NL2021249B1

NL2021249B1 - Membrane stack, stack assembly and foldable membrane

Info

Publication number: NL2021249B1
Application number: NL2021249A
Authority: NL
Inventors: Thaeke Russchen Albert; Kunteng Damnearn; Alexander Jager Peter; Grasman Simon; Swart Hendrik
Original assignee: Redstack Bv
Priority date: 2018-07-04
Filing date: 2018-07-04
Publication date: 2020-01-15
Also published as: WO2020009579A1; EP3817844A1

Abstract

The present invention relates to a membrane stack, stack assembly, foldable membrane, and a method for manufacturing such membrane. The membrane stack comprises a number of membranes that are positioned adjacent each other to form a membrane stack, Wherein each membrane of the number of membranes has a central section and two foldable edge sections that are positioned on opposite sides of the central section of the membrane, and Wherein each foldable edge section is folded around an associated edge of an adjacent membrane in the membrane stack.

Description

Θ 2021249 ©B1 OCTROOI (2?) Aanvraagnummer: 2021249 (22) Aanvraag ingediend: 4 juli 2018 (51) Int. Cl.:

B01D 61/50 (2018.01) B01D 63/08 (2018.01) H01M

8/22 (2019.01) (30) Voorrang:

Q Aanvraag ingeschreven:

januari 2020 (43) Aanvraag gepubliceerd:

(73) Octrooihouder(s):

Redstack B.V. te SNEEK

Octrooi verleend:

januari 2020 (45) Octrooischrift uitgegeven:

januari 2020 (72) Uitvinder(s):

Albert Thaeke Russchen te SNEEK Damnearn Kunteng te SNEEK Simon Grasman te SNEEK

Peter Alexander Jager te SNEEK Hendrik Swart te SNEEK (74) Gemachtigde:

drs. P.F.H.M. van Someren c.s. te Den Haag (54) MEMBRANE STACK, STACK ASSEMBLY AND FOLDABLE MEMBRANE (57) The present invention relates to a membrane stack, stack assembly, foldable membrane, and a method for manufacturing such membrane. The membrane stack comprises a number of membranes that are positioned adjacent each other to form a membrane stack, wherein each membrane of the number of membranes has a central section and two foldable edge sections that are positioned on opposite sides of the central section of the membrane, and wherein each foldable edge section is folded around an associated edge of an adjacent membrane in the membrane stack.

NLB1 2021249

Dit octrooi is verleend ongeacht het bijgevoegde resultaat van het onderzoek naar de stand van de techniek en schriftelijke opinie. Het octrooischrift komt overeen met de oorspronkelijk ingediende stukken.

MEMBRANE STACK, STACK ASSEMBLY AND FOLDABLE MEMBRANE

The invention relates to a membrane stack for an (electro)membrane process comprising foldable membranes, a stack assembly with such a membrane stack, a foldable membrane for such a stack and a method for manufacturing such a membrane stack.

Membrane stacks for (electro)membrane processes are known in practice and are used in a wide variety of applications, including (reverse) electrodialysis (RED/ED), energy storage, fuel cells and/or flow batteries and/or filtration. The known membrane stacks comprise a number of membranes that are stacked on top of each other, and each two adjacent membranes together form a flow compartment or membrane cell (also referred to as cell or cell pair) that is configured to accommodate a fluid flow from one side (a feed side) to an opposite side (discharge side). The other ends (i.e. side edges) are fixedly connected to each other. To prevent fluid leakage between adjacent membranes, membrane stacks are provided with spacers and/or flow guides and/or gaskets that are configured to prevent leakage.

A disadvantage of these known solutions is that significant fluid leakage between flow compartments still occurs, while it also increases complexity of manufacturing of the membrane stack.

The invention is therefore aimed at providing a membrane stack that substantially eliminates fluid leakage.

To that end, the invention provides a membrane stack for an (electro)membrane process, the membrane stack comprising:

- a number of membranes that are positioned adjacent each other to form a membrane stack; wherein each membrane of the number of membranes has a central section and at least two foldable edge sections that are positioned on opposite sides of the central section of the membrane, and wherein each foldable edge section is folded around an associated edge of at least one adjacent membrane in the membrane stack.

An advantage of the membrane stack according to the invention is that, due to the folded edge, fluid leakage between adjacent flow compartments is substantially eliminated. Due to the elimination of fluid leakage between flow compartments, a significant increase in performance of the membrane stack is achieved.

Another advantage is that the membrane stack according to the invention is relatively easy to manufacture, while providing improved, or at least similar, protection against fluid leakage. Folding of the foldable edge sections around the edges of an adjacent membrane is easily performed and can also very well be automated. This results in significant reduction of manufacturing complexity and, consequently, a reduction of the manufacturing cost of a membrane stack.

Yet another advantage is that the membrane stack according to the invention is stronger and more robust than existing membrane stacks. The robustness is increased due to the fact that the folded part of the membrane increases strength and reduces risk of undesired bending. The robustness and strength are further enhanced by the fact that the membrane stack comprises less components than existing membranes stacks.

An advantage of the abovementioned robustness is that a more even distribution of the flow and a reduction of the pressure drop is achieved, which leads to an increased performance of the membrane stack.

A further ad vantage is that, due to the simplified manufacturing, the risk of production errors is significantly reduced. This results in lower manufacturing costs (due to lower loss rates). The risk of production errors can be reduced even further by automating the manufacturing process. The reduced risk is for example achieved by the fact that due to the folding, it is virtually impossible to place to subsequent/adjacent spacers of stacked membranes in parallel (i.e. having flow openings directed in the same direction). This is due to the fact that a visual check is achieved at the moment of folding to establish whether each of the adjacent membranes is oriented correctly.

Furthermore, in some embodiments, a reduced number of components is required for manufacturing. This also (additionally) reduces the risk of production errors.

Yet another advantage of the membrane stack according to the invention is that, by virtue of the folded edge sections of the membranes, the flow of fluid to the flow compartments is automatically directed into the flow compartments, since it has no other direction in which it can flow. As a result, flow is relatively smooth and the pressure drop over the flow compartment openings (i.e. the openings of the flow compartments) is relatively low, therewith increasing membrane stack performance. Furthermore, the automatic directing of the flow also results in a more even distribution over the flow compartments in the membrane stack.

The adjacent membrane is preferably positioned above and/or on top of the membrane, such that the membrane which is folded around the adjacent membrane is positioned below the adjacent membrane.

Another advantage of the membrane stack according to the invention is that the tolerances with regard to the stacking of the membranes in the membrane stack are less stringent than in conventional stacks without reducing the performance. As a result, the membrane stack according to the invention can be manufactured more easily.

Furthermore, an advantage of the membrane stack according to the invention is that, due to the increased tolerance during stacking, the folding of the membranes more easily allows dynamic cleaning.

Yet a further advantage is that the membrane stack according to the invention is highly suitable for modular building of (larger) membrane stacks by stacking and connecting multiple membrane stacks according to the invention with each other. The membrane stack according to the invention can easily be connected to a subsequent membrane stack according to the invention, since the connection only requires connecting the foldable edge section of the top and/or bottom membrane in the membrane stack. Known membrane stacks could not easily be connected to each other due to the fact that gluing or welding of membrane stacks to each other could not be performed without having to at least partially disassemble the membrane stack or provide alternative coupling means which take up space in the (larger) membrane stack.

It should be noted that each of the membranes has a length and a width or a diameter that is significantly larger than a thickness of the membrane, wherein the length and the width of the diameter of the membrane define a membrane surface. The membrane surfaces of the membranes are positioned adjacent each other in the membrane stack, and the positioning of the adjacent membranes is such that each foldable edge section at least partially extends over the (central section of the) adjacent membrane around which it is folded. For the purpose of the invention, adjacent is also referred to as 'on top' or 'above’ and ‘below’, whereas the directions are considered along an axis that extends substantially perpendicular to the membrane surface. Thus, on top or above means that the adjacent membrane, when viewed along the perpendicular axis, is positioned at a higher level that the membrane. Other orientations may however also be used without departing from the scope of the invention.

It is noted that to the purpose of the invention, the terms flow compartment, membrane cell, cell, cell pair and/or membrane compartment are considered to have a similar meaning and can thus interchangeably be used in the application.

In an embodiment according to the invention, each membrane in the stack extends transversally with regard to adjacent membranes.

An advantage of positioning adjacent membranes transversally from each other is that it provides a relatively simple manner in which a cross-flow membrane stack can be manufactured. Each folded section effectively seals a flow compartment around which it is folded and prevents fluid leakage between adjacent flow compartments.

In an embodiment according to the invention, the membranes may have a hexagonal shape in which the foldable sections are located on at least two opposite edges of the membrane.

Foldable membranes may be provided in various shape and/or forms, yet one of the preferred embodiments is a hexagonal form. A hexagonal membrane stack has the advantage that it is well-suited tor using foldable membranes. Preferably, adjacent membranes in the stack are rotated with respect to each other around an axis that extends perpendicular to the membrane surface. Each foldable edge section of a membrane is folded around two adjacent membrane compartments that are stacked on top of the membrane. In this embodiment, each foldable edge section thus effectively seals of the two flow compartments around which it is folded.

More generally, it is noted that each foldable edge section is used to effectively seal of the flow compartments around which it is folded (regardless of the specific shape of the membrane).

In an embodiment according to the invention, the membranes may have a rectangular shape in which the foldable edge sections are located near the opposite longitudinal ends of the membrane, and wherein the central section is preferably square-shaped.

The advantage of a rectangular shape with a square-shaped central section is that the membranes can easily be stacked on each other by positioning the central sections of subsequent membranes above each other before connecting the membranes and/or the edge sections thereof to each other. This configuration is especially beneficial in cross-flow membrane stacks in which the membranes are positioned transversally, since it allows the central sections (each preferably having a similar form) to be positioned above each other such that the membrane stack has a consistent (useable) membrane surface.

In an embodiment according to the invention, the foldable edge sections have inwardly bevelled corners, wherein a bevel angle with a longitudinal side of the membrane is between 0° and 90°, preferably between 30° and 60°, and more preferably around 45°.

When stacking foldable membranes, the comers of the foldable edge section of adjacent membranes are placed on top of each other, which increases the thickness. An advantage of providing bevelled corners to the foldable edge sections is that the foldable edge sections of adjacent membranes can be positioned adjacent (i.e. contiguous) to each other, instead of on top of each other. As a result, the overall thickness of the membrane stack is reduced and a more even surface is formed on which a subsequent membrane is placeable.

In an embodiment according to the invention, the foldable edge sections are provided with a cut-out section, for example a square-shaped cut-out section, wherein the cut-out section is provided near a side edge of the foldable edge section.

When stacking foldable membranes, the comers of the foldable edge section of adjacent membranes are placed on top of each other, which increases the thickness. An advantage of providing a cut-out section in the foldable edge sections is that the foldable edge sections of adjacent membranes can be positioned adjacent to each other (i.e. in the same plane), instead of on top of each other. As a result, the overall thickness of the membrane stack is reduced and a more even surface is formed on which a subsequent membrane is placeable.

In an embodiment according to the invention, the membrane stack further comprises a number of spacer elements, wherein a spacer element of the number of spacer elements is positioned between the folded edge sections of adjacent membranes, and wherein each spacer element extends substantially parallel with the folded edge section of an upper membrane of adjacent membranes.

The spacer elements preferably extend substantially parallel to the folded sections of the upper of two membranes and, when used in a cross-flow stack configuration, therefore extend substantially perpendicular across and over the upper membrane surface to connect both folded edge sections of the lower membrane.

The spacer elements have the advantage that they provide additional pressure on the folded edge sections of the membrane, which reduces the risk of the folded edge sections raising up from the folded position. Furthermore, the spacer elements also provide additional pressure on the sealing area below the spacer element. The spacer element can be manufactured using various different manufacturing techniques. This may involve providing a screen printed sealant and per se known netting, yet may also comprise printing, (spray) coating, screen printing and/or dispensing spacer elements on the membranes. Furthermore, it may also be possible to provide separate spacer elements, which are connected to the membranes during manufacturing of the membrane stack. The spacer elements may be spacer elements that only extend near the folded edge or may involve a spacer assembly which comprises spacer elements and a spacer that extends between these elements, such as a netting. Furthermore, the spacer elements may also be formed by a single spacer, such as a netting, that extends over substantially the entire surface of the membrane (including between the folded edge).

In an embodiment according to the invention, the spacer elements have a thickness that is substantially equal to the thickness of a membrane of the membrane stack.

The advantage of this embodiment is that the spacer element is at an even level with the folded section to form substantially flat surface on which the adjacent membrane is supported.

In an embodiment according to the invention, the membrane may be a profiled membrane having a membrane thickness, wherein the membrane thickness comprises a base thickness and a profile height.

In an embodiment according to the invention, the membrane may be a profiled membrane, wherein a side edge of the profiled membrane that extends under a folded edge section of an adjacent membrane is unprofiled.

hi an embodiment according to the invention, in which the membrane is a profiled membrane having an unprofiled side edge that extends under a folded edge section of an adjacent membrane, and wherein a spacer element of the number of spacer elements is positioned between the folded edge sections of the adjacent membranes, and wherein a thickness of the spacer is substantially equal to the profile height.

Alternatively or in addition to using spacers on the membrane surface, the membrane may be provided with a profile which is preferably located on the central section of the membrane. The side edge of the membrane that extends under the folded section of the adjacent membrane is preferably unprofiled and may be provided with a spacer or sealing. An advantage of this embodiment is that no additional spacers are required in the central section of the membrane surface, which reduces the number of manufacturing steps and, therewith manufacturing costs.

hi an embodiment according to the invention, the membrane stack may have a base membrane that is positioned at an end, preferably a lower end, of the membrane stack, wherein the central section of the base membrane is provided with base spacer elements, wherein the base spacer elements extend parallel to the foldable edge sections and adjacent with the foldable edge sections, and wherein preferably the base spacer elements have a thickness that is substantially twice the thickness of a spacer element.

The lowest or base element in the membrane stack is not covered with folded edge sections of a lower placed membrane. As a result, the distance between the adjacent membrane in the membrane stack (the membrane positioned on top of the base membrane) and the base membrane is smaller than the distance between other membranes in the membrane stack. In order to overcome this difference in distance, the base membrane may be provided with base spacer elements which are configured to provide a distance between the base membrane and the adjacent membrane that is substantially equal to the distance present between subsequent membranes in the membrane stack. If the membrane stack is provided with spacer elements, the base spacer elements preferably have a thickness that is twice the thickness of the spacer elements in the stack. The thickness of the spacer elements in the stack is preferably substantially equal to the thickness of a membrane, and thus, to provide a distance between the base membrane and the adjacent membrane that is equal to the distance between other membranes in the stack, the thickness of the base spacer must be twice the thickness of a spacer element.

In an embodiment according to the invention, the membrane stack may further comprise a number of flow guide elements, wherein each flow guide element is configured to be placed over a folded edge section on an outer side thereof, such that the folded edge section is at least partially enclosed by the flow guide element.

An advantage of a flow guide element that is connectable over a folded edge section of the membrane is that the folded edge section is held firmly in place by the flow guide element. This reduces the risk that the folded edge section raises up. Another advantage is that the flow guide element provides a more even distribution of the flow over the different membrane compartments.

In an embodiment according to the invention, at least part of the number of flow guide elements may be provided with at least one flow opening that is configured for guiding a flow into a flow compartment between two adjacent membranes.

An advantage of providing flow openings in the flow guide element is that the flow of fluid to the compartments may be distributed more evenly over the flow compartments. Furthermore, the flow guide elements, by virtue of providing different flow openings for different flow guide elements, may also be provided to differ the fluid flow to different compartments. This may for example be applied in a membrane stack in which different flow compartments have to be provided with a different amount of fluid during operation.

hi an embodiment according to the invention, the flow guide elements may be placed such that each side of the membrane stack comprises alternatingly a folded section that is provided with a flow guide element and a folded section that is not provided with a flow guide element.

The flow guide elements may advantageously also be used to differ the fluid flow to different compartments by selectively providing flow compartments with flow guide elements. This may for example be applied in a membrane stack in which different flow compartments have to be provided with a different amount of fluid during operation.

In an embodiment according to the invention, the membrane stack further may comprise at least one end membrane, wherein the at least one end membrane is not folded over an adjacent membrane, and wherein the end membrane is preferably operatively connectable to an electrode of a stack assembly.

An advantage of having a separate end membrane is that the end membrane may be adapted to the fact that is does not have a folded edge section and/or to provide a connection with an electrode. Preferably, the end membrane is adapted to cooperate with folded membranes in the membrane stack to provide an optimal fit in a stack assembly.

In an embodiment according to the invention, at least part of the central section of the membranes has a flow profile, wherein the flow profile is formed by spacers and/or an integrally formed profile in the membrane and/or a spacer netting that is positioned in or on the membrane surface.

In some embodiments it is advantageous to provide central section of the membranes with a flow profile, such as a spacer, a netting and/or a profiled membrane surface to create a specific flow pattern over the central section of the membrane (and thus in the flow compartment associated with this membrane).

In an embodiment according to the invention, the foldable edge sections may be unprofiled in that the foldable edge sections are substantially flat.

Preferably, the foldable edge sections are unprofiled, which means that the surfaces are substantially flat. The unprofiled edge section may be used in combination with an unprofiled central section (i.e. a completely unprofiled membrane) or in combination with a central section being profiled and/or having spacers.

In an embodiment according to the invention, the foldable edge section has a width in the range of 0.5 - 20 % of the total membrane width, more preferably 1.0 - 12.5 %, and is most preferably in the range of 2.5% - 5%. It will be understood that other dimensions can also be envisaged in accordance with the present invention.

The invention also relates to a stack assembly comprising a membrane stack according to the invention.

The stack assembly according to the invention provides similar effects and advantages as the abovementioned membrane stack according to the invention.

The membrane stack according to the invention can be advantageously used in a wide variety of different stack assemblies to improve performance of the stack assembly. As such, the stack assembly according to the invention may for example be a stack assembly comprising a tubelike housing, which may be provided with an enclosing structure and/or a solid manifold, yet may also be used in more traditional stack assemblies that are enclosed in a different housing to provide an improved performance to the stack assembly.

The invention further also relates to a foldable membrane for a membrane stack, the membrane comprising a central section and two foldable edge sections, which are positioned adjacent the central section on opposite sides thereof, and wherein the foldable edge sections are configured to be folded around the edge of an adjacent membrane, wherein the adjacent membrane is preferably positioned on top of the central section of the membrane.

The foldable membrane according to the invention provides similar effects and advantages as the abovementioned membrane stack according to the invention and the abovementioned stack assembly according to the invention.

The invention also relates to a method for manufacturing a stack assembly, the method comprising the steps of:

providing a number of membranes having a central section and two foldable edge sections that are positioned adjacent on opposite sides of the central section; placing a membrane of the number membranes;

placing a consecutive membrane of the number of membranes on the membrane, wherein the consecutive membrane is preferably transversally positioned with regard to the membrane;

folding the side areas of the membrane over associated side edges of the consecutive membrane; and repeating the preceding steps to form a stack of membranes.

The method for manufacturing a stack assembly according to the invention provides similar effects and advantages as the abovementioned membrane stack, stack assembly and/or foldable membrane according to the invention.

An advantage of the method according to the invention is that the membrane stack is easy to assemble and can therefore be manufactured with lower manufacturing costs. Another advantage of the method according to the invention is that the manufacturing process is easily automated.

This increases reliability and production speed, while simultaneously reducing the risk of defective products (i.e. membrane stack having production errors).

Due to the folding steps in the manufacturing as provided in the method according to the invention, the pressure needed to seal the stack is relatively low compared to existing methods for manufacturing a stack. As a result, the method reduces investment costs for machinery and equipment required to manufacture membrane stacks (and thus the manufacturing costs for each membrane).

Furthermore, the method for manufacturing a membrane stack according to the invention may easily replace a known membrane stack manufacturing process and can seamlessly be inserted in an existing stack assembly manufacturing method.

Yet another advantage is that the method according to the invention can also be used to manufacture a membrane stack using dry membranes, which obviates the step of wetting the membranes and/or stacking the membranes in a fluid such as water. This reduces complexity of the manufacturing process and, as a result, significantly reduce the manufacturing costs.

In an embodiment of the method according to the invention, the method may additionally comprise the step of positioning an end membrane on the membrane stack, wherein the end membrane is not folded.

In a preferred embodiment, the method also comprises positioning at least one end membrane on the membrane stack. This may for example also comprise positioning an end membrane on each end of the membrane stack. The end membranes may advantageously be configured to be operatively connectable to an electrode of a stack assembly and/or may be specifically adapted to a specific type of stack assembly.

Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, in which:

Figure 1 shows a perspective view of an example of a stack assembly according to the invention;

Figure 2 shows a front view of the stack assembly of figure 1 with the end plate removed;

Figure 3 shows a traditional stack assembly configuration in which a membrane stack according to the invention can be used;

Figure 4 shows a perspective view of a membrane stack according to the invention; Figures 5a - 5f show an example of the method for manufacturing a membrane stack according to the invention;

Figures 6a - 6b show a second example of the membrane stack according to the invention;

Figures 7a - 7b show a third example of the membrane stack according to the invention;

Figures 8a - 8b show a fourth example of the membrane stack according to the invention; and

Figure 9 shows a schematic overview of an example of the method according to the invention.

An example of stack assembly 2 according to the invention (see figures 1, 2) comprises elongated tube 4 having outer wall 4a and inner wall 4b and length LI. Elongated tube 4 extends around central axis A from first end 6 to second end 8, which in this example are open ends, and therewith forms housing space 10. First end 6 and second 8 are sealingly closeable by respective end plates 12, 14, therewith sealingly closing housing space 10 from environment 16. End plates 12, 14 are in this example provided with flow openings 18, 20 for allowing a fluid flow into and out of housing space 10. Sealing 15 may be provided between end plates 12, 14 and the respective end 6, 8 of tube 4. Furthermore, in this example, end plate 12 is provided with electrode plate 13 having an electrode 11.

Stack assembly 2 also comprises membrane stack 22, 200 (see also figures 4 - 8b). The sides of membrane stack 22, 200 are provided with respective side plates 26, 28, 30, 32, which are in this example contiguous with membrane stack 22, 200 and extend over the entire length L2 of membrane stack 22, 200. Side plates 26, 28, 30, 32 are connected to each other through sealing connectors 34, 36, 38, 40 to form enclosing structure 41. Each side plate 26, 28, 30, 32 may be formed of a single plate, yet may also be formed from a number of plates that are positioned next to each other. In this example, side plate 26 includes a number of adjacent side plates 26a, 26b, 26c, 26d, 26e, 26f, 26f, 26g, 26h, 26i, 26j. Side plates 28, 30, 32 includes a number of respective adjacent side plates 28a - 28j, 30a - 30j, 32a - 32j .

Each sealing connector 34, 36, 38, 40 may be formed of a single sealing connector or may be formed of a number of sealing connectors that are positioned adjacent to each other when viewed along length L2.

Side plates 26, 28, 30, 32 and sealing connectors 34, 36, 38, 40 together form enclosing structure 41 to enclose and hold membrane stack 22, 200. Enclosing structure 41 may be fixedly connected to membrane stack 22, 200, yet may also be releasably connected to membrane stack 22, 200. The latter can be performed by clamping membrane stack 22, 200 and/or individual membrane cells of membrane stack 22, 200 in enclosing structure 41.

Enclosing structure 41 is configured to be slidingly insertable in elongated tube 4, such that sealing connectors 34, 36, 38, 40 are in sealing connection with inner wall 4b of external housing 4, which in this case is elongated tube 4.

When enclosing structure 41 and enclosed membrane stack 22, 200 are inserted in elongated tube 4, the sealing connection between sealing connectors 34, 36, 38, 40 and inner wall 4b result in the formation of flow compartments 42, 44, 46, 48. In this example (see figure 2) each flow compartment 42, 44, 46, 48 is delineated by two sealing connectors, one side plate and a part of inner wall 4b. For example, as can be seen in the figures 1 and 2, flow compartment 42 is delineated by sealing connectors 34, 36, side plate 26 and a part of inner wall 4b.

Side plates 26, 28, 30, 32 are provided with a number of flow openings 50, which regulate the flow of fluid from flow compartments 42, 44, 46, 48 to the membrane cells of membrane stack 22, 200.

A conventional stack of membranes 122 (figure 3) comprises a top layer or a top plate 124 including an electrode compartment and a bottom layer 126 also including an electrode compartment. Stack 122 is placed between the two layers 124, 126. From a first side of stack 122 solutions are provided through supply plate 128 that in use is connected to the stack 122 through seal 130. On a second side of stack 122 a second plate 132 is provided with seal 134. A first solution is supplied to stack 122 by plate 128 and exits stack 122 through (discharge) plate 132 (indicated with an arrow). On a third side of stack 122 there is provided a supply plate 136 with seal 138. On a fourth side of stack 122 a fourth plate 140 with seal 142 is provided. Stack 122 and supply and discharge means 128, 132, 136, 140 define the membrane stack according to the invention. In the illustrated embodiment plates 128, 132, 136, 140 comprise two openings 143 for the electrolyte solutions. The number of openings 143 depend, amongst other things, on the dimensions of the stack. In the illustrated embodiment plates 128, 132, 136, 140 are oriented substantially perpendicular to membranes 118, 110.

In the illustrated embodiment a second solution is supplied by plate 136 to stack 122 and exits stack 122 through (discharge) plate 140 (indicated with a dashed arrow).

Membrane stack 200 according to the invention shows a number of membranes 202, 212, 218 that are stacked together to form cross-flow membrane stack 200. Membrane stack 200 (see figure 4) comprises a number of membranes 202, 212, 218 that are stacked onto each other and that are connected by means of respective foldable edge sections 206, 208, 214, 216, 220, 222.

In first step 1002 foldable membrane 202 is provided, which is provided with central section 204 and foldable edge sections 206, 208 (figure 5A). In subsequent steps 1004, 1006 (figure 5b - 5c), foldable edge sections 206, 208 are folded upwardly (1004) and subsequently inwardly (1006), such that open space 210 is formed in which a subsequent membrane 212 is placeable. In the following step 1008 (see figure 5d), subsequent membrane 212 is provided in open space 210 by sliding it into open space 210. Central section 213 of membrane 212 is positioned above central section 204 of membrane 202. The sequence of steps may however also be varied, for example by folding 1004 the foldable edge sections 206, 208 upwardly, placing 1008 subsequent membrane 212 and thereafter folding 1006 inwardly the foldable edge sections 206, 208. The sequence of steps is than repeated (see figures 5e - 5f), which encompasses folding 1010 foldable edge sections 214, 216 of membrane 212 upwardly, placing 1012 membrane 218 on top of membrane 212, and folding 1014 foldable edge sections 214, 216 inwardly around the edges of membrane 218. By repeating the folding and stacking steps, membrane stack 202 (figure 4) is manufactured.

In a second example, membrane 302 has inwardly bevelled corners 320, 322 on foldable edge section 306 and inwardly bevelled corners 324, 326 on foldable edge section 308 (figure 6a). Membrane stack 300 comprises multiple membranes 302, 312, 318, 338, 330, 340 having such inwardly bevelled comers (see figure 6b). The advantage during stacking of subsequent membranes 302, 312, 318, 238, 330, 340 is that the inwardly bevelled comers, which in this example have an angle of about 45°, of foldable edge sections of adjacent membranes can be positioned adjacent each other in a substantially horizontal plane to reduce the height of membrane stack 300. This is clearly visible in figure 6b, in which membrane 330 having foldable edge section 332 with inwardly bevelled angle 334 and foldable edge section 336 with inwardly bevelled angle 338 are positionable in the same horizontal plane by moving inwardly bevelled angles 344 and 346 of foldable edge section 342 of membrane 340 in direction F_d.

In a third example (see figure 7a), membrane 402 having central section 404 and foldable edge sections 406, 408 is provided with a spacer assembly 405, 407, 409, which comprises spacer elements 405, 407 and netting 409 that extends between oppositely positioned spacer elements 405, 407. Spacer assembly 405, 407, 409 is positioned in open space 410 of membrane 402 when foldable edge sections 406, 408 are folded inwardly, such that netting 409 covers substantially entire central section 404.

Membrane stack 400 comprising membranes 402, 412, 418, 428, 430, 440 is provided with a number of spacer assemblies that are positioned between the folded edge sections of the membranes. As shown in this example (see figure 7b), spacer element 448 is positioned on top of the folded edge sections of membrane 430 and extends from the first folded edge section towards the second folded edge section of membrane 430. Consequently, spacer element 448 is positioned directly underneath folded edge section 443 of membrane 440. Similarly, spacer element 450 extends underneath folded edge section 442 of membrane 440. Netting 452 extends between spacer elements 448, 450 over substantially the entire central section of membrane 440.

In a fourth example (see figure 8a), membrane 502 having central section 504 and foldable edge sections 506, 508 is provided with flow guide elements 505, 507 which are respectively connectable to folded edge sections 506, 508. Each flow guide element 505, 507 is provided with a number of flow openings, which are used to distribute the flow towards the flow compartments formed by the membranes of membrane stack 500. Flow guide elements 505, 507 further also serve to clamp folded edge sections 506, 508 and to provide a substantially even surface on which the adjacent membrane is placeable. Furthermore, optional spacers 509 are shown in the example of figures 8a, 8b, which may also be provided as a profiled membrane parts 509 or may be omitted completely. Optionally, flow guide elements 505, 507 may be manufactured as standard netting.

The present invention is by no means limited to the above described preferred embodiments thereof. The rights sought are defined by the following claims, within the scope of which many modifications can be envisaged.

Claims

CLAUSES

1. Membrane stack for an (electro) membrane process, the membrane stack comprising:

- a number of membranes that are positioned adjacent to each other to form a membrane stack;

have each membrane or the number of membranes has a central section and at least two foldable edge sections that are positioned on opposite sides of the central section of the membrane, and each foldable edge section is folded around an associated edge or at least one adjacent membrane in the membrane stack.

2. Membrane stack according to clause 1, each membrane in the stack extends transversally with regard to adjacent membranes.

3. Membrane stack according to any of the preceding clauses, regarding the foldable edge sections have inwardly ordered corners, regarding an angle with a longitudinal side of the membrane is between 0 ° and 90 °, preferably between 30 ° and 60 ° and more preferably around 45 °.

4. Membrane stack according to any one of the preceding clauses, the membrane stack further comprising a number of spacer elements, a spacer element or the number of spacer elements is positioned between the folded edge sections or adjacent membranes, and w'herein each spacer element extends substantially parallel with the folded edge section or an upper membrane or the adjacent membranes.

5. Membrane stack according to any one of the preceding clauses, the membrane stack further comprises a number of flow guide elements, each flow 'guide element is configured to be placed over a folded edge section on an outer side thereof, such that the folded edge section is at least partially enclosed by the flow guide element.

6. Membrane stack according to clause 5, where at least part of the number of flow guide elements is provided with at least one flow 'opening that is configured for guiding a flow into a flow compartment between two adjacent membranes.

7. Membrane stack according to clause 5 or 6, the flow guide elements are placed such that each side of the membrane stack comprises alternatingly a folded section that is provided with a flow guide element and a folded section that is not provided with a flow guide element.

8. Membrane stack according to any of the preceding clauses, the membrane stack further comprises at least one end membrane, the at least one end membrane is not folded over an adjacent membrane, and the end membrane is preferably operatively connectable to an electrode or a stack assembly.

9. Membrane stack according to any one of the preceding clauses, at least part of the central section of the membranes has a flow profile, the flow profile is formed by spacers and / or an integrally formed profile in the membrane and / or a spacer netting that is positioned in or on the membrane surface.

10. Membrane stack according to any of the preceding clauses, where the foldable edge sections are substantially flat in that the foldable edge sections are substantially flat.

11. Stack assembly comprising a membrane stack according to any of the clauses 1-10.

12. Foldable membrane for a membrane stack, the membrane including a central section and two foldable edge sections, which are positioned adjacent the central section on opposite sides, and the foldable edge sections are configured to be folded around the edge of an adjacent membrane, surrounding the adjacent membrane is preferably positioned on top of the central section of the membrane.

13. Method for manufacturing a stack assembly, the method including the steps of:

- providing a number of membranes having a central section and two foldable edge sections that are positioned adjacent on opposite sides of the central section;

- placing a membrane or the number membranes;

- placing a consecutive membrane or the number of membranes on the membrane, wherein the consecutive membrane is preferably transversally positioned with regard to the membrane;

- folding the side areas of the membrane over associated side edges or the consecutive membrane; and

- repeating the preceding steps to form a stack of membranes.

14. Method according to clause 13, where the method additionally includes the step of positioning an end membrane on the membrane stack, where the end membrane is not folded.

CONCLUSIONS

A membrane stack for an (electrical) membrane process, the membrane stack comprising:

- a number of membranes positioned next to each other to form a membrane stack;

wherein each membrane of the plurality of membranes has a central portion and at least two foldable side portions, wherein the foldable side portions are positioned on opposite sides of the central portion of the membrane, and wherein each foldable side portion is folded around an associated edge of at least one adjacent membrane in the membrane stack.

A membrane stack according to claim 1, wherein each membrane in the stack extends transversely with respect to adjacent membranes.

A membrane stack according to any one of the preceding claims, wherein the foldable side part is provided with inwardly beveled corners, wherein a beveled corner with a longitudinal side of the membrane is between 0 ° and 90 °, preferably between 30 ° and 60 ° and at more preferably around 45 °.

A membrane stack according to any one of the preceding claims, wherein the membrane stack further comprises a number of spacer elements, wherein a spacer element of the number of spacer elements is positioned between the foldable side parts of the adjacent membranes, and wherein each spacer element extends substantially parallel to the foldable side part of an upper membrane of the adjacent membranes.

A membrane stack according to any one of the preceding claims, wherein the membrane stack further comprises a number of liquid conductors, each liquid conductor being adapted to be placed over an outside of a folded side part so that the folded side part is at least partially enclosed by the liquid conductor.

The membrane stack of claim 5, wherein at least a portion of the plurality of fluid conductors is provided with at least one flow port adapted to guide a fluid flow to a fluid compartment between two adjacent membranes.

A membrane stack according to claim 5 or 6, wherein the liquid conductors are positioned such that each side comprises alternately a folded side part provided with a liquid guide and a folded side part which is not provided with a liquid guide.

A membrane stack according to any one of the preceding claims, wherein the membrane stack further comprises at least one end membrane, wherein the at least one end membrane is not folded over an adjacent membrane, and wherein the end membrane is preferably operatively connectable to an electrode of a stacking assembly.

A membrane stack according to any one of the preceding claims, wherein at least a part of the central part is provided with a flow profile, the flow profile being formed by spacers and / or an integrally formed profile in the membrane and / or a spacer net that is positioned is in or on the membrane surface.

A membrane stack according to any one of the preceding claims, wherein the foldable side parts are not profiled so that they are substantially flat.

11. Stacking assembly comprising a membrane stack as claimed in any of the claims 1-10.

12. Foldable membrane for a membrane stack, the membrane comprising a central part and two foldable side parts positioned next to the central part and on opposite sides thereof, and wherein the foldable side parts are arranged to be folded around an edge of an adjacent membrane, wherein the adjacent membrane is preferably positioned on the central part of the membrane.

A method for manufacturing a membrane stack, the method comprising:

- providing a number of membranes provided with a central part and two foldable side parts which are positioned on opposite sides of the central part;

- placing a membrane of the number of membranes;

- placing a subsequent membrane of the plurality of membranes on the membrane, wherein the subsequent membrane is preferably positioned transversely with respect to the membrane;

- folding the side portions of the membrane over associated side portions of the subsequent membrane; and

- repeating the previous steps for forming a membrane stack.

The method of claim 13, wherein the method further comprises the step of positioning an end membrane on the membrane stack, wherein the end membrane 5 is not folded.

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