| 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. |
- Hedlund, Jonas, et al.
(författare)
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ZSM-5 membranes synthesized without organic templates using a seeding technique
- 1999
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Ingår i: Journal of Membrane Science. - 0376-7388 .- 1873-3123. ; 159:1-2, s. 263-273
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Tidskriftsartikel (refereegranskat)abstract
- Porous α-alumina supports were seeded with colloidal TPA-silicalite-1 crystals and calcined. The supports were treated in a synthesis solution to grow the seed crystals into ZSM-5 films. The synthesis solution was free from organic template molecules in order to avoid the calcination step which often introduces cracks in the synthesized zeolite film. An SEM investigation indicated that the zeolite films on the supports were defect free and that the film thickness was approximately 1.5 μm. XRD data showed that the film consisted of well-crystallized ZSM-5. The permeance in single gas experiments decreased in the order H2O, H2, CO2, O2, N2 and CH4. The difference in permeance between each molecular species in the series was almost one order of magnitude which indicated that the membranes were of a high quality. Molecules larger than CH4 permeated with similar and low rates, independent of their kinetic diameters, indicating a non-selective permeation path through defects in the zeolite films. However, the permeance of these larger molecules was less than 1/10 000 of that for H2O. The highest measured separation factors for binary mixtures of N2/SF6 and H2/i-C4 were 110 and 99.
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| 5. |
- 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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| 6. |
- 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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| 7. |
- Aguilar-Sanchez, Andrea, et al.
(författare)
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Waterborne nanocellulose coatings for improving the antifouling and antibacterial properties of polyethersulfone membranes
- 2021
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 620
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Tidskriftsartikel (refereegranskat)abstract
- This article presents a waterborne nanocellulose coating process to change the surface characteristics and mitigate fouling of commercially available polyethersulfone (PES) microfiltration membranes. An extensive comparative study between nanoporous and nano-textured layers composed of cellulose nanocrystals (CNC) or TEMPO-oxidized cellulose nanofibrils (T-CNF), which were coated on the PES membrane by taking advantage of the electrostatic interactions between the PES substrate, a polyallylamine hydrochloride (PAHC1) anchoring layer, and the nanocellulose functional layer. Coated PES membranes exhibited decreased surface roughness and pore sizes as well as rejection of compounds with a M-w above 150 kDa, while the water permeability and mechanical properties of remained largely unaffected. The coatings improved the wettability as confirmed by a reduction of the contact angle by up to 52% and exhibited a higher negative surface charge compared to the uncoated membranes over a pH range of 4-8. A significant reduction in organic fouling was observed for the coated membranes demonstrated by bovine serum albumin (BSA) adsorption studies on T-CNF and CNC surfaces using Quartz Crystal Microbalance with Dissipation monitoring (QCM-D), UV-vis spectroscopy and FTIR mapping after exposing the membranes to dynamic adsorption of BSA. The T-CNF coating exhibited effective antibacterial action against Escherichia coli (E. coli) attributed to the pH reduction effect induced by the carboxyl groups; while CNC coatings did not show this property. This work demonstrates a simple, green, and easy-to-scale layer-by-layer coating process to tune the membrane rejection and to improve antifouling and antibacterial properties of commercially available membranes.
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| 8. |
- Akhtar, Farid, et al.
(författare)
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Preparation of graded silicalite-1 substrates for all-zeolite membranes with excellent CO2/H-2 separation performance
- 2015
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 493, s. 206-211
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Tidskriftsartikel (refereegranskat)abstract
- Graded silicalite-1 substrates with a high gas permeability and low surface roughness have been produced by pulsed current processing of a thin coating of a submicron silicalite-1 powder onto a powder body of coarser silicalite-1 crystals. Thin zeolite films have been hydrothermally grown onto the graded silicalite-1 support and the all-zeolite membranes display an excellent CO2/H-2 separation factor of 12 at 0 degrees C and a CO2 permeance of 21.3 x 10(-7) mol m(-2) s(-1) Pa-1 for an equimolar CO2/H-2 feed at 505 kPa and 101 kPa helium sweep gas. Thermal cracking estimates based on calculated surface energies and measured thermal expansion coefficients suggest that all-zeolite membranes with a minimal thermal expansion mismatch between the graded substrate and the zeolite film should remain crack-free during thermal cycling and the critical calcination step.
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| 9. |
- Andersson, Charlotte, et al.
(författare)
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Effects of exposure to water and ethanol on silicalite-1 membranes
- 2008
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 313:1-2, s. 120-126
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Tidskriftsartikel (refereegranskat)abstract
- The effects of long exposures to ethanol, water and 0.1 M aqueous solutions of ammonia, sodium hydroxide, tetrapropylammonium hydroxide (TPAOH) and hydrochloric acid on thin TPA-silicalite-1 membranes were studied. Single gas permeation experiments, porosimetry and scanning electron microscopy were used to characterize the membranes. It was found that a short exposure (24 h) will only dissolve synthesis residues and will not affect membrane quality negatively. The only medium that had an effect after 24 h was sodium hydroxide, which almost dissolved the film completely. After exposing TPA-silicalite-1 membranes for 30 days in the various liquids, the membrane quality decreased in the order ethanol < 0.1 M hydrochloric acid < 0.1 M TPAOH < water < 0.1 M ammonia < 0.1 M sodium hydroxide due to dissolution of the silicalite-1 crystals. This study has shown that prolonged exposure to aqueous solutions will lead to dissolution of silicalite-1 crystals causing an increase in micro- and mesopores in the film. The amount and size of the pores will depend on the pH of the aqueous medium. Higher pH gives a higher dissolution and hence more non-zeolitic pores in the silicalite-1 film. Ethanol has no effect on the dissolution of the zeolite film even after 30 days. This finding has an effect in membrane preparation and in several membrane applications such as pervaporation and separation of hydrocarbons isomer mixtures.
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| 10. |
- Arandia, Kenneth Gacutno, 1990, et al.
(författare)
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Fouling characteristics of microcrystalline cellulose during cross-flow microfiltration: Insights from fluid dynamic gauging and molecular dynamics simulations
- 2023
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 1873-3123 .- 0376-7388. ; 669
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Tidskriftsartikel (refereegranskat)abstract
- The fouling behaviour of microcrystalline cellulose (MCC) particles on polyethersulfone (PES) membranes was investigated using fluid dynamic gauging (FDG) and molecular dynamics (MD) simulations. Experimental cross-flow microfiltration (MF) of a dilute MCC suspension at 400 mbar transmembrane pressure using 0.45 μm PES membranes revealed an estimated fouling layer thickness of 616 ± 5 μm for both fouled and re-fouled membranes at an applied shear stress of 37 ± 2 Pa. A decline in pure water flux was observed after each membrane cleaning and flushing procedure, indicating that highly resilient layers were formed close to the membrane surface. A possible explanation for the formation of resilient cellulose layers was obtained through MD simulations of the free energy profiles, which predicted deep energy minima at close interparticle separations of the cellulose–cellulose and cellulose–PES systems. The consequence of this energy minima is that attractive and repulsive forces are in balance at a specific distance between the particles, suggesting high binding energy at close interparticle distances. This implies that a certain force is needed to remove the layer or redisperse the cellulose particles. MD simulations also suggested that contributions made by repulsive hydration forces negatively influenced the adsorption of cellulose particles onto the PES membrane. These results highlight how experimental FDG measurements, when complemented with MD simulations, can provide insights into the fouling behaviour of an organic model material during cross-flow filtration.
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