Alumina particles, porous ceramic laminate for separation membrane, and separation membrane

Abstract

The purpose of the present invention is to provide: alumina particles which are useful for the production of a porous ceramic layer that is suitable for use in a separation membrane which has excellent fluid permeation performance and in which generation of coarse voids in an upper layer is suppressed; and a porous ceramic laminate for a separation membrane and a separation membrane using the alumina particles. The present disclosure provides alumina particles in which the proportion of particles having a degree of three-dimensional particle unevenness of more than 6.0 is 0.7 vol% or more, and the 50% cumulative sphere equivalent diameter D50 on a volume basis is 0.1 μm to 10 μm inclusive.

Description

Alumina particles, porous ceramic laminates for separation membranes, and separation membranes

[0001] This disclosure relates to alumina particles, porous ceramic laminates for separation membranes, and separation membranes.

[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] Porous ceramic bodies can typically be formed by heat-treating a slurry containing inorganic oxides.

[0004] For example, Patent Documents 1 to 3 disclose inorganic oxide powders used to form porous inorganic oxide films, and disclose inorganic oxides having a predetermined shape and particle size.

[0005] Furthermore, Patent Document 4 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. Furthermore, Patent Document 5 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 discloses that the porosity and average pore diameter of the intermediate layer are adjusted to a predetermined range.

[0006] Japanese Patent Publication No. 5362132, Japanese Patent Publication No. 6386128, International Publication No. 2016 / 098579, Japanese Unexamined Patent Publication No. 2007-283219, International Publication No. 2017 / 169591

[0007] When a porous ceramic body is used as a separation membrane by laminating upper layers such as functional layers or cake layers on its outermost surface, it is desirable that the separation membrane has excellent fluid permeability and good separation performance, and that the generation of large voids in the upper layers be suppressed. In order to obtain a porous ceramic layer with these properties, it is considered important to appropriately control the shape of the inorganic oxide that serves as the raw material for the porous ceramic layer.

[0008] Patent documents 1 to 3 mentioned above all deal with inorganic oxides for insulating porous films formed on the surface of lithium-ion secondary batteries such as positive electrodes, and do not disclose inorganic oxides suitable for separation films. Furthermore, patent documents 4 and 5 mentioned above do not consider porous ceramic layers suitable for use in separation films that have excellent fluid permeability and suppress the generation of coarse voids in the upper layer.

[0009] Therefore, the problem to be solved by this disclosure is to provide inorganic oxide particles, particularly alumina particles, that are useful for producing a porous ceramic layer suitable for use in a separation membrane that has excellent fluid permeability and suppresses the generation of coarse voids in the upper layer, and to provide a porous ceramic laminate for a separation membrane and a separation membrane using the same.

[0010] The present disclosure, which has achieved the above objectives, is as follows: [1] Alumina particles in which the proportion of particles with a three-dimensional particle roughness exceeding 6.0 is 0.7 volume% or more, and the cumulative 50% sphere equivalent diameter D50 based on volume is 0.1 μm or more and 10 μm or less. [2] Alumina particles according to [1], wherein the proportion of particles with a three-dimensional particle roughness exceeding 6.0 is 80 volume% or less. [3] Alumina particles according to [1] or [2], wherein the proportion of particles with a three-dimensional particle roughness less than 4.2 is 90 volume% or less. [4] Alumina particles according to any one of [1] to [3], wherein the proportion of particles with a three-dimensional particle roughness less than 4.2 is 30 volume% or more. [5] Alumina particles according to any one of [1] to [4], wherein the proportion of particles with a three-dimensional particle roughness between 4.2 and 6.0 is 8 to 50 volume%. [6] Alumina particles according to any one of [1] to [5], wherein the α-adsorption rate of the alumina particles is 90% or more. [7] Alumina particles according to any one of [1] to [6] used in porous ceramics for separation membranes. [8] Use of alumina particles according to any one of [1] to [7] in porous ceramics for separation membranes. [9] A porous ceramic laminate for separation membranes 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 contains a sintered body of alumina particles according to any one of [1] to [7].

[10] The porous ceramic laminate for separation membranes according to [9], which is tubular, honeycomb, or monolithic.

[11] A separation membrane composed of the porous ceramic laminate for separation membranes according to

[10] .

[12] The separation membrane according to

[11] , in which a functional layer is directly laminated on the second porous layer. Use of the porous ceramic laminate for separation membranes described in

[13] , [9], or

[10] as a separation membrane.

[0011] A separation membrane comprising a porous ceramic layer obtained by sintering alumina particles according to the present disclosure, and an upper layer such as a functional layer, can improve fluid permeability and suppress the generation of coarse voids.

[0012] This is a schematic diagram illustrating the three-dimensional particle surface roughness of alumina particles.

[0013] 1. Alumina Particles <Three-Dimensional Particle Roughness of Alumina Particles> Three-dimensional particle roughness (hereinafter sometimes simply referred to as roughness) is a shape parameter when focusing on each individual alumina particle, and is expressed in terms of 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. Figure 1 shows a schematic diagram of the circumscribed rectangular parallelepiped of alumina particles. 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.

[0014] If the volume percentage of alumina particles with a roughness degree exceeding 6.0 is less than 0.7 volume%, it means that the proportion of particles with less roughness will be large, resulting in a densification of the particles. This leads to an increase in the number of adhesion points between particles, and it is thought that the particles will be excessively sintered, causing the pores to become blocked. On the other hand, if the volume percentage is too large, the surface smoothness of the resulting porous ceramic layer tends to decrease, so it is preferable to keep it at, for example, 80 volume% or less.

[0015] In equation (a1), La, Lb, Lc, and V can be determined by three-dimensional quantitative analysis of alumina particles, and the detailed procedure is shown in the examples described below.

[0016] The volume percentage of alumina particles with a roughness degree exceeding 6.0 is preferably 0.7 to 80 volume%, more preferably 3 to 70 volume%, even more preferably 5 to 60 volume%, even more preferably 10 to 50 volume%, and even more preferably 20 to 40 volume%.

[0017] It is also preferable to adjust the proportion of particles with a roughness degree of less than 4.2, and the volume percentage of particles with a roughness degree of less than 4.2 is preferably 90 volume% or less, more preferably 90 to 10 volume%, even more preferably 80 to 20 volume%, even more preferably 70 to 30 volume%, and even more preferably 50 to 30 volume%.

[0018] It is also preferable to adjust the proportion of particles with a roughness degree of 4.2 to 6.0, and the volume percentage of particles with a roughness degree of 4.2 to 6.0 is preferably 8 to 50 volume%, more preferably 15 to 45 volume%, even more preferably 25 to 40 volume%, and even more preferably 30 to 40 volume%.

[0019] <Equivalent Spherical Diameter of Alumina Particles> It is also important to use alumina particles that have a large degree of unevenness but whose average particle diameter (average spherical equivalent diameter) is between 0.1 μm and 10 μm. Here, "spherical equivalent diameter" is one parameter of the alumina particle, and is the volume V (μm) of the alumina particle. ３ V is the diameter d of a sphere that has the same volume as (a) and satisfies the following equation (a2): V = 4π / 3 × (d / 2) ３ ....(a2) Using the above formula (a2), the "equivalent spherical diameter" is calculated from 100 or more particles, and the cumulative 50% equivalent diameter based on volume is taken as the average particle diameter (average equivalent spherical diameter).

[0020] If the average equivalent spherical diameter of the alumina particles is less than 0.1 μm, the reactivity is high and sintering proceeds, causing the voids to collapse. If it is greater than 10 μm, the reactivity is poor, resulting in variations in reactivity. As a result, it becomes necessary to increase the thickness of the porous ceramic layer to ensure its strength, which tends to reduce its permeability. The average equivalent spherical diameter of the alumina particles is between 0.1 μm and 10 μm, and may be between 0.1 μm and 5 μm, between 0.1 μm and 1 μm, between 0.2 μm and 0.9 μm, between 0.3 and 0.7 μm, between 0.3 μm and 0.6 μm, between 0.3 μm and 0.55 μm, or between 0.5 μm and 0.6 μm.

[0021] The alumina particles are preferably chemically stable α-alumina excellent in heat resistance, and the α-phase conversion rate thereof is preferably 90% or more. The α-phase conversion rate is obtained from the peak height (I ２５．６ ) of the alumina α-phase (012 plane) appearing at 2θ = 25.6° in the powder X-ray diffraction spectrum and the peak height (I ４６ ) of the alumina γ-phase, η-phase, χ-phase, κ-phase, θ-phase or δ-phase appearing around 2θ = 46°, calculated by formula (1): α-phase conversion rate = I ２５．６ / (I ２５．６ +I ４６ )×100 (%) ... (1)

[0022] <Method for producing alumina particles> Alumina particles satisfying the aforementioned requirements of unevenness degree and average equivalent circular diameter can be produced by calcining an intermediate powder of alumina particles (intermediate 2 described later) in an atmosphere with adjusted water vapor partial pressure, and then performing jet mill pulverization under appropriate conditions.

[0023] In the atmosphere for calcining the intermediate of alumina particles (intermediate 2), the water vapor partial pressure is preferably 40 Pa or more (for a gas with a total pressure of 0.1 MPa, the dew point is -30°C or higher). This can prevent sintering when particles adhere to each other excessively, and enables sintering with necks formed at the interfaces between particles, thereby forming unevenness on the finally obtained particles. On the other hand, the water vapor partial pressure is preferably 600 Pa or less (for a gas with a total pressure of 0.1 MPa, the dew point is 0°C or lower). This allows good bonding between particles, and enables the average equivalent circular diameter of the finally obtained particles to fall within the above range.

[0024] In addition, calcination of the intermediate powder of alumina particles (intermediate 2) is preferably performed at 1000 to 1250°C for 2 to 4 hours. If the temperature is too low or too high, the average equivalent circular diameter cannot be adjusted to the above range; in addition, if the temperature is too high, it is also difficult to properly adjust the unevenness degree. Furthermore, if the calcination time is too short or too long, the average equivalent circular diameter cannot be adjusted to the above range; if the time is too long, sintering occurs and the particles become nearly spherical, resulting in decreased unevenness degree, while if the time is too short, sintering does not proceed, so necks cannot be formed, also resulting in decreased unevenness degree.

[0025] If the particles after firing (intermediate material 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, and the degree of roughness decreases drastically. 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, and if it is too low, pulverization is insufficient, making it difficult to keep the average spherical diameter of the particles within the above range.

[0026] The alumina particle intermediate (intermediate 2) is preferably an alumina intermediate powder obtained by, for example, hydrolyzing aluminum alkoxide to obtain aluminum hydroxide, calcining it to obtain an alumina intermediate (intermediate 1), and then jet milling this alumina intermediate (intermediate 1). The alumina intermediate powder (intermediates 1 and 2) preferably has a θ phase as its main crystalline 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 intermediate powder (intermediates 1 and 2) is 1 to 5% by mass.

[0027] 2. Porous Ceramic Laminate The alumina particles of this disclosure can be suitably used in porous ceramics for separation membranes. Specifically, a porous ceramic laminate for separation membranes can be obtained 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 contains a sintered body of the alumina particles of this disclosure. In such a laminate, not only the second porous ceramic layer but also the first porous ceramic layer may contain a sintered body of the alumina particles of this disclosure.

[0028] <Shape> The shape of the porous ceramic laminate is, for example, a plate shape, a tube shape, a honeycomb shape or a monolith shape. The tube shape refers to a pillar shape having one axially penetrating hole, and the monolith shape refers to a shape of a pillar (such as a cylinder, a prism, an elliptic cylinder, etc.) having a plurality of axially penetrating holes (preferably cylindrical shapes), and the honeycomb shape refers to a shape obtained by laminating hollow three-dimensional figures (regular hexagonal prisms, square prisms, triangular prisms, etc.) penetrating in the axial direction without gaps. The shape of the porous ceramic laminate is preferably a tube shape, a honeycomb shape or a monolith shape. When the porous ceramic laminate is tube-shaped, honeycomb-shaped or monolith-shaped, the shape of the through-holes and / or the outer shape of the pillars in a cross-section perpendicular to the axial direction is preferably a circle, an ellipse, a square (square or rectangle), or a polygon other than a square, and more preferably all are circles.

[0029] The length of the porous ceramic laminate is, for example, 50 to 5000 mm, preferably 90 to 3000 mm. When the porous ceramic laminate is tube-shaped, the outer diameter is, for example, 5 mm to 20 mm, and the inner diameter of the through-hole is, for example, 1 mm to 15 mm. When the porous ceramic laminate is monolith-shaped or honeycomb-shaped, 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.

[0030] <Laminated Structure> When the laminate is tube-shaped, honeycomb-shaped or monolith-shaped, the second porous ceramic layer is preferably formed only on the inner peripheral surface, only on the outer peripheral surface, or on both the inner and outer peripheral surfaces of the through-holes of the first porous ceramic layer, more preferably formed only on the inner peripheral surface or only on the outer peripheral surface, and still more preferably formed only on the inner peripheral surface. The second porous ceramic layer may be directly laminated on the first porous ceramic layer, or may be laminated on the first porous ceramic layer via one or more other layers. When other layers are included, 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 (the total thickness when there are a plurality of layers) may be about 5 to 50 µm.

[0031] <First Porous Ceramic Layer> The first porous ceramic layer is not particularly limited, except that it contains a metal oxide and has an average pore diameter larger than the average pore diameter of the second porous ceramic layer. It is preferable that the average pore diameter of the first porous ceramic layer measured by mercury porosimetry is, for example, in the range of 5 to 25 µm, more preferably 5 to 20 µm, still more preferably 5 to 15 µm, and most preferably 5 to 12 µm. Said pore diameter means the pore diameter that shows a peak in a graph where the horizontal axis represents pore diameter and the vertical axis represents log differential pore volume.

[0032] It is preferable that the first porous ceramic layer contains a metal oxide. Examples of 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. It is preferable that the first porous ceramic layer contains at least one of these metal atoms, more preferably contains at least one of Al, Si, and Ti, and still more preferably contains Al (aluminum). Based on 100 mol% in total of the 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%, still more preferably 80 to 100 mol%, and particularly preferably 90 to 100 mol%. Note that the term "metal" as used herein is meant to also include semimetals such as Si. The content of the metal oxide in 100% by mass of the first porous ceramic layer is preferably 80 to 100% by mass, more preferably 90 to 100% by mass.

[0033] The first porous ceramic layer has the same shape as the porous ceramic laminate, and is preferably in the form of a plate, a tube, a honeycomb or a monolith, and more preferably in the form of a tube, a honeycomb or a monolith. The thickness (average value) of the first porous ceramic layer is preferably 400 to 8000 µm. When the first porous ceramic layer is in the form of a honeycomb or a monolith, the thickness may be an average value of the closest distances between adjacent ducts on a plane perpendicular to the major axis.

[0034] <Second Porous Ceramic Layer> The second porous ceramic layer may include a sintered body of alumina particles as disclosed herein, as well as a sintered body of metal oxide particles other than alumina particles. Examples of metal atoms other than aluminum atoms that constitute 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 may include at least one of these, with Ti being particularly preferred. When the second porous ceramic layer includes a sintered body of alumina particles and a sintered body of Ti oxide as disclosed herein, 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.

[0035] In the second porous ceramic layer, the amount of sintered alumina particles of this disclosure is preferably 70 to 100% by mass, more preferably 85 to 100% by mass, and most preferably 90 to 100% by mass, in the total mass of sintered metal oxides contained in the second porous ceramic layer. The amount of metal oxides in the 100% by mass of the second porous ceramic is preferably 80 to 100% by mass, and more preferably 90 to 100% by mass.

[0036] The thickness of the second porous ceramic layer is, for example, 3 to 300 μm, preferably 5 to 100 μm.

[0037] Furthermore, the pore diameter of the second 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 pore diameter on the horizontal axis and log differential pore volume on the vertical axis. 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.

[0038] <He transmission amount and He transmission amount from coarse voids> The He transmission amount (1) when the porous ceramic laminate after the upper layer lamination is measured by the method described in the example below is preferably 2.5 × 10 －５ ~5.0 x 10 －５ (mol / (m) ２ sec・Pa)) and more preferably 3.0 × 10 －５ ~4.8 x 10 －５ (mol / (m) ２ secPa)) and more preferably 3.5 × 10 －５ ~4.5 x 10 －５ (mol / (m) ２ sec・Pa)). Furthermore, the amount of He permeation (2) from coarse channels (voids) in the porous ceramic laminate after the upper layer lamination is preferably 0 to 3.0 × 10 －８ (mol / (m) ２ sec・Pa)) and more preferably 0 to 2.0 × 10 －８ (mol / (m) ２ sec・Pa)) and more preferably 0 to 1.5 × 10 －８ (mol / (m) ２ sec Pa)) and 0 (mol / (m ２ It is most preferable that the pressure be sec Pa. The amount of He permeate (2) from the coarse channel (void) relative to the above He permeate amount (1) ((2) / (1)) is preferably 0 to 1.0 × 10 －３ More preferably 0 to 7.0 × 10 －４ And more preferably 0 to 4.0 × 10 －４ That is the case.

[0039] 3. Method for manufacturing a porous ceramic laminate A porous ceramic laminate is obtained by applying a slurry containing alumina particles and a thickener according to the present disclosure to a substrate (including a first porous layer) and heat-treating it, but it is preferable to adjust the temperature when adding the thickener to a predetermined range.

[0040] Specifically, a slurry containing the alumina particles of the present disclosure and a thickening agent is prepared by adjusting the temperature when adding the thickening agent to 60°C or higher. This slurry is then applied to a substrate which is a first porous ceramic layer, and heat-treated to obtain a porous ceramic laminate in which a second porous ceramic layer containing a sintered body of the alumina particles of the present disclosure is laminated on the first porous ceramic layer.

[0041] <Preparation of Slurry> The slurry containing alumina particles according to the above disclosure is for use in porous ceramic separation membranes, and contains a thickener, and usually also contains a solvent. It is preferable to add the thickener at a temperature of 60°C or higher, and it is important to then 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 alumina particles and the thickener are uniformly mixed, and the aggregation state of the alumina particles is controlled. The slurry temperature when adding the thickener is preferably 60°C or higher and 90°C or lower.

[0042] After adding the thickener to the solvent, it is preferable to thoroughly disperse the thickener in the solvent by stirring or other means. The order in which the alumina particles and thickener are added is not particularly limited; for example, the alumina 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.

[0043] The amount of alumina particles in 100% by mass of the slurry is preferably 5 to 15% by mass. Furthermore, the amount of alumina particles in 100% by mass of solid content in the slurry is preferably 50 to 70% by mass.

[0044] 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.

[0045] The solvent typically included in the slurry may be water or an organic solvent.

[0046] 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 Sunnopco can be used. The concentration of the dispersant in the slurry (calculated in terms of active ingredients) is preferably 0.02 to 5 parts by mass per 100 parts by mass of alumina particles in the slurry.

[0047] <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.

[0048] 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.

[0049] Examples of the functional layers mentioned above include zeolites, MOFs (Metal Organic Frameworks), porous silica films, and porous alumina films.

[0050] 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.

[0051] This application claims the benefit of priority based on Japanese Patent Application No. 2025-041171, filed on 14 March 2025. The entire specification of Japanese Patent Application No. 2025-041171, filed on 14 March 2025, is incorporated herein by reference.

[0052] 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.

[0053] <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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] <Measurement of the α-conversion rate of alumina particles> Powder X-ray diffraction spectra were measured using an X-ray diffractometer (product name "Rint-2100", manufactured by Rigaku Denki Co., Ltd.). The peak height (I25.6) of the alumina α phase (012 plane) appearing at 2θ = 25.6° and the peak height (I46) of the alumina γ phase, η phase, χ phase, κ phase, θ phase, or δ phase appearing around 2θ = 46° were used to determine the α-conversion rate using equation (1). α-conversion rate = I25.6 / (I25.6 + I46) × 100 (%) ... (1)

[0059] <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

[0060] 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.

[0061] <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.

[0062] <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.

[0063] Next, water vapor is mixed with helium gas so that the helium gas concentration (P / Ps (%), where Ps is the saturated water vapor pressure and P is the actual water vapor pressure) 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.

[0064] Example 1-1: 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).

[0065] 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 a calcined alumina product. After that, alumina particles 1 were obtained by crushing the material 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 1, the volume percentage of particles with a roughness degree exceeding 6.0 was 8.5%, the average equivalent sphere diameter D50 was 0.31 μm, and the alpha-gelatinization rate was 90% or more.

[0066] Example 1-2: Alumina powder 2 was obtained in the same manner as in Production Example 1, except that the heating temperature of the alumina powder, an intermediate in 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 particles 2 was 32.7%, the average equivalent sphere diameter D50 was 0.59 μm, and the gelatinization rate was 90% or more.

[0067] Example 2-1 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 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.

[0068] 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 mass%. The thickness of the second porous ceramic layer was measured using the above method and found to be 18 μm.

[0069] Example 2-2 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.

[0070] Comparative Example 2-1 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, with 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 average equivalent spherical diameter D50 was 0.24 μm.

[0071] Comparative Example 2-2 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, and 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 average equivalent sphere diameter D50 was 0.45 μm.

[0072] Table 1 shows the average equivalent spherical diameter and roughness of the alumina particles used in the examples and comparative examples, the pore size of the obtained second porous ceramic layer, and the results of measuring the He permeability performance of the laminate.

[0073]

[0074] Comparing Example 2-1 with Comparative Example 2-1, and Example 2-2 with Comparative Example 2-2, it was found that in Examples 2-1 and 2-2, where alumina particles with an appropriate degree of unevenness and average spherical equivalent diameter were used to form the second porous ceramic layer in the laminate, 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 low, thus suppressing the generation of coarse voids.

Claims

1. Alumina particles in which the proportion of particles with a three-dimensional particle roughness degree exceeding 6.0 is 0.7% by volume or more, and the cumulative 50% sphere equivalent diameter D50 based on volume is 0.1 μm or more and 10 μm or less.

2. Alumina particles according to claim 1, wherein the proportion of particles with a three-dimensional particle roughness degree exceeding 6.0 is 80 volume% or less.

3. Alumina particles according to claim 1, wherein the proportion of particles with a three-dimensional particle roughness of less than 4.2 is 90% by volume or less.

4. Alumina particles according to claim 3, wherein the proportion of particles with a three-dimensional particle roughness of less than 4.2 is 30% by volume or more.

5. Alumina particles according to claim 1, wherein the proportion of particles with a three-dimensional particle roughness of 4.2 to 6.0 is 8 to 50 volume percent.

6. The alumina particles according to claim 1, wherein the alpha-adsorption rate of the alumina particles is 90% or more.

7. Alumina particles according to any one of claims 1 to 6, used in porous ceramics for separation membranes.

8. 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 contains a sintered body of alumina particles as described in any one of claims 1 to 6.

9. The porous ceramic laminate for separation membrane according to claim 8, which is tubular, honeycomb, or monolithic.

10. A separation membrane comprising a porous ceramic laminate for separation membranes as described in claim 9.

11. The separation membrane according to claim 10, wherein the functional layer is directly laminated onto the second porous layer.

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