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Journal of Membrane Science 184 (2001) 245255 Modeling permeation through anisotropic zeolite
 

Summary: Journal of Membrane Science 184 (2001) 245255
Modeling permeation through anisotropic zeolite
membranes with nanoscopic defects
Peter H. Nelsona, Michael Tsapatsisb, Scott M. Auerbacha,b,
a Department of Chemistry, University of Massachusetts, Amherst, MA 01003, USA
b Department of Chemical Engineering, University of Massachusetts, Amherst, MA 01003, USA
Received 2 August 2000; received in revised form 29 September 2000; accepted 19 October 2000
Abstract
We have modeled permeation through anisotropic zeolite membranes with nanoscopic defects that create shortcuts perpen-
dicular to the transmembrane direction (x). We have found that the dimensionless ratio Dy/(kd y) can be used to estimate
whether the shortcuts contribute significantly to the overall flux. Here Dy is the diffusion coefficient for motion in the plane
of the membrane, kd is the rate of desorbing into defect voids, and y is the spacing between adjacent defects. For values of
Dy/(kd y) 1, we find that shortcuts increase the flux by significant amounts. The magnitude of the flux is increased as
the imperfection spacing y is decreased. For small values of y, permeation through shortcuts becomes sorption-limited
so that decreasing y further does not increase the flux through a single shortcut. However, as y is decreased, the concen-
tration of shortcuts increases, thereby increasing the total contribution of the shortcuts to the flux. We have found regimes
where increasing y or decreasing Dy decreases the overall flux, showing that permeation can be diffusion-limited by motion
perpendicular to the transmembrane direction. 2001 Elsevier Science B.V. All rights reserved.
Keywords: Diffusion; Gas and vapor permeation; Microporous membranes; Theory
1. Introduction

  

Source: Auerbach, Scott M. - Department of Chemistry, University of Massachusetts at Amherst

 

Collections: Chemistry