Membrane Gas Separation

Figure 10.6 Carbon dioxide permeability of [hmim][Tf 
2
 N] on cross - linked nylon; 
 
䊏

→
without H 
2
 S;
䊐

→
0.9% H 
2
 S;
䉫

→
10 ppm H 
2
 S;
䊊

→
100 ppm H 
2
 S;  
Δ

→

500 ppm H 
2
 S

---

Ionic Liquid Membranes for Carbon Dioxide Separation
193
1
10
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
CO
2
/H
2
Selectivity
1000T
-1
/ K
-1
310 K
323 K
348 K
373 K
423 K
473 K
Figure 10.7 Carbon dioxide selectivity of [hmim][Tf 
2
 N] on cross - linked nylon; 
 
䊏

→
without H 
2
 S;
䊐

→
0.9% H 
2
 S;
䉫

→
10 ppm H 
2
 S;
䊊

→
100 ppm H 
2
 S;  
Δ

→

500 ppm H 
2
 S
1.00E–14
CO
2
Permeability/m
2
s
–1
Pa
–1
1.00E–16
2.0
2.2
2.4
2.6
1000T
–1
/K
–1
2.8
3.0
3.2
3.4
423 K
373 K
348 K
323 K 310 K
Figure 10.8 Carbon dioxide permeability of [H 
2
 NC 
3
 H 
6
 mim][Tf 
2
 N] on cross - linked nylon; 
 
䊏

→
without contaminants;
䊐

→
5% CO;  
Δ

→
0.9 % H 
2
 S

---

194
Membrane Gas Separation
as shown in Figure 10.8 . The CO 
2
/H 
2
selectivity in the presence of 5% CO decreases from 
7.82 to 2.64 over the temperature range from 310 K to 423 K and shows a rough Arrhenius 
dependence in Figure 10.9 . In the presence of 0.9% H 
2
S, CO 
2
permeability for supported 
[H 
2
NC 
3
H 
6
mim][Tf 
2
N] increases from 3.87
×
10 
−
16
to 1.10
×
10 
−
15
m 
2
s 
−
1
Pa 
−
1
over the 
temperature range from 310 K to 373 K with a roughly Arrhenius dependence exhibited 
in Figure 10.8 . The CO 
2
/H 
2
selectivity decreases from 5.14 to 3.72 with a similarly rough 
Arrhenius dependence exhibited in Figure 10.9 . Given the observed Arrhenius behav-
iours, which are consistent with solution - diffusion instead of facilitated transport, it is 
reasonable to suggest that both CO and H 
2
S are interfering with the ability of the ionic 
liquid to form complexes with CO 
2
.
The membrane performance of the supported ionic liquids was examined in a simulated 
fuel gas (SFG) containing both H 
2
S and CO. The CO 
2
permeability for both supported 
ionic liquids in separations from SFG, as shown in Figure 10.10 , differs in magnitude but 
not trend from that in mixtures not containing contaminants shown in Figure 10.8 . While 
separation from the SFG shows more of an effect on [H 
2
NC 
3
H 
6
mim][Tf 
2
N] than on 
[hmim][Tf 
2
N] [20] , the facilitated transport behaviour is only reduced but not eliminated 
as in the case of the higher concentrations of CO and H 
2
S. Selectivity results for 
[H 
2
NC 
3
H 
6
mim][Tf 
2
N] and [hmim][Tf 
2
N] with SFG, as shown in Figure 10.11 , also follow 
similar trends to the [H 
2
NC 
3
H 
6
mim][Tf 
2
N] and [hmim][Tf 
2
N] mixtures without contami-
nants shown in Figure 10.9 .