Porous ceramic layer for separation membrane, porous ceramic laminate for separation membrane, and separation membrane

Abstract

The purpose of the present invention is to provide a porous ceramic layer useful for a separation membrane, which has excellent permeation performance and in which the occurrence of coarse voids is suppressed. The present disclosure provides a porous ceramic layer for a separation membrane, the porous ceramic layer having a survival bone rate (SBR) value of more than 6.1% but less than 15%, and pores spreading three-dimensionally.

Description

Porous ceramic layer for separation membrane, porous ceramic laminate for separation membrane, and separation membrane

[0001] This disclosure relates to a porous ceramic layer for separation membranes, a porous ceramic laminate for separation membranes, and a separation membrane.

[0002] Porous ceramic materials for separation membranes are used in various fields as membranes that have the function of separating fluids, whether gas or liquid, (including concentration or filtration), such as microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, reverse osmosis membranes, ion exchange membranes, and gas separation membranes.

[0003] For example, Patent Document 1 discloses a ceramic filter in which a ceramic film having a mode diameter of 0.05 to 0.3 μm and a maximum pore diameter of 0.8 μm or less is formed on the surface of an alumina substrate tube, and the porosity is 35% or more. Patent Document 2 also discloses a porous support comprising a substrate, an intermediate layer formed on the inner surface of the substrate, a support layer formed on the inner surface of the intermediate layer, and an outermost layer formed on the inner surface of the support layer, and states that it is preferable for the porosity of the intermediate layer to be 5 to 60% and the average pore diameter to be 0.05 to 5 μm.

[0004] Japanese Patent Publication No. 2007-283219, International Publication No. 2017 / 169591

[0005] When a porous ceramic body is used as a separation membrane by laminating an upper layer, such as a functional layer or a cake layer, onto its outermost surface, it is desirable that the separation membrane has excellent fluid permeability and that the generation of large voids in the upper layer be suppressed in order to achieve good separation performance. However, a porous ceramic layer useful for separation membranes that has excellent permeability and suppresses the generation of large voids has not yet been proposed.

[0006] Therefore, the problem to be solved by this disclosure is to provide a porous ceramic layer useful for separation membranes that has excellent permeability and suppresses the generation of coarse voids, a porous ceramic laminate containing the same, and a separation membrane.

[0007] The present disclosure, which has achieved the above objectives, is as follows: [1] A porous ceramic layer for separation membranes having a Survival Bone Rate (SBR) value greater than 6.1% and less than 15%, and having pores that extend in three dimensions. [2] The porous ceramic layer for separation membranes according to [1], wherein the porous ceramic layer contains a metal oxide, and the amount of aluminum atoms is 50 mol% or more of the total 100 mol% of metal atoms constituting the metal oxide. [3] The porous ceramic layer for separation membranes according to [2], wherein the amount of aluminum atoms is 90 to 100 mol% of the total 100 mol% of metal atoms constituting the metal oxide, and the amount of metal oxide in 100 mass% of the porous ceramic layer for separation membranes is 80 to 100 mass%. [4] The porous ceramic layer for separation membranes according to any one of [1] to [3], wherein the pore diameter measured by the mercury intrusion method is 0.01 to 0.7 μm. [5] A porous ceramic layer for separation membranes according to any one of [1] to [4], having a thickness of 3 to 300 μm. [6] Use of the porous ceramic layer for separation membranes according to any one of [1] to [5] as a separation membrane. [7] A porous ceramic laminate having a first porous ceramic layer and a second porous ceramic layer laminated on the surface of the first porous ceramic layer, wherein the average pore diameter of the first porous ceramic layer is larger than the average pore diameter of the second porous ceramic layer, the first porous ceramic layer and the second porous ceramic layer contain a metal oxide, and the second porous ceramic layer is the porous ceramic layer according to any one of [1] to [5]. [8] A porous ceramic laminate for separation membranes according to [7], wherein the amount of aluminum atoms is 50 to 100 mol% of the total 100 mol% of metal atoms constituting the metal oxide contained in the first porous ceramic layer, and the amount of metal oxide in 100 mass% of the first porous ceramic layer is 80 to 100 mass%. [9] A porous ceramic laminate for a separation membrane according to [7] or [8], wherein the average pore size of the first porous ceramic layer, as measured by the mercury intrusion method, is 5 to 25 μm.

[10] A porous ceramic laminate for a separation membrane according to any one of [7] to [9], wherein the thickness of the first porous ceramic layer is 400 to 8000 μm.

[11] A porous ceramic laminate for separation membranes according to any one of [7] to

[10] , which is tubular, honeycomb, or monolithic.

[12] A separation membrane composed of a porous ceramic laminate for separation membranes according to any one of [7] to

[11] .

[13] The separation membrane according to

[12] , in which a functional layer is directly laminated to the second porous layer.

[14] Use of a porous ceramic laminate for separation membranes according to any one of [7] to

[11] as a separation membrane.

[0008] According to the porous ceramic layer of this disclosure, in a separation membrane having an upper layer such as a functional layer on top of the porous ceramic layer, it is possible to improve the fluid permeability performance and suppress the generation of coarse voids.

[0009] Figure 1 shows the results of a pore analysis of the second porous ceramic layer in the laminate obtained in Example 1. Figure 2 shows the results of a pore analysis of the second porous ceramic layer in the laminate obtained in Comparative Example 1.

[0010] 1. The porous ceramic layer for the separation membrane has a Survival Bone Rate (SBR) value greater than 6.1% and less than 15%, and its pores are three-dimensionally extended. Three-dimensional extension of pores means that the pores are irregular in shape, or that the pores are not linear (for example, the pores found in an anodic oxide film).

[0011] <Survival Bone Rate (SBR)> SBR is a parameter that indicates the ratio of remaining trabeculae in osteoporosis. It is a value calculated by considering the trabeculae as channels through which electricity flows. It can be obtained by performing a pore analysis (3D-VNET) on a series of slice images of a porous ceramic layer using quantitative analysis software such as TRI / 3D-BON-FCS64 (manufactured by RATOC Systems Engineering). In this document, the SBR of a porous ceramic layer refers to the SBR calculated by considering the pore network structure as channels through which electricity flows in a porous ceramic layer composed of trabeculae and pores.

[0012] The specific method for calculating SBR using TRI / 3D-BON-FCS64 is as follows. First, perform NodeStrut intermediate file output during communication hole measurement to create an intermediate file. At this time, the target data is the binarized void, the CT data is the outermost pixel of the trimmed region (a box with 6 faces), and the target region is the result of inverting the CT data (the inside of the box). Next, in the flow path detailed analysis, specify the created intermediate file, set the first slice in the Z direction of the continuous slice image as the starting surface "From", and the last slice as the ending surface "To", and perform the flow path analysis to calculate the SBR. The volume resistivity ρ in the flow path analysis is set to 1.0. A specific method of analysis using the software can be found, for example, in the example described below.

[0013] SBR is an indicator of the ease of flow in a flow path; a larger SBR indicates a more fluid-friendly network structure. Specifically, the internal resistance is calculated from the cross-sectional area S and length L of the connecting holes (parts where multiple pores connect to form a single flow path) obtained from the image analysis of continuous slice images. The current for each connecting hole is then determined by applying a voltage of 1V between "From" and "To". The equivalent resistance of the entire pore network within the analysis region is obtained from the sum of the calculated currents and the applied voltage V. A smaller equivalent resistance indicates a more fluid-friendly network structure. Furthermore, if RE is the equivalent resistance of the pore network, SE is the equivalent cross-sectional area, and LE is the distance between From and To, then RE can be expressed as RE = ρLE / SE, and the equivalent resistance decreases as the equivalent cross-sectional area increases. SBR is the value obtained by dividing this equivalent cross-sectional area by the area of ​​the reference From surface, and it is an indicator of how much equivalent cross-sectional area is present relative to the input area, that is, how fluid-friendly the network is. It should be noted that "porosity," which is commonly used when evaluating porous materials, includes closed pores that do not penetrate both surfaces of the porous material. Therefore, a high porosity does not necessarily mean a high SBR. Unlike porosity, SBR is an index that focuses on interconnected pores.

[0014] If the SBR of the porous ceramic layer is 6.1% or less, the permeability of the separation membrane on which the upper layer, such as a functional layer, is laminated decreases. Furthermore, when the upper layer is coated and laminated, the liquid in the coating slurry does not completely escape from the porous ceramic layer and remains in the upper layer when the upper layer is laminated, resulting in voids after drying, which can cause large voids to form in the upper layer. On the other hand, if the SBR is too high, it becomes necessary to increase the thickness of the porous ceramic layer to ensure its strength, which tends to reduce its permeability. From this viewpoint, the SBR of the porous ceramic layer is greater than 6.1%, preferably 6.5% or more, more preferably 6.5% or more and less than 15%, even more preferably 7.0% to 13%, and even more preferably 7.5% to 10%. From the viewpoint of suppressing He permeation from large voids, the SBR of the porous ceramic layer may be greater than 6.1% and 8.0% or less.

[0015] <Composition of Porous Ceramic Layer> The porous ceramic layer preferably contains a metal oxide, and in this case, it is preferable that the amount of aluminum atoms is 50 mol% or more of the total 100 mol% of metal atoms constituting the metal oxide. Examples of metal atoms other than aluminum atoms constituting the metal oxide include Li, Be, B, Na, Mg, Si, K, Ca, Sc, Ti, V, Cr, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Ag, Cd, In, Sn, Sb, Te, Cs, Ba, La, Ta, W, Hg, Tl, Pb, and Th, and at least one of these can be included, with Ti being particularly preferable. When Al and Ti are included as metals constituting the metal oxide, in terms of oxide, Al ２ O ３ TiO2 per 100 parts by mass ２ The amount is preferably 3 to 20 parts by mass, and more preferably 5 to 15 parts by mass. In this specification, "metal" includes metalloids such as Si.

[0016] Of the total 100 mol% of metal atoms constituting the metal oxide, the amount of aluminum atoms is preferably 50 to 100 mol%, more preferably 70 to 100 mol%, even more preferably 80 to 100 mol%, and particularly preferably 90 to 100 mol%. The amount of metal oxide in 100 mass% of the porous ceramic layer is preferably 80 to 100 mass%, and more preferably 90 to 100 mass%.

[0017] <Pore Diameter of Porous Ceramic Layer> The pore diameter of the porous ceramic layer, as measured by the mercury intrusion method, is preferably 0.01 to 0.7 μm, more preferably 0.05 to 0.6 μm, and even more preferably 0.08 to 0.3 μm. From the viewpoint of suppressing He transmission from coarse voids, a range of 0.2 to 0.4 μm is also acceptable. The pore diameter refers to the pore diameter that shows a peak in a graph with the horizontal axis as pore diameter and the vertical axis as log differential pore volume. As described in the examples below, the pore distribution by the mercury intrusion method refers to the value evaluated in the range of pore diameters from 0.025 to 200 μm. It is preferable that the porous ceramic layer does not have pores with a diameter exceeding 200 μm.

[0018] <Thickness of the porous ceramic layer> The thickness of the porous ceramic layer is, for example, 3 to 300 μm, preferably 5 to 100 μm.

[0019] 2. Porous ceramic laminate The porous ceramic layer is preferably used as a porous ceramic laminate by laminating it on other porous ceramic layers. Specifically, such a laminate is a porous ceramic laminate having a first porous ceramic layer and a second porous ceramic layer laminated on the surface of the first porous ceramic layer, wherein the average pore diameter of the first porous ceramic layer is larger than the average pore diameter of the second porous ceramic layer, the first porous ceramic layer and the second porous ceramic layer contain a metal oxide, and the second porous ceramic layer is the porous ceramic layer. In such a laminate, not only the second porous ceramic layer but also the first porous ceramic layer may be the porous ceramic layer.

[0020] <Shape> The shape of the porous ceramic laminate may be, for example, plate-like, tubular, honeycomb-like, or monolithic. A tubular shape is a columnar shape having one hole penetrating in the axial direction, a monolithic shape is a columnar shape (cylinder, prism, elliptical prism, etc.) having multiple holes penetrating in the axial direction (cylindrical shape is preferred), and a honeycomb shape is a shape in which hollow three-dimensional figures (regular hexagonal prism, square prism, triangular prism, etc.) penetrating in the axial direction are stacked without gaps. The shape of the porous ceramic laminate is preferably tubular, honeycomb-like, or monolithic. When the porous ceramic laminate is tubular, honeycomb-like, or monolithic, the shape of the through-hole and / or the outer shape of the column in a cross-section perpendicular to the axial direction is preferably a circle, ellipse, square (square or rectangle), or a polygon other than a square, and it is more preferable that all of them are circles.

[0021] The length of the porous ceramic laminate is, for example, 50 to 5000 mm, preferably 90 to 3000 mm. If the porous ceramic laminate is tubular, the outer diameter is, for example, 5 mm to 20 mm, and the inner diameter of the through-holes is, for example, 1 mm to 15 mm. If the porous ceramic laminate is monolithic or honeycomb, the outer diameter is, for example, 5 mm to 300 mm, and the inner diameter of each through-hole is, for example, 0.1 mm to 10 mm.

[0022] <Laminated Structure> When the laminate is tubular, honeycomb, or monolithic, the second porous ceramic layer is preferably formed only on the inner circumferential surface, only on the outer circumferential surface, or on both the inner and outer circumferential surfaces of the through-holes of the first porous ceramic layer, more preferably on only the inner circumferential surface or only on the outer circumferential surface, and even more preferably on only the inner circumferential surface. The second porous ceramic layer may be laminated directly onto the first porous ceramic layer, or it may be laminated onto the first porous ceramic layer via one or more other layers. If there are other layers, the average pore diameter of the other layers is, for example, 0.1 to 5 μm, preferably 0.1 to 1 μm, and the thickness (total thickness if there are multiple layers) may be about 5 to 50 μm.

[0023] <First Porous Ceramic Layer> The first porous ceramic layer is not particularly limited except that it contains a metal oxide and that its average pore diameter is larger than that of the second porous ceramic layer. The average pore diameter of the first porous ceramic layer, as measured by the mercury intrusion method, is preferably in the range of 5 to 25 μm, more preferably 5 to 20 μm, even more preferably 5 to 15 μm, and most preferably 5 to 12 μm. This pore diameter refers to the pore diameter that shows a peak in a graph with the horizontal axis representing the pore diameter and the vertical axis representing the log differential pore volume.

[0024] The first porous ceramic layer preferably contains a metal oxide, in which case the metal atoms constituting the metal oxide include Al, Li, Be, B, Na, Mg, Si, K, Ca, Sc, Ti, V, Cr, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Ag, Cd, In, Sn, Sb, Te, Cs, Ba, La, Ta, W, Hg, Tl, Pb, and Th, and it is preferable to contain at least one of these, more preferably at least one of Al, Si, and Ti, and even more preferably Al (aluminum). Of the total 100 mol% of metal atoms constituting the metal oxide of the first porous ceramic layer, the amount of aluminum atoms is preferably 50 to 100 mol%, more preferably 70 to 100 mol%, even more preferably 80 to 100 mol%, and particularly preferably 90 to 100 mol%. The amount of metal oxide in 100% by mass of the first porous ceramic layer is preferably 80 to 100% by mass, and more preferably 90 to 100% by mass.

[0025] The first porous ceramic layer has a shape similar to that of the porous ceramic laminate, and is preferably plate-shaped, tubular, honeycomb-shaped, or monolithic, with tubular, honeycomb-shaped, or monolithic being more preferred. The thickness (average value) of the first porous ceramic layer is preferably 400 to 8000 μm. When the first porous ceramic layer is honeycomb-shaped or monolithic, the thickness may be the average value of the closest proximity distance between adjacent tubes in a plane perpendicular to the long axis.

[0026] <He Permeation Amount and He Permeation Amount from Coarse Voids> The He permeation amount (1) when the porous ceramic laminate after laminating the upper layer is measured by the method described in the Examples below is preferably 2.5×10 －５ to 5.0×10 －５ (mol / (m ２ ·sec·Pa)), more preferably 3.0×10 －５ to 4.8×10 －５ (mol / (m ２ ·sec·Pa)), still more preferably 3.5×10 －５ to 4.5×10 －５ (mol / (m ２ ·sec·Pa)). Further, the He permeation amount (2) from coarse flow paths (voids) in the porous ceramic laminate after laminating the upper layer is preferably 0 to 3.0×10 －８ (mol / (m ２ ·sec·Pa)), more preferably 0 to 2.0×10 －８ (mol / (m ２ ·sec·Pa)), still more preferably 0 to 1.5×10 －８ (mol / (m ２ ·sec·Pa)), and most preferably 0 (mol / (m ２ ·sec·Pa)). The ratio of the He permeation amount (2) from coarse flow paths (voids) to the He permeation amount (1) ((2) / (1)) is preferably 0 to 1.0×10 －３ , more preferably 0 to 7.0×10 －４ , still more preferably 0 to 4.0×10 －４ .

[0027] 3. Method for Producing Porous Ceramic Layer and Porous Ceramic Laminate The porous ceramic layer of the present disclosure can be obtained by applying a slurry containing raw material particles and a thickener to a substrate (including a first porous ceramic layer) and performing heat treatment. In this process, it is important to use particles whose three-dimensional particle unevenness (described later) and equivalent spherical diameter fall within predetermined ranges, and to adjust the temperature when adding the thickener to a predetermined range.

[0028] Specifically, a slurry is prepared containing raw material particles having a roughness of 6.0 or more in proportion to 0.7 volume% or more (preferably 80 volume% or less) of particles with a roughness exceeding 6.0 and an equivalent spherical diameter D50 of 0.1 μm or more and 10 μm or less, and a thickening agent, and the temperature when adding the thickening agent is adjusted to 60°C or higher to obtain the slurry, and the slurry is applied to a substrate which is a first porous ceramic layer, and heat treatment is performed to obtain a porous ceramic laminate in which the porous ceramic layer of the present disclosure is laminated as a second porous ceramic layer on the first porous ceramic layer.

[0029] <Three-dimensional particle roughness of raw material particles> Three-dimensional particle roughness (hereinafter sometimes simply referred to as roughness) is a shape parameter when focusing on each individual raw material particle, and is related to the particle volume V (μm). ３ ) and the volume of the rectangular parallelepiped circumscribing the particle La × Lb × Lc (μm ３ Based on the above, the value is defined by the following formula (a1): Three-dimensional particle roughness = La × Lb × Lc / V ・・・・・(a1) Here, La, Lb, and Lc represent the lengths of the three sides of the circumscribed rectangular parallelepiped of the particle, and La, Lb, and Lc are orthogonal. Using the above formula (a1), the three-dimensional particle roughness can be obtained from 100 or more particles as an index that shows the shape characteristics of each particle. Furthermore, the ratio (volume %) is obtained by dividing the total volume of particles with a roughness exceeding 6.0 among all measured particles by the total volume of all measured particles.

[0030] When the volume ratio of raw material particles having an unevenness degree exceeding 6.0 is less than 0.7% by volume, this means that the proportion of particles with few unevenness increases, leading to a direction in which particles are densified. As a result, the number of bonding sites between particles increases, and it is considered that particles are excessively sintered with each other, resulting in clogging of pores. On the other hand, if the volume ratio is too large, the smoothness of the surface of the obtained porous ceramic layer tends to decrease, so the volume ratio is preferably, for example, 80% by volume or less. In the raw material particles, it is also preferable to adjust the ratio of particles having an unevenness degree of less than 4.2, and the volume ratio of particles having an unevenness degree of less than 4.2 is, for example, 90 to 10% by volume. It is also preferable to adjust the ratio of particles having an unevenness degree of 4.2 or more and 6.0 or less, and the volume ratio of particles having an unevenness degree of 4.2 or more and 6.0 or less is, for example, 8 to 50% by volume. The raw material particles are preferably metal oxide particles, and all the descriptions of metal oxides exemplified as the composition of the porous ceramic layer can be referred to.

[0031] La, Lb, Lc and V in formula (a1) can be obtained by three-dimensional quantitative analysis of raw material particles, and the detailed procedure is as shown in the Examples described later.

[0032] <Equivalent Spherical Diameter of Raw Material Particles> Furthermore, as raw material particles for forming a porous ceramic layer, it is also important to use raw material particles that have a high unevenness degree and an average equivalent spherical diameter (particle diameter) of 0.1 µm or more and 10 µm or less (preferably 0.1 µm or more and 1 µm or less, more preferably 0.1 µm or more and 0.7 µm or less). Here, the "equivalent spherical diameter" is one parameter of raw material particles, and corresponds to the volume V (µm ３ ) of the raw material particle, and refers to the diameter d of a sphere having the same volume as that, and is a value that satisfies the following formula (a2). V = 4π / 3 × (d / 2) ３ ...... (a2) The "equivalent spherical diameter" is calculated from 100 or more particles using the above formula (a2), and the cumulative 50% equivalent diameter on a volume basis is taken as the average particle diameter (average equivalent spherical diameter).

[0033] When the equivalent spherical diameter of the raw material particles is 0.1 µm or more and 10 µm or less (preferably 0.1 µm or more and 1 µm or less, more preferably 0.1 µm or more and 0.7 µm or less), the SBR of the porous ceramic layer can be adjusted within the above range. If the diameter is smaller than the above lower limit, the reactivity is high, sintering progresses, voids collapse, and the SBR decreases. If the diameter is larger than the above upper limit, the reactivity is poor, and sufficient bonding with the aggregate does not progress.

[0034] <Method for producing raw material particles> The raw material particles satisfying the above requirements for unevenness degree and equivalent spherical diameter can be produced by firing an intermediate powder of raw material particles (intermediate 2 described later) in an atmosphere with adjusted water vapor partial pressure, and then performing jet mill pulverization under appropriate conditions.

[0035] It is preferable that the water vapor partial pressure in the atmosphere for firing the intermediate (intermediate 2) of the raw material particles is 40 Pa or more (when the total pressure is 0.1 MPa gas, the dew point is -30°C or higher). This can prevent sintering in a state where particles are excessively adhered to each other, and enables sintering in a state where a neck is formed at the interface between particles, so that unevenness can be formed on the finally obtained particles. On the other hand, it is preferable that the water vapor partial pressure is 600 Pa or lower (when the total pressure is 0.1 MPa gas, the dew point is 0°C or lower). By this means, the equivalent spherical diameter of the finally obtained particles can be adjusted to the above range.

[0036] Furthermore, it is preferable that the firing of the intermediate powder (intermediate 2) of raw material particles is performed at 1000 to 1250°C for 2 to 4 hours. If the temperature is too low or too high, the equivalent spherical diameter cannot be adjusted to the above range; in addition, when the temperature is too high, it is also difficult to properly adjust the unevenness degree. Furthermore, if the firing time is too short or too long, the equivalent spherical diameter cannot be adjusted to the above range; in addition, if the firing time is too long, sintering occurs and the particles become nearly spherical, so the unevenness degree decreases, and if the firing time is too short, sintering does not progress, so no neck is formed, and the unevenness degree decreases.

[0037] If the particles after firing (intermediate 2 after firing) are not pulverized, the particles are aggregated into nearly spherical particles with some sintering, resulting in a low degree of particle roughness. In other pulverizing devices such as ball mills, the particles wear down, drastically reducing the degree of roughness. When pulverizing the particles after firing with a jet mill, it is preferable to set the G pressure (Grinding Pressure) to 0.4 to 0.8 MPa. If the G pressure is too high, the uneven parts wear down, making it impossible to control the degree of roughness. If it is too low, pulverization is insufficient, making it difficult to keep the equivalent spherical diameter of the particles within the above range.

[0038] When the raw material particles are alumina, for example, it is preferable to obtain an alumina intermediate (intermediate 1) by calcining aluminum hydroxide obtained by hydrolyzing aluminum alkoxide, and then obtain an alumina intermediate powder (intermediate 2) by jet milling this alumina intermediate (intermediate 1). It is preferable that the main crystalline phase of these alumina intermediates (intermediate 1 and 2) is the θ phase (the proportion of the θ phase is greater than 50% by mass), and it is also preferable that the proportion of the α-alumina phase in 100% by mass of the alumina intermediates (intermediate 1 and 2) is 1 to 5% by mass.

[0039] <Preparation of Slurry> The slurry containing the above raw material particles contains a thickener and usually a solvent. In order to obtain the porous ceramic layer of this disclosure in which the SBR is within a predetermined range, it is important to set the temperature when adding the thickener to 60°C or higher, and then to cool it to a range of 0 to 10°C. Specifically, the thickener should be added to a solvent adjusted to 60°C or higher to disperse the thickener well, and then the solvent in which the thickener is dispersed should be cooled to a range of 0 to 10°C to uniformly dissolve the thickener. In this way, the raw material particles and the thickener are uniformly mixed, the aggregation state of the raw material particles is controlled, and the SBR of the resulting porous ceramic layer can be within the above range. The slurry temperature when adding the thickener is preferably 60°C or higher and 90°C or lower.

[0040] After adding the thickener to the solvent, it is preferable to stir for 5 to 15 minutes to thoroughly disperse the thickener in the solvent. The order in which the raw material particles and thickener are added is not particularly limited; for example, the raw material particles, thickener, and other components to be mixed as needed may be added to the solvent simultaneously. After preparing the slurry, it is preferable to perform a defoaming treatment.

[0041] The amount of raw material particles in 100% by mass of the slurry is preferably 5 to 15% by mass. Furthermore, the amount of raw material particles in 100% by mass of solid content in the slurry is preferably 50 to 70% by mass.

[0042] Examples of thickening agents include methylcellulose, hydroxyethyl methylcellulose, hydroxyethylcellulose, hydroxypropyl methylcellulose, polyalkylene oxide, polyvinyl alcohol, sodium polyacrylate, polyvinylpyrrolidone, polyacrylamide, and polydimethylaminoethyl methacrylate, with hydroxypropyl methylcellulose being particularly preferred. The concentration of the thickening agent in 100% by mass of the slurry is preferably 0.5 to 5% by mass. Furthermore, the amount of the thickening agent in 100% by mass of the solid content in the slurry is preferably 20 to 30% by mass.

[0043] The solvent typically included in the slurry may be water or an organic solvent.

[0044] The slurry may contain a dispersant. The dispersant may be a cationic surfactant, anionic surfactant, nonionic surfactant, or amphoteric surfactant. Among these, anionic surfactants such as ammonium polycarboxylate salts and amine polycarboxylate salts are preferred, and products such as SN Dispersant 5020, SN Dispersant 5023, SN Dispersant 5027, SN Dispersant 5468, Noparfa D-6010, Nopcol 5200, Nopcosanto RFA, Nopcospers 6100, and Nopcospers 6150 from Sunopco can be used. The concentration of the dispersant in the slurry (in terms of active ingredient) is preferably 0.02 to 5 parts by mass per 100 parts by mass of raw material particles in the slurry.

[0045] <Slurry Application> The method of applying the slurry to the substrate (first porous ceramic layer) is not particularly limited, and methods such as spray coating, dip coating, suction coating, ultrasonic atomization, spray coating, or ball injection (see Japanese Patent Publication No. 2025-022448) can be employed. After applying the slurry, it is preferable to heat treat at, for example, 1000 to 1500°C for 1 to 8 hours. Within the above range, the lower the heat treatment temperature, the smaller the average pore size of the resulting porous ceramic layer tends to be.

[0046] 4. Applications The porous ceramic laminate of this disclosure can be used as a filtration membrane such as a microfiltration membrane, ultrafiltration membrane, or nanofiltration membrane, and if necessary, a functional layer can be further laminated as an upper layer to be used as a separation membrane for fluids (liquids, liquids containing solids, or gases such as He gas or water vapor) such as a filtration membrane such as a microfiltration membrane, ultrafiltration membrane, or nanofiltration membrane; a reverse osmosis membrane; an ion exchange membrane; or a separation membrane for gases, etc. In a separation membrane, it is preferable that the second porous layer and the functional layer of the porous ceramic laminate of this disclosure are laminated together, and it is more preferable that the second porous layer and the functional layer are directly laminated together.

[0047] Examples of the functional layers mentioned above include zeolites, MOFs (Metal Organic Frameworks), porous silica films, and porous alumina films.

[0048] A separation membrane equipped with a functional layer can be manufactured by applying a liquid containing inorganic particles or MOF constituting a functional layer to the surface of the second porous layer of the porous ceramic laminate of this disclosure and heat-treating it. The heat treatment conditions can be appropriately selected according to the functional layer to be laminated, but for example, a separation membrane can be manufactured by heat-treating at 80 to 800°C for 1 to 10 hours. The amount of inorganic particles or MOF in the liquid containing inorganic particles or MOF constituting the functional layer is preferably 1 to 10% by mass.

[0049] This application claims the benefit of priority based on Japanese Patent Application No. 2025-041169, filed on 14 March 2025. The entire specification of Japanese Patent Application No. 2025-041169, filed on 14 March 2025, is incorporated herein by reference.

[0050] The present disclosure will be described in more detail below with reference to examples. The present disclosure is not limited by the following examples, and it is certainly possible to implement it with appropriate modifications to the extent that it is in line with the spirit described above and below, and such modifications will all be included within the technical scope of the present disclosure.

[0051] <SBR Measurement> The porous ceramic layer was evaluated using a FIB-SEM (FEI; HELIOS600). First, a sample was prepared by impregnating the porous ceramic layer with epoxy resin to fill the voids in the porous layer, and then curing the epoxy resin. After curing, the sample was cut so that the cross-section of the epoxy resin-impregnated porous ceramic layer (corresponding to the second porous layer) was the surface layer of the sample. After cutting, a processed surface parallel to the porous ceramic layer (an observation surface with the thickness direction of the porous ceramic layer perpendicular to it) was prepared by performing FIB processing from the surface layer of the sample in the depth direction (towards the interior of the sample, i.e., toward the first porous layer) using a FIB-SEM (JEOL; JIB-4700F was used in Example 1 and Comparative Example 1 below, and FEI; HELIOS600 was used in Example 2 and Comparative Example 2 below). In this process, FIB processing is performed starting from the surface closest to the surface of the porous ceramic layer, and continues until a porous structure is observed across the entire observation area. When the pore size is 150 to 500 nm, the observation area has an HFW of 19.7 μm and an image resolution of X, Y = 19.2 nm / px. When the pore size is 30 to 150 nm, the observation area has an HFW of 8.8 μm and an image resolution of X, Y = 7 nm / px.

[0052] The obtained processed surface was observed using SEM (backscattered electron imaging) at an accelerating voltage of 5 kV (Example 1 and Comparative Example 1) or 2.1 kV (Example 2 and Comparative Example 2). After the above SEM observation, a new observation surface was created by FIB processing in the thickness (film thickness) direction of the porous ceramic layer, and SEM observation (backscattered electron imaging) was performed on this new observation surface. When the pore diameter was 150 to 500 nm, a new processed surface was created by FIB processing at a thickness of 20 nm, and when the pore diameter was 30 to 150 nm, a new processed surface was created by FIB processing at a thickness of 10 nm, and SEM observation was performed on this new processed surface. In this way, by repeating FIB processing and SEM observation of the processed surface at thickness intervals of 20 nm or 10 nm until a porous structure could be seen throughout the entire observation area, a continuous slice image over a wide area in the thickness direction of the porous layer was obtained. Furthermore, it was confirmed from the obtained slice images that the pores were spreading three-dimensionally.

[0053] Then, position correction was performed using position correction software (Stack N Viz from System Frontier was used in Example 1 and Comparative Example 1, and Avizo ver. 6.0 from Visualization Sciences Group was used in Example 2 and Comparative Example 2), and corrected continuous slice images were obtained. The scale was set as follows: for porous ceramic layers with pore diameters of 30 to 150 nm, X, Y = 7 nm / px, Z axis 10 nm / px; and for porous ceramic layers with pore diameters of 150 to 500 nm, X, Y = 19.2 nm / px, Z axis 20 nm / px.

[0054] The obtained serial slice images are trimmed to approximately 6 μm × 3 μm × 1.8 μm for porous ceramic layers with pore diameters of 30 nm to 150 nm, and to approximately 18 μm × 9 μm × 5.4 μm for porous ceramic layers with pore diameters of 150 nm to 500 nm, and then a three-dimensional quantitative analysis of the voids in the porous ceramic layers is performed.

[0055] For three-dimensional quantitative analysis, the quantitative analysis software TRI / 3D-BON-FCS (manufactured by RATOC Systems Engineering) is used. Specifically, the software is opened, and the image is converted to two tones using Auto-LW to identify the ceramic parts and voids that make up the porous layer.

[0056] For the voids identified through these processes, the software's communication hole analysis (3D-VNET) was performed to calculate the Survival Bone Rate (SBR). First, the NodeStrut intermediate file output was performed using the communication hole measurement option to create an intermediate file. At this time, the target data was the binarized void, the CT data was the outermost pixel of the trimmed area (a box with 6 faces), the target area was the CT data inverted (the inside of the box), and the Node Strut parameters were set to NdNd effective length 1.5 × Thickness and NdTm effective length 2.0 × Thickness.

[0057] Next, in the flow path detailed analysis, the created intermediate file was specified, and the first slice in the Z direction of the continuous slice image was designated as the starting surface "From" and the last slice as the ending surface "To". The flow path analysis was then performed to calculate the SBR, which is an indicator of flow ease. At this time, the volume resistivity ρ was set to 1.0 and the input voltage to 1.0V.

[0058] <Measurement of Pore Diameter> After drying the porous ceramic laminates obtained in the examples and comparative examples, and the support structures within these laminates, at 120°C for 4 hours, the pore diameter of the porous ceramic layer was measured using an Autopore V9600 (manufactured by micromeritics) by the mercury intrusion method. The details of the measurement conditions are as follows: Adv. Contact Angle: 140.0° Rec. Contact Angle: 140.0° Mercury Temperature: 21°C Sample Mass: 1.0g Assembly Mass: 1.0g Penetrometer Volume: 1.0mL Penetrometer Mass: 1.0g Report Range: 1.07 to 8,570 psia

[0059] Specifically, a laminate consisting of a first porous ceramic layer (support) with another layer laminated on the outermost surface, and a second porous ceramic layer laminated on top of it, was measured. The pore diameter showing a peak was evaluated from a graph with pore diameter on the horizontal axis and log differential pore volume on the vertical axis. Measurements were also performed on the first porous ceramic layer (support) alone, with another layer laminated on the outermost surface. In the log differential pore volume distribution with pore diameter on the horizontal axis, two or more peaks were observed in the measurements of the laminate containing the first and second ceramic layers. The pore diameter of the first porous ceramic layer was evaluated based on the peaks observed in the measurement of the support only. The pore diameter of the layer formed by the slurry (second porous ceramic layer) was evaluated by considering the two or more peaks observed in the measurement of the laminate, as well as the peaks observed in the measurement of the support only. The pore distribution was evaluated in the range of pore diameter from 0.025 to 200 μm.

[0060] <Method for Measuring the Thickness of the Second Porous Ceramic Layer> The tubular porous ceramic laminates obtained in the following examples and comparative examples were cut 3-4 cm from each end perpendicular to the axial direction. The cut surfaces were embedded in resin so that they could be observed, and mechanical polishing was performed. The polished surfaces were coated with platinum, and observed and photographed at 500x magnification using an FE-SEM (JEOL, JSM-7500FA). Observation points were set at an arbitrary point (0 degrees) and at points 90, 180, and 270 degrees away in the circumferential direction from that point. From the obtained images, the thickness of the second porous ceramic layer was measured at the four positions mentioned above. At each of the 0, 90, 180, and 270 degree positions, the distance from the outermost surface of the second porous ceramic layer of the laminate to the interface between the first porous ceramic layer (support) and the second porous ceramic layer was measured, and the average value of the thickness at the four observation positions was taken as the thickness of the second porous ceramic layer.

[0061] <Measurement of the degree of unevenness and average sphere equivalent diameter of alumina particles> 100 parts by mass of epoxy resin was mixed with 2 parts by mass of dispersant and 2 parts by mass of alumina particles. After vacuum degassing, 12 parts by mass of hardener was added, and the epoxy resin with dispersed alumina particles was poured into a silicone mold and cured.

[0062] After the cured sample was fixed to the sample stage, Pt-Pd was deposited onto it, and the sample was set in a FIB-SEM (JEOL JIB-4700F was used in Example 1 and Comparative Example 1 below, and FEI HELIOS600 was used in Example 2 and Comparative Example 2 below). A cross-section was prepared by FIB processing, and the cross-section was observed by SEM at an acceleration voltage of 5 kV or less. After observation, if the particle size was 0.1 μm or more and less than 0.35 μm, a new cross-section was prepared by FIB processing with a thickness of 10 nm or 15 nm in the depth direction of the sample, and if the particle size was 0.35 μm or more and less than 0.7 μm, a new cross-section was prepared with a thickness of 50 nm, and the cross-section was observed by SEM. In this manner, FIB processing and cross-sectional SEM observation were repeated at regular intervals of 10 nm to 15 nm or 50 nm to acquire more than 100 consecutive images. Position correction was performed using image analysis software (Stack N Viz from System Frontier was used in Example 1 and Comparative Example 1, and Avizo ver. 6.0 from Visualization Sciences Group was used in Example 2 and Comparative Example 2) to obtain continuous slice images. The scale was set to 10 nm / px or 10.4 nm / px for the X and Y axes and 10 nm / px or 15 nm / px for the Z axis when the particle size was 0.1 μm or more and less than 0.35 μm, and to 50 nm / px for the X, Y, and Z axes when the particle size was 0.35 μm or more and less than 0.7 μm.

[0063] Three-dimensional quantitative analysis of alumina particles was performed on the obtained serial slice images to calculate the three-dimensional particle roughness and particle diameter. The quantitative analysis software TRI / 3D-PRT (manufactured by RATOC Systems Engineering) was used for the three-dimensional quantitative analysis.

[0064] For the 3D quantitative analysis, the continuous slice images were first opened on TRI / 3D-PRT, a median filter was applied to remove noise, then isolated particles were identified and labeled, and finally, particles that were interrupted at the outer edge of the measurement area were removed. In addition, during the cross-sectional SEM observation stage, alumina particles with a size of 2 μm or more in some parts were considered aggregated particles and were removed from the analysis.

[0065] From the more than 100 particles that remained after the above process, the particle volume V, major axis La, medium axis Lb, and minor axis Lc of any given particle were determined, and the particle diameter (equivalent diameter of the mean sphere) d and the 3D particle roughness were calculated from the above equations (a1) and (a2). The volume ratio was calculated as the ratio of the total volume of each particle with its respective 3D particle roughness to the total volume of all particles.

[0066] <Measurement of Fluid Permeation Performance> The porous ceramic laminate after the upper layer was laid was placed in a nanopalm porometer manufactured by Microtrac Bell, and pre-treated by heating at 140°C for 120 min while flowing He at 20 sccm. Then, helium gas was flowed at 40°C, 100 sccm, and Δ1000 Pa to measure the amount of He permeation (mol / (sec·m)) after the upper layer was laid. ２ - Pa) was measured.

[0067] Next, water vapor is mixed with helium gas so that the helium gas concentration (P / Ps_%) is 90.67, and the mixed gas is flowed at 100 sccm and Δ1000 Pa. The amount of He permeation after filling pores smaller than 20 nm in Kelvin diameter with water vapor is measured, thereby determining the amount of He permeation from the coarse channel after the upper layer is laminated (mol / (sec·m)). ２ - Pa) was measured.

[0068] Production Example 1: Preparation of Alumina Particles 1 Aluminum hydroxide (alumina precursor) obtained by hydrolysis of aluminum isopropoxide was calcined to obtain a θ-phase intermediate alumina (intermediate 1) containing 3% by mass of α-alumina. The α-alumina content in the intermediate alumina (intermediate 1) was calculated by analyzing the intermediate alumina with an X-ray diffractometer, comparing the obtained XRD pattern with a standard pattern obtained by adding a predetermined amount of α-alumina to the intermediate alumina. The intermediate alumina (intermediate 1) was pulverized with a jet mill to obtain intermediate alumina powder (intermediate 2).

[0069] 100 g of this intermediate alumina powder (intermediate 2) was placed in a tubular atmosphere furnace (manufactured by Motoyama Co., Ltd., capacity 8 L), and while introducing dry air with a dew point of -15°C (water vapor partial pressure 165 Pa) at a rate of 1 L / min into the furnace, it was heated at 1170°C for 3 hours to obtain calcined alumina material. After that, alumina particles 1 (raw material particles) were obtained by crushing with a jet mill (FS-4 manufactured by Seishin Enterprise Co., Ltd.) at a grinding pressure (G pressure) of 0.65 MPa. In the obtained alumina particles, the volume percentage of particles with a roughness degree greater than 6.0 was 8.5%, the volume percentage of particles with a roughness degree between 4.2 and 6.0 was 28.3%, and the volume percentage of particles with a roughness degree less than 4.2 was 63.2%, and the equivalent spherical diameter D50 was 0.31 μm.

[0070] Production Example 2: Alumina powder 2 (raw material particles) was obtained in the same manner as in Production Example 1, except that the heating temperature of the alumina powder (intermediate 2), an intermediate for the preparation of alumina particles 2, was set to 1230°C. The volume percentage of particles with a roughness degree exceeding 6.0 of the obtained alumina was 32.7%, the volume percentage of particles with a roughness degree between 4.2 and 6.0 was 33.2%, the volume percentage of particles with a roughness degree less than 4.2 was 34.1%, and the equivalent spherical diameter D50 was 0.59 μm.

[0071] Example 1 A tubular alumina support with a surface pore size of 0.3 μm (inner diameter 7.0 mm, outer diameter 10.0 mm, length 12.5 cm, average pore size of the part excluding the surface layer is 8.5 μm) was used as the first porous ceramic layer. Alumina particles 1, hydroxypropyl methylcellulose 60SH-4000 manufactured by Shin-Etsu Chemical Co., Ltd. as a thickener, and SN Dispersant 5468 (5% concentration) as a dispersant were mixed in water at concentrations of 6.00% by mass, 2.60% by mass, and 0.60% by mass, respectively. When adding hydroxypropyl methylcellulose 60SH-4000 to the water, the water temperature was raised to 70°C and stirred for 10 minutes before addition, and then cooled to 5°C. The mixture containing the alumina particles 1 was degassed to prepare a slurry.

[0072] Next, the slurry was filled into a Terumo catheter syringe and left standing upright with the outlet facing downwards for one hour. A tube was attached to the tip of the Terumo catheter syringe, and the tip of the tube was connected to the lower end of a vertically positioned alumina tubular support. The slurry was then injected into the entire inner circle of the substrate at a speed of 100 ml / h. After the slurry injection, a 6.00 mm diameter resin ball was placed on the end of the substrate opposite to the end where the slurry was injected, and the slurry was discharged with an air pressure of 0.015 MPa. The substrate was dried by rotating it at 6.9 rpm while blowing warm air at approximately 1 m / s through the inner circle of the substrate, forming a layer containing alumina particles 1 on the alumina tubular support. The substrate, with the layer containing alumina particles 1 (corresponding to the second porous ceramic layer) formed on its inner surface, was heat-treated at 1100°C for three hours to obtain a porous ceramic laminate. The upper layer (functional layer) of the porous ceramic laminate was applied by coating it with boehmite sol and heat-treating it at 600°C for 3 hours. The boehmite sol was prepared using Aluminium Sol-10A manufactured by Kawaken Fine Chemicals Co., Ltd., with a boehmite concentration of 2 wt%. The thickness of the second porous ceramic layer was measured using the above method and was found to be 18 μm.

[0073] In Example 2, a porous ceramic laminate was obtained in the same manner as in Example 1, except that a slurry was prepared by mixing alumina particles 2, STS-21 manufactured by Ishihara Sangyo Co., Ltd., hydroxypropyl methylcellulose 60SH-4000 manufactured by Shin-Etsu Chemical Co., Ltd. as a thickener, and SN Dispersant 5468 (5% concentration) as a dispersant in water at concentrations of 9.00% by mass, 1.19% by mass, 3.20% by mass, and 0.90% by mass, respectively, and the firing temperature was set to 1200°C. The thickness of the second porous ceramic layer was measured using the method described above and was found to be 30 μm.

[0074] Comparative Example 1 A laminate was prepared in the same manner as in Example 1, except that a slurry was prepared by mixing AKP-53, manufactured by Sumitomo Chemical Co., Ltd., as alumina particles and hydroxypropyl methylcellulose 60SH-4000, manufactured by Shin-Etsu Chemical Co., Ltd., as a thickener, in water at concentrations of 4.00% by mass and 2.45% by mass, respectively, and the water temperature when adding the hydroxypropyl methylcellulose to the water was set to 25°C. In AKP-53, the volume percentage of particles with a roughness degree exceeding 6.0 was 0%, and the equivalent spherical diameter D50 was 0.24 μm.

[0075] Comparative Example 2 A laminate was prepared in the same manner as in Example 1, except that AKP-20 manufactured by Sumitomo Chemical Co., Ltd. and STS-21 manufactured by Ishihara Sangyo Co., Ltd. were mixed in water at concentrations of 13.50% by mass, 0.68% by mass, 3.20% by mass, and 1.35% by mass, respectively, as alumina particles, hydroxypropyl methylcellulose 60SH-4000 manufactured by Shin-Etsu Chemical Co., Ltd. as a thickener, and SN Dispersant 5468 as a dispersant, respectively, the water temperature when adding the hydroxypropyl methylcellulose to the water was set to 25°C, and the firing temperature was set to 1200°C. In AKP-20, the volume percentage of particles with a roughness degree exceeding 6.0 was 0.67%, and the equivalent spherical diameter D50 was 0.45 μm.

[0076] Table 1 shows the pore size and SBR of the second porous ceramic layer obtained in the examples and comparative examples, and the results of measuring the He permeability performance of the laminate.

[0077]

[0078] Comparing Example 1 with Comparative Example 1, and Example 2 with Comparative Example 2, it was found that in Examples 1 and 2, where the SBR value was greater than 6.1 and less than 15, sufficient He permeation was ensured throughout the entire laminate after the upper layer was laminated, while the amount of He permeation from coarse voids was small, thus suppressing the generation of coarse voids.

[0079] Furthermore, Figures 1 and 2 show the results of the interconnection pore analysis in the second porous ceramic layer of the laminates obtained in Example 1 and Comparative Example 1, respectively. In the interconnection pore analysis, interconnection pores are distinguished by color, from largest to smallest cross-sectional area, using red, orange, yellow, green, blue, and purple. In Figure 1, which shows the analysis results for Example 1, a large number of interconnection pores were observed, as well as many interconnection pores with large cross-sectional areas (red, orange, yellow). In contrast, in Figure 2, which shows the analysis results for Comparative Example 1, a small number of interconnection pores were observed, as well as many interconnection pores with small cross-sectional areas (green, blue, purple).

Claims

1. A porous ceramic layer for separation membranes having a Survival Bone Rate (SBR) value greater than 6.1% and less than 15%, with pores extending in three dimensions.

2. The porous ceramic layer for separation membrane according to claim 1, wherein the porous ceramic layer contains a metal oxide, and the amount of aluminum atoms is 50 mol% or more of the total 100 mol% of metal atoms constituting the metal oxide.

3. The porous ceramic layer for separation membrane according to claim 2, wherein the amount of aluminum atoms is 90 to 100 mol% of the total 100 mol% of metal atoms constituting the metal oxide, and the amount of metal oxide in 100 mass% of the porous ceramic layer for separation membrane is 80 to 100 mass%.

4. The porous ceramic layer for separation membrane according to claim 1, wherein the pore size measured by the mercury intrusion method is 0.01 to 0.7 μm.

5. The porous ceramic layer for separation membrane according to claim 1, wherein the thickness is 3 to 300 μm.

6. A porous ceramic laminate for a separation membrane, having a first porous ceramic layer and a second porous ceramic layer laminated on the surface of the first porous ceramic layer, wherein the average pore diameter of the first porous ceramic layer is larger than the average pore diameter of the second porous ceramic layer, the first porous ceramic layer and the second porous ceramic layer contain a metal oxide, and the second porous ceramic layer is the porous ceramic layer described in claim 1.

7. The porous ceramic laminate for separation membrane according to claim 6, wherein the amount of aluminum atoms is 50 to 100 mol% of the total 100 mol% of metal atoms constituting the metal oxide contained in the first porous ceramic layer, and the amount of metal oxide in 100 mass% of the first porous ceramic layer is 80 to 100 mass%.

8. The porous ceramic laminate for separation membrane according to claim 6, wherein the average pore size of the first porous ceramic layer, as measured by the mercury intrusion method, is 5 to 25 μm.

9. The porous ceramic laminate for separation membrane according to claim 6, wherein the thickness of the first porous ceramic layer is 400 to 8000 μm.

10. The porous ceramic laminate for separation membrane according to claim 6, which is tubular, honeycomb, or monolithic.

11. A separation membrane comprising a porous ceramic laminate for separation membranes as described in claim 10.

12. The separation membrane according to claim 11, wherein the functional layer is directly laminated onto the second porous layer.

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