JP5154023B2 - Catalyst carrier holding material and catalytic converter - Google Patents

Description

  The present invention relates to a catalytic converter mainly used in automobiles, and more particularly to an inorganic fiber molded body used as a carrier holding material.

  A catalytic converter is a device that removes harmful components such as carbon monoxide, hydrocarbons, and nitrogen oxides contained in the exhaust gas of an internal combustion engine with a noble metal catalyst.

  In recent years, catalytic converters are installed as close as possible to the engine because the decomposition efficiency of harmful substances increases if the catalyst and exhaust gas are heated to high temperatures. In recent years, the exhaust gas temperature has been increased in order to improve fuel efficiency, and it may exceed 950 ° C. Therefore, the constituent articles of the catalytic converter are required to have heat resistance that can be used in an environment of 950 ° C.

  Patent Document 1 describes the configuration of a catalytic converter. The catalytic converter has a cylindrically shaped exhaust gas purification catalyst carrier, a metal casing that contains the carrier and is connected to an exhaust gas conduit, and is wound around the carrier and is placed in a gap between the carrier and the casing. And a catalyst carrier holding material to be filled.

  The catalyst carrier holding material includes an alumina fiber and a heat-resistant layer having an organic binder dispersed in the alumina fiber and disappeared by thermal decomposition; a ceramic fiber laminated on the heat-resistant layer; and the ceramic fiber. A thermally expandable layer having an organic binder that disappears due to dispersed thermal decomposition, and an inorganic expansion material dispersed in the ceramic fiber. It is intended to prevent high-temperature thermal deterioration of the thermally expandable layer by the alumina fiber layer. However, here, a fiber of mullite composition having an alumina content of less than 90% is also described as an alumina fiber, but is different from the crystalline alumina fiber of the present invention.

  However, this catalyst carrier holding material has insufficient heat resistance in view of the recent required performance as described above. For example, when the exhaust gas temperature exceeds 950 ° C., the catalyst carrier holding power of the catalyst carrier holding material decreases in a short period of about 50 hours.

  The reason why the heat resistance is insufficient is considered to be vermiculite which is usually used as an expansion material for this kind of catalyst carrier holding material. For example, Patent Document 2 paragraph 0004 describes that the surface pressure characteristics of a thermally expandable layer obtained by adding vermiculite to alumina silica fiber is lowered to 800 to 900 ° C. as an upper limit. In paragraph 0012 of Patent Document 3, it is described that a thermal expansion material in which vermiculite or the like is added to ceramic fibers deteriorates severely when exposed to exhaust gas exceeding 850 ° C.

  Patent Document 4 describes the configuration of a catalytic converter, and describes that a carrier holding material obtained by molding a mixture of vermiculite and ceramic fibers into a sheet is inferior in heat resistance. And the cause is explained that vermiculite decomposes when it exceeds 850 ° C. (paragraph 0004).

  Patent Document 4 describes a compressed crystalline alumina fiber layer that is needle punched together with organic fibers as a carrier holding material of a catalytic converter having excellent heat resistance. This carrier holding material is characterized by not using vermiculite which is inferior in heat resistance.

However, all of the conventional catalyst carrier holding materials still have insufficient heat resistance, and an appropriate catalyst carrier holding force cannot be maintained for a long time in an environment exceeding 950 ° C.
Japanese Patent Laid-Open No. 10-288032 JP-A-7-77036 JP-A-8-338237 JP-A-7-197811

  The present invention solves the above-mentioned conventional problems, and the object of the present invention is to have excellent heat resistance and maintain sufficient holding power to support the catalyst carrier for a long time even in an environment exceeding 950 ° C. It is an object of the present invention to provide a carrier holding material for a catalytic converter.

The present invention comprises a heat-resistant layer having crystalline alumina fibers and an organic binder that is dispersed in the crystalline alumina fibers and disappears by thermal decomposition; and the crystalline alumina fibers integrated in the heat-resistant layer; A thermally expandable layer having an organic binder dispersed in the crystalline alumina fiber and disappearing by pyrolysis, and vermiculite dispersed in the alumina fiber;
A catalyst carrier holding material comprising:
The crystalline alumina fiber is present in the catalyst carrier holding material in an amount of 1457 to 1777 g / m ² ;
The ratio of the amount of crystalline alumina fibers present in the heat resistant layer to the amount of crystalline alumina fibers present in the thermally expandable layer is 0.98 to 1.98;
The present invention provides a catalyst carrier holding material in which the vermiculite is present in the thermally expandable layer in an amount of 23 to 30% by weight, whereby the above object is achieved.

  The carrier holding material of the catalytic converter of the present invention is excellent in heat resistance and can maintain a holding force sufficient to support the catalyst carrier for a long time even in an environment exceeding 950 ° C.

  FIG. 1 is a perspective view showing a part of the catalyst carrier holding material of the present invention. This catalyst carrier holding material 3 has a heat-resistant layer 1 and a heat-expandable layer 2 laminated thereon.

  The heat-resistant layer 1 is an aggregate of crystalline alumina fibers accumulated almost uniformly in the thickness direction, and includes what is called a blanket or a block. As the crystalline alumina fiber, one having a fiber diameter of 1 to 50 μm and a fiber length of 0.5 to 500 mm is usually used. From the viewpoint of compressive restoring force and shape retention, the fiber diameter is 3 to 8 μm. A fiber having a fiber length of 0.5 to 300 mm is particularly preferable.

  The composition of the crystalline alumina fiber refers to one having an alumina content of 90% by weight or more and a silica content of less than 10% by weight. Preferably, the alumina content is 94% by weight or more.

Crystalline alumina fibers are superior in heat resistance compared to non-crystalline ceramic fibers, and heat degradation due to shrinkage accompanying the progress of crystallization is extremely low, as is the case with ceramic fibers. It is rich in elasticity. That is, the crystalline alumina fiber layer has a property that it generates a high holding force at a low bulk density and has little property change at a high temperature. Therefore, when used as a carrier holding material for a catalytic converter, even if the gap between the carrier and the casing changes due to the difference in thermal expansion between the carrier and the casing, and the bulk density changes, the change in the holding pressure on the carrier also changes. Can be small.

  The organic binder can be used without particular limitation as long as it can maintain the thickness of the compressed layer at room temperature and can restore the thickness of the layer after disappearance due to thermal decomposition. Further, it is necessary to avoid the use of an organic binder having such a property that it impedes the flexibility and restoring surface pressure characteristics of the layer by impregnating the organic binder and promotes the destruction of the support. As the organic binder, various rubbers, water-soluble organic polymer compounds, thermoplastic resins, thermosetting resins and the like can be used.

  Examples of the rubbers include natural rubber; acrylic rubber such as copolymer of ethyl acrylate and chloroethyl vinyl ether, copolymer of n-butyl acrylate and acrylonitrile, copolymer of ethyl acrylate and acrylonitrile; copolymer of butadiene and acrylonitrile. Examples of the water-soluble organic polymer compound include carboxymethyl cellulose and polyvinyl alcohol. Thermoplastic resins include acrylic resins that are homopolymers and copolymers such as acrylic acid, acrylic ester, acrylamide, acrylonitrile, methacrylic acid, methacrylic ester; acrylonitrile / styrene copolymer; acrylonitrile / butadiene / styrene copolymer A polymer etc. are mentioned. Examples of the thermosetting resin include bisphenol type epoxy resins and novolac type epoxy resins.

  Aqueous solutions, water-dispersed emulsions, latexes, and organic solvent solutions (collectively referred to as “binder liquids”) containing the above organic binders as active ingredients are commercially available. Since it can be used after being diluted with a solvent, it can be applied relatively inexpensively. In addition, the organic binder does not need to be 1 type, and 2 or more types of mixtures may be sufficient as it.

  The content of the organic binder is not particularly limited, and the type and shape of the crystalline alumina fiber, the absolute thickness of the layer, the thickness as the molded body containing the organic binder before being incorporated into the metal casing of the catalytic converter, and Determined by repulsive force. The organic binder content is usually 3-30 parts by weight of the active component of the organic binder with respect to 100 parts by weight of the crystalline alumina fiber. If the content of the organic binder is less than 3 parts by weight, the thickness of the molded body may not be maintained due to the repulsion of the base material layer. If the content exceeds 30 parts by weight, it will be retained due to weight reduction due to burnout of the organic binder. In addition to an increase in force reduction, the flexibility of the molded body may be impaired. From such a viewpoint, the range of 5 to 20 parts by weight of the organic binder is usually used.

The heat resistant layer 1 can be formed using a papermaking method. A step of preparing a slurry in which an organic binder is added to crystalline alumina fibers dispersed in water, a step of dehydrating the slurry on a mesh by a papermaking method, a step of compressing a layer formed on the mesh in the thickness direction, It is manufactured through a step of removing the solvent and water of the organic binder by drying.

The heat-resistant layer 1 can also be formed using a crystalline alumina fiber blanket that has been subjected to needle punching. In that case, manufactured through a step of impregnating a needle punched blanket with an organic binder, a step of compressing the layer impregnated with the organic binder solution in the thickness direction, and a step of removing the solvent content of the organic binder solution by drying Is done. If necessary, the organic binder may be diluted with water.

The heat-expandable layer 2 is produced in the same manner as the heat-resistant layer 1 formed by a papermaking method, except that vermiculite particles are dispersed in a slurry containing crystalline alumina fibers. In addition, for example, sepiolite mineral can be included as other inorganic filler as required.

The holding material thus formed preferably has the following characteristics. In other words, it preferably has a restoring force of 0.1 to 8.0 kgf / cm ² in a compressed state having a thickness corresponding to the gap between the outer peripheral surface of the carrier and the inner surface of the casing. Such restoring force, the carrier is a 0.5~8.0kgf / cm ² approximately in the case of a ceramic carrier is a 0.1~4.0kgf / cm ² approximately in the case of metal.

  The restoring force is maintained even after the organic binder dispersed in the layer disappears by thermal decomposition. The restoring force of the layer corresponds to a force (compression force) required to compress the layer to a thickness corresponding to the gap between the outer peripheral surface of the carrier and the inner surface of the casing. Therefore, in the present invention, the restoring force is used as an index of the restoring force based on the compressive force at the time of layer formation.

In the resulting thermally expandable layer, vermiculite is present in an amount of 23 to 33% by weight, preferably 25 to 32% by weight. If the amount of vermiculite is less than 23% by weight, the pressure generated by the expansion of vermiculite at a high temperature is insufficient, and sufficient catalyst carrier holding power cannot be obtained. If the amount exceeds 33% by weight, the effect of deterioration of the vermiculite is greater than the pressure obtained by the expansion of vermiculite when exposed to a high temperature for a long time. However, the pressure at which vermiculite is generated when exposed to a high temperature for the first time becomes excessive, and as a result, the pressure at which the holding material is generated may exceed the surface pressure during canning, and the catalyst carrier may be damaged.

  The obtained catalyst carrier holding material has a thickness of 7 to 25 mm, preferably 10 to 20 mm. When the thickness is less than 7 mm, it is necessary to perform excessive compression for controlling the thickness at the time of production, whereby the crystalline alumina fibers constituting the holding material are broken. As a result, there is a possibility that a problem such as the holding material scattering and dropping due to the pressure of the exhaust gas of the automobile occurs. If the thickness exceeds 25 mm, the tension generated by the difference between the inner and outer circumferences will be excessive when the holding material is wound around the catalyst carrier in the canning process, causing problems such as cracks in the outer circumferential layer, that is, the thermal expansion layer. there's a possibility that.

The catalyst carrier holding material to be obtained, the crystalline alumina fibers 1400 g / ^{m 2} or more, preferably present in an amount of 1500~2500g / ^{m 2.} If the amount of crystalline alumina fiber is less than 1400 g / m ² , the heat-resistant layer for preventing deterioration due to heat of the vermiculite contained in the heat-expandable layer is insufficient, and the heat resistance as a holding material is insufficient. There is a possibility.

  The ratio between the amount of crystalline alumina fibers present in the heat resistant layer and the amount of crystalline alumina fibers present in the thermally expandable layer is 0.98 to 1.98, preferably 1.2 to 1.2. Nine. If this ratio is less than 0.98, the heat-resistant layer cannot sufficiently block the heat generated by the catalyst carrier, the deterioration of vermiculite due to the heat is promoted, and sufficient holding power performance may not be obtained.

On the other hand, if it exceeds 1.98, the amount of vermiculite in the entire holding material is insufficient, and sufficient holding power performance cannot be obtained.

  FIG. 2 is a perspective view showing a typical configuration of the catalytic converter according to the present invention. For easy understanding of the configuration, the state where the catalytic converter is deployed is shown. The illustrated catalytic converter 10 includes a metal casing 11, a monolithic solid catalyst carrier 20 disposed in the metal casing 11, and a catalyst carrier holding material 30 disposed between the metal casing 11 and the catalyst carrier 20. Prepare.

  The catalyst carrier holding material 30 has a heat resistant layer and a thermally expandable layer according to the present invention. And it arrange | positions so that a heat resistant layer may face the catalyst support side. The catalytic converter 10 is provided with an exhaust gas inlet 12 and an exhaust gas outlet 13 each having a truncated cone shape.

  With the above configuration, a catalytic converter that can be used in an environment of 950 ° C. can be provided.

  The following examples further illustrate the present invention, but the present invention is not limited thereto.

Examples 1-10 and Comparative Examples 1-3
Crystalline alumina fibers (Saffil's “LA” alumina content 96% by weight) and water were added to a Waring blender to a solid content concentration of 0.5% and stirred for about 10 seconds. This was transferred to a 12 liter beaker, and an acrylic latex having a solid content of 45.5% (“Rhoplex HA-8” manufactured by Rohm and Haas) was added to a water content of 0.06% with respect to water. Mix with a mixer. A sufficient amount of 50% aqueous solution of aluminum sulfate was added to adjust the pH to 4-6. 10 grams of a 0.1% solution of a flocculant (Nalco “7530”) was added and mixed with a propeller mixer to form a first slurry that would be a heat resistant layer.

  Similarly, crystalline alumina fibers (“LA” manufactured by Saffil) and water were added to a Waring blender so as to have a solid concentration of 0.5%, and stirred for about 10 seconds. This was transferred to a 12 liter beaker, and an acrylic latex having a solid content of 45.5% (“Rhoplex HA-8” manufactured by Rohm and Haas) was added to 0.06% with respect to water. Unexpanded vermiculite (manufactured by Cormetals Inc.) having a mesh size of 18 to 50 mesh was added and mixed with a propeller mixer. A sufficient amount of 50% aqueous solution of aluminum sulfate was added to adjust the pH to 4-6. 10 grams of a 0.1% solution of a flocculant (Nalco “7530”) was added and mixed with a propeller mixer to form a second slurry that would be a thermally expandable layer.

After forming the first slurry by the papermaking method, the second slurry was poured and dehydrated continuously to obtain a molded article having a two-layer structure. This was compressed with a pair of pressure rollers to increase the density, and dried with a heating roll to obtain a catalyst carrier holding material having a binder content of about 12%.
The amount of fiber added to each slurry and the amount of vermiculite added to the second slurry were adjusted to obtain Examples 1 to 10 and Comparative Examples 1 to 3 shown in Table 1.

Comparative Example 4
Crystalline alumina fiber (Saffil's “LA”) and water were added to a Waring blender to a solid content concentration of 0.5% and stirred for about 10 seconds. This was transferred to a 12 liter beaker, and an acrylic latex having a solid content of 45.5% (“Rhoplex HA-8” manufactured by Rohm and Haas) was added to a water content of 0.06% with respect to water. Mix with a mixer. A sufficient amount of 50% aqueous solution of aluminum sulfate was added to adjust the pH to 4-6. 10 grams of a 0.1% solution of a flocculant (Nalco “7530”) was added and mixed with a propeller mixer to form a first slurry that would be a heat resistant layer.

Similarly, ceramic fibers (“Cao wool ^TM HA bulk” alumina content 55% by weight manufactured by Thermal Ceramics Co., Ltd.) and water were added to a Waring blender so as to have a solid content concentration of 0.5%, and stirred for about 20 seconds. This was transferred to a 12 liter beaker, and an acrylic latex having a solid content of 45.5% (“Rhoplex HA-8” manufactured by Rohm and Haas) was added to 0.06% with respect to water. Unexpanded vermiculite (manufactured by Cormetals Inc.) having a mesh size of 18 to 50 mesh was added and mixed with a propeller mixer. A sufficient amount of 50% aqueous solution of aluminum sulfate was added to adjust the pH to 4-6. 10 grams of a 0.1% solution of a flocculant (Nalco “7530”) was added and mixed with a propeller mixer to form a second slurry that would be a thermally expandable layer.

  After forming the first slurry by the papermaking method, the second slurry was poured and dehydrated continuously to obtain a molded article having a two-layer structure. This was compressed with a pair of pressure rollers to increase the density, and dried with a heating roll to obtain a catalyst carrier holding material having a binder content of about 12%.

High-temperature endurance surface pressure test The high-temperature endurance surface pressure test is a test for creating actual conditions found in a catalytic converter having a standard catalyst carrier and measuring the pressure generated by the catalyst carrier holding material under the assumed use conditions.
“Syntec 1 / D” manufactured by MTS Systems Corporation is equipped with a pair of sample tables that can vary the gap (gap) between the sample tables in order to sandwich a catalyst carrier holding material sample having a diameter of 45 mm.

  A load cell for measuring the pressure generated by the holding material sandwiched in the gap between the sample stands is provided at the upper part. Moreover, a pair of sample stand holding a sample can be heated to different temperatures, respectively.

  Further, in the catalytic converter, the temperature rises, and the gap in which the catalyst carrier holding material exists is widened by the difference in thermal expansion coefficient between the metal case and the catalyst carrier. In order to reproduce this phenomenon, the gap between the sample stands is continuously increased as the temperature rises so that the gap assumed with the temperature is obtained in this measurement.

  In the measurement in this example, the temperature of the heat-resistant layer side sample stage is from room temperature (about 25 ° C.) to 920 ° C. at high temperature, and the temperature of the thermally expandable layer side sample stage is from room temperature (about 26 ° C.) to 680 ° C. at high temperature. The gap change amount increased from room temperature to high temperature was 0.5 mm when the temperature was raised. The time from the room temperature to the high temperature was about 40 minutes, kept at the high temperature for 16 minutes, then cooled to room temperature in about 60 minutes, and this was repeated 500 cycles.

  The surface pressure at the end of high temperature holding for 500 cycles was defined as the post-endurance surface pressure, and the case of 32 kPa or more was determined to have sufficient heat resistance. The test results are shown in Table 1.

  The gap set at the start of the test, that is, the gap set at the start of the test, is the gap at which the holding material generates a surface pressure of 150 kPa when the gap between the sample stands is compressed at a speed of 25 mm / min. did.

Initial high temperature surface pressure test Using the same test method as the above high temperature endurance test, the test was conducted with the following setting gap at the start of the test, and the maximum peak surface pressure value near the first cycle high temperature retention was set as the initial high temperature surface pressure value. . The test results are shown in Table 1.

  The gap set at the start of the test, that is, the gap set at the start of the test is the gap at which the holding material generates a surface pressure of 400 kPa when the gap between the sample tables is compressed at a speed of 25 mm / min. did. The surface pressure at the start of the test was taken as the canning surface pressure.

a：触媒担体保持材中の結晶質アルミナ繊維量
b：結晶質アルミナ繊維量の耐熱性層と熱膨張性層との比率
c：熱膨張性層中のバーミキュライト量
d：総繊維量は耐熱性層結晶性アルミナファイバー１０５６ｇ／ｍ^２と熱膨張性層のセラミックファイバー６５９ｇ／ｍ^２の和 [Table 1]

a: Amount of crystalline alumina fiber in catalyst carrier holding material
b: Ratio of heat-resistant layer and thermally expandable layer with crystalline alumina fiber content
c: Vermiculite content in the thermally expandable layer
d: Total fiber amount is the sum of heat resistant layer crystalline alumina fiber 1056 g / m ² and thermally expandable layer ceramic fiber 659 g / m ²

The fiber amount ratio indicated by the fiber amount ratio heat-resistant layer fiber amount / thermally expandable layer fiber amount was compared for Examples 1 to 4. It was confirmed that the surface pressure after the high-temperature endurance test exceeded 32 kPa, which is determined to have sufficient heat resistance in the fiber amount ratio range of 0.98 to 1.98.

Total fiber amount The total fiber amount was compared for Examples 3 and 6 and Comparative Example 1. It was confirmed that the surface pressure after the high-temperature durability test exceeded 32 kPa, which is judged to have sufficient heat resistance when the total fiber amount is 1400 g / m ² or more.

Vermiculite content rate The vermiculite content rate was compared for Example 3, Examples 6 to 8, and Comparative Example 2. It was confirmed that the surface pressure after the high-temperature endurance test exceeded 32 kPa, which was judged to have sufficient heat resistance at a vermiculite content of 23 to 33% by weight contained in the thermally expandable layer.

  Further, Examples 9 and 10 and Comparative Example 3 were compared in terms of canning surface pressure-initial high temperature surface pressure. If the initial high-temperature surface pressure exceeds the canning surface pressure, it means that the pressure generated at the high temperature in the first cycle of the holding material exceeds the surface pressure set by canning, and the catalyst carrier may be damaged by the pressure difference. There is. In Comparative Example 3, since the canning surface pressure-initial high temperature surface pressure is positive, the vermiculite content is preferably 33% by weight or less.

When a ceramic fiber with poor heat resistance is used for the thermally expandable layer When comparing Example 3 and Comparative Example 4, the temperature is high for Example 3 in which crystalline alumina fiber is used for the thermally expandable layer. It was confirmed that the surface pressure after the durability test exceeded 32 kPa, which is determined to have sufficient heat resistance, but the comparative example 4 in which the thermally expandable layer is composed of ceramic fibers having an alumina content of about 50% by weight is sufficient. It was confirmed that heat resistance could not be obtained.

It is a perspective view which shows a part of catalyst carrier holding material of this invention. It is the perspective view which showed the typical structure of the catalytic converter by this invention.

Explanation of symbols

1 ... heat-resistant layer,
2 ... thermal expansion layer,
3 ... Catalyst carrier holding material.

Claims (3)

A heat-resistant layer having a crystalline alumina fiber and an organic binder that is uniformly impregnated in the crystalline alumina fiber and disappears by thermal decomposition; and the crystalline alumina fiber laminated on the heat-resistant layer, and the crystal A heat-expandable layer having an organic binder dispersed in the porous alumina fiber and disappearing by pyrolysis, and vermiculite dispersed in the crystalline alumina fiber;
A catalyst carrier holding material comprising:
The crystalline alumina fiber is present in the catalyst carrier holding material in an amount of 1457 to 1777 g / m ² ;
The ratio of the amount of crystalline alumina fibers present in the heat resistant layer to the amount of crystalline alumina fibers present in the thermally expandable layer is 0.98 to 1.98;
A catalyst carrier holding material, wherein the vermiculite is present in the thermally expandable layer in an amount of 23 to 30% by weight.   The catalyst carrier holding material according to claim 1, which is compressed in the thickness direction and has a thickness of 7 to 25 mm. A support for the exhaust gas purification catalyst formed in a cylindrical shape, a casing that contains the support and is connected to an exhaust gas conduit, and a catalyst support that is wound around the support and is filled in a gap between the support and the casing A catalytic converter having a material,
A catalytic converter, wherein the catalyst carrier holding material is the catalyst carrier holding material according to claim 1 or 2, and the heat-resistant layer is arranged to face the carrier side.

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