Membrane Gas Separation

Solution Diffusion
H
2
H
2
H
2
H
2
H
2
H
2
H
2
CO
2
CO
2
CO
2
Dissolution
Diffusion
Evolution
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
D
CO2
D
H2
Facilitated Transport
H
2
H
2
H
2
H
2
H
2
H
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
Dissolution
Diffusion
Evolution
Comple
xing
Decomple
xing
Figure 10.3 Potential improvement of CO 
2
permeability through facilitated transport

---

Ionic Liquid Membranes for Carbon Dioxide Separation
189
[10] . NETL has embarked on a programme to make use of these properties to develop 
technologies for cost effective and effi cient capture and sequestration of the CO 
2
emis-
sions from power generation. One of the areas being investigated is the use of ionic liquid 
transport media in supported liquid membranes for high temperature capture applications 
such as the IGCC process.
10.2
Experimental 
The ionic liquid 1 - n - hexyl - 3 - methylimidazolium bis(trifl uorosulfonyl)imide, [hmim]
[Tf 
2
N], was synthesized and characterized using standard procedures
[17 
– 
19] 
at the 
University of Notre Dame. The ionic liquid 1 - (3 - aminopropyl) - 3 - methylimidazolium 
bis(trifl uoromethylsulfonyl)imide, [H 
2
NC 
3
H 
6
mim][Tf 
2
N], was also synthesized and char-
acterized at the University of Notre Dame [20] . 
The supported ionic liquid membranes (SILMs) were prepared by depositing the ionic 
liquids [hmim][Tf 
2
N] and [H 
2
NC 
3
H 
6
mim][Tf 
2
N] on top of cross - linked nylon support 
discs in a shallow glass container. A suffi cient amount of ionic liquid to cover the mem-
brane was used. The membrane was allowed to absorb the ionic liquid for at least 4 hours, 
and then the SILMs were removed from container and blotted dry. Further details 
concerning this procedure were published earlier [19] . 
Membrane performance testing was carried out using a constant pressure fl ow system 
equipped with a Clarus 500 gas chromatograph (GC) with twin thermal conductivity 
detector (TCD) and Alltech Hayesep D100/200 packed columns for measurement of the 
permeate and retentate gas compositions. A commercially available fi lter holder was used 
to mount the membrane discs for testing with gas mixtures of known concentration as 
previously described [19] . 
Membrane permeabilities for both CO 
2
and H 
2
and the CO 
2
/H 
2
separation factor were 
evaluated in the presence of varying concentrations of CO (10, 100, 500 ppm) in mixtures 
containing
∼
20 mol% CO 
2
,
∼
20% H 
2
, and a balance of Ar. Performance was also evalu-
ated in the presence of varying concentrations of H 
2
S (10, 100, 500 ppm). 
Membrane performance was also tested in a simulated fuel gas (SFG) with the follow-
ing gas composition: 30.1% CO 
2
, 40.1% H 
2
, 1.01% CO, 0.992% CH 
4
, 202 ppm H 
2
S, and 
balance Ar.