Molecular dynamics study of electric field enhanced hydrate growth for gas storage

Abstract

Clathrate Hydrates have gained much attention not only as a natural energy resource, their unique molecular structure and thermodynamic properties also hold promising applications in various industrial fields. However, sluggish formation kinetics limits the development of hydrate-based techniques, such as gas capture, separation and storage. Previous simulations and experimental studies have suggested the possibility that electric fields promote hydrate growth, but the mechanism behind the phenomenon has not been explained. To reveal the mechanism of the electric field promoting hydrate growth, the mass transfer of guest molecules and the hydrate crystal growth under the electrostatic fields are investigated by molecular dynamics simulations. Results show that electric fields with field intensities in the range of 0.4–0.9 V/nm have a significant promotion effect on methane hydrate growth. Under the effect of the electric field, the dipole direction of water molecules in the polarized hydrates is at three characteristic angles of 25, 50 and 75° from the electric field direction. Then, the orientation of the water molecules in the liquid phase approaches the characteristic angles of the hydrate crystal with the rising field intensity, which accelerates the ordering of the water molecules and the formation of hydrate cages. Methane molecules are gathered into an ellipsoidal bubble with non-uniform gas-liquid interface tension, creating a dominant channel for dissolution. Then, guest molecules can enter the bulk water by the dominant channel to aggregate with high concentrations, providing a driving force for the diffusion of guest molecules to the solid-liquid interface. In this study, the mechanism of how the electrostatic field promotes hydrate growth was revealed by molecular simulations. It provides a theoretical basis for the electric field's application in hydrate-related hydrogen and natural gas storage technologies.