Membrane Gas Separation

13 
 CO
2
Permeation with 
Pebax ® - based Membranes 
for Global Warming Reduction
Quang Trong Nguyen 
a
, Julie Sublet 
b
, Dominique Langevin 
a
, Corinne Chappey 
a
, 
St é phane Marais 
a
, Jean - Marc Valleton 
a
and Fabienne Poncin - Epaillard 
c


a
 Laboratoire ‘ Polym è res, Biopolym è res, Surfaces ’ , Universit é de Rouen - CNRS, 
Mon - Saint - Aignan Cedex, France
b
 Institut de recherches sur la catalyse et l ’ environnement de Lyon, CNRS - Universit é de Lyon 1, 
Villeurbanne Cedex, France
 
c
 Laboratoire ‘ Polym è res, Collo ï des, Interfaces ’ , CNRS - Universit é du Maine, Le Mans Cedex, 
France
13.1
Introduction 
There is a worldwide accepted viewpoint that global warming is real, and that anthr-
opological carbon dioxide is a major cause of this. Adding more greenhouse gas would 
lead to a serious increase in the planet ’ s surface temperature. Although nobody knows 
for sure what will happen, the resulting climate changes appear as the greatest threat to 
the planet. Therefore, reducing CO 
2
emissions to the atmosphere is an important issue 
worldwide. 
Major CO 
2
emissions sources are generated by fossil fuel combustion within the power 
and industrial sectors. Storage of the greenhouse gas in empty gas fi elds and aquifers 
could be a solution. To store CO 
2
underground it should be captured fi rst. The most cur-
rently used post - combustion technology is absorption columns by means of an organic 
liquid. The fl ue gases are scrubbed in several reactors in which the CO 
2
is bound by 

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256
Membrane Gas Separation
amines. This technology consumes a lot of energy and is therefore not very cost effective. 
As well as the energy consumption and pollution due to amine loss to the environment, 
huge installations are needed. The use of membranes to selectively remove CO 
2
from gas 
mixtures would be of great interest due to the known advantages of the membrane proc-
esses [1] . However, the extraction of CO 
2
from low concentration fumes is diffi cult. 
According to a study, it is necessary to have at least a CO 
2
concentration of 10 – 15 vol.% 
(coal fumes, steel production fumes) to have a competitive membrane process [2] . 
The major problem for the use of membrane - based CO 
2
separation is the lack of com-
mercial membranes with both high permeability and high selectivity. Gas separation 
membranes based on polymer blends were shown to have improved mechanical proper-
ties, better membrane - forming ability and higher gas permeability [3] . By blending, a 
combination of useful properties of each polymer can be obtained without the tedious 
work required in the design of a new product. Compared with other modifi cation 
technologies or the synthesis of entirely new materials, polymer blending has several 
advantages, such as simplicity, reproducibility and low fabrication cost, thus membrane 
fabrication is commercially feasible [4] . 
Most of the research work has been focused on polymer membrane materials involving 
a solution - diffusion mechanism. The performances of such materials generally fall within 
the trade - off relationship between permeability and selectivity suggested by Robeson [5] , 
with an ‘ upper bound ’ limit for the membrane performances. 
Kawakami et al. [6] in a study on PEG loaded in porous regenerated cellulose con-
cluded that the acid – base reaction between the acidic CO 
2
and the electron - rich ether 
oxygen atoms of the PEG molecules is probably responsible for the enhanced solubility 
of CO 
2
in PEG. 
The upper bound relationship between permeability and selectivity might also be 
overcome with facilitated transport membranes, because the latter have both a high per-
meability and a high selectivity via reversible reactions between reactive carriers and the 
target gas, carbon dioxide. 
Recently, a new type of polymer material was reported to have a great potential for 
carbon dioxide separation from natural gas. It very selectively removed carbon dioxide 
by permeation through hourglass - shaped pores of molecular size, while impeding that of 
methane through these same pores [7] . 
Ward and Neulander [8] investigated the separations of SO 
2
/CO 
2
mixtures by liquid 
membranes and found that polyethylene glycol (PEG) exhibited much higher solubility 
coeffi cients (0.7 mol L 
−
1
atm 
−
1
) for SO 
2
compared to that of CO 
2
(0.1 mol L 
−
1
atm 
−
1
) at 
25 ° C. Although the separation of CO 
2
/SO 
2
was not effective, PEG was found to be an 
excellent solvent for polar gases. 
Lin and Freeman [9] have reported an overview about material selection for membrane 
preparation for removal of CO 
2
from gas mixtures. In that article, CO 
2
solubility and CO 
2
/
gas solubility selectivity in solvents and polymers containing different polar groups were 
discussed. They have concluded that ethylene oxide (EO) units in the polymer appear 
to be the most useful groups to achieve high CO 
2
permeability and high CO 
2
/light gas 
selectivity. Although homo - poly(ethylene oxide) (PEO) consists of EO monomer units, 
the disadvantage of pure PEO membranes lies in their strong tendency to crystallize, 
leading to a low membrane permeability. They defi ned three strategies for incorporating 
high concentrations of PEO with low crystallization tendency into polymers: 

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