Membrane Gas Separation

(cm
2
/s)
1/FFV
(b)
10
-9
10
-8
10
-7
10
-6
2.90
2.95
3.00
3.05
3.10
3.15
D
M
0
t
(cm
2
/s)
1/FFV
(c)
10
1
10
2
10
3
0.31
0.32
0.33
0.34
0.34
b
(g/g
pol
)
FFV
(d)
10
0
10
1
10
2
0.31
0.32
0.33
0.34
0.35
0.36
b
(g/g
pol
)
FFV
n-C
4
n-C
5
n-C
5
n-C
4
Figure 7.7 Infi nite dilution diffusion coeffi cient of (a) n - C 
4
and (b) n - C 
5
in the polymeric 
phase of mixed matrices based on AF 2400 as a function of FFV.  
β
coeffi cient for diffusion 
of (c) n - C 
4
and (d) n - C 
5
in the mixed matrices based on AF 2400 as a function of FFV
It is apparent that, for the case of the n - C 
4
/n - C 
5
pair, the matrices considered are vapour -
selective (solubility selective), meaning that they are more permeable to the more con-
densable penetrant, and that the selectivity increases with increasing penetrant pressure. 
It is also clear from Figure 7.9 that the n - C 
5
/n - C 
4
selectivity of the matrices, at fi xed 
permeability, decreases with increasing fi ller content. In any event, the behaviour of the 
matrices with the higher inorganic content would be much closer to a hypothetical trade -
off curve traced for this particular mixture for vapour selective materials. Of course the 
ideal values of selectivity obtained above from pure vapour measurements could be dif-
ferent from the actual case of mixed gases in the feed, in which different interactions take 
place between the penetrants and between penetrants and polymer phase.

---

140
Membrane Gas Separation