Membrane Gas Separation

Molecular weight of PEO segment [g/mol]
CO
2
 Permeability [Barrer]
designed polymer
4000PEO77PBT23
4000PEO55PBT45
blend with PEG
4000PEO84PBT16
hypothetical blend with PEG
4000PEO80PBT20
Blend with PEG
1500PEO77PBT23
hypothetical blend with PEG
4000PEO80PBT20
Figure 12.9 CO 
2
permeability of 1500PEO77PBT23 and 4000PEO55PBT45 blends with 
50 wt.% of PEG as function of molecular mass of PEO segment (hypothetical blend, dash 
line) [modifi ed plot from ref. 67 ]

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Tailoring Polymeric Membrane Based on Segmented Block Copolymers
241
Table 12.4  Permselectivity, solubility and diffusivity selectivity of 4000 PEO 55 PBT 45 
blend membranes with PEG [Reprinted with permission 67 ]
Permselectivity
PEO [wt.%]
55.0
59.5
64.0
68.5
73.0
77.5
CO 
2
/H 
2
10.8
10.6
11.7
12.3
12.4
13.2
CO 
2
/N 
2
43.5
46.8
44.9
45.4
49.1
47.3
CO 
2
/CH 
4
17.1
15.8
16.4
16.4
16.4
15.9
Solubility selectivity
CO 
2
/H 
2
67.5
58.8
61.7
64.9
72.9
77.8
CO 
2
/N 
2
82.1
85.0
62.3
66.7
68.2
71.7
CO 
2
/CH 
4
12.6
13.5
13.8
14.5
14.5
16.1
Diffusivity selectivity
CO 
2
/H 
2
0.16
0.18
0.19
0.19
0.17
0.17
CO 
2
/N 
2
0.53
0.55
0.72
0.68
0.72
0.66
CO 
2
/CH 
4
1.36
1.17
1.19
1.13
1.13
0.99
Source: Reprinted with permission from Advanced Functional Materials, Tailor - made polymeric membranes based 
on segmented block copolymers for CO 
2 
separation, by A. Car, C. Stropnik, W. Yave, K. - V. Peinemann, 23, 
2815 – 2823. Copyright (2008) Wiley - VCH. 
CO 
2
separation by using a membrane prepared from a rubbery polymer is based on high 
solubility selectivity, while diffusivity selectivity should be maintained or even increased. 
The CO 
2
/H 
2
permselectivity is increased (due to the increased EO units), which is a con-
sequence of solubility selectivity increase. The strategy of increasing the solubility plays 
an important role, because of the unfavourable diffusivity selectivity. Incorporation of 
PEG increases the permselectivity of the pair CO 
2
/H 
2
to 13. However, the CO 
2
/N 
2
and 
CO 
2
/CH 
4
permselectivities are maintained almost constant due to the similar penetrants 
size.
Numerous models have been developed to describe transport properties in heterogene-
ous polymer systems, but the one mostly used is the Maxwell approach [89] . The Maxwell 
equation has been used by Robeson et al. [90] to calculate the gas permeability of block 
copolymers. Other authors also applied it to mixed matrix membranes, and permeability 
has been calculated:
P
P
P
P
P
P
P
P
P
=
+ ⋅ − ⋅ ⋅
−
(
)
+ ⋅ + ⋅
−
(
)
(
⎛
⎝⎜
⎞
⎠⎟
d
c
c
d
d
c
c
d
2
2
2
Φ
Φ
(12.9)
where P is the effective permeability,