CN118807354A

CN118807354A - Honeycomb filter

Info

Publication number: CN118807354A
Application number: CN202310433184.XA
Authority: CN
Inventors: 高室佑基
Original assignee: NGK Insulators Ltd
Current assignee: NGK Insulators Ltd
Priority date: 2023-04-21
Filing date: 2023-04-21
Publication date: 2024-10-22
Also published as: JP2024155787A; DE102024203663A1

Abstract

The invention provides a honeycomb filter which can inhibit the increase of pressure loss and improve the purification performance. The honeycomb filter includes: a columnar honeycomb structure (4) having porous partition walls (1) arranged so as to surround a plurality of cells (2), wherein the plurality of cells (2) form fluid channels extending from an inflow end surface (11) to an outflow end surface (12); and a porous hole sealing part (5) which is arranged at either one of the end part on the inflow end surface (11) side and the end part on the outflow end surface (12) side of the cell (2), wherein the thickness of the cell wall (1) is 152-254 [ mu ] m, the cell density of the honeycomb structure (4) is 38.8-62.0/cm ², the pore diameter distribution of the cell wall (1) obtained by measuring by mercury intrusion method is such that the pore diameter D50 with the cumulative pore volume reaching 50% of the total pore volume is 11-15 [ mu ] m, the porosity of the cell wall (1) obtained by measuring by mercury intrusion method is 60-75%, and the value obtained by dividing the wetted area A of the pores formed in the porous cell wall (1) by the sectional area S of the pores, namely the cell wall wetted area ratio (A/S) is 0.21-0.35 m ²/m².

Description

Honeycomb filter

Technical Field

The present invention relates to a honeycomb filter. More particularly, the present invention relates to a honeycomb filter capable of suppressing an increase in pressure loss and improving purification performance.

Background

As a method for reducing the amount of particulate matter contained in exhaust gas discharged from an internal combustion engine, there is known: a method of providing a particulate filter for trapping particulate matter deposited in an exhaust passage of an internal combustion engine is disclosed (for example, patent document 1). In particular, in recent years, from the viewpoint of saving mounting space and the like, studies have been made: the particulate filter is coated with a catalyst slurry and calcined to provide a catalyst layer for simultaneously suppressing the emission of particulate matter and removing harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx).

As a particulate filter for purifying exhaust gas, for example, there is known: a honeycomb filter using a honeycomb structure. The honeycomb structure has partition walls made of porous ceramics such as cordierite, and a plurality of cells are partitioned by the partition walls. The honeycomb filter is obtained by alternately sealing the openings on the inflow end face side and the openings on the outflow end face side of the plurality of cells in the honeycomb structure.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2002-219319

Disclosure of Invention

In a honeycomb filter provided with a catalyst layer, in order to improve the purification performance of purifying exhaust gas by a catalyst, it is useful to increase the surface area of porous partition walls (in other words, porous carriers) on which the catalyst is supported and to increase the contact frequency between the catalyst and the exhaust gas. For example, as a method of increasing the surface area of the porous support constituting the partition wall, there is considered to increase the cell density of the honeycomb structure, but there is a problem that the increase in cell density causes a significant increase in pressure loss. In particular, for a honeycomb filter represented by a Gasoline Particulate Filter (GPF), development of: a honeycomb filter capable of suppressing an increase in pressure loss and improving purification performance.

The present invention has been made in view of the above-described problems of the prior art. According to the present invention, a honeycomb filter capable of suppressing an increase in pressure loss and improving purification performance is provided.

According to the present invention, there is provided a honeycomb filter shown below.

[1] A honeycomb filter, comprising:

a columnar honeycomb structure having porous partition walls arranged to surround a plurality of cells, the plurality of cells forming fluid flow paths extending from an inflow end face to an outflow end face; and

A hole sealing portion provided at either one of an end portion on the inflow end face side and an end portion on the outflow end face side of the compartment,

The thickness of the partition wall is 152-254 μm,

The cell density of the honeycomb structure is 38.8-62.0 cells/cm ²,

In the pore diameter distribution of the partition walls obtained by measurement by mercury intrusion, the pore diameter D50 at which the cumulative pore volume reaches 50% of the total pore volume is 11 to 15 μm,

The porosity of the partition wall measured by mercury intrusion method is 60-75%,

The wet area ratio (A/S) of the porous partition walls, which is a value obtained by dividing the wet area A of the pores formed in the partition walls by the cross-sectional area S of the pores, is 0.21 to 0.35m ²/m².

[2] The honeycomb filter according to the above item [1], wherein, in the pore diameter distribution of the partition walls obtained by measurement by mercury intrusion, the pore diameter D10 at which the cumulative pore volume is 10% of the total pore volume is 5.5 to 7.5. Mu.m.

[3] The honeycomb filter according to the above [1] or [2], wherein in the pore diameter distribution of the partition walls obtained by measurement by mercury intrusion, a pore diameter D90 at which a cumulative pore volume reaches 90% of a total pore volume is 35.0 μm or less.

Effects of the invention

The honeycomb filter of the present invention can suppress an increase in pressure loss and improve purification performance. For example, in the case where the catalyst layer is provided by applying a catalyst slurry to a honeycomb filter and firing the catalyst slurry, the catalyst slurry is applied so as to permeate into porous partition walls constituting the honeycomb structure. In the honeycomb filter of the present invention, the small-diameter pores among the pores formed in the partition walls can be relatively increased by setting the partition wall wet area ratio (a/S) to 0.21 to 0.35m ²/m², and the surface area for catalyst coating in the partition walls can be increased. Therefore, when the catalyst layer is provided in such a honeycomb filter, the contact frequency between the exhaust gas and the catalyst increases, and the purification performance of the honeycomb filter can be improved. In the honeycomb filter of the present invention, the cell density of the honeycomb structure is set to be in the range of 38.8 to 62.0 cells/cm ², and the purification performance can be improved as described above without excessively increasing the cell density. Therefore, the honeycomb filter of the present invention can effectively suppress an increase in pressure loss and can more effectively improve the purification performance than the conventional method of improving the purification performance by increasing the cell density.

Drawings

Fig. 1 is a perspective view schematically showing an embodiment of the honeycomb filter of the present invention.

Fig. 2 is a plan view showing the inflow end face side of the honeycomb filter shown in fig. 1.

Fig. 3 is a sectional view schematically showing a section A-A' of fig. 2.

Fig. 4 is a conceptual diagram of voxel data for solving the partition wall wet area ratio (a/S).

Description of the reference numerals

1: Partition wall, 2: compartment, 2a: inflow compartment, 2b: outflow compartment, 3: peripheral wall, 4: honeycomb structure, 5: hole sealing portion, 11: inflow end face, 12: outflow end face, 60: voxel data, 64: enlarged view, 100: a honeycomb filter.

Detailed Description

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. Thus, it should be understood that: the following embodiments are appropriately modified and improved based on the general knowledge of those skilled in the art within the scope of the present invention without departing from the gist of the present invention.

(1) Honeycomb filter:

One embodiment of the honeycomb filter of the present invention is a honeycomb filter 100 shown in fig. 1-3. Here, fig. 1 is a perspective view schematically showing an embodiment of the honeycomb filter of the present invention. Fig. 2 is a plan view showing the inflow end face side of the honeycomb filter shown in fig. 1. Fig. 3 is a sectional view schematically showing a section A-A' of fig. 2.

As shown in fig. 1 to 3, the honeycomb filter 100 includes a honeycomb structure 4 and a plugged portion 5. The honeycomb structure 4 has a columnar shape and includes porous partition walls 1 arranged to surround a plurality of cells 2, and the plurality of cells 2 form fluid flow paths extending from an inflow end face 11 to an outflow end face 12. In the honeycomb filter 100, the honeycomb structure 4 has a columnar shape and has an outer peripheral wall 3 on its outer peripheral side surface. That is, the outer peripheral wall 3 is provided with: surrounding the partition walls 1 arranged in a lattice shape.

The hole sealing portion 5 is disposed in an opening portion of each cell 2 on the inflow end face 11 side or the outflow end face 12 side. In the honeycomb filter 100 shown in fig. 1 to 3, the plugging portions 5 are disposed in the openings of the end portions of the predetermined cells 2 on the inflow end face 11 side and the openings of the end portions of the remaining cells 2 on the outflow end face 12 side, respectively. The compartment 2 in which the hole sealing portion 5 is disposed in the opening portion on the outflow end face 12 side and the inflow end face 11 side is opened is referred to as an inflow compartment 2a. The compartment 2 in which the hole sealing portion 5 is disposed in the opening portion on the inflow end face 11 side and the outflow end face 12 side is opened is referred to as an outflow compartment 2b. The inflow cells 2a and the outflow cells 2b are preferably alternately arranged with the partition wall 1 interposed therebetween. It is preferable that both end surfaces of the honeycomb filter 100 are formed in a checkered pattern by the hole sealing portions 5 and the "openings of the cells 2".

The honeycomb filter 100 has main characteristics particularly in terms of the structure of the honeycomb structure 4 and the partition walls 1 constituting the honeycomb structure 4. That is, the thickness of the partition walls 1 constituting the honeycomb structure 4 is 152 to 254 μm. The cell density of the honeycomb structure 4 is 38.8 to 62.0 cells/cm ². In the pore diameter distribution of the partition wall 1 measured by the mercury porosimetry method, the pore diameter D50 at which the cumulative pore volume reaches 50% of the total pore volume is 11 to 15 μm, and the porosity of the partition wall 1 measured by the mercury porosimetry method is 60 to 75%. The wet area ratio (A/S) of the partition walls, which is a value obtained by dividing the wet area A of the pores formed in the porous partition walls 1 by the cross-sectional area S of the pores, is 0.21 to 0.35m ²/m². Hereinafter, the minute voids formed in the porous partition wall 1 may be referred to as "pores" or "micropores" of the partition wall 1.

The honeycomb filter 100 thus constructed can suppress an increase in pressure loss and improve the cleaning performance. For example, in the case where the honeycomb filter 100 is provided with a catalyst layer by applying a catalyst slurry and firing the catalyst slurry, the catalyst slurry is applied so as to permeate into the porous partition walls 1 constituting the honeycomb structure 4. In the honeycomb filter 100, the partition wet area ratio (a/S) is set to 0.21 to 0.35m ²/m², whereby small-diameter pores among the pores of the partition 1 can be relatively increased, and the surface area for catalyst application can be increased. Therefore, when the honeycomb filter 100 is provided with the catalyst layer, the contact frequency of the exhaust gas with the catalyst increases, and the purification performance of the honeycomb filter 100 can be improved. In the honeycomb filter 100, the cell density of the honeycomb structure 4 is set to be in the range of 38.8 to 62.0 cells/cm ², and the purification performance can be improved without excessively increasing the cell density. Therefore, the honeycomb filter 100 can effectively suppress an increase in pressure loss and can more effectively improve the purification performance than the conventional method of improving the purification performance by increasing the cell density. The honeycomb filter 100 of the present embodiment will be described in further detail below.

The thickness of the partition walls 1 constituting the honeycomb structure 4 is 152 to 254 μm. By setting the thickness of the partition wall 1 to the above-described numerical range, the strength as a structural body can be ensured and the increase in pressure loss can be suppressed. For example, if the thickness of the partition wall 1 is less than 152 μm, the strength is lowered, which is undesirable in this respect. If the thickness of the partition wall 1 exceeds 254. Mu.m, the pressure loss increases greatly, which is undesirable. Although not particularly limited, the thickness of the partition wall 1 is preferably 203 to 254 μm, more preferably 203 to 229 μm. For example, the thickness of the partition wall 1 may be measured using a scanning electron microscope or a microscope (microscope).

In the honeycomb structure 4 having the partition walls 1 as described above, the cell density of the honeycomb structure 4 is 38.8 to 62.0 cells/cm ². By setting the cell density to the above-described numerical range, an increase in pressure loss at the time of soot (hereinafter also referred to as "Ash" or "Ash") accumulation can be suppressed. For example, if the cell density is less than 38.8 cells/cm ², the Geometric Surface Area (GSA) is decreased, the thickness of the Ash bulk layer is increased, and the pressure loss is greatly increased, so that it is not preferable. If the cell density exceeds 62.0 cells/cm ², the hydraulic diameter of the gas inlet end face becomes small, and the pressure loss increases sharply, which is not preferable. Although not particularly limited, the cell density of the honeycomb structure 4 is preferably 43 to 54 cells/cm ², more preferably 45 to 48 cells/cm ².

In the partition wall 1, in the pore diameter distribution of the partition wall 1 measured by the mercury intrusion method, the pore diameter D50 at which the cumulative pore volume reaches 50% of the total pore volume is 11 to 15 μm. Hereinafter, the pore diameter D50 in which the cumulative pore volume in the pore diameter distribution of the partition wall 1 reaches 50% of the total pore volume may be simply referred to as "D50" in the pore diameter distribution of the partition wall 1. The "D50" is: the value calculated by defining the pore diameter of the partition wall 1, which is a half of the total pore volume, is sometimes referred to as the average pore diameter of the partition wall 1. If the D50 is less than 11. Mu.m, the pressure loss after the catalyst application may be increased drastically, which is undesirable. If the pore diameter D50 exceeds 15. Mu.m, the trapping performance is lowered, which is undesirable in this respect. Although not particularly limited, D50 is preferably 12 to 15. Mu.m, more preferably 13 to 15. Mu.m.

The cumulative pore volume of the partition wall 1 is a value measured by mercury porosimetry. For example, the cumulative pore volume of the partition wall 1 can be measured by using an Autopore 9500 (trade name) manufactured by Micromeritics corporation. The measurement of the cumulative pore volume of the partition wall 1 can be performed by the following method. First, a part of the partition wall 1 was cut out from the honeycomb filter 100 to prepare a test piece for measuring the cumulative pore volume. The test piece is not particularly limited in size, and is preferably a rectangular parallelepiped having a length of about 10mm, or about 20mm in each of the longitudinal direction, the transverse direction, and the height. The portion of the partition wall 1 from which the test piece is to be cut is not particularly limited, but it is preferable to cut from the vicinity of the center in the axial direction of the honeycomb structure portion to produce the test piece. The obtained test piece was stored in a measurement cell of the measurement device, and the inside of the measurement cell was depressurized. Next, mercury was introduced into the measurement cells. Next, the volume of mercury pressed into the pores present in the test piece is measured by pressurizing the mercury introduced into the measurement cells. At this time, as the pressure applied to the mercury increases, the mercury is pushed into the pores having smaller pore diameters in order from the pores having larger pore diameters. Therefore, from the relationship between "the pressure applied to mercury" and "the volume of mercury pressed into the pores", the relationship between "the pore diameter of the pores formed in the test piece" and "the cumulative pore volume" can be obtained. More specifically, as described above, when mercury is gradually introduced into the pores of the sample (test piece) in the container sealed in a vacuum state by gradually applying pressure by the mercury porosimetry method, the mercury to which the pressure is applied sequentially enters from the larger pores to the smaller pores of the sample. From the pressure and the amount of mercury pressed in at this time, the pore diameter of the pores formed in the sample and the pore volume thereof can be calculated. Hereinafter, when the pore diameters are D1, D2, and D3 …, the relationship of D1 > D2 > D3 … is satisfied. Here, the average pore diameter D between the measurement points (e.g., D1 to D2) may be shown on the horizontal axis in the form of "average pore diameter d= (d1+d2)/2". In addition, the Log differential pore volume of the vertical axis can be set as: the increase dV in pore volume between each measurement point is divided by the difference in log processing of the pore diameter (i.e., "log (D1) -log (D2)").

The porosity of the partition wall 1 measured by mercury intrusion method is 60 to 75%. If the porosity of the partition wall 1 is less than 60%, the pressure loss during catalyst application may be increased rapidly, which is undesirable. If the porosity of the partition wall 1 exceeds 75%, the strength is lowered, which is undesirable. Although not particularly limited, the porosity of the partition wall 1 is preferably 61 to 70%, more preferably 62 to 66%. For example, the porosity of the partition wall 1 can be measured by using Autopore 9500 (trade name) manufactured by Micromeritics corporation. A part of the partition wall 1 may be cut out from the honeycomb filter 100 to prepare a sample sheet, and the porosity may be measured using the sample sheet thus obtained.

In the honeycomb filter 100, the partition wet area ratio (a/S) described below is 0.21 to 0.35m ²/m². The wet area ratio (A/S) of the partition walls is: the wet area a (m ²) of the pores formed in the porous partition wall 1 is divided by the cross-sectional area S (m ²) of the pores. The wet area a (m ²) and the cross-sectional area S (m ²) of the air hole are calculated using three-dimensional voxel data 60 obtained by CT scanning of the partition wall 1. Fig. 4 is a conceptual diagram of voxel data 60. First, the thickness direction of the partition wall 1 (see fig. 3, for example) is defined as the X direction, the axial direction of the compartment 2 (the up-down direction of fig. 3, for example) is defined as the Y direction, and the XY plane is defined as the imaging cross section. Next, CT scanning of the partition wall 1 is performed so that the imaging cross section is deviated in the Z direction perpendicular to the XY direction and imaged several times, a plurality of image data are obtained, and voxel data 60 as shown in the upper part of fig. 4 is obtained based on the image data. X, Y, Z has a resolution of 1.2 μm in each direction, and the resulting cube having a side length of 1.2 μm becomes the voxel that is the smallest unit of the three-dimensional voxel data 60. The image data of the imaging section obtained by CT scan is: the data of the plane having no thickness in the Z direction, however, each imaging section is processed with a thickness of a distance (1.2 μm) in the Z direction of the imaging section. That is, each pixel of the two-dimensional image data is treated as a cube (voxel) having a side length of 1.2 μm. As shown in the upper part of fig. 3, the size of the voxel data 60 is a rectangular parallelepiped having an X direction of 300 μm (=1.2 μm×250 voxels), a Y direction of 480 μm (=1.2 μm×400 voxels), and a Z direction of 480 μm (=1.2 μm×400 voxels). Each voxel represents a position by X, Y, Z coordinates (a value 1 of the coordinates corresponds to a side length of 1.2 μm of the voxel), and it is discriminated whether a spatial voxel representing a space (air hole) or an object voxel representing an object. The spatial voxel is discriminated from the object voxel by the 2-valued processing using the modal method as follows. The plurality of image data actually obtained by CT scan are: x, Y, Z luminance data for each coordinate. Based on the luminance data, a histogram of luminance is created for all coordinates (all pixels of the plurality of image data). Then, the luminance value of the portion between 2 mountains (valleys) appearing in the histogram is set as a threshold value, and the luminance of each coordinate is 2-valued according to whether the luminance is greater than the threshold value or less than the threshold value for each coordinate. Accordingly, whether the voxels of each coordinate are spatial voxels or object voxels is discriminated. An example of a state in which a spatial voxel and an object voxel are distinguished is shown in two dimensions in the middle of fig. 4. An enlarged view 64 of a portion thereof is shown in two dimensions in the lower part of fig. 4. The CT scan may be performed by using, for example, SMX-160CT-SV3 (trade name) manufactured by Shimadzu corporation. The position of the partition walls 1 to be subjected to CT scanning is not particularly limited, and is preferably a central portion in the direction in which the cells 2 of the honeycomb structure 4 extend (the axial direction of the cells 2 described above).

Next, using the voxel data 60, the cross-sectional area S 'of the air outlet hole and the wetted area a' of the air hole are calculated. The cross-sectional area S' of the air holes is the area of the region where the "spatial voxels" exist as shown in the middle and lower portions of fig. 4. Therefore, the cross-sectional area S 'of the air hole can be calculated as the cross-sectional area S' =the number of spatial pixels×1.2 μm×1.2 μm. The wetted area a' is calculated as the sum of areas of boundary surfaces between the spatial voxels and the object voxels in the voxel data 60. More specifically, the wet area a' = (the number of boundary surfaces in the voxel data 60) × (the area of 1 boundary surface) is derived. The area of 1 boundary surface is 1.44 μm ² (=1.2 μm×1.2 μm). For example, since the enlarged view 64 shown in the lower part of fig. 4 has boundary surfaces between 6 spatial voxels and object voxels, the total area of the boundary surfaces in the enlarged view 64 is 6×1.44=8.64 μm ². The wet area a' was calculated in this manner. In the above description, the case where the unit of the cross-sectional area S 'of the air hole and the wet area a' of the air hole is "μm ²" is described, but the wet area a (m ²) of the air hole and the cross-sectional area S (m ²) of the air hole can be obtained by converting the unit of the size (length) or the like of the voxel data 60 into "m" as appropriate. Then, the partition wall wet area ratio (A/S) was calculated from the cross-sectional area S and wet area A of the air hole.

In the honeycomb filter 100, if the partition wall wetted area ratio (a/S) is less than 0.21m ²/m², the surface area of the catalyst to be coated in the partition wall 1 (i.e., the wetted area in the partition wall 1) becomes small. Therefore, when the honeycomb filter 100 is provided with the catalyst layer, the contact frequency between the exhaust gas and the catalyst is not easily increased, and sufficient improvement of the purification performance cannot be expected. On the other hand, if the partition wet area ratio (a/S) exceeds 0.35m ²/m², there is a possibility that the pressure loss increases after the catalyst is coated, which is undesirable in this respect. The wet area ratio (A/S) of the partition walls may be 0.21 to 0.35m ²/m², for example, preferably 0.23 to 0.30m ²/m², more preferably 0.25 to 0.27m ²/m².

In the honeycomb filter 100, the pore diameter D10 in which the cumulative pore volume is 10% of the total pore volume is preferably 5.5 to 7.5 μm in the pore diameter distribution of the partition walls 1 described above. Hereinafter, the pore diameter D10 at which the cumulative pore volume reaches 10% of the total pore volume may be simply referred to as "D10" in the pore diameter distribution of the partition wall 1. If D10 is 5.5 to 7.5. Mu.m, the increase in pressure loss after the catalyst application can be suppressed, which is preferable. Although not particularly limited, D10 is more preferably 6.0 to 7.0. Mu.m.

In the honeycomb filter 100, the pore diameter D90 at which the cumulative pore volume reaches 90% of the total pore volume in the pore diameter distribution of the partition walls 1 is preferably 35.0 μm or less. Hereinafter, the pore diameter D90 at which the cumulative pore volume reaches 90% of the total pore volume may be simply referred to as "D90" in the pore diameter distribution of the partition wall 1. When the D90 is 35.0 μm or less, sufficient trapping performance can be exhibited, and it is preferable in terms of this. Although not particularly limited, D90 is more preferably 27.0 to 35.0. Mu.m, particularly preferably 27.0 to 32.0. Mu.m.

The shape of the compartment 2 partitioned by the partition wall 1 is not particularly limited. For example, examples of the shape of the cell 2 in a cross section orthogonal to the direction in which the cell 2 extends include: polygonal, circular, oval, etc. As the polygon, there may be mentioned: triangle, quadrilateral, pentagon, hexagon, octagon, etc. The shape of the cells 2 is preferably triangle, quadrangle, pentagon, hexagon, octagon. In addition, regarding the shape of the cells 2, the shape of all the cells 2 may be the same shape or may be different shapes. For example, although not shown, quadrangular cells and octagonal cells may be mixed. In addition, regarding the size of the compartments 2, the sizes of all the compartments 2 may be the same or different. For example, although not shown, among the plurality of compartments, the size of a part of the compartments may be increased and the size of the other compartments may be relatively decreased. In the present invention, the compartment means: a space surrounded by the partition wall.

The shape of the honeycomb structural body 4 is not particularly limited. The shape of the honeycomb structure 4 may be: the inflow end face 11 and the outflow end face 12 have a columnar shape such as a circle, an ellipse, or a polygon.

The size of the honeycomb structure 4 is not particularly limited, and for example, the length from the inflow end face 11 to the outflow end face 12, and the size of a cross section of the honeycomb structure 4 orthogonal to the direction in which the cells 2 extend, are not particularly limited. When the honeycomb filter 100 is used as a filter for purifying exhaust gas, the respective sizes may be appropriately selected so as to obtain the optimum purification performance.

The material of the partition walls 1 constituting the honeycomb structural body 4 is not particularly limited. For example, the material of the partition wall 1 preferably contains at least 1 selected from the group consisting of cordierite, silicon carbide, silicon-silicon carbide composite, cordierite-silicon carbide composite, silicon nitride, mullite, alumina, and aluminum titanate. In the honeycomb filter 100 of the present embodiment, as a material of the partition walls 1, a material containing at least 1 of cordierite, silicon carbide, and aluminum titanate is preferable.

The material of the plugging portion 5 is not particularly limited. For example, the same material as that of the partition wall 1 described above can be used.

The honeycomb filter 100 is preferably: the partition wall 1 that partitions the plurality of cells 2 carries a catalyst for purifying exhaust gas. The supporting of the catalyst on the partition wall 1 means: catalyst is applied to the surfaces of the partition walls 1 and to the inner walls of the pores formed in the partition walls 1. By configuring in this manner, CO, NOx, HC and the like in the exhaust gas can be made harmless by catalytic reaction. In addition, oxidation of PM such as trapped soot can be promoted.

The catalyst supported on the partition wall 1 is not particularly limited. For example, a catalyst containing a platinum group element and an oxide of at least one element selected from aluminum, zirconium, and cerium is given.

(2) The manufacturing method of the honeycomb filter comprises the following steps:

the method for producing the honeycomb filter of the present invention is not particularly limited, and the following methods are exemplified. First, a plastic blank for manufacturing a honeycomb structure is prepared. The green body for producing the honeycomb structure can be prepared by appropriately adding an additive such as a binder, a pore-forming material, and water to a material selected from the preferable materials of the partition walls as a raw material powder. In the production of the honeycomb filter of the present invention, for example, kaolin, talc, alumina, aluminum hydroxide, silica, or the like may be used as a raw material powder for producing a green body, and these raw material powders may be prepared so as to be: a chemical composition of silica in the range of 42 to 56 mass%, alumina in the range of 30 to 45 mass% and magnesia in the range of 12 to 16 mass%. The kaolin, alumina, and aluminum hydroxide are materials having an average particle diameter of 7 μm or less, so that the number of small pores in the material can be increased to increase the wet area of the partition wall.

Next, the thus obtained preform was extrusion molded, thereby producing: a honeycomb formed body having a columnar shape and having partition walls partitioning a plurality of cells and disposed so as to surround the peripheral walls of the partition walls. In extrusion molding, as a die for extrusion molding, there may be used: the extrusion face of the preform is provided with a die which is a slit of a reverse shape of the honeycomb formed body to be formed.

The obtained honeycomb formed body is dried by, for example, microwaves and hot air, and the openings of the cells are sealed by the same material as that used for the honeycomb formed body, thereby producing sealed portions. After the plugging portion is produced, the honeycomb formed body may be further dried.

Next, the honeycomb formed body having the plugged portions formed therein was fired to produce a honeycomb filter. The firing temperature and firing atmosphere vary depending on the raw materials, and if one skilled in the art would choose: the firing temperature and firing atmosphere are optimal for the selected material.

Examples

Hereinafter, the present invention will be described in further detail with reference to examples, but the present invention is not limited to these examples.

Example 1

To 100 parts by mass of the cordierite forming raw material, 2 parts by mass of the pore-forming material, 2 parts by mass of the dispersion medium, and 7 parts by mass of the organic binder were added, followed by mixing and kneading to prepare a green body. Alumina, aluminum hydroxide, kaolin, talc, and silica were used as cordierite forming raw materials. As the dispersion medium, water was used. As the organic binder, methylcellulose (Methylcellulose) was used. As the dispersant, dextrin (Dextrin) was used. Aluminum hydroxide was used as a material having an average particle diameter of 5. Mu.m, to prepare a green body for use in the production of a honeycomb structure.

Next, the obtained preform was molded by an extrusion molding machine to produce a honeycomb molded body. Then, the obtained honeycomb formed body was subjected to high-frequency dielectric heating and drying, and then further dried by a hot air dryer. The cells in the honeycomb formed body are quadrangular in shape.

Next, a plugged portion was formed in the dried honeycomb formed body. First, a mask is applied to the inflow end face of the honeycomb formed body. Next, the end to which the mask is applied (end on the inflow end face side) is immersed in the plugging slurry, and the opening of the compartment to which the mask is not applied (outflow compartment) is filled with the plugging slurry. In this way, the plugging portion is formed on the inflow end face side of the honeycomb formed body. In addition, the plugged portions are formed in the inflow cells in the same manner as in the outflow end face of the dried honeycomb formed body.

Next, the honeycomb formed body having the plugged portions formed therein was dried by a microwave dryer, and then completely dried by a hot air dryer, and both end faces of the honeycomb formed body were cut and adjusted to a predetermined size. Next, the dried honeycomb formed body was degreased and fired to produce a honeycomb filter of example 1.

In the honeycomb filter of example 1, the end face had a diameter of 132.6mm and the cell length in the direction of extension was 127.3mm. The thickness of the partition wall was 210.8. Mu.m, and the cell density was 46.8 cells/cm ². The values of the thicknesses of the partition walls are shown in table 1.

For the honeycomb filter of example 1, the following procedure was used: measurement of "porosity (%)", "D50 (μm)", "D10 (μm)", and "D90 (μm)", of the partition walls. The "wet area ratio of partition wall" of the partition wall was determined by the following method. The results are shown in Table 1.

[ Porosity (%), D50 (. Mu.m), D10 (. Mu.m) and D90 (. Mu.m) ]

The porosities (%), D50 (. Mu.m), D10 (. Mu.m) and D90 (. Mu.m) of the partition walls were measured by using Autopore 9500 (trade name) manufactured by Micromeritics Co. The respective pore diameters (μm) at which the cumulative pore volume reached 50%, 10% and 90% of the total pore volume were confirmed in the pore diameter distribution of the partition walls, and the respective values of D50 (μm), D10 (μm) and D90 (μm) were obtained. In these measurements, a part of the partition wall was cut out of the honeycomb filter to prepare a test piece, and the measurement was performed using the obtained test piece. The test piece was a rectangular parallelepiped having a length of about 10mm, and about 20mm in each of the longitudinal, transverse, and height directions. The sampling position of the test piece was set near the center of the honeycomb structure in the axial direction.

[ Wet area ratio of partition wall ]

By the method described above, CT scanning is performed on the partition walls of the honeycomb structure, thereby obtaining three-dimensional voxel data 60 shown in fig. 4. Then, using the three-dimensional voxel data 60 obtained, the partition wall wet area ratio was calculated in the above-described manner.

TABLE 1

The honeycomb filter of example 1 was evaluated for pressure loss, purification performance, and trapping performance by the following method. The results are shown in Table 1.

(Pressure loss)

The pressure on the inflow end face side and the outflow end face side of the honeycomb filter were measured by flowing a gas at 25℃at a flow rate of 10Nm ³/min using a large wind tunnel tester. Then, the pressure difference between the inflow end face side and the outflow end face side was calculated, and the pressure loss (kPa) of the honeycomb filter was obtained. Then, the following was found: the rate of increase (%) of the pressure loss of the honeycomb filter of each example relative to the value of the pressure loss of the honeycomb filter of comparative example 1. In the evaluation of the pressure loss, the honeycomb filters of the respective examples were evaluated based on the following evaluation criteria.

Evaluation of "good": when the rate of increase (%) of the pressure loss was less than 10%, the evaluation was set as "good".

Evaluation of "difference": when the rate of increase (%) of the pressure loss was 10% or more, the evaluation was set to "poor".

(Purification Performance)

The NOx purification rate (%) of the honeycomb filter was determined by performing a bench test of the running mode RTS95 cycle by mounting the honeycomb filter supporting the three-way catalyst at 100g/L at an underfloor position of a vehicle having an exhaust gas amount of 1500 cc. Further, the NOx purification rate (%) of the honeycomb filter of each example was compared with the value of the NOx purification rate (%) of the honeycomb filter of comparative example 1, whereby the purification performance was evaluated. Specifically, in the evaluation of the purification performance, the honeycomb filters of the respective examples were evaluated based on the following evaluation criteria.

Evaluation of "you": the evaluation was "excellent" when an improvement of the NOx purification rate (%) of 1.0% or more was observed with respect to the value of the NOx purification rate (%) of the honeycomb filter of comparative example 1.

Evaluation of "good": the evaluation was set to "good" when an increase in NOx purification rate (%) of 0.5% or more and less than 1.0% was observed with respect to the value of NOx purification rate (%) of the honeycomb filter of comparative example 1.

Evaluation of "difference": the evaluation was set to "poor" when an increase in NOx purification rate (%) of less than 0.5% was observed with respect to the value of NOx purification rate (%) of the honeycomb filter of comparative example 1.

(Trapping Performance)

A honeycomb filter was mounted at an underfloor position of a vehicle having an exhaust gas amount of 1500cc, and a bench test of a running mode RTS95 cycle was performed to circulate exhaust gas containing PM through the honeycomb filter. At this time, the collection efficiency (%) of the honeycomb filter was obtained by measuring the number of PM in the exhaust gas before flowing into the honeycomb filter and the number of PM in the exhaust gas flowing out of the honeycomb filter. In the evaluation of the trapping performance, the honeycomb filters of the respective examples were evaluated based on the following evaluation criteria.

Evaluation of "good": when the collection efficiency (%) was 70% or more, the evaluation was regarded as "good".

Evaluation "cocoa": when the collection efficiency (%) is 65% or more and less than 70%, the evaluation is "ok".

Evaluation of "difference": when the collection efficiency (%) is less than 65%, the evaluation is set to "poor".

Examples 2 to 4

In examples 2 to 4, the structure of the honeycomb structure was changed as shown by "properties of partition walls" in table 1. In examples 2 and 4, the particle size of the pore-forming material added to the raw material powder was made smaller to produce a honeycomb structure. In example 3, a honeycomb structure was produced by making the particle size of the pore-forming material added to the raw material powder larger.

Comparative example 1

In comparative example 1, the structure of the honeycomb structure was changed as shown by "properties of partition walls" in table 1. In comparative example 1, a honeycomb structure having a particle size of Kong Rongbian or less was produced by adjusting the particle size of the pore-forming material and the amount of the pore-forming material added.

The honeycomb filters of examples 2 to 4 were evaluated for pressure loss, purification performance, and trapping performance in the same manner as in example 1. The results are shown in Table 1. The honeycomb filter of comparative example 1 was used as an evaluation criterion in the evaluation of the pressure loss and the cleaning performance.

(Results)

The honeycomb filters of examples 1 to 4 showed in the evaluation of the pressure loss and the purification performance: more excellent results than the honeycomb filter of comparative example 1 as the evaluation reference. In particular, in the honeycomb filter of example 4, the partition wet area ratio was 0.3m ²/m², and the cleaning performance was evaluated to be particularly excellent. In the honeycomb filters of examples 1 and 3, the partition wet area ratio showed the same value, however, the detailed trapping performance was compared, and as a result, it was found that the honeycomb filter of example 1 showed more excellent trapping performance. It can be speculated that: the honeycomb filter of example 1 has a D90 value less than that of the honeycomb filter of example 3, and the trapping performance is improved.

Industrial applicability

The honeycomb filter of the present invention can be used as a filter for trapping particulate matter in exhaust gas.

Claims

1. A honeycomb filter, comprising:

A columnar honeycomb structure having porous partition walls arranged to surround a plurality of cells forming fluid flow paths extending from an inflow end face to an outflow end face; and

The thickness of the partition wall is 152-254 μm,

The cell density of the honeycomb structure is 38.8-62.0 cells/cm ²,

2. The honeycomb filter of claim 1 wherein the filter is configured to filter the liquid,

In the pore diameter distribution of the partition walls measured by mercury intrusion, the pore diameter D10 at which the cumulative pore volume is 10% of the total pore volume is 5.5 to 7.5 μm.

3. The honeycomb filter according to claim 1 or 2, wherein,

In the pore diameter distribution of the partition walls measured by mercury intrusion, the pore diameter D90 at which the cumulative pore volume reaches 90% of the total pore volume is 35.0 μm or less.