Membrane Gas Separation

Partial Pressure of Hexane (kPa)
Experimental Data
Model Predictions (Equation 13)
Henrys Law Contribution to the Model
Methane Permeability (barrer)
50
45
40
35
30
25
20
15
10
5
0
0
5
10
15
20
25
Partial Pressure of Hexane (kPa)
Experimental Data
20
18
16
14
12
10
8
6
4
2
0
0
5
10
15
20
25
Partial Pressure of Hexane (kPa)
Figure 11.15 The effect of an addition of hexane to a mixture of methane (90%) and 
carbon dioxide (10%) at a feed pressure of 1025 kPag. (a) CO 
2
permeability, (b) CH 
4

permeability, (c) CO 
2
 /CH 
4
selectivity. Reprinted with permission from Ind Eng Chem Res., 
The effect of hydrocarbons on the separation of carbon dioxide from methane through a 
polyimide gas separation membrane by Hasan, R., C. A. Scholes, G. W. Stevens and S. E. 
Kentish, 48, 5415 – 5419, Copyright (2009) American Chemical Society

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224
Membrane Gas Separation
0
50
100
150
200
250
300
350
400
450
500
-100
0
100
200
300
400
500
Time since Hexane Addition (minutes)
CO
2
Permeability (Barrer)
-250
-150
-50
50
150
250
350
Time Since Hexane Removal (minutes)
Run 1 - Absorption
Run 2 - Absorption
Absorption Model
Run 1 - Desorption
Run 2 - Desorption
Figure 11.16 The time dependent effect of addition of hexane on the permeability of 
CO 
2
in 6FDA - TMPDA from a methane (90%) and carbon dioxide (10%) gas mixture. 
Reprinted with permission from Ind Eng Chem Res., The effect of hydrocarbons on the 
separation of carbon dioxide from methane through a polyimide gas separation membrane 
by Hasan, R., C. A. Scholes, G. W. Stevens and S. E. Kentish, 48, 5415 – 5419, Copyright 
(2009) American Chemical Society
with the correlation between the critical temperature of a component and this Langmuir 
constant (Figure
11.1 
). The determined Langmuir constant is slightly higher than 
that reported for other species with similar critical temperatures and refl ects the use of 
fugacity as the basis for calculations. As a fugacity is lower than the corresponding partial 
pressure, the corresponding b value will be higher. 
Upon reaching steady - state conditions, the feed gas was returned to dry conditions 
and the permeability of both CO 
2
and CH 
4
was observed to recover (Figure 11.16 ). The 
permeabilities approach initial values after around 300 minutes, implying performance is 
recoverable and that the polymeric structure is not permanently altered by the presence 
of hexane.