Membrane Gas Separation

EC + 1.30 g 
Nd
out of the case
2.5
±
0.2
6.1
±
0.6
5.2
±
0.5
0.8
±
0.1
1.0
±
0.1
2.2
±
0.4
6.5
±
1.2
5.6
±
1.0
0.7
±
0.1
0.4
±
0.1
3.2
±
0.3
6.8
±
0.6
8.1
±
0.3
1.0
±
0.1
0.5
±
0.05
EC + 1.38 g 
Nd
out of the case
3.0
±
0.3
8.6
±
0.8
7.2
±
0.7
0.9
±
0.1
1.5
±
0.1
4.5
±
0.9
11.7
±
2.2
12.2
±
2.4
1.2
±
0.2
1.0
±
0.2
9.4
±
0.9
18.6
±
1.2
25.5
±
2.7
2.5
±
0.2
1.8
±
0.15
Source: Reprinted with permission from Journal of Membrane Science, On the air enrichment by polymer magnetic membranes by A. Rybak, Z. J. Grzywna and W. Kaszuwara, 
336, 1 – 2, 79 – 85, Copyright (2009) Elsevier Ltd 

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Air Enrichment by Polymeric Magnetic Membranes
175
Table 9.4  Drift coeffi cients estimated via eq. 9.26 for different magnetic induction 
Membrane
B (mT)
w 10 
3
(cm/s)
EC + 1.30 g Nd
0.00
0.01
EC + 1.23 g Nd
0.50
0.91
EC + 1.38 g Nd
0.79
3.10
EC + 1.49 g Nd
1.25
4.70
Source: Reprinted with permission from Journal of Membrane Science, On the air enrichment by polymer magnetic 
membranes by A. Rybak, Z. J. Grzywna and W. Kaszuwara, 336, 1 – 2, 79 – 85, Copyright (2009) Elsevier Ltd 
From what we have shown it is clear that fl at EC shows no selectivity. So it can be 
concluded that the magnetic fi eld, and its strength, has to be a reason for the air enrich-
ment reported in this work. The overall situation is, however, much more complicated. 
As was found by Tagirov et al. [36] the molecular clusters could be formed in suffi ciently 
strong magnetic fi elds. The clusters N 
2
– O 
2
– O 
2
are preferable for the case of air. So it 
means that a magnetic fi eld, when suffi ciently strong, can affect also the transport of N 
2
by means of dragging its clusters along with O 
2
. This is exactly the situation that has been 
presented. As can be seen from Table 9.6 , the diffusion coeffi cients increase both for O 
2
and N 
2
in air, and the ratio of their values is roughly 2:1, like the composition of a cluster. 
They have much larger values than for pure components. It could simply be explained 
by a larger magnetic dipole being developed on a cluster, and its interaction with the 
magnetic fi eld. This leads to a conclusion that the mechanism of gas transport has no 
solely diffusion character, and for a stronger fi eld drift dominates (see Equations 9.24 and 
9.25 ), providing the basis for the two components to be separated. 
As can be seen from Table 9.7 , the fl ux of oxygen in air is smaller than that of the pure 
gas, contrary to nitrogen where the trend is the opposite. As we already have mentioned, 
this is probably due to the clusters forming [36] . Table 9.7 also shows some interesting, 
directional properties of a mass transport through ‘ magnetic membranes ’ , i.e. the fl uxes 
measured from two opposite sides are different. The reason for that is straightforward, 
and is simply a consequence of a neodymium powder sedimentation during the membrane 
casting process. The description, analysis, and practical aspects, of this phenomena is 
under our current investigation.
Additional interesting information is provided by Table
9.8 
, which presents some 
results for PPO magnetic membranes. The idea behind these experiments was to show 
the constructive role of a magnetic fi eld in improving the already good separation proper-
ties of PPO membranes. As can be seen from Tables 9.2 and 9.8 , it works in both direc-
tions, i.e. the air enrichment is remarkably high, and the oxygen fl ux is also bigger, as 
compared with plain PPO membrane [2,8,46,47] . It can be assumed that the tight structure 
of the PPO membrane cause the deaggregation of N 
2
- O 
2
- O 
2
clusters, while the magnetic 
powder softens the structure a bit.