Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
  • B01D39/14—Other self-supporting filtering material ; Other filtering material
  • B01D39/20—Other self-supporting filtering material ; Other filtering material of inorganic material, e.g. asbestos paper, metallic filtering material of non-woven wires
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
  • B01D39/14—Other self-supporting filtering material ; Other filtering material
  • B01D39/20—Other self-supporting filtering material ; Other filtering material of inorganic material, e.g. asbestos paper, metallic filtering material of non-woven wires
  • B01D39/2068—Other inorganic materials, e.g. ceramics
  • B01D39/2072—Other inorganic materials, e.g. ceramics the material being particulate or granular
  • B01D39/2079—Other inorganic materials, e.g. ceramics the material being particulate or granular otherwise bonded, e.g. by resins

Definitions

• the present invention relates to filters with a graded structure, made of sinterable material from at least two layers of different pore sizes, and to a method for producing the same and its use.
• a filter of graduated construction made of sinterable material from at least two layers of different pore sizes, with a first layer having a pore size of at least 0.005 ⁇ m and being made of metal oxide or mixtures thereof, and the further, with the first Layer connected layer is not made of metal oxide.
• the further layer has larger pores.
• the filters according to the invention advantageously have defined transitions between the at least two layers present.
• a defined transition in the sense of the invention means that the transition region between in particular the first and the further layer is narrow, and its width can be adjusted.
• the width of the transition region between the first (metal oxide) layer and the further layer, or in other words, the depth of penetration of the metal oxide material into the large-pore further layer is preferably in a range from 1-5 pore layers, more preferably 2 pore layers.
• the pore size of the first layer is preferably 1/3 to 1/6 of that of the further layer.
• Graded filters constructed in this way have flow rates of 1 to 1,500 m 3 / hm 2 for gases, for example air, at a differential pressure of approximately 100 millibars. For liquids, for example water, the same differential pressure flow rates result in about 10 to 30m 3 / hm 2 .
• the permeability coefficient is approximately 0.002 x 10 "12 to 3 x 10 " 12 m 2 with a total layer thickness of less than 100 ⁇ m, measured according to DIN ISO 4022. They have a bubble point pressure in a range of approximately 8 x 10 6 to 2 x 10 3 Pa, particularly preferably in one Range of approximately 8.6 x 10 6 to 1.72 x 10 3 Pa, determined according to DIN 30 911.
• the metal oxides used are easy to process because they do not tend to ignite or oxidize in finely divided form. They are also available as mass products. The graded filters according to the invention can therefore be manufactured inexpensively.
• 'Sinterable materials' which can be used for the further layer connected to the first layer are understood to mean powders or fibers or wires, made from metals, ceramics and / or plastics, and metal oxides can also be added to these.
• Usable metallic materials are not only powders made of pure metals, but also powders made of metal alloys and / or powder mixtures made of different metals and metal alloys. These include in particular steels, preferably chromium-nickel steels, bronzes, nickel-based alloys such as Hastalloy, Inconel or the like, it being possible for powder mixtures to also contain high-melting constituents, such as platinum or the like.
• the metal powder used and its particle size depend on the respective application. Preferred powders are the alloys 316 L, 304 L, Inconel 600, Inconel 625, Monel and Hastalloy B, X and C.
• the first layer of the graded filters preferably has a pore size in a range from approximately 0.01 ⁇ m to approximately 1 ⁇ m, preferably 0.05 ⁇ m to 0.6 ⁇ m.
• the layer thickness of this first layer should be in a range from approximately 0.5 to 50 ⁇ m, preferably 0.5 to 10 ⁇ m. Because the thinner the first layer, the lower the flow resistance for gases and / or liquids that occurs with the small pore size that is present.
• the graded filters according to the invention preferably have at least three layers.
• the first layer is advantageously made of metal oxide
• the another (second) layer consists of a preferably metallic material and is also fine-pored.
• the layers are applied to a coarse-porous carrier body (third layer), which is also made of preferably metallic materials.
• the further (second) layer has a layer thickness in a range of max. 5 to 500 ⁇ m, preferably 5 to 300 ⁇ m, even more preferably 5 to 20 ⁇ m.
• the metallic powders used for the production of the further (second) layer still have particle sizes which can be used without problems in the production of the layer.
• the grain size and thus the diameter of the powder particles that can be used here are in a range from about 0.05 ⁇ m to 150 ⁇ m, preferably in a range from 0.5 ⁇ m to 100 ⁇ m, even more preferably in a range from 0.5 ⁇ m to 6 ⁇ m.
• the metal oxide powders used to produce the first layer have particle sizes with a grain size in a range from about 0.001 ⁇ m to 0.1 ⁇ m, preferably 0.01 to 0.3 ⁇ m.
• the filters of graded construction preferably have a pore size that decreases in the direction of flow, ie the layer made of metal oxide is arranged on the inflow side.
• the metal oxide or mixtures thereof is preferably selected from a group comprising reducible and / or non-reducible metal oxides.
• Reducible oxides for the purposes of the present invention are metal oxides which can be reduced to the respective metal in a reducing hydrogen atmosphere.
• Metal oxides or mixtures thereof are preferably selected from a group comprising AgO, CuO, Cu 2 0, Fe 2 0 3 , Fe 3 0 4 and / or NiO (see claim 6).
• oxides which are difficult to reduce in the sense of the present invention are oxides which cannot be reduced with technical atmospheres, in particular hydrogen.
• Oxides are preferably selected from a group comprising Ti0 2 , Al 2 0 3 , Zr0 2 , Cr 2 0 3 , MgO, CaO and / or Si0 2 . If the first layer of the filters according to the invention is made from metal oxides that are difficult to reduce, then after the sintering process it consists of the metal oxide in question. The particle shape of the non-reducible metal oxides used is retained in the sintering process.
• a mixed oxide layer is preferably arranged between the first layer and the further layer. This can be formed by solid-state reactions with the oxide skin of the second metal layer, which ensures that the oxide layer adheres to the substrate. The filter properties remain unaffected.
• Such graded filters with a first layer of non-reducible metal oxides have excellent properties with regard to flow resistance due to the precisely defined transition areas, on the other hand they also have excellent values in terms of ductility and impact resistance, for which the metallic support body (third layer) is essentially responsible. In this way it is possible to provide durable and backwashable graded filters.
• Their tensile strength is preferably in a range from about 5 to 500 N / mm 2 , preferably 20 to 400 N / mm 2 , measured in accordance with DIN EN 309116.
• the filters according to the invention Backwashing pressures of up to 8 bar possible, which cannot be achieved with plastic membranes.
• the present invention relates to a method for producing the filter of the invention with a gradient structure, a suspension containing metal oxides being applied to an existing layer in a first step and then sintered in a second step.
• the layer can be applied in the form of casting, screen printing or immersion in the suspension or spraying. However, the application is preferably carried out by spraying on the suspension containing metal oxide.
• the already existing layer is preferably produced by spraying on a suspension containing sinterable materials by subsequent sintering thereof.
• the method used for the application of the suspension containing metal oxide or sinterable materials is called 'wet powder spraying' here.
• a suspension of the respective metal oxide or sinterable material is used, which also comprises solvents and other auxiliary substances.
• the mixing ratio between the metal oxide or sinterable material and the solvent used in the suspension is preferably about 2: 3.
• the suspension can be applied with a modified spray gun that is mounted on an X-Y movement system. After the suspension has been applied, the solvent is evaporated or it evaporates on its own due to its low vapor pressure, and the respective layer is then sintered.
• the sintering process essentially comprises two steps, on the one hand debinding of the binder used in a first step and the actual sintering process in the further step.
• the debinding process itself is not limited to specific time-temperature programs.
• the green body is gradually heated to a temperature in a range from 280 to 420 ° C. at a rate of 3 to 10 ° C./min and, depending on the size of the filter body, kept at this temperature for a certain period of time until the binder is completely removed.
• the graded sintered body is then gradually heated further until the necessary sintering temperatures of 800 ° C to 1,250 ° C are reached, which depend on the material and its grain size.
• Both the debinding process and the actual sintering process are carried out in the case of the use of reducible oxides under protective gas (such as H 2 , N 2 , Ar and / or a mixture of these) or in vacuo.
• protective gas such as H 2 , N 2 , Ar and / or a mixture of these
• the existing layer is preferably mechanically smoothed before the first layer is applied.
• the smoothing can be done by mechanical pressing using a calender, for example. Calibration by simple rolling can also be provided.
• the carrier body can also be mechanically smoothed before the existing layer is applied. Mechanical smoothing has the advantage that it improves the adhesive properties of the first layer on the further layer.
• the suspension containing metal oxide preferably further comprises solvents, binders, stabilizers and / or Dispersant.
• Particularly preferred solvents are selected from a group comprising water, methanol, ethanol, isopropanol, terpenes, C 2 -C 5 -alkenes, toluene, trichlorethylene, diethyl ether and / or Cj-Cg aldehydes and / or ketones. Solvents which are preferred at temperatures below
• the amount of solvent used is in a range from approximately 40 to 70% by weight, based on the sinterable material or metal oxide used, preferably in a range from approximately 50 to 65% by weight.
• the solvent is preferably selected such that the spray drops which form when applied by means of spraying do not even partially or completely dry out during the spraying process even before contact with the existing layer or carrier body. Mixtures of solvents are therefore preferably used. Mixtures of alcohols with terpenes, in particular ethanol with terpineol, in particular those with viscosities in a range from about 0.006 to about 0.016 Pas, or mixtures of alcohols with lower ketones, in particular methyl ethyl ketone, are preferred.
• the binder contained in the suspension containing metal oxide is preferably selected from a group comprising polyvinyl acetates, waxes, shellac, polyethylene oxides and / or polyglycols.
• Polyalkylene oxides and glycols are preferably used as polymers and / or copolymers with average molecular weights in a range from 100 to 500,000 g / mol, preferably 1,000 to 350,000 g / mol, more preferably 5,000 to 6,500 g / mol.
• the binders are preferably used in an amount in a range from about 0.01 to 12% by weight, preferably in a range from 2 to 5% by weight, in each case based on the total amount.
• Spraying process by electrostatically charging the body pers to which they are to be applied, or the powder or both.
• the suspension containing the metal oxide preferably has a stabilizer selected from a group comprising organic and / or inorganic acids, inorganic bases, polyacrylamides, polyacrylic acid and / or amines.
• a stabilizer selected from a group comprising organic and / or inorganic acids, inorganic bases, polyacrylamides, polyacrylic acid and / or amines.
• Acetic acid, citric acid, hydrochloric acid, oxalic acid, lithium hydroxide, ammonium hydroxide, triethandiamine and tetramethylammonium hydroxide are particularly preferred.
• Acetic acid is particularly preferably used.
• the amount of stabilizer used is in a range from about 3 to 13% by weight, based on the total amount, more preferably in a range from 5 to 8% by weight.
• the suspension containing metal oxide preferably comprises dispersants selected from a group comprising polyamines, phthalic acid esters and / or polyethyleneimines. Polyamines selected from the group of polyethyleneimines are particularly preferred.
• the viscosity of the metal oxide suspension to be sprayed can be optimally adjusted by adding dispersants, in particular polyethyleneimines. Preferred viscosities of the suspensions are in a range from approximately 0.003 to approximately 0.96 Pas, preferably approximately 0.005 to approximately 0.008 Pas.
• graded filters which have excellent flow properties, in particular low flow resistances, in particular due to precisely defined transitions between the respective layers of the graded filters, and moreover to produce such graded filters without risk, since the inflammation There are practically no longer any danger of oxidation or oxidation.
• the present invention further relates to the use of graded filters with the abovementioned properties for the filtration of coolants, lubricants and cleaning agents, for the fine separation of catalyst particles, in membrane reactors, as filter candles and / or filter tubes, in the food and beverage industry, laboratory technology, medical technology , Environmental technology and / or as a cross-flow filter for micro or ultrafiltration.
• the graded filters according to the invention are used in filter tubes and filter candles, which can have a length of 10 mm to 1,500 mm.
• the filter candles can also have coatings on the end face.
• Fig. 1 is a greatly enlarged view of a cross section through a filter according to the invention.
• FIG. 1 shows a filter according to the invention, designated overall by reference number 1.
• This has a first layer 2 of TiO 2 with an average grain size of 0.45 ⁇ m, a further sintered layer 3, made of stainless steel (material designation 316L) with an average grain size of less than 20 ⁇ m, and a coarse-porous carrier body 4 made of 316L stainless steel with an average grain size in a range from 86 ⁇ m to 234 ⁇ m.
• the powder particles of layer 2 penetrate to a depth of approximately 2 pore layers, corresponding to approximately 3 ⁇ m, into layer 3 and thus bring about a good anchoring of the layer.
• a mixed oxide layer consisting of Cr 012 T 078 0 174 (determined on the basis of an X-ray spectrum) with a thickness of 2 pore layers is arranged between the first layer 2 and the further layer 3.
• the very sharp and defined one is clear Detect transition from the first layer 2 to the further layer 3.
• the suspension 1 mentioned above it is ensured that during the spraying of the metal oxide suspension onto an existing layer, which can also be a carrier body, it does not dry out partially or even completely before contact with the latter. This in particular prevents the metal oxide layer to be applied from having disjointed areas and therefore being formed irregularly after the sintering process, which is accompanied by an uneven porosity over the entire application area.
• the suspension 2 Due to the addition of the stabilizer acetic acid, the suspension 2 has virtually no tendency to agglomerate the fine metal oxide particles suspended in it, so that an extremely uniform distribution thereof is achieved on the layer to be sprayed.
• the above-mentioned suspension 3 has an optimal viscosity in a range from about 0.005 to 0.008 Pas, which means that when the metal oxide suspension is applied to a further layer by means of a modified spray gun, the best results with regard to the spraying process were achieved.
• suspensions 1 to 3 are free of binders.
• Suspensions 1 to 3 were sprayed onto a further layer produced by the wet powder spraying process.
• the further layer consisted of a steel powder, which had an average particle diameter of less than 5 ⁇ m. This further layer had a thickness of approximately 15 ⁇ m.
• the further layer was sintered at temperatures below 950 ° C. in a sintering furnace.
• the metal oxide suspensions 1 to 3 were then applied to the further layer using a modified spray gun which is mounted on an X-Y movement system.
• the layer was dried in a desiccator over a period of 4 hours and then sintered in a range between 800 ° C. and 1,050 ° C., preferably about 850 ° C. to 950 ° C., under a protective gas atmosphere or vacuum.
• the further layer to which the metal oxide suspension has been applied can itself be applied to a carrier body, but in particular can also consist of more than two layers.
• the filters according to the invention produced by means of the method according to the invention have excellent properties with regard to the flow through of liquids and / or gases. The reason for this is in particular that there is a precisely defined transition area between the first and the further layer, in which the flow resistance increases suddenly. The reason for this is that the metal oxide particles in the first layer do not penetrate into the open pores of the further layer when applied by means of the method according to the invention (wet powder spraying without a binder).
• the further layer (s) can optionally be produced using binders.

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• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Geology (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Ceramic Engineering (AREA)
• Inorganic Chemistry (AREA)
• Filtering Materials (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Porous Artificial Stone Or Porous Ceramic Products (AREA)
• Oxygen, Ozone, And Oxides In General (AREA)

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• 2001
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• 2002
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