Molecular dynamics characterization of the interfacial structure and forces of the methane-ethane sII gas hydrate interface

TL;DR

This study uses molecular dynamics to analyze the interfacial structure and forces of methane-ethane sII gas hydrate interfaces, revealing temperature-dependent surface tension and complex water molecule behaviors relevant to hydrate nucleation.

Contribution

It provides detailed molecular-level insights into the interfacial tension and behavior of methane-ethane gas hydrates under various conditions, advancing understanding of hydrate formation.

Findings

Surface tension increases with temperature.

Water molecules form a quasi-liquid pre-melting layer.

Molecular dipole behavior is complex at the interface.

Abstract

The nucleation of gas hydrates is of great interest in flow assurance, global energy demand, and carbon capture and storage. A complex molecular understanding is critical to control hydrate nucleation and growth in the context of potential applications. Molecular dynamics is employed in this work combined with the mechanical definition of surface tension to assess the surface stresses that control some of the behavior at the interface. Ensuring careful sampling and simulation behavior, this work extracts meaningful results from molecular properties. We characterize the interfacial tension for sII methane/ethane hydrate and gas mixtures for different temperatures and pressures. We find that the surface tension trends positively with temperature in a balance of water-solid and water-gas interactions. The molecular dipole shows the complexities of water molecule behavior in small, compressed pre-melting layer that emerges as a quasi-liquid. These behaviors contribute to the developing knowledge base surrounding practical applications of this interface.