Membrane Gas Separation

214
Membrane Gas Separation
is only susceptible to H 
2
S 
- 
induced plasticization at certain temperature and partial 
pressure conditions. 
The increased occurrence of plasticization at high pressures and temperatures is attrib-
uted to the concentration of H 
2
S within the membrane, as well as the mobility of polymer 
chains. At high H 
2
S partial pressures, the concentration of H 
2
S within the glassy polymeric 
membrane reaches a critical concentration (the plasticization pressure) where the number 
of H 
2
S molecules per polymeric chain ratio is great enough to disrupt the polymeric 
chain – chain interactions network, allowing plasticization to occur. Bos et al. [39] postu-
lates that this critical concentration is the same for polymeric membrane groups. 
Temperature also plays a critical role; polymer chains at higher temperature require less 
1450
1400
1350
1300
1250
1200
Permeability (barrer)
Permeability (barrer)
1150
1100
1050
1000
2300
2250
2200
2150
2100
2050
Permeability (barrer)
2000
1950
1900
1850
1750
1700
1650
1600
1550
1500
2000
1950
1900
1850
1800
1750
1700
1650
1600
Permeability (barrer)
2650
2600
2550
2500
2450
2400
2350
2300
2250
2200
200
400
Pressure (kPa)
600
200
400
Pressure (kPa)
600
200
400
Pressure (kPa)
600
200
400
Pressure (kPa)
600
15°C
35°C
55°C
75°C
Figure 11.4 CO 
2
permeability in PDMS under mixed gas conditions with (grey) and 
without (black) 500 ppm or H 
2
 S present. Reprinted with permission from Journal of 
Membrane Science, The effect of hydrogen sulfi de, carbon monoxide and water on the 
performance of a PDMS membrane in carbon dioxide/nitrogen separation by Colin Scholes, 
Sandra Kentish and Geoff Stevens, 350, 1 – 2, 189 – 199, Copyright (2010) Elsevier Ltd

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The Effects of Minor Components on the Gas Separation Performance
215
Permeability (barrer)
Permeability (barrer)
Permeability (barrer)
Permeability (barrer)
200
400
Pressure (kPa)
600
200
400
Pressure (kPa)
600
200
400
Pressure (kPa)
600
200
400
Pressure (kPa)
600
15°C
320
310
300
290
280
730
720
710
700
680
670
660
690
650
640
630
620
950
940
930
920
900
890
880
910
870
860
850
840
590
580
570
560
550
35°C
55°C
75°C
Figure 11.5 N 
2
permeability in PDMS under mixed gas conditions with (grey) and 
without (black) 500 ppm H 
2
 S present. Reprinted with permission from Journal of 
Membrane Science, The effect of hydrogen sulfi de, carbon monoxide and water on the 
performance of a PDMS membrane in carbon dioxide/nitrogen separation by Colin 
Scholes, Sandra Kentish and Geoff Stevens, 350, 1 – 2, 189 – 199, Copyright (2010) 
Elsevier Ltd
energy to disrupt the chain – chain intermolecular bonding network, due to increased chain 
mobility. Therefore, it becomes easier for H 
2
S to disrupt this network at higher tempera-
ture and generate the plasticized state. 
N 
2
also experiences competitive sorption from H 
2
S, correspondingly the permeability 
of N 
2
through the glassy membranes decreases. The reduction is not as pronounced as 
that reported above for CO 
2
, because the CO 
2
/N 
2
selectivity during the competitive sorp-
tion event is reduced. An example measurement is provided in Figure 11.8 . Hence, H 
2
S 
undergoes greater competitive sorption with CO 
2
, because both molecules are competing 

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216
Membrane Gas Separation
in the microvoids, while N 
2
transport through these microvoids in comparison is already 
low. H 
2
S - induced plasticization also increases the permeability of N 
2
, because of the 
increase in fractional free volume. However, the CO 
2
/N 
2
selectivity rises, revealing that 
while increased diffusivity occurs for both gases, it favours CO 
2
because of it is high 
concentration within the microvoids, which benefi ts from the increase in pathways 
between them due to plasticization.
Permeability (barrer)
Permeability (barrer)
4.3
(a)
400 kPa
800
1000
1200
1600
4.2
4.1
4.0
3.9
3.8
3.7
0
50
100
150
Time (min)
H
2
S Present
200
250
7.0
(b)
400 kPa
800
1000
1200
1600
6.5
6.0
5.5
5.0
4.5
4.0
0
50
100
150
Time (min)
H
2
S Present
200
Figure 11.6 CO 
2
permeability through polysulfone at pressures between 400 – 1600 kPa 
(increasing greyscale); (a) 15 ° C and (b) 55 ° C [38]
Permeability (barrer)
Permeability (barrer)
1.70
(a)
800 kPa
1200
1600
1.60
1.65
1.55
1.50
1.45
1.40
1.35
0
50
100
150
Time (min)
H
2
S Present
200
10.4
10.2
(b)
400 kPa
800
1200
1600
10.0
9.8
9.6
9.4
9.2
9.0
8.8
8.6
0
50
100
150
Time (min)
H
2
S Present
200
Figure 11.7 CO 
2
permeability through Matrimid 5218 at pressures between 400 –
 1600 kPa (increasing grayscale); (a) 15 ° C and (b) 55 ° C [38]

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The Effects of Minor Components on the Gas Separation Performance
217