Membrane Gas Separation

12 
Tailoring Polymeric Membrane 
Based on Segmented Block 
Copolymers for CO
2
Separation
Anja Car 
a
, Wilfredo Yave 
a
, Klaus - Viktor Peinemann 
a
and Chrtomir Stropnik 
b


a
 Institute of Material Research, GKSS - Research Centre Geesthacht GmbH, Geesthacht, Germany
b
 University of Maribor, Faculty of Chemistry and Chemical Engineering, Smetanova, Slovenia
12.1
Introduction 
The problems of global warming and climate change are today being popularly discussed 
in terms of CO 
2
emission by human activities [1] . CO 
2
is produced by different industrial 
processes. Finding a proper separation technology for the removal of CO 
2
from different 
gas streams will drastically lead to the reduction of emissions. Although CO 
2
production 
contributes to global warming, it is also considered as a raw material in many industries 
[2] . Global CO 
2
consumption for example has reached approximately 20 million tons 
per year, which is strictly dedicated to the so - called merchant market, food, beverage, 
chemical and other industries [3] . Nevertheless, either for storage or for its utilization, 
CO 
2
must be separated. 
At present, the most widely used CO 
2
separation processes consist of reversible chemi-
cal and physical absorption. Membrane processes are not used very much; however, they 
are attractive because of their simplicity and energy effi ciency [4] . 
Actually, there are not yet suitable technologies or technical solutions which can 
effectively fi ght against CO 
2
increase in the atmosphere. In the membrane community, it 
is believed that membrane technology capable of operating under a wide variety of con-
ditions will have a considerable impact on the separation and purifi cation of CO 
2
[5 – 9] . 

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228
Membrane Gas Separation
As known, membranes have become an established technology for CO 
2
removal since 
1981 (natural gas purifi cation) [10] . The multiple benefi ts of membrane technology prom-
ised by early innovators have been proven in a wide variety of installations around the 
world, and one of the world ’ s largest membrane systems for CO 
2
removal from natural 
gas is the Grissik processing plant in South Sumatra, Indonesia [11] . The Grissik plant is 
a hybrid separation system (membrane plus amine treatment) which offers particularly 
attractive operational benefi ts. Thus, it was demonstrated that the most economical 
approach is to combine membranes with existing technologies. 
Commercial membranes for CO 
2
removal are polymer based, and the materials of choice 
are cellulose acetate, polyimides, polyamides, polysulfone, polycarbonates, and polyeth-
erimide [12] . The most tested and used material is cellulose acetate, although polyimide 
has also some potential in certain CO 
2
removal applications. The properties of polyimides 
and other polymers can be modifi ed to enhance the performance of the membrane. For 
instance, polyimide membranes were initially used for hydrogen recovery, but they were 
then modifi ed for CO 
2
removal [13] . Cellulose acetate membranes were initially developed 
for reverse osmosis [14] , and now they are the most popular CO 
2
removal membrane. To 
overcome state - of - the - art membranes for CO 
2
separation, new polymers, copolymers, 
block copolymers, blends and nanocomposites (mixed matrix membranes) have been 
developed [15 – 22] . However, many of them have failed during application because of 
different reasons (expensive materials, weak mechanical and chemical stability, etc.). 
In order to design new membrane materials with superior separation performance, low 
cost and feasible for massive production, the old work of Kulprathipanja can be consid-
ered as a proper tool [23] . He dispersed polyethylene glycol (PEG) in PDMS and improved 
the CO 
2
permeability. A similar idea led us to modify or blend existing commercial block 
polymers containing ethylene oxide (EO) units with poly(ethylene) glycol [24] ; and thus 
by a blending process it was possible to produce high CO 
2
- selective membrane materials 
with improved permeability. 
Permeability of polymers is an important feature for a broad range of applications 
including packaging, bio 
- 
materials (e.g. for controlled drug release or encapsulating 
membranes), barrier materials, high performance impermeable breathable clothing and 
membrane separation processes [25 – 27] . Copolymers were considered many years ago, 
starting with the most investigated polyurethanes and polyurethane - ureas followed by 
polyimides, polyamides and miscellaneous types of block copolymers (e.g. block copoly-
mers containing siloxane segments, hydrocarbon block copolymers and related materials) 
[28,29] . Block copolymers offer a great structural versatility which is highly interesting 
for a fundamental analysis of permeation through polymeric materials. Systematic struc-
ture/property relationships allow one to design block copolymers with improved gas 
transport properties [30] . 
The simplest are diblock copolymers, where two different polymeric chains are bound 
together; and with an increase of block number, tri - or multiblocks with a variety of 
structures can be obtained [31,32] . Most block copolymers used today are prepared by 
living anionic polymerization, which is a feasible method to prepare block copolymers 
with controlled architecture. Different polymers do not mix well due to thermodynamic 
reasons [33] , especially if their molecular mass is suffi ciently high, they have a strong 
tendency to form separated phases. In block copolymers, this phase separation can occur 
only intermolecularly (micro - or nanophase separation) [34] . Those block copolymers 

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