CA1214114A

CA1214114A - Film for separating multicomponent liquid or gaseous systems

Info

Publication number: CA1214114A
Application number: CA000416705A
Authority: CA
Inventors: Axel Walch; Ekkehard Beer
Original assignee: Hoechst AG
Current assignee: Trespaphan GmbH and Co KG
Priority date: 1981-12-07
Filing date: 1982-11-30
Publication date: 1986-11-18
Also published as: NZ202711A; NO823916L; DK539382A; ES517965A0; DE3272379D1; FI824184A0; DE3148312A1; EP0081182A2; AU9094782A; FI71493B; EP0081182B1; ES8404865A1; FI71493C; JPS58104604A; FI824184L; AU555429B2; EP0081182A3

Abstract

ABSTRACT OF THE DISCLOSURE

Disclosed is a film which is suitable for separating multicomponent liquid or gaseous systems, comprised of a semipermeable membrane which has profiling on its surface and which is preferably applied to a support material which has a strengthen-ing function. The profiling is formed either when the membrane is prepared on profiled release materials, or by profile-imparting elements which are fixed to the surface of the film or are located in the membrane layer or between the support material and the mem-brane layer. Processes for preparing this film and a membrane separating device having a spiral-like or layered structure are also disclosed.

Description

~4 ~

FI~M FOR SEPAR~TING MULTICOMPONENT LIQUID
_ _ _ OR GASEOUS STEMS

B~CK~ROU~D OF I~IE INVENTI _ The present inv~ntion relates to a film 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 componenks from various liquid mixtures, in particular from solutions.
Thus, for example r 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 from a mlxture containing these solvents and a material dissolved therein. Such separation pro-cesses are becoming increasi~gly more important, especially in connection with producing fresh water from seawater and vther sources of salt~con~aining water.

, ~, The material from which these semipermeable membranes have been made is usually an organic polyrner, such as, for example, cellulose acetate. However, a membrane of such material must be cons~ructed 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 there-fore customary to provide these materials with a 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. 3l950,255 and U.S. Patent No. 3,894,166 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 amount of liquid supplied is one of the operating parameters and afects the throughput quantity obtainable. In order to obtain a membrane sur-~ace area which is as large as possible per unit of volume, numerous devices have been described which contain membrane stacks, membrane bags or tubes wound from membrane materials. German Patent No . 1,442,366, U.S. Patent No. 3,367,504 and U.S. Patent No. 3,397,790 describe, ~or example, spiral-shaped membrane separating devices.
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 sur-face must be taken into consideration in this type ., of device as a second parameter. Optimally guided currents prevent deposits on the membrane which can cause blockages, lower to a rninirnum the concen-tra-tion polarization on the active mernbrane layer and 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 No. 2,000,69~
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 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 add~tion it also acts as a flow breaker and turbulence promoter, 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 tur-bulences indeed reduce the tendency for deposlts to build up on the membrane, but, on the other hand,

2~ dead ~ones are formed where the flow is insufficient-ly high, and the en-tire device has a relatively high flow resistance. A uniform laminar flow, whic~
favors the prevention of concentration polari~ation, can therefore not be achieved in the known combina-tion of smooth membranes and fabric-like spacers.
The insertion of the spacer Layer also complicates the manufacture of memb~ane separating devices which have a spiral or layer structure, and hence increases the manufacturing costs.

Another way of pro~ucing flow paths in lavered or wound membrane separating devices is described in U.S. Patent No. 4,206,050. This docu-ment discloses à membrane unit wherein the support layer and the permselective membrane applied thereon have a profile. In this devlce, 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 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 addi-tion, relatively large raised areas form in the 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 invention to provide an improved film for separating multicomponent liquid or gaseous systemsO
Another object of the invention is to pro-vide such a ilm which makes it possible to simplify the manufacture of membrane separating devices which are built up in the form of layers or in a spiral-like 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 pro-vides improved flow conditions in the interspaces of the membrane layers, and, in so doing, eliminates the disadvan-tayes oE silpport material which has already been proEiled.
Ano-ther ob~ect of the inven-tion resides in provicling a process for pre-paring the film according to the invention.
I-t is also an objec-t oE the invention to provide an improved device ~or separating multicomponent liquid or gaseous systems.
In accomplishing the foregoing objects, there has been provided in acc-orcdance with one aspect of the present invention a film suitable for separating multicomponent liquid or gaseous sys-tems, which is comprised of a sheet-like semipermeable membrane having profiling on at leas-t one of its surfaces, and pre-ferably, a support layer to which the semipermeable membrane is applied, the sup-port 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 sup-port layer. Most preferably, the profiling is comprised of profile-impar-ting elements which are firmly boncled -to the surface of the membrane layer.
According to a further aspect of the presen-t invention there is provi-ded 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 firs-t and second smooth side, said first smooth side being immediately adjacen-t to said semipermeable membrane.
In accordance with another aspect of the invention, there has been pro-.. ~ .0 vided a process for prepariny a membrane Eilm which has profiliny on its sur:Eacecomprisiny the s-teps of pouring a solution which contains a material capable oE
mernbrane forma-tion onto a proEilecl substra-te comprising a release ma-terial; and conver-ting the material by phase inversion to produce a mer~rane without ~ SUpp-ort layer applied thereto, said men~rane having a negative pa-ttern of the profi-led substra-te on i-ts surface.
Another process Eor preparing a membrane film which has profiling on its surface comprises - 5a -the steps of spinnincJ into a coagulation bakh a solution which contains a materi.al capable of mem~
brane formation through a die which contains a slo-t which is delimited on one side hy a straight edge and on the other side by an edge with profiling;
and converting the spun mate.rial 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 ~y profile-imparting elements, comprises the steps of extruding a thermoplastic material into the form of the profile imparting elements; and applying the profile :imparting eI`ements in the ex-trusion 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 ~een provided a device for separating multicomponent liquid or gaseous systems, comprising a semipermeable membrane shaped in a spiral-like or layer structure, wherein the semi-permeable membrane comprises a film as defined above.
Fur~her objects, fea-tures and advantages of the present invention will become apparent to the person skilled in this art from the detailed description of preferred e~bodiments which follows, when considered toge~her with the attached figures of drawing~

13RIEF DESCRIPTION OF THE D~WINGS

In the drawings:

Figure 1 is a cross sectiona]. 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 to the invention.

D~TAILED DESCRIPTION OF PREFER~ED EMBODIMENTS

The invention provides a film, in particular a filrn for separating multicomponent liquid or gaseous s~stems, 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 profilin~ 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 (~igure 2), or are positionally fixed between the support layer and the membrane layer in such a way that t-hey are adjacent to the support layer and are covered by the membrane layer (Figure 3).
The semip~rmeable membrane can be comprised of material conventionally used for such purposes, such as, ~or example, regenerated cellulose, cellulose esters, cellulose ethers, caxbohydrate gels, polypeptides, proteins~ polyamides, pol~sulfones, block copolymers with polycarbonate, polymers or copolymers of deriva-tives of acrylic acid or methacrylic acid, such as nitriles and esters, or polymers or copolymers with vinyl alcohol. The pore size of the semipermeable membrane is within a ran~e of from about 2 x 10 ~ to 10 ~m.
The semipermeable membrane is preferably located ;, ~r on a support layex which is permeable to ~lowable media and which serves to absorb the permea-te and to conduc-t it away. The support layer also serves to strenythen and support the membrane, so that the membrane can be 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, o~ paper, a fabric, a web 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, 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 suppor~ layer can also be omitted so tha-t 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-able thermoplastics, such as ~olyamide, 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-wise ~ixed onto the surface of the membrane or, inother embodiments of the invention, these threads can be partially embedded into the Inembrane layer, or they can be present between the suppo~t la~er and the membrane layer in a positionally fixed manner. The threads can be fixed to the substrate over their entire contact area or onl~ within single discrete zones. The threads can be applied so as to be continuous or interrupted, and the threads can also be comprised of chains of successive point-shaped elevations. Pre~erably these threads or point chains are arranged parallel to one another, so that when the film is layered or wound, channels can form through whlch the mi~ture to be separated can flow. EIowever, the profile-imparting elements can also be arranged so as to form a cross-like network on the substrate, whereby, if desired, turbulences form in the current, or they can be arranged like curves, or alternatively as only point-like in an irregular distribu-tion 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 capable of membrane formation is poured onto a pro-filed substrate and converted by the phase inversion method to give the membrane. In the phase inversion method, the li~uid layer which contains a material capable of membrane formation is subjected to the 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 on the membrane surface~ The substra-te onto which the solution containing the membrane-orming material is poured is called a release material, because it can be used ayain and again. Support-free profiled membranes are thus obtained.
In a further process for prepariny films accord-ing 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 b~
a straight edge and on the other side by an eclge with profiling. The spun profile i5 passed into a coagula tion 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 permeahle 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 preparin~ 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 ~hermoplastic 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 matexial on solidifying, or the pre-extruded thermoplastic material of the profilinq elements can be fixed onto the surface of the membrane by means of an adhesive. Pre~erably, ~3 ~r3t.1 ~ ~1 ~

thermoplastic adhesives are used as thP adhesives, these thermoplastic adhesives can be,e.g., polyethylene, polypropylene, or polyure-thanes, as well as other kno~7n waxes of the synthetic or natural type.
In a further process for prepariny Eilms 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 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 obtained in this manner.
In a further process for preparing films accord-ing to the invention, threads which serve as profile-imparting elements are applied directly to the support material and are fixed there, and the semipermeable membrane is then applied in such a way to the resulting pro~iled surface of the support material that the mem brane 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 r in the construction of known membrane separating devices from this film, it is no longer necessary to incorporate a special spacer layer which enables the mi~ture to be separated to approach the membrane surface. This advantage is made possible by the profiling according to the inventlon, which is loc~ted on the surEace of the film and by which the formation oE flow channels is achieved when the filrn is arranged in the form of a spiral or in layers.
The attached drawings are intended to illustra-te the invention in more detail. ~n 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 10 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 ]atter. E'inally, Figure 3 is a sectional view of still another embodiment of the film according to the inven-tion, 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.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. 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, a sup-port layer to which the semipermeable membrane is applied, said support layer being smooth on both sides and permeable to fluid media, said profiling being on the surface of the film which faces away from the smooth support layer, wherein the profiling is com-prised of profile-imparting elements which are firmly bonded to the surface of the membrane layer.

2. A film as claimed in Claim 1, wherein the profile-imparting elements are partially embedded in the membrane layer.

3. A film as claimed in Claim 1, wherein the profile-imparting elements are positionally fixed in such a way between the support layer and the membrane layer that they are adjacent to the support layer.

4. A film as claimed in Claim 1, 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.

5. A film as claimed in Claim 4, wherein the threads ser-ving as profile-imparting elements are arranged parallel to the direction of flow of the liquid or gas.

6. A film as claimed in Claim 4, wherein the threads ser-ving as profile-imparting elements are firmly bonded to the semi-permeable membrane over the entire length of their support area.

7. A film as claimed in Claim 4, wherein the threads ser-ving as profile-imparting elements are firmly bonded to the semi-permeable membrane only within single discrete zones of their support area.

8. A film as claimed in Claim 4, wherein the threads ser-ving as profile-imparting elements are interrupted at regular intervals.

9. 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, wherein the profiling is formed by series of points which run parallel to one another which are arranged parallel to the direction of flow of the liquid or gas.

10. 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.

11. A film as claimed in claim 10, wherein said profiling is on a surface of said film which faces away from said first smooth side of said support layer.

12. A film as claimed in claim 10, wherein said profile-imparting elements are firmly bonded to the surface of the membrane layer which faces away from said first smooth side.

13. A film as claimed in claim 10, wherein said profile-imparting elements are at least partially embedded in the membrane layer and are firmly bonded thereto.

14. A film as claimed in claim 10, wherein said profile-imparting elements are positionally fixed in such a way between the support layer and the membrane layer that they are adjacent to the first smooth side of the support layer.

15. A film as claimed in claim 10, 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.

16. A film as claimed in claim 15, wherein said threads are arranged paral-lel to the direction of flow of the liquid or gas.

17. A film as claimed in claim 15, wherein said threads are firmly bonded to the semipermeable membrane over the entire length of their support area.

18. A film as claimed in claim 15, wherein said threads are firmly bonded to the semipermeable membrane only within single discrete zones of their support area.

19. A film as claimed in claim 15, wherein said threads are interrupted at regular intervals.

20. A film as claimed in claim 15, wherein said threads are comprised of a series of point-shaped elevations which run parallel to one another.

21. A film as claimed in claim 20, wherein said elevations are arranged parallel to the direction of flow of the liquid or gas.

22. A film as claimed in claim 10, wherein said means for imparting said profiling comprises a plurality of point-shaped elevations which are distributed in irregular fashion over the entire film surface.

23. A film as claimed in claim 10, wherein said profile-imparting elements are arranged to comprise a cross-like network.

24. A film as claimed in claim 10, wherein said profile-imparting elements are arranged to comprise one or more curves.

25. A film as claimed in claim 10, wherein said support layer is comprised of one selected from the group consisting of sintered polyethylene and regenera-ted cellulose.

26. A film as claimed in claim 10, wherein said semipermeable membrane corn-prises at least one of the groups consisting of regenerated cellulose, a cellul-ose ester, a cellulose ether, a carbohydrate gel, a polypeptide, a protein, a polyamide, a polysulfone, a block copolymer with polycarbonate, a polymer or a copolymer of a derivative of acrylic acid or methacrylic acid, and a polymer or a copolymer with vinyl alcohol.

27. A film as claimed in claim 10, wherein the pore size of said semiperme-able membrane is within the range of from about 2x10-4 micron to about 10 microns.

28. A film as claimed in claim 10, wherein said extrudable thermoplastic material comprises at least one of the groups consisting of a polyamide, a poly-ester, a polyethylene, and a polypropylene.

29. A process for preparing a membrane film which has profiling on its sur-face comprising the steps of:
pouring a solution which contains a material capable of membrane forma-tion onto a profiled substrate comprising a release material; and converting the material by phase inversion to produce a membrane with-out a support layer applied thereto, said membrane having a negative pattern of the profiled substrate on its surface.

30. A process for preparing a membrane film which has profiling on its sur-face 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 deli-mited on one side by a straight edge and on the other side by an edge with profi-ling; 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.

31. A process as claimed in claim 30, wherein the material exiting from the die is applied onto a support layer permeable to flowable media.

32. A process for preparing a membrane film which has on its surface profi-ling which is formed by profile-imparting elements, comprising the steps of:
extruding a thermoplastic material into the form of the profile-impart-ing 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.

33. A process for preparing a membrane film as claimed in claim 32, further comprising the step of bonding the profile-imparting elements to the surface of the membrane by means of a thermoplastic adhesive.

34. A process for preparing a membrane film as claimed in claim 32, wherein the profile-imparting elements are at least partially embedded in the membrane while the membrane is still in liquid form, so that said profile-imparting ele-ments become firmly bonded to the membrane upon solidification of the membrane.

35. A process for preparing a membrane film as claimed in claim 32, 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.

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

37. A device for separating multicomponent liquid or gaseous systems, com-prising a semipermeable membrane shaped in a spiral-like or layer structure, wherein the semipermeable membrane comprises a film 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.

38. A device as claimed in claim 37, wherein said means for imparting said profiling comprises a plurality of point-shaped elevations which are distributed in irregular fashion over the entire film surface.

39. A device as claimed in claim 37, wherein said profile-imparting elem-ents are comprised of threads which have a round or polygonal cross section and which are arranged parallel to one another, said threads being interrupted at regular intervals.