Environmental Engineering Reference
In-Depth Information
1.5
1.5
pressure difference:
80 mm Hg
pressure difference:
20 mm Hg
1.2
1.2
0.9
0.9
O
2
0.6
0.6
N
2
0.3
0.3
O
2
N
2
0
0
low
high
0
0
0
0
0
low
high
0
0
0
0
0
80
100
120
140
160
20
40
60
80
100
pressure, mm Hg
pressure, mm Hg
(a)
(b)
Figure 7.5.6
Facilitated transport of oxygen in blood
Transport of oxygen and nitrogen across a “membrane” of blood with hemoglobin. In
this experiment, the pressure difference between the retentate and permeate sides is
kept constant (left, 20 mm Hg and right, 80 mm Hg), while the total pressure on the
retentate side is increased.
Figure adapted from Scholander
[7.12].
For fl ue gasses, we need to replace the hemoglobin with a compo-
nent that selectively binds CO
2
. Amines are obvious candidates. Of
practical importance is how to make a CO
2
-reactive membrane. The
early solutions were to use a reactive liquid inside the pores [7.10].
Using an immobilized phase inside a membrane has as main disadvan-
tage that it may leak out or evaporate from the membrane, which will
slowly deteriorate the performance of the membrane. An alternative
strategy is to have the polymer of the membrane functionalized as illus-
trated in
Figure 7.5.7
.
The fi gure shows a system in which there is water. Without water one
needs two amine groups: one amine interacts with CO
2
to form a
zwitterion.
+
[
]
−
NHR R
+
CO
NHR R
CO
12
2
12
2
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