NZ202711A

NZ202711A - Profiled semipermeable membrane

Info

Publication number: NZ202711A
Application number: NZ202711A
Authority: NZ
Inventors: A Walch; E Beer
Original assignee: Hoechst Ag
Priority date: 1981-12-07
Filing date: 1982-12-06
Publication date: 1985-07-12
Also published as: AU9094782A; DE3148312A1; FI824184L; DE3272379D1; EP0081182B1; ES8404865A1; JPS58104604A; ES517965A0; DK539382A; FI824184A0; AU555429B2; CA1214114A; NO823916L; EP0081182A3; FI71493C; EP0081182A2; FI71493B

Description

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NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION "FILM FOR SEPARATING MULTICOMPONENT LIQUID OR GASEOUS SYSTEMS." We, HOECHST AKTIENGESELLSCHAFT, a corporation organized under the laws of the Federal Republic of Germany,of D-6230 Frankfurt/Main 80, Federal Republic of Germany, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the ;method by which it is to be performed,to be particularly described in and by the following statement (Followed by 1A.) - ifi- 2027 FILM FOR SEPARATING MULTICOMPONENT LIQUID OK GASEOUS SYSTEMS BACKGROUND OF THE INVENTION The present invention relates to a film 5 which has the function of separating a component or portions of a component from solutions or other liquid or gaseous multicomponent systems.

It is already known to use semipermeable membranes for separating individual components from 10 various liquid mixtures, in particular from solutions. Thus, for example, semipermeable membranes are used for separating liquid components from a mixture of liquids, for separating gaseous components from a mixture of gases and for separating liquid solvents 15 from a mixture containing these solvents and a material dissolved therein. Such separation processes are becoming increasingly more important, especially in connection with producing fresh water from seawater and other sources of salt-containing 20 water. 202711 The material from which these semipermeable membranes have been made is usually an organic polymer, such as, for example, cellulose acetate. However, a membrane of such material must be constructed 5 to be very thin and therefore has only a low tensile strength. To protect the structurally weak membrane materials against deformation or damage through hydraulic pressure or mechanical action, it is therefore customary to provide these materials with a 10 carrier or support material. Examples of support materials of this type have been described in British" Patent No. 1,595,299, and they usually consist of a porous, but solid, fabric-like material.

U.S. Patent No. 3,950,255 and U.S. Patent No. 3,894,166 15 disclose additional semipermeable membranes and processes for their preparation.

In the separation of liquid components from mixtures of liquids, the total surface area of the membrane which comes into contact with the 20 amount of liquid supplied is one of the operating parameters and affects the throughput quantity obtainable. In order to obtain a membrane surface area which is as large as possible per unit of volume, numerous devices have been described 25 which contain membrane stacks, membrane bags or tubes wound from membrane materials.

U.S. Patent No. 3,367,504 and U.S. Patent No. 3,397,790 describe, for example, spiral-shaped membrane separating devices. 30 However, the surface area of the membrane utilized is not the sole critical factor for the design of a membrane separating device, but in addition the type of flow over the membrane surface must be taken into consideration in this type 2027 of device as a second parameter. Optimally guided currents prevent deposits on the membrane which can cause blockages, lower to a minimum the concentration polarization on the active membrane layer and 5 ensure maximum permeation. In order to form current paths by which the liquid can approach the membrane, spacers are therefore introduced into layered or wound membrane separating devices. Such spacers: are described, for example, in British Patent 10 No. 2,000,694. . .

All these known designs, which are in the form of layers or are wound in the shape of spirals, have in common that they use membrane films having smooth planar surfaces and that these films are 15 combined with wide-meshed fabric-like spacers to ensure that the liquid approaches the membrane surface. In the known designs, such a spacer not only has a spacing function, but in addition it also acts as a flow breaker and turbulence promoter, 20 because it is a mesh of threads which has voids between the threads and enlargements at their points of intersection. On the one hand, the turbulences indeed reduce the tendency for deposits to build up on the membrane, but, on the other hand, 25 dead zones are formed where the flow is insufficiently high, and the entire device has a relatively high flow resistance. A uniform laminar flow, which favors the prevention of concentration polarization, can therefore not be achieved in the known combina-30 tion of smooth membranes and fabric-like spacers. The insertion of- the spacer layer also complicates the manufacture of membrane separating devices which have a spiral or layer structure, and hence increases the manufacturing costs. 20271 1 Another way of producing flow paths in layered or wound membrane separating devices is described in U.S. Patent No. 4,206,050. This document discloses a membrane unit wherein the support 5 layer and the permselective membrane applied thereon have a profile. In this device, a spacer can be dispensed with when arranging the membrane unit in layers or winding it up in the form of a-spiral, since the flow paths between the layers 10 are already predetermined by the profiling of the support material. However, these membrane units are only suitable for specific adsorption processes, for example, in medical applications, and, in addition, relatively large raised areas form in the 15 membrane units thus manufactured, which generally insufficiently reduce concentration polarization in the case of other applications.

SUMMARY OF THE INVENTION It is therefore an object of the present 20 invention to provide an improved film for separating multicomponent liquid or gaseous systems.

Another object of the invention is to provide such a film which makes it possible to simplify the manufacture of membrane separating devices which 25 are built up in the form of layers or in a spirallike form.

It is also an object of the invention to provide such a film which omits the separate spacer layer.

A further object of the invention resides in providing such a film which simultaneously provides improved flow conditions in the interspaces - 5 - 202711 of the membrane layers, and, in so doing, eliminates the disadvantages of support material which has already been profiled.

Another object of the invention resides in providing a process for preparing the film according to the invention.

It is also an object of the invention to provide an improved device for separating multi-component liquid or gaseous systems.

In accomplishing the foregoing objects, there has been provided in accordance with one aspect of the present invention a film suitable for separating multicomponent liquid or gaseous systems, which is comprised of a sheet-like semipermeable membrane having profiling on at least one of its surfaces, and preferably, a support layer to which the semipermeable membrane is applied, the support layer being smooth on both sides and permeable to flowable media, wherein the profiling is on the surface of the film which faces away from the smooth support layer. Most preferably, the profiling is comprised of profile-imparting elements which are firmly bonded to the surface of the membrane layer.

Broadly the invention comprises a film adapted for separating multi-component liquid or gaseous systems, which comprises; a) a sheet-like semipermeable membrane presenting profiling in cross section on at least one of its surfaces; b) means for imparting said profiling to said semipermeable membrane, comprising a plurality of flexible profile-imparting elements, each comprised of extrudable thermoplastic material; and c) a fluid media-permeable, flexible support layer presenting a first and second smooth side, said first smooth side being immediately adjacent to said semipermeable membrane.

In accordance with another aspect of the invention, there has been provided a process for preparing a membrane film which has profiling on its surface comprising the steps of pouring a solution which contains a material capable of membrane formation onto a profiled substrate; and converting the material by phase inversion to produce a membrane having a negative pattern of the profiled substrate on its surface.

Another process for preparing a membrane film which has profiling on its surface comprises ' 2027 the steps of spinning into a coagulation bath a solution which contains a material capable of membrane formation through a die which contains a slot which is delimited on one side by a straight edge 5 and on the other side by an edge with profiling; and converting the spun material in the coagulation bath by phase inversion to produce a membrane having profiling determined by the profiled die edge on its surface.

• Still another process for preparing a membrane film which has on its surface profiling which is formed by profile-imparting elements, comprises the steps of extruding a thermoplastic material into the form of the profile imparting elements? and 15 applying the profile-imparting elements in the extrusion step to the surface of a membrane in such a way as to firmly bond them to it.

In accordance with yet another aspect of the invention, there has been provided a device 20 for separating multicomponent liquid or gaseous systems, comprising a semipermeable membrane shaped in a spiral-like or layer structure, wherein the semipermeable membrane comprises a film as defined above.

Further objects, features and advantages of the present invention will become apparent to the person skilled in this art from the detailed description of preferred embodiments which follows, when considered together with the attached figures 30 of drawing. 2027 BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 is a cross-sectional view of one embodiment of the film according to the invention; Figure 2 is a cross-sectional view of * another embodiment of the film according to the invention; and Figure 3 is a cross-sectional view of still another embodiment of the film according 10 to the invention. 20271 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The invention provides a film, in particular a film for separating multicomponent liquid or gaseous systems, which is comprised of a semipermeable membrane which has profiling on its surface.

In one preferred embodiment of the invention, the semipermeable membrane has been applied to a support layer which is smooth on both sides and is permeable to flowable media, and the surface of the film which faces away from the smooth support layer has profiling.

In further particular embodiments of the invention, the profiling is generated by profile-imparting elements which are firmly bonded to the smooth surface of the membrane layer (Figure 1) or are partly embedded in the membrane layer but still project above the membrane layer (Figure 2), or are positionally fixed between the support layer and the membrane layer in such a way that they are adjacent to the support layer and are covered by the membrane layer (Figure 3).

The semipermeable membrane can be comprised of material conventionally used for such purposes, such as, for example, regenerated cellulose, cellulose esters, cellulose ethers, carbohydrate gels, polypeptides, proteins, polyamides, polysulfones, block copolymers with polycarbonate, polymers or copolymers of derivatives of acrylic acid or methacrylic acid, such as nitriles and esters, or polymers or copolymers with vinyl alcohol. The pore size of the semipermeable -4 membrane is within a range of from about 2 x 10 to 10 ym.

The semipermeable membrane is preferably located 2027 on a support layer which is permeable to flowable media and which serves to absorb the permeate and to conduct it away. The support layer also serves to strengthen and support the membrane, so that the membrane can be 5 easily handled and so that membrane damage is avoided. However, the semipermeable membrane can also be used equally well without support material.

The support layer is smooth on both sides and is comprised, for example, of paper, a fabric, a web . 10 or a mesh of plastic or metal. Sheets or films made of porous or absorbent material are also suitable as the support layer. They can be comprised, for example, of sintered polyethylene, as well as of absorbent synthetic sponge material, in particular of regenerated cellulose, 15 which is known as a sponge cloth material. Smooth is understood as meaning that each surface extends in a single plane, i.e., does not have projections.

In applications requiring very compact membrane units, the support layer can also be omitted so that 20 only the membrane and the profile-imparting elements are present. The profile-imparting elements are comprised of a material which is capable of forming a permanent bond with the membrane without adversely impairing the latter in its other properties. Extrud-25 able thermoplastics, such as polyamide, polyester, polyethylene or polypropylene, are preferably used. Threads, for example, made of these materials and having a round, triangular, rectangular or polygonal cross-section can be extruded, welded, bonded or other-30 wise fixed onto "the surface of the membrane or, in other embodiments of the invention, these threads can be partially embedded into the membrane layer, or they 2027 can be present between the support layer and the membrane layer in a positionally fixed manner. The threads can be fixed to the substrate over their entire contact area or only within single discrete zones. The threads 5 can be applied so as to be continuous or interrupted, and the threads can also be comprised of chains of successive point-shaped elevations. Preferably these threads or point chains are arranged parallel to one another, so that when the film is layered or wound,. 10 channels can form through which the mixture to be separated can flow. However, the profile-imparting elements can also be arranged so as to form a crosslike network on the substrate, whereby, if desired, turbulences form in the current, or they can be arranged 15 like curves, or alternatively as only point-like in an irregular distribution over the surface.

The present invention also relates to processes for manufacturing films according to the invention. In a first process, a solution which contains a material 20 capable of membrane formation is poured onto a profiled substrate and converted by the phase inversion method to give the membrane. In the phase inversion method, the liquid layer which contains a material capable of membrane formation is subjected to the 25 action of a precipitation liquid, with the result that the membrane-forming material coagulates. After the liquid has been removed, the membrane is then peeled from the substrate which is provided with profiling, and the profiling is thus obtained at a negative 30 on the membrane surface. The substrate onto which the solution containing the membrane-forming material is poured is called a release material, because it can 2027 - li - be used again and again. Support-free profiled membranes are thus obtained.

In a further process for preparing films according to the invention, a solution which contains a material capable of membrane formation is spun through a die having a slot which is delimited on one side by a straight edge and on the other side by an edge- with profiling. The spun profile is passed into a coagulation bath and is converted by the phase inversion method to give the membrane. In this case also, the phase inversion method is carried out in such a way that the liquid is removed after the material capable of membrane formation has coagulated, and a support-free membrane is thus obtained.

If the extrudate is applied from the die directly to a support layer permeable to flowable media and the phase inversion method is then carried out, a film is obtained which is comprised of the membrane layer, which has profiling on its surface and which is located on the support layer.

In a further process for preparing the film according to the invention, profile-imparting elements are applied and firmly bonded to the surface of the membrane which, optionally, can be bonded to a support material. This can take place, for example, in an extrusion process in which the thermoplastic material is extruded as a heat plastified melt, for example, in the form of a thread, onto the surface of the membrane and becomes firmly bonded to the membrane material on solidifying, or the pre-extruded thermoplastic material of the profiling elements can be fixed onto the surface of the membrane by means of an adhesive. Preferably, 2027 1 thermoplastic adhesives are used as the adhesives; these thermoplastic adhesives can be, e.g., polyethylene, polypropylene, or polyurethanes, as well as other known waxes of the synthetic or natural type.

In a further process for preparing films accord ing to the invention, the profile-imparting elements are partially embedded into the still liquid or "partially liquid membrane layer, so that they project sufficiently far to the desired height above the layer, and they 10 thus enter a firm adhesive bond with the membrane layer as it solidifies. The profile-imparting elements used can be either threads or networks; the intersection points of the networks can be knot-like enlargements, so that point-shaped profile-imparting elements are 15 obtained in this manner.

In a further process for preparing films according to the invention, threads which serve as profile-imparting elements are applied directly to the support material and are fixed there, and the semipermeable 20 membrane is then applied in such a way to the resulting profiled surface of the support material that the membrane adapts to the given profiling, with the result that the outer face of the membrane becomes profiled in a corresponding manner.

The film according to the invention can be used for preparing membrane separating devices having a spiral-type or layer structure. Such devices are known in the art, but the film according to the invention has the advantage that, in the construction of known 30 membrane separating devices from this film, it is no longer necessary to incorporate a special spacer layer which enables the mixture to be separated to approach the membrane surface. This advantage is made possible by the profiling according to the invention, which is 2027 located on the surface of the film and by which the formation of flow channels is achieved when the film is arranged in the form of a spiral or in layers.

The attached drawings are intended to illustrate the invention in more detail. In Figure 1, which is a sectional view of one embodiment of the film according to the invention, the profile-imparting elements 1 are firmly bonded to the surface of the smooth membrane layer 2, which is bonded to a support layer 3. Figure 2 illustrates a sectional view of another embodiment of the film according to the invention, in which the profile-imparting elements 1 are partially embedded in the membrane layer 2 and are firmly bonded to the latter. Finally, Figure 3 is a sectional view of still another embodiment of the film according to the invention, in which the profile-imparting elements 1 are positionally fixed in such a way between the support layer 3 and the membrane layer 2 that they are adjacent to the support layer.. 202711

Claims

WHAT WE CLAIM IS:

1. A film adapted for separating multicomponent liquid or gaseous systems, which comprises; a) a sheet-like semipermeable membrane presenting profiling in cross section on at least one of its surfaces; b) means for imparting said profiling to said semipermeable membrane, comprising a plurality of flexible profile-imparting elements, each comprised of extrudable thermoplastic material; and c) a fluid media-permeable, flexible support layer presenting a first and second smooth side, said first smooth side being immediately adjacent to said semipermeable membrane.

2. A film as claimed in claim 1, wherein the profiling is comprised of said profile-imparting elements which are firmly bonded to the surface of the membrane layer which faces away from said first smooth side.

3. A film as claimed in claim 1, wherein the profiling is comprised of profile-imparting elements which are partially embedded in the membrane layer and are firmly bonded thereto.

4. A film as claimed in claim 1, wherein the profiling is comprised of profile-imparting elements which are positionally fixed in such a way between the support layer and the membrane layer that they are adjacent to the support layer.

5. A film as claimed in claim 2, wherein the profile-imparting elements are comprised of threads which have a round or polygonal cross-section and which are arranged parallel to one another.

6. A film as claimed in claim 5, wherein the threads serving as profile-imparting elements are arranged parallel to the direction of flow of the liquid or gas. 202711

7. A film as claimed in claim 6, wherein the threads serving as profile-imparting elements are firmly bonded to the semipermeable membrane over the entire length of their support areas.

8. A film as claimed in claim 6, wherein the threads serving as profile-imparting elements are firmly bonded to the semipermeable membrane only within single discrete zones of their support area.

9. A film as claimed in claim 6, wherein the threads serving as profile-imparting elements are interrupted at regular intervals,

10. A film as claimed in claim 2, wherein the profiling is formed by series of points which run parallel to one another.

11. A film as claimed in claim 10, wherein the series of points serving as profiling are arranged parallel to the direction of flow of the liquid or gas.

12. A film as claimed in claim 2, wherein the profiling is comprised of a plurality of point-shaped elevations which are distributed in irregular fashion over the entire film surface.

13. A process for preparing a membrane film which has profiling on its surface comprising the steps of: pouring a solution which contains a material capable of membrane formation onto a profiled substrate; and converting the material by phase inversion to produce a membrane having a negative pattern of the profiled substrate on its surface.

*;14. A process for preparing a membrane film which has profiling on its surface comprising the steps of:;spinning into a coagulation bath a solution which contains a material capable of membrane formation through a die which contains a slot which is delimited on one side by a straight edge and on the other side by an edge with profiling; and;- 16 -;202-711;converting the spun material in the coagulation bath by phase inversion to produce a membrane having profiling determined by the profiled die edge on its surface.;

15. A process as claimed in claim 14, wherein the material exiting from the die is applied onto a support layer permeable to flowable media.;

16. A process for preparing a membrane film which has on its surface profiling which is formed by profile-imparting elements, comprising the steps of:;extruding a thermoplastic material into the form of the profile-imparting elements; and applying the profile-imparting elements in the extrusion step to the surface of a membrane in such a way as to firmly bond them to it.;

17. A process for preparing a membrane film as claimed in claim 16, further comprising the step of bonding the profile-imparting elements to the surface of the membrane by means of a thermoplastic adhesive.;

18. A process for preparing a membrane film as claimed in claim 16, wherein the membrane is still in liquid form and the profile-imparting elements are partially embedded in the still liquid membrane and become firmly bonded to the membrane upon solidification of the membrane.;

19. A process for preparing a membrane film as claimed in claim 16, which comprises extruding the profile-imparting elements onto a support layer and thereafter applying the membrane to the side of the support layer to which the profile-imparting elements have been applied.;•N \;13 MAR 1985 r];* - 17 - pf.Q7-f 1 ivUig I _jl JL

20. A device for separating multicomponent liquid or gaseous systems, comprising a semipermeable membrane shaped in a spiral-like or layer structure, wherein the semipermeable membrane comprises a film as defined by claim 1.

21. A film according to claim 1 substantially as herein described with reference to the accompanying drawings. HOECHST AKTIENGESELLSCHAFT By Their Attorneys HENRY HUGHES LIMITED