Spacer, process for its production and its use

Abstract

The present invention relates to a spacer (11) as a support insert for a membrane module, which spacer has support elements (1, 2) on both sides that are spaced apart from one another, wherein the base surfaces (3) and cover surfaces (4) and optionally also the lateral surfaces (9) of the support elements (1, 2) are provided with openings (5, 6, 10), and wherein the spacer surfaces (7) between the support elements (1, 2) as well as the openings (5, 6, 10) are permeable to a solid, liquid or gaseous medium, for use in a pressure-operated membrane module.

Description

[0001] The present invention relates to a support insert for a membrane module (hereinafter referred to as a spacer), a filtration device, or generally a device for separating gaseous, liquid, or solid substances using membranes for separation (membrane module). Furthermore, the invention relates to the production and use of such a spacer and to a module or device comprising one or more such spacers.

[0002] Such spacers of membrane modules, as are also known from US 5 254 259 A and DE 10 2014 100 659 B4, are used in a wide variety of membrane technology applications, for example in devices for pressure-retarded osmosis or forward osmosis applications, in devices for pressure-driven processes such as micro-, ultra-, nano- and hyperfiltration as well as for reverse osmosis processes, in devices for concentration-driven processes such as pervaporation, gas separation, dialysis, in devices for thermally driven processes such as membrane distillation and thermoosmosis as well as in devices for electrically driven processes such as electrodialysis, reverse electrodialysis, electrofiltration and in fuel cells.

[0003] The spacers are arranged either between two membranes or between a membrane and a membrane support, with the membrane(s) or the membrane support resting on the spacer so that the membrane on one side of the spacer is held at a distance from the opposite membrane or membrane support. The passages in the spacer are designed such that they form at least one flow path between at least one edge side and the front and / or back of the spacer so that, for example, a liquid can flow along or across (perpendicular) to the membrane surface or membrane support surface and onto the membrane surface(s) on the other hand. In this way, for example, a liquid flow can be introduced from the edge side into the spacer, distributed over the membrane surface(s) and guided through them.The reverse process is also possible, in which a liquid flow entering through the membrane surface(s) is guided via the passages into the spacer to its edge side.

[0004] For the above-mentioned applications, it is known from the prior art to use technical fabrics, knitted fabrics, or nonwovens, for example, made of plastic threads or fibers, as support inserts or spacers for the respective membrane modules. The fluid flows through the cavities formed between the individual threads or fibers of the fabric, knitted fabric, or nonwoven.

[0005] For example, EP 2 292 307 A1 discloses a membrane filter module in which a porous spacer material is arranged between a membrane and a membrane support plate. The spacer material consists of a nonwoven fabric that keeps the adjacent membrane at a distance from the surface of the membrane support plate, creating a flat flow path for the filtrate fluid through the nonwoven fabric between the membrane and the membrane support plate.

[0006] However, nonwovens, woven fabrics, knitted fabrics, and the like, when used as support inserts or spacers for membrane modules, usually exhibit too low a liquid volume flow rate or too high a flow resistance. Depending on the delivery pressure of the liquid flowing through the spacer, strong fluctuations in the flow resistance or volume flow rate sometimes occur. In particular, increasing delivery pressure leads to a rapid drop in the volume flow rate.

[0007] All of this has a detrimental effect on the applications mentioned above, since the efficiency of the respective processes depends on the largest possible volume throughput.

[0008] US 2008 / 0290031 A1 discloses a spacer for filter modules, which is arranged between two layers of a filter medium and comprises a substantially flat, structured sheet material with upper and lower projections. The upper and lower projections define an upper and a lower support surface for the layers of the filter medium, with the projections rising from the upper and lower surfaces by means of wall sections and terminating in upper sections. The upper and lower projections are spaced apart from each other in a direction parallel to the surface of the sheet material.

[0009] US 2007 / 0175812 A1 discloses a spiral-shaped separation membrane element intended to reduce the pressure drop of a feed-side channel and to be less susceptible to clogging in the feed-side channel. The separation membrane element comprises one or more separation membranes, one or more feed-side channel components, one or more permeation-side channel components, and a perforated hollow core tube around which the separation membranes, the feed-side channel components, and the permeation-side channel components are wound. The feed-side channel component is a mesh formed by fusion bonding (also called a spiral-wound element).

[0010] Finally, DE 10 2014 100 659 B4 describes a spacer for a membrane module. It is characterized by support elements formed on the front and back of the spacer, which serve as support surfaces for a membrane or membrane carrier and have through-holes. Flow paths between the edges and the front and back of the spacer serve to guide and distribute fluids.

[0011] All of these state-of-the-art spacers or support elements still have room for improvement in terms of performance. This means that the throughput of liquids, gases, or solids to be separated (volume flow rate) is still unsatisfactory. Fluctuations in flow resistance and thus in volume flow rate occur. Pressure building up in the module amplifies the drop in volume flow rate as the discharge pressure increases.

[0012] Additional problems arise with the handling and installation of the spacers known from the state of the art, which ultimately result in a reduced volume flow through the module and thus a loss of efficiency. This is particularly true with spacers made of woven, knitted, or nonwoven fabrics made from a wide variety of materials. In these cases, the membranes do not lie flat or evenly on or against the spacers, which, given the low thickness of these materials, can lead to uneven or wavy membrane surfaces, for example, and thus to a loss of volume flow. Attaching the membranes to the spacer is also often problematic, especially in these cases.

[0013] Nonwovens, knitted fabrics, woven fabrics, and the like consist of individual fibers or threads that are connected to form a textile fabric either by interlacing, looping, or via a system of intersecting, alternating warp and weft threads. However, the relative arrangement of the individual fibers and threads is not rigid, but can be subject to continuous changes or shifts, for example, due to fluctuations in the delivery pressure of the fluid flowing through the support insert. The displacement of the threads or fibers relative to one another simultaneously leads to a change in the flow cross-section of the passages formed between the threads or fibers, and consequently to the described fluctuations in flow resistance or volumetric throughput.

[0014] In the woven, knitted and nonwoven fabrics known from the prior art, all threads or fibres have a curved or twisted course, so that the contact surfaces between the support insert and the membrane on top are rounded due to the curvature of those fibre and thread sections that form the contact surface for the membrane. The rounded transition from the actual contact surface to the interior of the support insert, i.e. to the passages, sometimes has very shallow angles. When pressure is applied to the membrane in the direction of the support insert (the spacer), this means that the membrane, which deforms under the effect of pressure, adapts to the rounded fibre or thread sections.Thread sections cling to each other, thereby significantly increasing the membrane contact area and simultaneously reducing the volume flow through the membrane, since fluid transport through the membrane is impossible at those points where the membrane is in direct contact with the support insert. This disadvantageously reduces the active membrane area and thus the effectiveness of the membrane.

[0015] The object of the present invention was therefore to provide a spacer that is suitable for a wide variety of applications and that largely avoids the disadvantages of the prior art or at least improves its properties. This applies in particular to increasing the volume throughput.

[0016] This object is achieved by a spacer according to claim 1. Advantageous embodiments of the invention are specified in the subclaims.

[0017] The inventors started from their earlier invention DE 10 2014 100 659 B4 and were able to further develop and improve it in various respects, whereby in particular the main objective could be achieved, namely the generation of a maximum flow or volume flow rate while minimizing the pressure loss during use of a membrane module according to the invention.

[0018] The spacer according to the invention is characterized by a maximum of open and thus permeable areas. A preferred volume ratio of closed to open areas of the spacer is 30% (closed) to 70% (open areas). Both sides of the spacer have raised support elements, which are arranged in a grid pattern on each side and are arranged on horizontally running grid threads. These threads are spaced apart from one another and form the base of the spacer. Raised support elements on both sides are preferably arranged in a grid structure on this base. The support elements can be arranged with a wide variety of geometries. The horizontally running grid threads are held together in two dimensions (x / y plane) by the base surfaces or by the sides of the open base surfaces of the support elements arranged on both sides, ultimately forming a basic network or a basic grid as the basis of the spacer.

[0019] The support elements serve to support the filter membrane or both sides of the filter membranes, which rest flat and evenly on these support elements, i.e., without undesirable rippling of the membranes, as is often the case with state-of-the-art spacers. The support elements can have any desired geometry. Circular, triangular, rectangular, or square bases are preferred. The support elements as a whole preferably have the shape of a truncated cone or a truncated pyramid with the preferred bases.

[0020] To maximize the volume flow rate and minimize the flow resistance of the spacer, the support elements have through-holes, preferably with a round or rectangular cross-section. These through-holes can be located on the top and / or side surfaces of the support elements. The base surface of the support elements is preferably completely open and thus completely permeable, apart from the grid threads to which the support elements are attached and the side lines of the base surfaces that connect the grid threads. The through-holes on the top surfaces of the support elements are as large as possible but are also selected to ensure a secure and even support of the filter membranes.

[0021] The area between the grid or mesh threads between the support elements is also preferably completely open and thus permeable.

[0022] In principle, the support elements located on each side of the spacer according to the invention can have different geometries (cross-sectional shape and / or size).

[0023] The support elements according to the invention are arranged on both sides of the spacer at a predetermined distance. Open areas delimited by the grid threads are preferably located between the support elements. The distances between the support elements in the x / y plane of one side of the spacer preferably correspond to the size or edge length of the base area of ​​the support elements. The type and spacing of the support elements do not have to be identical on both sides of the spacer. The preferred arrangement of the support elements on the spacer is indicated in the drawings accompanying this description.

[0024] Preferably, the transition between that region of the support element which forms the support surface for the membrane or membrane carrier and the adjacent regions of the support element which form the boundary of the passages is essentially abrupt. Advantageously, the transition occurs at an angle of at most 135°, in particular at most 110°, preferably of approximately 90°, wherein the information relates to the angle enclosed by the said regions. This measure prevents the supported membrane from conforming, under the influence of pressure, to those regions of the support element which define the boundary of the passages but are not intended to be part of the support surface. The effective support surface for the membrane is thus well-defined and remains constant regardless of the pressure conditions in the membrane module, in particular regardless of any pressure fluctuations.Consequently, the active membrane area, i.e. those areas of the membrane that are not in contact with the support elements but can be freely flowed through, remains constant regardless of the pressure conditions in the membrane module.

[0025] The support elements are preferably arranged in a grid structure, in particular a cross grid, line grid, honeycomb grid, or ring grid structure. The geometry of the grid structure is preferably adapted to the geometry of the membrane module. For example, it is conceivable to use a ring grid structure in a cylindrical membrane module in which the membranes or membrane supports are designed as circular disks. Line grid structures are advantageously suitable for creating linear flow paths. Honeycomb grids are characterized by particularly high stability. Cross grids are advantageously used for essentially rectangular membranes or membrane support surfaces.

[0026] The support elements preferably have a base surface from which the support element emerges as a three-dimensional body. To adapt the arrangement of the individual support elements to the lattice structure of the support element with a view to achieving the lowest possible flow resistance while simultaneously maintaining a sufficiently large contact surface, at least one of the support elements, and preferably all of the support elements, has a rectangular, square, circular, honeycomb, or triangular base surface. Combinations of different base surface shapes are also conceivable.

[0027] For example, support elements with a triangular base are particularly suitable for arrangement in a ring lattice structure. Honeycomb-shaped bases are advantageous for a honeycomb lattice arrangement of support elements.

[0028] The choice of the shape and / or arrangement of the support elements can also depend on the physical properties, such as the viscosity, of the fluid flowing through the membrane module. For example, cylindrical support elements promote laminar flow, whereas edged support elements lead to turbulent flow.

[0029] As explained, the support elements are arranged in several, preferably two, planes. The arrangement is particularly advantageous with an offset grid structure in the respective planes. Such an arrangement is characterized by particularly low flow resistance. The term "arrangement in one plane" in this case refers not only to the arrangement in one plane in the strictly mathematical sense, i.e. in a plane spanned by two straight lines, but also to other two-dimensional arrangements of the support elements, for example in a curved plane, on a cylindrical surface, or the like. The top and bottom sides of the spacer are considered to be two different planes.

[0030] In order to form the spacer as a coherent unit, the support elements of different levels are connected to one another according to a further advantageous embodiment of the invention. The connection can be made either directly or via spacer elements.

[0031] According to a further advantageous embodiment of the invention, the support elements or the spacer consist of and / or are made entirely of metal, ceramic, and / or plastic, in particular of a polymeric plastic, for example, polypropylene. The choice of material for the support elements can depend, among other things, on the application area of ​​the membrane module and / or on the physical and chemical properties of the liquid flowing through the membrane module.

[0032] Depending on the geometry, material and arrangement of the support elements as well as the overall structure of the spacer, different manufacturing processes can be considered.

[0033] One possible method is injection molding using an injection molding machine, in which the material, preferably plastic, is plasticized in an injection unit and injected into an injection mold. The cavity of the mold determines the shape and surface structure of the finished workpiece. Injection molding is particularly suitable for large-scale production and is the preferred manufacturing method for the spacer, which is preferably made of plastic (e.g., polypropylene).

[0034] Alternatively, the spacer can be manufactured by compression molding, particularly by deep drawing or thermoforming. Various variants of compression molding are conceivable, such as compression molding using molds, compression molding using active media such as gases or liquids, or high-speed molding. These processes are particularly advantageous for forming the support elements in different planes from a film-like or thin, plate-like material, with at least parts of the starting material advantageously forming an intermediate layer that connects the support elements to one another.

[0035] Accordingly, stamping processes can also be used in which the support elements of the spacer are formed from a starting workpiece using stamping tools.

[0036] Preferred is production by selective laser sintering, i.e., by a 3D printing process in which spatial structures of the spacer are produced by sintering from a powdered starting material. This process is particularly suitable for complex, particularly multi-layered support inserts with multiple levels.

[0037] Stereolithography processes can also be considered, in which the workpiece is built up layer by layer from computer-generated CAD data using grid points that materialize freely in space. This process is also particularly suitable for complex, particularly multi-layered support inserts that are to be manufactured from a polymer plastic.

[0038] Similarly, a fused deposition modeling process can be used, with which a workpiece is built up layer by layer from a meltable plastic. The process is based on the liquefaction of a wire-shaped plastic material by heating and the subsequent solidification of the material by cooling after application. The material is typically applied by extrusion using a heating nozzle that can be freely moved within the production plane.

[0039] Alternatively, a multijet modeling process is also conceivable, in which the workpiece is built up layer by layer using a print head with several linearly arranged nozzles.

[0040] According to an advantageous embodiment of the invention, the thickness of the support insert (spacer) (between the cover surfaces of the support elements) from front to back is between 0.3 mm and 5 mm, in particular between 1.6 mm and 2.5 mm.

[0041] According to a further advantageous embodiment of the invention, the thickness of a plane is between 0.2 mm and 2 mm, in particular between 0.3 mm and 1 mm, particularly preferably between 0.4 mm and 0.7 mm.

[0042] According to a further advantageous embodiment of the invention, the distance between two adjacent planes (corresponding to the thickness of the grid threads) is between 0.05 mm and 1 mm, in particular between 0.1 mm and 0.4 mm.

[0043] According to a further advantageous embodiment of the invention, the diameter or edge length of the base area of ​​a support element is between 1 mm and 5 mm, in particular between 1.4 mm and 2.5 mm. This also preferably applies to the distances between the support elements on one side.

[0044] According to a further advantageous embodiment of the invention, the diameter or the edge lengths of the through-opening are between 0.2 mm and 4 mm, in particular between 0.5 mm and 1.5 mm.

[0045] According to a further advantageous embodiment of the invention, the distance between adjacent support elements of a plane is between 0.2 mm and 4 mm, in particular between 0.8 and 2 mm.

[0046] The spacer according to the invention can be designed with or without edges. The edges are preferably made of solid material and have no spacer structure. As a rule, no special fastening of the spacer in the membrane module is required. The spacer is preferably manufactured as a precisely fitting insert. Spacers with and without edges are manufactured in a single work step using one of the methods mentioned. The edges of the spacer can be of different widths as required. The thickness of the edges can be the same as, smaller than, or larger than the thickness of the spacer (DS). This depends in particular on the installation situation and the nature of the transition areas in the frame part of the module that accommodates the spacer.

[0047] The spacers according to the invention are characterized by high stability and high flexibility, which makes them advantageously suitable for use in all membrane modules, regardless of their geometry. At the same time, it ensures that the liquid volume flow through the spacer and the membranes adjacent to it is as high as possible, regardless of the discharge pressure of the medium to be treated, and that the flow resistance generated by the spacer is as low as possible, while still providing sufficient support for the often very thin and fragile membranes. Generally speaking, the spacer is designed in detail to match the respective membrane so that the membrane can achieve optimal performance under the specified operating conditions.

[0048] The spacers according to the invention are suitable for all separation or filtration processes that use pressure-driven membrane technology, such as in a plate-and-frame system. Examples include ultrafiltration, nanofiltration, and reverse osmosis. Examples of application areas and technologies include osmotic power, wound modules, and modules in which aeration and humidification of surfaces play a role (e.g., fuel cells), as well as general filtration and mass transfer at interfaces.

[0049] Further objects, advantages, features, and possible applications of the present invention will become apparent from the following description of an exemplary embodiment with reference to the drawings. All described and / or illustrated features, individually or in any meaningful combination, constitute the subject matter of the present invention, regardless of their summary or reference to the patent claims.

[0050] Preferred embodiments of the spacer according to the invention are presented below, without limiting the invention thereto. The features presented and their arrangement can be freely combined, as long as such a combination promotes the purpose of the invention. Fig. 1 shows a schematic representation or schematic diagram of a preferred embodiment of the spacer spanned in a two-dimensional X / Y coordinate system. Fig. 2 shows an isometric view of the spacer according to Fig. 1 with marked elevations (supporting elements) on the front and back. Fig. 3 shows a side view of the spacer according to Fig. 1. Fig. 4 shows an embodiment of the elevations or support elements on the front and back of the spacer.

[0051] Fig. 1 shows a schematic diagram of a preferred embodiment of the spacer 11, which is spanned in an X / Y coordinate system. This is a top view. Here, X denotes support elements above the x / y plane, i.e. in the +z direction in a three-dimensional representation, and O support elements on the underside of the spacer, which extend in the -z direction. The lines a parallel to the x-axis represent grid threads. Two parallel threads are connected to one another via the support elements X or by their boundaries b of the base surfaces of the support elements X, which run parallel to the y-axis. The connection of the line pairs a / a is made in an analogous manner via the base surfaces of the support elements O on the underside of the spacer.

[0052] Fig. Figure 2 shows the spacer 11 with the arrangement of the support elements (X=1 and O=2). The base surfaces 3 and the cover surfaces 4 of these support elements 1, 2 are provided with openings 5, 6. These openings 5, 6 can have any shape (e.g., round, elliptical, square, rectangular). The aim is to achieve an optimal compromise between the largest possible openings to maximize the volume throughput and a remaining cover surface that allows a dimensionally stable support of the membrane. In addition, the side or jacket surfaces 9 can also be equipped with corresponding openings. Finally, the spacer surfaces 7 between the support elements 1, 2 are also permeable, so that the medium to be cleaned or processed (preferably a liquid with a solid content) can pass through the spacer almost unhindered and in all directions (e.g., in directions a and b).

[0053] At the same time, the medium to be processed can flow on each side of the spacer in the x / y direction (directions a and b) and thus be distributed along and across the membrane surfaces. This means that flows in all three dimensions (x / y: along a plane and z-direction flow through the spacer) are possible.

[0054] Fig. 3 shows a side view of the spacer 11 according to Fig. 1. Where DS is the thickness of the spacer including the support elements 1, 2 on the front and back sides and DG is the thickness of the grid threads a and b on which the support elements 1, 2 are arranged.

[0055] Finally, Fig. 4 shows a preferred embodiment of the support elements 1, 2 with openings 5 ​​in the cover surfaces 4 and openings 6 in the base surfaces 3. Furthermore, openings 10 in the side walls or lateral surfaces 9 of the support elements 1, 2 are shown. List of reference symbols 1 support element X above the x / y plane 2 Support element O below the x / y plane 3 Floor space 4 Cover area 5 Opening in base area 3 6 Opening in cover area 4 7 Clearance area (open) 8 edges 9 Shell surface 10 Opening in shell surface 9 11 spacers DS Thickness of the spacer DG Thickness of the grid threads QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 5 254 259 A

[0002] DE 10 2014 100 659 B4 [0002, 0010, 0017] EP 2 292 307 A1

[0005] US 2008 / 0290031 A1

[0008] US 2007 / 0175812 A1

[0009]

Claims

[1] Spacer (11) as a support insert for a membrane module, which has support elements (1, 2) on both sides which are spaced apart from one another, wherein the base surfaces (3) and cover surfaces (4) and optionally also the lateral surfaces (9) of the support elements (1, 2) are provided with openings (5, 6, 10), and wherein the spacer surfaces (7) between the support elements (1, 2) as well as the openings (5, 6, 10) are permeable to a solid, liquid or gaseous medium. [2] Spacer (11) according to claim 1, characterized by that the ratio (area) of closed to open areas of the spacer (11) is not less than 30% : 70%, based on the total surface of the spacer (11). [3] Spacer (11) according to claim 1 or 2, characterized by that the support elements (1, 2) are arranged in a lattice structure. [4] Spacer (11) according to one of claims 1 to 3, characterized bythat the transition between the cover surfaces (4) of the support elements (1, 2) and the spacer surfaces (7) is abrupt, the transition taking place at an angle of at most 135 degrees. [5] Spacer (11) according to one of claims 1 to 4, characterized by that the support elements (1, 2) have a rectangular, square, circular, honeycomb-shaped or triangular base area (3). [6] Spacer (11) according to one of claims 1 to 5, characterized by that the openings (5, 6, 10) of the support elements (1, 2) have a round or rectangular cross-section. [7] Spacer (11) according to one of claims 1 to 6, characterized by that the support elements (1, 2) on the front and back of the spacer (11) have a lattice structure offset from one another. [8] Spacer (11) according to one of claims 1 to 7, characterized by that the spacer (1) is made of metal, ceramic or plastic, in particular polypropylene. [9] Use of a spacer (11) according to one of claims 1 to 8 in a membrane module, in particular in a pressure-operated membrane module. [10] Membrane module, in particular pressure-operated membrane module, which has a spacer (11) according to one of claims 1 to 8. [11] Method for producing a spacer (11) according to one of claims 1 to 8, by injection molding, laser sintering, stereolithography, fused deposition modeling, multi-jet modeling, pressure forming, deep drawing or embossing.

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