Ceramic membrane filter

Abstract

This further suppresses the occurrence of membrane defects in ceramic membrane filters. [Solution] A ceramic membrane filter 10 comprises a porous substrate 13 forming cells 12 through which a fluid flows, an intermediate membrane 15 formed on the porous substrate 13, and a separation membrane 18 formed on the intermediate membrane 15. In this ceramic membrane filter 10, the cells having cracks of 4 μm or less account for 9% or less of the total number of cells. Furthermore, in this ceramic membrane filter 10, the percentage of foamed cells having an initial foaming pressure in water of 0.08 MPa or more may be 9% or less of the total number of cells.

Description

Technical Field

[0001] The present disclosure disclosed in this specification relates to a ceramic membrane filter and a method for manufacturing the same.

Background Art

[0002] Conventionally, as a ceramic membrane filter, a ceramic membrane is formed on a titania UF membrane, which is an ultrafiltration membrane (UF membrane) with an average pore diameter of 2 to 20 nm and a membrane thickness of 0.1 to 1.0 μm, formed on a porous substrate that is a microfiltration membrane (MF membrane). A part of the ceramic membrane penetrates into the pores of the titania UF membrane or into the pores of the titania UF membrane and the porous substrate, and such a ceramic membrane filter has been proposed (see, for example, Patent Document 1). In this ceramic membrane filter, it is possible to provide a ceramic filter provided with a ceramic porous membrane having few defects, a thin and uniform membrane thickness, and high resolution.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the ceramic membrane filter described in this Patent Document 1, increasing the thickness of the membrane formed on the substrate has not been considered. When the thickness of the membrane formed on the substrate is increased, defects are likely to occur, such as cracks during drying, and it has been desired to further suppress such defects in the membrane.

[0005] The present disclosure has been made in view of such problems, and the main object thereof is to provide a ceramic membrane filter and a method for manufacturing the same that can further suppress the occurrence of membrane defects.

Means for Solving the Problems

[0006] As a result of intensive research to achieve the above-described main object, the inventors of the present invention have found that when an intermediate film is formed on a substrate using a raw material slurry to which a resin having a relatively small molecular weight and a chain structure is added, the generation of defects in the intermediate film can be further suppressed, and thus the invention disclosed in this specification has been completed.

[0007] That is, the ceramic membrane filter disclosed in this specification includes a substrate that forms a cell through which a fluid flows, an intermediate film formed on the substrate, and a separation film formed on the intermediate film, and the cell having cracks of 4 μm or less accounts for 9% or less of the total number of cells.

[0008] The method for manufacturing a ceramic membrane filter disclosed in this specification includes a forming step of forming a raw material layer of an intermediate film on a substrate using a raw material slurry obtained by mixing an organic binder containing a dry crack inhibitor, a peptizing agent, and a polysaccharide compound, which are resins having a chain structure and a molecular weight of 1000 or less, a ceramic raw material, and a solvent. In the forming step, the dry crack inhibitor is added in a range of 0.25 parts by mass or more and 0.95 parts by mass or less with respect to 100 parts by mass of the ceramic raw material, the peptizing agent is added in a range of 0.15 parts by mass or more and 0.25 parts by mass or less with respect to 100 parts by mass of the ceramic raw material, the polysaccharide compound is added to the raw material slurry in a range of 0.95 parts by mass or less with respect to 100 parts by mass of the ceramic raw material, and the raw material layer having an average film thickness of 150 μm or more and 480 μm or less is formed.

Advantages of the Invention

[0009] The ceramic membrane filter and its manufacturing method disclosed in this specification can further suppress the occurrence of film defects in the intermediate film formed on the substrate. The reason is speculated as follows. For example, the drying crack inhibitor of the organic binder contained in the raw material slurry has a relatively low molecular weight of 1000 or less, and it is considered that the increase in the viscosity of the raw material slurry can be more suppressed. Also, in such a raw material slurry, it is speculated that the organic binder can suppress breakage during drying. Therefore, for example, the thickening of the intermediate film such as 100 μm or more can be achieved.

Brief Description of the Drawings

[0010]

Figure 1

Embodiments for Carrying Out the Invention

[0011] Next, embodiments for carrying out the present disclosure will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing the schematic configuration of a ceramic membrane filter 10 which is an embodiment of the present disclosure. The ceramic membrane filter 10 includes a porous substrate 13, an intermediate film 15 formed on the porous substrate 13, and a separation film 18 formed on the intermediate film 15. The ceramic membrane filter 10 has a slit 17 formed on its outer peripheral surface, and seal portions 19 are formed on both end faces. This ceramic membrane filter 10 is a filter for separating a processing target fluid containing a separation target.

[0012] The ceramic membrane filter 10 has cells with cracks of 4 μm or less accounting for 9% or less of the total number of cells. That is, there are no cracks exceeding 4 μm, and the defects of the intermediate membrane 15 and the separation membrane 18 are very few. This ceramic membrane filter 10 may have an initial foaming pressure in water of 0.08 MPa or more and a ratio of the number of foamed cells of 9% or less of the total number of cells. Note that those with "an initial foaming pressure in water of 0.08 MPa or more and a ratio of the number of foamed cells of 9% or less of the total number of cells" correspond to those with "no cracks exceeding 4 μm and cells with cracks of 4 μm or less accounting for 9% or less of the total number of cells". Here, the crack refers to one through which fluid leaks and has a size of 1.0 μm or more. Here, the foaming pressure in water is the pressure (MPa) when the filter is placed in water at normal temperature (20 °C) and normal pressure (atmospheric pressure), and air is gradually pressurized from the side surface side (slit 17) of the filter and foaming occurs from the outlet side (or the inlet side). Also, the number of cells foamed at this time is measured, and the ratio of the number of foamed cells to the total number of cells is obtained. This foaming pressure is preferably 0.15 MPa or more. Also, this foaming cell ratio may be 2.0% or less. Within such a range, there are fewer membrane defects, which is preferable. Note that when the foaming cell ratio exceeds 3%, for example, in the sterilization test of JIS-K3835, the sterilization performance is less than 99.99%.

[0013] The ceramic membrane filter 10 can be used, for example, for gas separation and water separation. The ceramic membrane filter 10 may, for example, have a zeolite membrane as the separation membrane 18. This separation membrane 18 may be used as a MF membrane for sterilization. In particular, in the ceramic membrane filter 10 with a large membrane area, a zeolite membrane with few defects and small raw material particles can be formed. Also, a filter with few membrane defects that can achieve complete sterilization can be obtained.

[0014] The porous substrate 13 has a plurality of cells 12 that serve as flow paths for the fluid to be separated. In this ceramic membrane filter 10, among the fluid to be treated that enters the cells 12 from the inlet side, the fluid having a molecular size capable of permeating through the separation membrane 18 permeates through the separation membrane 18, the intermediate membrane 15, and the porous substrate 13, and is sent out as the permeated fluid through the slit 17 from the side surface of the ceramic membrane filter 10. On the other hand, the non-permeating fluid that cannot permeate through the separation membrane 18 flows along the flow path of the cell 12 and is sent out from the outlet side of the cell 12. The porous substrate 13 may have a monolithic structure including a plurality of cells 12, or may have a tubular structure including one cell. Its outer shape is not particularly limited, and it can be shaped like a cylinder, an elliptical cylinder, a square prism, a hexagonal prism, etc. Alternatively, the porous substrate 13 may be a tubular shape with a polygonal cross-section.

[0015] The porous substrate 13 may, for example, have an average pore diameter of about 0.1 μm to several hundred μm. Also, the porous substrate 13 may have a porosity in the range of 20% by volume or more and 70% by volume or less. Examples of the main material constituting the porous substrate 13 include one or more ceramics such as aluminum oxide (α-alumina, γ-alumina, anodic aluminum oxide, etc.), titanium oxide (titania), silicon oxide (silica), zirconia, cordierite, and mullite. Such a porous substrate 13 can be excellent in heat resistance, chemical resistance, impact resistance, etc. Among these, alumina is preferable from the viewpoints of ease of production and availability of the substrate. The porous substrate 13 is preferably formed by molding and sintering alumina particles with an average particle size of 0.001 to 30 μm as raw materials. This porous substrate 13 may have a single-layer structure or a multi-layer structure. The porous substrate 13 may, for example, include a fine-grained portion on which the intermediate membrane 15 is formed on the surface, and a coarse-grained portion on which the fine-grained portion is formed on the surface. The porous substrate 13 may be a member having a larger pore diameter than the intermediate membrane 15, or may be a member having a higher porosity. Also, the porous substrate 13 may be a member obtained by, for example, extrusion molding.

[0016] The intermediate film 15 is a film that functions as a base layer for the separation film 18. This intermediate film 15 may be, for example, a support layer formed with a thickness of 100 μm or more and not in multiple layers but in a single layer. When formed in a single layer (integrally), it is preferable because there are fewer interfaces compared to those formed in multiple layers and defects are less likely to occur. The intermediate film 15 may have an average film thickness of 120 μm or more and 450 μm or less. When it is a thick film and has few defects like this, the activation of defects in the separation film 18 can be more effectively suppressed. For the intermediate film 15, it is preferable that the maximum value of the film thickness difference between the film thickness of the central cell and the film thickness of the outermost peripheral cell is 50 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. The film thickness of the intermediate film 15 is measured by cutting the filter in the cell formation direction and observing it with an electron microscope (SEM, STEM, TEM), and measuring the intermediate film of the central cell and the upper and lower outermost peripheral cells at 24 arbitrary locations. The film thickness difference of the intermediate film 15 is obtained by finding the difference between the central cell and the outermost peripheral cell and taking its maximum value. The average film thickness of the intermediate film 15 is obtained by averaging all the measured film thicknesses. The intermediate film 15 preferably has an average pore diameter in the range of 0.1 μm or more and 0.6 μm or less.

[0017] Examples of the main materials constituting the intermediate film 15 include one or more ceramics such as alumina, titania, silica, cordierite, zirconia, and mullite. Such an intermediate film 15 can be made excellent in heat resistance, chemical resistance, impact resistance, etc. Among these, alumina is preferable from the viewpoints of ease of production and availability of the intermediate film 15. In addition to the main material, the intermediate film 15 may contain one or more sintering materials in the range of 5% by mass or more and 20% by mass or less of clay and 1% by mass or more and 35% by mass or less of titanium oxide. When containing a sintering material, the mechanical strength can be further increased.

[0018] The separation membrane 18 is formed on the intermediate membrane 15 and is a membrane that selectively permeates the separation target from the fluid to be treated. The separation membrane 18 may, for example, have an average membrane thickness in the range of 5 μm or more and 20 μm or less. When the membrane thickness is 5 μm or more, the strength of the membrane can be further increased, and when it is 20 μm or less, the permeation rate of the separation target can be ensured. For the separation membrane 18, it is preferable that the maximum value of the membrane thickness difference between the membrane thickness of the central cell and the membrane thickness of the outermost peripheral cell is 5 μm or less, more preferably 4 μm or less, and still more preferably 3 μm or less. The membrane thickness of the separation membrane 18 is measured by cutting the filter in the cell formation direction and observing it by electron microscopy (SEM, STEM, TEM), and measuring the separation membranes of the central cell and the upper and lower outermost peripheral cells at 24 arbitrary locations. The membrane thickness difference of the separation membrane 18 is obtained by finding the difference between the central cell and the outermost peripheral cell and taking the maximum value thereof. The average membrane thickness of the separation membrane 18 is obtained by averaging all the measured membrane thicknesses. The separation membrane 18 preferably has an average pore diameter in the range of 0.05 μm or more and 0.5 μm or less.

[0019] Examples of the main material constituting the separation membrane 18 include one or more ceramics such as alumina, titania, silica, cordierite, zirconia, and mullite. Such a separation membrane 18 can be made excellent in heat resistance, chemical resistance, impact resistance, and the like. Among these, alumina is preferable from the viewpoints of ease of production and availability of the separation membrane 18. Alternatively, the separation membrane 18 may be a zeolite membrane containing zeolite. Examples of zeolite include LTA (type A), MFI (ZSM-5, silicalite), MOR (mordenite), AFI (SSZ-24), FER (ferrierite), FAU (type X, type T), DDR (deca-dodecasil-3R), and the like.

[0020] The seal portion 19 is a fluid-impermeable sealant disposed so as to cover the end face of the porous base material 13. The seal portion 19 may be formed of a glass containing an alkaline component. The seal portion 19 prevents the fluid to be treated from entering the base material from the end face of the base material.

[0021] Next, a method for manufacturing the ceramic membrane filter 10 will be described. The manufacturing method of the ceramic membrane filter 10 may include, for example, a base material manufacturing step of manufacturing a base material, an intermediate membrane forming step of forming an intermediate membrane on the base material, and a separation membrane forming step of forming a separation membrane on the intermediate membrane. Note that the base material manufacturing step may be omitted by preparing the base material, or the separation membrane forming step may be omitted after manufacturing up to the intermediate membrane.

[0022] (Base material manufacturing step) In this step, a porous base material is manufactured. The raw material of the base material may be the same as those listed for the ceramic membrane filter 10. Also, the raw material of the base material may be a mixture of a first main raw material X having an average particle size of a first particle size and a second main raw material Y having a second particle size smaller than the first particle size. The first particle size of the first main raw material X may be, for example, in the range of an average particle size of 50 μm or more and 200 μm or less. The second particle size of the second main raw material Y may be, for example, in the range of an average particle size of 20 μm or more and 100 μm or less. The mass ratio X / Y of the first main raw material X and the second main raw material Y may be in the range of 1 / 2 to 2 / 1. Further, it is preferable to add a sintering material to this raw material. Examples of the sintering material include glass, clay, titania, etc. The addition amount of the sintering material is preferably in the range of 5% by mass or more and 20% by mass or less, and more preferably in the range of 15% by mass or less, based on the whole of the ceramic raw material. The shape of the base material may be formed by extrusion molding into, for example, the filter shape shown in FIG. 1. The filter shape can be, for example, a shape with a diameter of 30 mm × length of 500 mm and 37 cells, a shape with a diameter of 90 mm × length of 500 mm and 360 cells, or a shape with a diameter of 180 mm × length of 1000 mm and 2000 cells. This molded body can be fired in an oxidation atmosphere in a temperature range of 1000°C or more and 1400°C or less to obtain a fired body of the ceramic base material. Here, the "average particle size of the raw material particles" is the value measured by a laser particle size distribution analyzer (LA-920 manufactured by HORIBA).

[0023] (Intermediate membrane forming step) In this step, a raw material layer of the intermediate film is formed on a substrate. Also, in this step, a raw material slurry obtained by mixing an organic binder containing a drying crack inhibitor which is a resin having a chain structure and a molecular weight of 1000 or less, a ceramic raw material, and a solvent shall be used. Examples of the ceramic raw material include one or more ceramics such as alumina, titania, silica, zirconia, cordierite, and mullite. Among these, alumina, titania, etc. are preferable. The ceramic raw material preferably contains a main raw material and a sintering aid. As the sintering aid, it is preferable to use clay and titania, and the addition amount is preferably in the range of 5% by mass or more and 20% by mass or less with respect to the entire ceramic raw material for clay, and preferably in the range of 1% by mass or more and 35% by mass or less with respect to the entire ceramic raw material for titania. The concentration of the raw material slurry can be, for example, in the range of 10% by mass or more and 20% by mass or less in terms of the solid content of the ceramic raw material.

[0024] As the drying crack inhibitor contained in the organic binder, it is preferable to use polyvinyl alcohol. The molecular weight of this drying crack inhibitor is more preferably in the range of 300 or more and 600 or less. In this step, it is preferable to add the drying crack inhibitor in the range of 0.25 parts by mass or more and 0.95 parts by mass or less with respect to 100 parts by mass of the ceramic raw material. When the addition amount is 0.25 parts by mass or more, the occurrence of film defects due to incomplete drying can be more suppressed, and when it is 0.95 parts by mass or less, dehydration after film formation can be sufficiently performed. Also, in this step, it is preferable to use an organic binder further containing a peptizing agent and a polysaccharide compound. As the peptizing agent, for example, sodium polycarboxylate can be used. In this step, it is preferable to add the peptizing agent in the range of 0.15 parts by mass or more and 0.25 parts by mass or less with respect to 100 parts by mass of the ceramic raw material. When the addition amount of the peptizing agent is 0.15 parts by mass or more, the film raw material can be sufficiently dispersed, and the occurrence of film defects due to agglomerated particles can be suppressed. Also, when this addition amount is 0.25 parts by mass or less, the occurrence of re-aggregation can be more suppressed. The peptizing agent has a decreasing viscosity when the addition amount is gradually increased, but when further added, the viscosity starts to increase or the viscosity no longer changes. It is preferable to determine the addition amount of the peptizing agent in advance from the slurry viscosity. Also, examples of the polysaccharide compound include welan gum. In this step, it is preferable to add the polysaccharide compound in the range of 0.95 parts by mass or less with respect to 100 parts by mass of the ceramic raw material. When the addition amount of the polysaccharide compound is 0.95 parts by mass or less, dehydration by vacuum or the like can be performed, and film formation can be more reliably performed. Also, the addition amount of this polysaccharide compound is preferably 0.2 parts by mass or more. When the addition amount of the polysaccharide compound is 0.2 parts by mass or more, the film thickness can be made uniform, and the occurrence of film defects can be more suppressed, which is preferable.

[0025] In this step, it is preferable to form a raw material layer with an average film thickness of 150 μm or more and 480 μm or less. Due to the blending of the above-described organic binder, it is possible to further suppress chipping, etc. Therefore, for example, a thick film of 150 μm or more can be formed by a single film formation. In this intermediate film, when aiming for a thicker film, the blending of the organic binder becomes more effective. However, even in a thinner intermediate film of 100 μm or less, the occurrence of defects can be further suppressed. In the formation of the raw material layer of this intermediate film, it is preferable to use a ceramic raw material in which a first main raw material A having an average particle size of a first particle size and a second main raw material B having an average particle size smaller than the first particle size and having a second particle size are mixed in a mass ratio A / B in the range of 0.6 or more and 2 or less. The first particle size may be, for example, in the range where the average particle size is 1 μm or more and 5 μm or less. Also, the second particle size may be, for example, in the range where the average particle size is 0.1 μm or more and 1 μm or less. When raw materials with different particle sizes are mixed, the intermediate film can be produced by a single film formation and firing. As a method for forming the raw material layer of the intermediate film on a substrate, for example, it can be carried out using a cross-flow filtration film-forming apparatus. In this method, the control of the thickness of the intermediate film can be performed by the flow rate of the filtrate.

[0026] (Separation membrane formation step) In this step, a separation membrane is formed on the intermediate membrane. The formation of the separation membrane may use, for example, a raw material slurry obtained by mixing an organic binder, a ceramic raw material, and a solvent. As the ceramic raw material, alumina, titania, zeolite, etc. described above can be used. The organic binder may contain a peptizing agent, a polysaccharide compound, and a water-soluble acrylic resin. The peptizing agent and the polysaccharide compound described above can be used. In the formation of the separation membrane, the addition amount of the peptizing agent is preferably in the range of 0.25 parts by mass or more and 0.95 parts by mass or less with respect to 100 parts by mass of the ceramic raw material. Also, the addition amount of the polysaccharide compound is preferably in the range of 0.95% by mass or less with respect to 100 parts by mass of the ceramic raw material, and more preferably 0.2% by mass or more. Further, the addition amount of the water-soluble acrylic resin is preferably in the range of 0.5% by mass or more and 2.4% by mass or less. In such a range, the generation of membrane defects can be more suppressed and the separation membrane can be produced. The concentration of the raw material slurry can be, for example, in the range of 5% by mass or more and 10% by mass or less in terms of the solid content of the ceramic raw material. In this step, it is preferable to form a separation membrane with an average membrane thickness of 5 μm or more and 20 μm or less. As a method for forming the raw material layer of the separation membrane on the intermediate membrane, for example, it can be carried out using a cross-flow filtration membrane forming apparatus. In this method, the control of the thickness of the separation membrane can be performed by the flow rate of the filtrate.

[0027] The ceramic membrane filter thus obtained preferably has a seal portion formed on the end face. The seal portion may be, for example, glass. The formation of the seal portion may be carried out by a method of making a slurry of the weight loss and applying it, or by heating and melting the raw material and spraying it on the end face. Further, after forming the raw material layer of the intermediate membrane and the raw material of the separation membrane, firing can be performed in an oxidation atmosphere in a temperature range of 1000 °C or more and 1200 °C or less to obtain a ceramic membrane filter.

[0028] According to the ceramic membrane filter of the present embodiment described above, the generation of film defects in the intermediate film formed on the substrate can be further suppressed. Furthermore, since the separation film is formed on the intermediate film with few film defects, the generation of film defects in the separation film can be further suppressed. The reason is speculated as follows. For example, the drying crack inhibitor of the organic binder contained in the raw material slurry has a relatively low molecular weight of 1000 or less, and it is considered that the increase in the viscosity of the raw material slurry can be further suppressed. Also, in such a raw material slurry, it is speculated that the organic binder can suppress breakage during drying. Therefore, for example, the intermediate film can be thickened to 100 μm or more, 150 μm or more, etc.

[0029] Note that the present disclosure is not limited to the above-described embodiments at all, and it goes without saying that various embodiments can be implemented as long as they belong to the technical scope of the present disclosure.

Examples

[0030] Hereinafter, an example of specifically manufacturing a ceramic membrane filter will be described as an experimental example. Note that Experimental Examples 1 to 4, 8 to 11, 17 to 19, 21 to 24, 26 to 28, 30 to 39, 41 to 49 correspond to Examples, and Experimental Examples 5 to 7, 12 to 16, 20, 25, 29, 40, 50 to 52 correspond to Comparative Examples.

[0031] [Fabrication of Ceramic Membrane Filter] [Fabrication of Substrate] 30% by mass of alumina raw material with an average particle size of 100 μm, 60% by mass of alumina raw material with an average particle size of 40 μm, and 10% by mass of glass raw material with an average particle size of 5 μm were weighed. To 100 parts by mass of this raw material, 5 parts by mass of methyl cellulose, 1 part by mass of a fatty lubricant, and 35 parts by mass of water were added and kneaded, and a degassed clay intermediate formed body with a diameter of 250 mm and a length of 1000 mm was formed using a vacuum kneader. Next, a base metal was attached to the tip of a hydraulic plunger molding machine for this intermediate formed body, and a columnar base material with a diameter of 180 mm, a length of 1000 mm, and 2000 cells was produced by extrusion molding. Slits were made in the base material every 5 cells in the radial direction so that a film could be uniformly formed, and the base material was processed so that the drainage during filtration film formation would be uniform. This formed body was fired at 1250 °C for 2 hours in an oxidizing atmosphere to obtain a base material. This base material had an average pore diameter of 10 μm and a porosity of 38% by volume. The average particle size of the raw material particles was measured using a laser diffraction particle size distribution measuring device (LA-920 manufactured by HORIBA, Ltd.). The pore diameter and porosity of the base material were measured using a mercury porosimeter (AutoPore III 9400 manufactured by Shimadzu Corporation).

[0032] [Fabrication of Intermediate Film] The raw material slurry of the intermediate film was prepared by combining a ceramic raw material and a predetermined organic binder. The ceramic raw material was weighed such that the mass ratio A / B of alumina raw material A with an average particle size of 2 μm and alumina raw material B with an average particle size of 0.5 μm was 1 / 1. Further, 90% by mass of this alumina raw material and 10% by mass of clay as a sintering aid were mixed to obtain a ceramic raw material. As the organic binder, a peptizing agent, a polysaccharide compound, and polyvinyl alcohol as a dry crack inhibitor were used. As the peptizing agent, sodium polycarboxylate (Aron A6114 manufactured by Toagosei Co., Ltd.) was used. As the polysaccharide compound, welan gum (Welan gum K1A96 manufactured by PC Kelco) was used. As the dry crack inhibitor, polyvinyl alcohol with a molecular weight of 500 (PVA, JL-05E manufactured by Nippon Gohsei Co., Ltd.) was used and dissolved and added to a 2% by mass aqueous solution of solids. The slurry concentration was adjusted to 10 to 20% by mass in terms of alumina solids content. The preparation was carried out by adding water to the alumina raw material, and then adding the polysaccharide, PVA, and sodium polycarboxylate. The addition amounts of the organic binder were 0.2 parts by mass of the peptizing agent, 0.6 parts by mass of the polysaccharide compound, and 0.4 parts by mass of PVA with respect to 100 parts by mass of the ceramic raw material. Using a cross-flow filtration film-forming apparatus, the drainage volume of the slurry filtered through the substrate was adjusted so that a film thickness of 250 μm was formed on the film-forming surface of the substrate. After film formation, it was taken out from the apparatus and dried in a dryer. After drying, it was fired in an oxidizing atmosphere at 1200 °C for 5 hours.

[0033] [Preparation of Separation Membrane] A raw material slurry for the separation membrane was prepared by combining a ceramic raw material and a predetermined organic binder. As the ceramic raw material, an alumina raw material with an average particle size of 0.3 μm was used. As the organic binder, a peptizing agent, a polysaccharide compound, and a water-soluble acrylic resin (resin A) were used. As the peptizing agent, sodium polycarboxylate (Aron A6114 manufactured by Toagosei Co., Ltd.) was used. As the polysaccharide compound, welan gum (Welan gum K1A96 manufactured by PC Kelco) was used. As the water-soluble acrylic resin, an acrylic-based special water-soluble resin (Aron AS-7503 manufactured by Toagosei Co., Ltd.) was used. The slurry concentration was adjusted to 5 to 10% by mass in terms of alumina solid content. The preparation was carried out by adding water to the alumina raw material, then adding the peptizing agent, and then adding the polysaccharide, PVA, and sodium polycarboxylate. In Experimental Example 48, a slurry was prepared by adding organic binders other than the peptizing agent and then adding the peptizing agent. Using a cross-flow filtration membrane-forming apparatus, the drainage volume of the slurry filtered through the substrate was adjusted so that a membrane with a thickness of 10 μm was formed on the membrane-forming area. After membrane formation, it was taken out from the apparatus and dried in a dryer.

[0034] [End-face glass forming] Using a methyl cellulose solution previously dissolved at a solid content of 2% by mass, glass powder with an average particle size of 5 μm was mixed at 20% by mass of the powder and 80% by mass of the methyl cellulose solution, and spray coating was performed using a spray. At this time, the uncoated parts were covered so that the glass was applied only to both end faces and both ends of the outer periphery by about 15 mm (the part where the O-ring fits). The thickness of the glass was applied at 1 mm so that the surface of the substrate became smooth.

[0035] [Firing] After forming the glass on the end face, it was fired at 950 °C in an oxidizing atmosphere.

[0036] [Experimental Examples 1 to 5] The raw material mixing ratio of the intermediate film was examined. Among the above steps, those with the raw material mixing ratios of A / B = 2 / 1, 1 / 1, 0.6 / 1, 0.5 / 1, and 0.4 / 1 were taken as Experimental Examples 1 to 5.

[0037] [Experimental Examples 6 to 12] The thickness of the intermediate film was examined. Among the above steps, those with the thickness of the intermediate film set to 80 μm, 100 μm, 150 μm, 250 μm, 300 μm, 400 μm, and 500 μm were taken as Experimental Examples 6 to 12.

[0038] [Experimental Examples 13 to 28] The addition amount of the organic binder of the intermediate film was examined. Among the above steps, those with the addition amounts of the peptizing agent, polysaccharide compound, and PVA shown in Tables 1 and 2 were taken as Experimental Examples 13 to 28, respectively.

[0039] [Experimental Examples 29 to 33] The sintering material of the intermediate film was examined. With the sintering material being titania (rutile type) and the addition amount of the sintering material being 0.5% by mass, 1% by mass, 5% by mass, 10% by mass, and 35% by mass with respect to the whole of the main material and the sintering material, they were taken as Experimental Examples 29 to 33.

[0040] [Experimental Example 34] The shape of the base material was examined. With the shape of the base material being 90 mm in diameter × 1000 mm in length and three rows of slits being evenly arranged on the end face, it was taken as Experimental Example 34.

[0041] [Experimental Example 35] The sealing material of the end face was examined. Among the above steps, after forming the separation membrane, it was fired at 1200°C, and then an alumina thermal spray seal was performed on the end face. For the thermal spray, alumina heated and melted at 1000°C was formed with a thickness of 1 mm on both end faces of the fired ceramic membrane filter. What was obtained was taken as Experimental Example 35.

[0042] [Experimental Examples 36 to 50] The addition amount of the organic binder of the separation membrane was examined. Among the above steps, those with the addition amounts of the peptizing agent, polysaccharide compound, and resin A shown in Table 3 were taken as Experimental Examples 36 to 50, respectively.

[0043] [Experimental Examples 51, 52] The molecular weight of PVA contained in the organic binder used for the intermediate film was investigated. For the PVA contained in the organic binder used for the intermediate film, those with a molecular weight of 2400 and addition amounts of 0.2% by mass and 0.4% by mass were designated as Experimental Examples 51 and 52, respectively.

[0044] (Evaluation of Foaming in Water) After film formation of the ceramic membrane filters of Experimental Examples 1 to 52, an evaluation of foaming in water was carried out. The filter of each experimental example was placed in water at 20 °C and normal pressure (atmospheric pressure), air was gradually pressurized from the side surface side, and the pressure (MPa) at which foaming occurred from the outlet side and the number of foamed cells were measured. For the evaluation of foaming in water, those with "the initial foaming pressure in water is 0.08 MPa or more and the ratio of the number of foamed cells is 9% or less of the total number of cells" corresponded to "there are no cracks exceeding 4 μm and the number of cells with cracks of 1 μm or more and 4 μm or less is 9% or less of the total number of cells", and this was designated as "○", and those that did not satisfy this, that is, those with cracks exceeding 4 μm or those without cracks exceeding 4 μm but with the number of cells having cracks of 1 μm or more and 4 μm or less exceeding 9% of the total number of cells were designated as "×".

[0045] (Average Pore Diameter of Intermediate Film and Separation Film) The average pore diameters of the intermediate film and the separation film were determined by analyzing SEM images. The cross-section of the intermediate film was observed by SEM and separated into a pore region and a material region of the intermediate film by image processing. The diameter of the circle inscribed in the pore region was determined, and its average value was taken as the average pore diameter. The same applies to the separation film.

[0046] (Measurement of Film Thickness Difference) The film thickness differences of the intermediate film and the separation film between the central cell and the outermost peripheral cell of the ceramic membrane filter were measured. The filter was cut in the cell formation direction, and the thicknesses of the intermediate film and the separation film of the central cell and the upper and lower outermost peripheral cells were measured. The film thickness was measured at 24 arbitrary locations of the cell, the difference between the film thickness of the central cell and the film thickness of the outermost peripheral cell was determined, and the maximum value was taken as the film thickness difference (μm). Also, the average value of all the obtained film thicknesses was taken as the film thickness of the intermediate film and the film thickness of the separation film.

[0047] When manufacturing a ceramic membrane filter, the appropriate addition amount of an organic binder was determined. The addition amount of a peptizing agent to a raw material slurry containing a ceramic raw material was changed, the slurry viscosity at that time was determined, the relationship between the viscosity of the raw material slurry and the addition amount was determined, and the range where the viscosity became lower was set as the appropriate addition amount. Further, the addition amount was changed using the peptizing agent alone, a combination of a polysaccharide compound and PVA, and a combination of the peptizing agent and PVA, and the film thickness difference was determined. In that measurement, the substrate was set vertically, and an intermediate film or a separation film was formed using the raw material slurry. The relationship between the film thickness difference and the addition amount was determined, and the range where the film thickness difference became smaller, that is, the range of the addition amount where the thickness distribution in the radial direction and the thickness distribution in the cell formation direction became more uniform, was set as the appropriate addition amount.

[0048] (Results and Discussion) The preparation conditions and test results of Experimental Examples 1 to 52 are shown in Tables 1 to 3. As shown in Table 1, in Experimental Examples 1 to 5, when the blending ratio of the main raw materials of the intermediate film is such that the mass ratio A / B of alumina raw material A with an average particle size of 2 μm and alumina raw material B with an average particle size of 0.5 μm is in the range of 0.6 to 2, the number of foamed cells with an initial foaming pressure of 0.1 MPa or more in water is preferably 2.5% or less of the whole cells. Also, the average pore diameter of the intermediate film preferably ranges from 0.1 to 0.6 μm. As shown in Experimental Examples 6 to 12, the film thickness of the intermediate film is preferably more than 80 μm and less than 500 μm, and is presumably preferably in the range of 120 to 480 μm. As shown in Experimental Examples 13 to 28, the addition amount of the organic binder is preferably in the range of 0.15% by mass or more and 0.25% by mass or less with respect to 100% by mass of the ceramic raw material for the peptizing agent, preferably in the range of 0.95% by mass or less (more preferably in the range of 0.2% by mass or more) for the polysaccharide compound, and preferably in the range of 0.25% by mass or more and 0.95% by mass or less for PVA. Regarding the sintering aid, as shown in Experimental Examples 29 to 33, when the sintering aid is titania, it was found that the addition amount with respect to the whole ceramic raw material is preferably in the range of 1% by mass or more and 35% by mass or less. When the sintering aid is clay, when the relationship between the addition amount and the number of foamed cells in water was examined separately, it was found that the addition amount with respect to the whole ceramic raw material is preferably in the range of 5% by mass or more and 20% by mass or less. Also, as shown in Experimental Example 34, the same results were obtained even when the base material was changed.

[0049] In the formation of the separation membrane, as shown in Experimental Examples 36 to 50, the addition amount of the organic binder is preferably in the range of 0.20% by mass or more and 0.95% by mass or less with respect to 100% by mass of the ceramic raw material for the peptizing agent, preferably in the range of 0.95% by mass or less (more preferably in the range of 0.2% by mass or more) for the polysaccharide compound, and preferably in the range of 0.5% by mass or more and 2.4% by mass or less for the water-soluble acrylic resin (Resin A). It was also found that similar results can be obtained with alumina or titania as the main material of the separation membrane. Further, as shown in Experimental Examples 51 and 52, when PVA having a molecular weight of 2400 was used as the organic binder for the intermediate membrane, the viscosity was high and defects occurred in the intermediate membrane. On the other hand, it was found that the use of PVA having a molecular weight of 500 can suppress the occurrence of defects in the intermediate membrane.

[0050]

Table 1

[0051]

Table 2

[0052]

Table 3

[0053] Note that the present disclosure is not limited to the above-described embodiments at all, and it goes without saying that various embodiments can be implemented as long as they belong to the technical scope of the present disclosure.

[0054] This application claims the priority based on Japanese Patent Application No. 2016-68395 filed on March 30, 2016, and all of its contents are incorporated herein by reference.

Industrial Applicability

[0055] The invention disclosed in this specification can be used in the technical field of separation membranes.

Explanation of Reference Numerals

[0056] 10 ceramic membrane filter, 12 cell, 13 porous substrate, 15 intermediate membrane, 17 slit, 18 separation membrane, 19 seal part.

Claims

1. a substrate forming a cell through which a fluid flows; an intermediate film formed on the substrate; a separation film formed on the intermediate film, and comprising: the cells having cracks with a size of 4 μm or less obtained by underwater foaming evaluation accounting for 9% or less of the total number of cells; except for those in which the film thickness of the intermediate film is 170 μm or less; the intermediate film is a single layer; a ceramic membrane filter.

2. The ceramic membrane filter according to Claim 1, wherein the initial foaming pressure in water is 0.08 MPa or more, and the ratio of the number of foaming cells at the time of initial foaming is 9% or less of the total number of cells.

3. The ceramic membrane filter according to Claim 1 or 2, wherein the separation film has an average film thickness of 5 μm or more and 20 μm or less.

4. The ceramic membrane filter according to any one of Claims 1 to 3, wherein the intermediate film has an average film thickness of 120 μm or more and 450 μm or less.

5. The ceramic membrane filter according to any one of Claims 1 to 4, wherein the intermediate film has an average pore diameter in the range of 0.1 μm or more and 0.6 μm or less.

6. The ceramic membrane filter according to any one of Claims 1 to 5, wherein the intermediate film contains any one of aluminum oxide and titanium oxide as a main raw material, and contains any one of clay and titanium oxide as a sintering material.

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