Liquid purification or separation – Filter – Supported – shaped or superimposed formed mediums
Reexamination Certificate
1997-07-15
2001-02-13
Walker, W. L. (Department: 1723)
Liquid purification or separation
Filter
Supported, shaped or superimposed formed mediums
C210S488000, C210S500210, C210S500230
Reexamination Certificate
active
06186342
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a semipermeable capillary comprising a tubular semipermeable wall made of membrane-forming material.
Such a semipermeable capillary is disclosed in DE-A-22 36 226. In the latter, a capillary is described which is composed in its entirety of spun polymer solution. Said spun polymer solution is brought into contact with a coagulation liquid. Depending on the direction of flow of the coagulation liquid through the wall, a very dense skin is produced on the inside or outside, while a porous structure is produced on the other side. The dense skin serves as semipermeable membrane layer and the porous structure as supporting material.
A disadvantage of this known capillary is that it is weak as a result of the lack of a reinforcement. As a result, the semipermeable wall can rapidly become damaged. In order to make such a capillary stronger, the wall thickness can be increased, but this increases the flow resistance appreciably, as a result of which the filtration characteristics decrease considerably.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a reinforced tubular semipermeable capillary in which the above mentioned disadvantages are eliminated.
According to the invention, this object is achieved in that the capillary furthermore comprises a tubular strengthening layer composed of at least one elongated tape which is converted into a tubular shape and of which at least the longitudinal edges mutually overlap, the strengthening layer being joined to the wall and the mutually overlapping tape sections being joined together by the membrane-forming material. The capillary therefore advantageously comprises a semipermeable wall reinforced by a strengthening layer. To obtain a certain strength, the wall thickness can advantageously remain small, as a result of which the filtration characteristics remain high. In addition to forming the reinforced semipermeable wall, the membrane-forming material has yet another function, viz. the mutual joining of the mutually overlapping tape sections. The capillary according to the invention is cheap, rapid and simple to manufacture.
It is pointed out that GB-A-2 289 634 discloses a supported tubular semipermeable membrane. In this case, the membrane comprises a tubular supporting layer made of a nonwoven polyester material and a thin membrane layer applied thereto. In this structure, the tubular supporting layer is formed from an elongated tape, the longitudinal edges being welded to one another by means of ultrasonic welding. In this case, no capillary is involved and the technique described in this document cannot easily be applied to capillaries.
In particular, the tape of the semipermeable capillary according to the invention has an open cohesive structure which is embedded, preferably completely, in the membrane-forming material. The open cohesive structure of the strengthening layer serves as reinforcement of the membrane-forming material. The strengthening layer is completely anchored in the membrane-forming material and, consequently, the joint between the strengthening layer and the wall is very strong. The wall will not quickly become detached from the strengthening layer and will not quickly become damaged in the event of any deformation of the capillary. The strong bond is advantageous, in particular, in backflushing in countercurrent in order to clean the capillary because the flow direction of the semipermeable wall and the strengthening layer is then reversed with respect to that during use. The tape material may be composed, for example, of a strip of nonwoven, woven, knitted or braided material.
Since, according to the invention, at least the longitudinal edges of the tape or tapes converted to a tubular shape mutually overlap, the joint between the mutually overlapping tape sections is advantageously formed by the membrane-forming material itself. Gluing or welding the mutually overlapping tape sections is virtually impossible in the case of capillaries because the anvil which is needed for this purpose and which has to be accommodated in the tubular strengthening layer would have too little mass in the case of such small tube diameters. Furthermore, gluing or welding would appreciably slow down the production rate. In addition, in the case of the joint according to the invention, the joining seam is itself also semipermeable, which keeps the effective semipermeable membrane surface optimum and offers the possibility of making the joining seam in wide form in order to obtain a strong joint. This is in contrast to gluing and welding seams, which are usually impenetrable and are therefore kept as narrow as possible. Advantageously, the internal diameter of the capillary is smaller than, or equal to, 5 mm. A very large reinforced semipermeable wall surface can therefore be obtained for each m
3
of volume.
In particular, the overlap is greater than, or equal to, 90°. A very strong joint is therefore obtained between the mutually overlapping tape sections. By making the overlap still greater, in particular greater than, or equal to, 360°, not only is a very strong joint obtained, but also a very stiff tubular strengthening layer made up of a plurality of layers.
It is also possible to provide the semipermeable wall with a top layer having nanofiltration and/or reverse osmosis characteristics. A possible method for doing this is to wet the semipermeable capillary as described above with an aqueous solution of a suitably chosen amine, after which the capillary is brought into contact with a suitably chosen acid chloride dissolved in an organic solvent not miscible with water, for example hexane, to thus form a polyamide top layer having reverse osmosis and/or nanofiltration characteristics by means of boundary surface polymerisation. In this way an advantageous embodiment of the strengthened semipermeable capillary is obtained, which has the capacity to withstand the pressures prevaling during nanofiltration or reverse osmosis.
The invention also relates to a method for manufacturing a semipermeable capillary and also to a device for carrying out such a method.
REFERENCES:
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patent: 4039448 (1977-08-01), Etani
patent: 4061821 (1977-12-01), Hayano
patent: 5039413 (1991-08-01), Harwood et al.
patent: 0 362 917 (1990-04-01), None
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GB 2289634, Abstract only, Nov. 29, 1995.
7007713, Netherlands, Abstract only, Dec. 11, 1970.
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2236226, Germany, Abstract only, Feb. 14, 1974.
Pat. Abstracts of Japan vol.003, No. 109(C-058), Sep. 12, 1979 & JP 54 089980 A (Mitsubishi Rayon Co. Ltd.), Jul. 17, 1979.
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Pat. Abstracts of Japan vol.003, No. 109 (C-058), Sep. 12, 1979 & JP 54 087681 A (Ulvac Corp), Jul. 12, 1979.
Pat. Abstracts of Japan vol.005, No. 063(c-052), Apr. 25, 1981 & JP 56 013003 A (Daicel Chem Ind Ltd), Feb. 7, 1981.
Bednarek Michael D.
Cecil Terry K.
Pittman Shaw
Stork Friesland B.V.
Walker W. L.
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