NAMS 2002 Workshop - ICOM 2008

Gas Separation III – 3
Wednesday July 16, 10:45 AM-11:15 AM, Kaua’i
CO2 Permeation With Pebax-Based Membranes for Global Warming
Reduction
Q. Nguyen (Speaker), Rouen University, France - trong.nguyen@univ-rouen.fr
J. Sublet, Rouen University, France
D. Langevin, CNRS, France
C. Chappey, CNRS, France
J. Valleton, CNRS, France
P. Schaetzel, CAEN University, France
Carbon dioxide extraction from nitrogen- rich gas streams produced by fossil-
fuel- based power plants is of growing interest, both within industry and
government, for the gas sequestration in a global warming reduction strategy.
The classical gas- scrubbing process is energy- voracious and source of extra-
pollution due to the need of regeneration of amines, the absorbent. Membrane
processes may offer attractive alternatives to reduce the emission of this
greenhouse effect source, due to their well-known advantages from the
environmental and energetic viewpoints. The success of a gas permeation
process relies on the possibility of obtaining membranes with high- performances
and good mechanical/ thermal stabilities. Composite membranes consisting of an
asymmetric glassy membrane whose surface defects are sealed with a thin
polymer layer are generally the preferred structure, because of their
technological feasibility. Sofar, such a concept of composite membranes with a
gutter silicone layer has been successfully used for separation membranes e.g.
for the hydrogen recovery or oxygen/ nitrogen production from air. The
performances of the composite membranes depend critically on the gas nature
and on the intrinsic properties of the composite layers. Contrary to hydrogen and
other gases of very low normal boiling points, CO2 is a polar gas of similar
molecular size to nitrogen, that can significantly interacts with certain chemical
groups. We followed Lin and Freeman's approach* in developing new polymer
materials for the membrane selective layer. The approach consists of selecting
polymers of high CO2 solubility and CO2/light gas solubility selectivity by
introducing polar groups in polymers. Ether oxygens in polyethylene oxide (PEO)
appeared to be the most useful groups*. Commercial Pebax® copolymer
containing "soft" PEO /PTMO and "hard" polyamide (6 or 12) blocks were chosen
as the base polymers in this study because the compromise they provide
between a high content of PEO and good mechanical properties. Membranes
made of extruded and solvent- cast Pebax® block copolymers of different
structures were studied by gas permeation, DSC and AFM. The change in the
transport characteristics with the Pebax®- type appeared to be complex, due to
multiphase structure of the materials: EO content is not the sole factor that
controls the membrane performances. The best Pebax® material for CO2/N2