IL33211A - A method of producing membrane packs suitable for electrodialysis - Google Patents

Description

A method of producing membrane packs sui table for electrodlalysls ο'Β'κηοπ o»anp ins nvx»V no»w The invention relates to membrane packs. Such packs, which are used in processes involving reverse osmosis, dialysis and the like, and in particular electrodialysis, are conventionally formed of alternate membranes and permeable separators, each membrane being sealed to its adjacent membranes by a gasket formed of rubber or plastics material. These packs thus consist of a series of cells, each formed of two membranes separated from each other by a permeable separator and with their edges sealed to each other by a gasket.

Each cell is generally provided with ports through which fluid is fed into and removed from the cells, and these ports are in turn connected to manifolds extending at right angles to the plane of the membranes and cells.

Normally alternate cells share common manifolds.

The cells are desirably made as thin as possible, thereby ensuring that as much of the fluid as possible comes in contact with the membrane surface and, in the case of an electrodialysis pack, that the electrical resistance of the cell is kept low.

In conventional cells the manifolds are located within the area surrounded by the gaskets, and also within the area of the membranes. Whilst this location is usually necessary in order to ensure a proper peripheral seal of the membranes, it suffers the disadvantage of reducing the effective membrane, area. To overcome this disadvantage, the manifolds are usually kept as small and as few in number as is compatible with the pack functioning adequately. These restrictions tend to cause high flow rates in the manifolds resulting in distribution between large numbers of cells.

According to the present invention there is provided a membrane pack suitable for use in electrodialysis, dialysis or reverse osmosis which pack comprises membranes providing cells between them, separators between the membranes and a seal between peripheral parts of at least two adjacent membranes which seal is formed so as to provide a port through which fluid can enter or leave the cell between said adjacent membranes.

The seal will consist of sealing material or sealing pieces.

The seal can be formed so as to provide ports at opposed locations around the periphery of the adjacent membranes through which fluid can enter and leave respectively.

Although it is possible for some of the inlet or outlet ports to be formed in the conventional manner, for example by manifolds passing through the membrane area,, it is desirable for all the cells of the pack to be served entirely b "inlet and outlet ports formed according, to the present invention.

Normally the membrane packs of the invention will consist of' more than one pair of alternate membranes and separators and each adjacent pair of membranes has a seal between peripheral parts of the membranes which is formed to provide both inlet-and outlet ports.

The material for use as the sealing pieces or sealing material may be any suitable material from which gaskets can be made e.g. rubber or plastics material.

The sealing pieces or the sealing material may be fixed to their res ective ermeable separators in order to ease placing the sealing piece adjacent to the edge of the respective separator and applying a suitable glue to form a smooth butt joint or by filling the interstices of the separator with a sealing compound, rubber or polyurethane being preferred, either by casting or moulding to give a flat surface no thicker than the permeable separator.

Between those edge parts of the adjacent membranes not having a sealing piece or sealing material between them, there may be inserted a preformed sealing piece shaped so as to provide a port piece the cell either having a roughened surface to permit fluid to pass between it and the adjacent membrane, or being in some other way permeable to fluid. Such port pieces are desirably made of a plastics material such as polypropylene.

Preferably alternate cells in the pack communicate with common manifolds. In this case there will be two inlet manifolds and two outlet manifolds and preferably each inlet manifold will be opposed across the pack to its respective outlet manifolds. Thus in a pack of substantially rectangular cross section or square cross section, each cell will be formed of a pair of membranes separated. by a permeable separator and bounded on one pair of opposite sides by sealing pieces or sealing material and on the other pair by port pieces forming the inlet and outlet ports. Alternate cells will have ports on the same sides of the pack, and may therefore communicate with the same manifolds.

The pack may conveniently be housed within a box of sufficient dimensions to contain the pile of cells, and to contain the manifolds communicating with the cells. ni constituted, in each case, by a wall of the box. The inside wall of the manifold is desirably the side of the pack containing the ports with which the manifold is to communicate. In such cases, connections, for supplying process liquids to the manifolds, and withdrawing them -therefrom, may be provided through apertures in the appropriat walls of the box. The box may be constructed of any suitable material which can withstand the chemical and electrical conditions imposed by the process. Such materials include mild steel rubber lined, and plastics materials such as P.V.C. or polypropylene.

In order to hold the pack together as one unit, use may be made of a sealing material which is capable of adhering to the. sides of the pack. Where the pack is contained within a box, as described above, the sealing material may be cast so as to form fluid tight partitions between adjacent manifolds. Suitable sealing materials include any compound which will set or can be caused to set, and which will not decompose or deform to any substantial degree during the operation. of the pack.

It is also, of course, necessary that the material chosen meets the chemical and electrical requirements of the operating conditions of the pack and that it can be caused to adhere to the -side of the pack and to the inner surface of the walls of the box. Suitable materials for use as the sealing material include wax, cement, pitch, plaster of paris, epoxy resins, setting rubbers, soft flowing plastics and bitumens.

To form membrane packs according to the. present if any, are first correctly positioned relative to one another in the pack. The manifolds and the fluid-tight partitions between adjacent manifolds, may be formed in a number of ways will be appreciated by those skilled in the art.

One method of forming the partitions is to place the pack in a box as described above, and to pour into the space between the wall of the box and the side of the pack a sealing material, having first positioned . blocks of a material, such as wood, to ensure that spaces are left for the manifolds on removal of the blocks after the sealing material has been allowed to set. Another method is to place the pack into a box provided with partitions which extend from the inner walls of the box and finish in close proximity with one side of the pack. These partitions are desirably positioned in pairs, a pair being located between the spaces adapted to adjacent manifolds . Thus the space confined by each pair of projections may be filled with sealing material, which on setting will form the required fluid tight partitions between adjacent manifolds A further method of forming the necessary seals involves the use of sealing pieces which extend beyond the side of the pack. Thus in a pack of rectangular or square cross-section, the sealing pieces will project out of the pack from each corner, in directions parallel to the sides of the pack. Since the sealing pieces in alternate cells are located on alternate pairs of opposite ends of the pack, the projecting ends will cross over similar projections from sealing pieces in adjacent cells. If sealing material is applied to the projections at each corner of the pack, th f - the space forming the manifolds may be preserved by positioning blocks of wood or other material appropriately.

.To 'form the outside wall of. the manifolds, the same sealing material may be used as is used' for the fluid tight partitions. Alternatively a different material may be used, in which case the moulding process may be conducted in two stages. The external wall may also be preformed. When the sealing and moulding materials have all. set, the blocks of material filling the spaces constituting the manifolds may be removed.

The advantages of the membrane packs according to the invention, lie not only in the reduction of production costs, owing to there being no requirement for specially shaped gaskets, but also in the more efficient use of membrane area resulting from the fact that there is no need to make holes in the membranes to form the manifolds. This allows the manifolds to be large, ensuring good fluid distribution to the cells. A further advantage lies in the ability to connect the manifolds to side pipes. Thus each pack in a stack may be fed separately, rather than ajack/ merely from the ends of the pa-ekfagain improving distribution between packs and also virtually eliminating ■ any electrical power losses due to short-circuiting by the ducts.

Further advantages of packs in accordance with the present invention are that the large available area for flow through the ports and through the ducts enables higher flow rates to be treated without the usual disadvantages resulting and, as the ports may extend along the whole of one side of the membrane in a pack which is of rectangular or square shape, limitations to the dimensions of the cell, due to difficulty of distributing flow within the cell, fall away. The individual membrane packs may be free, from external leakages and constitute rigid self-contained subassemblies which may be easily handled and removed from a stack, for maintenance. As there is minimal contact between the sealing compound and the gasket edges and, more especially, the membranes, all components can be recovered for re-use once the packs, are dismantled.

In order that the invention may be more easily understood a specific embodiment will now be described with reference to the accompanying diagrammatic drawings. In the drawings:- Figure 1 is a cross-section of the pack parallel to one of the membranes; Figure 2 is an end elevation in the direction of arrow A of two adjacent cells, the outer sealing material being, omitted; and Figure 3 shows a similar view to Figure 2 , the upper cell employing an alternative form of port, pioeo i The specific embodiment of. the invention- comprises a rectangular membrane 11 separated from an adjacent membrane 1 2 by a separator 13.

One pair of opposite edges, 1 4 and 1 5 , of the membrane 1 1 are sealed in fluid tight engagement from the correspondin edges of the membrane 1 2 by the presence of sealing strips 1 6 and 1 7 respectively each formed of rubber and having a length greater than the length of the membrane edge.

Between the remaining pair of edges 1 8 and 1 9 of the membrane 1 1 , are situated ports g¾ e fl , 21 and 22 each portsp*-*ee- s n r e ri roughened edge so as to permit fluid to pass between that edge and the adjacent membrane, as shown in Figure 2, or comprising two components, shown in Figure 3, one.121 having a crenellated surface on which is placed the other 121 A, being a thin plane-surfaced strip. ' .

Between the membrane 12 and another membrane 23 adjacent to it, the construction is identical to that betwee membranes 11 and 12, except that the positions of the ports pieces and the sealing -i^ooo have been interchanged.

Thus the projecting end portions of the sealing pieces 25 and 26, between membranes 12 and 23, project from the pack at right angles to the projecting end. portions of the sealing pieces 16 and 17.

The assembly of the two cells formed by membranes 11, 12 and 23 is repeated throughout the length of the whole pack which may contain, for example, between twenty and two hundred membranes. The pack is housed in a box 31. The box can be constructed of rubber lined mild steel or a plastics material such as polyvinyl chloride or polypropylene. In each comer of the pack projecting portions of the sealing pieces are sealed together with a settable material such as polyuret hane , 27,.28, 29 and 30. Four manifolds 32, 33, 34 and 35 are thus created,, of which manifolds 32 and 33 communicate with alternate cells in the pack whereas manifolds 34 and 35 communicate with the remaining cells. Side pipes may be connected to the manifolds by fixing connection flanges 36, to the outer casing.

It is clear to the skilled man that many other . embodiments of the invention exist. For example, the orts fecooo and not the sealin ieces could form the r

Claims (12)

Claims:

1. A method of producing a pack of membrane cells suitable for use in electrodialysis which method comprises, h&yjpg inside edges and outside.edges ■ forming a framework ' from a pair of flexible material parallel sealing pieces and a pair of parallel portsgaseaaa butted up to and placed at right angles to the sealing pieces; placing a separator in the area defined by the inside edges-of the- framework; covering the area defined by the outside edges of the framework with an electrodialysis membrane; disposing a further framework formed as described above, on the electrodialysis membrane to seal the membrane between the two frameworks such that the sealing pieces and ports pi¾c¾f¾- of the further framework are aligned with the ports P¾GOOO and sealing pieces respectively of the adjacent framework and are separated from the adjacent 'framework by means of the electrodialysis membrane; placing a separator on the membrane,βκ* in an area of frameworks defined above, and repeating the \ above steps until the required size of membrane pack is formed, such that the arrangement of framework and membranes is capable of allowing fluid to flow at right angles to the direction of the fluid- in the next cell; housing the membrane pack ·ΐη a box; sealing each corner of the membrane pack against the box by pouring a oot a . fluid [that is settablej materiall around the- corners of the framework such that the outsides of the membrane pack and the sides of the box form manifolds sealed from adjacent manifolds.

2. A method as claimed in claim 1 wherein the sealing pieces are of rubber or plastics material.

3. Ο A method as claimed in claim 1 or claim 2 wherein the port pieces are of polypropylene.

4. A method as claimed in any one of claims 1 to 3 formed into a j wherein the frameworks are I rectangular*shape.

5.· A method as claimed in any one of claims .1 to' 3 forated into a/ wherein the frameworks arei square*shape.

6. A method as claimed in any one of claims 1 to 5 wherein the sealing pieces and porta asee-es constituting the sides of the frameworks are formed such that they extend at right angles past the point of intersection of the frameworks. —

7. A Vmethod as claimed in claim 6 wherein a settable sealing material is applied to the surfaces of the extended portions of the sealing pieces and extended portions of the port pieces between adjacent frameworks.

8. ; A method as claimed in any one of the preceding (membrane pack is housed in a hox which 1 claims wherein the ibwt is a mild steel rubber lined box.

9. A method as claimed in any one of the preceding claims wherein apertures^ are provided in the walls of the box such that process liquids can be supplied to the manifold.

10. A method as claimed in any one of the preceding claims wherein each corner of the membrane pack is sealed against each corner of the box by- means of a sealing material of wax, cement pitch, plaster of paris, epoxy resin, setting rubbers, ao t flowing plat-) l»lufcs ur i Luwwn,,. flowable plastics material capable of solidifying to a soft solid, or bitumen.

11. A method of producing a membrane pack substantially as hereinbefore described with reference to and as shown in the Figures 1 and 2 or Figure 3 of the accompanying drawings.

12. A membrane pack when produced by a method as claimed in any one of claims l~to 11. Attorney for. Applicants