Membrane Gas Separation

(a) 
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Teflon AF2400 
Teflon AF2400 + 25% FS
Teflon AF2400 + 40% FS
Pure Fumed Silica
Activity 
Solubility (g/g
solid
)
(b)
0.000
0.010
0.020
0.030
0.040
0.050
0.060
0.070
0.00
0.20
0.40
0.60
0.80
1.00
Teflon AF2400 
Teflon AF2400 + 25% FS
Teflon AF2400 + 40% FS
Pure Fumed Silica
Activity 
Solubility (g/g
solid
)
n-C
4
n-C
5
Figure 7.4 Solubility isotherms of (a) n - C 
4
and (b) n - C 
5
in Tefl on AF 2400, AF 
2400 + 25%wt FS and AF 2400 + 40%wt FS and adsorption onto pure silica at 25 ° C
(a) 
0
0.01
0.02
0.03
0.04
0
0.02
0.04
0.06
0.08
0.1
0.12
Teflon AF2400
NELF model
Teflon AF2400 + 25% FS
NELF model
Teflon AF2400 + 40% FS
NELF model
Solubility (g/g
polymer
)
Pressure (MPa)
(b) 
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040
Teflon AF2400
NELF model
Teflon AF2400 + 25% FS
NELF model
Teflon AF2400 + 40% FS
NELF model
Solubility (g/g
polymer
)
Pressure (MPa)
n-C
4
n-C
5
Figure 7.5 Experimental solubility of (a) n - C 
4
and (b) n - C 
5
in the polymeric phase of 
Tefl on 
 ® 
AF 2400 - based MMM at 25 ° C and comparisons with NELF model

---

136
Membrane Gas Separation
compared with the simulations obtained by the NELF model using the parameter values 
reported in Table 7.1 . The binary parameter used in the model calculations was adjusted 
on sorption data in the pure polymer and was kept constant even for composite materials, 
while the swelling coeffi cient was adjusted for each penetrant on the data of the isotherm 
at higher activities. In the absence of reliable experimental density data for the polymer 
phase alone of the mixed matrix, the polymer density value in the MMM was estimated 
by fi tting the NELF model on the solubility isotherms of n - C 
4
. It can be seen from Table 
7.2 that such values decrease with increasing FS content, and that the values thus obtained 
are good to calculate the solubility behaviour of n 
- 
C 
5
: this testifi es that the density 
obtained in this way is a good representation of the actual polymer density and the cor-
responding FFV value will also be used to correlate the diffusivity data shown in the 
following.
Table 7.1  NELF model parameters for n - C 
4
 , n - C 
5
 , mixed matrices and their mixtures 
Matrix
 
ρ
  * (kg/L)
T * (K)
P * (MPa)
ρ
2
0
(g/cm 
3
)
FFV (Equation 7.11 )
AF 2400 [18]
2.13
624
250
1.740
a
0.320
AF 2400/25%wt FS
1.714
b
0.330
AF 2400/40%wt FS
1.680 
b
0.344