| 1. |
- Andersson, Charlotte, et al.
(author)
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Silicalite-1 membranes with small crystal size
- 2004
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In: Recent advances in the science and technology of zeolites and related materials. Part A. - Amsterdam : Elsevier. - 0444518274 ; , s. 626-631
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Conference paper (peer-reviewed)abstract
- Silicalite-1 membranes with small crystal size were prepared using a multiseeding method, where the support was repeatedly seeded and exposed to a short hydrothermal treatment up to five times. The film were characterized using SEM, single gas permeation, porosimetry and mixture separation experiment Films with three or four layers were of high quality i.e with minor defects according to the porosimetry experiments but showed poor separation of binary mixtures. This result may be attributed to the small crystal size and/or large amount of grain boundaries in the films.
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| 2. |
- Hedlund, Jonas, et al.
(author)
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Factors affecting the performance of MFI membranes
- 2004
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In: Recent advances in the science and technology of zeolites and related materials. Part A. - Amsterdam : Elsevier. - 0444518274 ; , s. 640-646
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Conference paper (peer-reviewed)abstract
- Thin MFI membranes with varying morphology have been prepared using high flux alumina supports using all advanced synthesis procedure employing support masking and seeding. Evaluation of membrane quality by physical characterization and permeation measurements revealed a number of factors affecting the membrane performance. In the present work, the effects of film thickness, support type, preferred orientation and calcination rate are discussed. Some quality criteria for zeolite membranes are also debated and the porosimetry technique is discussed.
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| 3. |
- Lassinantti-Gualtieri, Magdalena, et al.
(author)
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Accurate measurement of the thermal expansion of MFI zeolite membranes by in situ HTXRPD
- 2004
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In: Recent advances in the science and technology of zeolites and related materials. Part A. - Amsterdam : Elsevier. - 0444518274 ; , s. 703-709
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Conference paper (peer-reviewed)abstract
- Template removal by calcination of MFI type membranes is often accompanied by crack formation. The thermal behavior of MFI type membranes, synthesized with and without masking, was studied to understand the mechanism. Masking prevents growth of zeolite in the interior of the Support during membrane synthesis. Rietveld refinements of powder diffraction data collected in situ at high temperature allowed to accurately determine the change in thermal expansion of the MFI film and the porous alpha-alumina support. During heating, a relatively large contraction of the cell volume during template removal occurred in the zeolite powder and in the film of the membrane prepared with masking. The much smaller decrease in the non-masked sample indicates that this membrane is under stress during heating and as a consequence, cracks are formed. The stress imposed in the membrane prepared without masking may be due to the opposite thermal behavior of the Substrate in combination with strong bonds between the membrane and the support.
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| 4. |
- Naydenov, Valeri, et al.
(author)
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Mesoporous Me-AlPO-5 spheres prepared using cation-exchange resins as templates
- 2004
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In: Recent advances in the science and technology of zeolites and related materials. Part A. - Amsterdam : Elsevier. - 0444518274 ; , s. 660-666
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Conference paper (peer-reviewed)abstract
- Mesoporous self-bonded transition metal-containing AIPO-5 spheres were prepared by a multi-step procedure using macroporous cation exchange resin beads as a template. Aluminum was firstly introduced into the resin by ion exchange using an aluminum chlorohydrate solution. After separation and drying, tf Al-resin composite was mixed with phosphoric acid, tetraethylammonium hydroxide distilled water and hydrothermally treated to yield AIPO-5-resiii composite. Thereafter, vanadium or chromium were ion exchanged into the AIPO-5-resiii composites utilizing the residual ion exchange capacity of the resistor. Finally, the resin was combusted leaving behind Me-AlPO-5 (where Me is V or Cr) spheres similar in shaping and size to the original resin beads. The appearance of the spheres and the nature of the metal species were dependent on the metal loading. The metal introduction affected mainly the mesopore structure of the Mesophare AlPO-5 spheres.
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| 5. |
- Naydenov, Valeri, et al.
(author)
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ZSM-5 crystalization of preformed amorphous aluminosilicate beads
- 2004
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In: Recent advances in the science and technology of zeolites and related materials. Part A. - Amsterdam : Elsevier. - 0444518274 ; , s. 654-659
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Conference paper (peer-reviewed)abstract
- Preformed aluminosilicate beads were prepared by ion exchange of aluminosilicate species into ion exchange resins followed by combustion of the organic resin. The resultant amorphous beads were zeolitized thereafter by aging in TPAOH solutions and subsequent hydrothermal treatment. The zeolitization process was realized by rearrangement of the fine particles building Lip the amorphous aluminosilicate because framework into larger ZSM-5 crystals by complex dissolution-crystallization processes. The crystallinity the products was dependent on the aging procedure and the composition of the mixture during the hydrothermal treatment. The shape and the pore structure of the initial beads were generally preserved during the ZSM-5 formation.
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| 6. |
- Öhrman, Olov, et al.
(author)
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ZSM-5 structured catalysts coated with silicalite-1
- 2004
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In: Recent advances in the science and technology of zeolites and related materials. Part A. - Amsterdam : Elsevier. - 0444518274 ; , s. 677-684
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Conference paper (peer-reviewed)abstract
- Alumina beads were coated with ZSM-5 films ranging from 150 nm to 2300 nm ill thickness. The ZSM-5 boated alumina beads were Subsequently hydrothermally treated in a silicalite-1 synthesis solution ill two steps Whereupon a dense silicalite-1 film was formed oil top of the ZSM-5 film. The materials were tested with two probe reactions and the reactivity was compared before and after coating with silicalite-1. As expected, the para-xylene (pX) isomerization reactivity showed no change for samples with and without the top layer of silicalite-1 for equal amounts Of zeolite. Surprisingly, the triisopropylbenzene (TIPB) conversion did not decrease after the silicalite-1 film was introduced. As measured by XPS, the aluminum concentration at the Surface of the uncalcined silicalite-1 film surface was lower compared to that at the Surface of the calcined ZSM-5 film. However, after calcination the concentration of aluminum was higher at the silicalite-1 film surface than at the ZSM-5 film Surface. These results Suggest that aluminum migrates from the ZSM-5 film into the silicalite-1 film during calcination and testing which results in all active top layer.
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