| 1. |
- Andersson, Charlotte, et al.
(författare)
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Silicalite-1 membranes with small crystal size
- 2004
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Ingår i: Recent advances in the science and technology of zeolites and related materials. Part A. - Amsterdam : Elsevier. - 0444518274 ; , s. 626-631
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Konferensbidrag (refereegranskat)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. |
- Anthonis, Marc Henry, et al.
(författare)
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Crystalline molecular sieve layers and processes for their manufacture
- 2000
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Patent (populärvet., debatt m.m.)abstract
- A process is described for the manufacture of crystalline molecular sieve layers with good para-xylene over meta-xylene selectivity's good para-xylene permeances and selectivities. The process requires impregnation of the support prior to hydrothermal synthesis using the seeded method and may be undertaken with pre-impregnation masking. The crystalline molecular sieve layer has a selectivity (.alpha..sub.x) for para-xylene over meta-xylene of 2 or greater and a permeance (Q.sub.x) for para-xylene of 3.27.times.10.sup.-8 mole(px)/m.sup.2.s.Pa(px) or greater measured at a temperature of .gtoreq.250.degree. C. and an aromatic hydrocarbon partial pressure of .gtoreq.10.times.10.sup.3 Pa.
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| 3. |
- Engström, V., et al.
(författare)
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The effect of seed size on the growth of silicalite-1 films on gold surfaces
- 2000
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Ingår i: Microporous and Mesoporous Materials. - 1387-1811 .- 1873-3093. ; 38:1, s. 51-60
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Tidskriftsartikel (refereegranskat)abstract
- Silicalite-1 films grown on gold surfaces seeded with colloidal crystals with a size of 60, 165 and 320 nm were investigated by reflection–absorption infrared spectroscopy, scanning electron microscopy and X-ray diffraction in order to follow up the formation of nano-scale defects and to determine the optimal synthesis conditions for preparation of silicalite-1 films with a low concentration of defects. Using 60-nm-sized colloidal crystals, the seeding method was capable of producing silicalite-1 films with low concentrations of defects and with thicknesses ranging from 100 to 300 nm, which are predominantly oriented with the a-axis perpendicular to the surface. Hydrothermal treatment times of the 60-nm-seeded surfaces longer than 36 h as well as the seeding with 165 or 320 nm colloidal crystals substantially enhanced the formation of defects in the films.
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| 4. |
- Hedlund, Jonas, et al.
(författare)
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A masking technique for high quality MFI membranes
- 2003
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Ingår i: Journal of Membrane Science. - 0376-7388 .- 1873-3123. ; 222:1-2, s. 163-179
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Tidskriftsartikel (refereegranskat)abstract
- A procedure for the preparation of high quality zeolite membranes was developed. This procedure relies on a masking approach that fills all support pores with wax while leaving the top surface free for deposition of the zeolite film, thus, protecting the support from the synthesis mixture. Zeolite films of different thickness were grown on masked and non-masked supports using a seeded growth method. The zeolite-coated supports were calcined in order to remove the wax from the support and the template molecules from the zeolite. The membranes were characterized by SEM, XRD, single gas and multi-component permeation measurements. Support masking reduces the zeolite membrane thickness and the width of the cracks in the zeolite film. Thicker films, especially those prepared without masking, are defective. Masked membranes with a film thickness of 500 nm show no cracks or pinholes. These membranes have a H2 permeance of 220×10−7 mol/(s m2 Pa), an n-butane permeance of 9.8×10−7 mol/(s m2 Pa) and an n-butane/iso-butane separation factor of 9.0 at 25 °C. The separation factor for a mixture of n-hexane/2,2-dimethyl-butane was 227 at 400 °C and the n-hexane permeance was 5.6×10−7 mol/(s m2 Pa). The p-xylene permeance was 2.7×10−7 mol/(s m2 Pa) and the para/ortho separation factor was 17 at 400 °C for a mixture of xylenes.
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| 5. |
- Hedlund, Jonas
(författare)
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Control of the preferred orientation in MFI films synthesized by seeding
- 2000
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Ingår i: Journal of porous materials. - 1380-2224 .- 1573-4854. ; 7:4, s. 455-464
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Tidskriftsartikel (refereegranskat)abstract
- Single crystal silicon and quartz wafers were seeded with colloidal TPA-silicate-1 crystals. Hydrothermal treatment of the seeded substrates was used to grow dense MFI films. The preferred orientation of the crystals constituting the films as a function of the amount and size of seeds, film thickness and hydrothermal treatment conditions was investigated. In thin films, most of the crystalline material was found to be oriented with the b-axes close to perpendicular to the substrate surface. In thick films, the a- or c-axes were close to perpendicular to the substrate surface depending on the conditions used for hydrothermal treatment. The seed size and amount was found to affect the rate of change in preferred orientation as a function of film thickness. A film growth mechanism which is able to explain the experimental results is proposed
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| 6. |
- Hedlund, Jonas, et al.
(författare)
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Factors affecting the performance of MFI membranes
- 2004
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Ingår i: Recent advances in the science and technology of zeolites and related materials. Part A. - Amsterdam : Elsevier. - 0444518274 ; , s. 640-646
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Konferensbidrag (refereegranskat)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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| 7. |
- Hedlund, Jonas, et al.
(författare)
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High-flux MFI membranes
- 2002
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Ingår i: Microporous and Mesoporous Materials. - 1387-1811 .- 1873-3093. ; 52:3, s. 179-189
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and evaluation of high performance MFI-type membranes is described. These systems exhibit fluxes that are one to two orders of magnitude higher than previous literature reports, with comparable selectivities, when tested for various single component gases and for mixtures of C4, C6 and xylene isomers.These materials are the result of a rational fabrication approach targeting ultra-thin, defect-free MFI films on open supports by using a two-step support masking technique and a monolayer of colloidal nucleation seeds, followed by in situ hydrothermal growth, producing a defect-free film with a thickness of 0.5 μm. Reproducibility of the membrane preparation was excellent.
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| 8. |
- Hedlund, Jonas, et al.
(författare)
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Synthetis of nanosized offretite crystals
- 2001
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Ingår i: Zeolites and mesoporous materials at the dawn of the 21st century. - Amsterdam : Elsevier. - 0444502386 ; , s. 187-
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Konferensbidrag (refereegranskat)
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| 9. |
- Hedlund, Jonas, et al.
(författare)
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The synthesis and testing of thin film ZSM-5 catalysts
- 2004
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 59:13, s. 2647-2657
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and catalytic testing of thin ZSM-5 films on glass and alumina beads is described. The thickness of the ZSM-5 films was controlled to 150, 350, 800 and 2300 nm. The samples were characterised by SEM, gas adsorption and p-xylene isomerisation and 1,3,5-tri-isopropyl benzene cracking test reactions. A reaction–diffusion model adequately described the p-xylene isomerisation data. Estimates of model parameters were obtained by fitting the model to the experimental data. In both cases, the reaction rate constant increased with increasing film thickness. The xylene reaction data showed that secondary reaction products increased as expected with increasing diffusion limitations, but the increase was less than that predicted by the variation of thickness only. The trends in the reaction data could be explained by more defects in the thicker films and/or partial poisoning of the zeolite by mobile support cations in thinner films and/or orientation effects.
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| 10. |
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