerland) Vol. 28; no. 7; p. 2960
• Main Authors: Belosludov, Rodion V, Gets, Kirill V, Zhdanov, Ravil K, Bozhko, Yulia Y, Belosludov, Vladimir R, Chen, Li-Jen, Kawazoe, Yoshiyuki
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 26.03.2023; MDPI
• Subjects: amorphous hydrate; Analysis; Cavities; Clathrate compounds; Clathrates; Computer simulation; Energy storage; gas hydrates; Health aspects; Holes; Hydration; Hydrogen; Hydrogen bonding; Hydrogen bonds; Hypotheses; intramolecular hydrogen bonds; Low pressure; Methane; Methods; Molecular dynamics; nucleation mechanism; Supersaturation; Water chemistry; Russia; nucleation mechanism; computer simulation; gas hydrates; amorphous hydrate; intramolecular hydrogen bonds
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules28072960

Using molecular dynamics, the evolution of a metastable solution for "methane + water" was studied for concentrations of 3.36, 6.5, 9.45, 12.2, and 14.8 mol% methane at 270 K and 1 bar during 100 ns. We have found the intriguing behavior of the system containing over 10,000 water molecules: the formation of hydrate-like structures is observed at 6.5 and 9.45 mol% concentrations throughout the entire solution volume. This formation of "blobs" and the following amorphous hydrate were studied. The creation of a metastable methane solution through supersaturation is the key to triggering the collective process of hydrate formation under low pressure. Even the first stage (0-1 ns), before the first fluctuating cavities appear, is a collective process of H-bond network reorganization. The formation of fluctuation cavities appears before steady hydrate growth begins and is associated with a preceding uniform increase in the water molecule's tetrahedrality. Later, the constantly presented hydrate cavities become the foundation for a few independent hydrate nucleation centers, this evolution is consistent with the labile cluster and local structure hypotheses. This new mechanism of hydrogen-bond network reorganization depends on the entropy of the cavity arrangement of the guest molecules in the hydrate lattice and leads to hydrate growth.