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

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2 Theoretical background Figure 9 Deca-dodecasil 3R (DDR) structure 66 Figure 10 Dodecasil 1H (DOH) structure 66 2.2.4.2 Synthesis of small SDA-free DOH crystals The all silica zeolite type Dodecasil 1H 67 (possessing the zeolite framework type DOH- Figure 10) 68 with a pore aperture of ~2.8 Å 44 might be a promising membrane material for separating hydrogen at elevated temperatures. The name dodecasil 1H originates from dodecahedra as the structural building units forming layers which are hexagonally stacked. Only a few groups have studied DOH as a potential candidate for gas separation. The research group of Gies 69,70 was among the first to study this zeolite type. Grebner et al. 71-74 and den Exter 66 studied this zeolite material for several applications. DOH zeolites can be synthesised with SDA’s only. The most common are 1-amino adamantine (ADA), piperidine and 1-adamantyl trimethylammonium bromide 71-73 in aqueous solutions or the metal organic salts 75 [Co(C5H4Me)2]PF6 or [Fe(C6H6)(C5H5)2]PF6 in solvent free systems. After synthesis the templates occupy pores in the zeolite structure and, hence, have to be removed. DOH zeolite material is stable at elevated temperatures, for instance up to temperature of 900ºC, while still trapping some of the SDA. 71-73 In contrast, ADA from deca-dodecasil 3R is removed at 450°C, 44 but 700ºC is preferred. 63 DOH as membrane materials must be prepared template free and these crystals should be prepared as small crystals in order to form thin layers. Small crystals might be prepared from a homogeneous gel for short crystallisation times or by means of aging. The number of crystals can be enhanced by decoupling the nucleation from crystal growth by means of aging the gel composition at moderate temperatures before applying the common crystallisation temperature. Synthesising SDA-free DOH might be possible by using seeds and SDA free gel compositions as Grebner et al. claimed. 71-73 Post synthesis treatment to remove the template can be achieved via conventional calcination for extended periods or calcination of smaller crystals to shorten the transport path length of oxygen or combusted organics. 23
2 Theoretical background 2.3 Sol-gel derived membranes Microporous initial amorphous derived membranes, particularly microporous silica membranes, have been studied intensively in the last decades. Silica membranes can be prepared via: o Chemical vapour infiltration or deposition o Sol-gel techniques Chemical vapour deposited silica membranes are prepared starting from gaseous silica precursors that either infiltrate or deposit a silica layer in or on top of meso or macroporous supports. This method can reach high permselectivities but is generally coupled with a significant decrease of permeability due to the effect of pore blocking. Sol-gel derived silica membranes offer high H2 permeance 1-2·10 -6 mol/m 2 sPa in combination with reasonable permselectivities (terms are explained on page 36). However, the stability of silica membranes in humid conditions at elevated temperatures is poor. First, the synthesis of sols is discussed, followed by the common preparation methods of microporous sol-gel derived membranes. An overview of these membranes is given in section 2.3.3 followed by the selection of the promising sol-gel derived microporous materials in section 2.3.4. 2.3.1 Sol-Gel chemistry The sol-gel process is one of the most appropriate methods for the preparation of mesoporous and microporous layers. There are two sol-gel routes, polymeric and colloidal (Figure 11). Different steps involved in the process determine the porous structure, even at the very first stage of precursor synthesis. The first step in sol-gel process is the preparation of a sol using molecular precursors. There are two types of precursors, metal organics (preferentially metal alkoxides) and metal salts. Clusters or colloids are formed at the sol stage by condensation reaction. The chemistry of the sol formation is well documented by Livage et al. 76 Depending on conditions, nearly linear polymeric structures (hereafter referred as polymeric sols) and dense colloidal particles (colloidal sols) can be prepared. These clusters and colloids collide at the final stage to form a gel. 24
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
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Page 14 and 15: 1 Introduction and aims 1 Introduct
Page 16 and 17: 1 Introduction and aims Candidate m
Page 18 and 19: 2 Theoretical background 2 Theoreti
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Page 28 and 29: 2 Theoretical background membranes
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Page 38 and 39: 2 Theoretical background due to its
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Page 48 and 49: 3 Experimental 3 Experimental The m
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Page 56 and 57: 3 Experimental 3.4 Characterisation
Page 58 and 59: 3 Experimental Element analysis The
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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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