| 1. |
- Hedlund, Jonas, et al.
(författare)
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Permporometry analysis of zeolite membranes
- 2009
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 345:1-2, s. 276-287
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Tidskriftsartikel (refereegranskat)abstract
- In permporometry analysis of zeolite membranes, the permeance of a non-adsorbing gas, such as helium, is measured as a function of pressure of a strongly adsorbing compound, such as n-hexane in the case of silicalite-1 membranes. The adsorbing compound effectively blocks the transport of the non-adsorbing gas already at very low activity of the adsorbing compound. The plot of the permeance of the non-adsorbing gas as a function of relative pressure of the adsorbing compound is denoted a permporometry pattern. The present work is based on experimental data for a number of thin MFI membranes with a film thickness ranging from 300 to 1800 nm. An adsorption-branch permporometry experiment is simple and straightforward and after activation of the membrane by removing adsorbed species at 300 °C in a flow of dry gas, a full permporometry pattern is recorded within about 7 h for such membranes. It is shown how the distribution of flow-through defects can be estimated from the permporometry pattern using a simple model for permeation based on Knudsen diffusion. The estimated defect distribution is supported by SEM observations. In addition, the permeance of the non-adsorbing gas through defects measured in permporometry can be used to predict the permeance of molecules diffusing through defects in the membrane in mixture separation experiments and also indicate the separation factor. For instance, the helium permeance through defects in an MFI membrane measured by helium/n-hexane permporometry at room temperature can be used to estimate the permeance of 2,2-dimethylbutane (DMB) in a mixture separation experiment at a higher temperature with a feed containing both DMB and n-hexane by assuming Knudsen diffusion for both helium and DMB in the defects. Also, the separation factor αn-hexane/DMB in a mixture separation experiment at a certain temperature with an MFI membrane with a given defect distribution can be estimated from n-hexane/helium permporometry data recorded at the same temperature through an empirical correlation. In summary, adsorption-branch permporometry is a very effective tool for analysis of thin zeolite membranes, that in short time gives data that can be used to estimate the distribution of flow-through defects in the membrane and to estimate the transport of large molecules through defects in separation experiments and also estimate separation performance.
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| 2. |
- Lindmark, Jonas, et al.
(författare)
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Carbon dioxide removal from synthesis gas using MFI membranes
- 2010
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 360:1-2, s. 284-291
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Tidskriftsartikel (refereegranskat)abstract
- A membrane processes may represent a more effective alternative compared to current technology for separation of CO2 from synthesis gas. In the present work, MFI membranes were prepared and the separation performance was evaluated. The Si/Al ratio and the counter ions in the membrane had a significant effect on both single gas permeation and mixture separation by modifying both the effective pore size and the adsorption properties of the membranes. The membranes were relatively unselective for binary mixtures of carbon dioxide and hydrogen, but when the feed also contained water, a CO2/H2 separation factor of 6.2 was achieved for a BaZSM-5 membrane at room temperature. The CO2 permeance for this membrane was as high as 13·10-7 mol · m-2 · s-1 · Pa-1. A suitable terminology for this effect, that a third component, in this case water, enhanced the separation of two other components, in this case CO2 and H2, is sorption enhanced separation. Due to the reduced adsorption of both CO2 and water at higher temperature, the CO2/H2 separation factor was always reduced as the temperature was increased. This work clearly shows that MFI membranes are promising candidates for CO2 separation from synthesis gas.
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| 3. |
- Lindmark, Jonas, et al.
(författare)
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Impregnation of zeolite membranes for enhanced selectivity
- 2010
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 365:1-2, s. 188-197
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Tidskriftsartikel (refereegranskat)abstract
- A new method to enhance the selectivity of zeolite membranes for alternative separation tasks has been developed. Calcined MFI membranes were impregnated with a solution of Ca(NO3)2 in methanol and calcined at 600 °C to thermally decompose the nitrate. SEM and EDS data indicated that calcium compounds were evenly distributed in the entire MFI film and in addition, a few crystals of a calcium compound were observed on top of the film in some locations. A HR-TEM investigation showed that calcium compounds were present in low concentration in the sample and that the interiors of the MFI crystals remained fully crystalline after impregnation and calcination. However, the HR-TEM investigation could neither confirm nor rule out the occurrence of calcium compounds in the pores in the interiors of the crystals. In accordance with the SEM and TEM observations, XRD data showed that calcium compounds on top of the film were relatively large CaCO3 crystals and that the zeolite film remained crystalline after impregnation. However, eventual calcium compounds in the pores of the zeolite could not be studied by XRD since these would probably generate a very weak signal of amorphous material. FTIR data indicated that impregnation increased the amount of both physisorbed and chemisorbed CO2, the latter resulting in carbonate species in the film. n-Hexane/helium adsorption branch permporometry showed that the high quality of the membranes remained after modification. The single component permeance ratio CO2/H2 increased from 0.6 to 1.5 after impregnation. Calculations indicated that the increased CO2/H2 single component permeance ratios were both an effect of increased adsorption of CO2 in the film and reduced pressure drop in the support. The dual component separation factor α CO2/H2 at room temperature increased drastically from 0.7 (H2 selective) to 3.4 (CO2 selective) after impregnation. This work shows for the first time that impregnation procedures can be used to tailor the diffusion properties of zeolite membranes in a similar way as impregnation procedures are used to tailor the catalytic performance of catalysts.
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| 4. |
- Lindmark, Jonas, et al.
(författare)
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Modification of MFI membranes with amine groups for enhanced CO2 selectivity
- 2010
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Ingår i: Journal of Materials Chemistry. - 0959-9428 .- 1364-5501. ; 20:11, s. 2219-2225
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Tidskriftsartikel (refereegranskat)abstract
- Much research on zeolite membranes has been devoted to MFI type zeolite and these membranes can be prepared reproducibly with high quality by our group. However, the MFI pores are too large for separation of small molecules such as CO2, H-2 CH4, and H2O by molecular sieving and the CO2 affinity is not sufficiently strong in our current membranes with quite high Si/Al ratio to achieve CO2 selective membranes. In the present work, existing MFI membranes with high Si/Al ratio are modified with methylamine to increase the CO2 affinity and thus increase the CO2 selectivity. To the best of our knowledge, this is the first time this type of modification is reported for zeolite membranes. These membranes were then evaluated for separation of CO2 from various mixtures of CO2, H-2, CH4 and H2O. The modification had significant effects on both permeances and separation factors and the selectivity towards CO2 was increased considerably for all the feed mixtures tested. The highest separation factor was observed for a CO2/CH4/H2O mixture and alpha-CO2/CH4 was 12 at about 40 degrees C. At the same time, the CO2 permeance was as high as 9 x 10(-7) mol m(-2) s(-1) Pa-1. The separation factor for the amine-modified silicalite-1 membranes was comparable to the highest reported separation factors for MFI membranes, while the CO2 permeance was higher than reported for other selective MFI membranes.
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| 5. |
- Lindmark, Jonas, et al.
(författare)
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Separation of CO2 and H2 with modified MFI membranes
- 2007
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Ingår i: From Zeolites to Porous MOF Materials. - Amsterdam : Elsevier. - 9780444531858 ; , s. 975-980
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Konferensbidrag (refereegranskat)abstract
- MFI membranes with equal film thickness were grown on graded alumina supports and modified by ion exchange or impregnation. Single gas permeances of CO2 and H2 were measured for all membranes. Both impregnation and ion exchange had a significant effect on the permeation properties of the membranes. The single gas CO2/H2 permeance ratios were 0.57, 0.82, 1.7 and 2.2 for silicalite-1, NaZSM-5, BaZSM-5 and silicalite-1 impregnated with Ca(NO3)2 , respectively. Selected membranes were tested for separation of a mixture of 90 kPa CO2 and 90 kPa H2 in the temperature range 25-400 °C. The separation factors at 25 °C were 0.7, 2.0 and 4.1 for silicalite-1, BaZSM-5 and impregnated silicalite-1, respectively and decreased with increasing temperature. The results show that the separation factor can be enhanced significantly by impregnation, lowering of the Si/Al ratio or ion exchange.
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| 6. |
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| 7. |
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| 8. |
- Perdana, Indra, 1973, et al.
(författare)
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Influence of NOx adsorbed species on component permeation through ZSM-5 membranes
- 2010
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 1873-3123 .- 0376-7388. ; 349:1-2, s. 83-89
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Tidskriftsartikel (refereegranskat)abstract
- A thin ZSM-5 film was grown on an alpha-alumina support, resulting in a composite membrane. The membraneswere characterized by SEM and adsorption branch n-hexane/helium permporometry. In addition,the permeation of gas mixtures containing NO2, NO, N2 and argon was evaluated. The effect of temperatureand gas mixture composition on the component permeation and selectivity was investigated.It was found that NOx permeation through the ZSM-5 membrane was partially surface concentrationdependent and was thermally activated. However, transport by gas translational diffusion seemed todominate at the conditions studied. The presence of various NOx adsorbed species appeared to influencediffusion of NO2 in ZSM-5 and reduced transport of other inert and weakly adsorbed components overa wide temperature range (20–400◦C). Strongly adsorbed surface nitrate species formed in the presenceof gas phase NOx should be responsible for the reduced transport of these components at the elevatedtemperature. The findings are of interest for possible applications of ZSM-5 membranes for componentseparation at high temperature.
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| 9. |
- Rezai, Seyed Alireza Sadat, et al.
(författare)
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Water/hydrogen/hexane multicomponent selectivity of thin MFI membranes with different Si/Al ratios
- 2008
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 108:1-3, s. 136-142
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Tidskriftsartikel (refereegranskat)abstract
- MFI films with a thickness of about 550 nm were prepared on α-alumina substrates. The surface Si/Al ratios (XPS) were 157 and 62 for silicalite-1 and ZSM-5 films, respectively, and in accordance, XRD data indicated lower ratios for ZSM-5 films. Higher ratios were observed by ICP-AES for crystals grown in the bulk of the synthesis mixtures. Six membranes of each type were prepared. Porosimetry measurements showed that all membranes were of high and similar quality. Single gas permeances for H2, N2, He, CO2 and SF6 at 25 °C were very similar within each type of membranes. However, the average hydrogen permeance was 27% lower and the average H2/SF6 single gas permeance ratio was 67% higher for ZSM-5 membranes. These differences are attributed to a narrower effective pore diameter for the ZSM-5 membranes due to the sodium counter ions. Separation of mixtures of H2O, H2 and n-hexane (helium balance) was investigated in the temperature range 25-350 °C. The highest separation factors α-H2O/H2 were observed at 25 °C and were 14.3 and 19.7 for silicalite-1 and ZSM-5, respectively. The membranes were selective also at 100 °C and the separation factors were about 3.2 and 6 for silicalite-1 and ZSM-5, respectively. However, the selectivity decreased at elevated temperatures and the separation factor approached 1 at temperatures above 180 °C for both membrane types. The observed water selectivity was attributed to weak adsorption of water on polar sites. A low (1.5-3) α-H2O/n-C6 separation factor was observed for both membrane types for the entire investigated temperature range.
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| 10. |
- Sandström, Linda, et al.
(författare)
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Separation of methanol and ethanol from synthesis gas using MFI membranes
- 2010
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 360:2, s. 265-275
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Tidskriftsartikel (refereegranskat)abstract
- Methanol or ethanol production from synthesis gas is limited by thermodynamic equilibrium and separation of the alcohol product in or near the reactor at reaction conditions (about 250° C and 50 bar) could improve the process. Separation of methanol and ethanol from synthesis gas by MFI membranes with two different Si/Al ratios has therefore been evaluated in the present work. The synthesis gas was represented by hydrogen, carbon dioxide and water, and membrane separation performance was evaluated at atmospheric pressure and varying temperatures.The highest measured methanol/hydrogen separation factor, 32, was observed for the more polar membrane type with the lowest Si/Al ratio, while the highest ethanol/hydrogen separation factor, 46, was observed for the less polar membrane type with the highest Si/Al ratio, both at room temperature. The separation was controlled by adsorption, and consequently, the separation factors were reduced as the temperature increased, since the feed composition was kept constant.The methanol and ethanol permeances were about 10x10-7 mol m-2 s-1 Pa-1 independent of feed composition, membrane type or temperature, which is more than three times higher than previously reported for gas phase separation using zeolite membranes.A simple mathematical model was successfully fitted to the experimental data. The model suggests that membrane selectivity is temperature dependent, as also observed experimentally, but independent of feed pressure. Experimental data and mathematical modelling thus suggest that the membranes would be alcohol selective at reaction pressure (50 bar) and room temperature, but not at reaction temperature (250°C).
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