Behaviors of NaCl Ions Intruding into Methane Hydrate under a Static Electric Field

KH Li and BB Chen and MJ Yang and YC Song and LL Jiang, JOURNAL OF PHYSICAL CHEMISTRY C, 125, 18483-18493 (2021).

DOI: 10.1021/acs.jpcc.1c04691

In this study, nonequilibrium molecular dynamics simulations (NEMDs) were used to investigate the thermodynamic properties and structural changes of methane hydrate (MH) in the NaCl solution at different temperatures (270-290 K, 40 bar) and electric field intensities (0-0.07 V/A). The dissociation rate of hydrate increases exponentially with the increasing electric field. Compared to pure water, the presence of salt ions in solution enhances the inhibitory effect of electric field on methane hydrates significantly. This is because the intensive electric field can drive the Na+ and Cl- ions into the methane hydrate layer to randomly replace some water molecules and subsequently form temporary and unstable cage structures. Some typical hydrate structures containing ions were observed and found that the ions exist as part of the cage, causing the distortion of the hydrogen-bond network. These structures are unstable and the ions can migrate easily from the cage, leading to the breakdown of the structures. Generally, the movement of ions in the hydrate is leaping and jumping rapidly from a metastable position to another. With the intensification of ion migration, nearby hydrates break down and form a flow channel in the middle of the hydrate layer, enabling the ions to move freely through the channel. These results provide useful insights into the mechanism of inhibition of methane hydrates using an electric field.

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