58
D. Nedeljkovic
Table 3 Permeability and selectivity of the constructed membranes
Membrane number Thickness, μm P CO 2 , Barrer α (CO 2 /H 2 ) α (CO 2 /O 2 ) α (CO 2 /N 2 )
5
192
110
8.5
20.9
62.2
8
241
122
7.9
21.0
54.9
11
185
125
8.9
20.8
62.8
13
192
121
9.1
20.7
60.5
14
221
125
8.8
20.6
60.0
20
237
108
8.5
21.0
59.3
23
217
106
8.3
20.5
62.1
26
205
109
8.4
21.4
61.1
28
247
112
9
22.0
61.0
29
199
115
8.5
20.9
60.2
As it can be observed from Table 3, all membranes that were measured (transparent and opaque) have shown good and acceptable result for the permeability and
selectivity. Carbon dioxide permeability of the PEBAX based membranes was around
120 Barrer, and the value for Polyactive based membranes was around 110 Barrer.
For both of polymers, the values were slightly lower, but still comparable to similar
systems. The differences did not exceed 10%. The selectivity of the carbon dioxide
versus hydrogen, which is the second crucial parameter in membrane evaluation, was
in the acceptable range of 8–9 for all systems. Selectivity of carbon dioxide versus
nitrogen was around 60, and versus oxygen around 20.
If the values for permeability are analyzed based on the pore systems of the zeolite
powder, it can be concluded that three-dimensional systems (samples 11, 13, 14, 16,
28, and 29) have shown the best results. Possible explanation of the slight advantage
of three-dimensional over one- or two-dimensional system is the orientation of the
pores. The pores are oriented completely randomly in the bulk of the polymer, so in
the three-dimensional pore systems, there will always be the channel in the frame that
would provide the diffusion of the carbon dioxide molecule through the membrane.
On the other hand, if one-dimensional pore is perpendicular to the direction of the
diffusion, the potential diffusion path is significantly higher and diffusion is slower.
This effect might be avoided if the orientation of the zeolite particles and their pores
is controlled during the membrane synthesis process. However, the consequence
would be that the procedure is too tedious and demanding. The slight decrease in
the selectivity between the membranes that contain additive may be attributed to the
fact that additive increases the permeability of both carbon dioxide and hydrogen.
As a future task, few directions may be identified. The measurements of similar
systems should be conducted with the presence of more than one gas in the mixture.
This should provide more accurate results concerning the selectivity as the diffusion
of two gases will occur simultaneously which should give more accurate results.
Another set of measurements may be done for wet gases, by saturation the gases
and/or membranes with water vapor, which should give the condition similar to the
D. Nedeljkovic
Table 3 Permeability and selectivity of the constructed membranes
Membrane number Thickness, μm P CO 2 , Barrer α (CO 2 /H 2 ) α (CO 2 /O 2 ) α (CO 2 /N 2 )
5
192
110
8.5
20.9
62.2
8
241
122
7.9
21.0
54.9
11
185
125
8.9
20.8
62.8
13
192
121
9.1
20.7
60.5
14
221
125
8.8
20.6
60.0
20
237
108
8.5
21.0
59.3
23
217
106
8.3
20.5
62.1
26
205
109
8.4
21.4
61.1
28
247
112
9
22.0
61.0
29
199
115
8.5
20.9
60.2
As it can be observed from Table 3, all membranes that were measured (transparent and opaque) have shown good and acceptable result for the permeability and
selectivity. Carbon dioxide permeability of the PEBAX based membranes was around
120 Barrer, and the value for Polyactive based membranes was around 110 Barrer.
For both of polymers, the values were slightly lower, but still comparable to similar
systems. The differences did not exceed 10%. The selectivity of the carbon dioxide
versus hydrogen, which is the second crucial parameter in membrane evaluation, was
in the acceptable range of 8–9 for all systems. Selectivity of carbon dioxide versus
nitrogen was around 60, and versus oxygen around 20.
If the values for permeability are analyzed based on the pore systems of the zeolite
powder, it can be concluded that three-dimensional systems (samples 11, 13, 14, 16,
28, and 29) have shown the best results. Possible explanation of the slight advantage
of three-dimensional over one- or two-dimensional system is the orientation of the
pores. The pores are oriented completely randomly in the bulk of the polymer, so in
the three-dimensional pore systems, there will always be the channel in the frame that
would provide the diffusion of the carbon dioxide molecule through the membrane.
On the other hand, if one-dimensional pore is perpendicular to the direction of the
diffusion, the potential diffusion path is significantly higher and diffusion is slower.
This effect might be avoided if the orientation of the zeolite particles and their pores
is controlled during the membrane synthesis process. However, the consequence
would be that the procedure is too tedious and demanding. The slight decrease in
the selectivity between the membranes that contain additive may be attributed to the
fact that additive increases the permeability of both carbon dioxide and hydrogen.
As a future task, few directions may be identified. The measurements of similar
systems should be conducted with the presence of more than one gas in the mixture.
This should provide more accurate results concerning the selectivity as the diffusion
of two gases will occur simultaneously which should give more accurate results.
Another set of measurements may be done for wet gases, by saturation the gases
and/or membranes with water vapor, which should give the condition similar to the