This study investigated the gas separation properties of bilayer polymer membranes composed of polyethylenimine and polyacrylic acid deposited on ethylene-tetrafluoroethylene copolymer substrates. The permeability and selectivity of carbon dioxide, nitrogen, and hydrogen gases were measured for membranes with 6 and 8 bilayers of cross-linked and uncross-linked polymers. It was found that carbon dioxide permeability was highest due to its smaller kinetic diameter and stronger molecular affinity with the polymers. However, hydrogen/nitrogen selectivity was lower likely because of hydrogen saturation in the materials. Cross-linking the polymers resulted in reduced gas selectivity possibly by providing an additional diffusion barrier.

1.
Gas
Separa)on
Proper)es
of
Bilayer
Polymer
Polyethylenimine/Polyacrylic
Acid
on
Ethylene-­‐Tetrafluoroethylene
Copolymer
Substrate
Dwencel
John
Mamayson1,2,
Yixuan
Song3,
Jaime
Grunlan3,4
and
Benjamin
Wilhite1
1Ar)e
McFerrin
Department
of
Chemical
Engineering,
Texas
A&M
University,
College
Sta)on,
TX
77843,
USA
2Department
of
Chemical
Engineering,
University
of
California
Santa
Barbara,
Santa
Barbara,
CA
93106,
USA
3Department
of
Materials
Science
and
Engineering,
Texas
A&M
University,
College
Sta)on,
TX
77843,
USA
4Department
of
Mechanical
Engineering,
Texas
A&M
University,
College
Sta)on,
TX
77843,
USA
Mo)va)on
Equipment
Results
Materials
&
Method
• Polymer
membranes
are
widely
use
in
gas
separa3on
due
to
low
energy
and
produc3on
costs.
But
its
applica3ons
are
limited
to
certain
types,
and
it
face
certain
problems
such
as:
ü Inverse
propor3onality
of
selec3vity
&
permeability
ü Deforma3on
ü Plas3city
Ø Films
ü Ethylene-­‐Tetrafluoroethylene
(ETFE)
(Figure
6)
ü 6
LbL
polyethylenimine(PEI)/poly
acrylic
acid(PAA)
ü 8
LbL
PEI/PAA
ü 8
LbL
Cross-­‐linked
PEI/PAA
Ø Method
Figure
5.
Schema3c
of
the
Gas
Permea3on
System
(constant
volume,
variable
pressure)
used
in
obtaining
data
for
the
calcula3on
and
analyses
of
the
three
gasses
permeability
in
different
substrates.
References
Acknowledgement
• Gas
separa3on
and
purifica3on
are
required
in
many
important
applica3ons
such
as:
ü Hydrogen
and
carbon
dioxide
in
petrochemical
plants
from
natural
gas
(Figure
1).
ü Purifica3on
of
inert
gasses
for
food
and
pharmaceu3cal
uses
(Figure
2).
• Current
conven3onal
technologies
such
as
condensa3on,
cryogenic
dis3lla3on,
and
adsorp3on
require
high
amount
of
energy
due
to
phase
change
[3].
• For
gas
membrane
separa3on,
pressure
difference
is
the
only
driving
force.
Figure
2.
Different
food
packagings
[2]
Figure
1.
Hydrogen
produc3on
plant
[1]
Figure
3.
Polymer
membrane
developed
by
Freeman's
group
[4]
Ø Gas
Permeability
equa3on:
Figure
6.
Edited
Robison
plot
indica3ng
the
rela3ve
posi3on
of
the
LbL
thin
films
and
ETFE
25μm
in
terms
of
separa3on
performance
for
(a)
CO2/N2
gas
separa3on
and
(b)
H2/N2
gas
separa3on
from
Membrane
Society
of
Australasia
[6].
Ø Gas
Selec3vity
equa3on:
Ø Gas
Permeability
and
Selec3vity:
Table
1.
Individual
Polymer
Film
Permeability,
Pi,
(Barrer)
at
20°C
and
45Psia
and
Selec3vity,
α(i/j)
Ø Film
Deforma3on:
• Percent
deforma3on
of
the
membranes
were
found
to
be
in
the
range
of
1.84
to
3.62
%
for
ETFE
25μm
and
0.22
to
0.69%
for
ETFE
125μm.
• In
this
work,
permeability
and
selec3vity
(permselec3vity)
of
three
individual
pure
gasses
(CO2,
N2,
H2)
were
inves3gated
under
different
layer-­‐by-­‐layer
(LbL)
and
substrates.
FIlm
deforma3on
of
the
total
membrane
was
also
studied.
Figure
4.
A
25μm
ETFE
sample
measured
under
N2.
Discussion/Conclusion
The
Gas
Effect
Ø Kine3c
Diameter
(Diffusivity):
• It
was
found
that
CO2
has
the
highest
permeability
in
all
the
films
• The
kine3c
diameter
of
the
gasses
is
in
the
following
order:
• This
explains
the
big
difference
on
the
permeability
on
CO2
and
N2
• However,
it
does
not
explain
why
the
permeability
of
CO2
was
higher
than
H2
Ø Acidity/Molecular
Affinity
(Solubility):
• The
acidity
of
the
gasses
is
in
the
following
order:
(CO2
>
H2
>
N2)
• It
seems
that
the
acidity
of
a
gas
dominates
the
kine3c
diameter
effect
• It
can
also
be
noted
that
the
LbL
contains
molecular
groups
that
found
to
have
good
molecular
affinity
with
with
CO2
The
Polymer
Effect
Ø Layer-­‐by-­‐Layer:
• The
H2/N2
gas
permselec3vity
showed
lower
than
CO2/N2
gas
(Figure
8)
• One
posiible
explana3on
is
the
hydrogen
satura3on
in
both
the
substrate
and
the
polymer.
• On
the
other
hand,
CO2/N2
showed
high
CO2
permeability
but
lower
selec3vity
in
8LbL
and
vice
versa
in
6LbL.
Ø Crosslinking:
• The
crosslinking
in
both
CO2/N2
and
H2/N2
gas
separa3ons
(Figure1
and
Table1)
exhibited
lower
gas
permselec3vity.
• One
possible
reason
is
that
cross-­‐linking
acts
as
addi3onal
barrier
to
the
gases
[1]
Figure
1.
Hydrogen
Produc1on
Plants
-­‐
Steam-­‐Reforming
Process
[Online
Image].
(n.d).
Retrieved
June
29,
2016
from
hlp://www.cosmoeng.co.jp/english/service/ctg02/hydrogen/steampeforming.html.
Copyright
Cosmo
Engineering
Co.,Ltd
[2]
Figure
2.
Thermoformed
Food
Packaging
[Online
Image].
(n.d).
Retrieved
June
28,
2016
from
hlp://
www.brown-­‐machine.com/food-­‐packaging-­‐thermoforming.html.
Copyright
2009
Brown
Machine,
LLC.
[3]
M.
Freemantle,
"Chemical
&
engineering
news:
Cover
story
-­‐
Membranes
for
gas
separa3on,"
2010.
[Online].
Available:
hlp://pubs.acs.org/cen/coverstory/83/8340membranes.html.
Accessed:
Jul.
10,
2016.
[4]
Figure
3.
Xiaoyan
Wang
(Producer).
Membranes
For
Gas
Separa1on
[Online
Image].
(n.d).
Retrieved
June
20,
2016
from
hlp://pubs.acs.org/cen/coverstory/83/8340membranes.html.
Copyright
by
Xiaoyan
Wang.
[5]
E.
L.
L.
Romero,
"Supper
Hydrogen
and
Helium
Barrirs
with
Polyelectrolyte
Nanobrick
Wall
Thin
Film”
and
“Highly
Selec3ve
Mul3layer
Polymer
Films
for
CO2/N2
Separa3on,”
in
Modeling
and
Experimental
Design
of
Novel
Gas
Purifica1on
and
Separa1on
Systems,
2016,
ch.
4
and
5,
pp.
103
–
134
[6]
A.
Thornton,
L.
Robeson,
and
B.
Freeman,
"Polymer
Gas
Separa3on
Membranes,"
2012.
[Online].
Available:
hlps://www.membrane-­‐australasia.org/polymer-­‐gas-­‐separa3on-­‐membranes/.
Accessed:
Aug.
1,
2016.