| 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. |
- Jönsson, Ann-Sofi, et al.
(författare)
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A concentration polarization model for the ultrafiltration of nonionic surfactants
- 2006
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 304:1, s. 191-199
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical model has been developed that describes ultrafiltration of nonionic surfactants. The model takes into account the fact that surfactants start to aggregate and form micelles at the critical micelle concentration, The model can be used to predict the performance of the membrane if the transport properties inside and at the membrane surface as well as the surfactant association behavior, are known. Three hydrophilic ultrafiltration membranes, made of regenerated cellulose, were used in the investigation. The cut-offs of the membranes were 10,000, 20,000, and 30,000 Da. The surfactant used in the investigation was the nonionic surfactant Triton X-100. The influence of the concentration of surfactant, transmembrane pressure and pure water flux were studied theoretically and experimentally. From the results presented in this work it can be concluded that the calculated values are in good agreement with experimental data. (c) 2006 Elsevier Inc. All rights reserved.
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| 3. |
- Jönsson, Ann-Sofi, et al.
(författare)
-
Colloidal fouling during ultrafiltration
- 1996
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Ingår i: Separation Science and Technology. - : Informa UK Limited. - 0149-6395 .- 1520-5754. ; 31:19, s. 2611-2620
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal fouling causes serious problems in many membrane plants. Two different kinds of flux-reducing phenomena occur when treating colloidal dispersions, When treating stable dispersions the flux is reversible and can be restored after changing the operating parameters, such as the transmembrane pressure or the crossflow velocity. The flux reduction experienced when treating unstable colloidal dispersions is irreversible. In this study the DLVO theory, well-known from colloid chemistry, has been used to illustrate the mechanisms underlying the difference in filtration characteristics between stable and unstable colloidal dispersions.
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| 4. |
- Jönsson, Ann-Sofi, et al.
(författare)
-
Fluid flow in compressible porous media: I: Steady-state conditions
- 1992
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Ingår i: AIChE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 38:9, s. 1340-1348
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Tidskriftsartikel (refereegranskat)abstract
- This is the first of two articles dealing with fluid flow in compressible porous media. In this article a model describing fluid flow and pressure-induced variations in porosity under stationary conditions is developed. In a forthcoming article the dynamic behavior during filtration and wet pressing of compressible porous media are presented. Fluid flow through rigid porous media is generally described by Darcy's law. The corresponding expression for compressible materials is derived in this article. This expression, the steady-state flow (SSF) equation, allows the steady-state flow to be easily calculated, either numerically, or by using the approximative analytical solutions that are also presented here. In the SSF equation optional empirical and/or theoretical permeability and compressibility relationships may be combined. Further, a new compressibility model which also applies for viscoelastic materials is presented. The influence of the compressibility of the material and the influence of precompression is illustrated.
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| 5. |
- Jönsson, Ann-Sofi, et al.
(författare)
-
Fluid flow in compressible porous media: II: Dynamic behavior
- 1992
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Ingår i: AIChE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 38:9, s. 1349-1356
-
Tidskriftsartikel (refereegranskat)abstract
- This article deals with the dynamic behavior during filtration and wet pressing of compressible porous media. An equation is developed which permits the derivation of the time dependency of porosity and flow at varying locations in a medium subjected to hydraulic pressure and/or mechanical load. Furthermore, a numerical solution that allows the equation to be solved rapidly and with high accuracy on a common PC is presented. The computer program developed in conjunction with this work has been used to illustrate the dynamics of fluid flow in some industrially important applications, such as wet pressing of paper pulp and flow in chromatography columns. The program has also been used to calculate the flow and concentration variations during mechanical impulse loading (that is, a press pulse).
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| 6. |
- 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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| 7. |
- Jönsson, Ann-Sofi, et al.
(författare)
-
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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| 8. |
- Jönsson, Ann-Sofi, et al.
(författare)
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Ultrafiltration of colloidal dispersions - A theoretical model of the concentration polarization phenomena
- 1996
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 180:2, s. 504-518
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Tidskriftsartikel (refereegranskat)abstract
- A general thermodynamic model of the concentration polarization phenomena of colloidal particles at a membrane surface is presented. The model is based on the balance between a thermodynamic force, due to the osmotic pressure gradient, and a frictional force, due to the fluid flow around each particle. A cell model description is used to model the concentration dependence of the thermodynamic force as well as the how properties in the concentrated colloidal solution. Equilibrium thermodynamics of the colloidal system can be used in the cell calculations since local equilibrium is assumed in the neighborhood of each colloidal particle (i.e., in each cell). This means that the concentration dependence of the osmotic pressure can be obtained, either from an experimental determination or from a theoretical model of the bulk properties of the colloidal system. To exemplify the usefulness of the model when establishing the influence of different operating parameters, such as the transmembrane pressure, the fluid shear, or different solution properties, such as concentration, particle size, pH, and ionic strength, a model system of charged spherical colloidal particles is used. The interaction between the particles is in the presented examples assumed to be a combination of electrostatic interactions, calculated from the Poisson-Boltzmann equation, dispersion forces, calculated as additive 1/r(6) interactions, and a hard sphere interaction calculated from the Carnahan-Starling equation. (C) 1996 Academic Press, Inc.
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| 9. |
-
34th EMS Summer School : Membranes in Biorefineries
- 2017
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Proceedings (redaktörskap) (refereegranskat)abstract
- The EMS Summer School “Membranes in Biorefineries” is related to Annex XVII of the Industrial Energy Related Technologies and Systems (IETS)Implementing Agreement: “Membrane Filtration for Energy-efficient Separation of Lignocellulosic Biomass Components” co-ordinated by the Department of Chemical Engineering at Lund University, Sweden.The IETS Implementing Agreement is an initiative within IEA (International Energy Agency). The mission of IETS is to foster international co-operation among OECD and non-OECD countries for accelerated research and technology development of industrial energy-related technologies and systems. In doing so, IETS seeks to enhance knowledge of cost-effective new industrial technologies and system layouts that enable increase productivity and better product quality while improving energy efficiency and sustainability.
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| 10. |
- Andersson, Alexandra, et al.
(författare)
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Comparison of diafiltration and size-exclusion chromatography to recover hemicelluloses from process water from thermomechanical pulping of spruce
- 2007
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Ingår i: Applied Biochemistry and Biotechnology. - : Springer Science and Business Media LLC. - 1559-0291 .- 0273-2289. ; 137:1-12, s. 971-983
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Tidskriftsartikel (refereegranskat)abstract
- Hemicelluloses constitute one of the most abundant renewable resources on earth. To increase their utilization, the isolation of hemicelluloses from industrial biomass side-streams would be beneficial. A method was investigated to isolate hemicelluloses from process water from a thermomechanical pulp mill. The method consists of three steps: removal of solids by microfiltration, preconcentration of the hemicelluloses by ultrafiltration, and purification by either size-exclusion chromatography (SEC) or diafiltration. The purpose of the final purification step is to separate hemicelluloses from small oligosaccharides, monosaccharides, and salts. The ratio between galactose, glucose, and mannose in oligo- and polysaccharides after preconcentration was 0.8: 1: 2.8, which is similar to that found in galactoglucomannan. Continuous diafiltration was performed using a composite fluoro polymer membrane with cutoff of 1000 Da. After diafiltration with four diavolumes the purity of the hemicelluloses was 77% (gram oligo- and polysaccharides/gram total dissolved solids) and the recovery was 87%. Purification by SEC was performed with 5, 20, and 40% sample loadings, respectively and a flow rate of 12 or 25 mL/min (9 or 19 cm/h). The purity of hemicelluloses after SEC was approx 82%, and the recovery was above 99%. The optimal sample load and flow rate were 20% and 25 mL/min, respectively. The process water from thermomechanical pulping of spruce is inexpensive. Thus, the recovery of hemicelluloses is not of main importance. If the purity of 77%, obtained with diafiltration, is sufficient for the utilization of the hemicelluloses, diafiltration probably offers a less expensive alternative in this application.
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