Membrane Gas Separation

10.3
Results 
Performance testing of supported [hmim][Tf 
2
N] membranes was originally carried out 
using gas mixtures containing only CO 
2
, H 
2
and Ar [20] . The CO 
2
permeability progres-
sively increased over the temperature range from 310 K to 573 K from 3.75
×
10 
−
15
m 
2
s 
−
1
Pa 
−
1
to over 8.25
×
10 
−
15
m 
2
s 
−
1
Pa 
−
1
(490 – 1085 Barrer), while the selectivity steadily decreased 
with increasing temperature from 9.1 to 1.3. This behaviour is characteristic of solution -
diffusion without facilitation. 
CO 
2
permeabilities were evaluated using gas mixtures with varying concentrations of 
CO (10 ppm, 100 ppm, 500 ppm, and
∼
5 mol%) on the supported [hmim][Tf 
2
N] membrane 
over the temperature range 310 K to 423 K, as shown in Figure 10.4 . The CO 
2
permeability 

---

190
Membrane Gas Separation
in gas mixtures containing 10 ppm CO over the temperature range 310 K to 373 K ranged 
from 3.65
×
10 
−
15
to 5.37
×
10 
−
15
m 
2
s 
−
1
Pa 
−
1
, which is lower than the permeability measured 
for the mixture without CO. As the temperature increases the CO 
2
permeability in the 
presence of 10 ppm CO increases relative to the permeability without CO. The permeabili-
ties at 423 K and 448 K in the presence of 10 ppm CO are 7.44
×
10 
−
15
m 
2
s 
−
1
Pa 
−
1
and 
8.16
×
10 
−
15
m 
2
s 
−
1
Pa 
−
1
as compared to 6.46
×
10 
−
15
m 
2
s 
−
1
Pa 
−
1
at 423 K and 7.57
×
10 
−
15
m 
2
s 
−
1
Pa 
−
1
at 473 K with no CO present.
In gas mixtures containing 100 ppm CO, CO 
2
permeability is 3.82
×
10 
−
15
and 8.58
×
10 
−
15
m 
2
s 
−
1
Pa 
−
1
at 310 K and 448 K, respectively. These permeabilities represent a slight 
increase in CO 
2
permeability over the entire temperature range compared to mixtures not 
containing CO. 
CO 
2
permeabilities in the presence of 500 
ppm CO are 3.84 
×
10 
−
15
and 6.87 
×
10 
−
15
m 
2
s 
−
1
Pa 
−
1
at 310 K and 423 K, respectively. The observed permeabilities are quite 
similar to or slightly higher than those observed in the absence of CO. 
Permeabilities for CO 
2
in mixtures containing 5% CO show negligible change as com-
pared to CO 
2
permeabilities in mixtures without CO for temperatures between 373 K and 
473 K. Below 373 K, the permeability for CO 
2
in mixtures without CO was slightly higher 
(3.77
×
10 
−
15
– 5.79
×
10 
−
15
m 
2
s 
−
1
Pa 
−
1
) than in the mixture with 5% CO (3.28
×
10 
−
15
– 
4.87
×
10 
−
15
m 
2
s 
−
1
Pa 
−
1
). 
CO 
2
permeability in nylon - supported [hmim][Tf 
2
N] displayed Arrhenius behaviour for 
all the CO concentrations tested with the following coeffi cients of determination: 0.987, 
0.989 , 0.989, and 0.997, for the 10 ppm, 100 ppm, 500 ppm, and 5% CO, respectively, 
which is consistent with transport based on physical solubility. 
CO
2
Permeability/m
2
s
-1
Pa
-1
1000T
-1
/K
-1
473 K
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
423 K
373 K
310 K
348 K
323 K
1.00E-14
1.00E-15