| 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. |
- Gekas, Vassilis, et al.
(författare)
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Contact angles of ultrafiltration membranes and their possible correlation to membrane performance
- 1992
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 72:3, s. 293-302
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Tidskriftsartikel (refereegranskat)abstract
- The captive bubble method was used to describe the wetting characteristics of a number of commercial ultrafiltration (UF) membranes. The membranes belonged to one of two homologous (same material, different cut-off) series made by the same manufacturer. One series was made of polysulphone and the other one of cellulose triacetate. The porosimetric characteristics of the membranes have also been measured. The combined data were used to explain the fouling behaviour of the membranes upon ultrafiltration of solutions containing dextran, whey protein concentrate and silicate sols. The cellulose triacetate series is characterized by lower receding contact angle and smaller contact angle hysteresis and shows better flux behaviour (permeate flux during UF and pure water flux recovery at the end of UF) than the polysulphone series. Within the same series the mean permeability pore size shows a better correlation with membrane flux behaviour than with contact angle hysteresis.
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| 3. |
- 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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| 4. |
- Jönsson, Ann-Sofi
(författare)
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Influence of shear rate on the flux during ultrafiltration of colloidal substances
- 1993
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 79:1, s. 93-99
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Tidskriftsartikel (refereegranskat)abstract
- The shear rate at the surface of a membrane has a distinct influence on the membrane flux in systems containing colloidal substances. If the shear rate is decreased, flux decreases since the thickness of the boundary layer of retained solutes at the membrane surface then increases. When low molecular solutes are used, flux increases again when the shear rate is increased. However, if large solutes are used, polymeric and colloidal substances, for example, it sometimes happens that the flux cannot be increased to its original value again by increasing the shear rate: the flux decline is regarded as irreversible. Experiments, performed in a new type of turbulence-promoting module, which illustrate the influence of shear rate on flux when treating solutions containing colloidal substances, are presented in this paper. It is also shown that a flux decrease which can not be restored by increasing the shear rate, may be completely restored by a temporary interruption of the permeate flow.
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| 5. |
- 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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| 6. |
- Jönsson, Ann-Sofi, et al.
(författare)
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The influence of nonionic surfactants on hydrophobic and hydrophilic ultrafiltration membranes
- 1991
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 56:1, s. 49-76
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Tidskriftsartikel (refereegranskat)abstract
- The influence of different types of surfactants on ultrafiltration membranes has been investigated. A basic approach to membrane-surfactant interactions is also presented. A nonionic (Triton X-100), two anionic (potassium oleate and sodium dodecylbenzenesulphonate) and a cationic (hexadecyltrimethylammonium bromide) surfactant were investigated. The effects on commercial membranes of polysulphone, poly(vinylidene fluoride) and cellulose acetate were studied. The flux reductions of the hydrophobic membranes were found to be much more pronounced than the flux variations of the hydrophilic membranes. Both the material and the molecular weight cut-off were found to influence the performance of the hydrophobic membranes. A drastic influence of hydrophobic impurities was demonstrated. The retention of the nonionic surfactant was low at concentrations below the critical micelle concentration. The retention of the ionic surfactants was quite high, even at low concentrations.
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| 7. |
- 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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| 8. |
- Lindau, J, et al.
(författare)
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Cleaning of ultrafiltration membranes after treatment of oily waste water
- 1994
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 87:1-2, s. 71-78
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Tidskriftsartikel (refereegranskat)abstract
- The influences of different types of cleaning agents on a polysulphone ultrafiltration (UF) membrane which had been used to treat oily waste water were investigated. The cleaning experiments were performed with samples of polysulphone membranes removed from a commercial plant in which oily waste water is treated. Five different cleaning agents were used and their influences on the fluxes were investigated. The influence on the flux when cleaning with the different cleaning agents in succession was also studied. Deposits on the membrane surface, before and after cleaning, were analysed using different methods. Most of the analyses were carried out using scanning electron microscopy (SEM) in combination with energy dispersive X-ray (EDX) combined with a micro-analysis system permitting quantitative determination of elements. Some analyses were also performed using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS).
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| 9. |
- 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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| 10. |
- 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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