Overview
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ABSTRACT
Filtration membranes are semi-permeable or permselective membranes which allow for the retention of solutes or particles present in a solvent. The membranes are usually composed of a selective layer ensuring the separation associated to a support reinforcing the mechanical resistance. Their performances, which correspond to those of the selective layer are characterized by their permeability to the solvent and by their selectivity.
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Read the articleAUTHORS
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Jean-Christophe REMIGY: Senior Lecturer - ENSIC engineer - Chemical Engineering Laboratory (CNRS-UMR 5503) - Paul-Sabatier University (Toulouse III)
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Sandrine DESCLAUX: Design engineer - Chemical Engineering Laboratory (CNRS – UMR 5503) - Université Paul-Sabatier (Toulouse III) for documentation (Doc. J 2 791v2)
INTRODUCTION
Filtration membranes (reverse osmosis RO, nanofiltration NF, ultrafiltration UF, microfiltration MF) are semi-permeable (permselective) membranes that retain solutes or particles in a solvent. Membranes are usually composed of a selective layer ensuring separation, combined with a support reinforcing mechanical resistance. Their performance, which corresponds to that of the selective layer, is characterized by their solvent permeability (cf. ) and their selectivity.
The latter characteristic is linked to membrane pore size, expressed in terms of cut-off (molar mass of the compound retained at 90% (cf. ) (UF, NF), salt retention (NF, OI) or micrometric size (MF). Figure 1 shows schematically the correspondence between membrane filtration operations, pore size and retained compounds.
In practical terms, a membrane must have high permeability combined with high selectivity, and thermal, chemical and mechanical resistance, at a controlled installation and renewal cost in line with the product application in question.
Permeability is related to pore size and density, but also to the thickness of the selective layer, as shown by Poiseuille's law (cf. ). High permeabilities are therefore achieved, for a given pore size or selectivity, by producing an extremely thin selective layer. Figure 1 gives an indication of the thicknesses of selective membrane layers as a function of process.
Thermal and chemical...
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Membrane filtration (RO, NF, UF)
Membranes
Economic data
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Prices for organic reverse osmosis membranes
At the end of 2003, reverse osmosis membranes sold for between US$12 and US$26/m 2 , i.e. around e10/m 2 for the cheapest membranes, generally based on cellulose derivatives, and e22/m 2 for composites....
Bibliography
Focus articles
Standardization
Association française de normalisation Afnor
- Filtration des liquides. Membranes poreuses. Taux de rétention des membranes d'UF et de nanofiltration. - NF X 45-103 - déc. 1997
- Liquid filtration – Porous membranes – Permeability to reference water. - NF X 45-101 - déc. 1996
- Cartouches filtrantes....
Unit builders, suppliers and membrane manufacturers
(non-exhaustive list)
Manufacturers
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France
Aquasource (Degrémont/Suez) (ultrafiltration, hollow fiber modules, water treatment applications)
CTI (Céramiques Techniques et Industrielles S.A.) (nanofiltration, ultrafiltration, microfiltration; ceramic membranes)
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Organizations
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Learned societies
French Membrane Club (CFM)
European Membrane Society
French Process Engineering Society SFGP
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Technical centers
Institut de la filtration et des techniques séparatives (IFTS), Agen (association of industrialists, users and...
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