| 1. |
- Andersson, Charlotte, et al.
(författare)
-
Silicalite-1 membranes with small crystal size
- 2004
-
Ingår i: Recent advances in the science and technology of zeolites and related materials. Part A. - Amsterdam : Elsevier. - 0444518274 ; , s. 626-631
-
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.
|
|
| 2. |
- Gualtieri, Magdalena Lassinantti, et al.
(författare)
-
Crack formation in α-alumina supported MFI zeolite membranes studied by in situ high temperature synchrotron powder diffraction
- 2007
-
Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 290:1-2, s. 95-104
-
Tidskriftsartikel (refereegranskat)abstract
- Cracks are frequently formed in α-alumina supported MFI membranes during calcination. To better understand crack formation, in situ powder diffraction data were collected during calcination of a type of MFI membrane (ca. 1800 nm thick) which is known to crack reproducibly. In addition, data for MFI powder and a blank support were also collected. Both a synchrotron radiation facility and an in-house instrument were used. The unit cell parameters were determined with the Rietveld method, and the strain in the direction perpendicular to the film surface was calculated for the film as well as for the support. The microstrain in the support was also estimated. Based on the results obtained here, a model for crack formation in this type of MFI membrane was proposed. The lack of cracks in other types of MFI membranes (ca. 500 nm) prepared in our laboratory is also explained by the model. In thicker MFI films, the crystals are well intergrown. During heating, the MFI crystals contract and the α-alumina support expands. Consequently, a thermal stress develops in the composite which eventually leads to formation of cracks in the film and structural defects in the support. In thinner films, the crystals are less well intergrown and the thermal expansion mismatch leads to opening of grain boundaries rather than cracks.
|
|
| 3. |
- Hedlund, Jonas, et al.
(författare)
-
A masking technique for high quality MFI membranes
- 2003
-
Ingår i: Journal of Membrane Science. - 0376-7388 .- 1873-3123. ; 222:1-2, s. 163-179
-
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.
|
|
| 4. |
- Hedlund, Jonas, et al.
(författare)
-
Factors affecting the performance of MFI membranes
- 2004
-
Ingår i: Recent advances in the science and technology of zeolites and related materials. Part A. - Amsterdam : Elsevier. - 0444518274 ; , s. 640-646
-
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.
|
|
| 5. |
- Hedlund, Jonas, et al.
(författare)
-
Texture of MFI films grown from seeds
- 2005
-
Ingår i: Current Opinion in Colloid & Interface Science. - : Elsevier BV. - 1359-0294 .- 1879-0399. ; 10:5-6, s. 226-232
-
Tidskriftsartikel (refereegranskat)abstract
- This review describes how the texture of MFI films grown from seed crystal is developed during film preparation. Reports published during the last 5 years are in focus. Relative growth rates in various crystallographic directions, competitive growth, properties of the seed layer, defects, grain boundaries and other parameters influencing the film properties are discussed. Mathematical models describing competitive growth are also discussed. Suitable characterization methods for defects are described. The last part of the review is devoted to diffusion. Diffusion models accounting for texture in MFI films and the influence of texture on diffussion are discussed.
|
|
| 6. |
- Jareman, Fredrik, et al.
(författare)
-
Effects of aluminum content on the separation properties of MFI membranes
- 2003
-
Ingår i: Separation and Purification Technology. - 1383-5866 .- 1873-3794. ; 32:1-3, s. 159-163
-
Tidskriftsartikel (refereegranskat)abstract
- MFI membranes with almost identical film thickness and defect distribution but different Si/Al ratio were evaluated by separation of butane and hexane isomers. Film thickness was evaluated by SEM and defect distribution by porosimetry. When the temperature was varied, the membranes showed similar separation trends for butanes, but clear differences were observed for hexane separation. The hexane separation factor varied with temperature for the silicalite-1 membrane but was constant for the ZSM-5 membrane. It is believed that this difference may be a result of differences in adsorption properties.
|
|
| 7. |
- Jareman, Fredrik
(författare)
-
MFI-molecular sieve membranes : synthesis, characterization and modelling
- 2002
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work concerns evaluation by permeation measurements and modeling of thin (<2µm) MFI molecular sieve membranes and, to a smaller extent, synthesis of such materials. The membranes have been synthesized on graded a-alumina microfiltration filters using The seed film method. Scanning electron microscopy and x-ray diffraction were used for characterization in addition to permeation measurements. Mathematical models describing membrane flux for real membranes and defect distributions were developed. Defect distributions were calculated from porosimetry data and were further used for prediction of single gas permeation characteristics for real membranes. The models confirm the experimental findings, with respect to ideal selectivities as a measurement of membrane quality. Membrane permeation simulations indicate increasing ideal selectivities, with increasing film thickness, for quotients containing SF6. Thereby a high quality membrane could possess low ideal selectivities. This finding was confirmed by comparing experimental data of several membranes with varying thickness. The correlation between multi component separation data and commonly used quality criteria was investigated. It was found that commonly used single gas permeation quotients (ideal selectivity) between light inorganic gases, especially those containing sulphurhexaflouride (SF6), is less appropriate for membrane quality measurement. The porosimetry experiment showed on the other hand a good agreement between experimental data and separation performance of the membranes, as expected. ZSM-5 membranes with low aluminum content and silicalite-1 membranes with similar material properties, such as defect distribution and thickness were evaluated with multi component hydrocarbon isomers permeation. The ZSM-5 membrane had lower permeances and a slightly better butane isomer separation performance than the silicalite-1 membrane. The latter membrane showed a minimum in separation selectivity between two C6 isomers whereas the ZSM-5 membrane showed an almost constant selectivity, independent of temperature, but with lower permeances. ZSM-5 membranes with a high aluminum content catalyzed the formation of diethylether and ethylen at temperatures exceeding 150°C from a water/ethanol mixture. The membrane separated a mixture of C4 isomers with good performance at elevated temperatures. However these membranes suffered from temperature instability problems.
|
|
| 8. |
- Jareman, Fredrik, et al.
(författare)
-
Modelling of single gas permeation in real MFI membranes
- 2004
-
Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 236:1-2, s. 81-89
-
Tidskriftsartikel (refereegranskat)abstract
- A novel permeation model for flow through defects and zeolite pores in real MFI membranes, also accounting for substrate effects has been developed. Defect distributions for two types of MFI membranes were determined from porosimetry data using the model, which incorporated the Horvath Kawazoe (micropores) or the Kelvin equation (mesopores). The narrowest (1.08 nm) and also most common defects were found to be separated with a distance of 10–40 μm according to the model. Diffusion coefficients for hydrogen, helium, nitrogen and SF6 in the zeolite were further determined from single gas permeation data using the model using the independently determined defect distribution. The coefficients are consistent with values previously reported in the literature.
|
|
| 9. |
|
|
| 10. |
- Jareman, Fredrik, et al.
(författare)
-
Permeation of H2, N2, He and SF6 in real MFI membranes
- 2005
-
Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 83:1-3, s. 326-332
-
Tidskriftsartikel (refereegranskat)abstract
- This work shows that a previously developed model for single gas permeation in real MFI membranes is applicable to an arbitrary MFI membrane with a different film thickness and defect distribution. The model can predict the flow of H2, N2 and He resonably. Deviations in SF6 flux for thick and oriented films were observed and attributed to a lower diffusion coefficient for the narrower pores in the a-direction of the MFI crystals. By guidance from the model, variations in previously reported single gas permeance ratios for selected membranes can now be attributed to variations in feed pressure, film thickness preferred orientation and defect distribution. It was found that high feed pressures and thick oriented films resulted in large single gas permeance ratios with SF6 in the denominator, even though these membranes were more defective than thinner membranes with more randomly oriented crystals. In general, single gas permeance ratios are strongly dependent on material properties and experimental conditions. These ratios can only be used for comparison of membranes with similar morphology and the ratios must be measured under identical conditions.
|
|
