US20030173706A1 - Gel potting method and method to reduce twinning for filtering hollow fibre membranes - Google Patents

Abstract

To pot membranes in a header, a dense, viscous liquid, suspension or, preferably, a thixotropic, water soluble gel, is placed in a header pan in space reserved for a permeate channel. A plurality of hollow fibre membranes are collected together and their open ends are inserted into the gel. A fixing liquid, typically a resin, is placed over the gel. The fixing liquid surrounds each membrane and then solidifies, simultaneously sealing the outer surfaces of the membranes and forming a plug in the opening of the header to complete the permeate channel. After the fixing liquid has solidified, the gel is removed by various means. The space initially occupied by the gel becomes part of the permeate channel after the gel is removed. In one embodiment, membranes are grouped by a cushioning adhesive which later surrounds the membranes where they exit the completed header.

Description

• This application is a continuation of U.S. patent application Ser. No. 09/847,338 filed May 3, 2001, which is a non-provisional of U.S. Provisional Application No. 60/202,848 filed May 8, 2000 and claims benefit from Canadian Application No. 2,308,234 filed May 5, 2000. All of the applications mentioned above are incorporated into this document in their entirety by this reference to them.[0001]
FIELD OF THE INVENTION
• This invention relates to methods of potting filtering hollow fibre membranes into a header and to headers of potted hollow fibre membranes.[0002]
BACKGROUND OF THE INVENTION
• In order to filter or permeate with hollow fibre membranes, a large number of thin hollow fibres must be fixed to a header such that their outer surfaces are each completely sealed to the outside of header but their lumens are open to an inner space in the header. The inner space of the header is then connected to a source of suction or pressure to create a transmembrane pressure across the walls of the membranes.[0003]
• In U.S. Pat. No. 5,639,373, the ends of an array of spaced apart fibres are submerged in a fugitive liquid, such as a wax, until the fugitive liquid solidifies around them. A fixing liquid, such as a resin, is then poured over the fugitive liquid and allowed to harden around the membranes. The fugitive liquid is then removed, for example by heating or by dissolution, leaving the lumens of the membranes open to the space formerly occupied by the fugitive liquid. In U.S. Pat. No. 6,042,677, a similar process is used but the array of fibres is held in a bed of powder which is used in place of the solidified fugitive liquid.[0004]
• In U.S. Pat. No. 5,922,201, a continuous hollow fibre is made into a fabric such that adjacent lengths of the fibres are spaced apart from each other and do not have open ends. An edge of the fabric is inserted into a pot of liquid resin which is centrifuged or vibrated as it cures to encourage flow into the spaces between the fibres. After the resin is cured, the block of resin and fibre is cut to separate the fabric into individual lengths of fibres having open ends. The block of resin is then glued or attached through gaskets to the remainder of a header. The use of a centrifuge and the need to later attach the cured block of resin to the remainder of the header add to the cost and complexity of the method. Further, the ends of the fibres may be damaged when the fibres are cut while encased in resin.[0005]
• In European Patent Application No. EP 0 931 582, an elastic pipe is used as a header. An aperture is cut in the pipe and a weir is built up around the aperture. Open ends of hollow fibre membranes are inserted spaced apart in a line into the aperture by first pulling the aperture open and then allowing it to close on the membranes. Liquid resin is poured over the ends of the membranes and retained in placed by the weir until it cures. Surface tension prevents the resin from flowing through the aperture in spaces between adjacent fibres but only a single layer of fibres are potted in each aperture.[0006]
SUMMARY OF THE INVENTION
• The inventors have observed various difficulties with the method in U.S. Pat. No. 5,639,373. One difficulty is that the fugitive liquid wicks up the fibres to a certain wicking height. In order to secure a good bond to the outside of the fibres, the fixing liquid is applied to a depth that exceeds, by a required distance, the wicking height of the fugitive liquid. With large diameter fibres, around 2.0 mm outside diameter for example, the wicking height is about 2 to 10 mm. This requires some excess fixing liquid to be used at some increase in cost but the amount of excess fixing liquid is manageable. With smaller diameter fibres, for example about 1.0 mm outside diameter or less, the wicking height of the fugitive liquid can be 5 to 20 mm. Particularly at these wicking heights, the required excess thickness of the fixing liquid becomes significant and undesirable.[0007]
• Another difficulty with the U.S. Pat. No. 5,639,373 method is that the fibres are organized into a spaced apart relationship before insertion into the fugitive liquid. This is done because the fugitive liquid, when solidified, holds the fibres in whatever relationship that exists when the fibres are placed in the fugitive liquid. Although a very deep layer of the fixing liquid might adequately separate a random arrangement of fibres fixed in the solidified fugitive liquid, pre-spacing the fibres is a preferred solution even though it adds a step to the U.S. Pat. No. 5,639,373 process.[0008]
• Yet another difficulty with the U.S. Pat. No. 5,639,373 process is that the fugitive liquid is often difficult to work with. Solidified fugitive liquids that are dissolved with a solvent generate solvent handling and disposal concerns and limit the choice of permeate pan material to those that do not react with the solvent. Solidified fugitive liquids that are to be melted are typically made of a wax so that their melting temperature is low. Waxes, however, react with many otherwise suitable permeate pan materials and may also produce manageable but undesirable minor reactions with useful fixing resins. For these reasons, permeate pans for use with the U.S. Pat. No. 5,639,373 process are typically made of expensive fibreglass reinforced plastics.[0009]
• Finally, there is sometimes a difficulty in potting headers with “fibre twinning.” In fibre twinning, the fixing liquid wicks up the fibres by 1 to 2 cm before it hardens and joins two (or possibly a few) fibres together for a short distance above the top of the header. Thus, one side of the base of a fibre may be attached to another fibre while the other side of the base of the fibre is not contained in solidified fixing liquid. Under intense aeration or physical handling of the membranes (typically, unintentionally during shipping or maintenance or intentionally as part of physical de-sludging) the base of the fibre may be bent towards its uncontained side. The fibre may be damaged if it rips free of the resin that bonds it to a neighbouring fibre. In particular, where composite membranes are used (such as a coated braid as described in U.S. Pat. No. 5,472,607 or a polysulfone membrane coated with PVDF), the outer layer may stick to the resin while the remainder of the fibre pulls free. Since the outer coating typically contains the smallest pores, a defect is created in the fibre. The inventors have observed fibre twinning with the method in U.S. Pat. No. 5,639,373 but believe that it is likely present in all of the prior art methods described above. The inventors expect that fibre twinning may be less of a concern with centrifuged headers, although in those cases the cost and complexity of centrifuging is itself a concern. In summary, the inventors have noticed many areas in which membrane potting technology, including the process in U.S. Pat. No. 5,639,373, may be improved.[0010]
• It is an object of the present invention to improve on the prior art. This object is met by the combination of features, steps or both found in the claims. The following summary may not describe all necessary features of the invention which may reside in a sub-combination of the following features or in a combination with features described in other parts of this document.[0011]
• In various aspects, the invention provides a method of potting filtering hollow fibre membranes into a header. A plurality of hollow fibre membranes are collected together and their open ends are inserted into a dense, viscous liquid, suspension or, preferably, a gel in a container. The gel has sufficient viscosity and surface tension such that it does not wick up the fibres significantly and sufficient density to remain below a fixing liquid, typically an uncured resin, to be placed above the gel. The fixing liquid surrounds each membrane and then becomes a solid sealingly connected to the outside of each membrane but not blocking the lumens of the membranes.[0012]
• The membranes preferably have outside diameters of about[0013]1 mm or less, for example between 0.5 and 0.7 mm. The plurality of hollow fibre membranes may be arranged before they are potted randomly in a bundle. If randomly arranged before potting, the packing density and membrane and gel material are preferably selected such that the gel tends to disperse the membranes and create a desired closely spaced arrangement. The fixing liquid also wets the membranes and further separates them from each other. Since the ends of the membranes are only partially constrained by the gel, the fixing liquid may surround and space the membranes even if some membranes initially touch each other in the gel. Alternatively, the membranes can be pre-arranged to be closely spaced apart before inserting their open ends into the gel, particularly if a pre-determined spacing is desired.
• Preferably, the potting method is performed in the header. Header pans are prepared of a material which is substantially unreactive with the fixing liquid or the gel. This typically includes a broad range of materials of which ABS is preferred because of its low cost, durability and ease of molding or fabricating into a desired shape. Header pans are prepared with an opening to an inner space defining a permeate channel. The gel is placed in the header in the space reserved for the permeate channel. The open ends of the membranes are then inserted into the gel. The fixing liquid is placed over the gel. When the fixing liquid solidifies, it simultaneously seals the outer surfaces of the membranes and forms a plug in the opening of the header pan to complete the permeate channel. After the fixing liquid has solidified, the gel is removed. The solidified fixing liquid remains attached to the header pan in a position where the open ends of the membranes can be in fluid communication with the permeate channel. The space initially occupied by the gel becomes part of the permeate channel after the gel is removed.[0014]
• Preferably, the fixing liquid is a resin which continues to cure after it has solidified and a substantial portion of the gel is permitted to flow as a gel out of the header while the resin cures. The remaining gel can be removed by dissolving it or by mechanical means such as flushing with water. Further, the gel may be and is preferably thixotropic and can be removed in part by vibrating the gel to a liquid state. A thixotropic gel can also be vibrated to assist in placing the gel evenly in the header. The gel is also soluble in a solvent that does not dissolve the solidified fixing liquid. The solvent is preferably water and the gel may also be removed in part by dissolving the gel in the solvent. The gel may also be heated to assist in placing it in the header or later removing it.[0015]
• In another aspect, filtering hollow fibre membranes are potted in a header by first preparing a group of preferably closely spaced hollow fibre membranes surrounded and held together by a layer of solidified adhesive. The layer of solidified adhesive is located near the ends of the fibres but with the ends of the fibres extending beyond a first side the adhesive. A fixing liquid is placed around the membranes such that the fixing liquid extends from the periphery of the adhesive towards the ends of the membranes. The fixing liquid surrounds each membrane at least at a point between the adhesive and the open end of each membrane. The fixing liquid becomes a solid sealingly connected to the outside of each membrane but not blocking the lumens of the membranes and not contacting the membranes where they exit from a second side of the adhesive. The solidified fixing liquid is attached to a header pan in a position where the open ends of the membranes can be in fluid communication with a permeate channel in the header.[0016]
• The adhesive is chosen to be water insoluble and durable in a solution of any chemicals likely to be present in a substrate to be filtered. The adhesive preferably does not wick up the membranes to any significant degree and the adhesive/fibre bond is preferably weaker than the bond between any layers of a composite fibre. A suitable adhesive is polyethylene hot melt adhesive such as a mix of ethelene vinyl acetate co-polymers when used with fibres having an outer surface of polysulfone, polypropylene or PVDF. The mix of adhesive components is preferably chosen using techniques known to those skilled in the art to be fairly soft and flexible so as to cushion the membranes where they exit the second side of the adhesive.[0017]
BRIEF DESCRIPTION OF THE DRAWINGS
• Preferred embodiments of the present invention will now be described with reference to the following figures.[0018]
• FIG. 1 is a partial cross section of a completed header.[0019]
• FIG. 2 is a partial cross section of a partially completed header.[0020]
• FIG. 3 is a partial cross section of another partially completed header.[0021]
• FIG. 4 is a partial cross section of another partially completed header.[0022]
DETAILED DESCRIPTION OF EMBODIMENTS
• Gel Potting[0023]
• The Figures show[0024]headers17 for a membrane module containing hollowfibre filtering membranes10. Themembranes10 typically have a pore size in the microfiltration or ultrafiltration range, preferably between 0.003 and 10 microns and more preferably between 0.01 and 1.0 microns. Themembranes10 have each anopen end12 at which the lumen of themembrane10 is open to any adjacent space. Themembranes10 can be made, for example, of cellulose acetate, polypropylene, polyethylene, polysulfone or a complex of PVDF and calcined .alpha.-alumina particles. In order to produce a large surface area, themembranes10 preferably have outside diameters in the range of 0.2 mm to 2.0 mm.
• FIG. 1 shows a completed[0025]header17. Themembranes10 are held in a closely spaced apart relationship in a plug of a fixing liquid such as aresin14 which encloses one ormore permeate channels16 in aheader pan18. Theheader pan18 is typically moulded of a suitable plastic. Theresin14 surrounds eachmembrane10 for at least a portion of its length in theresin14. This seals the outer surface of eachmembrane10 so that water cannot enter thepermeate channel16 other than by passing through the walls of themembranes10 and into their lumens. The open ends12 of themembranes10 extend into thepermeate channel16 and put the lumens of themembranes10 in fluid communication with thepermeate channel16. Apermeate pipe20 is tapped to theheader pan18 and locked with anut22 to connect thepermeate channel16 with a source of negative pressure. With themembranes10 immersed in water, the negative pressure in thepermeate channel16 and the lumens of themembranes10 draws filtered permeate through the walls of the membranes. Alternatively, the water around the outside of themembranes10 may be pressurized to drive water through the walls of themembranes10. Further alternatively, feed water may be forced under pressure into the lumens of themembranes10 to force filtered permeate to the outside of themembranes10 in which case thepermeate channel16 becomes a feed channel.
• FIG. 2 shows a[0026]header17 being assembled according to a first embodiment. Aheader pan18 is laid open side up on a table and filled to about 10 to 20 mm with agel30. Thegel30 has a low enough viscosity to be placed in a layer on the bottom of theheader pan18 and to be generally self-levelling once in theheader pan18 but sufficient viscosity not to wick up themembranes10 or be temporarily displaced significantly when theresin14 is placed over it later. Temporary displacement of thegel30 may also be minimized by placing theresin14 over thegel30 in layers, typically about10 cm thick each. Typical viscosities for thegel30 range from 300 to 600 poise. Thegel30 is also denser than theresin14 so that theresin14 floats over thegel30.
• A preferred[0027]gel30 is polymethyl acrylate diluted with propylene glycol or glycerine to achieve the desired viscosity.Many gels30, including polymethyl acrylate diluted with propylene glycol or glycerine, may also be diluted with water to achieve very low viscosity if necessary, but this is not preferred because hydrophillic fibres may cause the water to leave thegel30 and wick up themembranes10. Water also reacts adversely to some resins, such as polyurethane resins, which is not desired.Other gels30 may also be used including gels that are not thixotropic.Preferred gels30, which include polymethyl acrylate diluted with appropriate amounts of propylene glycol or glycerine as mentioned above, are those that are stable in any heat given off by curingresin14, are water soluble, are thixotropic, and can be made to have the viscosity dependent characteristics described in this specification. Other materials such as dense, viscous liquids or suspensions including thixotropic clays or thick oils, resins or slurries might also be used.
• If necessary, the temperature of the[0028]gel30 may be raised to lower the viscosity of thegel30 without causing a phase change. This makes the gel easier to flow into theheader pan18 and improves the self levelling characteristics of thegel30. Similarly, thegel30 may be heated later to make it easier to flow out of theheader pan18. An increase in temperature of 5C to 10C for example, can cause a 10-20% decrease in viscosity of polymethyl acrylate diluted with appropriate amounts of propylene glycol or glycerine. Because of the effect of heat on viscosity, there is a possibility that the heat of theresin14 as it cures could detrimentally effect the viscosity of thegel30. In the inventors' experience, however, the curing heat has not caused a problem with moderate cure time resins without the need to cool the resin, for example with heat sinks, forced air circulation or refrigeration.
• The[0029]header pan18 is preferably made of ABS plastic which is relatively inexpensive, easily molded or fabricated into an appropriate shape, does not react appreciably withmost gels30, and bonds well tomost resins14.
• The[0030]gel30 is pumped into theheader pan18, preferably with a gear pump or positive displacement pump. With a nozzle nearly as wide as the opening of theheader pan18, thegel30 can be placed to a generally even depth, it not being necessary to leave a completely smooth upper surface. Athixotropic gel30 can also be vibrated to temporarily liquify it and then allowed to re-form, but this is not typically necessary.
• A[0031]group24 ofmembranes10 is made having of a plurality of layers ofmembranes10, six layers being illustrated. Methods of forming such agroup24 of membranes is known in the art, having been described at least in U.S. Pat. No. 5,639,373. Another suitable method which uses an adhesive to form a group is described further below. Themembranes10 are closely spaced apart either regularly or randomly within a layer and the layers are separated byspacers26 having a desired thickness, typically between 0.5 and 1 times the outside diameter of themembranes10. Thegroup24 is held together by aband28 wrapped around themembranes10 andspacers26 and the membranes may also be attached to the spacers with adhesive.Groups24 of other shapes may also be made. For example, cylindrical groups can be made by rolling up one or more layers ofmembranes10.
• The[0032]group24 is inserted into theheader pan18 such that the open ends12 of themembranes10 are inserted into thegel30 to a depth of about 5 to 10 mm.Liquid resin14 is then poured to a desired depth, typically about 20 to 50 mm and preferably covering thespacers26. Thespacers26 preferably do not penetrate into thegel30.Suitable resins14 include polyurethane, epoxy, rubberized epoxy and silicone resin. One ormore resins14 may also be used in combination and applied in one or more coats to meet objectives of strength and providing a soft interface with themembranes10 having no cutting edges. Theresin14 must also be water insoluble, durable in a solution of any chemicals likely to be present in the water to be filtered and non-reactive with the membrane material.
• The[0033]liquid resin14 may wick down themembranes10 slightly, but thegel30 prevents theresin14 from reaching the lumens of themembranes10. Theliquid resin14 surrounds themembranes10 and then cures sealing the outsides of themembranes10 to theheader pan18. Thegel30 is then removed to leave a permeate channel16 (as shown in FIG. 1) between theresin14 and the walls of theheader pan18. The lumens of themembranes10 are left in fluid communication with thepermeate channel16. Further, since thegel30 does not react appreciably with theresin14, the bottom surface of theresin14 remains uncompromised, at least when polyurethane is theresin14 and polymethyl acrylate diluted with appropriate amounts of propylene glycol or glycerine is thegel30.
• The[0034]gel30 is removed by one or more of flowing it out in the gel state, optionally with the assistance of heat or vibration, mechanically flushing it and dissolving it, preferably with water. In a preferred method, an opening is made in the permeate channel, such as the opening to admit thepermeate pipe20 shown in FIG. 1. A small air vacuum relief tube is inserted into theheader pan18 to prevent a vacuum from forming in theheader pan18 which might otherwise inhibit or prevent thegel30 from leaving. Theheader pan18 is then tilted to pour thegel30 out through the opening with thegel30 still in a gel state. These steps can begin after theresin14 has become solid but before it is fully cured and continue while theresin14 cures. Over a curing time of several hours, roughly one half to three quarters of thegel30 can be collected. This first collectedgel30 is most easily recycled and, accordingly, it is desirable to maximize the amount ofgel30 collected by simply flowing it out of theheader18. Next, the completed module is placed in a tank such that themembranes10 are immersed in water. A vacuum is applied to thepermeate channel16 to permeate water for about 20 minutes. This mechanically flushes particles ofgel30, particularly small plugs ofgel30 in the lumens of themembranes10. Next, any remaininggel30 is dissolved and removed which may be done by dissolving thegel30 with permeate during testing or start up procedures before the module is put on line. Alternatively or additionally, a tube carrying pressurized water, pressurized air or both may be inserted through the opening and into thegel30 to assist in moving thegel30 or to partially liquify it. Further alternatively or additionally, athixotropic gel30 can be vibrated to reduce its viscosity and increase its rate of flow.
• FIG. 3 shows a[0035]header17 being assembled according to a second embodiment. The second embodiment is preferred over the first, particularly for fibres having an outside diameter of about 1 mm or less. In the second embodiment,membranes10 are arranged in abundle32 and loosely held by areleasable collar34. Thecollar34 is generally of the same shape as theheader17, which is typically rectangular or round. Thebundle32 is produced by winding fibre material on a drum and then cutting the material to createdistinct membranes10 but without purposely arranging themembranes10 in a grid or matrix. The open ends12 of themembranes10 are placed intogel30 in aheader pan18 as described above. Thecollar34 is then removed andresin14 is poured into theheader18 pan. After theresin14 cures, thegel30 is removed, as described above.
• In this second embodiment, there are no spacers to force the[0036]membranes10 into a closely spaced apart relationship. However, thegel30 tends to spread themembranes10 as they are inserted into thegel30. Nevertheless, there is a possibility thatresin14 may not flow betweenadjacent membranes10 and not completely seal thosemembranes10. However, by selecting resins, membrane materials, membrane diameter, depth of resin (typically 20 to 50 mm) and packing density which allow theresin14 to wet eachmembrane10, successful potting is achieved. Theresin14 will wet themembranes10 with sufficient force to separate themembranes10 in at least part of the depth of theresin14. Since thegel30 is not solid, it resists but does not prevent themembranes10 from moving and being separated by theresin14. Factors or selections which encourage full wetting are known in the art. For example, U.S. Pat. No. 4,605,500 describes appropriate factors or selections to pot a random bundle of hollow fibre membranes into a resin.
• In this second embodiment, packing density (defined as the cross sectional area of the[0037]membranes10 divided by the cross sectional area filled by the membranes10) preferably ranges from 15% to 30%. Membrane outside diameter is preferably about 1 mm or less, typically 0.5 mm to 0.7 mm. Polyurethane resin has good wetting characteristics with PVDF membranes although epoxy, rubberized epoxy and silicone rubber are also suitable. With these parameters,resin14 depths of 20 to 50 mm have resulted in reliable, defect free potting.
• Reducing Membrane Fibre Twinning[0038]
• FIG. 4 shows a[0039]header17 being assembled according to a third embodiment. In this embodiment,membranes10 are arranged in asecond group124 having a plurality ofmembranes10 surrounded by a solidified adhesive100 near theends12 of themembranes10. The ends12 of themembranes10 extend beyond the adhesive. Themembranes10 are generally separated and individually surrounded by solidified adhesive100 although, with a sufficient depth of asuitable resin14 it is permissable, but not preferred, formembranes10 to be touching each other in the solidified adhesive100 provided that the overall packing density is not too high, preferably not over about 25%. Preferably, themembranes10 are closely spaced apart either regularly or randomly within layers separated roughly by a desired thickness, typically between ¼ to ¾, more typically between ⅓ to ½, of the outside diameter of themembranes10. The adhesive100 is water insoluble, durable in a solution of any chemicals likely to be present in a substrate to be filtered and substantially non-reactive with the membrane material orresin14.
• The bond between the adhesive[0040]100 and themembranes10 is weaker than all of the materials of themembranes10 and all bonds between materials in themembranes10. Thus, if amembrane10 is pulled away from the adhesive100, the bond between the adhesive100 and themembrane10 breaks before themembrane10 is damaged. The adhesive100 is also preferably sufficiently soft, flexible and non-brittle so as to cushion themembranes10 where they exit theheader17. Apreferred adhesive100 is polyethylene hot melt adhesive made of a blend of ethelyne vinyl acetate co-polymers. The mix of adhesive components is preferably chosen using techniques known to those skilled in the art to achieve the properties described above. Other adhesives which will not wick up themembranes10 appreciably before it cures, has the characteristics of bond to themembranes10 described above, cushions the membranes and is otherwise substantially unreactive with themembranes10, substrate to be filtered and theresin14 might also be sued. For example, thick, fast-curing epoxy resins with aluminum oxide or other additives to make the cured epoxy more flexible, might be used.
• The[0041]second group124 is formed of a number of layers of membranes. A layer is formed by placing a desired number ofmembranes10 onto a surface coated or covered with a strip of material that will not adhere to the adhesive100. Themembranes10 may have already been cut to length and have open ends or may be all continuous as in a fabric or a series of loops of fibres. Themembranes10 are preferably laid down so as to be spaced apart from each other by either random or, more preferably, regular width spaces. A strip ofadhesive100 of about 2-3 cm in width is placed across themembranes10 near any place where ends of themembranes10 will be potted according to this embodiment but leaving space for the open ends12 of themembranes10 to extend beyond the adhesive100. A groove may be made in the surface below where the adhesive100 will be laid down if necessary to allow the adhesive to surround themembranes10. Optionally, the adhesive may be re-melted with an iron to help the adhesive surround each membrane but the adhesive is re-solidified before it can wick up the membranes appreciably. After a desired number of layers have been made, the layers are put together at the bands of adhesive100 to form thesecond group124. The layers may be simply clamped together or glued together with more adhesive100. If themembranes10 will be potted using a fugitive material, themembranes10 are preferably cut open before the layers are put together into thesecond group124 if they were not cut open before being formed into layers. With minor variations to the procedure above, a group ofmembranes10 can be produced forheaders17 of various shapes. For example, a group ofmembranes10 for around header17 can be made by rolling one or more sheets ofmembranes10 into a cylinder if a sufficiently flexible adhesive is used or by sizing each sheet as a slice of a cylinder.
• The[0042]second group124 may be potted using various techniques. For example, thesecond group124 may be placed into a container holding a depth ofresin14. Thesecond group124 is immersed in theresin14 such that the ends of themembranes10 are covered by theresin14 and the adhesive100 is partially, typically about half way, submerged in theresin14. Thusresin14 extends from the periphery of the adhesive100 towards the ends of the membranes which protrude from a first side of the adhesive100. Theresin14 surrounds eachmembrane10 for at least a portion of its length in theresin14 between the adhesive100 and the end of eachmembrane10. When theresin14 solidifies, it sealingly connects to the outside of eachmembrane10 but does not contact the membranes where they exit on top of the adhesive100. Preferably, the ends of themembranes10 will have been placed in the fixing liquid unopened. The block of solidified fixing liquid is cut to open the ends of themembranes10. The solidified fixing liquid is attached to a header pan in a position where the open ends of the membranes can be in fluid communication with a permeate channel in the header.
• Preferably and as shown in FIG. 4, however, the[0043]second group124 is potted into a fugitive material. More preferably, thesecond group124 is potted into afugitive gel30 generally as described further above. Thesecond group124 is inserted into aheader pan18 such that the open ends12 of themembranes10 are inserted into thegel30 to a depth of about 5 mm. The adhesive100 is not inserted into thegel30.Liquid resin14 is then poured to a desired depth which surrounds the periphery of the adhesive100, and preferably extends about one half of the way to the top of the adhesive100, but does not flow over the top of the adhesive to contact themembranes10 on top (or second side) of the adhesive100.
• Using any of the potting methods above, the adhesive[0044]100 continues to surround themembranes10 at the point where they are first constrained by theheader17. This provides a softer interface with themembranes10 at this point and prevents theresin14 from causing fibre twinning.
• What has been described are preferred embodiments of the invention. In particular, and without limitation, the methods may be adapted to potting shelled modules, for example modules in which membranes[0045]10 are contained in a pressurizable vessel. For such modules, a cap or end of the module is thepermeate pan18, fugitive liquids or agel30 are pumped into or removed from the module through the cap or module end, and an access hole is provided in the side of the module for pumpingresin14 into the module above the level of thegel30. The invention is susceptible to other changes and alternative embodiments without departing from the subject invention, the scope of which is defined in the following claims.

Claims (21)

We claim:

1. A method of potting filtering hollow fibre membranes in a header, cap or end of a module comprising the steps of:

(a) collecting a plurality of hollow fibre membranes together;

(b) inserting ends of the membranes into a fugitive potting liquid, suspension or gel in a container, the fugitive potting liquid, suspension or gel having sufficient viscosity to not wick up the fibres significantly and sufficient density to not float on top of a fixing liquid to be placed in the container above the fugitive potting liquid;

(c) placing fixing liquid in the container over the fugitive potting liquid, suspension or gel which fixing liquid surrounds each membrane and then becomes a solid sealingly connected to the outside of each membrane but not blocking the lumens of the membranes;

(d) separating the fugitive potting liquid, suspension or gel from the fixing liquid after the fixing liquid has solidified;

(e) opening the ends of the membranes; and,

(f) attaching the solidified fixing liquid to a header pan, cap or end of a module in a position where the open ends of the membranes can be in fluid communication with a permeate channel in the header.

2. The method ofclaim 1 wherein the fugitive potting liquid, suspension or gel is a gel.

3. The method ofclaim 2 wherein the ends of the membranes are opened before the ends of the membranes are inserted in to the gel.

4. The method ofclaim 3 wherein

(a) the container is the header pan, cap or end of a module and the gel is placed in the header pan, cap or end of a module before the open ends of the membranes are inserted into the gel;

(b) the solidified fixing liquid is attached to the header pan, cap or end of a module by solidifying the fixing liquid in the header pan;

(c) the gel is separated from the fixing liquid after the fixing liquid has solidified by removing the gel from the header pan, cap or end of a module; and,

(d) the space initially occupied by the gel becomes part of the permeate channel after the gel is removed.

5. The method ofclaim 4 wherein the hollow fibre membranes have an outside diameter of about 1 mm or less.

6. The method ofclaim 4 wherein the hollow fibre membranes are collected together into a bundle in which they are randomly arranged.

7. The method ofclaim 5 wherein the hollow fibre membranes are collected together into a bundle in which they are randomly arranged.

8. The method ofclaim 4 wherein the gel is soluble in water and the gel is removed in part by dissolving the gel in water.

9. The method ofclaim 4 wherein the membranes are arranged into a group of closely spaced apart membranes before inserting their open ends into the gel.

10. The method ofclaim 4 wherein the gel is heated to assist in placing the gel in the header.

11. The method ofclaim 4 wherein the gel is heated to assist in removing the gel.

12. The method ofclaim 4 wherein the fixing liquid is a resin which continues to cure after it has solidified and a substantial portion of the gel is removed by flowing it out of the header while the resin cures.

13. The method ofclaim 7 wherein the gel is heated to assist in placing the gel in the header.

14. The method ofclaim 7 wherein the gel is heated to assist in removing the gel.

15. The method ofclaim 7 wherein the fixing liquid is a resin which continues to cure after it has solidified and a substantial portion of the gel is removed by flowing it out of the header while the resin cures.

16. A method of potting filtering hollow fibre membranes in a header comprising the steps of:

(a) collecting a plurality of hollow fibre membranes together;

(b) inserting ends of the membranes into a thixotropic material in a container, the thixotropic material having sufficient viscosity to not wick up the fibres significantly and sufficient density to not float above a fixing liquid to be placed in the container above the thixotropic material;

(c) placing fixing liquid in the container over the thixotropic material which fixing liquid surrounds each membrane and then becomes a solid sealingly connected to the outside of each membrane but not blocking the lumens of the membranes;

(d) separating the thixotropic material from the fixing liquid after the fixing liquid has solidified;

(e) opening the ends of the membranes; and,

(f) attaching the solidified fixing liquid to a header pan, cap or end of a module in a position where the open ends of the membranes can be in fluid communication with a permeate channel in the header, cap or end of a module.

17. The method ofclaim 16 wherein the thixotropic material is a gel.

18. The method ofclaim 16 wherein the ends of the membranes are opened before the ends of the membranes are inserted in to the thixotropic material.

19. The method ofclaim 18 wherein

(a) the container is the header pan, cap or end of a module and the thixotropic material is placed in the header pan, cap or module before the open ends of the membranes are inserted into the thixotropic material;

(b) the solidified fixing liquid is attached to the header pan, cap or end of a module by solidifying the fixing liquid in the header pan;

(c) the thixotropic material is separated from the fixing liquid after the fixing liquid has solidified by removing the thixotropic material from the header pan, cap or end of a module; and,

(d) the space initially occupied by the thixotropic material becomes part of the permeate channel after the thixotropic material is removed.

20. The method ofclaim 19 wherein the thixotropic material is removed at least in part by vibrating it to a less viscous state.

21. The method ofclaim 16 wherein the thixotropic material is vibrated to assist in placing the thixotropic material in the header.

Images