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

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2 Theoretical background 2 Theoretical background Membranes are semi-permeable barriers which are able to selectively transport different species. The selectivity is a measure of the different transport abilities of the species. Gas separation membranes inhibit the transport of favour gas molecules where others are either blocked or have a lower transport flux. The most common gas separation membranes can be distinguished by the choice of membrane material: o Organic polymer membranes o Ceramic or metallic membranes Organic polymer membranes can be applied in power plants for the capture of CO2. In the future, highly efficient power plants in combination with high temperature separation technology for CO2 capture will be preferred. Ceramic or metallic membranes may fulfil this role. This chapter contains a literature study on the state-of-the-art ceramic or metallic gas separation membranes. Review of this literature is important for understanding the restrictions and possibilities of promising gas separation membranes for the previously mentioned power plant concepts. Crystalline (page 14) and sol-gel derived (page 24) microporous ceramic membranes are the focus of this thesis. Finally, mass transport in microporous membranes is outlined. 2.1 Inorganic gas separation membranes Three types of inorganic membranes for gas separation applications can be distinguished: o Dense ceramic membranes o Dense metallic membranes o Molecular sieving membranes Dense ceramic membranes such as mixed ionic electronic conductive membranes are candidates for oxygen production from air with high selectivity due to their ability to transport oxygen ions and electrons at elevated temperatures in the range of 600-1000ºC. Dense ceramic protonic membranes are able to separate H2 from other gasses at temperatures between 500 and ~800ºC. Dense metallic membranes are able to separate H2 from other gasses in a temperature range of 300-600ºC. The operating temperatures of ceramic and metallic protonic conductors match the typical reforming reaction temperatures in the precombustion concept at 180-550ºC. 7
2 Theoretical background The development of molecular sieving membranes started about 50 years ago as a separating agent for 235 UF6 and 238 UF6 for nuclear fuel enrichment. 5 Since then, a number of other applications have emerged such as liquid-solid and liquid-liquid separation, pervaporation and finally gas separation, generally determined by the pore size of the selective layer. Microporous ceramic can be used as molecular sieve membranes and might have high prospects in the post and precombustion concepts provided that both the membrane permeability and permselectivity are substantial in order to minimise efficiency penalties in power plants. 2.1.1 Dense metallic and ceramic membranes Dense membranes are gastight layers. The first group of dense inorganic membranes studied in the past decade for gas separation is the metallic membrane type; primarily palladium alloy membranes for hydrogen (H2/CO2) separation. The latest development in this field is the study of supported thin metallic membranes, as thin as a few tenths of microns. 6 The most extensively studied group of dense membranes includes the oxygen ionic conductive and mixed oxygen ionic and electronic conductive ceramic membranes. 6 In the early 1980s, a third group of dense membranes emerged from high temperature hydrogen semi permeable dense ceramic membranes. These membranes are based on proton-conducting ceramics. 2.1.1.1 Dense metallic membranes The hydrogen transport properties of dense metallic membranes such as silver doped palladium (Pd/Ag) membranes are determined by many factors. The factors can be hydrogen transport to the metal membrane, adsorption of hydrogen on the surface, splitting of hydrogen to be incorporated into the lattice of the metallic membrane material, bulk diffusion of the protons and counter electrons, regeneration of the hydrogen molecules, desorption of the hydrogen and finally diffusion from the membrane which is extensively discussed in the article of Bredesen et al. 7 There are several methods used to coat thin metallic films on porous metallic or ceramic supports: electroless plating, chemical and physical vapour deposition or sputtering. All these methods can be used to obtain good quality, thin Pd/Ag membranes with hydrogen to helium (or nitrogen) permselectivity. Pex et al. 8 and Pan et al. 9 prepared palladium based membranes on alumina supports (see Table 1). Others prepared thin palladium 10 or palladium nickel 11 layers on stainlesssteel porous substrates, which offer high hydrogen permeance in combination with excellent permselectivities. A sandwich structure based on a dense vanadium layer and a thin porous palladium layer on both sides resulted in even higher permselectivitiy. 12 8
Page 1 and 2: Mitglied der Helmholtz-Gemeinschaft
Page 4 and 5: Forschungszentrum Jülich GmbH Inst
Page 6 and 7: List of Abbreviations Ac Acetyl Ace
Page 8 and 9: Summary CO2 capture and storage mig
Page 10 and 11: Zusammenfassung Die Abtrennung und
Page 12 and 13: Content Content CONTENT............
Page 14 and 15: 1 Introduction and aims 1 Introduct
Page 16 and 17: 1 Introduction and aims Candidate m
Page 20 and 21: 2 Theoretical background Despite th
Page 22 and 23: 2 Theoretical background Table 2 Ox
Page 24 and 25: 2 Theoretical background 2.1.2 Micr
Page 26 and 27: 2 Theoretical background Poly-cryst
Page 28 and 29: 2 Theoretical background membranes
Page 30 and 31: 2 Theoretical background Dry or wet
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Page 38 and 39: 2 Theoretical background due to its
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Page 42 and 43: 2 Theoretical background 2.4 Microp
Page 44 and 45: 2 Theoretical background Figure 15
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Page 48 and 49: 3 Experimental 3 Experimental The m
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4 Results and discussion hours usin
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4 Results and discussion Intensity
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4 Results and discussion The carbon
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4 Results and discussion DOH crysta
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4 Results and discussion 900 [ºC]
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4 Results and discussion characteri
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4 Results and discussion without a
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4 Results and discussion 4.3.1.1 Ke
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4 Results and discussion Solid Cont
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4 Results and discussion difference
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4 Results and discussion V [cm ads
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4 Results and discussion The averag
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4 Results and discussion DTA µV/mg
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4 Results and discussion Vads / cm
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4 Results and discussion The increa
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4 Results and discussion 20 30 40 5
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4 Results and discussion V micro /V
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4 Results and discussion In pure Ti
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4 Results and discussion In summary
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4 Results and discussion Intensity
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4 Results and discussion nanonic YS
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4 Results and discussion ~50nm TiO2
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4 Results and discussion Raman Inte
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4 Results and discussion Tungsten 5
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4 Results and discussion Mol% Carbo
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4 Results and discussion Permeance
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4 Results and discussion He Permean
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5 Conclusions and recommendations m
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5 Conclusions and recommendations m
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6 References 22. Shao, Z., Dong, H.
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6 References 65. Van den Berg, A. W
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6 References 108. Wen, T. L., Heber
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Curriculum Vitae - George van der D
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Last but not least, I would like to
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Band | Volume 8 ISBN 978-3-89336-52
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