| 1. |
- 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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| 2. |
- Jonsson, C, et al.
(författare)
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Influence of the membrane material on the adsorptive fouling of ultra-filtration membranes
- 1995
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 108:1-2, s. 79-87
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Tidskriftsartikel (refereegranskat)abstract
- The hydrophilic/hydrophobic properties of the membrane material have an important influence on the membrane flux reduction when treating solutions containing hydrophobic solutes. Different methods of measuring the hydrophobic properties of membranes have been evaluated; measurement of the contact angle being the most commonly used method. In this investigation the flux reduction of eight membranes of approximately the same cut-off, but of different materials, was determined and related to the contact angle. A low-molecular weight hydrophobic solute (octanoic acid) was used as foulant. The flux of the hydrophilic membrane was only marginally reduced, whereas the flux reduction of hydrophobic membranes was significant. Membranes of polyvinylidene fluoride had the lowest flux reduction of the hydrophobic membranes. Differences between membranes of the same material (polyethersulfone), but from different manufacturers, were observed. No relation was found between the flux reduction and the contact angle of the membrane, the initial pure water flux or the retention of a hydrophilic macromolecule (PEG20). The pure water flux of two of the hydrophobic membranes increased significantly during the experiments, whereas the pure water flux of the other hydrophobic membranes decreased. A membrane of polyaramide, with a contact angle of the same order of magnitude as the other hydrophobic membranes, behaved as a hydrophilic membrane, with no influence on the flux at concentrations below the solubility limit of the hydrophobic solute, but experienced the most severe flux decline of all the membranes included in the investigation at the solubility limit. Two modified membranes were included in the investigation. The flux reduction of these membranes was not significantly lower than for the corresponding unmodified membranes of the same materials.
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| 3. |
- Jönsson, Ann-Sofi, et al.
(författare)
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Influence of the concentration of a low-molecular organic solute on the flux reduction of a polyethersulphone ultrafiltration membrane
- 1997
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 135:1, s. 117-128
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Tidskriftsartikel (refereegranskat)abstract
- Drastic flux reductions are sometimes encountered during ultrafiltration of solutes much smaller than the membrane pores. This usually occurs during ultrafiltration of hydrophobic, low-molecular solutes, such as fatty acids, alcohols and alkanes. The influence of the concentration of a carboxylic acid, octanoic acid, on the flux of a polyethersulphone membrane was studied in this investigation. The concentration was found to have a marked influence on the flux. The flux reduction was moderate at low concentrations, but became severe above a certain, critical concentration. Two fur-reducing mechanisms were evaluated; reduction of the effective pore radius by adsorption of solute molecules on the pore walls, and blocking of pores by capillary condensation. The adsorption of octanoic acid on a hydrophobic solid surface was studied by null ellipsometry.
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| 4. |
- Lindau, J, et al.
(författare)
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Adsorptive fouling of modified and unmodified commercial polymeric ultrafiltration membranes
- 1999
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 160:1, s. 65-76
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Tidskriftsartikel (refereegranskat)abstract
- The fouling tendency, due to adsorption on the pore walls, of two pairs of modified and unmodified ultrafiltration membranes, with similar observed retentions determined by dextran and gel permeation chromatography, was studied. The membranes investigated were made of modified and unmodified polyaramide (PA) and modified and unmodified polyvinylidene fluoride (PVDF). The PVDF membrane was surface-modified and the PA membrane was made from a modified polymer solution. Membrane modification was used to reduce fouling by adsorption. Octanoic acid was used as the fouling substance, representing a large number of small, hydrophobic compounds. It is demonstrated in this investigation that membrane modification is not always successful. It was determined that at lower concentrations of octanoic acid, the modified PA membrane exhibits a smaller fouling tendency than the unmodified PA membrane, while the result is reversed for concentrations above 60% of the saturation concentration. The fouling tendency of the unmodified PVDF membrane is much lower than that of the modified PVDF membrane at all concentrations. The cross-sections of the membranes were visually examined with scanning electron microscopy, but no difference could be observed between the modified and unmodified membranes. The membranes were also examined with Fourier transform infrared spectroscopy. The spectra of the two PA membranes were different, while no difference was observed for the unmodified and surface-modified PVDF membranes. Remains of octanoic acid were found in the membranes, although they had been thoroughly rinsed with deionized water and the initial pure water flux was recovered. (C) 1999 Elsevier Science B.V. All rights reserved.
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| 5. |
- Lindau, J, et al.
(författare)
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Flux reduction of ultrafiltration membranes with different cut-off due to adsorption of a low-molecular-weight hydrophobic solute-correlation between flux decline and pore size
- 1998
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 149:1, s. 11-20
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Tidskriftsartikel (refereegranskat)abstract
- The flux of ultrafiltration membranes may be severely reduced when treating low-molecular-weight hydrophobic solutes even though the cut-off of the membrane is orders of magnitudes greater than the size of the solute molecules. In this investigation, the flux reduction was correlated to the membrane pore size using octanoic acid as a model substance. As a comparison, the pore size was also determined by measuring the retention of a dextran solution and by using the liquid-liquid displacement porometry method (LLDP). The membranes used were four asymmetric polysulphone and polyethersulphone membranes with nominal molecular weight cut-off (NMWCO) between 6 and 50 kDa. It is shown that the use of a low-molecular-weight hydrophobic solute may provide a rapid and simple method of characterising hydrophobic ultrafiltration membranes, both regarding their sensitivity to flux reduction due to adsorption, and their pore-size distribution (C) 1998 Published by Elsevier Science B.V. All rights reserved.
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| 6. |
- Lindau, J, et al.
(författare)
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The influence of a low-molecular hydrophobic solute on the flux of poly-sulphone ultrafiltration membranes with different cut-off
- 1995
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 106:1-2, s. 9-16
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Tidskriftsartikel (refereegranskat)abstract
- In this study the influence of a low-molecular hydrophobic solute on the Bur of a hydrophilic regenerated cellulose membrane and hydrophobic polysulphone membranes with different nominal molecular weight cut-off, NMWCO, was investigated. Octanoic acid was used as a model substance because it is considerably smaller than the NMWCO of all the membranes used in the investigation. Octanoic acid was found to decrease the flux of the polysulphone membranes considerably. The decrease was dependent on the NMCWO, although in all cases the NMWCO is many times larger than the size of the octanoic acid molecules. It is also shown that the Bur of the hydrophilic membrane, with a NMWCO of the same size as one of the denser hydrophobic membranes, is unaffected by the octanoic acid. The cross-sections of both used and unused membranes were examined in a scanning electron microscope (SEM). No visual difference was observed between the used and unused membrane samples. Analysis of the membranes with Fourier transform infrared spectroscopy (FTIR) showed that octanoic acid remained in the membranes even after thorough cleaning.
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| 7. |
- Lipnizki, Frank, et al.
(författare)
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Pervaporation-based hybrid process : A review of process design, applications and economics
- 1999
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 153:2, s. 183-210
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Forskningsöversikt (refereegranskat)abstract
- Pervaporation is one of the developing membrane technologies that can be used for various industrial applications but for a predefined task, the optimal process design is unlikely to consist solely of pervaporation. Often the optimised solution becomes a hybrid process combining pervaporation with one or more other separation technologies. A distinction will be made between hybrid and integrated processes. Hybrid processes are important and consequently need to be considered in process design. This paper focuses on pervaporation-based hybrid processes that have been realised on an industrial scale. Both present and future prospects of applying these process combinations will be reviewed. The emphasis of this paper is, therefore, on pervaporation combined with distillation and with chemical reactors. The economic potential of these hybrid processes is evaluated, for various applications, by cost comparisons between the pervaporation-based hybrid processes and alternative separation processes. Pervaporation-based processes for waste water treatment and biotechnology applications involve other types of pervaporation based hybrid processes and have been excluded from this review. Copyright (C) 1999 Elsevier Science B.V.
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