Different pathways for methane hydrate nucleation and crystallization at high supercooling: Insights from molecular dynamics simulations

Natural gas hydrates are potential energy sources in the future, and thus it is important to understand its microscopic formation process. In this study, fourteen molecular dynamics (MD)trajectories were performed using the all-atom models by direct molecular dynamics simulations to investigate the nucleation and crystallization of methane hydrate from two-phase system of methane and water at T = 250 K and P = 50 MPa. Due to the strong interaction parameters used between water and methane in this study, methane molecules from gas phase can quickly enter the water phase to form supersaturated solution in the initial stage, increasing the probability of nucleation and the formation rate of hydrates. It was found that the hydrate nucleation and growth rate were slow in the initial configurations with the low-content methane, which is more conducive to the formation of crystalline hydrate. In configurations with low-content methane, sI crystal domains, sII crystal domains and polycrystalline structures with the coexistence of sI-like and sII were observed obviously in three trajectories. Our simulated results show that, at high supercooling, methane and water can still directly form crystalline methane hydrate. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study investigated the nucleation and crystallization of methane hydrate using molecular dynamics simulations, revealing that configurations with low-content methane are more conducive to hydrate formation. The results show that under high supercooling conditions, methane and water can still directly form crystalline methane hydrate.