(325b) Knudsen Diffusion in Zeolite Channels and Networks

Knudsen Diffusion in Zeolite Channels
James Wei and Jichang Liu
Princeton University and East China University of Science and Technology
Knudsen diffusion is approximately valid when the channel diameters are much larger
than molecular diameters. The ray lengths between walls are distributed over an enormous range, and there is no upper bound for occasional extreme outliers. A Monte Carlo simulation produces an enormous range in the distribution of diffusivities, which follows a log-normal distribution.
The principal types of one-dimensional channels are the zig-zag channels and the connected cavities, and they have diffusivities that are much lower than the straight channels. The principal cause is lower vista which reduces the extreme lengths of the outlier rays, and the contributing causes are tortuosity and negative correlation. The principal types of two-dimensional channels investigated are: rectangular, oblique, brick, hexagon and straight-sinusoid. They give rise to highly anisotropic diffusion tensors.