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

4 Results and discussion
Permeance (10 -9 mol/s m2Pa)
Permeance (10 -9 mol/s m 2 Pa)
1.E-06
10 -6
1.E-07
10 -7
1.E-08
10 -8
1.E-09
10 -9
1.E-10 1E-08
10 -10
10 -8
10 -9
1E-09
10 -10
107
#204; 600ºC
#205; 600ºC
1E-10
0.2 0.3 0.4 0.5 0.6 0.7 0.8
Kinetic diameter (nm)
#143; 500ºC
#132; 500ºC
#202; 500ºC
Figure 74: Permeability (measured at 200ºC) of Ti0.5Zr0.5O2 membranes calcined at 500 and 600ºC for
different gasses as a function of their kinetic diameter. The lines serve only as a guide to the eye.
In Figure 74 the measured permeances of a series of gasses with kinetic diameters
ranging from 0.26 to 0.55 nm are presented for all membranes calcined at 500 and 600ºC.
All membranes, demonstrate a significant increase in permeability for gasses with a
kinetic diameter below 0.3 nm. These data are indicative of the existence of pores in the
Ti0.5Zr0.5O2 layers having dimensions which make them primarily accessible to relatively
small molecules such as He and H2. This is especially manifest in membrane #205, which
achieves a measured permselectivity for He/H2 and He/N2 of 2.0 and 14, respectively.
In Figure 75 the effect of temperature on H2 and CO2 permeation are presented for
membrane #205 in Arrhenius-type plots. The linearity of the relation between logarithm
of permeance and reciprocal temperature confirms a thermally activated transport
mechanism. The activation energy Ea can have any sign; in this study the sign is positive
when the permeation increases with temperature. The measured activation energy for H2
and CO2 transport amount to 8.4 and 4.9 kJ/mol, respectively. As a result of these