A molecular dynamics study on nanobubble formation and dynamics via methane hydrate dissociation

The formation condition of nanobubbles and its effect on the methane hydrate dissociation were studied using molecular dynamics (MD) simulations. To investigate the effect of liquid water proportion on the methane hy-drate dissociation path and nanobubble formation conditions, two different initial configurations were built. Considering low liquid water proportion simulation, four main dissociation stages were identified, and nano-bubbles formed when the methane supersaturation condition was met. During this period, hydrate dissociation rate decreases and fluctuates around zero, indicating that mass transfer limitation forms and hydrate cages undergo a long-term disappearance and rebuilding process. Nanobubbles can form in two distinct regions: the liquid water region and the final hydrate slice region. Hydrate dissociation rate increased after the first nano-bubble formed, which broke the mass transfer limitation. Small nanobubbles formed at the end of the hydrate dissociation process also contributed to the final hydrate slice collapsing by shortening the diffusion distance of methane molecules to the gas phase. At the end of the simulation, only one nanobubble survived in the system with a mole percent of methane in water for two systems remaining at 0.4 and 0.9, respectively.

Automated summary

This study investigated the formation condition of nanobubbles and its effect on the dissociation of methane hydrate through molecular dynamics simulations. Two different initial configurations were used to examine the influence of liquid water proportion on the dissociation path and nanobubble formation. The results revealed four main dissociation stages under low liquid water proportion, with nanobubbles forming when the methane supersaturation condition was met. The formation of nanobubbles broke the mass transfer limitation, leading to an increased hydrate dissociation rate. Small nanobubbles formed at the end of the dissociation process contributed to the collapse of the final hydrate slice by shortening the diffusion distance of methane molecules to the gas phase. One surviving nanobubble was observed at the end of the simulation for systems with methane mole percent in water of 0.4 and 0.9, respectively.