| 1. |
- Brinck, J, et al.
(författare)
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Influence of pH on the adsorptive fouling of ultrafiltration membranes by fatty acid
- 2000
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Ingår i: Journal of Membrane Science. - 0376-7388 .- 1873-3123. ; 164:1-2, s. 187-194
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Tidskriftsartikel (refereegranskat)abstract
- Fatty acids are found in many solutions treated in ultrafiltration plants, for example, in dairy products, fermentation broth, oily waste water and bleach plant effluents from pulp mills. The influence of fatty acids on the fouling of membranes is often ignored because their concentration is rather low. However, during recent years the significant influence of fatty acids on the flux reduction of ultrafiltration membranes has attracted much attention. The pore radius of the membrane, the concentration of fatty acids and the pH of the solution all have a profound influence on the flux reduction when treating solutions containing fatty acids. In the work presented in this paper, the influence of pH on the flux reduction of an ultrafiltration membrane made of polyethersulphone was studied. It was found that there was no flux reduction under alkaline conditions, whereas the flux reduction under acidic conditions was severe. In order to elucidate the adsorption process, the adsorption of octanoic acid on a planar, hydrophobized silica surface was studied by means of in situ null ellipsometry. In the ellipsometry study a sharp increase in the amount adsorbed was observed when the concentration of undissociated acid approached the saturation concentration as the pH was decreased. This explains the observed flux reduction under acidic conditions. (C) 2000 Elsevier Science B.V. All rights reserved.
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| 2. |
- Amandusson, H., et al.
(författare)
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Hydrogen permeation through surface modified Pd and PdAg membranes
- 2001
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Ingår i: Journal of Membrane Science. - 0376-7388 .- 1873-3123. ; 193:1, s. 35-47
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogen permeation through surface modified Pd and Pd70Ag30 membranes has been studied at temperatures between 100 and 350°C. Silver has been evaporated on Pd and Pd70Ag30 foils with a thickness of 25µm in order to study the role of the surface composition in comparison with the membrane bulk composition. The Pd70Ag30-based membranes display the largest permeation rates at temperatures below 200°C, while Pd membranes with 20Å silver evaporated on the upstream side show the largest permeation rates above 200°C. There are, consequently, different rate limiting processes above and below 200°C: at temperatures below 200°C, the bulk diffusion through the membrane is rate limiting, while at temperatures above 200°C, the influence of the surface composition starts to become significant. It has further been concluded that a sharp silver concentration gradient from the surface to the bulk is important for the hydrogen permeation rate at temperatures above 200°C. Adding oxygen to the hydrogen supply will almost totally inhibit the hydrogen permeation rate when a pure Pd membrane surface is facing the upstream side, while for silver-containing surfaces the presence of oxygen has almost no effect. On a clean Pd surface, oxygen effectively consumes adsorbed hydrogen in a water forming reaction. With Ag on the surface, no water formation is detected. Co-supplied CO inhibits the permeation of hydrogen in a similar manner on all studied membrane surfaces, independent of surface silver content. © 2001 Elsevier Science B.V. All rights reserved.
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| 3. |
- 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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| 4. |
- Mathew, Aji P., et al.
(författare)
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Transport of aromatic solvents through natural rubber/polystyrene (NR/PS) interpenetrating polymer network membranes
- 2002
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Ingår i: Journal of Membrane Science. - 0376-7388 .- 1873-3123. ; 20:1-2, s. 213-227
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Tidskriftsartikel (refereegranskat)abstract
- A series of interpenetrating polymer network membranes have been synthesised from natural rubber and polystyrene by the sequential polymerisation technique. The transport of aromatic hydrocarbons through semi- and full-interpenetrating polymer network membranes (IPNs) have been studied in detail by tracing the solvent uptake up to equilibrium. The sorption was carried out in a series of aromatic solvents viz. benzene, toluene and xylene. The effect of temperature on swelling is studied by carrying out the experiments in toluene in the temperature range of 30-75 °C. The effects of blend ratio, crosslinker content and nature of initiator on the diffusion of various solvents were analysed. It was found that in all cases, the uptake value increased by about 50% as the PS content decreased from 70-30%. The diffusion, sorption and permeation coefficients were evaluated. As the crosslink density was increased, the uptake decreased by 40%. Kinetic and thermodynamic parameters were evaluated from diffusion experiments. The diffusion profiles were compared with theoretical predictions. The influence of swelling on the mechanical performance of the membranes has been investigated by conducting tensile testing of swollen specimens.
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| 5. |
- Tantekin-Ersolmaz, S.B., et al.
(författare)
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Effect of zeolite particle size on the performance of polymer–zeolite mixed matrix membranes
- 2000
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Ingår i: Journal of Membrane Science. - 0376-7388 .- 1873-3123. ; 175:2, s. 285-288
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Tidskriftsartikel (refereegranskat)abstract
- The effect of zeolite particle size on the performance of silicalite–PDMS mixed matrix membranes is investigated at two different zeolite loadings. The separation properties of the membranes prepared are characterized by permeability measurements for O2, N2 and CO2 gases. The permeabilities of the silicalite–PDMS mixed matrix membranes are determined to increase with increasing particle size. The variations occurring in the permeability values with changes made in the particle size are much more pronounced at the higher zeolite loading. The ideal selectivity values corresponding to the mixed matrix membranes, on the other hand, generally seem to be less affected by the changes made in the particle size. The permeability values corresponding to the mixed matrix membranes exceed those pertaining to the original polymer membrane only at relatively higher zeolite loadings and/or for relatively larger particle sizes. The variations occurring in the permeabilities and selectivities with changes made in the zeolite particle size may be responsible for the different values of these parameters reported in the literature for the same types of zeolite filled polymeric membranes.
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| 6. |
- Jareman, Fredrik, et al.
(författare)
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Modelling of single gas permeation in real MFI membranes
- 2004
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 236:1-2, s. 81-89
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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.
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| 7. |
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| 8. |
- Uheida, Abdusalam, et al.
(författare)
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Transport of palladium(II) through hollow fiber supported liquid membrane facilitated by nonylthiourea
- 2004
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 241:2, s. 289-295
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Tidskriftsartikel (refereegranskat)abstract
- The facilitated transport of Pd(II) from chloride media has been investigated through a hollow-fiber supported liquid membrane using nonylthiourea (NTH) as a carrier. The influence of the chemical conditions on the permeability of Pd(II) is reported. A model is presented that describes the transport mechanism, consisting of diffusion through a feed aqueous diffusion layer, a fast interfacial chemical reaction, and diffusion of carrier and its metal complex through the organic membrane. The diffusion resistances through organic membrane (Delta(org)) and through aqueous layer (Delta(aq)), respectively, have been calculated from the proposed model. The permeability of Pd(II) seems to be governed by the diffusion of Pd(II) species through the hollow fiber supported liquid membrane with PdCl2(NTH)(2) as a predominant carrier and PdCl2(NTH)to a lesser extent, though both have similar diffusion coefficients.
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| 9. |
- Marshall, A D, et al.
(författare)
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Influence of ionic calcium concentration on fouling during the cross-flow microfiltration of b-lactoglobulin solutions.
- 2003
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 217:1-2, s. 131-140
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Tidskriftsartikel (refereegranskat)abstract
- The microfiltration (MF) fouling behaviour of -lactoglobulin solutions containing various levels of ionic calcium was investigated on a constant-flux, computer-controlled, cross-flow rig using zirconium oxide membranes. Fouling behaviour was highly dependent on both permeate flux and calcium concentration. At 200 l/(m2 h) on a 50 nm membrane the presence of 8.0 mmol/dm3 (8.0 mM) ionic calcium in the feed increased fouling resistance dramatically. The presence of 8.0 mmol/dm3 (8.0 mM) ionic calcium had little effect on protein transmission at 50 l/(m2 h) but decreased protein transmission dramatically from about 90% to about 10% at 200 l/(m2 h). Most of the additional fouling observed in the presence of calcium was reversible, i.e. removed by water flushing. In runs commenced without ionic calcium, addition of 8.0 mmol/dm3 (8.0 mM) ionic calcium after 1 h caused a rapid increase in fouling resistance and a rapid decrease in protein transmission. Similarly in runs commenced with 8.0 mmol/dm3 (8.0 mM) ionic calcium, changing to a calcium-free feed after 1 h caused a decrease in fouling resistance and an increase in protein transmission. Presumably calcium was leached from the deposited fouling layer causing it to "dissolve". The two dominant reactions responsible for these effects of permeate flux and ionic calcium on fouling by -lactoglobulin solutions are probably molecular unfolding by shear and calcium crosslinking.
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| 10. |
- Persson, Anna, et al.
(författare)
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Transmission of BSA during Cross-flow Microfiltration: Influence of pH and Salt Concentration
- 2003
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 223:1-2, s. 11-21
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Tidskriftsartikel (refereegranskat)abstract
- In many downstream processes microfiltration (MF) is used as the first step to separate the micro-organisms from the product-containing broth. The transmission of proteins through these MF membranes is of great importance, especially when a protein is the desired product. Usually, the largest fraction of the proteins retained in the membrane during the separation of micro-organisms is retained in the filter cake of micro-organisms that is built up on the membrane surface. However, this is not always the case. In some cases the transmission of proteins can decrease below 100% even though there are no micro-organisms present in the broth. In the present study the transmission of BSA through two different MF membranes (a nylon membrane, Pall Filtron Ultipore, Nylon66, 0.2 m, and a membrane made of polyether sulphone, Pall Filtron, Omega, 0.16 m) was investigated. The transmission of BSA was highest for the membrane that was said to be a low protein binding membrane (Omega) and it was affected by the pH in the solution. At pH 5, which is close to the IEP of the protein, the transmission was 100%, while at pH 3 and 7 the transmission was much lower (sometimes as low as 40%). However, when the ionic strength in the solution was increased the transmission of BSA through both MF membranes increased dramatically (at pH 3 and 7). This shows that the electrostatic interactions between the protein and the filter cake (made up of protein aggregates) and between the protein and the membrane affect the transmission. The increase in transmission when the protein is close to its IEP (at pH 5), is believed to be due to the lack of electrostatic repulsion between the proteins in the solution and filter cake of protein aggregates formed on the membrane. At high ionic strength the charged protein molecules are shielded from each other and from the membrane and the filter cake, by the ions in the solution. Due to this shielding effect the protein molecules act as if they were uncharged and the transmission of BSA is thus increased.
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