Kinetic rate of methane hydrate film growth from microsecond molecular dynamics simulations

Abstract

Microsecond molecular dynamics (MD) simulations are employed in the isobaric–isothermal ensemble for the determination of the growth rate of sI methane hydrate. Statistically meaningful measurements of the growth rate are given for a wide range of pressures and temperatures. The reported growth rates are measured from the MD trajectories with two different methods. The first method is based on the time evolution of the potential energy of the system by correlating the rate of potential energy decrease to the speed of the moving hydrate interface. The second method that was originally introduced in the current study uses Voronoi tessellation to characterize the molecules depending on their neighborhood and thus allows the identification for each time step of the exact position of the interface. Both methods yield practically identical results. At the low pressure regime, the MD results are compared to available experimental data with highly satisfactory agreement. A useful correlation for engineering applications is suggested, which offers prediction of the methane growth rate as a function of the concentration of methane in the aqueous phase between the supersaturated and the isobaric equilibrium conditions. The calculated hydrate growth rates are also compared to reported experimental and MD simulations data.