Micropore size estimation on gas separation membranes: A study in experimental and molecular dynamics

The effect of the gas molecular size and its affinity to the pore surface on gas permeation properties through the ceramic membranes was studied by both the gas permeation experiments and gas permeation simulations using a nonequilibrium molecular dynamics (MD) technique. A modified gas permeation model equation based on the gas translation (GT) mechanism was presented. MD simulation revealed that the effective diffusion length in a micropore depended on the gas molecular size, and the pre‐exponential coefficient of a modified GT model equation showed good correlation with the kinetic diameter of the gas molecules. Also presented is a simple method to estimate the mean pore size of microporous membranes. The estimated pore sizes were consistent with observed kinetic diameter dependencies of gas permeance for real silica membranes. The pore size of a Deca‐Dodecasil 3R (DDR) zeolite membrane was also reasonably estimated at ～0.4 nm from the reported gas permeation data. © 2012 American Institute of Chemical Engineers AIChE J, 59: 2179–2194, 2013