Theory and Kinetic Monte Carlo Simulation of Guest Molecule Transport in sI Clathrate Hydrates Based on Cage Hopping

Abstract

Guest migration in clathrate hydrates is a slow but important process for reaching thermodynamic equilibrium. The transport of guest molecules in a hydrate lattice is considered as a series of hopping events from an occupied cage to an empty neighboring cage facilitated by water vacancies and without significant lattice restructuring in the bulk. In this work, we developed an analytical model for determining the equilibrium distribution and the diffusivity of gas molecules in the cages of sI clathrate hydrate based on their hopping rate. Furthermore, kinetic Monte Carlo simulations were performed to verify the analytical model. The equilibrium occupancies, transport (Fickian) and jump (Maxwell–Stefan) diffusion coefficients, and the thermodynamic correction factors determined from the analytical model are in excellent agreement with the simulation results. Using the hopping rate constants determined based on transition path sampling calculations, we obtain the methane transport-diffusion coefficient at 27...