Molecular dynamics study of thermal-driven methane hydrate dissociation.

Nonequilibrium molecular dynamics simulations have been performed to investigate the thermal-driven breakup of both spherical methane hydrate nanocrystallites (with radii of approximately 18 and 21 A) and planar methane hydrate interfaces in liquid water at 280-340 K. The melting temperatures of each cluster were estimated, and dissociation was observed to be strongly dependent on temperature, with higher dissociation rates at larger overtemperatures vis-a-vis melting. For the 18 and 21 A radius nanocrystals, breakup was also seen to be dependent on cluster size, and different methane compositions (85%, 95%, and 100% of maximum theoretical occupation) in the planar case also lead to slight differences in the initial dissociation rate. In all cases, the diffusion of the methane into the surrounding liquid water was found to be an important step limiting the overall rate of breakup. A simple coupled mass and heat transfer model has been devised for both the spherical and planar hydrate systems that explains these findings, and distinguishes between the role of the overall thermal driving force and methane diffusional mass transfer in controlling the break-up rate.