Porous ceramic layered body and separation membrane

Abstract

One purpose of the present invention is to provide a porous ceramic layered body having two or more types of layers layered therein, wherein peeling at the layering interface is suppressed. The present invention is a porous ceramic layered body having a first porous layer and a second porous layer that is layered directly on the first porous layer, wherein the first porous layer includes a metal oxide X and includes the element Al and the element Fe, the mass ratio of Fe / Al in the first porous material is 5.7×10–4 to 1.6×10–2, and the second porous layer includes an oxide Y including at least one type of element selected from the group consisting of Al, Ti, Si and Mg.

Description

Porous ceramic laminate and separation membrane

[0001] The present invention relates to a porous ceramic laminate and a separation membrane.

[0002] Porous ceramic bodies are used in various fields as membranes that have functions such as separating, concentrating, or filtering gaseous or liquid fluids, 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 monolithic separation membrane structure comprising a substrate made of a porous material and having a plurality of through holes, a first support layer formed on the inner surfaces of the plurality of through holes, and a separation membrane disposed inside the first support layer, wherein the first support layer contains alumina, titania, and at least one of silica and magnesia. Patent Document 1 describes that the strength of the first support layer can be improved by containing the above-mentioned components in the first support layer.

[0004] In addition, Patent Document 2 discloses Li ２ O, Na ２ O, etc., and the balance is SiO ２ The document discloses a ceramic porous body formed by bonding ceramic particles together with glass, which is an inevitable impurity, as a binder, and states that such a ceramic porous body can be used for a long period of time as a filtration filter or the like, even in an environment where it is exposed to acid and alkali.

[0005] International Publication No. 2015 / 146571 Japanese Patent Application Laid-Open No. 2003-238257

[0006] It is important that porous ceramic bodies suitable for use in the above-mentioned fields allow fluids to flow easily through the porous ceramic body while fully fulfilling functions such as separation, i.e., that the pressure loss of the fluid is small, and therefore they are usually composed of a laminate of two or more layers including a functional layer with a small pore diameter and a support layer with a large pore diameter that supports the functional layer. In a laminate in which two or more layers are laminated, peeling will occur at the interface of the layers when a load is applied to the laminate unless the bond at the interface is strong.

[0007] Although Patent Documents 1 and 2 also disclose a laminate as a separation membrane structure, they do not consider peeling at the lamination interface. Therefore, an object of the present invention is to provide a porous ceramic laminate in which two or more types of layers are laminated, in which peeling at the lamination interface is suppressed.

[0008] The present invention achieves the above object as follows: [1] A porous ceramic laminate having a first porous layer and a second porous layer directly laminated on the first porous layer, wherein the first porous layer contains a metal oxide X, and also contains Al and Fe elements, and the mass ratio of Fe / Al in the first porous layer is 5.7 × 10 -４ That's it, 1.6 x 10 －２ [2] The porous ceramic laminate according to [1], wherein the second porous layer contains an oxide Y containing at least one selected from the group consisting of Al, Ti, Si, and Mg. [3] The porous ceramic laminate according to [1] or [2], wherein the first porous layer contains Na element and the mass ratio of Na / Fe in the first porous layer is greater than 0.132 and less than 40. [4] The porous ceramic laminate according to any one of [1] to [3], wherein the first porous layer contains Si element and the mass ratio of Si / Fe in the first porous layer is greater than 32.6. [5] The porous ceramic laminate according to [1] to [3], wherein the metal oxide X is Al. ２ O ３ [6] The porous ceramic laminate according to any one of [1] to [5], which is tubular or monolithic. [7] A separation membrane comprising the porous ceramic laminate according to any one of [1] to [6]. [8] The first porous layer contains Al, Fe, Na, and Si elements, and the Fe / Al mass ratio is 1.0 × 10 －３ ~8.0 x 10 －３The porous ceramic laminate according to any one of [1] to [6], wherein the mass ratio of Na / Fe is 0.5 to 30 and the mass ratio of Si / Fe is 40 to 90. [9] The pore diameter D of the first porous layer at which the value of the log differential pore volume is maximum in the log differential pore volume distribution obtained by measuring the first porous layer by mercury intrusion porosimetry ＬＤ－ｍａｘ is the pore diameter D of the second porous layer at which the log differential pore volume value is maximized in the log differential pore volume distribution obtained by measuring the second porous layer by mercury intrusion porosimetry. ＬＤ－ｍａｘ

[10] The porous ceramic laminate according to any one of [1] to [6], wherein the pore diameter D of the first porous layer is larger than ＬＤ－ｍａｘ is 1.0 to 18 μm, and the pore diameter D ＬＤ－ｍａｘ The porous ceramic laminate according to [9], wherein the average particle size is 0.1 to 2.0 μm.

[0009] According to the present invention, it is possible to provide a porous ceramic laminate having improved peel strength between the first porous layer and the second porous layer.

[0010] The porous ceramic laminate of the present invention is a porous ceramic laminate having a first porous layer and a second porous layer directly laminated on the first porous layer, wherein the first porous layer contains a metal oxide X, and also contains Al element and Fe element, and the mass ratio of Fe / Al in the first porous layer is 5.7 × 10 －４ That's it, 1.6 x 10 －２ The second porous layer contains an oxide Y containing at least one selected from the group consisting of Al, Ti, Si, and Mg.

[0011] (1) First Porous Layer The first porous layer contains a metal oxide X. The metal oxide X may be one type or two or more types. The metal oxide X preferably contains at least one oxide selected from the group consisting of Al, Ca, Na, Fe, and Si. ２ O ３ The at least one oxide selected from the group consisting of Al, Ca, Na, Fe, and Si includes oxides containing only one type of metal element, as well as composite oxides containing two or more types of metal elements.

[0012] The first porous layer contains Al and Fe elements. The Al and Fe elements may be contained in the form of the metal oxide X described above, or may be contained in a form other than the oxide.

[0013] The mass ratio of Fe / Al in the first porous layer is 5.7×10 －４ That's it, 1.6 x 10 －２ The Fe in the first porous layer easily forms a strong compound (preferably an oxide) with at least one oxide Y selected from the group consisting of Al, Ti, Si, and Mg in the second porous layer, thereby strengthening the bonding strength between the first porous layer and the second porous layer and increasing the peel strength between the two layers. Therefore, the Fe / Al mass ratio is 5.7 × 10 －４ or more, 1.0 × 10 －３ More than 2.0 × 10 －３ More preferably, 4.0 × 10 －３ Furthermore, if the amount of Fe in the first porous layer is too large, the compound formed between the first and second porous layers will undergo localized abnormal grain growth, causing cracks and reducing the strength, which will in turn weaken the peel strength between the first and second porous layers. Therefore, the Fe / Al mass ratio should be 1.6×10 －２ is less than or equal to 8.0 × 10 －３ Preferably, the value is 6.0 x 10 －３ More preferably, the Fe / Al mass ratio in the first porous layer is 1.0×10 －３ ~8.0 x 10 －３ is preferable, and 2.0 × 10 －３ ~6.0 x 10 －３ More preferably, 4.0 × 10 －３ ~6.0 x 10 －３ is more preferred.

[0014] The first porous layer preferably contains Na, with a Na / Fe mass ratio of more than 0.132 and preferably 40 or less. Na acts as an auxiliary agent to promote bonding when a compound is formed between the Fe element in the first porous layer and at least one oxide selected from the group consisting of Al, Ti, Si, and Mg in the second porous layer. When the Na / Fe mass ratio is greater than 0.132, the peel strength between the first porous layer and the second porous layer can be further improved, and a decrease in permeability can be suppressed when the flow rate of the fluid passing through the laminate of the present invention is switched from a high flow rate to a low flow rate. The Na / Fe mass ratio is more preferably 0.5 or more, even more preferably 1.0 or more, and even more preferably 2 or more. On the other hand, if the amount of Na in the first porous layer is too high, it may inhibit bonding of the Fe element or cause localized abnormal grain growth of the compound formed between the first and second porous layers, resulting in cracks and a decrease in strength, thereby reducing the peel strength between the first and second porous layers. The mass ratio of Na / Fe is more preferably 30 or less, even more preferably 25 or less, and even more preferably 20 or less. That is, the mass ratio of Na / Fe in the first porous layer is more preferably 0.5 to 30, even more preferably 1.0 to 25, and even more preferably 2 to 20. The Na element may be contained as a metal oxide X, or may be contained in a form other than an oxide.

[0015] Furthermore, the first porous layer preferably contains Si element, and the Si / Fe mass ratio in the first porous layer is preferably greater than 32.6. A large Si / Fe mass ratio can suppress a decrease in permeability when the flow rate of a fluid passing through the laminate of the present invention is switched from a high flow rate to a low flow rate. The Si / Fe mass ratio is more preferably 40 or more, even more preferably 50 or more, and even more preferably 60 or more, and the upper limit may be, for example, 90 or less. In other words, the Si / Fe mass ratio in the first porous layer is preferably greater than 32.6 to 90, more preferably 40 to 90, even more preferably 50 to 90, and even more preferably 60 to 90. The Si element may be contained as a metal oxide X, or in a form other than an oxide.

[0016] In the porous ceramic laminate of the present invention, the first porous layer contains Al, Fe, Na, and Si elements, and the Fe / Al mass ratio is 1.0×10 －３ ~8.0 x 10 －３ Preferably, the mass ratio of Na / Fe is 0.5 to 30, and the mass ratio of Si / Fe is 40 to 90. Furthermore, the first porous layer contains Al, Fe, Na, and Si elements, and the mass ratio of Fe / Al is 2.0×10 －３ ~6.0 x 10 －３ It is more preferable that the mass ratio of Na / Fe is 1.0 to 25 and the mass ratio of Si / Fe is 50 to 90.

[0017] The amount of elements contained in the first porous layer can be measured by X-ray fluorescence analysis, and can be measured by quantifying the first porous layer using the FP method using a commercially available X-ray fluorescence analyzer such as ZSX Primus II (manufactured by Rigaku Corporation).

[0018] The cumulative pore area of ​​the first porous layer in the range of pore diameters of 0.98 to 200 μm is 0.010 to 0.550 m ２ / g, and 0.060 to 0.389 m ２ / g. It is more preferable that the pore diameter D ＬＤ－ｍａｘ The log differential pore volume is a value expressed as dV / d(logD) where V is the pore volume, D is the pore diameter, dV is the difference in pore volume between measurement points, and d(logD) is the difference in logarithm of the pore diameter. ＬＤ－ｍａｘ can be calculated by measuring the porous ceramic laminate by mercury intrusion porosimetry to obtain the log differential pore volume distribution.

[0019] The first porous layer in the present invention contains the metal oxide X, and also contains Al element and Fe element, and the Fe / Al mass ratio is 5.7×10 -４ That's it, 1.6 x 10 －２The following commercially available substrates can be used, such as an alumina porous pipe manufactured by Iwao Porcelain Industry Co., Ltd., and a PM filter tube, AF filter tube, and AF-D filter tube manufactured by Nikkato Corporation. It is also possible to adjust the Fe / Al mass ratio in the substrate (first porous layer) by the following method.

[0020] The base material for the first porous layer of the present invention is a mixture containing inorganic particles as raw materials for metal oxide X, a pore-forming agent, and Fe, and the inorganic particles are Al. ２ O ３ The raw material is kneaded to obtain a mixture containing the above, and the resulting raw material is molded into a predetermined shape. The molded body is then dried and fired to burn off the pore-forming agent. The mass ratio of Fe to Al in the raw material (Fe / Al) is 5.7 × 10 -４ That's it, 1.6 x 10 －２ The mass ratio of Fe / Al in the substrate was adjusted to 5.7 × 10 -４ That's it, 1.6 x 10 －２ Furthermore, by setting the average particle size of the inorganic particles to 0.05 to 10 μm and the diameter of the pore-forming agent to 2 to 50 μm, the cumulative pore area of ​​the substrate having pore diameters in the range of 0.98 to 200 μm can be set to the above-mentioned 0.010 to 0.550 m ２ The average particle size of the inorganic particles is preferably 0.05 to 3 μm, and more preferably 0.1 to 1 μm.

[0021] The inorganic particles used as the raw material of the metal oxide X are, as described above, Al ２ O ３ In addition, it is preferable that the raw material contains iron oxide, so that the raw material contains an Fe component. It is preferable that the inorganic particles further contain one or more selected from the group consisting of calcium hydroxide, sodium hydroxide, and silicon oxide.

[0022] The inorganic particles serve as aggregates for the substrate for the first porous layer. By using inorganic particles having the above particle diameter, the aggregate portion becomes a dense ceramic with few pores, and the pore structure can be controlled with a pore-forming agent, which will be described later. In a preferred embodiment, the cumulative pore area of ​​pores with a diameter of 0.98 to 200 μm is 0.010 to 0.550 m ２ If the particle size of the inorganic particles is larger than the above range, irregular coarse pores may occur in the gaps between the particles, making it difficult to control the pore structure.

[0023] Furthermore, by appropriately adjusting the mass ratios of Na / Fe and Si / Fe in the raw materials, the mass ratios of Na / Fe and Si / Fe of the first porous layer in a preferred embodiment can be achieved, respectively. That is, for example, when weighing inorganic particles of sodium hydroxide and iron oxide, they can be separated so that the mass ratio of Na / Fe is greater than 0.132 and not greater than 40, and when weighing inorganic particles of silicon oxide and iron oxide, they can be separated so that the mass ratio of Si / Fe is greater than 32.6.

[0024] The pore-creating agent is preferably polymer particles controlled to be spherical, and is mixed with the inorganic particles, molded, and then fired to burn off the pore-creating agent, thereby forming pores in the shape of the pore-creating agent, and the cumulative pore area of ​​the pores having a diameter of 0.98 to 200 μm is 0.010 to 0.550 m ２ A substrate for the first porous layer having a pore diameter of 0.98 to 200 μm can be obtained. The particle diameter of the polymer particles used as the pore-generating agent is preferably 2 μm or more and 50 μm or less, more preferably 3 μm or more and 50 μm or less, and even more preferably 8 μm or more and 30 μm or less. By using this range, it is possible to generate pores with a pore diameter in the range of 0.98 to 200 μm after firing. When a pore-generating agent with a particle diameter smaller than 2 μm is used, the pore diameter will be smaller than 0.98 μm, and when the particle diameter is larger than 50 μm, the strength of the substrate will be insufficient.

[0025] The polymer constituting the polymer particles can be any polymer such as an acrylic resin or a styrene resin, and commercially available polymer particles can be used.

[0026] The mixing ratio of the inorganic particles and the pore-creating agent is determined by taking into consideration the density of the raw materials for the inorganic particles and the densities of the raw materials for the pore-creating agent, and the fact that the pore-creating agent burns off after firing, and is set so that the surface area of ​​the pore-creating agent is 0.010 to 0.550 m per 1 g of inorganic particles. ２ It is preferable to adjust the amount of the sintering agent so that the sintering agent is / g.

[0027] In addition to the inorganic particles and pore-forming agent described above, the components to be blended into the raw material mixture may include, for example, an organic binder, a dispersant, a surfactant, and water.

[0028] Examples of the organic binder include methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol.

[0029] Examples of dispersants and surfactants include fatty acid salts, alkyl sulfate ester salts, polyoxyethylene alkyl ether sulfate ester salts, alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkyl sulfosuccinates, alkyldiphenyl ether disulfonates, alkyl phosphates, polycarboxylates, polyacrylates, aliphatic quaternary ammonium salts, aliphatic amine salts, polyoxyethylene alkyl ethers, polyoxyethylene alcohol ethers, polyoxyethylene glycerin fatty acid esters, polyoxyethylene sorbitan (or sorbitol) fatty acid esters, polyethylene glycol fatty acid esters, alkyl betaines, amine oxides, and cationic cellulose derivatives.

[0030] The raw material mixture is kneaded and then molded into a predetermined shape to obtain a molded body. A preferred example of the kneading method is to first mix inorganic particles, a pore-forming agent, and water to obtain a slurry, and then add a binder, a surfactant, and an appropriate amount of water to the slurry and knead it.

[0031] The shape of the formed body (i.e., the shape of the first porous layer) is not particularly limited, and can be various shapes depending on the application, such as a plate, a tube, a honeycomb, or a monolith. For example, when used as a substrate for a ceramic filter for gas separation, a monolith or honeycomb shape is preferable. Note that the monolith shape refers to a columnar shape (cylindrical, rectangular, elliptical, etc.) having a plurality of axially penetrating holes (cylindrical shape is preferable), and the honeycomb shape refers to a shape in which axially penetrating hollow three-dimensional figures (regular hexagonal prism, square prism, triangular prism, etc.) are stacked without gaps. To form the raw material into a monolith or honeycomb shape, it is preferable to use a forming method such as extrusion molding.

[0032] The obtained molded body is dried by an appropriate drying method and then fired. There are no particular limitations on the drying method, but drying methods using microwaves, hot air, etc. are preferred. After drying the molded body, and before firing, it is possible to appropriately perform calcination to burn off and remove the pore-forming agent in the molded body. In general, the calcination temperature can be about 600°C. There are no particular limitations on the calcination time, but it is usually about 1 to 10 hours. The calcination atmosphere can be appropriately selected from air, nitrogen, etc.

[0033] The firing temperature is preferably 1400 to 1600°C, and more preferably 1400 to 1550°C. If the firing temperature is less than 1400°C, sintering may not proceed sufficiently. On the other hand, if the firing temperature exceeds 1600°C, the pores will shrink, making it difficult to adjust the pore structure. There is no particular limit to the firing time, but it is usually about 1 to 10 hours. The firing atmosphere can be selected appropriately from air, nitrogen, etc.

[0034] The thickness of the first porous layer is preferably 400 to 8000 μm. When the first porous layer has a monolithic or honeycomb shape, the thickness may be the average value of the closest distances between adjacent through holes in a plane perpendicular to the axis.

[0035] (2) Second porous layer The second porous layer contains an oxide Y containing at least one selected from the group consisting of Al, Ti, Si, and Mg. The oxide Y may be one type or two or more types. The oxide Y preferably contains an oxide of Al and Ti. The oxide of Al and Ti is an oxide of Al (Al ２ O ３ ) and Ti oxide (Ti ２ O ３ ) or a composite oxide of Al and Ti. Ti is useful for improving the strength of the compound (preferably an oxide) formed by the elements in the first porous layer and the elements in the second porous layer. The presence of an oxide of Ti in the second porous layer strengthens the bond between the first porous layer and the second porous layer, improving the peel strength between them. When the second porous layer contains an oxide of Al and Ti, the molar ratio of Ti / Al in the second porous layer is 0.005 or more and less than 0.10. The molar ratio of Ti / Al is preferably 0.01 or more, more preferably 0.03 or more, and may be 0.09 or less, or may be 0.08 or less. In other words, the molar ratio of Ti / Al in the second porous layer is preferably 0.01 to 0.09, more preferably 0.03 to 0.08.

[0036] The second porous layer may contain, in addition to an oxide containing at least one selected from the group consisting of Al, Ti, Si, and Mg, one or more oxides containing at least one selected from the group consisting of Fe, Zr, Cr, and Y. The oxide containing at least one selected from the group consisting of Fe, Zr, Cr, and Y includes oxides containing only one type as a metal element as well as composite oxides containing two or more types of metal elements. As the oxide containing Ti, commercially available oxide particles can be used, such as STS-21, ST-01, ST-21, ST-31, ST-41, STS-01, and STS-02 manufactured by Ishihara Sangyo Kaisha, Ltd., MT-500B, MT-600B, and MT-700B manufactured by Teika Corporation, and TAF-520, TAF-500, and TAF-1500 manufactured by Fuji Titanium Industries Co., Ltd., with STS-21, STS-01, and STS-02 manufactured by Ishihara Sangyo Kaisha being preferred.

[0037] The presence and content ratio of elements contained in the second porous layer can be measured by SEM-EDX analysis, and can be measured by performing a composition analysis of the second porous layer using a commercially available SEM-EDX device such as JSM-7500F (manufactured by JEOL Ltd.).

[0038] Pore ​​diameter D of the second porous layer ＬＤ－ｍａｘ is, for example, 0.1 to 2.0 μm, preferably 0.1 to 1 μm, more preferably 0.1 to 0.5 μm, and even more preferably 0.2 to 0.4 μm. ＬＤ－ｍａｘ As described in the description of the first porous layer, the pore diameter refers to the pore diameter at which the value of the log differential pore volume is maximum, and can be obtained by measuring the porous ceramic laminate using mercury intrusion porosimetry.

[0039] The thickness of the second porous layer is, for example, 1 μm to 3 mm, preferably 2 μm to 2 mm, more preferably 3 to 300 μm, even more preferably 20 to 100 μm, particularly preferably 25 to 80 μm, and most preferably 30 to 60 μm. The thickness of the second porous layer can be determined by the following procedure. First, an image of a cross section parallel to the lamination direction of the first porous layer and the second porous layer is obtained. In the image, the total length of the surface of the second porous layer facing the first porous layer is determined to be equal to the pore diameter D at which the value of the log differential pore volume of the first porous layer is maximized. ＬＤ－ｍａｘ An image is acquired so that the image is at least 10 times larger than the original image, and only the second porous layer is extracted by image analysis. The thickness (length in the stacking direction) of the second porous layer in the obtained image is then measured at five or more locations, and the average thickness of the measured locations is calculated. Note that the cross section parallel to the stacking direction of the first porous layer and the second porous layer can be, for example, a cross section perpendicular to the longitudinal direction of the laminate (e.g., the axial direction when the laminate is tubular or monolithic).

[0040] (3) Porous Ceramic Laminate (3-1) Structure and Shape The porous ceramic laminate of the present invention includes a first porous layer and a second porous layer, and the second porous layer is directly laminated on the first porous layer. "Directly laminated" means that the first porous layer and the second porous layer are laminated without any other layer in between. As long as a portion of the second porous layer is in contact with the first porous layer, the remaining portion may be laminated on the first porous layer via air present due to pores present on the surface of the first porous layer or inorganic particles other than the metal oxide particles constituting the second porous layer. The contact point between the second porous layer and the first porous layer may be the pore portion of the pores present on the surface of the first porous layer. Furthermore, in the porous ceramic laminate of the present invention, the pore diameter D of the first porous layer may be 0.05 mm. ＬＤ－ｍａｘ is the pore diameter D of the second porous layer ＬＤ－ｍａｘ Larger is preferred.

[0041] The shape of the porous ceramic laminate is not particularly limited, and examples thereof include plate-like, tubular, honeycomb-like, and monolithic shapes. Tube-like, honeycomb-like, and monolithic shapes are preferred. Monolithic shapes are particularly preferred when used as substrates for ceramic filters for gas separation. The term "monolithic" refers to a columnar (cylindrical, rectangular, elliptical, etc.) shape having a plurality of axially penetrating holes (preferably cylindrical), and the term "honeycomb-like" refers to a shape in which axially penetrating hollow three-dimensional figures (regular hexagonal, rectangular, triangular, etc.) are stacked without gaps. When the porous ceramic laminate is tubular, the second porous 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 tube. It is more preferred that the second porous layer be formed only on the inner circumferential surface or only on the outer circumferential surface, and even more preferred that the second porous layer be formed only on the inner circumferential surface. When the porous ceramic laminate is monolithic, the second porous layer is preferably formed only on the inner surface of each through-hole of the monolithic shape.

[0042] The thickness (average value) of the porous ceramic laminate is, for example, 450 to 10,000 μm, preferably 500 to 6,000 μm. When the porous ceramic laminate is monolithic or honeycomb-shaped, the thickness may be the average value of the closest distances between adjacent through holes in a plane perpendicular to the axis. The longitudinal length of the porous ceramic laminate is, for example, 50 to 5,000 mm. The longitudinal length refers to, for example, the length of the long side in the case of a plate-like shape, or the axial length in the case of a tube-like, honeycomb-like, or monolithic shape. When the porous ceramic laminate is tubular, the outer diameter is, for example, 5 mm to 20 mm, and the inner diameter of the tube is, for example, 1 mm to 15 mm. When the porous ceramic laminate is honeycomb-shaped or monolithic, i.e., when it has multiple through holes, the outer diameter is, for example, 5 mm to 100 mm, and the inner diameter of each through hole (particularly a cylindrical shape) is, for example, 0.1 mm to 10 mm.

[0043] (3-2) Properties of Porous Ceramic Laminate (3-2-1) Peel Strength The peel strength between the first porous layer and the second porous layer in the porous ceramic laminate of the present invention can be evaluated by measuring the pencil hardness from the second porous layer side of the porous ceramic laminate under the conditions described in the Examples. The second porous layer is a layer containing a metal oxide and typically has a high hardness, so the interface between the first porous layer and the second porous layer breaks first in a pencil hardness test. Therefore, the hardness calculated by this measurement can be used to evaluate the peel strength between the first porous layer and the second porous layer. The pencil hardness evaluated as described in the Examples is preferably F or harder, more preferably 2H or harder, and even more preferably 4H or harder, with an upper limit of 9H. In other words, the pencil hardness is preferably F to 9H, more preferably 2H to 9H, and even more preferably 4H to 9H.

[0044] (3-2-2) Permeance The porous ceramic laminate of the present invention can also reduce the pressure loss of a fluid, and the permeance at a flow rate of 1.0 m / s is evaluated in the examples described later. ３ / h, the permeance is 1.00 × 10 －５ m ３ / (m ２sec Pa) or more, and preferably 3.00×10 －５ m ３ / (m ２ sec Pa) or more, more preferably 1.00 × 10 －４ m ３ / (m ２ sec Pa) or more, and the upper limit is not particularly limited, but for example, 1.0 × 10 －３ m ３ / (m ２ In other words, the flow rate of the porous ceramic laminate of the present invention may be 1.0 m / s. ３ / h, the permeance is 1.00 × 10 －５ ~1.0 x 10 －３ m ３ / (m ２ sec Pa), and －５ ~1.0 x 10 －３ m ３ / (m ２ sec Pa), and 1.00 × 10 －４ ~1.0 x 10 －３ m ３ / (m ２ ·sec·Pa) is more preferred.

[0045] (3-2-3) Permeance maintenance rate when the flow velocity of the fluid is reduced. In addition, according to the examples described later, when the flow velocity of the fluid flowing through the porous ceramic body is 1.0 m / s, ３ / h, the permeance is 0.5m ３ The permeance maintenance rate, obtained by dividing the permeance at 1 / 2000 rpm by the permeance at 1 / 2000 rpm, can be set to 1.2 or less, preferably 1.18 or less, more preferably 1.10 or less, and even more preferably 1.04 or less, and the lower limit may be 1.0. In other words, the permeance maintenance rate can be set to 1.0 to 1.2, preferably 1.0 to 1.18, more preferably 1.0 to 1.10, and even more preferably 1.0 to 1.04.

[0046] (3-3) Method for Producing Porous Ceramic Laminate The porous ceramic laminate of the present invention contains the metal oxide X, and also contains Al element and Fe element, and the Fe / Al mass ratio is 5.7 × 10 -４That's it, 1.6 x 10 －２ The first porous layer substrate can be manufactured by preparing a first porous layer substrate having the following characteristics, preparing a slurry containing the oxide Y (metal oxide Y), applying the slurry to the surface of the substrate, and heat-treating the substrate. ２ / g. In particular, the D ＬＤ－ｍａｘ is the D of the second porous layer ＬＤ－ｍａｘ When the surface roughness is 10 times or more, it is preferable to subject the substrate for the first porous layer to a water- and oil-repellent treatment, and then apply a slurry containing the oxide Y to the surface of the substrate for the first porous layer that has been treated to be water- and oil-repellent.

[0047] In a preferred embodiment, a porous substrate that satisfies the above conditions is used, the substrate is treated to be water- and oil-repellent, and a slurry containing metal oxide Y is applied to the water- and oil-repellent treated surface. This makes it possible to prevent the slurry from entering the pores of the substrate when the pore sizes of the first porous layer and the second porous layer are significantly different.

[0048] Methods for the water- and oil-repellent treatment include spray coating, dip coating, bar coating, suction coating, ultrasonic spraying, brush coating, squeegee coating, and spray coating. The composition of the water- and oil-repellent agent is not limited, but for example, paraffin-based water- and oil-repellent agents, fluorine-based water- and oil-repellent agents, and polysiloxane-based water- and oil-repellent agents can be used. Examples of fluorine-based water- and oil-repellent agents include those having a perfluoroalkyl group and those having a perfluoropolyether structure.

[0049] In a preferred embodiment, the Ti / Al ratio in the second porous layer of the porous ceramic laminate of the present invention can be controlled by controlling the Ti / Al ratio in the slurry containing the metal oxide Y to be 0.005 or more and less than 0.10.

[0050] The metal oxide Y contained in the slurry may be one kind or two or more kinds, and it is sufficient that the metal oxide Y contains at least one kind selected from the group consisting of Al, Ti, Si and Mg. The metal oxide Y contained in the slurry is TiO ２ , Al ２ O ３It is preferable that the oxide contains either a composite oxide containing Ti and Al.

[0051] The average particle size of the metal oxide Y contained in the slurry is preferably, for example, 0.01 to 2 μm. In particular, metal oxides containing Al (e.g., Al ２ O ３ , or composite oxides containing Ti and Al) preferably have an average particle size of 0.1 to 2 μm. ２ The average particle size of the metal oxide (e.g., 0.01 to 0.1 μm) is preferably 0.01 to 0.1 μm. The particle size distribution of the metal oxide can be measured using a small-angle X-ray scattering method when the average particle size is about 0.1 μm or less, and can be measured using a laser diffraction / scattering particle size distribution analyzer when the average particle size is about 0.1 μm or more. The average particle size may be a diameter equivalent to 50% of the cumulative volume.

[0052] The concentration of the metal oxide Y in the slurry is, for example, 2% by mass or more and 22% by mass or less, and preferably 4% by mass or more and 17% by mass or less.

[0053] In addition to the metal oxide Y, the slurry preferably contains a solvent, a thickener, and a dispersant. Examples of the solvent include water or organic solvents. Examples of the thickener include methyl cellulose, hydroxyethyl methyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, polyalkylene oxide, polyvinyl alcohol, sodium polyacrylate, polyvinylpyrrolidone, polyacrylamide, and polydimethylaminoethyl methacrylate. The concentration of the thickener in the slurry is, for example, 0.5% by mass or more and 5% by mass or less, preferably 1% by mass or more and 4% by mass or less. The dispersant can suppress aggregation of the metal oxide particles in the slurry. The dispersant may be any of a cationic surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant. Among these, anionic surfactants such as ammonium polycarboxylates and amine polycarboxylates are preferred, and examples that can be used include SN Dispersant 5020, SN Dispersant 5023, SN Dispersant 5027, SN Dispersant 5468, Noparfa D-6010, Nopcol 5200, Nopcosant RFA, Nopcosperse 6100, and Nopcosperse 6150, manufactured by San Nopco Ltd. The concentration of the dispersant in the slurry is, for example, 0.1% by mass or more and 3% by mass or less, and preferably 0.3% by mass or more and 1% by mass or less.

[0054] After the slurry is applied, a heat treatment may be performed. The heat treatment temperature is, for example, 1000° C. or higher and 1500° C. or lower, and the heat treatment time is, for example, 1 hour or higher and 8 hours or lower.

[0055] (4) Separation Membrane The porous ceramic laminate of the present invention can be used as a microfiltration membrane, an ultrafiltration membrane, or a nanofiltration membrane, and if necessary, can be further laminated with a functional membrane to be used as a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane, a reverse osmosis membrane, an ion exchange membrane, a gas separation membrane, etc.

[0056] Examples of the functional membranes described above include zeolites, MOFs (Metal Organic Frameworks), porous silica membranes, and porous alumina membranes. A separation membrane equipped with a functional layer can be produced by applying a liquid containing inorganic particles or MOFs that form the functional layer to the surface of the ceramic porous laminate obtained by the present invention and allowing the mixture to react. The synthesis conditions can be appropriately selected depending on the functional layer to be laminated, but may be, for example, 80 to 800°C for 1 to 72 hours.

[0057] This application claims the benefit of priority based on Japanese Patent Application No. 2023-144373, filed on September 6, 2023. The entire contents of the specification of Japanese Patent Application No. 2023-144373, filed on September 6, 2023, are incorporated herein by reference.

[0058] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples, and can of course be practiced with appropriate modifications within the scope of the above and below-described aims, all of which are included in the technical scope of the present invention.

[0059] The materials used in the following examples and comparative examples and the resulting porous ceramic laminates were evaluated by the following methods.

[0060] (1) Measurement of Metal Content of Substrate (First Porous Layer) The contents of Fe, Al, Na, and Si in the substrate (first porous layer) were measured using an X-ray fluorescence analyzer (XRF, manufactured by Rigaku Corporation, ZSX Primus II) by the FP method.

[0061] (2) Method for Measuring Particle Diameter of Metal Oxide The particle size distribution of the alumina used in the examples and comparative examples was measured using a laser diffraction / scattering particle size distribution measuring device (Microtrac MT3300EX II, manufactured by Microtrac Co., Ltd., 0.2% by mass aqueous solution of sodium hexametaphosphate), and the volume-based cumulative 50% equivalent diameter was measured.

[0062] (3) Cumulative pore area of ​​pore diameters of 0.98 to 200 μm in the substrate After drying the substrate at 120 ° C for 4 hours, the cumulative pore area was measured by mercury intrusion using an Autopore IV9520 (manufactured by Micromeritics). The detailed measurement conditions are as follows: Hg Surface Tension: 480,000 dynes / cm Hg Density: 13.5335 g / mL Adv. Contact Angle: 140,000 degrees Rec. Contact Angle: 140,000 degrees Pen. Constant: 11.007 μL / pF Pen. Weight: 1.0000g Stem Volume: 0.3920mL Max. Head Pressure: 4.4500 psia Pen. Volume: 1.0000mL Assembly Weight: 141.0000g Low Pressure (Evacuation Pressure): 50μmHg Evacuation Time: 10secs Mercury Filling Pressure: 1.03 psia Equilibration Time: 10secs High Pressure (Evacuation Time): 10secs Maximum Intrusion Volume: 0mL / g

[0063] (4) Measurement of pencil hardness The porous ceramic laminates obtained in the examples and comparative examples were evaluated according to JIS K5600 General Test Method for Paint Scratch Hardness (Pencil Method). A pencil hardness tester (Yasuda Seiki Seisakusho Co., Ltd. 533-M1, weight: 750 g, pencil movement speed: 1 mm / sec) was used to draw a line from a soft pencil (Mitsubishi Pencil Co., Ltd.: Mitsubishi Uni Series 6B-9H) on the surface of the laminate (the surface opposite the first porous ceramic layer), and the surface was observed using a digital microscope (Keyence Corporation: VHX-5000). The hardness just before the hardness at which peeling, dents, or scratches were observed was evaluated as the hardness of the sample.

[0064] (5) Measurement of permeance Air was blown from the outside of the porous ceramic laminate sample to a depth of 1.0 m. ３The air was allowed to flow at a constant flow rate of 1 / h, and the air that permeated from the inside of the sample was allowed to flow downstream. At this time, the pressure difference between the upstream and downstream sides was measured. The measurement results were converted using the following formula to obtain permeance. Note that a higher permeance value means a lower pressure loss.

[0065]

[0066] (6) Evaluation of permeance maintenance rate when gas flow rate is reduced Air was blown 0.5 m from the outside of the porous ceramic laminate sample. ３ / h, and 1.0 m ３ The air was passed through the sample at a constant flow rate of 1.0 m / h, and the air that had permeated from the inside of the sample was passed downstream. At this time, the pressure difference between the upstream and downstream sides was measured. From the measurement results, the permeance of each side was calculated using an equation similar to the above equation (1). ３ / h, the permeance at a low flow rate of 0.5 m ３ The permeance maintenance rate when the gas flow rate is reduced was calculated by dividing the permeance at the time of gas flow rate reduction by the permeance at the time of gas flow rate reduction. The lower the permeance maintenance rate, the more it is possible to suppress the reduction in permeance when the gas flow rate is reduced.

[0067] Example 1: The substrate (first porous layer) was a porous material having a cumulative pore area of ​​0.102 m2 with pore diameters of 0.98 to 200 μm. ２ / g, and Al ２ O ３A commercially available ceramic substrate E1 (cylindrical, with an inner diameter of 6.9 mm, an outer diameter of 10.0 mm, and a length of 10 cm, with the Fe / Al mass ratio, Na / Fe mass ratio, and Si / Fe mass ratio as listed in Table 1) containing the above was prepared. The substrate was dipped in a water repellent agent SH Conc (containing fluororesin and petroleum hydrocarbons) manufactured by Columbus Co., Ltd. and dried at room temperature for 12 hours or more. Next, alumina powder AKP-3000 manufactured by Sumitomo Chemical Co., Ltd. and titanium oxide slurry (STS-21: manufactured by Ishihara Sangyo Kaisha, Ltd., 40 wt%) were mixed so that the Ti / Al molar ratio was 0.0336. The volume-based cumulative 50% equivalent diameter of the alumina powder AKP-3000 was approximately 0.67 μm, and the X-ray particle size (catalog value) of the titanium oxide was 20 nm. A slurry was prepared by mixing the mixture of alumina powder and titanium oxide slurry with hydroxypropyl methylcellulose 65SH-30000 manufactured by Shin-Etsu Chemical Co., Ltd. as a thickener, SN Dispersant 5468 as a dispersant, and water. The concentrations of alumina, thickener, and dispersant in the slurry were 5 wt%, 1.5 wt%, and 0.5 wt%, respectively. The upper and lower ends of the substrate (after water-repellent treatment) were sealed to prevent the slurry from entering the inner surface of the substrate, and the substrate was dip-coated with the slurry. Thereafter, the substrate with the slurry applied to its outer surface was heat-treated at 1200 °C for 3 hours, resulting in a porous ceramic laminate in which a second porous layer (a hardened layer of the slurry) was formed on the substrate (first porous layer).

[0068] Example 2: The substrate (first porous layer) was a porous substrate having a cumulative pore area of ​​0.389 m2 with pore diameters of 0.98 to 200 μm. ２ / g, and Al ２ O ３ A porous ceramic laminate of Example 2 was obtained in the same manner as in Example 1, except that a commercially available ceramic substrate E2 (cylindrical with an inner diameter of 7.0 mm, an outer diameter of 10.0 mm, and a length of 10 cm, and the Fe / Al mass ratio, Na / Fe mass ratio, and Si / Fe mass ratio are as shown in Table 1) containing

[0069] Example 3: The substrate (first porous layer) was a porous material having a cumulative pore area of ​​0.060 m2 with pore diameters of 0.98 to 200 μm. ２ / g, and Al ２O ３ A porous ceramic laminate of Example 3 was obtained in the same manner as in Example 1, except that a commercially available ceramic substrate E3 containing the compound (a cylindrical substrate having an inner diameter of 7.2 mm, an outer diameter of 9.5 mm, and a length of 10 cm, and having an Fe / Al mass ratio, an Na / Fe mass ratio, and an Si / Fe mass ratio as shown in Table 1) was used.

[0070] Example 4 A porous ceramic laminate of Example 4 was obtained in the same manner as in Example 2, except that the Al in the alumina powder and the Ti in the titanium oxide slurry were mixed so that the molar ratio of Ti / Al was 0.0130.

[0071] Example 5 A porous ceramic laminate of Example 5 was obtained in the same manner as in Example 2, except that the Al in the alumina powder and the Ti in the titanium oxide slurry were mixed so that the molar ratio of Ti / Al was 0.0555.

[0072] Example 6 A porous ceramic laminate of Example 6 was obtained in the same manner as in Example 3, except that the Al in the alumina powder and the Ti in the titanium oxide slurry were mixed so that the molar ratio of Ti / Al was 0.00645.

[0073] Example 7 A porous ceramic laminate of Example 7 was obtained in the same manner as in Example 3, except that the Al in the alumina powder and the Ti in the titanium oxide slurry were mixed so that the molar ratio of Ti / Al was 0.0197.

[0074] Example 8 A porous ceramic laminate of Example 8 was obtained in the same manner as in Example 3, except that the Al in the alumina powder and the Ti in the titanium oxide slurry were mixed so that the molar ratio of Ti / Al was 0.0709.

[0075] Comparative Example 1: The substrate (first porous layer) had a cumulative pore volume of 0.12 mL / g for pores with diameters of 0.98 to 200 μm, and contained Al ２ O ３A porous ceramic laminate of Comparative Example 1 was obtained in the same manner as in Example 1, except that a commercially available ceramic substrate containing the compound (a cylindrical substrate having an inner diameter of 6.0 mm, an outer diameter of 9.9 mm, and a length of 10 cm, and the Fe / Al mass ratio, Na / Fe mass ratio, and Si / Fe mass ratio are shown in Table 1) was used.

[0076] Comparative Example 2: The substrate (first porous layer) was a porous film having a cumulative pore area of ​​0.0010 m2 with pore diameters of 0.98 to 200 μm. ２ / g, and Al ２ O ３ A porous ceramic laminate of Comparative Example 2 was obtained in the same manner as in Example 1, except that a commercially available ceramic substrate containing the compound (a monolithic substrate (19 channels) with an inner diameter of 3.3 mm, an outer diameter of 25.4 mm, and a length of 10 cm, and the Fe / Al mass ratio, Na / Fe mass ratio, and Si / Fe mass ratio are as shown in Table 1) was used.

[0077] The results are shown in Table 1.

[0078]

[0079] Furthermore, the following measurements were also carried out for the examples and comparative examples. (7) Measurement of pore distribution of the first porous layer and the second porous layer The entire porous ceramic laminate was measured in the same manner as the measurement by mercury porosimetry described in the above section (3). In the log differential pore volume distribution with the pore diameter on the horizontal axis, one peak was observed in the measurement of the substrate alone, and two peaks were observed in the measurement of the entire porous ceramic laminate. The pore diameter D of the peak of the log differential pore volume of the substrate (first porous layer) was calculated from the peak (maximum value of the log differential pore volume) observed in the measurement of the substrate alone. ＬＤ－ｍａｘ Of the two peaks observed in the observation of the entire porous ceramic laminate, the peak on the lower pore diameter side was determined to be the D of the second porous layer. ＬＤ－ｍａｘ was evaluated.

[0080] (8) Thickness of the second porous layer A cylindrical porous ceramic laminate was embedded in resin and polished to obtain a cross section perpendicular to the axial direction (i.e., a cross section parallel to the stacking direction of the first porous layer and the second porous layer), and observed with a scanning electron microscope (SEM). An image was obtained so that the total length of the first porous layer side surface of the second porous layer was 1.5 mm or more in the circumferential direction, and only the second porous layer was extracted by image analysis. Then, the thickness of the second porous layer (length in the stacking direction) of the obtained image was measured at five or more points, and the average value of the thicknesses measured at multiple points was taken as the thickness of the second porous layer.

[0081] As a result of measurement according to the above item (7), the pore diameter D of the first porous layer ＬＤ－ｍａｘ The pore diameter D of the second porous layer was 1.5 μm in Examples 2, 4, and 5, 15 μm in Examples 3, 6, 7, and 8, 8.5 μm in Example 1, and 8.5 μm in Comparative Example 1. ＬＤ－ｍａｘ The thicknesses were 0.41 μm in Example 2, 0.27 μm in Example 3, 0.27 μm in Example 1, 0.46 μm in Example 4, 0.37 μm in Example 5, 0.28 μm in Example 6, 0.27 μm in Example 7, 0.30 μm in Example 8, and 0.28 μm in Comparative Example 1.

[0082] The thickness of the second porous layer was measured in accordance with the above item (8), and the results were 34.8 μm for Example 3, 35.9 μm for Example 1, and 53.1 μm for Comparative Example 1.

Claims

1. A porous ceramic laminate having a first porous layer and a second porous layer directly laminated on the first porous layer, wherein the first porous layer contains a metal oxide X, and also contains an Al element and an Fe element, and the Fe / Al mass ratio in the first porous layer is 5.7×10 -４ That's it, 1.6 x 10 －２ The second porous layer comprises an oxide Y containing at least one selected from the group consisting of Al, Ti, Si, and Mg.

2. A porous ceramic laminate as described in claim 1, wherein the oxide Y contains an oxide of Al and Ti, and the molar ratio of Ti / Al in the second porous layer is 0.005 or more and less than 0.

10.

3. A porous ceramic laminate as described in claim 1 or 2, wherein the first porous layer contains Na element and the mass ratio of Na / Fe in the first porous layer is greater than 0.132 and less than 40.

4. A porous ceramic laminate according to claim 1 or 2, wherein the first porous layer contains elemental Si and the mass ratio of Si / Fe in the first porous layer is greater than 32.

6.

5. The metal oxide X is Al ２ O ３ The porous ceramic laminate according to claim 1 or 2, comprising:

6. The porous ceramic laminate according to claim 1 or 2, which is in the form of a tube or a monolith.

7. A separation membrane comprising the porous ceramic laminate according to claim 1 or 2.

8. The first porous layer contains Al, Fe, Na and Si elements, and the Fe / Al mass ratio is 1.0×10 －３ ~8.0 x 10 －３ The porous ceramic laminate according to claim 1 or 2, wherein the mass ratio of Na / Fe is 0.5 to 30, and the mass ratio of Si / Fe is 40 to 90.

9. The pore diameter D of the first porous layer at which the log differential pore volume value is maximum in the log differential pore volume distribution obtained by measuring the first porous layer by mercury intrusion porosimetry ＬＤ－ｍａｘ is a pore diameter D of the second porous layer at which the log differential pore volume value is maximum in a log differential pore volume distribution obtained by measuring the second porous layer by mercury intrusion porosimetry. ＬＤ－ｍａｘ The porous ceramic laminate according to claim 1 or 2, wherein the porous ceramic laminate has a diameter of 100 mm or more.

10. Pore diameter D of the first porous layer ＬＤ－ｍａｘ is 1.0 to 18 μm, and the pore diameter D of the second porous layer ＬＤ－ｍａｘ The porous ceramic laminate according to claim 9, wherein the average particle size is 0.1 to 2.0 μm.

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