| 1. |
- Grahn, Mattias, et al.
(författare)
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Maxwell-Stefan modelling of High flux tubular silicalite-1 membranes for CO2 removal from CO2/H2 gas mixtures
- 2014
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 471, s. 328-337
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a Maxwell-Stefan model for high flux tubular silicalite-1 membranes for separation of CO2 from a CO2/H2 mixture was developed. The model concerns tubular membranes operating in a counter flow module and includes transport through flow-through defects in the silicalite-1 film and pressure drop over the graded alumina support. Adsorption and diffusion parameters for perfect silicalite-1 crystals were taken from literature. The flux and selectivity predicted by the model were in reasonably good agreement with experimentally observed data for a ZSM-5 membrane without any fitting of the model. However, the CO2 flux and selectivity measured experimentally for the ZSM-5 membrane were higher than that predicted by the model for a silicalite-1 membrane.The model was used to investigate a case with a 20 000 Nm3/d feed comprised of a 50/50 mixture of CO2/H2 at pressure of 25 bar and a membrane temperature of 296 K. The permeate pressure was 1 bar and 90% of the CO2 permeated the membrane. In this case, the membrane permselectivity and CO2 flux varied along the length of the tubes between 20–26 and 950–396 kg/(m2 h), respectively. Further, both defects and pressure drop over the support were shown to have an adverse effect on the selectivity, which indicates that membrane selectivity can be improved by reducing the flow-through defects and/or by preparing supports with less flow resistance. For a one-stage process, the required membrane area is as small as ca 0.85 m2 and the hydrogen loss through the membrane was 12.4%. For a two-stage process the required membrane area almost doubled to 1.6 m2, however the hydrogen loss through the second membrane is reduced to as little as 2.5%. In summary, this work shows that high flux zeolite membranes may be an interesting option for CO2 removal from synthesis gas.
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| 2. |
- Hedlund, Jonas, et al.
(författare)
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Mass transport in porous media from first principles : an experimental and theoretical study
- 2012
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 415-416, s. 271-277
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, the mass transport of helium through zeolite is experimentally determined by measuring the flow of helium through a zeolite membrane. By using a mathematical model, the mass transport through defects was accounted for to arrive at mass transport through zeolite pores. For the first time, we could thereby experimentally show that the mass transport of helium in zeolite pores is strongly controlled by the amount and location of hydrocarbons in the zeolite pores and varies several orders of magnitude. The mass transport of helium in ZSM-5 zeolite pores is first reduced gradually more than one order of magnitude when the loading of n-hexane is increased from 0 to 47% of saturation. As the loading of n-hexane is further increased to 54% of saturation, the mass transport of helium in the zeolite pores is further reduced abruptly by more than two orders of magnitude. This gradual decrease followed by an abrupt decrease of mass transport is caused by adsorption of n-hexane in the zeolite pores. In a similar yet different fashion, the mass transport of helium in the zeolite pores is reduced abruptly by almost two orders of magnitude when the loading of benzene is increased from 0 to 19% of saturation due to adsorption of benzene in the pore intersections. Effective medium approximation percolation models with parameters estimated using density functional theory employing the local density approximation, i.e. models with no adjustable parameters and the most sophisticated theory yet applied to this system, can adequately describe the experimental observations.
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| 3. |
- Henderson, R.K., et al.
(författare)
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Evaluation of effluent organic matter fouling in ultrafiltration treatment using advanced organic characterisation techniques
- 2011
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 1873-3123 .- 0376-7388. ; 382:1-2, s. 50-59
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Tidskriftsartikel (refereegranskat)abstract
- Membrane fouling remains an operational challenge in the ultrafiltration (UF) membrane treatment of wastewater effluent and research is on-going to improve understanding of the organic character of foulants. Two advanced organic characterisation techniques that have potential to lend insight into membrane fouling are size exclusion chromatography with organic carbon, UV254 and nitrogen detection (LC-OCD) and fluorescence excitation-emission matrix (EEM) spectroscopy. In this study, UF treatment was undertaken for five tertiary wastewater effluents. The total hydraulic resistance was determined as well as that contributed by foulant layers fractionated by rinsing, backwashing and chemically desorbing. Organic characterisation for UF feed samples, permeates and each foulant layer was then performed using LC-OCD and FEEM spectroscopy with the aim of improving understanding of the character of foulants present in effluent organic matter (EfOM) and to determine the potential for the use of FEEM spectroscopy as a foulant indicator in such systems. It was determined that the biopolymer fraction was most significantly reduced on UF treatment, as anticipated due to its high molecular size. This was supported by the observation that the majority of the foulant layer comprised predominantly protein-enriched biopolymers (38-60% of total foulant layer DOC) that could be removed by rinsing. The resistance attributed to rinsing was directly related to the combined DOC concentration associated with proteins and low molecular weight neutral compounds as defined by LC-OCD analysis. Furthermore, tyrosine-like fluorescence intensity (λex/em=250/304nm) of both the rinsing solutions and UF feed samples showed good correlation with associated hydraulic resistance for EfOM originating from domestic wastewater, suggesting that fluorescence has potential to be used as a foulant indicator for these systems. © 2011 Elsevier B.V.
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| 4. |
- Kangas, Jani, et al.
(författare)
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Maxwell-Stefan modeling of the separation of H2 and CO2 at high pressure in an MFI membrane
- 2013
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 435, s. 186-206
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, a Maxwell-Stefan based model was developed for the separation of CO2 from H2 at high pressure in an MFI membrane. The usage of the Vignes interpolation formula for mixture surface diffusivities together with the IAST (ideal adsorbed solution theory) using bulk gas phase fugacities for mixture adsorption proved to be a feasible combination for this case. Both the effects of defects in the zeolite film and the mass transfer resistance caused by the support layers were studied and included in the model. Only pure component experimental data was used in the model building to predict the gas mixture permeation. The fitted diffusion parameters were in line with the literature values. The occupancy fraction dependence of CO2 surface diffusivity was utilized for the first time in the prediction of binary separation of H2/CO2 at high pressure on a real MFI membrane. Usage of an occupancy fraction dependence for CO2 surface diffusivity improved the model predictions. The adsorption parameter fitting for hydrogen based on the permeation measurements resulted in a feasible adsorption model, but should be used with caution. The model predicts binary separation measurement results relatively well. Both defects and support have a noticeable impact on the overall performance of the membrane.
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| 5. |
- Korelskiy, Danil, et al.
(författare)
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Characterization of flow-through micropores in MFI membranes by permporometry
- 2012
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 417-418, s. 183-192
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Tidskriftsartikel (refereegranskat)abstract
- Permporometry was used for the first time to characterize flow-through micropore defects down to 0.7 nm in size in MFI zeolite membranes. Helium was used as the non-adsorbing gas and n-hexane or benzene was used as the adsorbate. The helium flow through zeolite pores was estimated using percolation theory and the remaining flow was assigned to flow-through defects. The area distribution of flow-through defects was estimated from the data using a simple model and similar results were obtained using both adsorbates. The total area of defects determined using n-hexane as the adsorbate was as low as about 0.7% of the membrane area and defects with a width below 1 nm constituted 97% of the total defect area for the best membrane. The permporometry results were supported by n-hexane/1,3,5-trimethylbenzene separation experiments. The permporometry data were also consistent with HR-SEM observations indicating the presence of narrow open grain boundaries, and absence of large cracks and pinholes
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| 6. |
- Korelskiy, Danil, et al.
(författare)
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High flux MFI membranes for pervaporation
- 2013
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 427, s. 381-389
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Tidskriftsartikel (refereegranskat)abstract
- MFI membranes with a thickness of 0.5 μm prepared on a graded α-alumina support were evaluated for separation of feed mixtures of 3 wt.% n-butanol/water and 10 wt.% ethanol/water by pervaporation. The membranes were selective to n-butanol and ethanol. The flux observed in the present work was about 100 times higher than that previously reported for n-butanol/water separation by pervaporation and about 5 times higher than that for ethanol/water separation by pervaporation. At 60 °C, the observed n-butanol/water flux was about 4 kg m−2 h−1 and the n-butanol/water separation factor was about 10 for the best membrane. At the same temperature, the membrane displayed an ethanol/water flux of ca. 9 kg m−2 h−1 and an ethanol/water separation factor of ca. 5. A mathematical model indicated significant mass transfer resistance in the support, which reduced the flux and the selectivity of the membranes.
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| 7. |
- 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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| 8. |
- 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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| 9. |
- Lv, Yuexia, et al.
(författare)
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Wetting of polypropylene hollow fiber membrane contactors
- 2010
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 362:1-2, s. 444-452
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Tidskriftsartikel (refereegranskat)abstract
- Membrane wetting by absorbents leads to an Increase in mass transfer resistance and a deterioration in CO2 absorption performance during the membrane gas absorption process In order to better understand the wetting mechanism of membrane pores during their prolonged contact with adsorbents, polypropylene (PP) hollow fibers were Immersed in three different absorbents for up to 90 days Monoethanolamine, methyldiethanolamine, and deionized water were applied as absorbent solutions The characterization results of membrane samples confirm that the absorbent molecules diffuse into PP polymers during the exposure process, resulting in the swelling of the membranes The absorption-swelling wetting mechanism is proposed to explain observations made during the wetting process The strong reduction of contact angles indicates that the membrane surface hydrophobicity decreases remarkably during immersion due to membrane-absorbent interaction Membrane surface morphologies and surface roughness suffer from significant and complicated changes after immersing the membrane fibers in the absorbents. Immersion in an absorbent with a high surface tension results in small changes in membrane surface morphology. As indicated by the experimental results, improving membrane surface hydrophobicity may be an effective way of overcoming wetting problems.
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| 10. |
- 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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