Mesh-like structure, porous composite, method for manufacturing mesh-like structure, and method for manufacturing porous composite

Abstract

A mesh-like structure having a novel structure is obtained by firing an aggregate of silica gel particles. The mesh-like structure comprises: a plurality of granular portions (51) formed from silica; and a plurality of connection portions (52) formed from silica and connecting to the plurality of granular portions (51) to form a continuous body that is continuous in a three-dimensional mesh-like shape together with the plurality of granular portions (51). The mesh-like structure is formed, for example, on a base material having air permeability.

Description

Network structure, porous composite, method for manufacturing network structure, and method for manufacturing porous composite

[0001] The present invention relates to a reticulated structure and a porous composite, and to a method for manufacturing the same. [Reference to Related Applications] This application claims the benefit of priority from Japanese Patent Application JP2023-53026, filed on March 29, 2023, the entire disclosure of which is incorporated herein by reference.

[0002] Vehicles equipped with diesel or gasoline engines are equipped with filters to capture particulate matter in exhaust gases. One such filter is a honeycomb filter in which, among a plurality of cells in a porous honeycomb substrate, plugging portions are provided at the outlet openings of some of the cells and at the inlet openings of the remaining cells.

[0003] For example, in the honeycomb filter of Japanese Patent Laid-Open No. 2012-200642 (Document 1), a porous trapping layer is provided on the surface inside cells that have plugging portions at the outlet openings. The trapping layer is formed by a plurality of particles that are bonded or entangled with each other, and the plurality of particles includes flat, plate-like particles. The honeycomb filter of Document 1 can suppress an increase in initial pressure loss and an increase in pressure loss when particulate matter accumulates.

[0004] Furthermore, in the honeycomb filter of International Publication No. 2020 / 194681 (Document 2), the arithmetic mean height, which indicates the surface roughness, of the trapping layer provided in a predetermined cell is set to 0.1 μm or more and 12 μm or less, and the average film thickness of the trapping layer is set to 10 μm or more and 40 μm or less, thereby reducing pressure loss and improving the particulate matter collection efficiency.

[0005] As mentioned above, for the porous composites that make up honeycomb filters, technologies have been proposed to improve the collection efficiency of particulate matter and the like while reducing pressure loss in order to improve fuel efficiency. Because there is a trade-off between the two, it is not easy to achieve high collection efficiency while also reducing pressure loss. However, due to stricter regulations in recent years, there is a demand for both reduced pressure loss and improved collection efficiency.

[0006] Meanwhile, filters have been used in various fields to separate particulates from fluids containing particulates or to increase the concentration of particulates in fluids. In such filters, particulates adhere to the filter during separation, resulting in a decrease in separation efficiency over time. Therefore, a new structure is needed to prevent this decrease in separation efficiency.

[0007] The present invention aims to provide a mesh structure having a novel structure. The mesh structure is used, for example, in a filter that separates fine particles from a fluid.

[0008] A first aspect of the present invention is a mesh-like structure comprising a plurality of granular portions formed of silica and a plurality of connecting portions formed of silica that connect the plurality of granular portions together to form a three-dimensional mesh-like continuum.

[0009] According to the first aspect of the present invention, a network structure having a novel structure can be provided.

[0010] A second aspect of the present invention is the network structure of the first aspect, wherein the average particle size of the plurality of granular portions is 0.8 μm or more and 10 μm or less.

[0011] A third aspect of the present invention is the network structure of the first aspect (which may be either the first or second aspect), wherein the chlorine content is less than 10 ppm (by weight) and the sulfur content is less than 0.01 wt %.

[0012] A fourth aspect of the present invention is a porous composite, comprising a substrate that is a porous sintered body having air permeability, and the network structure of the first aspect provided on the substrate.

[0013] A fifth aspect of the present invention is the porous composite of the fourth aspect, wherein the network structure has an average film thickness on the substrate of 5 μm or more and 200 μm or less.

[0014] A sixth aspect of the present invention is the porous composite of the fourth aspect (which may be either the fourth or fifth aspect), wherein the average pore size of the substrate is 10 μm or more and 30 μm or less.

[0015] A seventh aspect of the present invention is the porous composite of Aspect 4 (which may be any one of Aspects 4 to 6), further comprising an upper layer provided on the mesh structure, the upper layer being a porous sintered body having air permeability and an average pore size smaller than that of the substrate.

[0016] Aspect 8 of the present invention is the porous composite of aspect 7, wherein the upper layer is formed of alumina.

[0017] A ninth aspect of the present invention is the porous composite of the seventh aspect (or may be either the seventh or eighth aspect), wherein the upper layer has an average pore size of 1.0 μm or more and 1.5 μm or less.

[0018] A tenth aspect of the present invention is the porous composite of the seventh aspect (which may be any one of the seventh to ninth aspects), wherein the upper layer has an average thickness of 15 μm or more and 40 μm or less.

[0019] Aspect 11 of the present invention is a filter that is the porous composite of any one of Aspects 4 to 6, and separates microorganisms contained in a liquid from the liquid.

[0020] According to the eleventh aspect of the present invention, the decrease in filtration rate can be suppressed.

[0021] A twelfth aspect of the present invention is a particulate filter comprising the porous composite of any one of Aspects 7 to 10, for trapping particulate matter in exhaust gas emitted from a gasoline engine or a diesel engine.

[0022] According to the twelfth aspect of the present invention, a porous composite having high collection efficiency and low pressure loss can be provided.

[0023] A thirteenth aspect of the present invention is a method for producing a network structure, comprising: a) forming an aggregate of silica gel particles having an average particle size of 0.1 μm or more and 5.0 μm or less; and b) heating the aggregate at 1200° C. or more and 1400° C. or less for 0.5 hours or more and 2 hours or less to obtain a network structure formed of silica.

[0024] A fourteenth aspect of the present invention is the method for producing a network structure according to the thirteenth aspect, wherein the average pore volume of the silica gel particles is 0.2 ml / g or more and 3.0 ml / g or less.

[0025] A fifteenth aspect of the present invention is the method for producing a network structure according to the thirteenth aspect (which may be either the thirteenth or fourteenth aspect), wherein the chlorine content in the silica gel particles is 20 ppm (by weight) or more and 0.01 wt % or less, and the sulfur content is 0.1 wt % or less.

[0026] A sixteenth aspect of the present invention is the method for producing the network structure of Aspect 13 (which may be any one of Aspects 13 to 15), wherein in the step a), the aggregates are formed by molding a slurry containing the silica gel particles.

[0027] A seventeenth aspect of the present invention is a method for producing a porous composite, comprising: c) preparing a substrate that is a porous sintered body having gas permeability; and d) forming the mesh-like structure on the substrate by the method for producing the mesh-like structure of any one of Aspects 13 to 16.

[0028] Aspect 18 of the present invention is the method for producing the porous composite of Aspect 17, wherein in step a), the aggregate is formed on the substrate by depositing the silica gel particles on the substrate.

[0029] A nineteenth aspect of the present invention is the method for producing a porous composite according to the eighteenth aspect, wherein in the step a), the silica gel particles are deposited on the substrate to a thickness of 20 μm or more and 50 μm or less.

[0030] Aspect 20 of the present invention is the manufacturing method of aspect 18 or 19, wherein in step a), the aggregates of silica gel particles are formed on the substrate by bringing a slurry containing the silica gel particles into contact with the substrate while reducing the pressure inside the substrate.

[0031] Aspect 21 of the present invention is a method for producing a porous structure according to Aspect 17 (which may be any one of Aspects 17 to 20), comprising the steps of: e) depositing upper layer material particles having an average particle size of 0.05 μm or more and 1.0 μm or less on the mesh structure; and f) heating the upper layer material particles to form an upper layer that is a porous sintered body that is air-permeable and has an average pore size smaller than that of the substrate.

[0032] A twenty-second aspect of the present invention is the method for producing a porous composite according to the twenty-first aspect, wherein the upper layer material particles are alumina particles.

[0033] The above and other objects, features, aspects and advantages will become more apparent from the following detailed description of the invention which proceeds with reference to the accompanying drawings.

[0034] 5A is a simplified plan view of a porous composite; FIG. 5B is a cross-sectional view of a portion of the porous composite; FIG. 5C is an SEM image of a longitudinal section of a porous composite provided with a trapping layer; FIG. 5D is a simplified view of the structure of FIG. 3; FIG. 5E is an SEM image of the surface of the lower layer when only the lower layer is formed on the substrate; FIG. 5F is a simplified view of the structure of FIG. 5A; FIG. 5G is an SEM image of the longitudinal section of the substrate and the lower layer when only the lower layer is formed on the substrate; FIG. 5H is an SEM image of the longitudinal section when only an alumina trapping layer is formed on the substrate; FIG. 5I is a diagram showing the flow of manufacturing a porous composite; FIG. 5J is a diagram showing the configuration of a dry film-forming apparatus; FIG. 5I is a diagram for explaining how silica gel particles are deposited on a substrate; FIG. 5J is a diagram for explaining the average film thickness; FIG. 5I is a simplified view of an algae recovery device having a porous composite; FIG. 5I is a diagram showing a cross-section of a porous composite; FIG. 5I is a simplified view of an enlarged longitudinal section of a substrate and a surface layer; FIG. 5I is a diagram showing how algae particles are deposited; FIG. 5I is a diagram showing the flow of manufacturing a porous composite; FIG. 5I is a simplified view of the longitudinal section of a network structure; FIG. 5I is a diagram showing the flow of manufacturing a network structure.

[0035] Fig. 1 is a simplified plan view of a porous composite 1 according to one embodiment of the present invention. The porous composite 1 is a tubular member that is long in one direction, and Fig. 1 shows one end face of the porous composite 1 in the longitudinal direction. Fig. 2 is a cross-sectional view of a portion of the porous composite 1. Fig. 2 shows a portion of the cross section along the longitudinal direction, and the direction perpendicular to the plane of Fig. 1 corresponds to the left-right direction in Fig. 2. The porous composite 1 is used, for example, as a gasoline particulate filter (GPF) that captures particulate matter (i.e., fine particles) such as soot in exhaust gas emitted from a gasoline engine of an automobile or the like.

[0036] The porous composite 1 includes a porous substrate 12 and a porous collection layer 13 (see FIG. 2 ). In the example shown in FIGS. 1 and 2 , the substrate 12 is a member having a honeycomb structure. The substrate 12 includes a cylindrical outer wall 121 and partition walls 122. The cylindrical outer wall 121 is a cylindrical portion extending in the longitudinal direction (i.e., the left-right direction in FIG. 2 ). The cross-sectional shape of the cylindrical outer wall 121 perpendicular to the longitudinal direction is, for example, substantially circular. The cross-sectional shape may also be other shapes, such as a polygon.

[0037] The partition walls 122 are provided inside the cylindrical outer wall 121 and are lattice-shaped sections that divide the interior into multiple cells. As described below, the multiple cells include multiple first cells 1231 and multiple second cells 1232. In the following description, when the first cells 1231 and the second cells 1232 are not distinguished from each other, the first cells 1231 and the second cells 1232 are simply referred to as "cells 123." Each of the multiple cells 123 is a space extending in the longitudinal direction. The cross-sectional shape of each cell 123 perpendicular to the longitudinal direction is, for example, approximately square. The cross-sectional shape may be other shapes such as polygonal or circular. In principle, the multiple cells 123 have the same cross-sectional shape. The multiple cells 123 may include cells 123 with different cross-sectional shapes. The substrate 12 is a cell structure whose interior is divided into multiple cells 123 by partition walls 122.

[0038] The cylindrical outer wall 121 and the partition walls 122 are each a porous portion. The cylindrical outer wall 121 and the partition walls 122 are formed of a ceramic such as cordierite. The material of the cylindrical outer wall 121 and the partition walls 122 may be a ceramic other than cordierite, or may be a material other than ceramics.

[0039] The longitudinal length of the cylindrical outer wall 121 is, for example, 50 mm or more and 300 mm or less. The outer diameter of the cylindrical outer wall 121 is, for example, 50 mm or more and 300 mm or less. The thickness of the cylindrical outer wall 121 is, for example, 30 μm or more, and preferably 50 μm or more. The thickness of the cylindrical outer wall 121 is, for example, 1000 μm or less, preferably 500 μm or less, and more preferably 350 μm or less. The longitudinal length of the partition wall 122 is approximately the same as that of the cylindrical outer wall 121. The thickness of the partition wall 122 is, for example, 30 μm or more, and preferably 50 μm or more. The thickness of the partition wall 122 is, for example, 1000 μm or less, preferably 500 μm or less, and more preferably 350 μm or less.

[0040] The porosity of the substrate 12 including the cylindrical outer wall 121 and the partition walls 122 is, for example, 20% or more, and preferably 30% or more. The porosity of the substrate 12 is, for example, 80% or less, and preferably 70% or less. The open porosity of the substrate 12 is, for example, 40% or more, and preferably 55% or more. The open porosity of the substrate 12 is, for example, 65% or less. The porosity and open porosity of the substrate 12 can be measured by Archimedes' method.

[0041] The average pore diameter of the substrate 12 (the arithmetic mean value obtained by dividing the sum of the diameters of all pores by the number of pores, or an equivalent value; the same applies hereinafter) is, for example, 10 μm or more, preferably 12 μm or more. The average pore diameter of the substrate 12 is, for example, 30 μm or less, preferably 25 μm or less. The average pore diameter can be measured using a mercury porosimeter. The surface opening ratio of the substrate 12 is, for example, 20% or more, preferably 25% or more. The surface opening ratio of the substrate 12 is, for example, 60% or less, preferably 50% or less. The surface opening ratio is the proportion of the area of ​​the surface of the substrate 12 where pores are open, and can be determined by image analysis of an SEM (scanning electron microscope) image of the surface. The SEM image is taken at, for example, 500x magnification. The image analysis is performed, for example, using image analysis software "Image-Pro ver. 9.3.2" manufactured by Nippon Roper Co., Ltd.

[0042] The cell density of the substrate 12 (i.e., the number of cells 123 per unit area in a cross section perpendicular to the longitudinal direction) is, for example, 10 cells / cm ２ or more, preferably 20 cells / cm ２ More preferably, 30 cells / cm or more. ２ The cell density is, for example, 200 cells / cm ２ or less, preferably 150 cells / cm ２ 1, the size of the cells 123 is drawn larger than in reality, and the number of the cells 123 is drawn smaller than in reality. The size and number of the cells 123 may be variously changed.

[0043] When the porous composite 1 is used as a GPF, one end side of the porous composite 1 in the longitudinal direction (i.e., the left side in FIG. 2 ) serves as an inlet, and the other end side serves as an outlet, and gas such as exhaust gas flows inside the porous composite 1. Furthermore, among the multiple cells 123 of the porous composite 1, some of the multiple cells 123 are provided with plugging portions 124 at their inlet-side ends, and the remaining multiple cells 123 are provided with plugging portions 124 at their outlet-side ends.

[0044] Fig. 1 depicts the inlet side of the porous composite 1. To facilitate understanding of the drawing, the plugging portions 124 on the inlet side are indicated by diagonal lines in Fig. 1. In the example shown in Fig. 1, cells 123 provided with plugging portions 124 on the inlet side and cells 123 not provided with plugging portions 124 on the inlet side (i.e., cells 123 provided with plugging portions 124 on the outlet side) are alternately arranged in the vertical and horizontal directions in Fig. 1.

[0045] The first cell 1231 is a cell 123 provided with a plugging portion 124 on the outlet side. The second cell 1232 is a cell 123 provided with a plugging portion 124 on the inlet side. In the porous composite 1, a plurality of first cells 1231 each having one plugged end in the longitudinal direction and a plurality of second cells 1232 each having the other plugged end in the longitudinal direction are arranged alternately.

[0046] The trapping layer 13 is formed on the substrate 12. In the example shown in FIG. 2 , the trapping layer 13 is provided in a plurality of first cells 1231 that have plugging portions 124 provided on the outlet side, and covers the inner surfaces of the plurality of first cells 1231 (i.e., the surfaces of the partition walls 122). In FIG. 2 , the trapping layer 13 is indicated by a thick dashed line. The trapping layer 13 may also be provided on the inner surfaces of the outlet-side plugging portions 124 in the plurality of first cells 1231. On the other hand, the trapping layer 13 is not present in a plurality of second cells 1232 that have plugging portions 124 provided on the inlet side. In other words, the inner surfaces of the plurality of second cells 1232 are not covered by the trapping layer 13 and are exposed.

[0047] In the porous composite 1 shown in Figures 1 and 2, as indicated by arrow A1 in Figure 2, gas flowing into the porous composite 1 flows into the first cells 1231 through the inlets of the first cells 1231, whose inlet sides are not sealed, and then moves from the first cells 1231 through the porous trapping layer 13 and the partition walls 122 to the second cells 1232, whose outlet sides are not sealed. At this time, the trapping layer 13 efficiently traps the substances (here, particulate matter) in the gas. Furthermore, if the trapping layer 13 contains catalyst particles, as described below, the combustion (i.e., oxidative removal) of the trapped particulate matter is promoted. In the following description, the inner surfaces of the multiple first cells 1231 on which the trapping layer 13 is provided will also be referred to as the "trapping surface."

[0048] Fig. 3 is an SEM image of a longitudinal section of porous composite 1 provided with trapping layer 13, and Fig. 4 is a simplified diagram of the structure of Fig. 3. A "longitudinal section" is a plane perpendicular to the surface of substrate 12, and Figs. 3 and 4 show longitudinal sections parallel to the longitudinal direction of cells 123. In Fig. 3, the area indicated by reference numeral 12 indicates the area of ​​substrate 12, the area indicated by reference numeral 131 with fine white dots indicates the area of ​​lower layer 131 of trapping layer 13, and the gray area indicated by reference numeral 132 indicates the area of ​​upper layer 132 of trapping layer 13.

[0049] The substrate 12 has large pores, and the interconnected pores provide breathability. A lower layer 131 is formed on the substrate 12. An upper layer 132 is formed on the lower layer 131. FIG. 5A is an SEM image of a porous composite in which only the lower layer 131 is formed on the substrate 12, observed from a direction perpendicular to the surface of the substrate 12. FIG. 5B is a simplified view of the structure of FIG. 5A. FIG. 6 is an SEM image of a longitudinal cross section of a porous composite in which only the lower layer 131 is formed on the substrate 12.

[0050] As shown in FIGS. 5A and 5B, the lower layer 131 has a breathable three-dimensional mesh structure. The lower layer 131 is a mesh structure having a novel structure. The three-dimensional mesh structure is formed by connecting granular portions 51 of silica (SiO ２ ) are further connected in a three-dimensional network structure. In other words, the network structure formed by silica includes a plurality of granular parts 51 formed by silica and a plurality of connecting parts 52 formed by silica and connecting the plurality of granular parts 51 to form a three-dimensional network structure together with the plurality of granular parts 51. The connecting parts 52 have a constricted shape between the plurality of granular parts 51. As will be described later, such a structure can be formed by baking (so-called baking treatment) to form a continuum of silica gel (SiO ２ ・nH ２ O) It is formed by the particles densifying and bonding together.

[0051] Since the lower layer 131 has a mesh-like structure, when observing only the brightest area, as shown in the cross-sectional views of Figures 3 and 6, the lower layer 131 appears as if small dots are dispersed. However, when a bright image is acquired and observed including the gray areas, the lower layer can be recognized as having a mesh structure. The upper layer 132 is made of alumina (Al ２ O ３ The upper layer 132 is porous and has air permeability, and is formed by firing alumina particles.

[0052] The average pore diameter of the upper layer 132 is smaller than the average pore diameter of the lower layer 131, which is smaller than the average pore diameter of the substrate 12. Since the substrate 12, the lower layer 131, and the upper layer 132 are all breathable, the porous composite 1 is also breathable.

[0053] 4, the cross section of the large pores in the substrate 12 is shown as large cavities, the cross section of the mesh-like structure of the lower layer 131 is shown as many circles, and the small pores in the upper layer 132 are shown as many small cavities. The surface of the upper layer 132 is the surface of the porous composite 1.

[0054] FIG. 7 is an SEM image of a longitudinal section of a trapping layer 13 made of only alumina formed on a substrate 12 without forming a lower layer 131. Comparing FIG. 3 with FIG. 7, it can be seen that in FIG. 3, the mesh-like lower layer 131 covers the openings of the pores 120 of the substrate 12 to support the alumina upper layer 132, whereas in FIG. 7, the trapping layer 13 made of only alumina penetrates into the pores 120 of the substrate 12. Conventionally, to improve the trapping efficiency, it was necessary to reduce the size of the material particles of the trapping layer. In this case, as shown in FIG. 7, the material particles penetrate into the pores 120, significantly increasing pressure loss. In contrast, in the case of FIG. 3, even if the material particles of the upper layer 132 are reduced in size, they do not penetrate into the pores 120, and sufficient trapping efficiency is achieved while suppressing an increase in pressure loss.

[0055] The upper layer 132 of the trapping layer 13 may contain catalyst particles to promote the oxidative removal of the trapped materials. The catalyst particles become part of the upper layer 132, for example, by adhering the catalyst particles to the upper layer 132 and baking it. The catalyst particles are typically oxides, and preferably CeO ２ (ceria), lanthanum (La)-cerium (Ce) composite oxide, lanthanum-manganese (Mn)-cerium composite oxide, lanthanum-cobalt (Co)-cerium composite oxide, lanthanum-iron (Fe)-cerium composite oxide, or lanthanum-praseodymium (Pr)-cerium composite oxide. In other words, the particles of the trapping layer 13 are CeO ２, lanthanum-cerium composite oxide, lanthanum-manganese-cerium composite oxide, lanthanum-cobalt-cerium composite oxide, lanthanum-iron-cerium composite oxide, and lanthanum-praseodymium-cerium composite oxide.

[0056] Lanthanum-cerium composite oxide is an oxide containing La and Ce, and is also expressed as "La-Ce-O". Lanthanum-manganese-cerium composite oxide is an oxide containing La, Mn, and Ce, and is also expressed as "La-Mn-Ce-O". Lanthanum-cobalt-cerium composite oxide is an oxide containing La, Co, and Ce, and is also expressed as "La-Co-Ce-O". Lanthanum-iron-cerium composite oxide is an oxide containing La, Fe, and Ce, and is also expressed as "La-Fe-Ce-O". Lanthanum-praseodymium-cerium composite oxide is an oxide containing La, Pr, and Ce, and is also expressed as "La-Pr-Ce-O".

[0057] The composite oxide particles are produced, for example, by the citric acid method. The composite oxide particles may also be produced by an impregnation method, a complex polymerization method, or the like.

[0058] Next, an example of manufacturing the porous composite 1 will be described. FIG. 8 is a diagram showing the manufacturing flow of the porous composite 1. First, a porous sintered body having air permeability is prepared as the substrate 12 (step S11). Various known methods may be used to manufacture the substrate 12. Next, a step of depositing silica gel particles on the substrate 12 by a dry film-forming method is performed (step S12). As a result, an aggregate of silica gel particles is formed on the substrate 12. FIG. 9 is a diagram showing the configuration of a dry film-forming apparatus 8. FIG. 10 is a diagram for explaining how silica gel particles are deposited on the substrate 12, and schematically shows a portion of a cross section of the substrate 12 along the longitudinal direction.

[0059] 9 includes a first cylindrical portion 81, a second cylindrical portion 82, and a particle supply portion 83. The first cylindrical portion 81 and the second cylindrical portion 82 are both cylindrical members, and the cross-sectional shape perpendicular to the central axis thereof is substantially the same as the cross-sectional shape of the outer surface (the outer surface of the cylindrical outer wall 121) of the substrate 12. As described above, the substrate 12 is a member extending in the longitudinal direction, and one end of the substrate 12 in the longitudinal direction is inserted into the end of the first cylindrical portion 81, and the other end of the substrate 12 is inserted into the end of the second cylindrical portion 82. In the present embodiment, the end of the substrate 12 where the first cells 1231 (see FIG. 10 ) (more precisely, the first cells 1231 before the formation of the lower layer 131) are open (i.e., the end where the plugging portions 124 are provided on the second cells 1232 (more precisely, the second cells 1232 before the formation of the lower layer 131)) is inserted into the first cylindrical portion 81, and the end of the substrate 12 where the second cells 1232 are open is inserted into the second cylindrical portion 82. The outer surface of the substrate 12 may be in contact with the first cylindrical portion 81 or the second cylindrical portion 82 via an O-ring or the like. Gas and liquid are substantially impermeable between the outer surface of the substrate 12 and the inner surface of the first cylindrical portion 81, and between the outer surface of the substrate 12 and the inner surface of the second cylindrical portion 82.

[0060] A particle supply unit 83 is connected to the end of the first cylindrical portion 81 opposite the substrate 12. The particle supply unit 83 supplies an aerosol in which silica gel particles are dispersed in a gas into the first cylindrical portion 81. The dispersion medium of the aerosol is, for example, air. The dispersion medium of the aerosol may be a gas other than air. A pressure reduction mechanism (not shown) is connected to the end of the second cylindrical portion 82 opposite the substrate 12, and the pressure inside the second cylindrical portion 82 is reduced. As a result, the aerosol supplied into the first cylindrical portion 81 flows into the substrate 12.

[0061] As shown by arrow A2 in FIG. 10 , the aerosol flows into the first cell 1231. The gas contained in the aerosol enters the partition wall 122 through pores opening on the inner surface of the first cell 1231 and moves to the second cell 1232 adjacent to the first cell 1231. The gas that has moved to the second cell 1232 is discharged to the outside of the substrate 12 through the opening of the second cell 1232. As a result, silica gel particles 1311 are deposited on the inner surface of the first cell 1231. At this time, because the silica gel particles 1311 have a low specific gravity, most of the silica gel particles 1311 do not enter the pores on the inner surface. The average particle size of the silica gel particles 1311 is preferably 0.1 μm or more and 5.0 μm or less. The average particle size is an arithmetic mean value (the arithmetic mean value obtained by dividing the sum of the particle diameters by the number of particles, or an equivalent value (e.g., D50); the same applies hereinafter) and is determined from the particle size distribution of the particles obtained by laser diffraction.

[0062] Preferably, the density of the silica gel particles in the aerosol is 1.0 g / cm ３ 2.2g / cm or more ３ The aerosol suction rate is 10 L / (min / cm ２ ) or more 20L / (min / cm ２ ) or less ("L" represents liters). The thickness of the deposited layer of silica gel particles is preferably 20 μm or more and 50 μm or less. The thickness of the deposited layer is determined as the difference between the average height position of the surface of the deposited layer measured by a laser three-dimensional shape measuring device and the average height position of the surface of the substrate.

[0063] The substrate 12 on which the silica gel particles have been deposited is removed from the dry film-forming apparatus 8 and subjected to firing (step S13). This heats the aggregate of silica gel particles and sinters them into a network structure. The heating temperature during firing is preferably 1200°C or higher and 1400°C or lower. The heating time during firing is preferably 0.5 hours or higher and 2 hours or lower. The temperature rise rate during firing is 50°C / hour or higher and 100°C / hour or lower. As a result of firing, the lower layer 131 of the trapping layer 13 is formed on the substrate 12.

[0064] Next, a step of depositing upper layer material particles on the lower layer 131 by a dry film-forming method (step S14) is performed. The upper layer material particles are deposited by a dry film-forming apparatus in accordance with the deposition of silica gel particles shown in FIG. 9 .

[0065] The upper layer material particles are preferably alumina particles. The upper layer material particles may be particles other than alumina particles, such as silicon carbide (SiC) particles, cordierite (2MgO.2Al ２ O ３ 5SiO ２ ) particles, mullite (3Al ２ O ３ 2SiO ２ The upper layer material particles preferably have an average particle size of 0.05 μm or more and 1.0 μm or less. Preferably, the density of the upper layer material particles in the aerosol is 2.5 g / cm ３ 4.0g / cm or more ３ The aerosol suction rate is 10 L / (min / cm ２ ) or more 15L / (min / cm ２ The thickness of the deposited layer of upper layer material particles is preferably 15 μm or more and 40 μm or less.

[0066] The porous composite with the deposited upper layer material particles is removed from the dry film-forming apparatus and fired again (step S15). When the upper layer material particles are alumina, the heating temperature during firing is preferably 900°C or higher and 1500°C or lower. The heating time during firing is preferably 0.5 hours or higher and 2 hours or lower. By firing, an upper layer 132 is formed on the lower layer 131 on the substrate 12. This forms a trapping layer 13 having the lower layer 131 and the upper layer 132, and a porous composite 1 is obtained.

[0067] Next, with reference to Tables 1 and 2, Examples 1-1 to 1-6 of the porous composite according to the present invention and Comparative Examples 1-1 to 1-4 for comparison with the porous composite will be described.

[0068]

[0069]

[0070] (Example 1-1) In Example 1-1, first, a substrate made of cordierite and having the shape of a honeycomb filter (honeycomb structure) was prepared. The porosity of the substrate was 48%, and the average pore diameter (the arithmetic mean value obtained by dividing the total diameter of all pores by the number of pores, or an equivalent value; the same applies hereinafter) was 12 μm. The porosity was measured by the Archimedes method using pure water as a medium. The average pore diameter was measured using a mercury porosimeter.

[0071] By dry deposition method, a film with an average particle size of 4 μm and a pore volume of 1.5 cm was formed on a cordierite substrate. ３ / g of silica gel particles were deposited. During deposition, the flow rate was 13.7 L / (min cm ２ ) (unit surface area 1 cm within the first cell 1231 of the substrate 12 ２ Suction was carried out at a rate of suction per unit time of 1 minute (suction amount per unit time of 1 minute). Thereafter, firing was carried out at a temperature of 1240° C. for 2 hours to form the lower layer of the trapping layer.

[0072] Next, alumina particles having an average particle size of 0.1 μm were deposited on the lower layer by a dry film-forming method. During deposition, the flow rate was 13.7 L / (min cm ２ Then, the mixture was baked at a temperature of 1100° C. for 1.5 hours to form an upper layer of the trapping layer.

[0073] In the porous composite thus prepared, the penetration depth of the collection layer into the pores of the substrate in the longitudinal cross section of the lower silica layer, i.e., in the cross section of the porous composite taken along a plane perpendicular to the surface of the substrate, was 0 μm, the porosity of the lower layer in the longitudinal cross section was 68%, the average pore diameter in the longitudinal cross section was 4.5 μm, and the average film thickness (i.e., the average thickness of the layer) was 20 μm.

[0074] These measurements were obtained from 1000x SEM (scanning electron microscope) images of a cross section of a porous composite fragment embedded in resin and mirror-polished. Specifically, the "penetration depth of the trapping layer into the pores of the substrate" was determined by drawing a curve representing the surface of the substrate in the SEM image, determining the straight line closest to this curve using the least squares method or the like, and calculating the average depth to which the trapping layer (or the lower layer, if an upper layer is present) penetrated into the pores relative to this line. The "porosity of the lower layer in the longitudinal cross section" was obtained from the SEM image by image analysis using the above-mentioned Image-Pro. This image analysis is performed, for example, using a method similar to that described in WO 2020 / 194681. Specifically, in the region of the lower layer in the SEM image, the area of ​​the bright area where the bright part (i.e., the particles of the lower layer) appears and the area of ​​the dark area where the dark part (i.e., the pores of the lower layer) appears are calculated. The porosity of the lower layer is then calculated by dividing the total area of ​​the dark regions by the sum of the total area of ​​the light regions and the total area of ​​the dark regions.

[0075] The "average pore diameter of the lower layer in the longitudinal cross section" was determined by binarizing the SEM image using Image-Pro at a threshold value sufficient to distinguish the network structure skeleton from the cross section of the pores, obtaining the outlines of numerous pores from this image, and calculating the arithmetic mean value of the widths of the portions where pores are connected. As shown in FIG. 11, the average film thickness was determined by obtaining a curve 61 that traces the boundary between the surface of the substrate 12 and the lower layer 131, and a curve 62 that traces the boundary between the lower layer 131 and the upper layer 132, and calculating the arithmetic mean value of the distance between the curves 61 and 62 on the lines that divide the image into six equal parts horizontally. The horizontal direction of the image is the direction along the surface of the substrate 12.

[0076] The porosity of the lower layer in the membrane plane, i.e., the plane parallel to the surface of the substrate (hereinafter referred to as "in-plane membrane"), was 45%, the average pore diameter of the lower layer in the membrane plane was 3.9 μm, and the average diameter of the granular portions was 3.0 μm. These measurements were obtained from 1000x SEM images of a porous composite fragment embedded in resin, polished from the upper layer side to remove the upper layer, and a mirror cross section of the lower layer was obtained. Specifically, the "in-plane porosity of the lower layer" was obtained from the SEM image using Image-Pro in the same manner as for the longitudinal section. The "in-plane average pore diameter of the lower layer" was obtained by binarizing the SEM image using Image-Pro at a threshold value sufficient to distinguish between the network structure skeleton and the cross sections of the pores, and then, as with the longitudinal section, by taking the arithmetic mean value of the major axis of the ellipses that best fit the outlines of the numerous pores in the SEM image. The "average diameter of the granular portion" was determined by binarizing a 2000x SEM image using Image-Pro at a threshold value that allowed the mesh structure skeleton and the cross-sections of the pores to be distinguished, determining the outline of the skeleton, and obtaining ellipses along granular portions recognized as approximately circular within the skeleton (ellipses with the smallest difference area relative to parts other than those connected to adjacent granular portions), and then calculating the arithmetic mean value of the long diameters of these ellipses.

[0077] The porosity of the alumina upper layer in the vertical cross section was 88%, the average pore diameter of the upper layer in the vertical cross section was 1.3 μm, and the average film thickness of the upper layer was 15 μm.

[0078] These measurements were obtained from 1000x SEM images of porous composite fragments embedded in resin and polished to a mirror finish. Specifically, the "porosity of the upper layer in the longitudinal cross section" was obtained from SEM images using Image-Pro in the same manner as for the lower layer. The "average pore diameter of the upper layer in the longitudinal cross section" was obtained by binarizing the SEM image using Image-Pro at a threshold value sufficient to distinguish the network structure from the cross sections of the pores. The outlines of numerous pores were obtained from this image, and the arithmetic mean value of the widths of the connected pores was calculated. The average film thickness was calculated by obtaining a curve 62 that traces the boundary between the lower layer 131 and the upper layer 132, and a curve 63 that traces the surface of the upper layer 132, as shown in Figure 11. The average film thickness was calculated by calculating the arithmetic mean value of the distance between the curves 62 and 63 on the lines that divide the image into six equal parts horizontally and vertically. Note that the sample does not necessarily need to be embedded in resin for various measurements; observations and measurements can be performed in the same way even without resin embedding.

[0079] The methods for obtaining the above-mentioned measurements for the substrate, lower layer, and upper layer are the same in the following examples and comparative examples.

[0080] The collection efficiency of the porous composite in Example 1-1 was 99.3%, and the rate of increase in initial pressure loss was 15%.

[0081] The filtering efficiency of the porous composite was determined as follows. First, the porous composite was installed as a GPF in the exhaust system of a passenger vehicle equipped with a 2-liter direct-injection gasoline engine, and a vehicle test was conducted using a chassis dynamometer. In this vehicle test, the number of particulate matter particles emitted in the exhaust gas when the vehicle was driven in a European regulation driving mode (RTS95) was measured using a measurement method in accordance with PMP (European regulation particulate measurement protocol). In addition, a similar vehicle test was conducted without a GPF installed in the exhaust system, and the number of particulate matter particles emitted in the exhaust gas was measured using the same measurement method. The number of particulate matter particles emitted without a GPF was defined as the "reference emission number," and the difference between the number of particulate matter particles measured with the porous composite installed and the reference emission number was divided by the reference emission number to obtain the "filtering efficiency (%)."

[0082] To evaluate the initial pressure loss of the porous composite, first, air at room temperature was blown into the porous composite at a pressure of 10 Nm３ The air was supplied to the porous composite at a flow rate of 1 / min, and the pressure difference across the porous composite (i.e., the pressure difference between the air inlet and outlet sides) was measured. The pressure difference in the case of only the substrate (corresponding to Comparative Example 1-3) was used as the reference pressure difference, and the rate of increase in the pressure difference of the porous composite relative to the reference pressure difference was used as the rate of increase in initial pressure loss. The rate of increase in initial pressure loss (%) was calculated as (A-B) / B x 100, where A is the pressure difference of the porous composite and B is the reference pressure difference of the substrate. The methods for calculating the collection efficiency and initial pressure loss were the same in the following Examples 1-2 to 1-6 and Comparative Examples 1-1 to 1-3. The initial pressure loss of Comparative Example 1-4, which uses a different substrate 12, was calculated based on the rate of increase in the pressure difference of Comparative Example 1-3 using only the substrate.

[0083] (Example 1-2) The manufacturing conditions for the porous composite in Example 1-2 were the same as those in Example 1-1. In the produced porous composite, the penetration depth of the silica lower layer into the pores of the substrate in the longitudinal cross section was 0 μm, the porosity of the lower layer in the longitudinal cross section was 69%, the average pore diameter of the lower layer in the longitudinal cross section was 4.7 μm, and the average film thickness of the lower layer was 20 μm. The porosity of the lower layer in the membrane plane was 46%, the average pore diameter of the lower layer in the membrane plane was 3.5 μm, and the average diameter of the granular portions was 3.3 μm. The porosity of the alumina upper layer in the longitudinal cross section was 86%, the average pore diameter of the upper layer in the longitudinal cross section was 1.3 μm, and the average film thickness of the upper layer was 20 μm.

[0084] The collection efficiency of the porous composite in Example 1-2 was 99.5%, and the rate of increase in initial pressure loss was 18%.

[0085] (Example 1-3) The manufacturing conditions for the porous composite in Example 1-3 were the same as those in Example 1-1. In the produced porous composite, the penetration depth of the silica lower layer into the pores of the substrate in the longitudinal cross section was 0 μm, the porosity of the lower layer in the longitudinal cross section was 69%, the average pore diameter of the lower layer in the longitudinal cross section was 4.7 μm, and the average film thickness of the lower layer was 18 μm. The porosity of the lower layer in the membrane plane was 46%, the average pore diameter of the lower layer in the membrane plane was 3.3 μm, and the average diameter of the granular portions was 3.2 μm. The porosity of the alumina upper layer in the longitudinal cross section was 86%, the average pore diameter of the upper layer in the longitudinal cross section was 1.2 μm, and the average film thickness of the upper layer was 25 μm.

[0086] The collection efficiency of the porous composite in Example 1-3 was 99.6%, and the rate of increase in initial pressure loss was 25%.

[0087] (Example 1-4) The conditions for producing the porous composite in Example 1-4 were as follows: when depositing the alumina particles as the upper layer material, 11.0 L / (min cm ２ This is the same as Example 1-1, except that suction was performed in the same manner as in Example 1-1.

[0088] In the prepared porous composite, the penetration depth of the silica lower layer into the pores of the substrate in the longitudinal cross section was 0 μm, the porosity of the lower layer in the longitudinal cross section was 68%, the average pore diameter of the lower layer in the longitudinal cross section was 4.5 μm, and the average film thickness of the lower layer was 25 μm. The porosity of the lower layer in the membrane plane was 45%, the average pore diameter of the lower layer in the membrane plane was 3.0 μm, and the average diameter of the granular portions was 3.0 μm. The porosity of the alumina upper layer in the longitudinal cross section was 88%, the average pore diameter of the upper layer in the longitudinal cross section was 1.2 μm, and the average film thickness of the upper layer was 40 μm.

[0089] The collection efficiency of the porous composite in Example 1-4 was 99.9%, and the rate of increase in initial pressure loss was 39%.

[0090] (Example 1-5) The conditions for producing the porous composite in Example 1-5 were that the average particle size of the silica gel particles, which are the lower layer material, was 0.3 μm, and the pore volume of the silica gel particles was 1 cm ３This is the same as Example 1-1 except that the value is / g.

[0091] In the prepared porous composite, the penetration depth of the silica lower layer into the pores of the substrate in the longitudinal cross section was 0 μm, the porosity of the lower layer in the longitudinal cross section was 67%, the average pore diameter in the longitudinal cross section of the lower layer was 3.8 μm, and the average film thickness of the lower layer was 20 μm. The porosity of the lower layer in the membrane plane was 40%, the average pore diameter in the membrane plane of the lower layer was 2.8 μm, and the average diameter of the granular portions was 1.0 μm. The porosity of the alumina upper layer in the longitudinal cross section was 86%, the average pore diameter in the longitudinal cross section of the upper layer was 1.2 μm, and the average film thickness of the upper layer was 25 μm.

[0092] The collection efficiency of the porous composite in Example 1-5 was 99.6%, and the rate of increase in initial pressure loss was 25%.

[0093] (Example 1-6) The conditions for producing the porous composite in Example 1-6 were that the average particle size of the silica gel particles, which are the lower layer material, was 0.3 μm, and the pore volume of the silica gel particles was 1 cm ３ / g. That is, during deposition of the alumina particles, which are the upper layer material, the flow rate was 11.0 L / (min cm ２ ) and suction was performed.

[0094] In the prepared porous composite, the penetration depth of the silica lower layer into the pores of the substrate in the longitudinal cross section was 0 μm, the porosity of the lower layer in the longitudinal cross section was 68%, the average pore diameter of the lower layer in the longitudinal cross section was 3.8 μm, and the average film thickness of the lower layer was 24 μm. The porosity of the lower layer in the membrane plane was 40%, the average pore diameter of the lower layer in the membrane plane was 2.8 μm, and the average diameter of the granular portions was 1.2 μm. The porosity of the alumina upper layer in the longitudinal cross section was 88%, the average pore diameter of the upper layer in the longitudinal cross section was 1.2 μm, and the average film thickness of the upper layer was 40 μm.

[0095] The collection efficiency of the porous composite in Example 1-6 was 99.9%, and the rate of increase in initial pressure loss was 39%.

[0096] Comparative Example 1-1 The porous composite according to Comparative Example 1-1 was prepared under the same conditions as in Example 1-1, except that a lower layer was formed on the substrate but no upper layer was formed. In other words, the trapping layer consisted of only the lower layer.

[0097] In the porous composite thus prepared, the penetration depth of the silica lower layer into the pores of the substrate in the longitudinal cross section was 0 μm, the porosity of the lower layer in the longitudinal cross section was 69%, the average pore size of the lower layer in the longitudinal cross section was 4.7 μm, and the average film thickness of the lower layer was 20 μm. The porosity of the lower layer in the membrane plane was 46%, the average pore size of the lower layer in the membrane plane was 3.3 μm, and the average diameter of the granular portions was 0.9 μm.

[0098] The collection efficiency of the porous composite in Comparative Example 1-1 was 44.0%, and the rate of increase in initial pressure loss was 8%.

[0099] (Comparative Example 1-2) The porous composite according to Comparative Example 1-2 was prepared using alumina particles as the lower layer material, with no upper layer formed. In other words, the trapping layer was the lower layer only. Alumina particles with an average particle size of 0.1 μm were deposited on the same substrate as in Example 1-1 by a dry film-forming method. During deposition, a flow rate of 11.0 L / (min cm ２ Then, the mixture was baked at a temperature of 1100° C. for 2 hours to form a collection layer (a lower layer without an upper layer).

[0100] In the produced porous composite, the penetration depth into the pores of the lower layer substrate in the longitudinal cross section was 20 μm, the porosity of the lower layer in the longitudinal cross section was 88%, the average pore diameter of the lower layer in the longitudinal cross section was 1.2 μm, and the average film thickness of the lower layer was 40 μm.

[0101] The collection efficiency of the porous composite in Comparative Example 1-2 was 99.8%, and the rate of increase in initial pressure loss was 80%.

[0102] Comparative Example 1-3 In Comparative Example 1-3, the substrate itself of Example 1-1 was used as the measurement object. That is, the measurement object of Comparative Example 1-3 was not the porous composite, but a porous sintered body having no collection layer.

[0103] The collection efficiency of the porous body in Comparative Example 1-3 was 45.0%, and the initial pressure loss was compared with Comparative Example 1-3 itself, so the rate of increase was 0%.

[0104] Comparative Example 1-4 In Comparative Example 1-4, the substrate itself was used as the measurement object, which was different from that in Example 1-1. That is, the measurement object in Comparative Example 1-4 was not a porous composite, but a porous sintered body having no collection layer.

[0105] The porous substrate of Comparative Example 1-4 was made of cordierite and had a honeycomb filter shape (honeycomb structure). The porosity of the substrate was 55% and the average pore diameter was 9 μm. The porosity and average pore diameter were measured in the same manner as in Example 1-1.

[0106] The collection efficiency of the porous body in Comparative Example 1-4 was 75.0%, and the rate of increase in initial pressure loss was 10%.

[0107] As is clear from the above examples and comparative examples, porous composite 1 is characterized in that trapping layer 13 has a lower layer 131 made of fired silica gel particles and an upper layer 132 that has the function of trapping particulate matter. When upper layer 132 is not present, as in comparative example 1-1, trapping efficiency decreases, and when mesh-like silica lower layer 131 is not present, as in comparative example 1-2, initial pressure loss increases. Conventionally, it has been thought that a trapping layer with a two-layer structure increases pressure loss. However, porous composite 1 breaks away from conventional thinking and adopts a two-layer structure, thereby maintaining trapping efficiency and reducing pressure loss. The reduction in initial pressure loss shown in the examples also reduces pressure loss when particulate matter is trapped in trapping layer 13.

[0108] The "air permeability" of the porous composite 1 refers to the property of gas flowing from one surface of the porous composite 1 to the other surface via the internal pores when a pressure difference is applied between the other surface and the other surface of the porous composite 1. Naturally, therefore, the substrate 12, the lower layer 131, and the upper layer 132 also have air permeability. The substrate 12, the lower layer 131, and the upper layer 132 are all porous sintered bodies. The substrate 12 is not limited to cordierite, and may be, for example, Si-bonded SiC, Cd-bonded SiC, Si３ N ４ Bonded SiC, silicon carbide, silicon nitride (Si ３ N ４ ), alumina, mullite, etc. The upper layer 132 is preferably made of alumina, but is not limited to alumina and may be made of, for example, silicon carbide, cordierite, mullite, etc. However, in order for the trapping layer 13 to perform its function of trapping particulate matter, the average pore diameter of the upper layer 132 is smaller than the average pore diameter of the substrate 12. The average pore diameter of the substrate 12 is preferably 10 μm or more and 30 μm or less. This allows for sufficient breathability while suppressing penetration into the pores of the lower layer 131. On the other hand, in order to trap particulate matter while maintaining breathability, the average pore diameter of the upper layer 132 is preferably 1.0 μm or more and 1.5 μm or less. Note that the "average pore diameter of the upper layer 132" refers to the arithmetic mean value of the pore diameters of the upper layer 132 or a value equivalent thereto. The same applies to the substrate 12 and the lower layer 131.

[0109] In order to provide upper layer 132 having an average pore size smaller than that of substrate 12, the average particle size of the upper layer material particles deposited on lower layer 131 when forming upper layer 132 is preferably 0.05 μm or more and 1.0 μm or less.

[0110] In order to suppress a decrease in collection efficiency while suppressing an increase in pressure loss, the average film thickness of the upper layer 132 is preferably 15 μm or more and 40 μm or less. From the above Examples 1-3 to 1-6, in order to achieve a collection efficiency of 99.6% or more, the film thickness of the upper layer is more preferably 25 μm or more and 40 μm or less.

[0111] The lower layer 131 provided on the substrate 12 is made of silica (SiO ２ ) is connected in a three-dimensional mesh-like structure. "Continuum having granular portions" means that the granular portions are connected to other granular portions like threads. Preferably, the granular portions are not densely packed, and the spaces between the granular portions are thread-like or constricted. Each granular portion is irregularly connected to at least one other granular portion, thereby forming a three-dimensional mesh-like structure.

[0112] It is believed that the structure of the lower layer 131 is realized by depositing silica gel particles on the substrate 12, and then baking the silica gel particles, which causes the surfaces of the silica gel particles to connect with other silica gel particles and reduces the pores of the silica gel particles, thereby densifying the silica gel particles. As a result, a mesh is stretched over the substrate 12, and the upper layer 132 is formed on the mesh without contacting the substrate 12. It is believed that silica gel particles with larger particle sizes form the granular portion.

[0113] To achieve the above phenomenon, the average particle size of the silica gel particles is preferably 0.1 μm to 5.0 μm. The average pore volume of the silica gel particles is preferably 0.5 ml / g to 2.0 ml / g ("ml" means milliliters). The heating temperature and heating time are preferably 1200°C to 1400°C for 0.5 hours to 2 hours. The average particle size of the silica granular portion after firing is preferably 0.8 μm to 5 μm. The average film thickness of the lower layer 131 is preferably 15 μm to 30 μm. This allows the upper layer 132 to be formed at a distance from the substrate 12 and suppresses an increase in pressure loss. To achieve such an average film thickness of the lower layer 131, the thickness of the deposited layer of silica gel particles deposited on the substrate 12 by a dry film formation method during the formation of the lower layer 131 is preferably 20 μm to 50 μm. The thickness of the deposited layer refers to the average thickness of the deposited layer in the region to be deposited.

[0114] The "deposition" of silica gel particles and upper layer material particles during the formation of the lower layer 131 and the upper layer 132 means that the particles are simply piled up without the use of a binder or the like (however, other particles may be mixed in), and methods other than the method using the dry film-forming apparatus 8 may be employed to deposit the particles. For example, the particles may be deposited on the substrate 12 simply by utilizing gravity or centrifugal force, or deposition may be performed by other physical forces.

[0115] It should be noted that the various "preferred" numerical ranges in the above description do not limit the present invention.

[0116] The use of the porous composite 1 is not limited to gasoline particulate filters that capture particulate matter in exhaust gases emitted from gasoline engines. For example, the porous composite 1 may be used in diesel particulate filters (DPFs) that capture particulate matter in exhaust gases emitted from diesel engines. The porous composite 1 can also be used in other applications for capturing particulate matter in gases. Note that, since capturing particulate matter involves separating gases from particulate matter, the porous composite 1 can also be used in various applications for separating gases from particulate matter. Furthermore, the characteristic structure of the trapping layer has the potential for use in various applications other than capturing and separating particulate matter.

[0117] The structure of the porous composite 1 may be modified in various ways. For example, the plugging portions 124 may be omitted from the substrate 12. Alternatively, the inner surfaces of all the cells 123 may be used as collection surfaces, and a collection layer 13 may be provided. Furthermore, the substrate 12 does not necessarily have a honeycomb structure, and may have other shapes, such as a simple cylindrical or flat shape whose interior is not divided by partition walls. The porous composite 1 does not necessarily have to be a single independent component, but may be part of a single component.

[0118] 12 is a simplified diagram showing an algae collection device 20 having a porous composite 2 according to another embodiment of the present invention. The collection of microalgae (hereinafter simply referred to as "algae") has attracted attention in the field of so-called bioeconomy, and microalgae are used to produce food, fuel, CO2, and other products. ２ Applications for algae harvesting, sustainable materials, etc. are expected. The algae harvesting device 20 comprises a storage tank 21 and a porous composite 2. A culture solution 9 in which microalgae have been cultivated is stored in the storage tank 21. The culture solution 9 is guided by a pump to the porous composite 2 as shown by arrow 91, and the porous composite 2 extracts a portion of the water in the culture solution 9 as shown by arrow 92, and obtains a concentrated solution of the remaining microalgae as shown by arrow 93.

[0119] FIG. 13 is a diagram showing a cross section of the porous composite 2 cut along a plane parallel to the longitudinal direction. The porous composite 2 is a tubular member elongated in one direction and has a plurality of through-holes 221 parallel to the longitudinal direction. The porous composite 2 includes a porous substrate 22 and a porous surface layer 23. The surface layer 23 forms the inner circumferential surface of each through-hole 221. The cross-sectional shape of the substrate 22 perpendicular to the longitudinal direction is, for example, substantially circular. The cross-sectional shape may be other shapes, such as polygonal. The culture medium 9 in FIG. 12 is introduced from one longitudinal end of the porous composite 2 as indicated by arrow 91, and concentrated culture medium is discharged from the other end as indicated by arrow 93. Water is discharged from the outer circumferential surface of the porous composite 2 as indicated by arrow 92.

[0120] The substrate 22 is porous. The substrate 22 is made of, for example, cordierite, aluminum oxide (Al ２ O ３ The substrate 22 may be made of other ceramics or a material other than ceramics.

[0121] The length of the substrate 22 in the longitudinal direction is, for example, 160 mm or more and 1500 mm or less. The outer diameter of the substrate 22 is, for example, 20 mm or more and 180 mm or less. The inner diameter of the through hole 221 is, for example, 1.6 mm or more and 3.0 mm or less. The porosity of the substrate 22 is, for example, 30% or more and 60% or less, and preferably 35% or more and 50% or less. The open porosity of the substrate 22 is, for example, 30% or more and 60% or less, and preferably 35% or more and 50% or less. The porosity and open porosity of the substrate 22 can be measured by the Archimedes method.

[0122] The average pore diameter of the substrate 22 is, for example, 3.0 μm or more and 30.0 μm or less, and preferably 5.0 μm or more and 15.0 μm or less. The average pore diameter can be measured using a mercury porosimeter. The surface opening ratio of the substrate 22 is, for example, 20% or more and 60% or less, and preferably 25% or more and 50% or less. The surface opening ratio is the ratio of the area of ​​the surface of the substrate 22 where the pores are open, and can be determined by image analysis of an SEM (scanning electron microscope) image of the surface.

[0123] The surface layer 23 is formed on the through-holes of the substrate 22 and covers the inner circumferential surfaces of the through-holes. That is, the inner circumferential surfaces of the through-holes 221 of the porous composite 2 are the surfaces of the surface layer 23. In FIG. 13 , the surface layer 23 is indicated by a thick solid line. A portion of the water in the culture solution 9 introduced into the through-holes 221 passes through the surface layer 23 and the substrate 22 and is guided from the outer circumferential surface of the porous composite 2 to the outside of the porous composite 2. At this time, algae accumulate on the surface layer 23, and the remainder of the culture solution 9 is guided to the outside from the through-holes 221 as a culture solution with concentrated algae. That is, the culture solution 9 is concentrated as it passes through the through-holes 221.

[0124] FIG. 14 is a simplified diagram showing enlarged longitudinal cross sections of the substrate 22 and the surface layer 23. A "longitudinal cross section" refers to a plane perpendicular to the surface of the substrate 22, and FIG. 14 shows a longitudinal cross section parallel to the longitudinal direction of the through-hole 221. The basic structure shown in FIG. 14 is the same as the structure in FIG. 4 , omitting the upper layer 132. That is, the structure in FIG. 14 is the structure before the upper layer 132 in FIG. 4 is formed, and FIG. 14 corresponds to the structures in FIGS. 5A and 6 . However, the porosity, average pore size, surface opening ratio, and the like that characterize the materials and structures of the substrate 22 and the surface layer 23 are appropriately different from those of the substrate 12 and the lower layer 131 in FIG. 4 .

[0125] The substrate 22 has large pores, and the interconnected pores provide breathability. A surface layer 23 is formed on the substrate 22. The surface layer 23 is similar to the lower layer 131 in FIGS. 5A, 5B, and 6, and is a three-dimensional network structure having a novel breathable structure. That is, the surface layer 23 is made of silica (SiO ２ ) are connected in a three-dimensional network structure. This structure is formed by firing (a so-called baking process) to form silica gel (SiO ２ ・nH ２ O) particles are densified and bonded together. In Figure 14, the cross section of the large pores in the substrate 22 is shown as large cavities, and the cross section of the mesh-like structure of the surface layer 23 is shown as many circles. The surface of the surface layer 23 is the surface of the porous composite 2. Since the substrate 22 and the surface layer 23 are breathable, the porous composite 2 is naturally breathable as well. The definition of breathability is as already explained for the porous composite 1.

[0126] FIG. 15 is a diagram showing the state in which algae particles (hereinafter simply referred to as "particles") 95 have accumulated on the surface layer 23. When concentration of the culture solution 9 is started from the state shown in FIG. 14, the particles 95 begin to accumulate on the surface of the surface layer 23. After that, an algae cake layer is formed on the surface layer 23, and the state in which several cake layers are stacked is stabilized as shown in FIG. 15. During this time, the amount of water passing through the porous composite 2 per unit area per unit time (i.e., the water permeation rate) gradually decreases, but a certain level of water permeation rate is eventually maintained. Ideally, the porous composite 2 has a high water permeation rate immediately after concentration begins, and maintains a certain level of water permeation rate even as cake layers accumulate.

[0127] Next, an example of manufacturing the porous composite 2 will be described. FIG. 16 shows the manufacturing flow of the porous composite 2. First, a porous sintered body with air permeability is prepared as the substrate 22 (step S21). Various known methods may be used to manufacture the substrate 22. For example, raw materials such as alumina, glass containing alkali / alkaline earth elements, and silicon are mixed with a pore-forming agent such as starch or acrylic resin, a binder such as methyl cellulose, and water, and kneaded to form a kneaded clay. Sintering aids such as transition metal oxides or rare earth oxides may be used, and dispersants or surfactants may be added as molding aids. The pore-forming agent and binder may also be other organic materials. The kneaded clay is extruded using a plunger equipped with a nozzle to obtain a molded product with numerous through-holes. The moisture in the molded product is removed by hot air drying, and organic matter is removed by heating and degreasing, and the substrate 22 is obtained by firing.

[0128] Meanwhile, separately from step S21, i.e., before, after, or in parallel with step S21, a slurry containing silica gel particles is prepared (step S22). The slurry contains at least silica gel particles, a dispersant, and a solvent. Specifically, the silica gel particles, the dispersant, and the thickener are added to water, and the mixture is stirred to prepare a slurry. A binder may be added to the slurry.

[0129] Next, slurry is poured into the through holes of the substrate 22, and the pressure in the space on the outer peripheral surface of the substrate 22 is reduced, thereby removing the water contained in the slurry from the outer peripheral surface. As a result, a layer of slurry (more precisely, the solid content of the slurry) is formed on the inner peripheral surface (step S23). That is, silica gel particles are deposited on the inner peripheral surface of the through holes, and aggregates of silica gel particles are formed on the inner peripheral surface of the through holes. In the wet silica gel particle film formation described above, the "aggregates of silica gel particles" refer to aggregates of a material containing silica gel particles, and the silica gel particles in the aggregate do not necessarily need to be in direct contact with each other.

[0130] Thereafter, for example, the layer on the inner circumferential surface of the through hole is dried by hot air drying at 80°C for 12 hours in an air atmosphere, degreasing to remove organic matter by heating at 450°C for 6 hours in an air atmosphere, and further baking to bond the silica gel particles by heating at 1250°C for 10 hours in an air atmosphere, thereby forming a three-dimensional network structure as the surface layer 23 on the substrate 22 (step S24).

[0131] The hot air drying is preferably carried out at a temperature of from 50° C. to 100° C. for from 10 to 24 hours. The degreasing is preferably carried out at a temperature of from 400° C. to 500° C. for from 5 to 7 hours. The firing is preferably carried out at a temperature of from 1000° C. to 1350° C. for from 5 to 15 hours, with the temperature rising rate during firing being from 50° C. / hour to 100° C. / hour.

[0132] 9 may be used instead of the wet filtration membrane-forming method described above as a method for depositing silica gel particles on the inner circumferential surface of the through-holes of the substrate 22. Of course, the filtration membrane-forming method described above may also be used when forming the lower layer 131 shown in FIG.

[0133] Next, Examples 2-1 to 2-3 of the porous composite 2 and Comparative Example 2-1 for comparison with the porous composite 2 will be described with reference to Tables 3 and 4.

[0134]

[0135]

[0136] (Example 2-1) In Example 2-1, first, a substrate made of cordierite was prepared. The substrate had a length of 250 mm, an outer diameter of 30 mm, and 55 through-holes with an inner diameter of 2.4 mm. The distance between the central axes of adjacent through-holes was approximately 3.0 mm. The porosity of the substrate was 48%, and the average pore diameter was 12 μm.

[0137] By the filtration membrane formation method, a membrane with an average particle size of 4 μm and a pore volume of 1.5 cm was formed on a cordierite substrate. ３ / g of silica gel particles were deposited. The chlorine (Cl) impurity in the silica gel particles used was 37 ppm (by weight, the same applies below), and the sulfur (S) impurity was 0.02 wt%. The amount of Cl impurity was measured by dissolving a powdered measurement sample in acid and introducing the solution into an ICP optical emission spectrometer. The amount of S impurity was obtained by gas component analysis. The same applies to the following examples and comparative examples.

[0138] After hot air drying and degreasing, the porous composite was fired at 1240°C for 10 hours to form a surface layer. In the prepared porous composite, the penetration depth of the silica surface layer into the pores of the substrate in the longitudinal section, i.e., the cross section of the porous composite perpendicular to the surface of the substrate, was 0 μm, the porosity of the surface layer in the longitudinal section was 69%, the average pore diameter in the longitudinal section was 4.7 μm, and the average film thickness (i.e., the average layer thickness) was 20 μm. The porosity of the surface layer within the film plane of the surface layer was 46%, the average pore diameter of the surface layer within the film plane was 3.3 μm, and the average diameter of the granular portions was 6.0 μm. The Cl impurity in the surface layer was below the measurement limit (less than 10 ppm), and the S impurity was also below the measurement limit (less than 0.01 wt%).

[0139] The reason why the surface layer does not penetrate into the pores of the substrate is thought to be that the silica gel particles in the slurry aggregate and exist as clumps larger than the pores.

[0140] The various measurement values ​​for the substrate and surface layer were obtained in the same manner as described above with reference to Tables 1 and 2 (however, the surface layer corresponds to the lower layer in Table 2). The method for obtaining the measurement values ​​for the substrate and surface layer is the same in the following examples and comparative examples.

[0141] The algae permeation rate of the porous composite in Example 2-1 was 80 L / m ２ The algae permeation rate refers to the rate at which only water permeates from a solution containing microalgae, and is the water permeation rate after the pressure difference between the through-holes and the outer surface of the porous composite was set to 50 kPa and the culture solution was stably concentrated (the same applies hereinafter).

[0142] (Example 2-2) In Example 2-2, first, aluminum oxide (Al ２ O ３ A substrate was prepared in which aluminum oxide was the main constituent phase (i.e., the qualitative component identified by XRD was aluminum oxide). The substrate may also contain a crystalline phase other than aluminum oxide. The substrate had a length of 250 mm, an outer diameter of 30 mm, and 55 through-holes with an inner diameter of 2.4 mm. The distance between the central axes of adjacent through-holes was approximately 3.0 mm. The porosity of the substrate was 40%, and the average pore diameter was 12 μm.

[0143] By the filtration membrane formation method, an average particle size of 4 μm and a pore volume of 1.5 cm are formed on the substrate. ３ / g of silica gel particles were deposited. The silica gel particles used had a Cl impurity of 27 ppm and a S impurity of 0.02 wt %.

[0144] After hot air drying and degreasing, the surface layer was fired at 1240°C for 10 hours to form a surface layer. In the produced porous composite, the penetration depth of the silica surface layer into the pores of the substrate in the longitudinal section was 0 μm, the porosity of the surface layer in the longitudinal section was 68%, the average pore diameter in the longitudinal section was 4.5 μm, and the average film thickness was 20 μm. The porosity of the surface layer in the film plane was 46%, the average pore diameter of the surface layer in the film plane was 3.3 μm, and the average diameter of the granular portions was 6.0 μm. The Cl impurity in the surface layer was below the measurement limit (less than 10 ppm), and the S impurity was also below the measurement limit (less than 0.01 wt%).

[0145] The algae permeation rate of the porous composite in Example 2-2 was 80 L / m ２ ・It was h.

[0146] (Example 2-3) The substrate of Example 2-3 is the same as that of Example 2-2. A sieve having an average particle size of 10 μm and a pore volume of 1.5 cm was formed on the substrate by a filtration membrane formation method. ３ The silica gel particles used had a Cl impurity of 20 ppm and a S impurity below the detection limit (less than 0.01 wt%).

[0147] After hot air drying and degreasing, the surface layer was fired at 1240°C for 10 hours to form a surface layer. In the produced porous composite, the penetration depth of the silica surface layer into the pores of the substrate in the longitudinal section was 0 μm, the porosity of the surface layer in the longitudinal section was 68%, the average pore diameter in the longitudinal section was 5.0 μm, and the average film thickness was 20 μm. The porosity of the surface layer in the film plane was 40%, the average pore diameter of the surface layer in the film plane was 5.0 μm, and the average diameter of the granular portions was 8.5 μm. The Cl impurity in the surface layer was below the measurement limit (less than 10 ppm), and the S impurity was also below the measurement limit (less than 0.01 wt%).

[0148] The algae permeation rate of the porous composite in Example 2-3 was 50 L / m ２ ・It was h.

[0149] (Comparative Example 2-1) The substrate of Comparative Example 2-1 is the same as that of Example 2-2. In Comparative Example 2-1, no surface layer was formed. The algae permeation rate in Comparative Example 2-1 was 35 L / m ２ ・It was h.

[0150] As is clear from the above examples and comparative examples, the provision of a surface layer on a substrate improves the algae permeation rate. This is thought to be because the surface layer has a mesh structure, which prevents algae from adhering at a high density even when they accumulate, and the algae are easily peeled off from the accumulation layer and the surface layer.

[0151] The surface layer 23 provided on the substrate 22 is similar to the lower layer 131 in FIG. 4 and is made of silica (SiO ２) are connected in a three-dimensional network. Furthermore, since the diameter (minor axis in the case of long and thin algae particles) of algae particles is approximately 5 to 10 μm, from the viewpoint of allowing water to pass through without passing through the algae, the network structure is preferably a structure that does not allow particles with an average particle size of 6.0 μm or more to pass through, and more preferably a structure that does not allow particles with an average particle size of 4.0 μm or more to pass through. To achieve the above characteristics, the average particle size of the raw silica gel particles is preferably 3.0 μm or more and 12.0 μm or less, and more preferably 4.0 μm or more and 6.0 μm or less. The average pore volume of the silica gel particles is preferably 0.5 ml / g or more and 2.0 ml / g or less.

[0152] The silica gel particles are preferably heated at a temperature of 900°C to 1350°C for 5 to 15 hours, more preferably at a temperature of 1100°C to 1250°C for 8 to 10 hours. The average particle size of the silica granular portion after firing is preferably 5.0 μm to 10.0 μm, more preferably 5.5 μm to 6.5 μm. The average film thickness of the surface layer 23 is preferably 5 μm to 200 μm, more preferably 20 μm to 150 μm. This allows for appropriate separation of algae and water and suppresses a decrease in permeation rate. To achieve this average film thickness for the surface layer 23, the thickness of the silica gel particle deposition layer deposited on the substrate 22 after drying the slurry is preferably 5 μm to 200 μm, more preferably 20 μm to 150 μm. The thickness of the deposition layer refers to the average thickness of the deposition layer in the desired deposition area. The "accumulation" of silica gel particles during the formation of the surface layer 23 means that the particles are simply piled up by weak forces.

[0153] It should be noted that the various "preferred" numerical ranges in the above description do not limit the present invention.

[0154] The use of the porous composite 2 is not limited to a filter for increasing the concentration of algae in a culture solution. Microorganisms other than algae may also be used. One preferred use of the porous composite 2 is as a filter for separating microorganisms contained in a liquid from the liquid. Instead of microorganisms, the porous composite 2 may separate non-microbial organic or inorganic substances from a liquid or gaseous fluid. The porous composite 2 can be used as a filter for increasing the concentration of various particles in a liquid or gaseous fluid. In a broad sense, it can be used as a filter for separating a fluid containing particles into a fluid and particles. "Separation of a fluid and particles" is not limited to complete separation, but includes partial separation to increase the concentration of particles in a fluid or recovering some of the particles from a fluid. It also includes obtaining only the fluid from a fluid containing particles. Furthermore, the porous composite 2 has the potential to be used for various applications other than separation of a fluid and particles.

[0155] The structure of the porous composite 2 may be modified in various ways. For example, it is not necessary to provide a large number of through holes 221, and the porous composite 2 may have other shapes, such as a simple cylindrical shape or a flat plate shape. When the substrate 22 is plate-shaped, one main surface of the substrate 22 is brought into contact with a slurry, and the pressure is reduced from the other main surface, thereby forming a layer of aggregates of silica gel particles on the one main surface. In other words, aggregates of silica gel particles can be easily formed on the substrate 22 by bringing a slurry containing silica gel particles into contact with the breathable substrate 22 while reducing the pressure inside the substrate 22.

[0156] The porous composite 2 does not have to be a single independent member, but may be part of a single member.

[0157] Examples 2-1 to 2-3 reveal that the surface layer 23 contains less than 10 ppm of Cl and less than 0.01 wt% of S. On the other hand, the raw silica gel particles contain 20 to 37 ppm of Cl and less than the lower limit of the measurement limit (less than 0.01 wt%) to 0.02 wt% of S. Therefore, Cl and S are removed from the surface layer 23 by firing. The same can be said for the lower layer 131 of the porous composite 1 in FIG. 4 and the network structure 3 in FIG. 17 described below. Examples 2-1 to 2-3 reveal that a good network structure can be obtained by firing when the Cl content of the raw silica gel particles is at least 20 ppm to 37 ppm and the S content is 0.02 wt% or less. Furthermore, since the presence of at least 37 ppm of Cl and the presence of at least 0.02 wt % of S are acceptable, it is believed that a good network structure can also be obtained when the Cl content in the raw silica gel particles is 20 ppm or more and 0.01 wt % or less, and the S content is 0.1 wt % or less.

[0158] FIG. 17 is a vertical cross-sectional view showing a mesh structure 3 according to still another embodiment of the present invention.

[0159] The network structure 3 corresponds to the lower layer 131 of the porous composite 1 in Fig. 4 and to the surface layer 23 of the porous composite 2 in Fig. 14. That is, the network structure 3 fired on a porous support body is the porous composite 2 in Fig. 14, and the porous composite 1 in Fig. 4 is the network structure 3 fired on a porous support body with a porous layer further fired thereon. Although the network structure 3 in Fig. 17 is assumed to be not provided on a support body, the network structure 3 may be fired on a porous or non-porous support body, or may be bonded to a porous or non-porous support body with an adhesive.

[0160] When the network structure 3 is not provided on a support, the network structure 3 may be in the form of a plate or a block. A relatively fine network structure 3 may exist as a powder aggregate. The manner in which the network structure 3 is provided can be changed in various ways depending on the application. As already explained, the network structure 3 is formed by depositing silica (SiO ２ It has a characteristic structure in which a continuum of these molecules is connected in a three-dimensional mesh.

[0161] Considering various applications, the average particle size of the silica gel particles used as the raw material for forming the network structure is preferably 0.1 μm or more and 15 μm or less. The average pore volume of the silica gel particles is preferably 0.2 ml / g or more and 3.0 ml / g or less. The heating temperature and heating time are preferably 800°C or more and 1450°C or less for 3 hours or more and 20 hours or less. The average particle size of the silica granular portion after firing is preferably 0.8 μm or more and 10 μm or less.

[0162] It should be noted that the various "preferred" numerical ranges in the above description do not limit the present invention.

[0163] Figure 18 is a diagram showing the flow of manufacturing a network structure 3 that is not supported by a support. First, a temporary support that can be removed by burning is prepared (step S31). The temporary support may be in the form of a sheet, plate, or block, and may be made of, for example, a synthetic material such as polyurethane, or a natural material such as seaweed. Separately from step S31, a slurry of silica gel particles is prepared (step S32). The slurry is prepared by the same method as step S22 in Figure 16.

[0164] Then, a layer of the slurry is formed on the temporary support by a doctor blade method or the like (Step S33). This results in an aggregate of silica gel particles. The silica gel particles are sintered by hot air drying, degreasing, and calcination to form a network structure 3, and the temporary support is removed by incineration (Step S34). Through these steps, a network structure 3 having a novel structure is obtained. The hot air drying is preferably carried out at a temperature of 50°C to 90°C for 10 hours to 24 hours. The degreasing is preferably carried out at a temperature of 300°C to 600°C for 5 hours to 24 hours. The calcination is preferably carried out at a temperature of 1000°C to 1250°C for 5 hours to 24 hours, with a temperature increase rate during calcination of 10°C / hour to 300°C / hour.

[0165] The mesh structure 3 can be used as a filter that separates a fluid containing particulates into the fluid and the particulates. "Separation of the fluid and the particulates" is not limited to complete separation, but also includes partial separation to increase the concentration of the particulates in the fluid or to recover some of the particulates in the fluid. It also includes obtaining only the fluid from a fluid containing particulates. Furthermore, the mesh structure 3 has the potential to be used for various applications other than separation of the fluid and the particulates.

[0166] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0167] While the invention has been particularly illustrated and described, it should be understood that the foregoing description is illustrative and not restrictive, and that numerous modifications and variations are possible without departing from the scope of the invention.

[0168] 1, 2 Porous composite 3 Network structure 9 Culture solution 12, 22 Substrate 23 Surface layer 51 Granular portion 52 Connection portion 95 (Algae) fine particles 131 Lower layer 132 Upper layer 1311 Silica gel particles S11 to S15, S21 to S24, S31 to S34 Steps

Claims

1. A mesh-like structure, a plurality of granular portions formed of silica; a plurality of connecting portions formed of silica and connecting the plurality of granular portions to form a continuous body connected together with the plurality of granular portions in a three-dimensional mesh-like pattern; Equipped with The porosity in the longitudinal section is 67% or more and 69% or less, The average pore diameter in the longitudinal cross section is 3.8 μm or more and 5.0 μm or less, A network structure having an average pore diameter within the membrane surface of 2.8 μm or more and 5.0 μm or less.

2. The mesh structure according to claim 1, The mesh-like structure has an average particle size of the plurality of granular portions of 0.8 μm or more and 10 μm or less.

3. The mesh structure according to claim 1, A network structure containing less than 10 ppm (by weight) of chlorine and less than 0.01 wt % of sulfur.

4. 1. A porous composite comprising: a base material that is a porous sintered body having air permeability; a mesh structure provided on the substrate; Equipped with The network structure is a plurality of granular portions formed of silica; a plurality of connecting portions formed of silica and connecting the plurality of granular portions to form a continuous body connected together with the plurality of granular portions in a three-dimensional mesh-like pattern; Equipped with A porous composite in which the network structure does not penetrate into the pores of the substrate.

5. 5. The porous composite of claim 4, A porous composite in which the network structure has an average film thickness on the substrate of 5 μm or more and 200 μm or less.

6. 5. The porous composite of claim 4, A porous composite, wherein the substrate has an average pore size of 10 μm or more and 30 μm or less.

7. The porous composite of claim 4, The porosity in the longitudinal cross section of the network structure is 67% or more and 69% or less, The average pore diameter in the longitudinal cross section of the network structure is 3.8 μm or more and 5.0 μm or less, A porous composite in which the network structure has an average pore size within the membrane surface of 2.8 μm or more and 5.0 μm or less.

8. The porous composite of claim 4, A porous composite body, wherein the average particle size of the plurality of granular portions is 0.8 μm or more and 10 μm or less.

9. The porous composite of claim 4, A porous composite containing less than 10 ppm (by weight) chlorine and less than 0.01 wt % sulfur.

10. 5. The porous composite of claim 4, an upper layer provided on the mesh structure, the upper layer being a porous sintered body having air permeability and an average pore size smaller than that of the substrate; The porous composite further comprises:

11. 11. The porous composite of claim 10, The upper layer is a porous composite formed of alumina.

12. 11. The porous composite of claim 10, A porous composite, wherein the upper layer has an average pore size of 1.0 μm or more and 1.5 μm or less.

13. 11. The porous composite of claim 10, A porous composite, wherein the upper layer has an average thickness of 15 μm or more and 40 μm or less.

14. 10. The porous composite of claim 4, A porous composite that is a filter for separating microorganisms contained in a liquid from said liquid.

15. 14. The porous composite of any one of claims 10 to 13, A porous composite particulate filter that captures particulate matter in the exhaust gas emitted by gasoline or diesel engines.

16. A method for producing a network structure, comprising: a) forming an aggregate of silica gel particles having an average particle size of 0.1 μm or more and 5.0 μm or less; b) heating the aggregate at 1200°C or higher and 1400°C or lower for 0.5 hours or longer and 2 hours or shorter to obtain a network structure formed of silica; A method for manufacturing a mesh structure comprising:

17. A method for producing the mesh structure according to claim 16, comprising the steps of: The method for producing a network structure, wherein the silica gel particles have an average pore volume of 0.2 ml / g or more and 3.0 ml / g or less.

18. A method for producing the mesh structure according to claim 16, comprising the steps of: The method for producing a network structure, wherein the chlorine content in the silica gel particles is 20 ppm (by weight) or more and 0.01 wt % or less, and the sulfur content is 0.1 wt % or less.

19. A method for producing the mesh structure according to claim 16, comprising the steps of: In the step a), a slurry containing the silica gel particles is shaped to form the aggregates.

20. A method for producing a porous composite, comprising: c) preparing a base material that is a porous sintered body having air permeability; d) forming the mesh structure on the substrate by the method for manufacturing a mesh structure according to any one of claims 16 to 19; A method for producing a porous composite comprising:

21. 21. A method for producing a porous composite according to claim 20, comprising: In the step a), the silica gel particles are deposited on the substrate, thereby forming the aggregate on the substrate.

22. 22. A method for producing the porous composite of claim 21, comprising: In the step a), the silica gel particles are deposited on the substrate to a thickness of 20 μm or more and 50 μm or less.

23. 22. A method for producing the porous composite of claim 21, comprising: In the step a), a slurry containing the silica gel particles is brought into contact with the substrate while reducing the pressure inside the substrate, thereby forming the aggregate of the silica gel particles on the substrate.

24. 21. A method for producing a porous composite according to claim 20, comprising: e) depositing upper layer material particles having an average particle size of 0.05 μm or more and 1.0 μm or less on the network structure; f) heating the upper layer material particles to form an upper layer that is a porous sintered body having air permeability and an average pore size smaller than that of the base material; A method for producing a porous composite comprising:

25. 25. A method for producing the porous composite of claim 24, comprising: The method for producing a porous composite body, wherein the upper layer material particles are alumina particles.