Ceramic filter element

Abstract

The present disclosure relates to a method of making a ceramic filter element having a low defect rate and improved filtration performance. The ceramic filter element has a layered structure with coordinated layers to produce improved filtration performance.

Description

Technical Field

[0001] This invention relates to inorganic ceramic filter elements for nanofiltration and ultrafiltration in liquid purification and filtration methods, and methods for preparing said elements. Background Technology

[0002] Given global population growth, industrialization, and natural disasters, providing clean and drinkable water is an emerging unresolved issue. Water can be contaminated by bacteria, viruses, protozoa and fungi, bacterial and biological companions or microplastics, pharmaceutically active chemicals, toxic chemicals, pesticides, herbicides, proteins, and other contaminants that may threaten human health. In addition, industrial wastewater can be contaminated by organic chemicals, dissolved solids, or suspended materials.

[0003] To reduce the amount of pollutants and toxic waste released in an energy-efficient manner, filter elements are commonly used for filtration or separation purposes, namely in the purification of industrial wastewater. These filter elements can include polymer membranes or ceramic membranes. The latter is generally superior to polymer membranes, especially in filtration or separation methods that require harsh conditions for membrane cleaning or involve high-temperature and corrosive media such as strongly acidic or alkaline wastewater, process fluids, organic solvents, and highly reactive chemicals.

[0004] Generally, two types of ceramic filter membranes are used: oxide and non-oxide filter membranes.

[0005] Non-oxide ceramic filter membranes are typically prepared from particles such as silicon carbide (SiC), silicon nitride (Si3N4), tungsten carbide (WC), aluminum nitride (AlN), or boron nitride (BN) particles or mixtures thereof. Membranes prepared from non-oxide ceramic particles generally exhibit excellent properties in terms of resistance to corrosive media and low membrane fouling tendency due to their low isoelectric point.

[0006] Oxide ceramic filter membranes contain metal oxide particles, such as aluminum oxide (Al₂O₃), beryllium oxide (BeO), calcium oxide (CaO), hafnium oxide (HfO₂), iron oxide (FeO / Fe₂O₃), lanthanum oxide (La₂O₃), magnesium oxide (MgO), manganese oxide (MnO₂), silicon dioxide (SiO₂), strontium oxide (SrO), thorium oxide (ThO₂), titanium dioxide (TiO₂), yttrium oxide (Y₂O₃), zirconium dioxide (ZrO₂), or mixtures thereof. The manufacture of oxide ceramic filter membranes is typically achieved via a sol-gel process, in which a carrier surface is coated with a sol containing a precursor metal compound, such as a metal alkoxide. During drying and sintering, the precursor is oxidized to the corresponding metal oxide, forming a membrane layer with small pore sizes.

[0007] The disadvantage of ceramic filter membranes obtained by the sol-gel method is that they contain a high proportion of amorphous phase, which reduces their resistance to corrosive media, such as acids, alkalis or commercially available membrane cleaners, and mechanical abrasion.

[0008] Another major problem with membrane filtration is the reduction in permeate flux due to membrane fouling. The incidence of fouling is influenced by the properties of the solutes, their concentration, membrane type and pore size distribution, water quality, hydrodynamics, and membrane surface properties. Membrane fouling reduces the economic efficiency of membrane filtration by decreasing the quality of treated water, reducing durability, and increasing the frequency of membrane cleaning.

[0009] In addition, especially in the fields of nanofiltration (pore size 1-10 nm) and ultrafiltration (pore size approximately 10 nm-100 nm), membrane integrity is essential for filtration performance. Defects in membranes (such as cracks, holes, or excessively large pores) are typically much larger than the membrane's nominal pore size (up to several micrometers in diameter), which severely affects filtration and separation performance and reduces the quality of the filtrate, making purification methods inefficient.

[0010] Therefore, it is desirable to provide ceramic filter membranes with narrow pore size distribution, low defect quantity and high chemical and mechanical stability to achieve desired chemical retention, reduce membrane clogging and improve filtrate quality and increase residual fluid concentration. Summary of the Invention

[0011] This invention relates to composite materials for purifying and filtering liquids. In one aspect, this disclosure relates to multilayer ceramic filter elements comprising...

[0012] i) Ceramic carrier structure;

[0013] ii) film layer,

[0014] iii) at least one intermediate layer inserted between the ceramic carrier structure and the film layer; and

[0015] Each layer comprises particles of at least one ceramic compound selected from metal oxides, metal carbides, and metal nitrides, characterized in that...

[0016] The at least one intermediate layer comprises particles of the at least one ceramic compound, the particles having a Z-ratio of at most 4. 90 / D 10 .

[0017] In a second aspect, this disclosure relates to a method for preparing a ceramic filter element according to the first aspect, wherein a layer is formed by continuously applying a suspension comprising particles of at least one ceramic compound of different sizes to a ceramic carrier structure, thereby avoiding the sol-gel method. Attached Figure Description

[0018] Figure 1 The M1 membrane (polyethylene glycol (PEG) MWCO: 2.9 kDa, average pore size 3 nm membrane) according to this disclosure, with the lowest defect rate, is obtained from... Comparison of PEG sieving curves for existing nanofiltration membranes (pore size: 1 nm, manufacturer information).

[0019] Figure 2 Cross-sectional image of the M1 membrane (MWCO: 4kDa) according to this disclosure (Example 1) obtained by REM, which has a well-defined intermediate layer structure and a membrane layer with a minimum defect rate.

[0020] Figure 3 Cross-sectional image of the M1 membrane (MWCO: 4kDa) according to this disclosure (Example 1) obtained by REM, which has a well-defined intermediate layer structure and a membrane layer with a minimum defect rate.

[0021] Figure 4 Images of the surface of the M1 membrane (MWCO: 4kDa) according to this disclosure (Example 1), obtained by REM imaging, showing the minimum defect rate.

[0022] Figure 5 : Obtained through REM Surface images of existing technology films (surface TiO2, nominal pore size 1 nm) show a high defect rate (cracks in the film surface).

[0023] Detailed Explanation

[0024] This invention relates to composite materials for purifying and filtering liquids. In one aspect, this disclosure relates to a multilayer ceramic filter element having a layered structure, comprising...

[0025] i) Ceramic carrier structure;

[0026] ii) Film layer;

[0027] iii) at least one intermediate layer inserted between the ceramic carrier structure and the film layer; and

[0028] All layers comprise particles of at least one ceramic compound selected from metal oxides, metal carbides, and metal nitrides, characterized in that at least one intermediate layer comprises particles of the at least one ceramic compound, the particles having a Z-ratio D of at most 4. 90 / D 10 .

[0029] In the sense of this disclosure, each intermediate layer and film layer may consist of up to eight layers, characterized in that all up to eight layers have the same composition, i.e., particles having the same at least one ceramic compound and particle size. The up to eight layers forming the intermediate layer or film layer are also referred to as sublayers. In other words, the formation of the intermediate layer or film layer can be carried out by subsequently coating up to eight sublayers on top of each other, each of which is subsequently prepared in the same manner using the same coating composition. In the sense of this disclosure, a “layer” having the same composition is referred to as a layer, i.e., for example, the up to eight layers with the same composition forming the outermost layer are referred to as a film layer. The use of several layers constituting the intermediate layer or film layer may have procedural reasons. For example, the final film layer can be prepared by several coating steps using the same composition, thereby producing “layers” of the same type directly adjacent to each other, and thus forming a monolayer in the sense of this application.

[0030] The object of this invention is to provide a ceramic filter element formed on a porous carrier material, exhibiting satisfactory flow rate, high permeability to low molecular weight compounds, and high retention of high molecular weight compounds (including particles of a certain size). Due to the layered structure of the ceramic filter element, the membrane of this disclosure also exhibits a steep sieving curve slope (…). Figure 1 The membrane exhibits a high molecular weight cutoff (MWCO) and high flux, enabling it to provide a highly concentrated filtration residue containing molecular organic compounds. Furthermore, the membrane of this disclosure exhibits high stability to thermal, chemical, and mechanical stresses, resulting in excellent abrasion resistance and cleanliness. After the filtration process, the smooth membrane surface of this disclosure can be easily cleaned by mechanical rinsing, for example, by rinsing the filter with a solvent in the opposite direction of the filtrate flow, and / or by rinsing with commercially available membrane cleaners, acids, or alkalis. In this way, the original flow rate can be maintained over many filtration cycles without degrading the filtrate quality.

[0031] The inventors of this disclosure have discovered that the properties of ceramic filter elements, namely filtration performance, flow rate, and chemical retention, can be surprisingly improved through a coordinated arrangement of the carrier, intermediate layer, and membrane layer. This disclosure particularly relates to a coordinated arrangement of particles of at least one ceramic compound contained within the layers. Those skilled in the art can select the particles to form pores with smaller diameters in each subsequent layer. This results in adjacent layers with average pore sizes differing by approximately 50-95%, thereby allowing the formation of a continuous network of pores, which in turn allows liquid to pass through the filter element at low transmembrane pressures and produces optimal filtration performance. In the sense of this disclosure, average pore size is considered to be the pore diameter, i.e., the size of the pore as D. 50The proportion of pores with a diameter less than or equal to this value is 50% relative to the total number of pores. In the sense of this disclosure, the continuous network of pores allows liquid to flow easily from one side of the filter element to the other, driven by the pressure difference between the two sides of the filter element, i.e., the transmembrane pressure. Simultaneously, a smooth surface is formed, which allows the formation of a layer with a minimal defect rate (see...). Figure 2 , 3 (4 and 5). This is highly desirable because defects can be much larger than the pore size of the filter element, thus reducing the quality of the filtrate.

[0032] Figure 2 The image shows a REM photograph of the ceramic filter element prepared according to Example 1, where A is the carrier structure; 1 is the first intermediate layer; 2 is the second intermediate layer; and 3 shows the third intermediate layer and the membrane layer. Detector = InLens; Signal B = MPSE; Signal = 1.0000; EHT = 5.00 kV; Mag = 2.50 KX; WD = 3.3 mm; images were recorded on a Zeiss Leo 15340VP.

[0033] Figure 3 yes Figure 2 A 10x magnified image. The boundary between the membrane layer (3) and the third intermediate layer (2) on the second intermediate layer (1) can now be seen more clearly. Detector = InLens; Signal B = MPSE; Signal = 1.0000; EHT = 5.00kV; Mag = 25.00KX; WD = 3.3mm; Images were recorded on a Zeiss Leo 15340VP.

[0034] Figure 4 The image shows a REM photograph of the membrane layer of the ceramic filter element prepared according to Example 1. The outermost surface of the filter element, i.e., the membrane layer, shows no defects such as holes or cracks. Detector = InLens; Signal B = MPSE; Signal = 1.0000; EHT = 5.00kV; Mag = 1.00KX; WD = 6.9mm; Images were recorded on a Zeiss Leo 15340VP.

[0035] Figure 5 Showing from REM photographic illustration of the prior art membrane layer of the obtained ceramic filter element (surface material TiO2; nominal pore size 1 nm). The outermost surface of the filter element, i.e., the membrane layer, shows a high defect rate, such as cracks. Detector = InLens; Signal B = MPSE; Signal = 1.0000; EHT = 5.00 kV; Mag = 1.00 KX; WD = 6.6 mm; image recorded on a Zeiss Leo 15340VP.

[0036] In the following text, the carrier structure will be referred to as the "carrier". The intermediate layers will be numbered starting with the intermediate layer that is directly attached to the carrier, i.e., the first intermediate layer. All additional intermediate layers will be numbered sequentially according to their position relative to the carrier, i.e., the second intermediate layer is attached to the first intermediate layer, i.e., in direct contact with the first intermediate layer, and so on.

[0037] In the sense of this disclosure, the size of a batch of particles is characterized by its average diameter Q0, i.e., its numerical value D as determined by dynamic light scattering (DLS). 10 D 50 and D 90 Value. D 10 Defined as the diameter of the particles, where the proportion of particles with a diameter less than or equal to this value is 10% of the total number of particles. Therefore, 10% of the particles in a batch have a diameter less than or equal to D. 10 The diameter of the particles is greater than D; 90% of the particles have a diameter greater than D. 10 The value is the diameter. Therefore, this is the particle number distribution. In a similar way, D 50 Defined as the diameter of the particle, where the proportion of particles with a diameter less than or equal to this value is 50% relative to the total number of particles. Finally, D 90 Defined as the diameter of a particle, wherein the proportion of particles with a diameter less than or equal to this value is 90% relative to the total number of particles. For the purposes of this disclosure, all particle diameters were determined by DLS using a Nanotrac Flex nanoparticle size analyzer (obtained from Microtrac MRB).

[0038] In the sense of this disclosure, the D of particles determined by DLS 10 D 50 and D 90 This refers to primary particle size. It should be understood that primary particles are inorganic structures held together by atomic or molecular bonds. Primary particles cannot be separated into smaller particles except by applying extremely high energy (e.g., during grinding). Secondary particles consist of two or more primary particles bound together in point-to-point contact by weak electromagnetic forces, van der Waals forces, mechanical friction, and / or interlocking. Secondary particles can be broken down into primary particles using appropriate dispersion techniques. During the coating of porous surfaces with a particle suspension, capillary forces can cause secondary particles to break down, resulting in smaller primary particles penetrating into the pores of the surface to be coated. Therefore, in this case, transmembrane flux is reduced.

[0039] Typically, the particle size of the primary particles is necessary for the pore size of the layer formed by them. By approximation, it should be understood that the pore size of the layer is proportional to the average particle size D of the primary particles forming the layer. 50 About one-fifth (i.e., 1 / 5 or 20%).

[0040] In the sense of this disclosure, the particles have D 90Diameter ≤1000nm.

[0041] The particles in each layer x of this disclosure can be characterized by the width of their particle size distribution, expressed as:

[0042]

[0043] In other words, the Z ratio of layer x, i.e., Z x , is the particle size D of the particles that make up this layer. 90 Particle size D of the same particles that make up this layer 10 The business.

[0044] In the sense of this disclosure, the particles of the ceramic compound may be selected from particles of at least one metal oxide, particles of at least one metal carbide, and particles of at least one metal nitride. The particles of the ceramic compound may be considered as "particles" in the context of this disclosure.

[0045] In the sense of this disclosure, the particles of at least one metal oxide may be selected from oxide ceramic materials, such as aluminum oxide (Al2O3), beryllium oxide (BeO), calcium oxide (CaO), hafnium oxide (HfO2), iron oxide (FeO / Fe2O3), lanthanum oxide (La2O3), magnesium oxide (MgO), manganese oxide (MnO2), silicon dioxide (SiO2), strontium oxide (SrO), thorium oxide (ThO2), titanium dioxide (TiO2), yttrium oxide (Y2O3), zirconium dioxide (ZrO2), and mixtures thereof.

[0046] In a preferred embodiment, the particles of at least one metal oxide are selected from particles of alumina (Al2O3), silicon dioxide (SiO2), titanium dioxide (TiO2), zirconium dioxide (ZrO2), and mixtures thereof. For all layers, regardless of the layer type, those skilled in the art can individually select particles to provide a layered body with a smooth surface and a low defect rate.

[0047] In the sense of this disclosure, at least one metal carbide particle may be selected from silicon carbide (SiC), tungsten carbide (WC), boron carbide (B4C), and mixtures thereof.

[0048] In a preferred embodiment, at least one metal carbide particle is silicon carbide (SiC).

[0049] In the sense of this disclosure, the particles of at least one metal nitride may be selected from silicon nitride (Si3N4), aluminum nitride (AlN), titanium nitride (TiN), boron nitride (BN), and mixtures thereof.

[0050] In a preferred embodiment, the particles of at least one metal nitride are selected from silicon nitride (Si3N4), aluminum nitride (AlN), titanium nitride (TiN), and mixtures thereof.

[0051] In this disclosure, the use of metal oxides as materials in at least one intermediate layer and film layer is particularly preferred over the use of metal carbides or metal nitrides.

[0052] In the use of the term "comprising" in this disclosure and claims, other elements are not excluded. For the purposes of this invention, the term "consisting of..." is considered a preferred embodiment of the term "comprising...". If, hereinafter, a group is defined as including at least a certain number of embodiments, it will also be understood as disclosing a group preferably consisting only of these embodiments.

[0053] carrier structure

[0054] According to this disclosure, the carrier is formed of a porous material to allow liquid to pass through. The carrier is formed of a ceramic material. In one preferred embodiment, the average pore size of the carrier is ≤1.5 μm. In another preferred embodiment, the average pore size is 0.5 μm to 1.5 μm.

[0055] For the purposes of this disclosure, it is desirable that the pore size of the carrier is no greater than 1.5 μm to provide a suitable surface for coating intermediate layers, particularly the first intermediate layer directly adjacent to the carrier. If the pore size of the carrier surface is too large, it becomes more difficult to reduce the pore size through intermediate layers, particularly two or three intermediate layers, to provide a suitable surface for coating a film layer characterized by a low defect rate and / or a smooth surface. In cases where this requirement is not met, i.e., the pore size of the carrier is very large, one or more carrier layers can be coated onto the carrier to achieve the desired pore size at the carrier surface. In this case, the carrier layer is considered the carrier structure, i.e., the carrier itself. Specifically for this application, the pore size of the carrier surface is important and affects other layers, particularly the defect rate of those layers.

[0056] The carrier can have different shapes. There are no particular limitations on the shape of the carrier. Similarly, there are no particular limitations on the shape of the intermediate layer and the membrane layer. For example, the carrier can have shapes such as discs, polygonal plates, plates, flat plates, cylinders, box-shaped cylinders, rods, square pillars, etc., which can be selected according to the intended use. Except for its thickness, there are no limitations on the dimensions of the carrier, intermediate layer, or membrane layer, and the dimensions can be selected according to the intended use, as long as the dimensions ensure that the carrier has sufficient strength. Those skilled in the art select the thickness and material of the carrier in a manner that provides a filter element with sufficient mechanical strength for the intended use.

[0057] The support can be prepared by sintering. In other words, the support is a sintered substrate.

[0058] The carrier is not a green substrate. It should be understood that the green substrate is not fired and has a denser structure than a sintered substrate. Due to the specific structure of the green substrate, it cannot be coated with a suspension containing particles according to this disclosure; the green substrate must be fired in a subsequent step. Furthermore, the green substrate does not exhibit an immersion effect, i.e., the particles do not immerse into the pores during coating. In other words, because the green substrate has very small pores created during the drying process by removing water, small film-coating particles cannot penetrate into the substrate. In addition, the green substrate must be sintered at temperatures exceeding 1000°C in an inert gas atmosphere such as argon. This is explained by the fact that the green substrate contains non-oxide ceramic materials such as SiC and Si3N4 or composed of them. During the firing of the green substrate, a SiO2 layer is formed on the particle surface, significantly altering the properties of the filter element.

[0059] In one embodiment, the carrier is a hollow fiber carrier structure with an average pore size of 0.1 μm to 1.5 μm. Where the pore size of the carrier is already within the range of the pore size of the intermediate layer disposed on the carrier surface, the purpose of the first intermediate layer is to provide a smooth surface for subsequent processes of coating another intermediate layer or film layer.

[0060] In another embodiment, the carrier is a multi-channel tube structure with an average pore size of 1.5 μm to 12 μm. In a preferred embodiment, the carrier is a multi-channel tube structure with an average pore size of 1.5 μm to 3 μm, or 3 μm to 4 μm, or 7 μm to 10 μm, or 10 μm to 12 μm, depending on the commercial supplier. In this case, another carrier layer is coated onto the carrier to obtain the desired average pore size of 0.5 μm to 1.5 μm. In this case, the carrier layer is considered part of the carrier structure, i.e., the carrier structure includes the selected carrier element and the carrier layer, simply referred to as the carrier.

[0061] According to one embodiment of this disclosure, the optionally coated carrier layer comprises or is composed of particles of at least one ceramic compound.

[0062] In one embodiment, the optionally coated carrier layer comprises particles of at least one metal oxide selected from Al₂O₃, BeO, CaO, HfO₂, FeO, Fe₂O₃, La₂O₃, MgO, MnO₂, SiO₂, SrO, ThO₂, TiO₂, Y₂O₃, ZrO₂, and mixtures thereof. In another embodiment, the optionally coated carrier layer comprises particles of at least one metal oxide selected from Al₂O₃, SiO₂, TiO₂, ZrO₂, and mixtures thereof. In a preferred embodiment, the optionally coated carrier layer comprises particles of at least one metal oxide selected from Al₂O₃, SiO₂, TiO₂, ZrO₂, and mixtures thereof. In another preferred embodiment, the optionally coated carrier layer comprises Al₂O₃ particles.

[0063] In another preferred embodiment, the optionally coated carrier layer comprises particles of at least one metal oxide selected from Al₂O₃, BeO, CaO, HfO₂, FeO, Fe₂O₃, La₂O₃, MgO, MnO₂, SiO₂, SrO, ThO₂, TiO₂, Y₂O₃, ZrO₂, and mixtures thereof. In another preferred embodiment, the optionally coated carrier layer comprises particles of at least one metal oxide selected from Al₂O₃, SiO₂, TiO₂, ZrO₂, and mixtures thereof. In another preferred embodiment, the optionally coated carrier layer comprises particles of at least one metal oxide selected from Al₂O₃, SiO₂, TiO₂, ZrO₂, and mixtures thereof. In another preferred embodiment, the optionally coated carrier layer comprises Al₂O₃ particles.

[0064] In another embodiment, the optionally coated support layer comprises particles of at least one ceramic compound of a metal carbide selected from SiC, WC, B4C, and mixtures thereof. In another embodiment, the optionally coated support layer comprises particles of at least one metal carbide compound selected from SiC, WC, and mixtures thereof. In another preferred embodiment, the optionally coated support layer comprises SiC particles.

[0065] In another preferred embodiment, the optionally coated carrier layer consists of particles of at least one metal carbide selected from SiC, WC, B4C, and mixtures thereof. In another preferred embodiment, the optionally coated carrier layer consists of particles of at least one metal carbide selected from SiC, WC, and mixtures thereof. In another preferred embodiment, the optionally coated carrier layer consists of SiC particles.

[0066] In another embodiment, the optionally coated support layer comprises at least one particle of a metal nitride selected from Si3N4, BN, AlN, TiN, and mixtures thereof. In another embodiment, the optionally coated support layer comprises at least one particle of a metal nitride compound selected from Si3N4, AlN, TiN, and mixtures thereof. In a preferred embodiment, the optionally coated support layer comprises at least one particle of a metal nitride selected from AlN, TiN, and mixtures thereof. In another preferred embodiment, the optionally coated support layer comprises particles of AlN or TiN.

[0067] In another preferred embodiment, the optionally coated support layer consists of particles of at least one metal nitride selected from Si3N4, BN, AlN, TiN, and mixtures thereof. In another preferred embodiment, the optionally coated support layer consists of particles of at least one metal nitride selected from Si3N4, AlN, TiN, and mixtures thereof. In another preferred embodiment, the optionally coated support layer consists of particles of at least one metal nitride selected from AlN, TiN, and mixtures thereof. In another preferred embodiment, the optionally coated support layer consists of particles of AlN or TiN.

[0068] It should be understood that, even in the absence of an optional coated carrier layer, the carrier structure may contain or be composed of the aforementioned materials.

[0069] Intermediate layer

[0070] In order to provide a layer with a low defect rate, such as a membrane, on a porous carrier material, the pore size of the carrier surface is reduced by at least one intermediate layer, and in a preferred embodiment by a gradual reduction through several intermediate layers, thereby also making the carrier surface smooth.

[0071] In one embodiment, an intermediate layer is coated on a carrier. This intermediate layer reduces the average pore size of the carrier surface by approximately 60-95%. This provides a smoother surface for coating the film. However, the reduction in the average pore size and the smoothness of the intermediate layer surface may not be sufficient to obtain a film with a low defect rate, because the average pore size of the intermediate layer may still be too large, or the intermediate layer may still have a high defect rate.

[0072] In another embodiment, two intermediate layers are coated on the carrier. The first intermediate layer, which is in direct contact with the carrier, can reduce the average pore size of the carrier surface by approximately 60-95%. The second intermediate layer, which is in direct contact with the first intermediate layer, can further reduce the average pore size of the first intermediate layer surface by approximately 87-95%. Thus, the pore size of the carrier is reduced in two steps.

[0073] However, reducing the average pore size and improving the smoothness of the intermediate layer surface may not be sufficient to obtain a membrane with a low defect rate, narrow pore size distribution, and a rapidly changing molecular weight cutoff. Therefore, in a preferred embodiment, three intermediate layers are arranged between the carrier and the outermost membrane layer. Thus, the first intermediate layer, in direct contact with the carrier, can reduce the average pore size of the carrier structure surface by about 60-95%, the second intermediate layer, in direct contact with the first intermediate layer, can reduce the average pore size of the first intermediate layer surface by about 87-95%, and the third intermediate layer, in direct contact with the second intermediate layer, can further reduce the average pore size of the second intermediate layer surface by about 55-80%. This coordinated structure allows those skilled in the art to reduce the average pore size of the carrier with each subsequent layer in three steps. However, a continuous pore network can still be formed between the layers to allow liquid to easily pass through the filter element from one side to the other without having to apply the high transmembrane pressure that produces high liquid flow rates. Simultaneously, a smooth surface is provided on which a membrane layer can be coated, and a membrane layer can be stacked on a third intermediate layer. This membrane layer is characterized by exhibiting a low defect rate and a smooth membrane surface, thus displaying improved filtration properties, namely a narrow pore size distribution and a low molecular weight cutoff, inhibiting and / or delaying fouling layer formation during the filtration process, and improved cleaning properties due to the smooth membrane surface. On the other hand, the three intermediate layers exhibit a sufficient pore network to allow liquid to flow from one side of the filter element to the other without requiring high transmembrane pressure. Therefore, the presence of the three intermediate layers allows for optimal filtration properties of the filter element, as they create a smooth outermost surface while maintaining high permeability of the filter element that allows for high transmembrane flow rates at low transmembrane pressures.

[0074] In another embodiment, four or more intermediate layers are arranged between the carrier and the outermost membrane layer. Therefore, the coordinated structure allows those skilled in the art to reduce the average pore size of the carrier with each subsequent layer in four or more steps. Although a continuous network of pores can still be formed between the layers to allow liquid to pass through the filter element from one side to the other, fabricating a filter element with four or more intermediate layers is costly and time-consuming, without improving filtration performance compared to a filter element with three intermediate layers. The carrier, all intermediate layers, and membrane layers differ in their thickness and composition, such as the chemical composition and size of the particles used in the coating. In each layer, the material is independently selected from particles of at least one ceramic compound that provides different properties. In particular, the particle sizes of the layers differ, thereby providing different average pore sizes between the layers.

[0075] In one implementation, the first intermediate layer contains the largest particles that result in the maximum average pore size.

[0076] In a preferred embodiment, the particle size decreases with each successive intermediate layer; the membrane layer contains the smallest particles resulting in the minimum average pore size. The particles of different layers are selected such that the average pore size of subsequent intermediate layers is smaller than that of the previous layer, in order to provide a smooth surface and a suitable pore network to allow easy passage of liquid.

[0077] These materials, or mixtures thereof, exhibit advantageous strength, resulting in good pressure stability for the filter element. Furthermore, the ceramic material may contain additives, preferably in the form of alkali metal and / or alkaline earth metal oxide compounds.

[0078] For each layer, the chemical composition and particle size of at least one ceramic compound are individually selected. In a preferred embodiment, careful selection and matching of the particles of at least one ceramic compound yields optimal properties regarding average pore size, surface smoothness, and the continuity of the pore network. The coordinated selection of particles of at least one ceramic compound, considering the inherent properties of average pore size, porosity, and microstructure in each layer, results in an optimized layered ceramic filter element.

[0079] Another aspect of the invention relates to the thickness of the various intermediate layers x and membrane layers m, whereby the thickness of each layer is adapted to the thickness of adjacent layers to produce a coordinated membrane filtration device. In a preferred embodiment, the first intermediate layer has the greatest thickness, and the thickness of each layer decreases with each subsequent layer.

[0080] In the sense of this disclosure, for the purposes of this disclosure, the thickness between the two layers is greater than T. x / x+1 This is represented by the following equation:

[0081]

[0082] Furthermore, for each layer, the thickness of each layer x, i.e., t x The particle size D of each ceramic nanoparticle in the same layer x 50 The ratio Y x The calculation is as follows:

[0083]

[0084] The average pore size of the layer was determined using conventional methods established by Barret, Joyne, and Halenda, by capillary flow porosity determination, molecular weight cutoff (MWCO) analysis, or N2 adsorption experiments. For the purposes of this disclosure, the average pore size is defined as the D-value of the pore. 50 The diameter, wherein the proportion of holes with a diameter smaller than this value is 50% of the total number of holes.

[0085] In a preferred embodiment, the pore size of the layers, particularly the membrane layer, is determined by MWCO analysis, as demonstrated in the examples. Specifically, the characterization of the filter element according to this disclosure can be performed using an aqueous test mixture containing dextran, i.e., biopolymers, of different molecular weights, as these are reliable for MWCO determination. The reproducibility of the results from this analysis has been demonstrated. For MWCO analysis, a feed solution is prepared by dissolving a mixture of selected and commercially available dextrans of known molecular weights in water, and said feed solution is filtered through the filter element at a defined transmembrane pressure. The concentrations of the individual dextran fractions are selected such that their mixture produces the most uniform molecular weight distribution possible. The total concentration of the polymer solution should be as low as possible so that the formation of a top layer can be avoided during filtration. A total dextran concentration of about 0.2% by weight is optimal. A biocide, such as sodium azide, is added to stabilize the polymer solution, thereby preventing the biodegradation of the dextran. The extent to which such an additive can impair the detector signal must be examined in each individual case. The preferred composition of the feed solution is as follows:

[0086] 0.1 g / L of dextran 1 (molecular weight determined by GPC: 1,000-20,000 kDa)

[0087] 0.1 g / L of dextran 2 (molecular weight determined by GPC: 3,000-50,000 kDa)

[0088] 1 g / L of dextran 3 (molecular weight determined by GPC: 50,000-1,000,000 kD)

[0089] 0.8 g / L of dextran 4 (molecular weight determined by GPC: 50,000-2,000,000 kD).

[0090] The feed solution consisted of a mixture of four different dextran fractions in varying mass ratios, with a total dextran content of 2 g / L (0.2 wt%). After filtration testing—i.e., after the feed solution had passed through a filter element to determine the pore size—the polymer distribution in the feed and resulting permeate solutions was determined by size exclusion chromatography (GPC). Using suitable evaluation software (e.g., PSS WinGPC), the polymer distributions of two different samples could be mutually canceled out, resulting in a graphical representation of retention or sieving curves.

[0091] According to one embodiment of this disclosure, at least one intermediate layer comprises or is composed of particles of at least one ceramic compound.

[0092] According to another embodiment, at least one ceramic compound in the at least one intermediate layer is selected from Al2O3, BeO, CaO, HfO2, FeO, Fe2O3, La. gO3, MgO, MnO2, SiO2, SrO, ThO2, TiO2, Y2O3, ZrO2, SiC, Si3N4, BN, AlN, WC, B4C, TiN and mixtures thereof, preferably selected from Al2O3, SiO2, TiO2, ZrO2, SiC, Si3N4, AlN, TiN and mixtures thereof, more preferably wherein the at least one ceramic compound is Al2O3, TiO2 or ZrO2, SiC, TiN or mixtures thereof, and most preferably wherein the at least one ceramic compound is SiC or Al2O3.

[0093] According to one embodiment of this disclosure, the first intermediate layer comprises particles of at least one metal oxide selected from Al₂O₃, BeO, CaO, HfO₂, FeO, Fe₂O₃, La₂O₃, MgO, MnO₂, SiO₂, SrO, ThO₂, TiO₂, Y₂O₃, ZrO₂, and mixtures thereof. In another embodiment, the first intermediate layer comprises particles of at least one metal oxide selected from Al₂O₃, SiO₂, TiO₂, ZrO₂, and mixtures thereof.

[0094] According to a preferred embodiment, the at least one intermediate layer is composed of particles of Al2O3, BeO, CaO, HfO2, FeO, Fe2O3, La2O3, MgO, MnO2, SiO2, SrO, ThO2, TiO2, Y2O3, ZrO2, or mixtures thereof. In another preferred embodiment, the at least one intermediate layer is composed of particles of Al2O3, SiO2, TiO2, ZrO2, or mixtures thereof. In yet another preferred embodiment, the at least one intermediate layer is composed of particles of Al2O3 or TiO2. In yet another preferred embodiment, the at least one intermediate layer is composed of Al2O3 particles.

[0095] In another embodiment, the at least one intermediate layer comprises particles of at least one metal carbide selected from SiC, WC, B4C, and mixtures thereof. In another embodiment, the at least one intermediate layer comprises particles of at least one metal carbide compound selected from SiC, WC, and mixtures thereof. In another preferred embodiment, the at least one intermediate layer comprises particles of SiC.

[0096] In another preferred embodiment, the at least one intermediate layer comprises particles of at least one metal carbide selected from SiC, WC, B4C, and mixtures thereof. In another preferred embodiment, the at least one intermediate layer comprises particles of at least one metal carbide selected from SiC, WC, and mixtures thereof. In another preferred embodiment, the at least one intermediate layer comprises particles of SiC.

[0097] In another embodiment, the at least one intermediate layer comprises at least one particle of a metal nitride selected from Si3N4, BN, AlN, TiN, and mixtures thereof. In another embodiment, the at least one intermediate layer comprises at least one particle of a metal nitride selected from Si3N4, AlN, TiN, and mixtures thereof. In a preferred embodiment, the at least one intermediate layer comprises at least one particle of a metal nitride selected from AlN, TiN, and mixtures thereof. In another preferred embodiment, the at least one intermediate layer comprises AlN or TiN particles.

[0098] In another preferred embodiment, the at least one intermediate layer comprises particles of at least one metal nitride selected from Si3N4, BN, AlN, TiN, and mixtures thereof. In another preferred embodiment, the at least one intermediate layer comprises particles of at least one metal nitride selected from Si3N4, AlN, TiN, and mixtures thereof. In another preferred embodiment, the at least one intermediate layer comprises particles of at least one metal nitride selected from AlN, TiN, and mixtures thereof. In another preferred embodiment, the at least one intermediate layer comprises particles of AlN or TiN.

[0099] In the sense of this disclosure, a first intermediate layer is arranged in a sandwich manner between a carrier and a second intermediate layer, wherein the carrier has an average pore size of 0.5 μm to 1.5 μm as determined by capillary flow porosity measurement. When the average pore size is greater than a specified range, another carrier layer is coated on top of the original carrier. For the first intermediate layer, particles of at least one ceramic compound with a particle size distribution of Z ≤ 4 are used.

[0100] In one embodiment, the at least one intermediate layer comprises having granularity D 10 The wavelength range is 70-250nm, preferably 100-180nm, and further preferably D. 90 The particles are 200-500nm, more preferably 250-400nm.

[0101] The ratio Y1 between the thickness of the first intermediate layer and the particle size of the particles in the first intermediate layer can be selected in the range of 18.5 to 313 (i.e., a thickness of 5 to 50 μm). Therefore, the average pore size can be 110 to 170 nm, determined by capillary flow porosity measurement.

[0102] According to one embodiment of this disclosure, the second intermediate layer, if present, comprises or consists of particles of at least one ceramic compound.

[0103] According to another embodiment, at least one ceramic compound in the second intermediate layer is selected from Al2O3, BeO, CaO, HfO2, FeO, Fe2O3, La2O3, MgO, MnO2, SiO2, SrO, ThO2, TiO2, Y2O3, ZrO2, SiC, Si3N4, BN, AlN, WC, B4C, TiN, and mixtures thereof, preferably selected from Al2O3, SiO2, TiO2, ZrO2, SiC, Si3N4, AlN, TiN, and mixtures thereof, more preferably the at least one ceramic compound is Al2O3, TiO2 or ZrO2, SiC, TiN, or mixtures thereof, and most preferably the at least one ceramic compound is SiC or Al2O3.

[0104] According to another embodiment of this disclosure, the second intermediate layer comprises particles of at least one metal oxide selected from Al₂O₃, BeO, CaO, HfO₂, FeO, Fe₂O₃, La₂O₃, MgO, MnO₂, SiO₂, SrO, ThO₂, TiO₂, Y₂O₃, ZrO₂, and mixtures thereof. In another embodiment, the second intermediate layer comprises nanoparticles of at least one metal oxide selected from Al₂O₃, SiO₂, TiO₂, ZrO₂, and mixtures thereof. In yet another embodiment, the second intermediate layer comprises nanoparticles of at least one metal oxide selected from Al₂O₃, TiO₂, and ZrO₂.

[0105] According to a preferred embodiment, the second intermediate layer is composed of particles of Al2O3, BeO, CaO, MgO, FeO, Fe2O3, La2O3, MgO, MnO2, SiO2, SrO, ThO2, TiO2, Y2O3, ZrO2, or mixtures thereof. In another preferred embodiment, the second intermediate layer is composed of particles of Al2O3, SiO2, TiO2, ZrO2, or mixtures thereof. In yet another preferred embodiment, the second intermediate layer is composed of particles of Al2O3 or TiO2. In yet another preferred embodiment, the second intermediate layer is composed of particles of Al2O3.

[0106] In another embodiment, the second intermediate layer comprises particles of at least one metal carbide selected from SiC, WC, B4C, and mixtures thereof. In another embodiment, the second intermediate layer comprises particles of at least one metal carbide compound selected from SiC, WC, and mixtures thereof. In another preferred embodiment, the second intermediate layer comprises particles of SiC.

[0107] In another preferred embodiment, the second intermediate layer comprises particles of at least one metal carbide selected from SiC, WC, B4C, and mixtures thereof. In another preferred embodiment, the second intermediate layer comprises particles of at least one metal carbide selected from SiC, WC, and mixtures thereof. In another preferred embodiment, the second intermediate layer comprises particles of SiC.

[0108] In another embodiment, the second intermediate layer comprises at least one particle of a metal nitride selected from Si3N4, BN, AlN, TiN, and mixtures thereof. In another embodiment, the second intermediate layer comprises at least one particle of a metal nitride selected from Si3N4, AlN, TiN, and mixtures thereof. In a preferred embodiment, the second intermediate layer comprises at least one particle of a metal nitride selected from AlN, TiN, and mixtures thereof. In another preferred embodiment, the second intermediate layer comprises particles of AlN or TiN.

[0109] In another preferred embodiment, the second intermediate layer comprises particles of at least one metal nitride selected from Si3N4, BN, AlN, TiN, and mixtures thereof. In another preferred embodiment, the second intermediate layer comprises particles of at least one metal nitride selected from Si3N4, AlN, TiN, and mixtures thereof. In another preferred embodiment, the second intermediate layer comprises particles of at least one metal nitride selected from AlN, TiN, and mixtures thereof. In another preferred embodiment, the second intermediate layer comprises particles of AlN or TiN.

[0110] Therefore, the second intermediate layer is disposed in a sandwich manner between the first and third intermediate layers or film layers. For the second intermediate layer, particles of at least one ceramic compound with a particle size distribution Z ≤ 2.7 can be used. In another embodiment, the second intermediate layer comprises a Z ratio D 90 / D 10 The particles are of at most 3, preferably of particle size D. 10 The wavelength range is 50 to 170 nm, preferably 80 to 120 nm, and further preferably D. 90 The thickness is 150 to 350 nm, more preferably 180 to 210 nm. The ratio Y between the thickness of the second intermediate layer and the particle size of the particles in the second intermediate layer can be selected in the range of 6 to 250 (i.e., the thickness can be 1 to 30 μm). One or more of these layers can be stacked on top of each other.

[0111] According to one embodiment of this disclosure, a third or additional intermediate layer, if present, comprises or consists of particles of at least one ceramic compound.

[0112] According to another embodiment, at least one ceramic compound of the third or additional intermediate layer (if present) is selected from Al2O3, BeO, CaO, HfO2, FeO, Fe2O3, La2O3, MgO, MnO2, SiO2, SrO, ThO2, TiO2, Y2O3, ZrO2, SiC, Si3N4, BN, AlN, WC, B4C, TiN and mixtures thereof, preferably selected from Al2O3, SiO2, TiO2, ZrO2, SiC, Si3N4, AlN, TiN and mixtures thereof, more preferably at least one of the ceramic compounds is Al2O3, TiO2 or ZrO2, SiC, TiN or mixtures thereof, and most preferably at least one of the ceramic compounds is Al2O3 or TiO2.

[0113] According to another embodiment of this disclosure, the third or additional intermediate layer comprises particles of at least one metal oxide selected from Al₂O₃, BeO, CaO, HfO₂, FeO, Fe₂O₃, La₂O₃, MgO, MnO₂, SiO₂, SrO, ThO₂, TiO₂, Y₂O₃, ZrO₂, and mixtures thereof. In another embodiment, the third or additional intermediate layer comprises particles of at least one metal oxide selected from Al₂O₃, SiO₂, TiO₂, ZrO₂, and mixtures thereof.

[0114] According to one preferred embodiment, the third or additional intermediate layer is composed of particles of Al2O3, BeO, CaO, HfO2, FeO, Fe2O3, La2O3, MgO, MnO2, SiO2, SrO, ThO2, TiO2, Y2O3, ZrO2, or mixtures thereof. In another preferred embodiment, the third or additional intermediate layer is composed of particles of Al2O3, SiO2, TiO2, ZrO2, or mixtures thereof. According to another preferred embodiment, the third or additional intermediate layer is composed of particles of Al2O3 or TiO2. In another preferred embodiment, the third or additional intermediate layer is composed of particles of Al2O3, SiO2, TiO2, ZrO2, or mixtures thereof. According to another preferred embodiment, the third or additional intermediate layer is composed of particles of TiO2.

[0115] In another embodiment, the third or additional intermediate layer comprises particles of at least one metal carbide selected from SiC, WC, B4C, and mixtures thereof. In another embodiment, the third or additional intermediate layer comprises particles of at least one metal carbide compound selected from SiC, WC, and mixtures thereof. In another preferred embodiment, the third or additional intermediate layer comprises particles of SiC.

[0116] In another preferred embodiment, the third or additional intermediate layer consists of particles of at least one metal carbide selected from SiC, WC, B4C, and mixtures thereof. In another preferred embodiment, the third or additional intermediate layer consists of particles of at least one metal carbide selected from SiC, WC, and mixtures thereof. In another preferred embodiment, the third or additional intermediate layer consists of SiC particles.

[0117] In another embodiment, the third or additional intermediate layer comprises at least one particle of a metal nitride selected from Si3N4, BN, AlN, TiN, and mixtures thereof. In another embodiment, the third or additional intermediate layer comprises at least one particle of a metal nitride compound selected from Si3N4, AlN, TiN, and mixtures thereof. In a preferred embodiment, the third or additional intermediate layer comprises at least one particle of a metal nitride selected from AlN, TiN, and mixtures thereof. In another preferred embodiment, the third or additional intermediate layer comprises AlN or TiN particles.

[0118] In another preferred embodiment, the third or additional intermediate layer comprises particles of at least one metal nitride selected from Si3N4, BN, AlN, TiN, and mixtures thereof. In another preferred embodiment, the third or additional intermediate layer comprises particles of at least one metal nitride selected from Si3N4, AlN, TiN, and mixtures thereof. In another preferred embodiment, the third or additional intermediate layer comprises particles of at least one metal nitride selected from AlN, TiN, and mixtures thereof. In another preferred embodiment, the third or additional intermediate layer comprises particles of AlN or TiN.

[0119] A third or additional intermediate layer is arranged in a sandwich manner between the preceding intermediate layer (e.g., the second intermediate layer) and the film layer. For the third or additional intermediate layer, particles of at least one ceramic compound having a particle size distribution of Z ≤ 6 can be used. In another embodiment, the third or additional intermediate layer, if present, comprises a Z ratio D 90 / D 10 The particle size is at most 6, preferably at most 3, and more preferably, the particle size D is... 10 The wavelength is 8 to 25 nm, preferably 12 to 17 nm, and further preferably D. 90 The particles are 18 to 50 nm, more preferably 25 to 35 nm. The ratio Y between the thickness of the third intermediate layer and the particle size in the third intermediate layer can be selected in the range of 9 to 176 (i.e., the thickness of the third or additional intermediate layer can be selected in the range of 0.2 to 3 μm).

[0120] membrane

[0121] According to this disclosure, the membrane layer is arranged in direct contact with a third or other intermediate layer, i.e., the membrane layer is the outermost layer.

[0122] In one embodiment, at least one ceramic compound of the film layer is selected from Al2O3, BeO, CaO, HfO2, FeO, Fe2O3, La2O3, MgO, MnO2, SiO2, SrO, ThO2, TiO2, Y2O3, ZrO2, SiC, Si3N4, BN, AlN, WC, B4C, TiN, and mixtures thereof, preferably selected from Al2O3, SiO2, TiO2, ZrO2, SiC, Si3N4, AlN, TiN, and mixtures thereof, more preferably said at least one ceramic compound is Al2O3, TiO2 or ZrO2, SiC, TiN, or mixtures thereof, and most preferably said at least one ceramic compound is Al2O3, TiO2, or ZrO2.

[0123] In one embodiment, the film layer comprises or is composed of particles of at least one ceramic compound. In one embodiment, the film layer comprises particles of at least one metal oxide selected from Al₂O₃, BeO, CaO, HfO₂, FeO, Fe₂O₃, La₂O₃, MgO, MnO₂, SiO₂, SrO, ThO₂, TiO₂, Y₂O₃, ZrO₂, and mixtures thereof. In another embodiment, the film layer comprises particles of at least one metal oxide selected from Al₂O₃, SiO₂, TiO₂, ZrO₂, and mixtures thereof. In another embodiment, the film layer comprises particles of at least one metal oxide selected from TiO₂, ZrO₂, and mixtures thereof. In yet another embodiment, the film layer comprises particles of at least one metal oxide selected from both TiO₂ and ZrO₂.

[0124] In one preferred embodiment, the membrane layer is composed of particles of Al₂O₃, BeO, CaO, HfO₂, FeO, Fe₂O₃, La₂O₃, MgO, MnO₂, SiO₂, SrO, ThO₂, TiO₂, Y₂O₃, ZrO₂, or mixtures thereof. In another preferred embodiment, the membrane layer is composed of particles of Al₂O₃, SiO₂, TiO₂, ZrO₂, or mixtures thereof. In yet another preferred embodiment, the membrane layer is composed of particles of TiO₂, ZrO₂, or mixtures thereof. In yet another preferred embodiment, the membrane layer is composed of particles of either TiO₂ or ZrO₂.

[0125] In another embodiment, the film layer comprises particles of at least one metal carbide selected from SiC, WC, B4C, and mixtures thereof. In another embodiment, the film layer comprises particles of at least one metal carbide compound selected from SiC, WC, and mixtures thereof. In another preferred embodiment, the second intermediate layer comprises particles of SiC.

[0126] In another preferred embodiment, the film layer consists of particles of at least one metal carbide selected from SiC, WC, B4C, and mixtures thereof. In another preferred embodiment, the film layer consists of particles of at least one metal carbide selected from SiC, WC, and mixtures thereof. In another preferred embodiment, the film layer consists of SiC particles.

[0127] In another embodiment, the film layer comprises at least one metal nitride particle selected from Si3N4, BN, AlN, TiN, and mixtures thereof. In another embodiment, the film layer comprises at least one metal nitride compound particle selected from Si3N4, AlN, TiN, and mixtures thereof. In a preferred embodiment, the film layer comprises at least one metal nitride particle selected from AlN, TiN, and mixtures thereof. In another preferred embodiment, the film layer comprises AlN or TiN particles.

[0128] In another preferred embodiment, the film layer comprises particles of at least one metal nitride selected from Si3N4, BN, AlN, TiN, and mixtures thereof. In another preferred embodiment, the film layer comprises particles of at least one metal nitride selected from Si3N4, AlN, TiN, and mixtures thereof. In another preferred embodiment, the film layer comprises particles of at least one metal nitride selected from AlN, TiN, and mixtures thereof. In another preferred embodiment, the film layer comprises particles of AlN or TiN.

[0129] In a preferred embodiment, the particles of at least one ceramic compound are selected from those having a particle size distribution Z ≤ 15 (e.g., an average particle size of D). 10 =1-9nm, D 50 =2-10nm, D 90 TiO2 or ZrO2 with a thickness of 3-15 nm (DLS) can be used. The thickness of the film can be selected from 10-800 nm.

[0130] In another embodiment, the film layer is composed of Z ratio D 90 / D 10 The composition consists of TiO2 particles smaller than 3, preferably with a particle size D. 10 The wavelength is 5-9nm, and D is further preferred. 90 It is 9-15nm.

[0131] In another embodiment, the film layer is composed of Z ratio D 90 / D 10 The composition consists of ZrO2 particles smaller than 5 μm, preferably with a particle size D. 10 The wavelength is 1-3nm, and D is further preferred. 90 It is 3-5nm.

[0132] In one embodiment, the membrane has an average pore size of 0.3-10 nm, as determined by filtering a mixture containing dextran. In another embodiment, the membrane has an average pore size of 0.5-5 nm, as determined by filtering a mixture containing dextran. In a preferred embodiment, the membrane has an average pore size of 0.8-1.5 nm, as determined by filtering a mixture containing dextran.

[0133] Layer arrangement

[0134] In a preferred embodiment, the laminar body includes a carrier, three intermediate layers, and a membrane layer.

[0135] In a preferred embodiment, the first intermediate layer is composed of Al2O3 particles, the second intermediate layer is composed of Al2O3 particles, and the third intermediate layer is composed of Al2O3 particles.

[0136] In another preferred embodiment, the first intermediate layer is composed of Al2O3 particles, the second intermediate layer is composed of Al2O3 particles, and the third intermediate layer is composed of TiO2 particles.

[0137] In another preferred embodiment, the first intermediate layer is composed of Al2O3 particles, the second intermediate layer is composed of Al2O3 particles, and the third intermediate layer is composed of ZrO2 particles.

[0138] In another preferred embodiment, the first intermediate layer is composed of Al2O3 particles, the second intermediate layer is composed of ZrO2 particles, and the third intermediate layer is composed of Al2O3 particles.

[0139] In another preferred embodiment, the first intermediate layer is composed of Al2O3 particles, the second intermediate layer is composed of TiO2 particles, and the third intermediate layer is composed of Al2O3 particles.

[0140] In another preferred embodiment, the first intermediate layer is composed of Al2O3 particles, the second intermediate layer is composed of TiO2 particles, and the third intermediate layer is composed of TiO2 particles.

[0141] In another preferred embodiment, the first intermediate layer is composed of Al2O3 particles, the second intermediate layer is composed of TiO2 particles, and the third intermediate layer is composed of ZrO2 particles.

[0142] In another preferred embodiment, the first intermediate layer is composed of Al2O3 particles, the second intermediate layer is composed of ZrO2 particles, and the third intermediate layer is composed of ZrO2 particles.

[0143] In another preferred embodiment, the first intermediate layer is composed of Al2O3 particles, the second intermediate layer is composed of ZrO2 particles, and the third intermediate layer is composed of TiO2 particles.

[0144] In another preferred embodiment, the first intermediate layer is composed of TiO2 particles, the second intermediate layer is composed of Al2O3 particles, and the third intermediate layer is composed of Al2O3 particles.

[0145] In another preferred embodiment, the first intermediate layer is composed of TiO2 particles, the second intermediate layer is composed of Al2O3 particles, and the third intermediate layer is composed of TiO2 particles.

[0146] In another preferred embodiment, the first intermediate layer is composed of TiO2 particles, the second intermediate layer is composed of Al2O3 particles, and the third intermediate layer is composed of ZrO2 particles.

[0147] In another preferred embodiment, the first intermediate layer consists of TiO2 particles, the second intermediate layer consists of ZrO2 particles, and the third intermediate layer consists of Al2O3 particles.

[0148] In another preferred embodiment, the first intermediate layer is composed of TiO2 particles, the second intermediate layer is composed of TiO2 particles, and the third intermediate layer is composed of Al2O3 particles.

[0149] In another preferred embodiment, the first intermediate layer is composed of TiO2 particles, the second intermediate layer is composed of TiO2 particles, and the third intermediate layer is composed of TiO2 particles.

[0150] In another preferred embodiment, the first intermediate layer is composed of TiO2 particles, the second intermediate layer is composed of TiO2 particles, and the third intermediate layer is composed of ZrO2 particles.

[0151] In another preferred embodiment, the first intermediate layer is composed of TiO2 particles, the second intermediate layer is composed of ZrO2 particles, and the third intermediate layer is composed of ZrO2 particles.

[0152] In another preferred embodiment, the first intermediate layer is composed of TiO2 particles, the second intermediate layer is composed of ZrO2 particles, and the third intermediate layer is composed of TiO2 particles.

[0153] In another preferred embodiment, the first intermediate layer is composed of ZrO2 particles, the second intermediate layer is composed of Al2O3 particles, and the third intermediate layer is composed of Al2O3 particles.

[0154] In another preferred embodiment, the first intermediate layer consists of ZrO2 particles, the second intermediate layer consists of Al2O3 particles, and the third intermediate layer consists of TiO2 particles.

[0155] In another preferred embodiment, the first intermediate layer consists of ZrO2 particles, the second intermediate layer consists of Al2O3 particles, and the third intermediate layer consists of ZrO2 particles.

[0156] In another preferred embodiment, the first intermediate layer is composed of ZrO2 particles, the second intermediate layer is composed of ZrO2 particles, and the third intermediate layer is composed of Al2O3 particles.

[0157] In another preferred embodiment, the first intermediate layer consists of ZrO2 particles, the second intermediate layer consists of TiO2 particles, and the third intermediate layer consists of Al2O3 particles.

[0158] In another preferred embodiment, the first intermediate layer is composed of ZrO2 particles, the second intermediate layer is composed of TiO2 particles, and the third intermediate layer is composed of TiO2 particles.

[0159] In another preferred embodiment, the first intermediate layer is composed of ZrO2 particles, the second intermediate layer is composed of TiO2 particles, and the third intermediate layer is composed of ZrO2 particles.

[0160] In another preferred embodiment, the first intermediate layer is composed of ZrO2 particles, the second intermediate layer is composed of ZrO2 particles, and the third intermediate layer is composed of ZrO2 particles.

[0161] In another preferred embodiment, the first intermediate layer is composed of ZrO2 particles, the second intermediate layer is composed of ZrO2 particles, and the third intermediate layer is composed of TiO2 particles.

[0162] In another preferred embodiment, the first intermediate layer is composed of ZrO2 particles, the second intermediate layer is composed of ZrO2 particles, and the third intermediate layer is composed of SiC particles.

[0163] In another preferred embodiment, the first intermediate layer is composed of ZrO2 particles, the second intermediate layer is composed of SiC particles, and the third intermediate layer is composed of SiC particles.

[0164] In another preferred embodiment, the first intermediate layer is composed of SiC particles, the second intermediate layer is composed of SiC particles, and the third intermediate layer is composed of SiC particles.

[0165] In another preferred embodiment, the first intermediate layer is composed of TiO2 particles, the second intermediate layer is composed of TiO2 particles, and the third intermediate layer is composed of SiC particles.

[0166] In another preferred embodiment, the first intermediate layer is composed of TiO2 particles, the second intermediate layer is composed of SiC particles, and the third intermediate layer is composed of SiC particles.

[0167] In another preferred embodiment, the first intermediate layer is composed of Al2O3 particles, the second intermediate layer is composed of SiC particles, and the third intermediate layer is composed of SiC particles.

[0168] In another preferred embodiment, the first intermediate layer is composed of Al2O3 particles, the second intermediate layer is composed of Al2O3 particles, and the third intermediate layer is composed of SiC particles.

[0169] It should be understood that those skilled in the art can combine any of the combinations described herein with any of the materials disclosed herein suitable for forming film layers.

[0170] In another preferred embodiment, the layered body comprises a carrier, three intermediate layers, and a membrane layer. Thus, the first intermediate layer is composed of particles with an average particle size D. 10 =100-180nm, D 50 =160-270nm, D 90 The first layer consists of particles with a diameter of 250-400 nm (DLS), a thickness of 5-50 μm, and an average pore size of 110-170 nm. The second intermediate layer is composed of particles with an average particle size of D... 10 =80-120nm, D s0 =120-160nm, D 90 It consists of particles with a diameter of 180-210 nm (DLS), a thickness of 1-30 μm, and an average pore size of 9-14 nm. The third intermediate layer is composed of particles with an average particle size D... 10 =12-17nm, D 50 =17-22nm, D 90 It consists of particles with a diameter of 25-35 nm (DLS) and a thickness of 0.2-3 μm. The film layer is composed of particles with an average particle size D... 10 =5-9nm, D 50 =6-10nih,D 90The particles consist of 9-15 nm (DLS), with a thickness of 40-800 nm and an average pore size of 0.8-1.5 nm, and are determined by filtering a mixture containing dextran. After determining the dextran in the filtrate, the average pore size is calculated using the empirical relationship between Granath and Kvist (1967) for correlating the molecular weight of the retained dextran with the pore size of the filter element (PSS WinGPC Unity, build 9350, GLC; obtained from PSS GmbH).

[0171] In another preferred embodiment, the layered body comprises a carrier, three intermediate layers, and a membrane layer. Thus, the first intermediate layer is composed of particles with an average particle size D. 10 =100-180nm, D 50 =160-270nm, D 90 The first layer consists of particles with a diameter of 250-400 nm (DLS), a thickness of 5-50 μm, and an average pore size of 110-170 nm. The second intermediate layer is composed of particles with an average particle size of D... 10 =80-120nm, D 50 =120-160nm, D 90 It consists of particles with a diameter of 180-210 nm (DLS), a thickness of 1-30 μm, and a D50 pore size of 9-14 nm. The third intermediate layer consists of particles with an average particle size of D... 10 =12-17nm, D so =17-22nm, D 90 It consists of particles with a diameter of 25-35 nm (DLS) and a thickness of 0.2-3 μm. The film layer is composed of particles with an average particle size D... 1o =5-3nm, D 50 =2-4nm, D 90 =3-7nm (DLS) particle composition, with a thickness of 10-150nm and an average pore size of ~0.6nm (determined by N2 adsorption experiments using the BJH method, obtained from the equipment evaluation of ThermoFisher Scientific).

[0172] This disclosure also relates to a coordinated arrangement of layers with respect to their thickness. In one embodiment, the thickness ratio between the first and second intermediate layers is at least T. 1 / 2 =0.15. In another embodiment, the thickness ratio between the first and second intermediate layers is less than T. 1 / 2 =50. In a preferred embodiment, the thickness ratio between the first and second intermediate layers is T. 1 / 2 =0.15 to T 1 / 2 =50. In another preferred embodiment, the thickness ratio between the first and second intermediate layers is T. 1 / 2 =1 to T 1 / 2=50. In another preferred embodiment, the thickness ratio between the first and second intermediate layers is T. 1 / 2 =1.5 to T 1 / 2 =10.

[0173] In one embodiment, the thickness ratio between the second and third intermediate layers is at least T. 2 / 3 =0.3. In another embodiment, the thickness ratio between the second and third intermediate layers is less than T. 2 / 3 =150. In a preferred embodiment, the thickness ratio between the second and third intermediate layers is T. 2 / 3 =0.3 to T 2 / 3 =150. In another preferred embodiment, the thickness ratio between the second and third intermediate layers is T. 2 / 3 =1 to T 2 / 3 =150. In another preferred embodiment, the thickness ratio between the second and third intermediate layers is T. 2 / 3 =5 to T 2 / 3 =20.

[0174] In one embodiment, the thickness ratio between the third intermediate layer and the film layer is at least T. 3 / m =0.25. In another embodiment, the thickness ratio between the third intermediate layer and the film layer is less than T. 3 / m =300. In a preferred embodiment, the thickness ratio between the third intermediate layer and the film layer is T. 3 / m =0.25 to T 3 / m =300. In another preferred embodiment, the thickness ratio between the third intermediate layer and the film layer is T. 3 / m =1 to T 3 / m =300. In another preferred embodiment, the thickness ratio between the third intermediate layer and the film layer is T. 3 / m =2 to T 3 / m =20.

[0175] The ceramic filter element disclosed herein features a narrow pore size distribution, minimal defect rate in a smooth surface, and excellent stability against high temperatures and corrosive chemicals over a wide pH range of 1 to 14. Furthermore, the low defect rate in the layer results in reduced clogging inside the filter element caused by large compounds and / or particles entering through defects and cracks, allowing for the maintenance of high permeability of solvents and low molecular weight chemicals, i.e., salts, over many filtration cycles, even at high tangential fluxes or in dead-end filtration methods. Therefore, the ceramic filter element is highly durable and can be found in a variety of applications in industrial separation and filtration methods. Consequently, the disclosed ceramic filter element enables more efficient treatment, purification, and recycling of industrial wastewater and its process fluids generated during reaction or purification steps in the chemical or pharmaceutical industries.

[0176] Comparative experiments on flux performance in two types of membranes (one with a rough surface and the other with a smooth surface) showed that the membrane with a smooth surface exhibited higher permeate flux and normalized flux compared to the membrane with the rough surface. Based on SEM images, this can be attributed to the greater filtrate fouling of the rough surface structure compared to the smooth surface structure. These results indicate that a smooth membrane surface can significantly influence the improvement of antifouling properties during solution filtration at low transmembrane pressures. In other words, a smoother membrane surface can increase transmembrane flux and reduce membrane resistance by reducing susceptibility to membrane fouling.

[0177] Manufacturing method of filter element

[0178] This disclosure also relates to a method for producing the aforementioned ceramic filter element. Therefore, a second aspect of this disclosure relates to a method for manufacturing a multilayer ceramic filter element according to the first aspect detailed above, wherein a layer is formed by continuously applying a suspension comprising particles of at least one ceramic compound of different sizes to a ceramic carrier structure, thereby avoiding the sol-gel method. In other words, the method according to this disclosure relates to a method in which said layer can be prepared directly from ceramic particles. Therefore, the production step of reacting precursor particles, such as metal alkoxides, into ceramic compounds, such as sol-gel and chemical vapor deposition (CVD) methods, is omitted. It should be understood that the coating method does not use sol-gel or chemical vapor deposition (CVD) methods.

[0179] The advantage of the method for manufacturing ceramic filter elements according to this disclosure is that it avoids the sol-gel process steps. The sol-gel process may require higher temperatures and / or drying steps, which can lead to voids and cracks in the layer.

[0180] Furthermore, CVD methods produce very dense coatings with small pore sizes. However, these properties reduce the flux of liquid through the filter element and / or necessitate high transmembrane pressures. Therefore, filter elements prepared by CVD methods with one or more layers cannot be used for liquid filtration but only for gas separation. Moreover, CVD is impractical for coating large-area substrates due to the high cost and effort required in the process. In the membrane according to the invention, this CVD method is omitted.

[0181] The preparation method of each layer includes the following steps (A) to (F):

[0182] (A) A ceramic particle dispersion for coating is prepared from a crystalline powder of at least one ceramic compound particles and a solvent in the presence of a dispersing additive to form a coating suspension.

[0183] In one embodiment, the coating suspension for the intermediate layer comprises particles of at least one ceramic compound, preferably in an amount ≤20% by weight based on the total weight of the coating suspension, more preferably ≤15% by weight based on the total weight of the coating suspension, and most preferably ≤10% by weight based on the total weight of the coating suspension. In another embodiment, the coating suspension for the intermediate layer comprises particles in an amount of at least 0.1% by weight based on the total weight of the coating suspension. In a preferred embodiment, the coating suspension for the intermediate layer comprises particles in an amount of 0.1% to 20% by weight. In another preferred embodiment, the coating suspension for the intermediate layer comprises particles in an amount of 0.1% to 15% by weight. In yet another preferred embodiment, the coating suspension for the intermediate layer comprises particles in an amount of 0.1% to 10% by weight.

[0184] In one embodiment, the coating suspension for the membrane layer comprises particles of at least one ceramic compound, preferably in an amount ≤5% by weight based on the total weight of the coating suspension, more preferably ≤2.5% by weight based on the total weight of the coating suspension, and most preferably ≤1% by weight based on the total weight of the coating suspension. In another embodiment, the coating suspension for the membrane layer comprises at least 0.02% by weight of particles based on the total weight of the coating suspension. In a preferred embodiment, the coating suspension for the membrane layer comprises from 0.02% by weight to 5% by weight of particles. In another preferred embodiment, the coating suspension for the membrane layer comprises from 0.02% by weight to 2.5% by weight of particles. In yet another preferred embodiment, the coating suspension for the membrane layer comprises from 0.02% by weight to 1% by weight of particles.

[0185] The suspension also contains dispersing additives to promote optimal mixing and prevent accelerated aggregation. Dispersing additives may be selected from surfactants, such as carbonic acid or fatty alcohols, or inorganic acids. In one preferred embodiment, the dispersing acid is selected from inorganic acids. In one preferred embodiment, the dispersing additive is nitric acid. In another preferred embodiment, the dispersing additive is hydrochloric acid. In another preferred embodiment, the dispersing additive is selected from carbonic acid. In yet another preferred embodiment, the dispersing additive is acetic acid.

[0186] In addition, an adhesive can be added to promote sintering and enhance bond strength. This adhesive can be selected from polymers, particularly polyvinyl alcohol, polyvinylpyrrolidone, or cellulose or mixtures thereof. In one preferred embodiment, the adhesive is polyvinyl alcohol. In another preferred embodiment, the cellulose is selected from methylcellulose and carboxymethylcellulose or mixtures thereof.

[0187] In another embodiment, the adhesive is present in an amount of ≤15% by weight, preferably ≤10% by weight, based on the total weight of the coating suspension. In another embodiment, the adhesive is present in an amount of at least 0.5% by weight, based on the total weight of the coating suspension used to form the intermediate layer. In another preferred embodiment, the adhesive is present in an amount of 0.5% to 15% by weight, based on the total weight of the coating suspension used to form the intermediate layer. In another preferred embodiment, the adhesive is present in an amount of 0.5% to 10% by weight, based on the total weight of the coating suspension used to form the intermediate layer. In another preferred embodiment, the adhesive is not present in the coating suspension used to form the film layer.

[0188] Mechanical energy is applied to achieve a uniform distribution of particles in the coated suspension. This mechanical energy can be applied by stirring, shaking, or grinding, with an energy input of approximately 0.1 kWh / kg suspension to approximately 6 kWh / kg suspension. In a preferred embodiment, the energy input increases for each subsequent layer of suspension.

[0189] (B) In another step of the preparation method, a layer is formed by contacting the outermost layer of the laminar body with a coating suspension. In a preferred embodiment, the outermost layer of the laminar body is tubular. For coating, the tube is arranged vertically and filled with the coating suspension by a pump. In another preferred embodiment, the tube is completely filled.

[0190] The coating suspension contacts the outermost layer of the laminar body for a certain residence time. In one embodiment, the residence time between the suspension and the outermost layer of the laminar body is less than 120 seconds. In a preferred embodiment, the residence time between the suspension and the outermost layer of the laminar body is less than 60 seconds. In another preferred embodiment, the residence time between the suspension and the outermost layer of the laminar body is 60 seconds. In another preferred embodiment, the residence time between the suspension and the outermost layer of the laminar body is 30 seconds. In another embodiment, the residence time between the suspension and the outermost layer of the laminar body is at least 10 seconds. In one preferred embodiment, the residence time between the suspension and the outermost layer of the laminar body is 10 to 120 seconds. In another preferred embodiment, the residence time between the suspension and the outermost layer of the laminar body is 10 to 60 seconds. In another preferred embodiment, the residence time between the suspension and the outermost layer of the laminar body is 30 to 60 seconds.

[0191] After the residence time, the coating suspension is carefully removed, leaving a film on the carrier. The carefully removed coating suspension is also referred to as excess coating suspension. Thus, the film of the coating suspension adheres to the surface to be coated by adhesive forces, while the coating suspension that does not adhere to the surface is gently removed. In one embodiment, the suspension permeates from a tube, leaving a film of coating suspension on the outermost surface of the laminar column. In this case, the amount of suspension permeating from the tube and not adhering to the surface is excess coating suspension. The thickness of the film remaining on the outermost layer of the laminar column can be controlled by the residence time by concentration polarization and the shear force caused by the velocity of the coating suspension during discharge from the surface to be coated. Particles form a layer on top of the outermost layer of the laminar column through interlocking between particles and enhanced adhesion via capillary effects through the solid layer beneath the film. The layer thickness is controlled by the residence time and the concentration of particles in the coating suspension.

[0192] (C) Then, the remaining membrane coated with the suspension is dried. In one embodiment, the membrane is dried in an air atmosphere. In another embodiment, the membrane is dried in an air atmosphere at room temperature. In a preferred embodiment, the membrane is dried for at least 12 hours. In another embodiment, the membrane is dried in an air atmosphere at a temperature of 60°C to 90°C. In a more preferred embodiment, the membrane is dried in an air atmosphere at a temperature of 60°C to 90°C for 2 to 6 hours.

[0193] The dried membrane is then sintered.

[0194] (D) The sintering temperature must be selected to match the maximum sintering temperature of the carrier and the material to be sintered. With at least one layer already coated onto the carrier, the sintering temperature must be selected based on the maximum sintering temperature of one of these layers or the carrier, depending on which is the lowest. In a preferred embodiment, the sintering temperature is 300°C to 1400°C. In another preferred embodiment, the sintering temperature of each subsequent layer decreases compared to the previous layer. In another preferred embodiment, the sintering temperature during the sintering of the first intermediate layer is 1000°C to 1400°C. In yet another preferred embodiment, the temperature decreases by at least 100°C during each sintering step in the preparation of any subsequent layer.

[0195] In one embodiment, sintering is carried out at a temperature above 300°C, preferably above 350°C, more preferably below 1700°C, further preferably below 1500°C, further preferably below 1400°C, further preferably between 300°C and 1700°C, further preferably between 300°C and 1500°C, further preferably between 300°C and 1500°C, and most preferably between 300°C and 1400°C or between 350°C and 1400°C.

[0196] In the sense of this disclosure, all sintering steps for metal oxide sintering are performed in an air atmosphere.

[0197] It should be understood that the conditions during sintering of metal carbides and metal nitrides require careful selection. Therefore, in one embodiment of this disclosure, the filter element comprising metal carbides and / or metal nitrides can be sintered in an air atmosphere at a temperature below 900°C. In another embodiment of this disclosure, the filter element comprising metal carbides and / or metal nitrides can be sintered in an inert atmosphere such as argon or nitrogen, or in a vacuum, at a sintering temperature of 1000°C to 2000°C.

[0198] (E) In one embodiment, steps (A) through (D) of the manufacturing method can be repeated using the same suspension until a layer of the desired thickness is obtained. In a preferred embodiment, all steps are performed at least once per layer. In another preferred embodiment, all steps of the method are performed no more than six times per layer. For the purposes of this disclosure, a layer composed of materials that are identical in chemical composition and particle size is considered a single layer.

[0199] (F) In another embodiment, steps (A) through (E) are repeated to form layers with different chemical properties, while changing the suspension to a suspension containing particles of at least one ceramic compound that respectively constructs the subsequent layers. Steps (A) through (E) are repeated until all desired layers are attached to the laminar body.

[0200] In a preferred embodiment, three intermediate layers and one film layer are formed by continuously repeating steps (A) to (E) with different coating suspensions.

[0201] In another embodiment, the filter element described herein is used in a liquid filtration method.

[0202] The present disclosure is illustrated below by way of examples and is not intended to limit the scope of the disclosure. The scope of protection of the present disclosure is defined only by the claims. Example

[0203] General method for preparing a suspension of crystalline particles of at least one metal oxide

[0204] The crystalline particles of at least one metal oxide are obtained from a commercial supplier or ground to obtain the desired particle size and shape. The average particle size is expressed as a numerical value D. 10 D 50 and D 90 These values ​​are given and were determined by DLS prior to coating using a NANO-flex machine (available from MicrotracEurope GmbH).

[0205] To prepare the dispersion, energy is applied using a bead mill to mix a solvent (e.g., water), crystalline particles of at least one metal oxide, and an optional dispersant (e.g., nitric acid or acetic acid). The amount of milling energy is thus adjusted to meet the requirements for the crystalline particles of at least one metal oxide.

[0206] In this way, a basic suspension containing a 1:1 mixture of solvent and crystalline ceramic nanoparticles in their weight ratio (weight (solvent): weight (particles)) and dispersing additives can be obtained.

[0207] Coated suspension

[0208] Prior to the coating process, a suitable base suspension is diluted with a solvent and mixed with the binder. Unless otherwise specified, the amount of nanoparticles in the resulting coating suspension is expressed as a weight percent (wt.-%) based on the total amount of the mixture.

[0209] For each type of nanoparticle used in the preparation method, the amount of crystalline particles of at least one metal oxide is individually adjusted.

[0210] To prepare the ceramic coating suspension, a base suspension and water were uniformly mixed. Then, a binder was added while stirring.

[0211] A suitable coating suspension has the following composition:

[0212] Table 1. Exemplary compositions for coating layers

[0213]

[0214] Coating on ceramic substrate

[0215] The above-described coating suspension is filled into the interior of a vertically oriented ceramic carrier tube. The solution is allowed to remain in the carrier tube for 60 seconds, after which the coating suspension is drained. The remaining film on the inner surface of the tube is dried. The coated tube can then be sintered until sufficient strength is achieved. After sintering, the next layer can be coated on top of the previous layer in the same manner. These steps are repeated until a film layer is coated on the final intermediate layer.

[0216] By applying this method, it is possible to manufacture products with a minimum defect rate (see...). Figure 2 , 3 And 4) and therefore have the best properties for separation and filtration purposes, ceramic filter element (M1).

[0217] Characterization of filter elements - MWCO

[0218] MWCO analysis was used to analyze filtration quality using PEG (see MWCO analysis). Figure 1For polyethylene glycol, MWCO is calculated as D. 90 =2.9kDa, indicating that the average pore size is in the low nanometer range. Figure 1 It is also shown that, despite having a larger nominal average pore size, the membrane M1 according to this disclosure exhibits a steeper sieving curve slope and improved high molecular weight PEG retention compared to competing membranes.

[0219] The retention performance of the ceramic filter element M1 with respect to dextran of different molecular weights was also analyzed. The MWCO was determined to be D using dextran. 90 =4kDa, at which point 90% of the molecules remain on the element.

[0220] Compared to ceramic filter elements described in the prior art, the filter element M1 of this disclosure exhibits the following improved filtration behavior:

[0221] A mixture of high molecular weight derivatives (MW: 20,000 Da to 50,000 Da) and medium molecular weight derivatives (MW: 2,000 Da to 3,000 Da) of biopolymers simulating industrial filtration problems is passed through the aforementioned filter element and from... A commercially available membrane filtration system (MWCO = 1 kDa) was obtained and constitutes an example of the prior art, and the following results are given:

[0222] Table 2 compares the filtration performance of the filter element according to this disclosure and a comparative element with a smaller nominal pore size.

[0223]

[0224] The test results show that when M1 is used in the filtration method, the flux is almost 100% higher than that of the control element at lower transmembrane pressures. Simultaneously, more high molecular weight biopolymers are retained in the mixture. Therefore, compared to known control elements in the prior art, filtration with M1 is less time-consuming, more energy-efficient, and exhibits improved performance in terms of higher selectivity and separation efficiency.

[0225] Characterization of filter elements - reusability

[0226] In another experiment, the separation of high molecular weight biopolymers from primary industries with low molecular weight aromatic compounds (MW: 100 to 500 Da) was investigated. The feed (a mixture of components in H₂O) volume was reduced by 60%, and the mixture was filtered through various prior art ceramic filter elements obtained from commercial suppliers and the filter element (MI) of this disclosure at a crossflow velocity of 3 m / s and a transmembrane pressure of 2 bar. All filter elements had the same geometry.

[0227] After the first filtration process, clean the filter element with a commercially available membrane cleaner (such as P3-Ultrasil (available from Ecolab), acid, or alkali) and repeat the filtration process.

[0228] Table 3 compares the filter elements according to this disclosure with various comparative filter elements (CFEs) obtained from commercial suppliers in complex filtration tasks. Retention rates are expressed as retention rates of high molecular weight biopolymers from the primary industry.

[0229]

[0230] A: From A: Obtain; B: From Obtain; C: From Obtain; D: From Obtain; E: From Obtain; F: from Obtain; G: from get.

[0231] The filter element disclosed herein effectively retains high molecular weight biopolymers while allowing low molecular weight aromatic compounds to pass through the membrane. The membrane permeability remains high compared to all comparative filter elements known in the prior art and those obtained from commercial suppliers. This is surprising considering that the disclosed membrane has a larger MWCO and therefore a larger pore size compared to comparative filter elements. This indicates that it is highly advantageous to prepare membranes with low defect rates, as the high retention rate of high molecular weight biopolymers from primary industries is paired with high permeability as a result of narrow pore size distribution and a smooth membrane surface.

Claims

1. A multilayer ceramic filter element, comprising: i) A ceramic support structure, wherein the support structure has an average pore size of 0.5-1.5µm; ii) Film layer, iii) At least one intermediate layer interposed between the ceramic support structure and the film layer, wherein the at least one intermediate layer comprises a particle size D 10 Particles ranging from 70 to 250 nm; and Each layer comprises particles of at least one ceramic compound selected from metal oxides, metal carbides, and metal nitrides, characterized in that... The at least one intermediate layer comprises particles of the at least one ceramic compound, the particles having a Z-ratio of at most 4. 90 / D 10 , Multilayer ceramic filter elements are fabricated by continuously applying a suspension containing particles of at least one ceramic compound of different sizes to a ceramic carrier structure, thereby avoiding the sol-gel method, where the ceramic carrier structure is a sintered substrate. The particle size decreases with each successive intermediate layer, such that the average pore size of the subsequent intermediate layer is smaller than that of the previous layer. The membrane contains the smallest particles that result in the minimum average pore size, wherein the average pore sizes of the carrier structure, at least one intermediate layer, and adjacent layers of the membrane differ by 50%-95%.

2. The multilayer ceramic filter element according to claim 1, wherein at least one ceramic compound in the at least one intermediate layer is selected from Al2O3, BeO, CaO, HfO2, FeO, Fe2O3, La2O3, MgO, MnO2, SiO2, SrO, ThO2, TiO2, Y2O3, ZrO2, SiC, Si3N4, BN, AlN, WC, B4C, TiN, and mixtures thereof.

3. The multilayer ceramic filter element according to claim 2, wherein the at least one ceramic compound is SiC or Al2O3.

4. The multilayer ceramic filter element according to any one of claims 1 to 3, wherein the at least one intermediate layer comprises particles of size D 10 The wavelength is 100 to 180 nm, D 90 Particles ranging from 200 to 500 nm in size.

5. The multilayer ceramic filter element according to claim 4, wherein D 90 The wavelength ranges from 250 to 400 nm.

6. The multilayer ceramic filter element according to any one of claims 1 to 3, wherein... a) Includes at least two intermediate layers, wherein the first intermediate layer is directly loaded on the ceramic carrier structure, and the second intermediate layer is directly loaded on the first intermediate layer; or b) Includes at least three intermediate layers, wherein the first intermediate layer is directly loaded on the ceramic carrier structure, the second intermediate layer is directly loaded on the first intermediate layer, and the third intermediate layer is directly loaded on the second intermediate layer.

7. The multilayer ceramic filter element according to claim 6, wherein at least one ceramic compound in the second intermediate layer is selected from Al2O3, BeO, CaO, HfO2, FeO, Fe2O3, La2O3, MgO, MnO2, SiO2, SrO, ThO2, TiO2, Y2O3, ZrO2, SiC, Si3N4, BN, AlN, WC, B4C, TiN, and mixtures thereof.

8. The multilayer ceramic filter element according to claim 7, wherein the at least one ceramic compound is SiC or Al2O3.

9. The multilayer ceramic filter element according to claim 6, wherein the second intermediate layer comprises a Z ratio D 90 / D 10 For a maximum of 3, the particle size is D. 10 The wavelength range is 50 to 170 nm, D 90 The particles are 150 to 350 nm in size.

10. The multilayer ceramic filter element according to claim 9, wherein the particle size D 10 The wavelength is 80 to 120 nm, D 90 The wavelength ranges from 180 to 210 nm.

11. The multilayer ceramic filter element according to claim 6, wherein, when comprising at least three intermediate layers, at least one ceramic compound of the third intermediate layer is selected from Al2O3, BeO, CaO, HfO2, FeO, Fe2O3, La2O3, MgO, MnO2, SiO2, SrO, ThO2, TiO2, Y2O3, ZrO2, SiC, Si3N4, BN, AlN, WC, B4C, TiN, and mixtures thereof.

12. The multilayer ceramic filter element according to claim 11, wherein the at least one ceramic compound is Al2O3 or TiO2.

13. The multilayer ceramic filter element of claim 11, wherein the third intermediate layer comprises a Z ratio D 90 / D 10 For a maximum of 6, the particle size is D. 10 The wavelength is 8 to 25 nm, D 90 The particles are 18 to 50 nm in size.

14. The multilayer ceramic filter element of claim 11, wherein the third intermediate layer comprises a Z ratio D 90 / D 10 For a maximum of 3, the particle size is D. 10 The wavelength is 12 to 17 nm, D 90 The particles are 25 to 35 nm in size.

15. The multilayer ceramic filter element according to any one of claims 1 to 3, wherein at least one ceramic compound of the membrane layer is selected from Al2O3, BeO, CaO, HfO2, FeO, Fe2O3, La2O3, MgO, MnO2, SiO2, SrO, ThO2, TiO2, Y2O3, ZrO2, SiC, Si3N4, BN, AlN, WC, B4C, TiN, and mixtures thereof.

16. The multilayer ceramic filter element according to claim 15, wherein the at least one ceramic compound is Al2O3, TiO2 or ZrO2.

17. The multilayer ceramic filter element according to any one of claims 1 to 3, wherein a) The membrane layer is composed of a Z-ratio D 90 / D 10 Less than 3, particle size D 10 The wavelength is 5 to 9 nm, D 90 Composed of TiO2 particles of 9 to 15 nm; or b) wherein the film layer is composed of a Z ratio D 90 / D 10 Less than 5, particle size D 10 D is 1 to 3 nm. 90 It consists of ZrO2 particles of 3 to 5 nm in size.

18. The multilayer ceramic filter element of claim 1, wherein the method for each layer comprises the following steps: a) Provide a coated suspension containing particles comprising at least one ceramic compound; b) Contact the surface of the ceramic carrier structure with the coated suspension for 10 to 120 seconds; c) Remove excess coating suspension without removing the residual film of coating suspension on the surface; d) Dry the remaining film; e) Sintering the layered structure at a temperature below 1500°C, wherein the temperature is reduced for each subsequent sintering step; and f) Optionally repeat steps a) – d) until a layer of the desired thickness is obtained.

19. The multilayer ceramic filter element according to claim 1 or 18, wherein at least two intermediate layers and a membrane layer are formed.

20. The multilayer ceramic filter element of claim 19, wherein for two directly adjacent intermediate layers, the layer adjacent to the ceramic carrier structure has a greater thickness than the layer adjacent to the membrane layer.

21. The multilayer ceramic filter element of claim 18, wherein the coated suspension comprises a) Particles of at least one ceramic compound, in an amount ≤20% by weight, based on the total weight of the coating suspension; b) An adhesive, in an amount ≤ 5% by weight, based on the total weight of the coating suspension; and c) Solvent, wherein the solvent constitutes the remaining weight of the coated suspension.

22. The multilayer ceramic filter element of claim 18, wherein the coated suspension comprises a) Particles of at least one ceramic compound, in an amount ≤10% by weight, based on the total weight of the coating suspension; b) An adhesive, which is polyvinyl alcohol, polyvinylpyrrolidone, or cellulose or a mixture thereof, in an amount ≤ 1% by weight, based on the total weight of the coating suspension; and c) Solvent, which is water or C 1-6 Alcohol, wherein the solvent comprises the remaining weight of the coated suspension.

23. The multilayer ceramic filter element of claim 18, wherein the drying step comprises air drying for at least 12 hours and less than 48 hours.

24. The multilayer ceramic filter element according to claim 18, wherein sintering is carried out at a temperature of 300°C to 1700°C.

25. The multilayer ceramic filter element according to claim 18, wherein sintering is carried out at a temperature of 350°C to 1400°C.

26. The multilayer ceramic filter element according to claim 19, wherein the sintering temperature of the layers adjacent to the membrane layer is at least 100°C lower than the sintering temperature of all layers adjacent to the carrier structure.

27. The multilayer ceramic filter element according to claim 19, wherein the sintering temperature of the membrane layer is higher than 300°C and lower than 600°C.

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