Inorganic Microporous Membranes for Gas Separation in Fossil Fuel ...

2 Theoretical background
Table 2 Oxygen permeation (j(O2)), thickness (d) and temperature (T) of various oxygen conductive
membranes. The flux is normalised for membranes with a thickness of more 500 µm to a thickness of
1000 µm assuming that the bulk diffusion is rate determined.
Membrane material
j(O2)
normalised
j(O2) T D Feed-
Side
ml/(min·cm 2 ) °C mm
11
Sweep-
side
La0.2Sr0.8Fe0.8Co0.1Cr0.1O3-δ 5.47 5.47 800 1 Air He/CH4
(Ni cat.)
SrCo0.8Fe0.2O3 1.6 1.1 900 1.5 Air He
SrCo0.33Fe0.66O3 3.37 2.73 1000 1.2 Air He
SrCo0.66Fe0.33O3 2.79 2.79 1000 1 Air He/air
SrCo0.66Fe0.33O3 4.11 4.11 1000 1 Air He/air
Ba0.5Sr0.5Co0.8Fe0.2O3 3.1 900 0.2 p(O2) = 0.2 atm He
Ba0.5Sr0.5Co0.8Fe0.2O3 13.3 1000 0.2 p(O2)= 1.0 atm He
Ba0.5Sr0.5Co0.8Fe0.2O3 2 1.35 900 1.5 Air He
2.1.1.3 Dense protonic conductive membranes
The hydrogen transport through dense ceramic protonic membrane materials is similar to
the oxygen ion transport. The oxygen vacancies in mixed electronic and protonic
conductors are in equilibrium with water vapour, see equation (3) and (4) below:
•• 1
x •
VO + O2 ↔ OO + 2h
2
(3)
x
H O V O 2OH
•
••
+ + ↔ (4)
2
O O O
The OHO • is an interstitial proton that associates strongly with a neighbouring oxygen
ion. Protons can also be formed in the lattice of the membrane material when H2 gas is in
equilibrium (5) with the oxides:
2O + H ↔ 2OH + 2e′
(5)
x
•
O 2
O
The hydrogen transport through these membranes is dependent on many factors such as
the mobility of the interstitial proton as a function of the hydrogen partial pressures
gradient. 24
Lin et al. 6,25 studied the hydrogen permeance of strontium thulium doped ceria (see
Table 3). Balachandran et al. 26 and Meulenberg et al. 27 prepared BaCe0.8Y0.2O3-δ (BCY)
based membranes and found similar results as Lin et al. 6 Eltron U.S. 28 produced a
strontium iron cobaltate with a reasonable hydrogen permeation. Balachandran et al. 26
Ref
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