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

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5 Conclusions and recommendations method by Grebner et al. 71,72 was not confirmed which might be explained by the absence of SDAs or guest molecules to form DOH cages. DOH Calcination in air for extended periods (21 days) at elevated temperatures (900ºC) could not result in complete SDA removal. A minor calcination enhancement is observed for the DOH samples that are doped with traces of titanium. It is not certain if this can be explained by catalytic oxidation of titanium. Significant DOH cages were emptied by calcination when the DOH crystal size was reduced mechanically. However, crystal structure loss is inevitable during ball milling DOH crystals. Quasi SDA-free DOH, with an cage occupancy of only 1% and high crystallinity, was obtained after calcination at 900ºC for 5 hours when the atmospheric pressure was increased twice to 50 MPa for 30 min (Hot isostatic pressure calcination). All silica DOH that is quasi SDA-free was prepared and might present hydrothermal stable microporous material with pores that are inaccessible for CO2 and possibly open to H2. These DOH crystals should be studied with gas sorption to prove the H2 accessibility and diffusion. First DOH layers on α-Al2O3 supports were prepared with crystallisation times of only 24 hours. Sol-Gel derived membranes Polymeric Y2O3 or TiO2 mixed ZrO2 sols are synthesised for the preparation of ultramicroporous powders and thin films on γ-Al2O3 supporting membranes as potential gas separation membranes. Two routes have been selected, the Ketone and the Amine approach based on the precursor modifiers. Acetyl acetone modified Zr-precursor, carboxylic catalysed and yttrium-hydrated sol syntheses resulted in ~5 nm stable yttrium stabilised zirconia (YSZ) sols. Structure directing agents (SDA) such as Pluronic F127 did not change the particle size in the sol. Caproic and nanonic acids catalysed sols resulted in the highest viscous stable sols. Fractal dimensions of these Ketone-sols would be informative to study. 8 mol % Y2O3 addition to the zirconia sols resulted in cubic 8YSZ material at temperatures above 400ºC. 8YSZ calcined dried sols are microporous with BET specific surface areas of ~50 m 2 /g. SDA addition to the 8YSZ sols, to mesostructure the cubic 8YSZ nanoparticles, transformed the material to a more mesoporous nature. TEM investigations on powders and on the surface of mesostructured 8YSZ membranes are advised. 8YSZ layers with the absence of SDAs might form microporous layers with low permeability. Optimal calcination conditions such as drying, heating ramp, dwell time calcination time and cooling ramp should be studied in detail. 30-50 nm cubic 8YSZ films prepared by the Ketone-approach show He and N2 transport by Knudsen diffusion due to defects or by too large pores in the final membrane layer. Defect free 8YSZ layers using the Ketone-approach should be prepared in order to 111
5 Conclusions and recommendations study the permeability of these films as a function of pressure difference over the membrane. TiO2-ZrO2 and mixtures of 25, 50, 66, 75 and 90% mol TiO2 in ZrO2 were prepared using the Amine-approach. Diethanolamine or diisopropanolamine precursor modified Ti/Zr precursors can result in ~5 nm stable linear polymeric sols similar to the state of the art SiO2 sols. It is believed that sol-gel derived ultramicroporous materials can be synthesised with linear polymeric sols alone. The solid concentration and the molar composition of these Amine sols should be studied by means of SAXS and viscosity measurements. The single oxides TiO2 and ZrO2 crystallise at temperatures below 400ºC resulting in mesoporous and microporous material, respectively. As expected from the linear Amine-sols, the amorphous binary TiO2/ZrO2 materials are microporous between 400 and 500ºC. The highest BET specific surface area of ~200 m 2 /g with ~1.0 nm estimated pore size (gas physisorption) is obtained for the Ti0.5Zr0.5O2 calcined at 500ºC. The crystallisation temperature of orthorhombic Ti0.5Zr0.5O2 is between 550 and 600ºC which is ~250ºC higher than the single oxides. Diisopropanolamine instead of diethanolamine postponed the crystallisation temperature of the TiO2-ZrO2 mixture. These microporous materials exhibit even higher specific surface areas at 400ºC. This might be explained by the higher viscosity of the Amine sols. The crystallisation temperature and the specific surface areas of the binary TiO2/ZrO2 material prepared by the Amine-approach are higher than the Ketone-approach. However, the solid concentration and the sol composition of both approaches are different which make them difficult to compare. State of the art silica membranes have pores in the range of 0.3 nm mainly due to their small particles of amorphous nature. It might not be excluded that ultramicroporous inorganic membranes can be prepared from sol-gel derived amorphous ceramics alone. Amorphous Ti0.5Zr0.5O2 layers might be ultramicroporous. Nevertheless, the physical properties such as the results form XRD and gas sorption (H2, CO2, N2 at low and high pressures and temperatures) on bulk material should be studied in more detail on these TiO2-ZrO2 microporous materials. Changing the sol composition, drying and calcination procedures might be beneficial. 20-60 nm thin homogeneous films can be prepared from TiO2, ZrO2 and binary oxides on γ-Al2O3 membranes using calcination temperatures in the range of 400 to 600ºC. Knudsen mass transport is observed in anatase TiO2 or tetragonal ZrO2 films prepared by the Amine approach. This indicates the presence of pores larger than the kinetic diameter of the transported gasses (~0.5 nm). The larger pores in TiO2 films are in agreement with the mesoporous nature of the TiO2 bulk material. Larger pores in ZrO2 films can be 112
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Mitglied der Helmholtz-Gemeinschaft
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Forschungszentrum Jülich GmbH Inst
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List of Abbreviations Ac Acetyl Ace
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Summary CO2 capture and storage mig
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Zusammenfassung Die Abtrennung und
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Content Content CONTENT............
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1 Introduction and aims 1 Introduct
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1 Introduction and aims Candidate m
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2 Theoretical background 2 Theoreti
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2 Theoretical background Despite th
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2 Theoretical background Table 2 Ox
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2 Theoretical background 2.1.2 Micr
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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 the materi
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2 Theoretical background Figure 9 D
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2 Theoretical background Figure 11
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2 Theoretical background due to its
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2 Theoretical background 2.3.3.2 Mi
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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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3 Experimental Another solution was
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3 Experimental 3.4 Characterisation
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3 Experimental Element analysis The
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3 Experimental Additionally, the hy
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4 Results and discussion Abundance
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4 Results and discussion 4.2 Zeolit
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4 Results and discussion Table 14 D
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4 Results and discussion hours usin
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4 Results and discussion Intensity
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Page 100 and 101: 4 Results and discussion V micro /V
Page 102 and 103: 4 Results and discussion In pure Ti
Page 104 and 105: 4 Results and discussion In summary
Page 106 and 107: 4 Results and discussion Intensity
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Page 112 and 113: 4 Results and discussion Raman Inte
Page 114 and 115: 4 Results and discussion Tungsten 5
Page 116 and 117: 4 Results and discussion Mol% Carbo
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Page 126 and 127: 6 References 22. Shao, Z., Dong, H.
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Page 130 and 131: 6 References 108. Wen, T. L., Heber
Page 132 and 133: Curriculum Vitae - George van der D
Page 134: Last but not least, I would like to
Page 137: Band | Volume 8 ISBN 978-3-89336-52
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