Molecular Dynamics Simulation Studies of Gas Hydrate Growth with Impingement.

During hydrate growth with impingement, hydrate cages were found to be occupied simultaneously by two methane molecules, even in the 51262 cage which was thought to be impossible. The diffusion during the methane hopping process is found to be 3~4 order of magnitude faster than that during hopping between one-occupied and empty hydrate cages. [Display omitted] • hydrate growth with impingement has been first investigated using molecular simulation. • 51262 hydrate cages with two methane molecules have been found. • 3~4 order of magnitude faster diffusion has been found caused by two-occupied cages. Clathrate hydrates have attracted much attention in energy and environment technology as well as the nature of icy bodies. We report a molecular dynamics simulation study of methane hydrate growth with impingement which has not been investigated by either experiment or simulation as far as the authors' knowledge. Several unique features have been discovered including dislocation, two occupied hydrate cages and fast methane diffusion. A certain proportion of hydrate cages were found to be occupied simultaneously by two methane molecules, even in the 51262 cage which was thought to be impossible. Methane molecules were demonstrated to hop between two-occupied and one-occupied hydrate cages as well as between gas bubble and nearby hydrate cages when a gas bubble was present. The diffusion rate during the hopping process is in the order of 10-9 to 10-8 m2/s, which is 3~4 order of magnitude faster than that during hopping between one-occupied and empty hydrate cages. [ABSTRACT FROM AUTHOR]