Molecular Insights on Methane Hydrate Dissociation in the Presence/Absence of Poly-N-vinylcaprolactam: Effects of Gas Saturation and Nanobubbles

Abstract

Natural gas hydrate (NGH) is a promising clean energy source with abundant reserves. Unveiling the mechanisms controlling hydrate dissociation and finding chemical agents that promote hydrate dissociation are of great significance for achieving controllable exploitation of NGH. This study utilized molecular dynamics simulation to investigate the dissociation mechanism of hydrates under different gas saturation levels as well as the influence of poly-N-vinylcaprolactam (PVCap) on hydrate dissociation. The simulation results indicate that in the systems without PVCap, the release rate of methane molecules from the methane hydrate increases with the methane content in the initial liquid phase. The systems with different methane saturations undergo different hydrate dissociation stages. For the systems with PVCap, it was found that PVCap has a certain promoting effect on methane hydrate dissociation; the promotion effect decreased with the increase in methane content in the initial liquid phase. The mechanism by which PVCap on methane hydrate dissociation was proposed: PVCap can adsorb methane molecules, promoting the formation of nanobubbles, reducing methane concentration in the liquid phase, thereby increasing the driving force for methane hydrate dissociation, and promoting the dissociation of methane hydrates.