JP6069072B2 - Honeycomb structure and exhaust gas purification device - Google Patents

Description

  The present invention relates to a honeycomb structure and an exhaust gas purification device. More specifically, the present invention relates to a honeycomb structure in which breakage due to thermal stress is effectively prevented and an exhaust gas purification device.

Exhaust gas discharged from internal combustion engines such as automobile engines contains harmful substances such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NO _X ). Catalytic reactions are widely used to reduce such harmful substances and purify exhaust gas. For exhaust gas purification using a catalyst, a honeycomb structure having a catalyst supported thereon is widely adopted. In the honeycomb structure, a honeycomb structure (honeycomb structure) is formed by partition walls that partition and form cells serving as fluid flow paths. By supporting the catalyst on the partition walls of the honeycomb structure, the surface area of the catalyst per volume in the catalyst body is increased, so that the exhaust gas and the catalyst come into contact with each other at a high frequency. As a result, in the honeycomb structure carrying the catalyst, the catalytic reaction is promoted, and the exhaust gas can be purified with high efficiency (for example, Patent Document 1).

Zeolite or vanadium may be used as the catalyst supported on the honeycomb structure. For example, metal-substituted zeolites (e.g., copper ion-exchanged zeolite, iron ion-exchanged zeolite) is used as _the NO _X selective reducing SCR catalyst for the exhaust gas purifying. The catalyst containing at least one kind of noble metal such as Pt, Rh, Pd and at least one kind of alumina, ceria, zirconia is hydrocarbon (HC), carbon monoxide (CO), nitrogen oxide (NO _x ). It is used as a catalyst for purifying water. Alkali metals (Li, Na, K, Cs, etc.) and alkaline earth metals (Ca, Ba, Sr, etc.) are used as NO _X storage catalysts. Such a catalyst is supported on the surface of the partition walls of the honeycomb structure and inside the pores of the partition walls to purify the exhaust gas. In addition, an exhaust gas purifying apparatus in which such a honeycomb structure is housed in a can body having, for example, an inlet through which exhaust gas flows in and an outlet through which purified exhaust gas flows out has been proposed. Hereinafter, as described above, housing the honeycomb structure in the can of the exhaust gas purification apparatus may be referred to as “canning”.

JP 2005-52750 A

  However, when the above-mentioned catalyst is supported on the partition walls of the honeycomb structure, there is a problem that the catalyst is separated from the surface of the partition walls due to a mismatch between the thermal expansion coefficient of the partition walls and the thermal expansion coefficient of the catalyst. was there.

  In addition, when the thermal expansion coefficient of the partition wall is compared with the thermal expansion coefficient of the catalyst, the thermal expansion coefficient of the catalyst is higher, so the thermal expansion coefficient of the partition wall is higher than the thermal expansion coefficient of the partition wall of the conventional honeycomb structure. Attempts have also been made to raise the price. However, when the thermal expansion coefficient of the partition walls is increased, the heat resistance of the honeycomb structure itself is lowered. For example, when such a honeycomb structure is used for purification of exhaust gas discharged from an engine such as an automobile, there is a problem that cracks are likely to occur in the honeycomb structure in an environment exposed to high temperature exhaust gas. It was.

  The present invention has been made in view of the above-described problems, and provides a honeycomb structure and an exhaust gas purification device in which breakage due to thermal stress is effectively prevented.

  In order to solve the above-described problems, the present invention provides the following honeycomb structure and an inspection method for an exhaust gas purification apparatus.

[1] a porous partition wall that flow path to become the first end face from the compartment a plurality of cells extending to a second end surface forming a fluid, and disposed the outer peripheral wall outermost so as to surround the partition wall, the And a catalyst layer containing at least a catalyst component for purifying NO _x supported on the surface of the partition wall, and the thermal expansion coefficient of the partition wall at 40 to 800 ° C. is 1.0 × 10 ^{−6 to} 7.0 ×. A honeycomb structure having a surface roughness of 10 ⁻⁶ / K and a surface roughness of the outer peripheral wall of 0.5 to 4.0 μm.

[2] The honeycomb structure according to [1], wherein the outer peripheral wall has a thickness of 1.0 to 3.0 mm.

[3] The honeycomb structure according to [1] or [2], wherein the outer peripheral wall has a surface subjected to polishing treatment.

[4] The above [1] to [3], wherein the partition wall is made of a material containing as a main component at least one selected from the group consisting of cordierite, silicon carbide, aluminum oxide, aluminum titanate, mullite, and aluminum nitride. The honeycomb structure according to any one of the above.

[ 5 ] A can body having the honeycomb structure according to any one of [1] to [ 4 ] and an inlet through which the exhaust gas flows and an outlet through which the purified exhaust gas flows out, containing the honeycomb structure. And the honeycomb structure is stored in a fixed state in the can while being held by a holding material disposed so as to cover the outer peripheral wall of the honeycomb structure. Purification equipment.

In the honeycomb structure of the present invention, the thermal expansion coefficient at 40 to 800 ° C. of the partition walls is 1.0 × 10 ^{−6 to} 7.0 × 10 ⁻⁶ / K. However, the catalyst is hardly separated from the partition wall. That is, since the thermal expansion coefficient of the partition walls is lowered in accordance with the thermal expansion coefficient of the catalyst, the thermal expansion coefficient can be prevented from being unbalanced (mismatch). Therefore, the honeycomb structure of the present invention can be used very suitably as a catalyst carrier for supporting a catalyst. In addition, since the honeycomb structure of the present invention has a surface roughness of the outer peripheral wall surface of 0.5 to 4.0 μm, the honeycomb structure is accommodated when the honeycomb structure is housed in the can of the exhaust gas purification apparatus. Surface pressure is applied evenly to the outer peripheral wall of the body. For this reason, it becomes possible to apply a large surface pressure to the outer peripheral wall of the honeycomb structure, and even if the thermal expansion coefficient of the partition walls is increased, breakage such as cracks can be made difficult to occur. That is, by applying an even and large surface pressure to the outer peripheral wall of the honeycomb structure to prevent the honeycomb structure from being damaged, and reducing the surface roughness of the outer peripheral wall surface to a predetermined numerical range. Further, damage due to the surface pressure applied to the outer peripheral wall can be effectively prevented.

An embodiment of the honeycomb structure is a perspective view schematically showing. One embodiment of the honeycomb structure is a plan view schematically showing a first end face. One embodiment of the honeycomb structure is a cross-sectional view schematically showing a cross section parallel to the cell extending direction. It is a perspective view which shows typically other embodiment of the honeycomb structure of this invention. It is a top view which shows typically the 1st end surface of other embodiment of the honeycomb structure of this invention. It is sectional drawing which shows typically the cross section parallel to the cell extending direction of other embodiment of the honeycomb structure of this invention. It is sectional drawing which shows typically the cross section parallel to the cell extending direction of one Embodiment of the exhaust gas purification apparatus of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be added without departing from the scope of the present invention.

(1) Honeycomb structure:
First, a description will be given of an embodiment of a honeycomb structure. As shown in FIGS. 1 to 3, the honeycomb structure of the present embodiment includes a porous partition wall 1 that partitions and forms a plurality of cells 2 extending from a first end surface 11 to a second end surface 12 serving as a fluid flow path. And an outer peripheral wall 3 disposed on the outermost periphery so as to surround the partition wall 1. And in this honeycomb structure 100, the thermal expansion coefficient at 40 to 800 ° C. of the partition walls 1 is 1.0 × 10 ^{−6 to} 7.0 × 10 ⁻⁶ / K. Furthermore, the honeycomb structure 100 has a surface roughness of the outer peripheral wall 3 of 0.5 to 4.0 μm.

Such a honeycomb structure 100 is one in which breakage of the honeycomb structure 100 due to thermal stress is effectively prevented. That is, since the honeycomb structure 100 of the present embodiment has a surface roughness of the outer peripheral wall 3 of 0.5 to 4.0 μm, the surface pressure of the honeycomb structure 100 is equal to the outer peripheral wall 3 of the honeycomb structure 100. Can be multiplied. Therefore, for example, when the honeycomb structure 100 is housed in the can of the exhaust gas purification device and used to purify harmful components in the exhaust gas, the honeycomb structure 100 is evenly distributed with respect to the outer peripheral wall 3 of the honeycomb structure 100. It can apply a certain surface pressure. Therefore, it is possible to apply a large surface pressure to the outer peripheral wall 3 of the honeycomb structure 100, and even if the thermal expansion coefficient of the partition wall 1 is increased, breakage such as cracks hardly occurs. That is, the honeycomb structure 100 includes the partition wall 1 having a high thermal expansion coefficient that is easily damaged by thermal expansion. On the other hand, by reducing the surface roughness of the outer peripheral wall 3, the outer peripheral wall during thermal expansion is reduced. The stress applied to 3 can be evenly dispersed to prevent the honeycomb structure 100 from being damaged. For example, when the surface roughness of the surface of the outer peripheral wall 3 is more than 4.0 μm, stress is not uniformly applied to the surface of the outer peripheral wall 3 when used in the can of the exhaust gas purification device, Local stress concentrations may occur. In the partition wall 1 having a high thermal expansion coefficient such as a thermal expansion coefficient of 1.0 × 10 ^{−6 to} 7.0 × 10 ⁻⁶ / K, the amount of thermal expansion increases even if the temperature is low. The honeycomb structure may be damaged by stress concentration. The stress applied to the outer peripheral wall 3 described above is, for example, stress generated when a holding material used to hold and fix the outer peripheral wall 3 in the can body tries to press down the thermal expansion of the outer peripheral wall 3. That is.

Further, the honeycomb structure 100 of the present embodiment can be suitably used as a catalyst carrier for supporting a catalyst for purifying harmful components in exhaust gas discharged from an internal combustion engine such as an automobile engine. In the conventional honeycomb structure, since the difference between the thermal expansion coefficient of the partition walls and the thermal expansion coefficient of the catalyst is large, the catalyst layer made of the catalyst supported on the partition walls may be peeled off due to the thermal expansion of the partition walls. It was. In particular, when a catalyst such as alumina, zeolite, or vanadium was supported on the partition walls, the separation of the catalyst layer was extremely remarkable. The thermal expansion coefficient of catalysts such as alumina, zeolite, and vanadium was higher than the thermal expansion coefficient of the partition walls in the conventional honeycomb structure. Therefore, by setting the thermal expansion coefficient of the partition to 1.0 × 10 ^{−6 to} 7.0 × 10 ⁻⁶ / K, the thermal expansion coefficient of the partition is brought close to the thermal expansion coefficient of the catalyst, and the catalyst is supported on the partition. Even in such a case, peeling of the catalyst layer made of the catalyst was suppressed.

Here, FIG. 1 is a perspective view schematically showing one embodiment of a honeycomb structure. 2, one embodiment of the honeycomb structure is a plan view schematically showing a first end face. 3, one embodiment of the honeycomb structure is a cross-sectional view schematically showing a cross section parallel to the cell extending direction.

  There is no particular limitation on the shape of the honeycomb structure. For example, as the shape of the honeycomb structure, the end surface of the honeycomb structure may be a cylindrical shape (cylindrical shape), the end surface may be an oval cylindrical shape, and the end surface may be a polygonal cylindrical shape. Examples of the polygon include a quadrangle, a pentagon, a hexagon, a heptagon, and an octagon. 1 to 3 show examples in which the honeycomb structure has a cylindrical shape with a circular end surface.

  As described above, the honeycomb structure 100 includes the porous partition wall 1 and the outer peripheral wall 3 disposed on the outermost periphery so as to surround the partition wall 1. The outer peripheral wall 3 may be formed together with the partition walls 1 when the honeycomb formed body is extruded in the process of manufacturing the honeycomb structure 100. Further, it is not necessary to form the outer peripheral wall at the time of extrusion molding. For example, the outer peripheral wall 3 can be formed by coating a ceramic material on the outer peripheral portion of the partition wall 1 that defines the cell 2. Further, the outer peripheral portion of the honeycomb structure 100 can be ground and removed once, and the outer peripheral wall 3 can be formed by applying a ceramic material so as to surround the partition wall 1.

  As described above, the outer peripheral wall 3 has a surface roughness of 0.5 to 4.0 μm. The surface roughness of the outer peripheral wall can be obtained by measuring the arithmetic average roughness in the axial direction with a PGI-type roughness measuring machine manufactured by Taylor Hobson. The axial direction is a direction from the first end face of the honeycomb structure toward the second end face. The surface roughness is preferably measured at, for example, three locations near the end portion on the first end surface side, near the central portion in the axial direction, and near the end portion on the second end surface side. Specifically, it is more preferable to measure at three positions of 45 ° in the circumferential direction of the honeycomb structure, that is, the end portion on the first end surface side of the side surface, the central portion in the axial direction, and the end portion on the second end surface side. . The surface roughness of the outer peripheral wall 3 is preferably 0.8 to 3.0 [mu] m, and more preferably 0.8 to 2.6 [mu] m. When the surface roughness of the outer peripheral wall 3 exceeds 4.0 μm, the surface roughness of the outer peripheral wall 3 is too rough, and the stress applied to the surface of the outer peripheral wall 3 is not evenly distributed and a large surface pressure is applied. The outer peripheral wall 3 may be damaged. Although it is preferable to make the surface roughness of the outer peripheral wall 3 smaller, from the viewpoint of cost and time required for the surface processing of the outer peripheral wall 3 at the time of manufacture, 0.5 μm was set as the lower limit.

  The outer peripheral wall 3 is preferably one in which the surface of the outer peripheral wall 3 is polished. There is no restriction | limiting in particular about the specific method of grinding | polishing processing, What is necessary is just the grinding | polishing processing which can make the surface roughness of the surface of the outer peripheral wall 3 into 0.5-4.0 micrometers. For example, examples of the polishing treatment include a method of polishing the outer wall surface with sandpaper or the like.

  In the honeycomb structure 100 of the present embodiment, the thickness of the outer peripheral wall 3 is preferably 1.0 to 3.0 mm, more preferably 1.0 to 2.5 mm, and 1.5 to Particularly preferred is 2.5 mm. By providing the outer peripheral wall 3 having such a thickness, even if the thermal expansion coefficient of the partition wall 1 is large, the isostatic strength of the honeycomb structure is improved and it is less likely to be damaged by thermal shock. Furthermore, it is possible to prevent an increase in pressure loss when a fluid (for example, exhaust gas) flows through the cells 2 while maintaining the isostatic strength of the honeycomb structure moderately. For example, when the thickness of the outer peripheral wall 3 is less than 1.0 mm, it may be difficult to apply a large surface pressure when the honeycomb structure is housed in the can of the exhaust gas purification apparatus. Therefore, the effect of improving the heat resistance of the honeycomb structure may be difficult to express. On the other hand, if the thickness of the outer peripheral wall 3 exceeds 3.0 mm, the heat capacity may increase due to the increase in mass, and the temperature rise performance may deteriorate.

  The isostatic strength of the honeycomb structure is not particularly limited, but is preferably 1.5 MPa or more, more preferably 2.0 MPa or more, and particularly preferably 3.0 MPa or more. In addition, the measurement of isostatic strength can be performed based on the isostatic breaking strength test prescribed | regulated by M505-87 of the automobile specification (JASO specification) by the Japan Society for Automotive Engineers. The isostatic fracture strength test is a test in which a honeycomb structure is placed in a rubber cylindrical container, covered with an aluminum plate, and isotropically compressed under water.

As described above, the thermal expansion coefficient at 40 to 800 ° C. of the partition wall 1 is 1.0 × 10 ^{−6 to} 7.0 × 10 ⁻⁶ / K, and 1.0 × 10 ^{−6 to} 5.0 ×. It is preferably 10 ⁻⁶ / K, and more preferably 1.0 × 10 ^{−6 to} 3.0 × 10 ⁻⁶ / K. Hereinafter, the thermal expansion coefficient at 40 to 800 ° C. of the partition wall 1 may be simply referred to as “thermal expansion coefficient of the partition wall 1”. When the thermal expansion coefficient of the partition wall 1 is less than 1.0 × 10 ⁻⁶ / K, the catalyst layer is easily peeled off when the catalyst layer is formed on the surface of the partition wall 1. Further, if the thermal expansion coefficient of the partition wall 1 is more than 7.0 × 10 ⁻⁶ / K, the thermal expansion of the partition wall 1 becomes excessive, and the surface roughness of the surface of the outer peripheral wall 3 is not limited to the above numerical range. May not be sufficiently suppressed.

  In the honeycomb structure 100 of the present embodiment, the partition wall 1 is made of a material containing as a main component at least one selected from the group consisting of cordierite, silicon carbide, aluminum oxide, aluminum titanate, mullite, and aluminum nitride. Is preferred. By using such a material, a honeycomb structure having excellent heat resistance is obtained. The above-mentioned “main component” means that the component contained in the material constituting the partition wall 1 is 30% by mass or more. The partition walls are preferably made of a material containing at least 40% by mass of at least one selected from the above group, and more preferably made of a material containing 50% by mass or more. In addition, for example, the partition wall 1 made of such a material can be adjusted to have a desired coefficient of thermal expansion by adjusting a firing temperature when firing a formed body in which a predetermined forming raw material is formed into a honeycomb shape. it can.

  The thickness of the partition wall 1 is preferably 0.5 to 4.0 μm, more preferably 0.8 to 3.0 μm, and particularly preferably 0.8 to 2.6 μm. By setting the partition wall thickness within the above numerical range, the pressure loss can be reduced while maintaining the strength of the partition wall 1.

The cell density of the honeycomb structure 100 is preferably 15 to 140 cells / cm ² . By setting the cell density within the above numerical range, an increase in pressure loss can be effectively prevented. Further, when the catalyst is supported on the partition walls 1 of the honeycomb structure 100, high purification performance can be obtained. The cell density of the honeycomb structure means the number of cells per unit area in a cross section perpendicular to the cell extending direction. The cell density of the honeycomb structure is more preferably 45 to 125 cells / cm ² , and particularly preferably 45 to 65 cells / cm ² .

  The porosity of the partition wall 1 is preferably 25 to 70%, more preferably 35 to 65%, and particularly preferably 45 to 60%. If the porosity is less than 25%, the substrate may not be filled with a sufficient amount of catalyst. If the porosity is higher than 70%, the strength of the honeycomb structure 100 may be lowered. The porosity of the partition wall 1 can be measured with a mercury porosimeter. As a mercury porosimeter, the product name: Autopore 9500 made by Micromeritics can be mentioned.

  Examples of the shape of the cell in the cross section orthogonal to the cell extending direction include a quadrangle, a hexagon, an octagon, a circle, and a combination thereof. Among squares, squares and rectangles are preferable.

  The length from the first end surface 11 to the second end surface 12 of the honeycomb structure 100 is preferably 76.2 to 203.2 mm, and more preferably 76.2 to 152.4 mm. However, the length from the first end surface 11 to the second end surface 12 of the honeycomb structure 100 is not limited to the above numerical range, and when the honeycomb structure 100 is used in various exhaust gas purification apparatuses, What is necessary is just to select suitably so that optimal purification performance may be obtained.

  The size in a cross section perpendicular to the direction extending from the first end surface 11 to the second end surface 12 of the honeycomb structure 100 is not particularly limited, and is optimal when the honeycomb structure 100 is used in various exhaust gas purification apparatuses. May be appropriately selected so as to obtain a proper purification performance. In the honeycomb structure 100 of the present embodiment, when the cross-sectional shape is circular, the cross-sectional diameter is preferably 25.4 to 330.2 mm, and 143.8 to 266. More preferably, it is 7 mm.

  Although not shown, the honeycomb structure may be a segment structure honeycomb structure. Specifically, examples of the honeycomb structure having a segment structure include a honeycomb structure in which a plurality of honeycomb segments are joined in a state of being arranged adjacent to each other so that their side faces face each other. The honeycomb segment has a porous partition wall defining a plurality of cells serving as a fluid flow path extending from the first end surface to the second end surface, and an outer wall disposed so as to surround the partition wall. An outer peripheral wall is disposed on the outermost periphery of the joined body obtained by joining a plurality of honeycomb segments. In addition, by processing the outer peripheral portion of the joined body obtained by joining a plurality of honeycomb segments by grinding or the like, and making the shape of the cross section perpendicular to the cell extending direction circular or the like, the ceramic material is applied to the outermost periphery. An outer peripheral wall may be arranged. Even in such a so-called segment structure honeycomb structure, the same effects as the so-called integral honeycomb structure as shown in FIGS. 1 to 3 can be obtained. A honeycomb structure having such a segment structure is suitable when the cross-sectional diameter is 266.7 mm or more.

  The outer peripheral wall 3 may be the same material as the partition wall 1 or a different material. For example, the outer peripheral wall 3 is preferably made of a material containing as a main component at least one selected from the group consisting of cordierite, silicon carbide, aluminum oxide, aluminum titanate, mullite, and aluminum nitride. By using such a material, a honeycomb structure having excellent heat resistance is obtained.

Next, another embodiment of the honeycomb structure of the present invention will be described. As shown in FIGS. 4 to 6, the honeycomb structure of the present embodiment is a honeycomb structure 200 further including a catalyst layer 60 that is supported on the surface of the partition wall 1 and that includes a catalyst component 60 that contains at least a NO _x purification catalyst. is there. About the structure of the porous partition wall 1 and the outer peripheral wall 3, it is comprised similarly to the honeycomb structure 100 shown to FIGS. 1-3 demonstrated until now. That is, the partition wall 1 partitions and forms a plurality of cells 2 extending from the first end surface 11 to the second end surface 12 serving as a fluid flow path. The outer peripheral wall 3 is disposed on the outermost periphery so as to surround the partition wall 1. Also in the honeycomb structure 200 of the present embodiment, the thermal expansion coefficient at 40 to 800 ° C. of the partition walls 1 is 1.0 × 10 ^{−6 to} 7.0 × 10 ⁻⁶ / K, and the surface of the outer peripheral wall 3 is The surface roughness is 0.5 to 4.0 μm.

  Here, FIG. 4 is a perspective view schematically showing another embodiment of the honeycomb structure of the present invention. FIG. 5 is a plan view schematically showing a first end face of another embodiment of the honeycomb structure of the present invention. FIG. 6 is a cross-sectional view schematically showing a cross section parallel to the cell extending direction of another embodiment of the honeycomb structure of the present invention.

The honeycomb structure 200 shown in FIGS. 4 to 6 has a catalyst layer 60 disposed on the surface of the partition wall 1 of the honeycomb structure 100 shown in FIGS. There is no particular limitation on the type of catalyst, but as described above, a catalyst for purifying at least hydrocarbon (HC), carbon monoxide (CO), nitrogen oxide (NO _x ), or for purifying NO _x. It is preferable that the catalyst is. As such a catalyst, for example, a catalyst containing at least one selected from the group consisting of noble metals such as Pt, Rh, Pd and at least one selected from the group consisting of alumina, ceria, zirconia, or zeolite, A catalyst containing at least one selected from the group consisting of vanadium can be mentioned. In particular, in the honeycomb structure 200 of the present embodiment, zeolite and vanadium are preferable examples from the viewpoint of suppressing mismatch between the thermal expansion coefficient of the partition walls 1 and the thermal expansion coefficient of the catalyst layer 60. it can.

  There is no particular limitation on the amount of catalyst supported on the partition walls 1 of the honeycomb structure 200 (hereinafter referred to as “the amount of catalyst supported”). The amount of the catalyst supported is preferably 50 to 300 g / L, more preferably 100 to 300 g / L, and particularly preferably 150 to 300 g / L.

  When the amount of the catalyst supported exceeds 300 g / L, it is possible to expect improvement in purification performance by the honeycomb structure 200. On the other hand, the area of the opening portion of the cell 2 is reduced, and the pressure loss is increased. May end up. Further, when the catalyst loading is less than 50 g / L, the purification performance by the honeycomb structure 200 may not be sufficiently exhibited. In the present specification, the supported amount (g / L) is the amount (g) of the catalyst supported per unit volume (1 L) of the partition walls 1 of the honeycomb structure 200. The method for supporting the catalyst on the partition wall 1 is not particularly limited, and can be performed according to a conventionally known method.

  Next, a method for manufacturing the honeycomb structure of the present embodiment will be described.

  When producing a honeycomb structure, first, a forming raw material containing a ceramic raw material is mixed and kneaded to obtain a clay. As the ceramic raw material, it is preferable to use at least one selected from the group consisting of cordierite, silicon carbide, aluminum oxide, aluminum titanate, mullite, and aluminum nitride. The cordierite forming raw material is a ceramic raw material blended so as to have a chemical composition that falls within the range of 42 to 56% by mass of silica, 30 to 45% by mass of alumina, and 12 to 16% by mass of magnesia. The cordierite forming raw material is fired to become cordierite.

  The forming raw material is preferably prepared by further mixing the ceramic raw material with a dispersion medium, an organic binder, an inorganic binder, a surfactant, a pore former, and the like. The composition ratio of each raw material is not particularly limited, and is preferably a composition ratio in accordance with the structure and material of the honeycomb structure to be manufactured.

  Water can be used as the dispersion medium. It is preferable that the addition amount of a dispersion medium is 10-30 mass parts with respect to 100 mass parts of ceramic raw materials.

  The organic binder is preferably methyl cellulose, hydroxypropyl methyl cellulose, hydroxypropyl ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, or a combination thereof. Moreover, the addition amount of the organic binder is preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the ceramic raw material.

  As the surfactant, ethylene glycol, dextrin, fatty acid soap, polyalcohol and the like can be used. These may be used individually by 1 type and may be used in combination of 2 or more type. The addition amount of the surfactant is preferably 0.5 to 2 parts by mass with respect to 100 parts by mass of the ceramic raw material.

  As the pore former, resin particles, starch, carbon and the like can be used. The pore former is for forming pores in the partition walls of the honeycomb structure to be manufactured. The amount of pore former added is preferably adjusted as appropriate in consideration of the average pore diameter and porosity of the partition walls of the honeycomb structure to be produced.

  There is no restriction | limiting in particular as a method of kneading | mixing a shaping | molding raw material and forming a clay, For example, the method of using a kneader, a vacuum clay kneader, etc. can be mentioned.

  Next, the obtained clay is formed to form a cylindrical honeycomb formed body. The honeycomb formed body has partition walls that form a plurality of cells and an outer peripheral wall. A method for forming a kneaded clay to form a honeycomb formed body is not particularly limited, and a known forming method such as extrusion molding or injection molding can be used. For example, a preferable example includes a method of extrusion molding using a die for extrusion molding having a desired cell shape, partition wall thickness, and cell density.

  Next, the obtained honeycomb formed body is dried. Examples of the drying method include hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, freeze drying, and the like. Among them, it is preferable to perform dielectric drying, microwave drying, or hot air drying alone or in combination.

  Next, the honeycomb formed body is fired. Prior to firing the honeycomb formed body, the honeycomb formed body is preferably calcined. Calcination is performed for degreasing. There is no restriction | limiting in particular about the method of calcination. For example, it is sufficient that at least a part of the organic matter in the honeycomb formed body can be removed. Examples of the organic material include an organic binder, a surfactant, and a pore former. The combustion temperature of the organic binder is about 100 to 300 ° C. For this reason, calcination is preferably performed at about 200 to 1000 ° C. for about 10 to 100 hours in an oxidizing atmosphere.

  The firing of the honeycomb formed body is performed in order to sinter and densify the forming raw material constituting the calcined formed body to ensure a predetermined strength. Since the firing conditions differ depending on the type of molding raw material, appropriate conditions may be selected according to the type. For example, when the cordierite forming raw material is used, the firing temperature is preferably 1350 to 1440 ° C. In addition, the firing time is preferably 3 to 10 hours as the keep time at the maximum temperature. Examples of the apparatus for performing calcination and main firing include an electric furnace and a gas furnace. Thus, a honeycomb structure can be obtained by calcining and firing the honeycomb formed body. Adjustment of the thermal expansion coefficient of a partition can be performed by adjustment of the baking temperature mentioned above. For example, by performing firing at a moderate temperature rise rate, the resulting honeycomb structure tends to have a high thermal expansion coefficient. Specifically, a honeycomb structure having a high thermal expansion coefficient can be obtained by setting the heating rate to a moderate temperature of 5 to 40 ° C./hr and setting the firing temperature to 1300 to 1400 ° C. The heating rate is preferably 5 ° C./hr, and the firing temperature is preferably 1400 ° C.

  Next, the surface of the outer peripheral wall of the obtained honeycomb structure is polished so that the surface roughness of the outer peripheral wall surface is 0.5 to 4.0 μm. Specifically, for example, the surface of the outer peripheral wall is polished using sandpaper or the like. The sandpaper count is preferably 100 to 1000.

As described above, the thermal expansion coefficient of the partition walls at 40 to 800 ° C. is 1.0 × 10 ^{−6 to} 7.0 × 10 ⁻⁶ / K, and the surface roughness of the outer peripheral wall surface is 0.00. A honeycomb structure having a thickness of 5 to 4.0 μm can be produced.

(2) Exhaust gas purification device:
Next, an embodiment of the exhaust gas purification apparatus of the present invention will be described. The exhaust gas purifying apparatus of the present embodiment includes the honeycomb structure described so far, and a can body that houses the honeycomb structure and has an inlet port through which exhaust gas flows and an outlet port through which purified exhaust gas flows out. It is provided. In the exhaust gas purification apparatus of the present embodiment, the honeycomb structure is stored in a state of being fixed in the can body while being held by a holding material arranged so as to cover the outer peripheral wall of the honeycomb structure. ing.

  Hereinafter, the exhaust gas purification apparatus of the present embodiment will be described in more detail with reference to FIG. FIG. 7 is a cross-sectional view schematically showing a cross section parallel to the cell extending direction of one embodiment of the exhaust gas purifying apparatus of the present invention. The exhaust gas purification apparatus 300 includes the honeycomb structure 200 shown in FIGS. 4 to 6 and the can body 21 in which the honeycomb structure 200 is accommodated. The can 21 has an inlet 22 through which exhaust gas flows and an outlet 23 through which purified exhaust gas flows out. A holding material 31 for holding the honeycomb structure 200 in the can 21 is disposed on the surface of the outer peripheral wall 3 of the honeycomb structure 200. The honeycomb structure 200 is press-fitted into the can body 21 while being held by the holding material 31 and is housed in a state where it is fixed within the can body 21. Hereinafter, the portion in which the honeycomb structure 200 is accommodated in the can body 21 is referred to as the body portion 24 of the can body 21. Further, fasteners 32 and 32 are disposed around the first end surface 11 and the second end surface 12 of the honeycomb structure 200. The honeycomb structure 200 is fixed by the fasteners 32, 32 so as not to move in the gas G flow direction in the can 21.

The honeycomb structure 200 is disposed on the outermost periphery so as to surround the partition walls 1 and the porous partition walls 1 that form a plurality of cells 2 extending from the first end surface 11 to the second end surface 12 serving as a fluid flow path. And an outer peripheral wall 3 provided. A catalyst layer 60 is disposed on the surface of the partition wall 1. As described above, the honeycomb structure 200 has a partition wall 1 with a coefficient of thermal expansion of 1.0 × 10 ^{−6 to} 7.0 × 10 ⁻⁶ / K, and the surface roughness of the outer peripheral wall 3. Is 0.5 to 4.0 μm. Thus, the honeycomb structure 200 is configured such that the partition wall 1 has a high coefficient of thermal expansion and a difference from the coefficient of thermal expansion of the catalyst layer 60 is small. Therefore, the honeycomb structure 200 is exposed to a high temperature. Even in this case, peeling of the catalyst layer 60 from the partition wall 1 can be effectively prevented. Further, when the honeycomb structure 100 housed in the can 21 is exposed to a high temperature, the honeycomb structure 100 tends to thermally expand toward the outside of the outer peripheral wall 3. On the other hand, as described above, since the honeycomb structure 100 is press-fitted into the can 21 while being held by the holding material 31, the honeycomb structure 100 is pressed against the surface of the outer peripheral wall 3 from the holding material 31. The stress which tries to suppress the thermal expansion of the structure 100 works. Since the surface of the outer peripheral wall 3 has a very small surface roughness and is a smooth surface as described above, the stress applied from the holding material 31 is uniformly applied to the entire surface of the outer peripheral wall 3. Become. For this reason, even if a stress is exerted from the holding material 31 to suppress the thermal expansion, the honeycomb structure 200 is hardly damaged. That is, the exhaust gas purifying apparatus 300 uses the honeycomb structure 200 having the partition walls 1 having a high thermal expansion coefficient, and reduces the surface roughness of the outer peripheral wall 3 to uniformly disperse the stress applied during the thermal expansion. Damage to the structure 200 is prevented.

The honeycomb structure 200 accommodated in the can body 21 of the exhaust gas purification apparatus 300 is not limited to the honeycomb structure 200 shown in FIGS. That is, in the honeycomb structure 200, the thermal expansion coefficient of the partition wall 1 is 1.0 × 10 ^{−6 to} 7.0 × 10 ⁻⁶ / K, and the surface roughness of the surface of the outer peripheral wall 3 is 0.5. It should just be -4.0 micrometers.

  The can body 21 has an inlet port 22 and an outlet port 23 so as to conform to the aperture of the engine exhaust manifold and the aperture of the exhaust system from which the purified exhaust gas is discharged (for example, the aperture of the exhaust pipe, the muffler, etc.). Is formed.

  The body portion 24 of the can body 21 and the inlet 22 and the outlet 23 of the can body 21 include an expanded tube portion whose diameter gradually increases from the inlet 22 and a narrow tube portion whose diameter gradually decreases toward the outlet 23. Furthermore, you may have. For example, when the diameter of the engine exhaust manifold, exhaust pipe, muffler, etc. and the diameter of the body portion 24 of the can body 21 are the same, the above-described expanded tube portion and narrow tube portion may not be particularly provided.

  For example, the material of the can body 21 is preferably made of stainless steel, and is particularly preferably made of chromium or chromium / nickel stainless steel.

  Examples of a method for holding the honeycomb structure 200 inside the trunk portion 24 of the can body 21 include the following methods. That is, a method of wrapping the surface of the outer peripheral wall 3 of the honeycomb structure 200 with a holding material 31 such as a ceramic fiber mat and press-fitting into the body portion 24 of the can body 21 can be exemplified. By using the holding material 31 such as a ceramic fiber mat, the honeycomb structure 200 can be protected from external impacts and insulated. Moreover, by using such a holding material 31, it becomes easy to apply stress evenly to the surface of the outer peripheral wall 3 having a small surface roughness. After the honeycomb structure 200 is held inside the trunk portion 24 of the can body 21, a previously produced expanded tube portion or narrow tube portion may be welded to the trunk portion 24. Moreover, you may create a pipe expansion part or a narrow pipe part by spinning the can 21. The can body can be manufactured using a conventionally known metal processing method using stainless steel or the like.

  As the holding material 31, the ceramic fiber mat described above can be cited as a suitable example. Such a ceramic fiber mat is easy to obtain and process, and has sufficient heat resistance and cushioning properties. Examples of the ceramic fiber mat include a non-thermal expansion mat substantially free of vermiculite, a low thermal expansion mat including a small amount of vermiculite, and the like. In addition, it is preferable that the surface of the holding material 31 is in close contact with the surface of the outer peripheral wall. For example, in the above-described ceramic fiber mat or the like, fine fibers or excellent flexibility are preferable.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples.

Example 1
In Example 1, an exhaust gas purification apparatus including a honeycomb structure and a can body that accommodates the honeycomb structure and has an inlet port through which exhaust gas flows and an outlet port through which purified exhaust gas flows out was manufactured.

  In Example 1, first, a honeycomb structure used for an exhaust gas purification apparatus was produced. Specifically, first, a kneaded material for forming a honeycomb formed body was prepared using a forming raw material containing a ceramic raw material. As a ceramic raw material, a cordierite forming raw material was used. A clay for molding was prepared by adding a dispersion medium, an organic binder, a dispersant and a pore former to the cordierite forming raw material. The addition amount of the dispersion medium was 10 parts by mass with respect to 100 parts by mass of the cordierite forming raw material. The addition amount of the organic binder was 10 parts by mass with respect to 100 parts by mass of the cordierite forming raw material. The addition amount of the pore former was 20 parts by mass with respect to 100 parts by mass of the cordierite forming raw material. The obtained ceramic forming raw material was kneaded using a kneader to obtain clay.

  Next, the obtained kneaded material was extruded using a vacuum extrusion molding machine to obtain a honeycomb formed body. Next, the honeycomb formed body was dried by high frequency dielectric heating and then dried at 120 ° C. for 2 hours using a hot air dryer. Then, it fired at 1350-1440 degreeC for 10 hours, and obtained the honeycomb structure.

  Thereafter, the surface of the outer peripheral wall of the honeycomb structure was polished. This polishing process was performed by polishing the surface of the outer peripheral wall using sandpaper or the like.

The obtained honeycomb structure has a length from the first end face to the second end face of the honeycomb structure of 152.4 mm, and a diameter of a cross section perpendicular to the direction extending from the first end face to the second end face is 143.8 mm. It was cylindrical. This honeycomb structure had a partition wall thickness of 165 μm and a cell density of 46.5 cells / cm ² . Further, the porosity of the partition walls was 50%, and the thermal expansion coefficient of the partition walls was 3.5 × 10 ⁻⁶ / K. The porosity of the partition wall is a value measured by “Autopore III 9420 (trade name)” manufactured by Micromeritics. Further, the thickness of the outer peripheral wall of the honeycomb structure was 2.1 mm, and the surface roughness of the outer peripheral wall of the honeycomb structure was 1.7 μm. The surface roughness of the outer peripheral wall is a value measured by a PGI type roughness measuring machine manufactured by Taylor Hobson.

  Next, a catalyst was supported on the partition walls of the obtained honeycomb structure. ZSM-5 zeolite was used as the catalyst. The amount of catalyst supported was 150 g / L. The catalyst loading (g / L) refers to the amount (g) of the catalyst supported per unit volume (1 L) of the honeycomb structure.

  Next, a holding material is disposed so as to cover the outer peripheral wall of the honeycomb structure in which the catalyst is supported on the partition walls, and the honeycomb structure is accommodated in the inside of the can body having the inlet, the trunk, and the outlet. did. Then, the expanded pipe part and the narrow pipe part of the can were formed by spinning process, and the exhaust gas purification apparatus of Example 1 was manufactured. A ceramic fiber mat was used as the holding material. When the honeycomb structure was housed in the can, the distance from the inner surface of the can to the outer peripheral wall surface of the honeycomb structure was 0.6 mm. In other words, the holding material (ceramic fiber mat) is filled in the intervals described above. Inside the body of the can body, the first end surface of the honeycomb structure is positioned on the inlet side of the can body, and the second end surface of the honeycomb structure is positioned on the outlet side of the can body did.

Table 1 shows the configuration of the honeycomb structure used in the exhaust gas purification apparatus of Example 1. That is, “thickness of partition wall (μm)”, “cell density (pieces / cm ² )”, “porosity (%)”, “thermal expansion coefficient (× 10 ⁻⁶ / K)”, “thickness of outer peripheral wall” Table 1 shows “thickness (mm)” and “surface roughness of outer peripheral wall (μm)”.

  Moreover, about the exhaust gas purification apparatus of Example 1, the heat resistant temperature (degreeC) was measured with the following method. Furthermore, a vibration resistance test was performed on the exhaust gas purification apparatus of Example 1 by the following method. Table 1 shows the measurement results of the heat resistance temperature (° C) and the test results of the vibration resistance test.

[Heat-resistant temperature (℃)]
The honeycomb structure in the can was left in an electric furnace having a high temperature atmosphere for 1 hour, and then taken out to a room temperature atmosphere to confirm the occurrence of cracks with the naked eye. The heat-resistant temperature (° C.) of the honeycomb structure of the exhaust gas purification apparatus was measured from the temperature difference between the heating temperature of the electric furnace and room temperature.

[Vibration resistance test]
The honeycomb structure in the can body was vibrated at 15 G and 150 Hz, and heated air at a holding time of 10 minutes at 100 ° C. and a holding time of 10 minutes at 500 ° C. was passed through the carrier (honeycomb structure), The vibration resistance test of the exhaust gas purification apparatus was performed 100 cycles. The maximum temperature increase / decrease rate was 10 ° C./second. The flow rate of the heated air was 5 Nm ³ / min. A saucer was placed on the bottom of the honeycomb structure, and after a vibration resistance test, the presence or absence of catalyst separation was confirmed. The case where the catalyst did not deviate was determined as “good”, and the case where the catalyst deviated was determined as “impossible”.

(Examples 2-12 and Comparative Examples 1-7)
Except for producing a honeycomb structure configured such that the partition wall thickness, cell density, porosity, coefficient of thermal expansion, outer peripheral wall thickness, and outer peripheral wall surface roughness are the values shown in Table 1. An exhaust gas purification apparatus was manufactured in the same manner as in Example 1. In addition, about Examples 7-9 and Comparative Examples 4-6, the thermal expansion coefficient of the partition was set to 6.7 * 10 < ^-6 > / K by using mullite as a main raw material. About Comparative Examples 1-3, the thermal expansion coefficient of the partition was set to 0.9 * 10 < ^-6 > / K by using cordierite. For Comparative Example 7, the thermal expansion coefficient of the partition walls was 8.0 × 10 ⁻⁶ / K by using aluminum oxide as the main raw material. The surface roughness of the outer peripheral wall was adjusted by changing the sandpaper count.

  For the exhaust gas purifying apparatuses of Examples 2 to 12 and Comparative Examples 1 to 7, the heat resistant temperature (° C.) was measured in the same manner as in Example 1, and a vibration resistance test was performed. Table 1 shows the measurement results of the heat resistance temperature (° C) and the test results of the vibration resistance test.

(result)
As shown in Table 1, in the exhaust gas purifying apparatuses of Examples 1 to 12, all of the heat resistance temperatures of the honeycomb structures were 600 ° C. or higher. If the heat resistance temperature of the honeycomb structure is 600 ° C. or higher, it can be said that the heat resistance is sufficiently excellent. In the exhaust gas purifying apparatuses of Examples 1 to 12, all the results of the vibration resistance test were “good”, and good results could be obtained. Moreover, regarding the thickness of the outer peripheral wall, the surface pressure of the carrier can be increased by increasing the thickness. By increasing the surface pressure, it was possible to relieve the stress caused by thermal expansion and improve the heat resistance. If the outer peripheral wall is too thin, the strength tends to decrease. If the outer peripheral wall is too thick, it may take time to raise the temperature of the honeycomb structure to a predetermined temperature.

In the exhaust gas purifying apparatuses of Comparative Examples 1 to 3, after the vibration resistance test, the catalyst layer peeled off from the partition walls of the honeycomb structure was found on the tray at the bottom of the honeycomb structure. This is because the thermal expansion coefficient of the partition walls is as low as 0.9 × 10 ⁻⁶ / K and the thermal expansion coefficient difference from the catalyst layer is large, so that the catalyst layer was peeled from the honeycomb structure by the vibration resistance test. Therefore, the vibration resistance test resulted in “impossible”. Further, in the exhaust gas purifying apparatuses of Comparative Examples 4 to 6, since the surface roughness of the outer peripheral wall was large, the heat resistance temperature of the honeycomb structure was low. That is, when the honeycomb structure is thermally expanded, the force for suppressing the thermal expansion is not evenly applied to the surface of the outer peripheral wall, and an excessive surface pressure is partially applied locally. Oops. In addition, since the thermal expansion coefficient of the partition walls is too high at 8.0 × 10 ⁻⁶ / K in the exhaust gas purification device of Comparative Example 7, the heat resistance temperature of the honeycomb structure is high even if the surface roughness of the outer peripheral wall is reduced. It was low. That is, even if the honeycomb structure is thermally expanded, the surface roughness is low, so that a surface pressure is applied relatively uniformly during the process of thermal expansion. Too large a contact pressure exceeding the strength of the honeycomb structure was applied, and the honeycomb structure was damaged. From the results of Comparative Examples 1 to 7 described above, it is difficult to obtain good results in both the heat resistance temperature and vibration resistance tests by adjusting only the thermal expansion coefficient of the partition walls or adjusting only the surface roughness of the outer peripheral wall. It turns out that. As in Examples 1 to 12, by setting the thermal expansion coefficient of the partition walls and the surface roughness of the outer peripheral wall within a predetermined numerical range, each weak point is complemented and damage due to thermal stress is effectively prevented. A honeycomb structure can be obtained.

  The honeycomb structure of the present invention can be used as a catalyst carrier for supporting a catalyst for purifying exhaust gas. Moreover, the exhaust gas purification apparatus of the present invention can be used for purification of exhaust gas.

1: partition, 2: cell, 3: outer peripheral wall, 11: first end surface, 12: second end surface, 21: can body, 22: inflow port, 23: outflow port, 24: trunk, 31: holding material, 32: Fastener, 60: Catalyst layer, 100, 200: Honeycomb structure, 300: Exhaust gas purification device.

Claims (5)

A porous partition wall defining a plurality of cells extending from a first end surface to a second end surface serving as a fluid flow path; an outer peripheral wall disposed at an outermost periphery so as to surround the partition wall; and a surface of the partition wall carried on, and a catalyst layer containing a catalyst component for purifying at least NO _X,
The thermal expansion coefficient at 40 to 800 ° C. of the partition wall is 1.0 × 10 ^{−6 to} 7.0 × 10 ⁻⁶ / K,
A honeycomb structure having a surface roughness of the outer peripheral wall of 0.5 to 4.0 µm.   The honeycomb structure according to claim 1, wherein the outer peripheral wall has a thickness of 1.0 to 3.0 mm.   The honeycomb structure according to claim 1 or 2, wherein the outer peripheral wall has a surface subjected to polishing treatment.   The partition wall is made of a material containing as a main component at least one selected from the group consisting of cordierite, silicon carbide, aluminum oxide, aluminum titanate, mullite, and aluminum nitride. The honeycomb structure described. The honeycomb structure according to any one of claims 1 to 4 ,
A can body that houses the honeycomb structure and has an inlet through which exhaust gas flows in and an outlet through which purified exhaust gas flows out;
An exhaust gas purification apparatus, wherein the honeycomb structure is stored in a state of being fixed in the can body while being held by a holding material disposed so as to cover the outer peripheral wall of the honeycomb structure.

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