4 years ago

Diffusion Model for Gas Replacement in an Isostructural CH4–CO2 Hydrate System

Diffusion Model for Gas Replacement in an Isostructural CH4–CO2 Hydrate System
A. Falenty, W. F. Kuhs, A. N. Salamatin
Guest exchange in clathrates is a complex activated phenomenon of the guest–host cage interaction on the molecular-scale level. To model this process, we develop a mathematical description for the nonequilibrium binary permeation of guest molecules during gas replacement based on the microscopic “hole-in-cage-wall” diffusive mechanism. The transport of gas molecules is envisaged as a series of jumps between occupied and empty neighboring cages without any significant lattice restructuring in the bulk. The gas exchange itself is seen as two-stage swapping initiated by almost instantaneous formation of a mixed hydrate layer on the hydrate surface followed by a much slower permeation-controlled process. The model is constrained by and validated with available time-resolved neutron diffraction data of the isostructural CH4 guest replacement by CO2 in methane hydrate, a process of possible importance for the sequestration of CO2 with concomitant recovery of CH4 in marine gas hydrates.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b04391

DOI: 10.1021/acs.jpcc.7b04391

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