Membrane Gas Separation

5 
Modelling Gas Separation 
in Porous Membranes
Aaron W. Thornton 
a
, James M. Hill 
b
and Anita J. Hill 
a


a
 CSIRO Materials Science and Engineering, Clayton, Victoria, Australia
 
b
 Nanomechanics Group, School of Mathematics and Applied Statistics, University of 
Wollongong, New South Wales, Australia
5.1
Introduction 
Instead of adopting a trial - and - error approach to membrane development, it is far more 
effi cient to have a real understanding of the separation phenomena to guide membrane 
design. For example, relationships have been found between experimental separation 
results and pore sizes which have been determined from positron annihilation lifetime 
spectroscopy (PALS) [1 – 4] and small angle X - ray scattering [5 – 7] , and these may be 
used to guide the tailoring of pore sizes to enhance separation performance. Similarly, 
methods such as Monte Carlo, molecular dynamics and other computational techniques 
[8 – 19] have improved our understanding of the relationships between membrane charac-
teristics and separation properties. In addition to these inputs, it is also benefi cial to have 
simple models and theories that give an overall insight into separation performance 
[20 – 33] . Recently, an increased interest can be noted in gas transport in porous (micro -
porous or nano - porous) membranes, both inorganic and polymeric. In this chapter a brief 
review of the current models and conceptual frameworks of the transport in porous media 
are given. In addition, we present a new approach to describe the diffusion of gas mol-
ecules in small pores as outlined in more detail in ref. 23, which does indeed provide 
some new insight into the gas separation phenomena, and therefore facilitate the optimiza-
tion of material design.

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Membrane Gas Separation