FILTER MEDIUM COMPRISING A REINFORCED NONWOVEN FABRIC

Description

[0001] The present invention relates to a filter medium comprising a reinforced nonwoven fabric, a process for its production and its use.

[0002] Reinforced nonwovens are used in many areas. One area of application is for filters, for example for dust separation in various industries such as waste incineration, the coal and power industry, mining, foundry applications or graphite production. The filter media used can consist of several layers, for example three layers which are bonded together by mechanical consolidation (e.g. needling or hydroentanglement). The following three layers are given as examples: 1) a first nonwoven layer as the filter layer, 2) a reinforcing layer, e.g. a fabric insert, for mechanical reinforcement, in particular for cleaning by means of compressed air blast, 3) a second nonwoven layer as a protective layer for the reinforcing layer.Important parameters of a filter medium are the dust separation performance, the pressure loss, as well as the mechanical, chemical and thermal resistance of the material.

[0003] WO 2017 / 127638 A1 describes a filter medium comprising a mixture of filter media fibers comprising oxidized polyacrylonitrile fibers and fibers of at least one other polymer.

[0004] US 4 444 574 A describes a filter material made of polyacrylonitrile fibers which are partially carbonized.

[0005] US 4 181 513 A describes an adsorptive filter material comprising an adsorptive layer of activated carbon fibers and a reinforcing layer of fibers

[0006] EP 0 962 243 A1 describes a filter medium which has a filter fabric made of glass fibers which is covered by needling with temperature-resistant, polymeric staple fibers.

[0007] EP 1 862 208 A1 describes a filter medium comprising a supporting fabric containing basalt fibers, wherein at least one side of the supporting fabric is covered with staple fibers.

[0008] For demanding conditions, textile filter media made of high-performance polymer fibers, particularly polytetrafluoroethylene (PTFE, Teflon), m-aramid, and polyimide, are used. Due to their thermal resistance, these filter media can only be used up to approximately 260 °C. Although PTFE has a slightly higher thermal resistance, it is not used at temperatures higher than 260 °C due to the evolution of toxic gases and the strong creep that leads to mechanical failure of the filter medium.

[0009] To be able to use textile filters at temperatures higher than 260 °C, for example during potential temperature peaks, a reinforced nonwoven fabric is required that can withstand temperatures of more than 260 °C. This applies to both the nonwoven layer(s) and the reinforcement layer of the reinforced nonwoven fabric.

[0010] Static charging of non-conductive filter media can lead to sparking and flying sparks, which in turn can damage the filter structure. Thermal hotspots can also cause such damage. Therefore, there is a need for a reinforced nonwoven fabric with at least one thermally and / or electrically conductive layer.

[0011] Reinforced nonwovens are also used for filtering liquid substances. Important parameters here are, in particular, the chemical resistance and corrosion resistance of the reinforced nonwovens used. One application area where chemical resistance is critical is the filtration of strongly acidic or strongly alkaline substances.

[0012] The object of the present invention is therefore to provide a filter medium that can be used, in particular, at temperatures greater than 260°C. Furthermore, this filter medium should be electrically and / or thermally conductive, exhibit chemical and corrosion resistance, and be non-flammable. Furthermore, the filter medium should be suitable for filtering both gases and liquids.

[0013] Within the scope of the present invention, this object is achieved by providing a filter medium comprising a reinforced nonwoven fabric, wherein the nonwoven fabric has at least one nonwoven layer consisting of pre-oxidized polyacrylonitrile (PAN) and at least one reinforcement layer, wherein the reinforcement layer has a first side and a second side, and wherein the reinforcement layer is covered by the first side and / or the second side of the at least one nonwoven layer, and wherein a material of the at least one reinforcement layer (20) is selected from the group consisting of metal fibers, metal wires, pre-oxidized PAN fibers, partially carbonized PAN fibers or carbon fibers.

[0014] According to the invention, it was found that if at least one nonwoven layer of the reinforced nonwoven fabric consists of pre-oxidized PAN, the nonwoven fabric - and thus also the filter medium - has a temperature resistance of more than 260 °C. This property is enhanced if a further

[0015] The pre-oxidized PAN is subjected to a thermal treatment under the exclusion of oxygen and a protective gas atmosphere. This thermal treatment can produce partially carbonized PAN or carbonized PAN. Furthermore, the reinforced nonwoven fabric—and thus the filter medium—can then exhibit higher electrical and thermal conductivity than conventional filter materials. The pre-oxidized PAN, partially carbonized PAN, or carbonized PAN is preferably used in fiber form, with the carbonized PAN then being in the form of carbon fibers.

[0016] Partially carbonized or carbonized reinforced nonwovens are characterized not only by their media resistance but also by their electrical conductivity. Therefore, they can also be used as electrode materials for electrochemical processes such as energy storage or electrolysis. The textile structure of the nonwoven can be tailored by selecting the process and the manufacturing parameters. Compared to other common electrode materials, reinforced textiles based on carbon fibers can be manufactured relatively cost-effectively as roll goods.

[0017] PAN is the polymer of acrylonitrile and is widely used as a textile fiber. It can be in the form of a homopolymer or a copolymer. Copolymers typically contain more than 85% acrylonitrile and a comonomer such as methyl methacrylate or vinyl chloride.

[0018] Pre-oxidized PAN means that PAN has been heat-treated in the presence of oxygen, typically at 200–300°C. Other terms for pre-oxidized PAN are thermally stabilized PAN or oxidized PAN. Pre-oxidized PAN is commercially available as a fiber, for example as PANOX ®< from SGL TECHNOLOGIES GmbH. PANOX ®< is an oxidized, thermally stabilized polyacrylonitrile (PAN) fiber that, due to its chemical structure, does not burn, melt, soften, or drip. With a LOI (limiting oxygen index) value of over 50%, pre-oxidized PAN performs significantly better than other organic fibers and corresponds to combustion class Sa according to DIN 66083. Flammability exists when a material continues to burn after ignition, even when the ignition source is removed. Pre-oxidized PAN also exhibits high temperature and chemical resistance.The carbon content of pre-oxidized PAN is typically between 60% and 65%.

[0019] Partially carbonized PAN means that pre-oxidized PAN is subjected to a heat treatment in a protective gas atmosphere between 300 °C and 1000 °C. The carbon content of partially carbonized PAN ranges from more than 65% to less than 92%. When pre-oxidized PAN is subjected to a heat treatment in a protective gas atmosphere above 1000 °C, carbonized PAN is created, i.e., carbon fibers with a carbon content of more than 92%.

[0020] Instead of PAN, especially PAN fibers, cellulose fibers can also be used as precursors for the production of partially carbonized fibers or carbonized fibers (carbon fibers). These cellulose-based fibers can also be contained in at least one nonwoven layer and / or at least one reinforcement layer of the reinforced nonwoven fabric of the filter medium. It is also possible to use partially carbonized or carbonized fibers, for the production of which a mixture of pre-oxidized PAN fibers and cellulose fibers is used.

[0021] The filter medium according to the invention can be used for filtering both gases and liquids.

[0022] The filter medium according to the invention preferably has a flat or round shape. The round shape can be in the form of a tube, hose, or cylindrical shape (hollow cylinder).

[0023] According to one embodiment of the present invention, the at least one reinforcing layer of the reinforced nonwoven fabric of the filter medium is a woven fabric, a scrim, a warp-knitted fabric, a mesh, or a grid, whereby these reinforcing layers can be produced using continuous fibers (filaments) or yarns. This type of reinforcing layer increases the mechanical strength of the reinforced nonwoven fabric. When using at least one such reinforcing layer, in particular in the form of a mesh, warp-knitted fabric, or a mesh, the reinforced nonwoven layer can be designed in a round, stretchable, or elastic shape, which allows for easier use of the filter medium. For example, this elastic filter medium can be more easily slipped over support structures or shrunk into a partially carbonized or carbonized reinforced nonwoven fabric through heat treatment.The stretchability is an additional advantage in the production of the partially carbonized or carbonized filter medium, since the shrinkage of the nonwoven layer can be compensated even better during partial carbonization or carbonization.

[0024] Woven fabrics and non-woven fabrics are made from continuous fibers or yarns. In non-woven fabrics, the fiber strands are laid down and then knitted using a thread or bonded with a plastic. The fibers can be all aligned in one direction (unidirectional) or as a multi-layer system in which the different layers are laid at defined angles (multiaxial).

[0025] Fabrics consist of perpendicularly interlaced thread systems (warp and weft). Various weaves, such as plain weave or twill weave, are possible, allowing for adjustment of strength, drapability, or surface structure.

[0026] Braided structures are created by regularly interlacing several fiber or yarn strands. Unlike weaving, the threads are not fed perpendicular to the main product direction.

[0027] Knitted and warp-knitted fabrics are textile fabrics, also known as knitwear, characterized by their flexible and elastic structure. Knits are created by forming loops from horizontally placed individual threads. Warp-knitted fabrics also use individual threads, but the loops are formed by simultaneously moving needles.

[0028] A grid typically refers to a net-like knitted fabric. Fine- or coarse-mesh nets or knitted fabrics with various structures are possible. Grids are further described by the orientation of the individual ribs, the enclosed hole area, the respective angles of the ribs to each other, and the width of the ribs. All shapes are possible as reinforcement within the scope of the invention.

[0029] According to the present invention, a material of the reinforcement layer of the reinforced nonwoven fabric of the filter medium is a material selected from the group consisting of metal fibers, metal wires, pre-oxidized PAN fibers, partially carbonized PAN fibers, or carbonized PAN fibers (carbon fibers). The material used for this reinforcement layer is preferably pre-oxidized PAN fibers, partially carbonized PAN fibers, or carbon fibers, more preferably partially carbonized PAN fibers or carbon fibers, and particularly preferably carbon fibers. These materials have the advantage of being temperature-resistant, even at temperatures greater than 260°C, and of exhibiting high chemical resistance. If metal fibers or metal wires are used as at least one reinforcement layer of the reinforced nonwoven fabric, pleated filter structures can be produced.

[0030] The filter medium according to the invention containing a reinforced nonwoven fabric preferably comprises at least one nonwoven layer consisting of pre-oxidized PAN, which has been partially carbonized or carbonized, preferably partially carbonized. In this case, a material of the reinforcement layer of the reinforced nonwoven fabric of the filter medium is a material selected from the group consisting of metal fibers, metal wires, pre-oxidized PAN fibers, partially carbonized PAN fibers, or carbonized PAN fibers (carbon fibers). The inventor has conducted a series of tests with reinforced nonwoven fabrics in which at least one nonwoven layer is carbonized PAN. It was found that these embodiments according to the invention exhibit significantly higher temperature resistance than known polymeric high-performance fibers, such as PTFE, m-aramid, or polyimide.When using such a filter medium according to the invention at higher temperatures, in particular at temperatures of at least up to 260 °C, it is possible to filter the medium to be filtered (gas or liquid) at temperatures of at least 260 °C and to subject it to a catalysis process (e.g. denitrification) subsequently or during the filtering process. This catalysis process typically requires higher temperatures than the temperature resistance of common filter materials. Therefore, the filter medium previously had to be cooled for filtration and warmed up again for denitrification. With the nonwoven fabric according to the invention, this cooling and warming step is no longer necessary, thereby saving energy. In addition, the filter medium according to the invention can advantageously be used as a filter upstream of a heat exchanger, since the filter can prevent contamination of the heat exchanger and thus improve its service life and efficiency.

[0031] More preferably, pre-oxidized PAN, which has been at least partially carbonized, preferably carbonized, also represents the reinforcement layer of the reinforced nonwoven fabric of the filter medium according to the invention, so that at least one nonwoven layer and at least one reinforcement layer of the reinforced nonwoven fabric are made of partially carbonized PAN, preferably of carbonized PAN (carbon fibers). This allows the reinforced nonwoven fabric to have high electrical and thermal conductivity. By carbonizing both at least one nonwoven layer and the at least one reinforcement layer, the reinforcement layer is also temperature-resistant at higher temperatures, thereby enabling aging of the reinforced nonwoven fabric at 280°C in air for 5 days to result in a mass loss of no more than 5%. Furthermore, the filter medium exhibits very high chemical resistance and is extremely corrosion-resistant.Furthermore, this filter medium is non-flammable and shows no visible creep behavior.

[0032] The reinforced nonwoven fabric of the filter medium according to the invention preferably has at least two nonwoven layers arranged on the first side (one side) of the reinforcement layer, each of these nonwoven layers being made of a different material and thus having different properties. For example, if two such nonwoven layers are used, one nonwoven layer may be made of fibers with a larger average diameter than the fibers of the other nonwoven layer, or both nonwoven layers may have different densities. If such a reinforced nonwoven fabric is used in a filter medium, these different nonwoven layers can be used to filter different components and also to control the penetration depth of particles into the nonwovens.

[0033] According to a further preferred embodiment of the present invention, at least one nonwoven layer and / or at least one reinforcement layer, preferably at least one nonwoven layer, of the filter medium can comprise an active component. The active component can be, for example, a catalyst and / or activated carbon. Activated carbon refers to a carbon material with a high specific surface area. This can be used to adsorb pollutants, such as mercury or toxic organic solvents, or as a support for catalysts. The active component can, through combinatorial action, supplement mechanical filtration with chemical adsorption or reactive, catalytic purification. For example, the filtration of flue gas can be combined with catalytic denitrification.The structure of the fleece layer also allows the residence time of media (e.g. liquids or gases) in the filter to be controlled in order to generate the necessary reaction time for the catalytic reaction.

[0034] If fibers, preferably pre-oxidized PAN fibers, are used to produce the nonwoven layers or reinforcement layers, these fibers have an average fiber diameter in a range from 200 nm to 35 µm, preferably in a range from 300 nm to 30 µm, particularly preferably in a range from 400 nm to 25 µm, and most particularly preferably in a range from 500 nm to 20 µm. Carbon fibers typically have an average fiber diameter of 5 to 10 µm. The average fiber diameter is determined by measuring with the aid of a microscope. The separation efficiency can be controlled via the average fiber diameter.

[0035] In yet another preferred embodiment of the present invention, the reinforced nonwoven fabric of the filter medium comprises at least one electrically conductive nonwoven layer and / or at least one electrically conductive reinforcement layer and is configured to enable electrical discharge and / or heating of the filter by applied electrical current. When used as a filter, the discharge can be enabled by the filter having an electrical connection to the reinforced nonwoven fabric for electrically discharging the nonwoven fabric. This can prevent electrical charging of the reinforced nonwoven fabric and reduce possible flying sparks, which could have a damaging effect on the filter structure. Heating can be enabled by the filter having an electrical heating circuit for heating the reinforced nonwoven fabric by means of an electrical current passed through the reinforced nonwoven fabric.Heating the reinforced nonwoven fabric allows the filter to be cleaned. Furthermore, heating can limit or prevent contamination due to condensation of components. Furthermore, the filter can also be used to heat the medium to be filtered, for example, liquids. Advantageously, at least one nonwoven layer and at least one reinforcement layer are electrically conductive. This electrical conductivity means that the reinforced nonwoven fabric can be used not only in a filter medium but also as an electrode.

[0036] The reinforced nonwoven fabric of the filter medium according to the invention preferably has a tear strength of at least 10 dN / 5 cm, preferably of at least 50 dN / 5 cm, particularly preferably of at least 100 dN / 5 cm and / or an air permeability of at least 20 L / (dm 2 < *min) and at most 1000 L / (dm 2 < *m) at 200 Pa. The tear strength is determined according to DIN EN 29073-3:1992-08 (Test method for nonwovens, Part 3). This tear strength increases the mechanical stability of the filter medium due to increased dimensional stability and leads to longer service lives because more cleaning cycles can be carried out. The air permeability is determined according to DIN EN ISO 9073-15:2008-08 (Test method for nonwovens, Part 15).

[0037] According to a further embodiment of the present invention, the reinforced nonwoven fabric of the filter medium comprises at least one nonwoven layer with a basis weight of at least 50 g / m 2 and at most 1000 g / m 2 and / or at least one reinforcement layer with a basis weight of at least 25 g / m 2 and at most 1000 g / m 2 . The thickness of the filter medium can be between 0.2 mm and 10 mm. The basis weight is determined according to DIN EN 29073-1:1992-08 (Test method for nonwovens, Part 1) and the thickness is determined according to DIN EN ISO 9073-2:1997-02 (Test method for nonwovens, Part 2).

[0038] According to yet another preferred embodiment of the present invention, a coating is applied to at least one nonwoven layer of the filter medium. This coating can preferably be applied in the form of fibers, membranes, or particles. The coating can be applied to one side or both sides of the reinforced nonwoven fabric. The coating can comprise fibers with a fiber diameter of 50 nm to 5000 nm, preferably 200 nm to 1000 nm. If a coating is applied with particles, these particles have an average particle size between 10 nm and 100 µm. The average particle size is determined by laser granulometry (ISO 13320). A coating can also be applied with a membrane, wherein the thickness of the membrane is less than 100 µm.Preferably, the coating comprises a material selected from the group consisting of fluoropolymer fibers, PAN fibers, ceramic fibers, PTFE membranes, carbon black, or other carbon particles such as graphite or ceramic particles. Applying a coating to at least one nonwoven layer can increase wear resistance and / or reduce abrasion, as well as increase the separation efficiency.

[0039] Within the scope of the invention, it is possible for the individual embodiments of the filter medium mentioned to be combined with one another.

[0040] The filter medium according to the invention is suitable for filtering liquids or gases.

[0041] The filter media according to the invention, in particular the partially carbonized and carbonized media with a reinforcement layer selected from the group consisting of pre-oxidized PAN fibers, partially carbonized PAN fibers, or carbon fibers, exhibit very good chemical resistance in various media. For example, inorganic and / or oxidizing inorganic acids, such as hydrochloric acid (37%), sulfuric acid (80%), or nitric acid (65%), as well as in alkaline media such as ammonia (28%), the filter media are not attacked or degraded. Weight loss after exposure to room temperature or reflux for 100 hours shows no measurable weight loss.

[0042] Furthermore, the filter media according to the invention are highly water and oil resistant. All filter media according to the invention exhibit no measurable weight loss at room temperature or under reflux for 100 hours. The oil resistance up to 200°C is particularly surprising. Furthermore, the filter media according to the invention are suitable for cold applications. Contact with media or cold mixtures in the temperature range down to -190°C shows no embrittlement or mechanical damage to the material, even after mechanical stress based on ISO 974 (Plastics - Determination of the brittleness temperature by impact).

[0043] In particular, the filter media according to the invention are suitable for filtering gases at a temperature of at least up to 260 °C, wherein the filter medium is heat-resistant and non-flammable up to at least 260 °C, or the filter media can be used for filtering liquid substances, in particular chemically reactive substances.

[0044] The present invention also relates to a process for producing the filter media according to the invention comprising the steps: Providing at least one nonwoven layer consisting of pre-oxidized PAN and at least one reinforcement layer, wherein the reinforcement layer has a first side and a second side; wherein a material of the at least one reinforcement layer (20) is selected from the group consisting of metal fibers, metal wires, pre-oxidized PAN fibers, partially carbonized PAN fibers, or carbon fibers; and consolidating the at least one nonwoven layer consisting of pre-oxidized PAN to the reinforcement layer such that the reinforcement layer is covered by at least one of the first side and / or the second side of the at least one nonwoven layer.

[0045] The term "bonding" describes the assembly of certain components into a reinforced nonwoven fabric using, for example, needling or hydroentanglement.

[0046] A temperature treatment can be carried out either before or after solidification, preferably after solidification.

[0047] Such a temperature treatment preferably takes place in a range from 260°C to 900°C, more preferably in a range from 500°C to 900°C. If a metal fiber or a metal wire is used to produce the reinforcement layer, the temperature treatment advantageously takes place before consolidation. However, if the same material is used for at least one nonwoven layer and at least one reinforcement layer, the temperature treatment advantageously takes place after consolidation.

[0048] With the above-mentioned method, the filter media according to the invention can be produced in a flat form as well as in a round form, such as a tube, hose or hollow cylinder.

[0049] The present invention will now be further described by way of illustrative but non-limiting examples with reference to the drawings. Example:

[0050] To produce a filter medium, a flat reinforced nonwoven fabric was manufactured using a grid consisting of carbon fibers as a reinforcement layer, with a basis weight of approximately 150 g / m². The ribs in the warp and weft directions had a 90° angle and were made of carbon fibers in both directions. The thread spacing (relative to the center of the ribs) was approximately 25 mm. The resulting grid opening / distance between the sides of the ribs was approximately 23 mm.

[0051] Furthermore, a nonwoven layer consisting of pre-oxidized PAN (SGL - PANOX; C63-1.7 / 1.39-A110) was produced by hydroentanglement (PANOX) and then bonded to both sides of the above reinforcement layer by water jet. This resulted in a reinforced nonwoven with a basis weight of approximately 800 g / m², a thickness of 3.5 mm (measured on the grid ribs), and a tensile strength of 60 dN / cm.

[0052] The figures are schematic and serve to illustrate specific embodiments of the present invention.

[0053] In this regard, directional terms such as "first side," "second side," etc., are used without reference to the orientation of the described figure(s). For a filter application, these terms are preferably, but not necessarily, described in connection with any flow direction of a substance to be filtered. Because components of embodiments can be positioned in a number of different orientations, directional terms are used for illustrative purposes only and should not be considered limiting in any way. In particular, in some embodiments, there may be no "substance to be filtered" (e.g., this could be the case when using the nonwoven fabric as an electrode material). In such cases, descriptions such as "first side," "second side" are to be understood as any orientation.

[0054] The figures show various embodiments of the reinforced nonwoven fabric according to the invention: Figure 1 shows a cross-section of a reinforced nonwoven fabric according to one embodiment, Figure 2 shows a cross section of a reinforced nonwoven fabric according to another embodiment, Figure 3 shows a cross-section of a reinforced nonwoven fabric according to yet another embodiment, Figure 4 shows a cross section of a reinforced nonwoven fabric according to yet another embodiment.

[0055] The individual figures are discussed in more detail below.

[0056] Figure 1shows a cross-section of a reinforced nonwoven fabric according to one embodiment. The reinforced nonwoven fabric (1) has at least one nonwoven layer (12) consisting of pre-oxidized PAN and a reinforcing layer (20). The reinforcing layer (20) has a first side (22) and a second side (24), wherein the reinforcing layer (20) is covered by at least one of the first side (22) and the second side (24) of the at least one nonwoven layer (12). Preferably, the first side (22) is arranged towards a flow direction of a substance to be filtered and the second side (24) is arranged away from the flow direction of the substance to be filtered.

[0057] Figure 2 shows a further preferred embodiment of the reinforced nonwoven fabric, in which the reinforcing layer (20) covers both the first side (22) and the second side (24) of the at least one nonwoven layer (12).

[0058] According to one embodiment, the reinforced nonwoven fabric may comprise at least two nonwoven layers (12, 14), wherein a first nonwoven layer (12) may be arranged on the first side (22) of the reinforcing layer (20) and a second nonwoven layer (14) may be arranged on the second side (24) of the reinforcing layer (20), as in Figure 3 shown.

[0059] Figure 4shows a further embodiment of the reinforced nonwoven fabric, which has at least three nonwoven layers (12, 14, 16), wherein at least two nonwoven layers (12, 16) are arranged on the first side (22). In this case, each of the nonwoven layers (12, 16) arranged on the first side (22) can have different material properties. When using the reinforced nonwoven fabric as a filter, each of the nonwoven layers (12, 16) arranged on the first side (22) can be suitable for filtering different components. Advantageously, the nonwoven layers (12, 16) arranged on the first side (22) can each be suitable for filtering components above a certain size. This can make it possible to filter the substance to be filtered gradually according to the size of the components. LIST OF REFERENCE SYMBOLS

[0060] 1 reinforced nonwoven fabric 12, 14, 16 nonwoven layer made of pre-oxidized PAN 20 reinforcement layer 22 first side of the reinforcement layer 24 second side of the reinforcement layer

Claims

1. A filter medium comprising a reinforced nonwoven material (1), wherein the nonwoven material comprises at least one nonwoven layer (12, 14, 16) consisting of preoxidized polyacrylonitrile (PAN) and at least one reinforcing layer (20), wherein the at least one reinforcing layer (20) comprises a first side (22) and a second side (24), wherein the at least one reinforcing layer (20) is covered on the first side (22) and / or the second side (24) by the at least one nonwoven layer (12, 14, 16), and wherein a material of the at least one reinforcing layer (20) is selected from the group consisting of metal fibers, metal wires, preoxidized PAN fibers, partially carbonized PAN fibers or carbon fibers.

2. The filter medium according to claim 1, wherein the filter medium comprises a flat or round shape.

3. The filter medium according to claim 1 or 2, wherein the at least one reinforcing layer (20) is a woven material, a laid material, a warp-knitted material, a knitted material, a braid or a grid.

4. The filter medium according to any one of the preceding claims, wherein the at least one nonwoven layer (12, 14, 16) and / or the at least one preoxidized PAN-based reinforcing layer (20) is partially carbonized or carbonized.

5. The filter medium according to claim 1, wherein the reinforced nonwoven material (1) comprises at least two nonwoven layers (12, 14), wherein a first nonwoven layer (12) is arranged on the first side (22) of the reinforcing layer (20) and a second nonwoven layer (14) is arranged on the second side (24) of the reinforcing layer (20).

6. The filter medium according to claim 1, wherein at least two nonwoven layers (12, 16) are arranged on the first side (22) of the reinforcing layer (20), wherein each of the nonwoven layers (12, 16) arranged on the first side (22) of the reinforcing layer has different material properties.

7. The filter medium according to claim 1, wherein at least one of the reinforcing layers (20) comprises an active component.

8. The filter medium according to claim 1, wherein at least one of the nonwoven layers (12, 14, 16) comprises fibers having an average fiber diameter which is in a range from 200 nm to 35 µm.

9. The filter medium according to claim 1, wherein the reinforced nonwoven material (1) comprises at least one electrically conductive nonwoven layer (12, 14, 16) and / or at least one electrically conductive reinforcing layer (20), and is configured in such a way that an electrical discharge and / or a heating of the filter is made possible by an applied electrical current.

10. The filter medium according to claim 1, wherein the reinforced nonwoven material (1) has a tensile strength of at least 10 dN / 5cm according to DIN EN 29073-3:1992-08, and / or an air permeability of at least 20 L / (dm2*min) and at most 1000 L / (dm2*min) at 200 Pa according to DIN EN ISO 9073-15:2008-08.

11. The filter medium according to claim 1, wherein the mass per unit area of the at least one nonwoven layer (12, 14, 16) is at least 50 g / m2 and at most 1000 g / m2 and / or the mass per unit area of the reinforcing layer (20) is at least 25 g / m2 and at most 1000 g / m2.

12. The filter medium according to claim 1, wherein a coating is applied to at least one of the nonwoven layers (12, 14, 16).

13. Use of a filter medium according to any one of claims 1 to 12 for filtering gases, wherein the filter medium is suitable for filtering gases having a temperature of at least up to 260°C, and the filter medium is heat-resistant and non-flammable up to at least 260°C.

14. A method of manufacturing a filter medium according to any one of claims 1 to 13, comprising the steps of: - providing at least one nonwoven layer (12, 14, 16) consisting of preoxidized PAN and at least one reinforcing layer (20), wherein the at least one reinforcing layer (20) comprises a first side (22) and a second side (24), and wherein a material of the at least one reinforcing layer (20) is selected from the group consisting of metal fibers, metal wires, preoxidized PAN fibers, partially carbonized PAN fibers or carbon fibers and - strengthening the at least one non-woven layer (12, 14, 16) consisting of preoxidized PAN with the at least one reinforcing layer (20), so that the at least one reinforcing layer (20) is covered on the first side (22) and / or the second side (24) by the at least one non-woven layer (12, 14, 16).

15. The method of manufacturing a filter medium according to claim 14, wherein a step of temperature treatment is carried out before or after the step of strengthening, preferably after the step of strengthening.