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

Abstract

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 hydrate 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 nanobubbles 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 nanobubble 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.