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 275 K to be 5.06 × 10–14 m2/s, which is in good agreement with the recent experimental measurements (4.00 × 10–14 m2/s at 275 K). In addition, the analytical model is useful for identifying the predominant cage hopping pathways for equilibrium and transport properties.

Understanding the effect of moderate concentration SDS on CO2 hydrates growth in the presence of THF

“…Such aggregates are roughly spherical in shape, which is typical of an SDS micelle in water at low concentration [54]. However, SDS micelles in water at ambient conditions are usually between 3.5 to 4 nm in size, which is larger than the aggregate obtained within our system, which is only 2.5 nm.…”

CH/CH2 Group Clusters Doping Methane Hydrate Cages

“…When nanoscale methane hydrate forms in the confined silica gel pores, methane gas absorbs into the surface of the confined hydrate. Surface defects, distortions, and water vacancies − are widely present in nanoscale methane hydrate confined in silica gel pores. Surface defects and distortions are more likely responsible for the low activation energy of methane derived from previous results − on the dissociation and adsorption of methane on hydrate surfaces.…”