NAMS 2002 Workshop - ICOM 2008

Gas Separation II – 2
Tuesday July 15, 3:00 PM-3:30 PM, Kaua’i
Modeling Molecular-Scale Gas Separation
A. Thornton (Speaker), CSIRO, Clayton, Australia - aaron.thornton@csiro.au
T. Hilder, University of Wollongong, Wollongong, Australia - tah429@uow.edu.au
A. Hill, CSIRO, Clayton, Australia - anita.hill@csiro.au
J. Hill, University of Wollongong, Wollongong, Australia- jhill@uow.edu.au
The ability to separate gas mixtures is a vital skill in a world that emits excess
carbon dioxide into the atmosphere, needs purified water, wants artificial kidneys,
requires hydrogen for energy alternatives and demands many more
improvements and developments. Gas separation membranes are composed of
nano- sized pores which may be designed to separate a gas mixture. In this
paper we employ mathematical modeling using the Lennard-Jones interactions
between the gas molecule and the pore wall to determine an ideal pore radius in
terms of efficiently separating molecules. The method adopted is closely related
to carbon nanotube forest-based membranes and can also be used to explain
the performance of polymer membranes such as thermally rearranged (TR), poly
(trimethylsilylpropyne) (PTMSP) and conventional dense polymers. All the
nanotubes in a carbon nanotube forest have the same radius enabling a more
deterministic separation outcome. While polymers on the other hand have a
distribution of pore sizes and therefore have an inbuilt capacity to perform
various separations. This investigation reveals the acceptance radius and the
radius of pores which provide a maximum suction energy for gases He, H2, CO2,
O2, N2 and CH4. By assuming there are three different separation mechanisms
namely blockage, suction and freeway, we may qualitatively explain the
separation outcomes of TR, PTMSP and conventional polymer membranes.