JP7093200B2 - Honeycomb filter - Google Patents

Description

The present invention relates to a honeycomb filter.

Recently, particulates such as soot (hereinafter referred to as PM) and other harmful components contained in exhaust gas emitted from vehicles such as buses and trucks and internal combustion engines such as construction machinery are harmful to the environment and human body. It's a problem. Therefore, various honeycomb filters made of porous ceramics have been proposed as honeycomb filters that collect PM in the exhaust gas and purify the exhaust gas.

As the honeycomb filter, a honeycomb filter composed of one honeycomb fired body (hereinafter, may be referred to as an integrated honeycomb filter) or a honeycomb filter having a structure in which a plurality of honeycomb filters are bound via an adhesive layer (honeycomb filter). Hereinafter, it may be referred to as an collective honeycomb filter).

As a honeycomb fired body constituting the collective honeycomb filter, a honeycomb segment in which the cell arrangement on the outermost periphery is adjusted so that the outermost peripheral wall after joining has a uniform thickness is disclosed (Patent Document 1).
Further, in order to improve the strength of the outer peripheral portion of the segment, a honeycomb segment having an adjusted aperture ratio of cells existing in the first to third rows from the side surface is disclosed (Patent Document 2).

International Publication No. 2008/126335 Japanese Unexamined Patent Publication No. 2014-188400

However, when an SCR (Selective Catalytic Reduction) catalyst is supported on a honeycomb segment as described in Patent Documents 1 and 2, sufficient NOx purification performance may not be exhibited with respect to the amount of the supported catalyst.
In Patent Document 1, attention is paid to the cell that is the outermost periphery of the collective honeycomb filter, and among the cells existing on the outer periphery of the honeycomb segment, the shape of the small capacity cell adjacent to the adhesive layer is other than the outer periphery of the honeycomb segment. It has the same shape as the small capacity cell existing in.
Patent Document 2 reduces the zigzag swing width of the cell partition wall near the outer periphery, and does not focus on the difference in cell shape.

When the catalyst is supported on the honeycomb segments described in Patent Documents 1 and 2, the catalyst in an expected amount or more adheres to the cells existing on the outermost periphery of the honeycomb segment (hereinafter, also referred to as the outermost cells). If more than the expected amount of catalyst adheres to the outermost cell of the honeycomb segment, the amount of catalyst supported on the cells other than the outermost cell decreases, and the volume of the cell becomes smaller in the outermost cell in which the catalyst is excessively present. , It is considered that the NOx purification performance is deteriorated.

As a result of diligent studies by the inventor, in the honeycomb segments described in Patent Documents 1 and 2, the speed of the gas passing through the outermost cell while carrying the catalyst is the speed of the gas passing through the cells other than the outermost cell. It was speculated that the cause was that the SCR catalyst was concentrated and supported on the portion where the speed of the passing gas was slow (the outermost cell) due to the slower speed.
FIG. 5A is an SEM photograph of a cell near the center of a conventional honeycomb fired body on which an SCR catalyst is supported, and FIG. 5B is an SEM photograph of the outermost cell of the honeycomb fired body. From FIGS. 5 (a) and 5 (b), it can be confirmed that an excessive amount of catalyst is supported on the outermost cell of the honeycomb fired body.

The present invention has been made to solve the above problems, and an object of the present invention is to improve the uniformity of the amount of the catalyst supported in the honeycomb calcined body when the catalyst is supported, and to improve the NOx purification performance. It is to provide a honeycomb filter that can be improved.

That is, in the honeycomb filter of the present invention, a porous cell partition wall that partitions a plurality of cells serving as an exhaust gas flow path, an end portion on the exhaust gas inlet side is opened, and an end portion on the exhaust gas outlet side is sealed. A plurality of honeycomb fired bodies having an exhaust gas introduction cell and an exhaust gas discharge cell having an open end on the exhaust gas outlet side and a sealed end on the exhaust gas inlet side were bound via an adhesive layer. A honeycomb filter composed of ceramic blocks, in a cross section perpendicular to the longitudinal direction of the cells, the plurality of cells are a large-capacity cell arranged alternately and a small-capacity cell having a cross-sectional area smaller than that of the large-capacity cell. In the cross section perpendicular to the longitudinal direction of the cell, the cross-sectional areas of the large-capacity cell and the small-capacity cell adjacent to the outer peripheral wall on one surface are the large-capacity cell and the small-capacity cell not adjacent to the outer peripheral wall, respectively. It is characterized in that it is 60 to 80% of the cross-sectional area of the capacity cell.

As a method of applying a catalyst to the honeycomb filter, a method of removing the dispersion medium by contacting the dispersion medium containing the catalyst with the honeycomb filter and then sucking an excess dispersion medium from the end face of the honeycomb filter is used.
When the catalyst is supported on the honeycomb filter containing the honeycomb segment described in Patent Documents 1 and 2 by the above method, the speed of the gas passing through the outermost cell of the honeycomb segment at the time of suction is the speed of the gas passing through other than the outermost cell. Since it is slower than that, the dispersion medium tends to remain in the outer peripheral portion rather than the central portion of the honeycomb segment. Therefore, a large amount of catalyst is supported on the cell partition wall constituting the outermost cell.
On the other hand, in the honeycomb filter of the present invention, in the cross section of the honeycomb fired body perpendicular to the longitudinal direction of the cell, the cross-sectional areas of the large-capacity cell and the small-capacity cell adjacent to the outer peripheral wall on one surface are the outer peripheral walls, respectively. Since it is 60 to 80% of the cross-sectional area of the large-capacity cell and the small-capacity cell that are not adjacent to each other, the cell that is adjacent to the outer peripheral wall on one surface and the cell that is not adjacent to the outer peripheral wall pass through the cell. The speed of the gas is about the same.
Therefore, the catalyst is not concentratedly supported on the cell partition wall constituting the outermost cell, and high NOx purification performance can be exhibited.

In the honeycomb filter of the present invention, the honeycomb fired body is preferably made of silicon carbide.
The honeycomb fired body made of silicon carbide is excellent in heat resistance, mechanical strength, heat conduction characteristics and the like.

In the honeycomb filter of the present invention, it is preferable that the SCR catalyst is supported on the cell partition wall.
Since the SCR catalyst acts as a NOx purification catalyst, high NOx purification performance can be exhibited when the SCR catalyst is supported on the cell partition wall.

In the honeycomb filter of the present invention, in the cross section perpendicular to the longitudinal direction of the cell, the cross-sectional shape of the large-capacity cell excluding the cell adjacent to the outer peripheral wall is octagonal, and the cell adjacent to the outer peripheral wall is excluded. The cross-sectional shape of the small capacity cell is preferably square.
When the cross-sectional shapes of the large-capacity cell and the small-capacity cell excluding the cell adjacent to the outer peripheral wall are octagonal and quadrangular, respectively, the pressure loss when used as a filter can be reduced.

In the honeycomb filter of the present invention, in the cross section perpendicular to the longitudinal direction of the cell, the cross-sectional shape of the large-capacity cell excluding the cell adjacent to the outer peripheral wall is square, and the cell excluding the cell adjacent to the outer peripheral wall is excluded. The cross-sectional shape of the small capacity cell is preferably square.
When the cross-sectional shapes of the large-capacity cell and the small-capacity cell excluding the cell adjacent to the outer peripheral wall are both square, the pressure loss when used as a filter can be reduced.

In the honeycomb filter of the present invention, the porosity of the cell partition wall is preferably 40 to 65%.
By setting the porosity of the cell partition wall constituting the honeycomb fired body within the above range, the strength of the honeycomb fired body can be maintained.

In the honeycomb filter of the present invention, the thickness of the cell partition wall is preferably 150 to 400 μm.

FIG. 1 is a perspective view schematically showing an example of the honeycomb filter of the present invention. FIG. 2A is a perspective view schematically showing an example of a honeycomb fired body constituting the honeycomb filter of the present invention, and FIG. 2B is a sectional view taken along line AA in FIG. 2A. be. FIG. 3 is a part of a sectional view taken along line BB in FIG. 2 (a). 4 (a), 4 (b) and 4 (c) are diagrams showing simulation results of the gas flow velocity of the honeycomb fired bodies according to Examples 1 and 2 and Comparative Examples 1 to 3. FIG. 5A is an SEM photograph of a cell near the center of a conventional honeycomb fired body on which an SCR catalyst is supported, and FIG. 5B is an SEM photograph of a cell near the outer peripheral cell of the honeycomb fired body.

(Detailed description of the invention)
[Honeycomb filter]
First, the honeycomb filter of the present invention will be described.

FIG. 1 is a perspective view schematically showing an example of the honeycomb filter of the present invention.
The honeycomb filter 1 shown in FIG. 1 is formed by adhering a plurality of honeycomb fired bodies 10 via an adhesive layer 16.
An outer peripheral coat layer 18 is formed on the outer periphery of the ceramic block 17 in which a plurality of honeycomb fired bodies 10 are bonded via an adhesive layer 16, and the outer shape thereof is columnar.

The number of honeycomb fired bodies 10 constituting the honeycomb filter 1 is not particularly limited.

The honeycomb fired bodies 10 constituting the honeycomb filter 1 are joined to each other via an adhesive layer 16.
The average thickness of the adhesive layer 16 is not particularly limited, but is preferably 0.5 to 1.5 mm.
When the average thickness of the adhesive layer 16 is 0.5 to 1.5 mm, the thickness of the adhesive layer 16 becomes an appropriate thickness, the peeling from the honeycomb firing body 10 is less likely to occur, and the honeycomb firing is performed. Cracks and the like are less likely to occur in the body 10.
If the average thickness of the adhesive layer 16 is less than 0.5 mm, the thickness of the adhesive layer 16 is too thin, so that the force for adhering the honeycomb fired bodies 10 to each other is weakened, and cracks are formed from the portion of the adhesive layer 16. Is more likely to occur. On the other hand, if the average thickness of the adhesive layer 16 exceeds 1.5 mm, the ratio of the cross-sectional area of the adhesive layer 16 becomes too large, and the pressure loss increases.

The average thickness of the outer peripheral coat layer 18 is preferably 0.2 to 2.5 mm.
When the average thickness of the outer peripheral coat layer 18 is 0.2 to 2.5 mm, the thickness of the outer peripheral coat layer 18 does not significantly affect the characteristics of the honeycomb filter 1.

The shape of the honeycomb filter is not limited to a columnar shape, and examples thereof include a prismatic column, an elliptical columnar shape, an oblong columnar shape, and a round chamfered prismatic shape (for example, a round chamfered triangular columnar shape).

[Honeycomb fired body]
Subsequently, the honeycomb fired body constituting the honeycomb filter of the present invention will be described.

FIG. 2A is a perspective view schematically showing an example of a honeycomb fired body constituting the honeycomb filter of the present invention, and FIG. 2B is a sectional view taken along line AA in FIG. 2A. be.
The honeycomb fired body 10 shown in FIGS. 2 (a) and 2 (b) has a plurality of cells (12, 13) whose one end is sealed by a sealing material 11 and serves as an exhaust gas flow path. It is provided with a porous cell partition wall 20 for partitioning the cell. The cells are composed of alternately arranged large-capacity cells 12 (12a, 12b) and small-capacity cells 13 (13a, 13b). Further, the large-capacity cell 12 has a large-capacity cell 12a that is not adjacent to the outer peripheral wall 15 and a large-capacity cell 12b that is adjacent to the outer peripheral wall 15 on one surface. The small-capacity cell 13 has a small-capacity cell 13a that is not adjacent to the outer peripheral wall 15 and a small-capacity cell 13b that is adjacent to the outer peripheral wall 15 on one surface. Further, in the cross section perpendicular to the longitudinal direction of the cells (the direction indicated by the double-headed arrow a in FIG. 2A), the cross-sectional areas of the small-capacity cells 13a and 13b are smaller than the cross-sectional areas of the large-capacity cells 12a and 12b, respectively. ..
The cells adjacent to the outer peripheral wall 15 on one surface do not include the cells adjacent to the outer peripheral wall on two surfaces.
The large-capacity cell 12 is also an exhaust gas introduction cell in which the end portion 10a on the exhaust gas inlet side is opened and the end portion 10b on the exhaust gas outlet side is sealed with a sealing material 11, and the small-capacity cell 13 is on the exhaust gas outlet side. It is also an exhaust gas discharge cell in which the end portion 10b of the exhaust gas is opened and the end portion 10a on the exhaust gas inlet side is sealed with a sealing material 11.
With respect to the cross section perpendicular to the longitudinal direction of the cell, the large capacity cell 12a is octagonal and the small capacity cell 13a is square. Further, the large-capacity cell 12b and the small-capacity cell 13b have shapes obtained by cutting out a part of the large-capacity cell 12a and the small-capacity cell 13a, respectively.

FIG. 3 is a part of a sectional view taken along line BB in FIG. 2 (a).
As shown in FIG. 3, the cross-sectional areas of the large-capacity cell 12b and the small-capacity cell 13b adjacent to the outer peripheral wall 15 of the honeycomb fired body 10 on one surface (in FIG. 3, the area S _12b of the area surrounded by the broken line and filled). S _13b ) is smaller than the cross-sectional area of the large-capacity cell 12a and the small-capacity cell 13a that are not adjacent to the outer peripheral wall 15 (the areas S _12a and S _13a of the area surrounded by the broken line in FIG. 3), respectively. The ratio is 60 to 80%. That is, both 0.6S _12a ≤ S _12b ≤ 0.8S _12a and 0.6S _13a ≤ S _13b ≤ 0.8S _13a are satisfied.
More specifically, the cross-sectional shapes of the large-capacity cell 12b and the small-capacity cell 13b in FIG. 3 include a large-capacity cell and a small-capacity cell adjacent to the outer peripheral wall, and a large-capacity cell and a small-capacity cell not adjacent to the outer peripheral wall. Corresponds to the cell shape obtained by reducing the external dimensions of the honeycomb fired body having the same shape without changing the shape of the cell not adjacent to the outer peripheral wall. In FIG. 3, it is assumed that the large-capacity cell 12b and the small-capacity cell 13b adjacent to the outer peripheral wall 15 on one surface have the same shape as the large-capacity cell 12a and the small-capacity cell 13a not adjacent to the outer peripheral wall 15. The cross-sectional shape of the cell and the outer peripheral wall are shown by a two-dot chain line.
The cross-sectional shape of the large-capacity cell 12b has the same length in one of the x-direction and the y-direction as the large-capacity cell 12a, but the other length is shorter than that of the large-capacity cell 12a. The small-capacity cell 13b is the same as the large-capacity cell 12b, and the length of one of the x-direction and the y-direction is the same as that of the small-capacity cell 13a, but the length of the other is shorter than that of the small-capacity cell 13a. There is.
Therefore, the cross-sectional area of the large-capacity cell 12b and the small-capacity cell 13b adjacent to the outer peripheral wall 15 on one surface is 60 to 80% of the cross-sectional area of the large-capacity cell 12a and the small-capacity cell 13a not adjacent to the outer peripheral wall 15, respectively. be.

In the honeycomb filter of the present invention, the shape of the cell adjacent to the outer peripheral wall of the honeycomb fired body does not have to be a shape obtained by cutting out a part of the cell shape not adjacent to the outer peripheral wall 15 as shown in FIG. good. That is, even if the cross-sectional area of the large-capacity cell and the small-capacity cell adjacent to the outer peripheral wall on one surface is 60 to 80% of the cross-sectional area of the large-capacity cell and the small-capacity cell not adjacent to the outer peripheral wall, respectively. For example, the cross-sectional shape of the large-capacity cell and the small-capacity cell adjacent to the outer peripheral wall on one surface may be a shape obtained by cutting out a part of the large-capacity cell and the small-capacity cell not adjacent to the outer peripheral wall. It may have a shape other than that.

The large-capacity cell may be an exhaust gas introduction cell or an exhaust gas emission cell.
The small-capacity cell may be an exhaust gas introduction cell or an exhaust gas discharge cell in the same manner as the large-capacity cell.

The ratio of the cross-sectional area of the small-capacity cell to the cross-sectional area of the large-capacity cell is not particularly limited, but is preferably 35 to 70%. The cross-sectional area of the cell is calculated from the average value of the cross-sectional area of the large-capacity cell not adjacent to the outer peripheral wall and the average value of the small-capacity cell.

The cross-sectional shape of the cell constituting the honeycomb fired body is not particularly limited, and examples thereof include a polygon such as a triangle, a quadrangle, a pentagon, a hexagon, and an octagon, and a circle. Further, it may be a shape obtained by cutting out a part of these shapes.
However, the cross-sectional shapes of the large-capacity cells not adjacent to the outer peripheral wall are substantially the same, and the cross-sectional shapes of the small-capacity cells not adjacent to the outer peripheral wall are substantially the same.
Among these, the cross-sectional shape of the large-capacity cell excluding the cell adjacent to the outer peripheral wall is octagonal, and the cross-sectional shape of the small-capacity cell excluding the cell adjacent to the outer peripheral wall is square, or the cross-sectional shape is adjacent to the outer peripheral wall. It is preferable that the cross-sectional shapes of the large-capacity cell and the small-capacity cell excluding the cell are square.

The cross-sectional shape and cross-sectional area of the cells constituting the honeycomb fired body can be obtained from an electron micrograph of the cross section of the honeycomb fired body cut to an appropriate size so as to include the outer peripheral wall.

The porosity of the cell partition wall constituting the honeycomb fired body is preferably 40 to 65%.
By setting the porosity of the cell partition wall constituting the honeycomb fired body within the above range, high exhaust gas purification performance can be exhibited while maintaining the strength of the honeycomb fired body.

The porosity of the cell bulkhead can be measured by the mercury intrusion method.
The conditions for measurement by the mercury intrusion method are a contact angle of 130 ° and a surface tension of 485 mN / m.

The thickness of the cell partition wall constituting the honeycomb fired body is preferably 150 to 400 μm.
If the thickness of the cell partition wall constituting the honeycomb fired body is less than 150 μm, the thickness of the cell partition wall is thin and the strength of the honeycomb fired body cannot be maintained. On the other hand, if the thickness of the cell partition wall exceeds 400 μm, the pressure loss of the honeycomb filter tends to increase.

It is desirable that the average pore diameter of the cell partition wall constituting the honeycomb fired body is 10 to 30 μm.
If the average pore diameter of the honeycomb fired body is less than 10 μm, the pressure loss of the honeycomb filter becomes high. On the other hand, when the average pore diameter of the honeycomb fired body exceeds 30 μm, the PM collection efficiency of the honeycomb filter becomes low.

The cell density in the cross section perpendicular to the longitudinal direction of the honeycomb fired body is not particularly limited, but the preferable lower limit is 31.0 pieces / cm ² (200 pieces / in ² ), and the preferable upper limit is 93.0 pieces / cm ² (preferably 93.0 pieces / cm 2). 600 pieces / in ² ), a more preferable lower limit is 38.8 pieces / cm ² (250 pieces / in ² ), and a more preferable upper limit is 77.5 pieces / cm ² (500 pieces / in ² ).

The material constituting the honeycomb fired body is not particularly limited, and for example, oxide ceramics such as cordierite, alumina, silica, mulite and aluminum titanate, carbide ceramics such as silicon carbide, zirconium carbide and titanium carbide, and aluminum nitride. , Nitride ceramics such as silicon carbide, composites of silicon carbide and silicon, etc. Among these, silicon carbide having high heat resistance, excellent mechanical properties, and excellent thermal conductivity characteristics is mentioned. preferable.

It is preferable that an SCR catalyst is supported on the cell partition wall constituting the honeycomb fired body.
Since the SCR catalyst acts as a NOx purification catalyst, high NOx purification performance can be exhibited when the SCR catalyst is supported on the cell partition wall.

Examples of the SCR catalyst include zeolite.
Zeolites include CHA, BEA, AEI, AFX and ERI structures. Of these, the CHA structure is preferable from the viewpoint of thermal durability and NOx purification performance. Zeolites are also exchanged for metal ions. Examples of the metal ion include Cu, Fe, Ce, Mn, Ag and the like. Of these, from the viewpoint of NOx purification performance, ion exchange with Cu ions is preferable.
The amount of the SCR catalyst supported is preferably 50 to 200 g / L, more preferably 70 to 180 g / L.
As used herein, the amount of SCR catalyst supported refers to the weight of the SCR catalyst per apparent volume of the honeycomb filter. The apparent volume of the honeycomb filter is the volume including the volume of the cell.

[How to manufacture a honeycomb filter]
Subsequently, a method for manufacturing the honeycomb filter of the present invention will be described.
In the following, the case where silicon carbide is used as the ceramic powder which is the material of the fired honeycomb body will be described, but the material of the fired honeycomb body is not limited to silicon carbide.

The honeycomb filter of the present invention is, for example, a molding step of obtaining a honeycomb molded body by extrusion-molding a raw material composition containing silicon carbide, and a degreasing step of degreasing the above-mentioned honeycomb molded body to obtain a honeycomb degreased body. , A firing step of firing the honeycomb degreased body to obtain a honeycomb fired body, a joining step of joining the honeycomb fired body via an adhesive layer to obtain a ceramic block, and an outer peripheral coat layer on the outer periphery of the ceramic block. It can be produced by the step of forming the outer peripheral coat layer to be formed.

(1) Molding Step A wet mixture for producing a honeycomb molded body is prepared by mixing silicon carbide powder having a different average particle size as a ceramic powder, an organic binder, a plasticizer, a lubricant, and water.

The particle size of the silicon carbide powder is not particularly limited, but for example, it has 100 parts by weight of the silicon carbide powder having an average particle size of about 3.0 to 50 μm and an average particle size of about 0.1 to 1.0 μm. A combination of 5 to 65 parts by weight of silicon carbide powder is preferable. This is because a high-strength porous body can be obtained by mixing the silicon carbide powder having the particle size with the above composition.

The organic binder is not particularly limited, and examples thereof include polyvinyl alcohol, methyl cellulose, ethyl cellulose, and carboxymethyl cellulose. These may be used alone or in combination of two or more. Among the above organic binders, methyl cellulose is preferable.

If necessary, a balloon, which is a micro hollow sphere containing an oxide-based ceramic, or a pore-forming agent such as spherical acrylic particles or graphite may be added to the wet mixture.
The balloon is not particularly limited, and examples thereof include an alumina balloon, a glass microballoon, a shirasu balloon, a fly ash balloon (FA balloon), and a mullite balloon. Of these, alumina balloons are preferred.

The wet mixture is put into an extrusion molding machine and extruded to produce a honeycomb molded product having a predetermined shape.
The shape of the honeycomb molded body obtained in the molding step includes a porous cell partition for partitioning a plurality of cells serving as a flow path for exhaust gas, and a cell partitioned by the cell partition and arranged side by side in the longitudinal direction. Further, as shown in FIG. 3, large-capacity cells and small-capacity cells are alternately arranged, and the cross-sectional areas of the large-capacity cells and the small-capacity cells adjacent to the outer peripheral wall on one surface are adjacent to the outer peripheral wall. 60-80% of the cross-sectional area of large-capacity cells and small-capacity cells.
This honeycomb molded body is dried by a dryer to obtain a dried body of the honeycomb molded body (also referred to as a honeycomb dried body).

Next, a predetermined amount of the sealing material paste is filled in any end of the cell constituting the dried body of the honeycomb molded body, and the cell is sealed. When sealing cells, for example, a mask for cell sealing is applied to the end face of the honeycomb molded body (that is, the cut surface after cutting both ends), and the sealing material is applied only to the cells that need to be sealed. Fill the paste and allow the encapsulant paste to dry. Through such a process, a dried honeycomb body in which one end of the cell is sealed is produced.
As the encapsulant paste, the above-mentioned wet mixture can be used.

(2) Degreasing step In the degreasing step, organic substances are oxidatively decomposed and completely removed by heating at 300 to 650 ° C. in an oxygen-containing atmosphere.

(3) Calcining Step After the degreasing step, in the firing step, the degreased honeycomb molded body (also referred to as honeycomb degreased body) is calcined in a completely inert gas atmosphere. The firing step is usually performed at 1400 to 2200 ° C.
The completely inert gas atmosphere refers to an inert gas atmosphere that does not contain oxygen, hydrogen, or the like at all, and examples thereof include an argon atmosphere and a nitrogen atmosphere.

(4) Joining Step An adhesive paste is applied to the side surface of the honeycomb fired body obtained by the firing step to form an adhesive paste layer, and another honeycomb fired body is sequentially laminated via the adhesive paste layer. .. This procedure is repeated to prepare an aggregate (also referred to as a ceramic block) of the fired honeycomb bodies in which a predetermined number of fired honeycomb bodies are adhered with an adhesive paste. As the adhesive paste, for example, a paste composed of an inorganic binder, an organic binder, inorganic fibers and / or inorganic particles can be used.
The obtained ceramic block may be cut into a predetermined shape by cutting with a diamond cutter or the like.

Examples of the inorganic particles contained in the adhesive paste include carbide particles and nitride particles. Specific examples thereof include silicon carbide particles, silicon nitride particles, and boron nitride particles. These may be used alone or in combination of two or more. Among the inorganic particles, silicon carbide particles having excellent thermal conductivity are preferable.

Examples of the inorganic fiber contained in the adhesive paste include inorganic fiber made of silica-alumina, mullite, alumina, silica and the like. These may be used alone or in combination of two or more. Among the inorganic fibers, alumina fibers are preferable. Further, the inorganic fiber may be a biosoluble fiber.

Further, balloons, spherical acrylic particles, graphite and the like, which are micro hollow spheres containing an oxide-based ceramic as a component, may be added to the adhesive paste, if necessary. The balloon is not particularly limited, and examples thereof include an alumina balloon, a glass microballoon, a shirasu balloon, a fly ash balloon (FA balloon), and a mullite balloon.

[Outer peripheral coat layer forming process]
The outer peripheral coat layer is formed by applying the outer peripheral coat layer paste to the outer periphery of the ceramic block, drying and solidifying the paste.
The honeycomb filter of the present invention can be manufactured by the above procedure.
As the material constituting the outer peripheral coat layer paste, the same material as the adhesive paste can be used. The paste for the outer peripheral coat layer may use a material different from that of the adhesive paste.

In the honeycomb filter of the present invention, it is preferable that the SCR catalyst is supported on the cell partition wall.
When the SCR catalyst is supported on the cell partition wall, for example, the SCR catalyst supporting step shown below may be performed.

[SCR catalyst supporting step]
In the SCR catalyst supporting step, for example, a method of immersing a honeycomb filter in a dispersion liquid containing an SCR catalyst, pulling it up, removing excess dispersion liquid by suction, and then drying it can be mentioned.

The speed at which the gas is circulated by suction into the cells constituting the honeycomb fired body is not particularly limited, but the flow velocity of the gas flowing into the honeycomb filter is preferably 1 to 10 m / s.
Further, when the gas flow velocity in the cell not adjacent to the outer peripheral wall is 1, the ratio of the gas flow velocity (gas flow velocity ratio) in the cell adjacent to the outer peripheral wall on one surface is 0.9 to 1.2. Is preferable.

(Example)
Hereinafter, examples for confirming the effect of the configuration of the honeycomb filter of the present invention will be shown, but the present invention is not limited to these examples.

The gas flow velocity when the gas was flowed into the honeycomb filter of the present invention was simulated and analyzed by the following method.
The simulation was performed using the software "ANSYS Fluent" (general-purpose thermo-fluid analysis software manufactured by Ansys Co., Ltd.).

(Reference example)
As a reference example, the pore ratio is 60.5%, the median diameter D50 of the pores is 20 μm, the thickness of the cell partition wall is 330 μm (13 mil), the cell density is 350 cpsi (pieces / in ² ), and the length in the longitudinal direction is 150 mm. , The cross-sectional dimension in the direction perpendicular to the longitudinal direction is a square of 34.3 mm × 34.3 mm, and the cross-sectional shape of the large-capacity cell extending in the longitudinal direction is a square with a side of 1.15 mm (cross-sectional area 1.3214 mm ² ), small. Data of a honeycomb fired body in which the cross-sectional shape of the capacity cell was a square with a side of 0.91 mm (cross-sectional area: 0.82685 mm ² ) was prepared.
In this data, the ratio of the cross-sectional area of the large-capacity cell adjacent to the outer peripheral wall on one surface to the large-capacity cell not adjacent to the outer peripheral wall is 91.8%, and the small-capacity cell not adjacent to the outer peripheral wall. The ratio of the cross-sectional area of the small-capacity cell adjacent to the outer peripheral wall on one surface was 100%.

(Example 1)
From the reference example, the cross-sectional dimension in the direction perpendicular to the longitudinal direction of the honeycomb fired body is changed to 33.77 mm without changing the thickness of the outer peripheral wall, the thickness of the cell partition wall, and the cell arrangement, and the length per side is changed. By cutting 0.53 mm, the cross-sectional area of the large-capacity cell adjacent to the outer peripheral wall on one surface is 68.7% of the reference example, and the cross-sectional area of the small-capacity cell adjacent to the outer peripheral wall on one surface is the reference example. The data of the honeycomb fired body changed to 73.6% were prepared. The results of simulating the gas flow velocity when gas is sent to the honeycomb fired body at a gas flow velocity of 1 m / s, 5 m / s, and 10 m / s are shown in FIGS. 4 (a), 4 (b), and FIGS. It is shown in 4 (c).
In FIGS. 4 (a), 4 (b) and 4 (c), the horizontal axis is the small capacity cell adjacent to the outer peripheral wall on one surface with respect to the cross-sectional area of the small capacity cell not adjacent to the outer peripheral wall. The ratio of the cross-sectional area (indicated as the area [%] of the small-capacity cell in the figure), and the vertical axis is the ratio of the gas flow velocity of each cell to the flow velocity of the gas sent to the honeycomb fired body (flow velocity). Ratio). Further, the average value of the gas flow rate ratios of the small-capacity cells not adjacent to the outer peripheral wall (indicated as the gas flow rate ratio of the central cell in the figure) is shown by a broken line. Further, the gas flow velocity in the 45 ° direction is a small capacity closest to the other outer peripheral wall orthogonal to the outer peripheral wall to which the cell row is adjacent among the cell rows adjacent to the outer peripheral wall of the honeycomb fired body on one surface. The gas flow velocity in the cell means the gas flow velocity in the 90 ° direction, and the gas flow velocity in the 90 ° direction means the gas flow velocity in the small capacity cell located in the center of the cell row adjacent to the outer peripheral wall of the honeycomb fired body on one surface.

(Example 2)
From the reference example, by changing the cross-sectional dimension of the honeycomb fired body in the direction perpendicular to the longitudinal direction to 33.57 mm without changing the thickness of the outer peripheral wall in the same manner as in the first embodiment, one surface is formed on the outer peripheral wall. Same as in Example 1 except that the cross-sectional area of the adjacent large-capacity cell was changed to 60% of the reference example and the cross-sectional area of the small-capacity cell adjacent to the outer peripheral wall on one surface was changed to 63% of the reference example. The gas flow velocity was simulated in the procedure. The results are shown in FIGS. 4 (a), 4 (b) and 4 (c).

(Comparative Example 1)
From the reference example, the gas flow velocity was simulated by the same procedure as in Example 1 without changing the cross-sectional shapes of the large-capacity cell and the small-capacity cell adjacent to the outer peripheral wall. The results are shown in FIGS. 4 (a), 4 (b) and 4 (c).

(Comparative Example 2)
From the reference example, by changing the cross-sectional dimension of the honeycomb fired body in the direction perpendicular to the longitudinal direction to 34.03 mm without changing the thickness of the outer peripheral wall in the same manner as in the first embodiment, one surface is formed on the outer peripheral wall. Same as in Example 1 except that the cross-sectional area of the adjacent large-capacity cell was changed to 80% of the reference example and the cross-sectional area of the small-capacity cell adjacent to the outer peripheral wall on one surface was changed to 88% of the reference example. The gas flow velocity was simulated in the procedure. The results are shown in FIGS. 4 (a), 4 (b) and 4 (c).

(Comparative Example 3)
From the reference example, by changing the cross-sectional dimension in the direction perpendicular to the longitudinal direction to 33.34 mm without changing the thickness of the outer peripheral wall in the same manner as in the first embodiment, the large size adjacent to the outer peripheral wall on one surface. The gas flow velocity is the same as in Example 1 except that the cross-sectional area of the capacity cell is changed to 50% of the reference example and the cross-sectional area of the small capacity cell adjacent to the outer peripheral wall on one surface is changed to 50% of the reference example. Was simulated. The results are shown in FIGS. 4 (a), 4 (b) and 4 (c).

As shown in FIGS. 4 (a), 4 (b) and 4 (c), the cross-sectional area of the small-capacity cell adjacent to the outer peripheral wall on one surface is adjacent to the outer peripheral wall at any gas flow velocity. When the cross-sectional area of the small-capacity cell is 60 to 80%, the gas flow velocity is approximately the same between the small-capacity cell adjacent to the outer peripheral wall on one surface and the small-capacity cell not adjacent to the outer peripheral wall. It turns out that they are the same.
On the other hand, in the case of Comparative Example 3 in which the ratio of the cross-sectional area of the small-capacity cell adjacent to the outer peripheral wall on one surface to the cross-sectional area of the small-capacity cell not adjacent to the outer peripheral wall is less than 60%, and 80%. In Comparative Examples 1 and 2 exceeding the above, both the gas flow velocity in the 45 ° direction and the gas flow velocity in the 90 ° direction in the small capacity cell adjacent to the outer peripheral wall on one surface are the same as the flow velocity of the small capacity cell not adjacent to the outer peripheral wall. Since the difference is large, it is considered that when the SCR catalyst is carried, an excess SCR catalyst is carried in the vicinity of the small-capacity cell adjacent to the outer peripheral wall on one surface.
From the above results, it is considered that the honeycomb filter of the present invention can exhibit high NOx purification efficiency because the carrier variation of the SCR catalyst can be suppressed.

1 Honeycomb filter 10 Honeycomb fired body 10a Exhaust gas inlet side end 10b Exhaust gas outlet side end 11 Encapsulant 12, 12a, 12b Large capacity cell (exhaust gas introduction cell)
13, 13a, 13b Small capacity cell (exhaust gas emission cell)
15 Outer wall of honeycomb fired body 16 Adhesive layer 17 Ceramic block 18 Outer peripheral coat layer 20 Cell partition S _12a Cross-sectional area of large-capacity cell 12a S _{12b Cross} -sectional area of large-capacity cell 12b S _13a Cross-sectional area of small-capacity cell 13a S _13b Cross-sectional area of small capacity cell 13b

Claims (7)

A porous cell partition that divides a plurality of cells that serve as an exhaust gas flow path, an exhaust gas introduction cell in which an end on the exhaust gas inlet side is opened and an end on the exhaust gas outlet side is sealed, and an exhaust gas outlet side. A honeycomb filter composed of a plurality of honeycomb fired bodies having an exhaust gas discharge cell having an open end and an exhaust gas inlet side end sealed, and a ceramic block bound via an adhesive layer. There,
In a cross section perpendicular to the longitudinal direction of the cell, the plurality of cells are composed of alternately arranged large-capacity cells and small-capacity cells having a cross-sectional area smaller than that of the large-capacity cell.
In the cross section perpendicular to the longitudinal direction of the cell, the cross-sectional area of the large-capacity cell and the small-capacity cell adjacent to the outer peripheral wall on one surface is the disconnection of the large-capacity cell and the small-capacity cell not adjacent to the outer peripheral wall, respectively. 60-80% of the area ,
A honeycomb filter characterized in that the thickness of the outer peripheral wall is constant . The honeycomb filter according to claim 1, wherein the honeycomb fired body is made of silicon carbide. The honeycomb filter according to claim 1 or 2, wherein an SCR catalyst is supported on the cell partition wall. In the cross section perpendicular to the longitudinal direction of the cell, the cross-sectional shape of the large-capacity cell excluding the cell adjacent to the outer peripheral wall is octagonal, and the cross-sectional shape of the small-capacity cell excluding the cell adjacent to the outer peripheral wall is The honeycomb filter according to any one of claims 1 to 3, which is a square. In the cross section perpendicular to the longitudinal direction of the cell, the cross-sectional shape of the large-capacity cell excluding the cell adjacent to the outer peripheral wall is square, and the cross-sectional shape of the small-capacity cell excluding the cell adjacent to the outer peripheral wall is square. The honeycomb filter according to any one of claims 1 to 3. The honeycomb filter according to any one of claims 1 to 5, wherein the cell partition has a porosity of 40 to 65%. The honeycomb filter according to any one of claims 1 to 6, wherein the thickness of the cell partition wall is 150 to 400 μm.

Images