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

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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. 93
4 Results and discussion Vads / cm 3 g -1 150 100 50 Table 26 Microstructure properties of dried binary oxide TiO2-ZrO2 DIPA sols Calcination Temp. Mol% Ti SBET m 2 /g 400ºC 25 334 50 224 500ºC 25 219 50 115 600ºC 50 48 50 mol% TiO2 in ZrO2 DIPA 400ºC 500ºC 600ºC 0,0 0,2 0,4 0,6 0,8 1,0 p/p 0 0 25 mol% TiO2 in ZrO2 A DIPA-DEA 400ºC B 200 94 Vads / cm 3 g -1 150 100 50 DIPA DEA 0,0 0,2 0,4 0,6 0,8 1,0 p/p 0 0 Figure 60 A) N2 isotherms 50 mol% TiO2 in ZrO2 calcined at (□) 400, (○) 500 and (◊) 600ºC using DIPA. B) N2 isotherms 25 mol% TiO2 in ZrO2 calcined at 400ºC using DIPA (○) and DEA (□). Open symbols present the adsorption and closed symbols the desorption points. Ti0.5Zr0.5O2 calcined at 600ºC is XRD-amorphous when diethanolamine is replaced by diisopropanolamine in the sol synthesis (Figure 61). The crystallisation temperature of TiZrO4 prepared by DIPA is delayed and could be explained by a more porous structure (larger specific surface area). Acidification of the hydrolysis solution in the DIPA sol synthesis is less effective compared to the DEA sol synthesis. The specific surface area and relative microporous adsorbed volume are comparable when the hydrolysis solution is prepared with H2O instead of 1 M HNO3. These results suggest that the DIPA is better bonded to alkoxide precursors. Therefore, DIPA might be an interesting alternative to DEA for the formation of microporous membrane materials.
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Summary CO2 capture and storage mig
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1 Introduction and aims 1 Introduct
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2 Theoretical background 2 Theoreti
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2 Theoretical background Poly-cryst
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2 Theoretical background membranes
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2 Theoretical background Dry or wet
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2 Theoretical background 2.4 Microp
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2 Theoretical background Figure 15
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2 Theoretical background wall inter
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3 Experimental 3 Experimental The m
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3 Experimental vacuum sample holder
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3 Experimental o of as-made DOH cry
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