US20070158257A1 - Membrane filter unit and method for the production of the membrane filter unit - Google Patents

Abstract

The invention relates to a membrane filter unit for liquid or gaseous media, comprising a bundle of capillary membranes which are open on at least one front surface side and which are cast in an area which is close to the end of the open membrane ends, in a sealing layer forming a hardened head part. The open membrane ends protrude on the outer side of the sealing layer. The sealing layer is arranged on a spacer element which has a layer which is penetrated by the capillary membranes and which is non-permeable in relation to the casting material which hardens in order to form the sealing layer. the invention also relates to a method for the production of a membrane filter unit.

Description

• The invention relates to a membrane filter unit for liquid or gaseous media, with a bundle, or a plurality disposed in any desired manner, of capillary membranes open on at least one face, which are cast into a sealing layer that has hardened to form a solid head piece, in a region close to the end, with regard to the open membrane end, whereby the open membrane ends protrude on the outside of the sealing layer.
• The capillary membranes used for membrane filtration can have outside diameters between 200 μm and about 5 mm, depending on the configuration and case of use. In order to assure proper function during membrane filtration, the capillary membranes must be cast into the head piece without defects. Furthermore, it must be assured that the capillary membranes are not glued shut, plugged up, or mechanically damaged at their ends, during production of the head piece, which is produced as a cast part. Mechanical processing by means of cutting should be avoided, since many membrane materials fray during mechanical processing.
• In the case of a method for the production of a membrane filter unit having the characteristics described initially, which is known from U.S. Pat. No. 5,639,373, the end of the membrane bundle is dipped into a liquid layer that solidifies to form a solid carrier. Subsequently, the sealing layer, which consists of plastic mass, is applied to this carrier layer, and the capillary membranes are cast into the plastic mass. After the plastic mass has hardened, the carrier layer is liquefied again and removed, whereby the ends of the capillary membranes are exposed. Problems in terms of production technology occur if the capillary membranes are packed tightly, as the result of capillary forces that act between the capillary membranes. When the membrane bundle is dipped into the liquid, the liquid climbs upward on the outside of the capillary membranes, as determined by the capillary forces that are in effect. During subsequent production of the head piece, penetration of the plastic mass from the outside into the interior of the membrane fiber bundle is prevented, and reliable enclosure of the individual membrane fibers with plastic mass is no longer guaranteed.
• In the case of a method known from U.S. Pat. No. 6,294,039, the membranes to be cast into the head piece are inserted into a layer of fine-particle solids, onto which the plastic mass that hardens to form a head piece is applied. After the head piece has hardened, the solid layer is removed again, whereby the ends of the capillary membranes are exposed. The method is disadvantageous in terms of production technology, in that only a relatively small number of capillary membranes can be dipped into the solid layer at the same time, since the material allows only a slight displacement.
• A method using a volatile liquid, a suspension, or a gel, into which the ends of the capillary membranes are dipped, is known from WO 01/85315. The capillary membranes are subsequently cast into a sealing mass. The substance into which the ends of the capillary membranes have been dipped has a relatively high viscosity, in order to avoid significant creep of the substance as the result of capillary forces. However, in this method, as well, it cannot be prevented that the substance also climbs slightly upward on the outside of the capillary membranes. For this reason, there are production technology problems here, too.
• All of the known production methods have in common that in a first process step, the open ends of the capillary membranes are first dipped into a layer that prevents contact of the ends with the casting material during casting in of the capillary membranes. After the head piece has hardened, the ends of the capillary membranes must be exposed again by means of removal of this layer. The known production methods therefore require a relatively great amount of effort.
• In EP 0 771 233 B1, a method for the production of head pieces of a membrane filter unit is described, in which capillary membranes are guided through a bottom of a casting mold configured as a perforated plate. A viscous casting material is placed into the casting mold, which fills the free space between the capillary membranes and hardens to form a solid head piece. The head piece is subsequently pulled out of the casting mold, with the capillary membranes. In a last method step, the head piece is cut through in order to open the capillary membranes. After the head piece has been cut open, the open ends of the capillary membranes end in a plane with the outer surface of the hardened sealing layer. The method is not suitable for capillary membranes that fray during mechanical processing.
• Proceeding from the problems described, the invention is based on the task of indicating a membrane filter unit having the characteristics described initially, the head piece of which can be produced in simple manner, free of defects, without mechanical processing.
• This task is accomplished according to the invention in that the sealing layer is disposed on a spacer that has a layer that is penetrated by the capillary membranes and is impermeable for the casting material that hardens to form the sealing layer. In the production of the membrane filter unit, it is practical if a wall that encloses the totality or individual groups of the capillary membranes to be processed is set onto the side of the spacer that faces the open ends of the capillary membranes, which wall forms the casting mold for the sealing layer, together with the spacer that forms a bottom. It also lies within the scope of the invention that a collar is formed onto the spacer, which forms an accommodation space for the casting material and can be used as a casting mold. In particular, the wall can also be an integral component of a head piece, which has a permeate collection space, which is in fluid communication with the open membrane ends that protrude out of the casting material. Production of the head piece takes place by means of filling the casting mold, whereby the layer of the spacer that is impermeable for the casting material prevents flow of the casting material out of the casting mold. In this connection, the height of the casting layer is dimensioned in such a manner that the open ends of the capillary membranes remain unclosed. In this manner, defect-free head pieces can be produced without problems. In the case of the membrane filter unit according to the invention, structured arrangements of the capillary membranes, such as star-shaped, ring-shaped, or rectangular geometries, can be implemented without problems. Such arrangements allow cleaning of the capillary membranes during operation, for example, by means of central air application. By means of the spacer, it is possible to ensure a defined distance between the individual capillary membranes. In this way, it is guaranteed that each individual capillary membrane is enclosed by casting material, without defects. The spacer can furthermore be provided with feed lines, for example for air application.
• The spacer can consist of a perforated plate whose openings enclose the capillary membranes essentially without a gap. In this case, the capillary membranes are pushed through the openings in the perforated plate. Subsequently, the casting material is applied to the top of the spacer. The perforated plate can consist of metal or plastic or an elastomer material, for example.
• It also lies within the scope of the invention that the spacer consists of a flexible plastic strip that has openings or lateral slots for accommodation of the capillary membranes. The plastic strip can be wound up in spiral shape, or segments of the plastic strip can be combined to form a multi-layer package.
• Another embodiment of the invention provides that the spacer has a functional layer of fine-particle solid and/or a soft substance and/or a film, which is punctured by the ends of the capillary membranes before the casting process. In the case of larger capillary diameters, for example, it can be practical in this connection to first close the open membrane ends with a substance that can easily be removed again after puncturing. The functional layer can be disposed in a carrier provided with openings.
• The object of the invention is also a method for the production of the membrane filter unit described. In this method, capillary membranes are inserted into a spacer with one protruding end, which spacer has a layer that is penetrated by the capillary membranes and is impermeable for casting material. A sealing layer of viscous casting material is then applied to the spacer, which material fills the free space between the capillary membranes that protrude at the top of the spacer, up to a level below the membrane ends, and hardens to form a solid head piece. Preferred embodiments of this method are described inclaims8 to16 and are explained in the following, using exemplary embodiments. The drawing schematically shows:
• FIG. 1 a membrane filter unit according to the invention during the production process,
• FIGS.2 to5 further embodiments of the teaching according to the invention,
• FIG. 6 the section A-A fromFIG. 3.
• The figures show a membrane filter unit for liquid or gaseous media with a bundle, or a plurality disposed in any desired manner, ofcapillary membranes1 open on at least one face, which are cast into asealing layer3 that has hardened to form a solid head piece, in a region close to the end, with regard to theopen membrane end2. It is evident from the drawings that the open membrane ends2 protrude at the top of thesealing layer3, in other words on the outside of the head piece. Thesealing layer3 is applied, on its side that faces away from theopen ends2 of thecapillary membranes1, to the side of aspacer4 that points upward. Thespacer4 has a layer that is penetrated by thecapillary membranes1 and is impermeable, or at least impermeable to a great extent, for the casting material that has cured to form thesealing layer3. In the exemplary embodiment ofFIG. 1, thespacer4 consists of a perforated plate, theopenings5 of which enclose the capillary membranes essentially without a gap. Depending on the embodiment, the openings or part of the openings of the perforated plate can be widened or stretched. Charging of the perforated plate with the capillary membranes can take place by means of pushing or pulling them in.
• In the production of the membrane filter unit, thecapillary membranes1 are inserted into theperforated plate4 with a protruding end, in that thecapillary membranes1 penetrate theperforated plate4. Afterwards, awall6 is set onto theperforated plate4, on the top, which wall forms a casting mold for thesealing layer3, together with theperforated plate4, which forms a bottom. Thesealing layer3, which consists of viscous casting material, is subsequently applied to theperforated plate4. The casting material fills the free space between the ends of thecapillary membranes1 that protrude at the top of theperforated plate4, and hardens to form a solid head piece. It is furthermore evident from the figures that eachopening5 of theperforated plate4 has acapillary membrane1 assigned to it. This guarantees defect-free enclosure of each individualcapillary membrane1 by the casting material. Furthermore, structured arrangements of thecapillary membranes1 can be implemented in this manner, without problems. The ends2 of thecapillary membranes1 that protrude above theperforated plate4 remain unclosed during application of the casting material. In the exemplary embodiment ofFIG. 1, the casting material is passed to the top of thespacer4 by means of afeed channel7, next to thecapillary membranes1. It lies within the scope of the invention that thesealing layer3 is applied to theperforated plate4 in one or more layers. In the case of multi-layer application of the sealing layer, the lower layer, in each instance, has hardened at least partially before the next layer is applied. The multi-layer structure can have an advantageous effect on the physical properties of thesealing layer3. Thermoplastic or duroplastic plastics, for example polyurethane resins or epoxy resins, can be used as the casting material. After the casting material has hardened, thewall6 can be removed, if necessary.
• In the exemplary embodiment ofFIG. 2, acollar8 is molded onto thespacer4, which collar forms an accommodation space for the casting material. Thespacer4, which is configured with acollar8, forms a lost castingmold14. In the exemplary embodiment, this mold has one or more openings15, through which the casting material is supplied. In the exemplary embodiment, the component that forms the castingmold14 is additionally supplied with apipe socket9 that can be used for applying gas to the membrane filter unit. Another preferred possibility for supplying the casting material is shown inFIG. 3. In this connection, the casting material is fed through a pipe16 that encloses thepipe socket9 of thecomponent14 with a ring gap.
• In the exemplary embodiment ofFIG. 4, thespacer4 has a functional layer10 of a soft substance, which has been punctured by the ends of thecapillary membranes1. The functional layer10 is disposed on a carrier provided with openings. Instead of a soft substance, a fine-particle solid or a film can also be used.
• In the exemplary embodiment ofFIG. 5, thespacer4 consists of a flexibleplastic strip12, which has openings orlateral slots13 for accommodating thecapillary membranes1. Thecapillary membranes1 are inserted into thelateral slots13 or openings of theplastic strip12, which strip is wound up into a spiral. Instead of the spiral-shaped arrangement shown inFIG. 5, segments of theplastic strip12 can also be combined into a multi-layer package.
• In the case of the membrane filter unit according to the invention, structured arrangements of the capillary membranes, for example star-shaped, ring-shaped, or rectangular geometries, can be implemented without problems. In the case of the arrangement shown inFIG. 6, thecapillary membranes1 are bundled in arcs. A free space remains between the arcs, which allows flow on the untreated water side, all the way into the interior of the membrane fiber bundle.

Claims (16)

1. Membrane filter unit for liquid or gaseous media, with a bundle, or a plurality disposed in any desired manner, of capillary membranes (1) open on at least one face, which are cast into a sealing layer (3) that has hardened to form a solid head piece, in a region close to the end, with regard to the open membrane end (2), whereby the open membrane ends (2) protrude on the outside of the sealing layer (3), wherein the sealing layer (3) is disposed on a spacer (4) that has a layer that is penetrated by the capillary membranes (1) and is impermeable for the casting material that hardens to form the sealing layer (3).

2. Membrane filter unit according toclaim 1, wherein the spacer (4) consists of a perforated plate whose openings (5) enclose the capillary membranes (1) essentially without a gap.

3. Membrane filter unit according toclaim 1, wherein the spacer (4) consists of a flexible plastic strip (12) that has openings or lateral slots (13) for accommodation of the capillary membranes (1).

4. Membrane filter unit according toclaim 3, wherein the plastic strip (12) is wound up in spiral shape, or that segments of the plastic strip can be combined to form a multi-layer package.

5. Membrane filter unit according toclaim 1, wherein the spacer (4) has a functional layer of fine-particle solid and/or a soft substance and/or a film, which is punctured by the ends of the capillary membranes.

6. Membrane filter unit according toclaim 5, wherein the functional layer is disposed in a carrier provided with openings.

7. Method for the production of the membrane filter unit according toclaim 1, whereby capillary membranes are inserted into a spacer with one protruding end, which spacer has a layer that is penetrated by the capillary membranes and is impermeable for casting material, and whereby a sealing layer of viscous casting material is applied to the spacer, which material fills the free space between the capillary membranes that protrude at the top of the spacer, up to a level below the membrane ends, and hardens to form a solid head piece.

8. Method according toclaim 7, wherein a plate with openings is used, into which the capillary membranes are introduced.

9. Method according toclaim 8, wherein each opening has a capillary membrane assigned to it, in each instance.

10. Method according toclaim 7, wherein the spacer has a layer that is impermeable for the casting material, which is punctured during insertion of the capillary membranes.

11. Method according toclaim 10, wherein the layer that is punctured during insertion of the capillary membranes consists of fine-particle solid, a soft substance, or a film.

12. Method according toclaim 7, wherein the capillary membranes are inserted into openings or lateral slots of a plastic strip and the plastic strip is wound up into a spiral or segments of the plastic strip are combined to form a package.

13. Method according toclaim 7, wherein the ends of the capillary membranes that protrude above the spacer remain unclosed during application of the casting material.

14. Method according toclaim 7, wherein the casting material is fed in at the top of the spacer, next to the capillary membranes.

15. Method according toclaim 7, wherein the casting material is fed in through one or more openings of a component that accommodates the casting material.

16. Method according toclaim 7, wherein the sealing layer is applied to the spacer in several layers, whereby the lower layer, in each instance, has hardened at least partially before the next layer is applied.

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