NAMS 2002 Workshop - ICOM 2008

Gas Separation IV – 5
Thursday July 17, 11:00 AM-11:30 AM, Kaua’i
Glassy Perfluoropolymer - Zeolite Hybrid Membranes for Gas and Vapor
Separations
G. Golemme (Speaker), Univ. della Calabria; ITM-CNR; and INSTM, Rende (CS), Italy -
ggolemme@unical.it
J. Jansen, ITM - CNR
D. Muoio, Univ. della Calábria, Rende, Italy
G. De Luca, Univ. della Calábria, Rende, Italy
A. Bruno, Univ. della Calábria, Rende, Italy
R. Manes, Dip, Univ. della Calábria, Rende, Italy
J. Choi, University of Minnesota, Minneapolis, Minnesota
M. Tsapatsis, University of Minnesota, Minneapolis, Minnesota
This paper reports on the successful preparation of hybrid membranes of glassy
perfluoropolymer and MFI zeolites, with significantly improved transport
properties compared to the pure polymers. Perfluoropolymers withstand easily
temperatures beyond 100°C, organic solvents and aggressive chemicals. As a
result of the unusual sorption properties of glassy and amorphous
perfluoropolymers, the permeability-selectivity combinations of some gas pairs
exceed the Robeson upper bound [1,2]. Nanoscale fumed silica as a filler of
highly permeable, stiff backbone polymers (Teflon AF 2400, PMP, PTMSP) was
found to increase the free volume due to the disruption of the packing ability of
the organic phase [3-6]; in Teflon AF 2400 and PMP, the increased free volume
in turn was responsible of a higher permeability, especially for the most
condensable species, and therefore, at the same time, of a better n-butane/CH4
separation factor.
Since porous fillers may have an even better effect on the performance of hybrid
membranes than dense fumed silica, the scope of the present work was to study
the separation capabilities of Teflon AF and Hyflon hybrid membranes with
Silicalite-1 (MFI) crystals of different size. In the past it was demonstrated that
surface modified sub-micron zeolites can be effectively dispersed inside the
extremely hydrophobic matrix of glassy perfluoropolymer membranes [7]. Hybrid
membranes containing up to 42 wt % of fluorophilic MFI crystals (80 to 1500 nm)
were thus prepared. Their morphology was observed by SEM and TEM. Single
gas permeation experiments (O2, N2, H2, He, CH4, CO2, n-butane) were carried
out at 25°C and 1 bar of feed pressure in a constant volume - variable pressure
device [8]. The gas diffusion coefficients were derived from the time-lag, the
permeability from the steady state pressure increase rate, and the solubility from
the permeability-to-diffusion ratio.