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

4 Results and discussion
In summary, anatase TiO2 contains mesopores in the temperature range of 400 to 600ºC.
The average crystal size and the pore size seem to be coupled and increase with
increasing calcination temperature. Tetragonal ZrO2 is mainly microporous below 600ºC.
However, the ZrO2 powder with a specific surface area of approximately 75 m 2 /g might
result in low permeable membrane layers. Besides, both TiO2 and ZrO2 show phase
transformations in the temperature range of 500-600ºC. This could lead to cracks during
the calcination as a result of thermal expansion mismatches of the phases.
The crystallisation temperature of Ti0.5Zr0.5O2 is between 550 and 600ºC which is
approximately 250ºC higher than single oxides 320-360ºC. The higher crystallisation
temperature could suppress the crystal growth while maintaining the microporosity. The
crystallisation temperature, high porosity, high microporosity and small pore size bulk
material properties of Ti0.5Zr0.5O2 calcined at 500ºC are similar to state of the art SiO2.
This indicates that Ti0.5Zr0.5O2 might form microporous membrane layers as well.
However, amorphous microporous materials might have a lower chemical stability
compared to their single oxide relatives.
4.3.2.6 Amine approach – Diethanolamine / Diisopropanolamine
The precursor modifier diethanolamine (DEA) is replaced in the sol synthesis by
equimolar diisopropanolamine (DIPA) to i) increase the viscosity, ii) better compatibility
with the propanol solvent and iii) prevention of densification by forming higher porosity.
No literature was found on this potential precursor modifier.
No significant difference in the DTA/TG analyses and carbon content results are obtained
when DIPA was used instead of DEA as precursor modifier for the formation of binary
oxides with 25 and 50 mol % TiO2 in ZrO2 up to 500ºC.
Figure 60-A presents type I sorption isotherms of 50 mol % TiO2 in ZrO2 using DIPA,
which have specific surface area trends comparable with 50 mol % TiO2 in ZrO2 using
DEA (Table 26). However, the specific surface areas of 25 and 50 mol % TiO2 in ZrO2 at
400ºC using DIPA are a factor 2 higher than when DEA was used (Table 26 and Figure
60-B). The higher specific surfaces are of dried and calcined DIPA sols may be explained
by the longer organic chain of DIPA compared to DEA.
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