Revealing the Impact of Temperature, Pressure, and Ethylene Glycol Concentration on Methane Hydrate Melting: A Molecular Dynamics Perspective

Hydrates are a highly promising clean energy resource; however, the large-scale melting of hydrate deposits could trigger geological disasters, potentially causing seabed instability and impacting the global climate. Therefore, understanding the mechanisms behind natural gas hydrate melting is of great significance to both science and industry. Most research on the melting of hydrates under varying temperature and pressure conditions has been experimental in nature, and the same applies to studies on the effects of hydrate inhibitor concentrations on hydrate melting. There are few studies based on molecular dynamics simulations. Currently, the hydrate inhibitors that have been investigated primarily include NaCl, methanol, amino acids, certain types of kinetic hydrate inhibitors, and some polymers. As one of the representative thermodynamic inhibitors of hydrates, ethylene glycol theoretically has a significant effect on hydrate decomposition; yet, there has been limited research on this topic. Through molecular dynamics simulations, we investigated the effects of temperature and pressure on methane hydrate melting as well as the impact of ethylene glycol at both low and high concentrations on the melting of methane hydrates. We also analyzed the underlying mechanisms. Additionally, we examined how ethylene glycol promotes hydrate melting. The study revealed that an increase in the system temperature facilitates the melting of hydrates, whereas an increase in the system pressure inhibits this process. A 15 wt % concentration of ethylene glycol emerged as a critical turning point: when the concentration of ethylene glycol is below 15 wt %, an increase in its concentration hinders hydrate melting, but above 15 wt %, increasing ethylene glycol concentrations promotes hydrate melting. Ethylene glycol primarily promotes hydrate melting in two ways: first, the hydrophilic part of the ethylene glycol molecules can insert into the lattice voids of the hydrate, disrupting the hydrogen-bond network and destabilizing the lattice. Second, ethylene glycol molecules also facilitate the release of methane molecules from the hydrate cages.