WO2005044425A1

WO2005044425A1 - Honeycomb filter for exhaust gas purification and method of manufacturing the same

Info

Publication number: WO2005044425A1
Application number: PCT/JP2004/007771
Authority: WO
Inventors: Hiroki Sato; Masafumi Kunieda
Original assignee: Ibiden Co., Ltd.
Priority date: 2003-11-07
Filing date: 2004-05-28
Publication date: 2005-05-19

Abstract

A honeycomb filter for exhaust gas purification manufacturable with rather low temperature at low cost and excellent in characteristics such as acid resistance, alkali resistance, and strength (thermal shock) and a method of manufacturing the honeycomb filter. The honeycomb filter comprises honeycomb-shaped porous ceramic members in which a large number of cells are formed along the axial direction thereof and is formed so that a part or all of partition walls separating the adjacent cells from each other function as particulate collecting filters. The filter is characterized in that the ceramic members are formed of those containing silicon carbide, silicon, and silicon nitride.

Description

Description Honeycomb filter for purifying exhaust gas and method for manufacturing the same

The present invention relates to a filter for removing particulates or the like in exhaust gas discharged from an internal combustion engine such as a diesel engine, a honeycomb filter for purifying exhaust gas used as a catalyst carrier and the like, and a method of manufacturing the same. Background art

A porous honeycomb structure is widely used as a filter for removing particulate matter contained in exhaust gas of a diesel engine or a catalyst carrier carrying a catalyst component for purifying harmful substances in exhaust gas. ing. As a material for forming such a honeycomb structure, a refractory ceramic such as silicon carbide is known.

For example, as an example of such a honeycomb structure, a silicon carbide powder having a predetermined specific surface area and an impurity content is used as a starting material, formed into a desired shape, dried, and then heated to 1600 to 2000 ° C. Porous silicon carbide filters and catalyst carriers that have been formed into a honeycomb structure by firing at a temperature are known.

As the porous silicon carbide sintered body used for such a honeycomb structure, a binder such as vitreous flux or clay is added to silicon carbide powder to be an aggregate, and then molded. It is manufactured by a method of baking at the temperature at which it melts. (For example, Japanese Patent Application Laid-Open No. Hei 6-182822)

However, the technology for combining silicon carbide powder raw materials with a vitreous material has the following problems. That is, when a sintered body produced by such a method is used as a material for a diesel particulate filter (DPF), the particulate matter collected by the filter is burned for regeneration of the filter. Then the heat Due to the low conductivity, local heat was generated and the structure could be destroyed. Further, the metal silicon powder and the organic binder are added to the silicon carbide powder, mixed and kneaded, the obtained kneaded material is formed into a honeycomb shape, and the obtained formed body is calcined to form the formed body. There is also a method of producing a honeycomb structure by removing the organic binder therein and then performing main firing. However, in the above-described conventional technique in which the raw material silicon carbide powder is bonded via the metal silicon powder, it is difficult to manufacture the silicon carbide powder at a relatively low firing temperature (for example, Japanese Patent Application Laid-Open No. 2002-1544876). Thus, a honeycomb structure having high thermal conductivity, sufficiently porous and high specific surface area can be obtained, but there is a problem that the metallic silicon powder is relatively easily dissolved in an acid. Moreover, when the sintered body obtained in this way is used as a DPF, the sintered body is exposed to an acid gas generated by combustion of sulfur contained in the fuel, so that it cannot dissolve metallic silicon. There was a risk that destruction or the like would occur.

In addition, since metallic silicon is relatively easily dissolved in alkali, when such a sintered body is used as a catalyst carrier, the metallic silicon dissolves when a catalyst which is an alkali component is supported. There was a possibility that destruction or the like caused by the occurrence would occur.

Furthermore, a sintered body obtained by bonding silicon carbide powder with metallic silicon has a low strength, and when used as a DPF, may be broken by vibration during traveling or the like. On the other hand, conventionally, a silicon carbide-based porous body including a silicon carbide powder serving as an aggregate and a metal silicon powder, and forming a phase including oxygen on the surface of or around the bracket silicon carbide powder and Z or the metal silicon Has been proposed. (For example, Japanese Patent Application Laid-Open No. 2000-15054 882)

According to such a proposed technique, since a phase containing oxygen is present on or around silicon carbide and metallic silicon, when it is used as a DPF, the acid resistance is improved, but the alkali resistance and strength are sufficient. There was a problem that was not.

Further, silicon carbide powder having an average particle size of 5 to 100 m, a metal silicon powder having a particle size smaller than the average particle size of the powder, and a molding aid are mixed and molded, and the compact is formed in a nitriding gas atmosphere. Baking below the melting temperature of There are also proposals for a method of manufacturing the body. (For example, Japanese Patent Application Laid-Open No. 611-101665)

There has also been proposed a method of manufacturing a ceramic heater made of silicon carbide and silicon nitride by mixing silicon carbide and metal silicon to form a honeycomb shape, and sintering in an inert gas.

(For example, Japanese Patent Application Laid-Open No. 9-106683)

In addition, among the techniques disclosed after filing the earlier application filed under the present application, a technique for converting silicon metal to silicon nitride using silicon carbide and metal silicon has been proposed (for example, Japanese Patent Application Laid-Open No. 2000-35056384, Japanese Patent Application Laid-Open No. 2003-154424).

The sintered body obtained by these proposed technologies is manufactured in a nitrogen atmosphere at a temperature of 1300 ° C or more and for a relatively long time of 5 hours or more, and converts all metallic silicon to silicon nitride. It can be called technology. That is, it is a force excellent in heat resistance, corrosion resistance, oxidation resistance, and impact resistance. It does not have high strength that can be applied to a honeycomb filter, and has a problem in thermal shock resistance. Disclosure of the invention

It is an object of the present invention to provide an inexpensive production at a relatively low temperature in spite of containing a refractory powder such as silicon carbide, as well as acid resistance, alkali resistance and strength (thermal shock resistance). An object of the present invention is to propose a honeycomb filter (including a catalyst carrier) for purifying exhaust gas comprising a silicon carbide porous body having excellent characteristics and an advantageous method for producing the same.

In a study aimed at realizing the above object, the present inventors obtained the finding that it is advantageous to include silicon nitride in a porous body for forming a ceramic member (block). The invention was developed.

That is, according to the present invention, when a large number of cells are provided along the axial direction, and some of these cells are sealed at one end, at the other end, One or more of the honeycomb-structured porous ceramic members having a structure to be released and configured so that a part or all of the partition walls separating adjacent cells function as a filter for collecting particles. An exhaust gas purifying honeycomb filter comprising two or more aggregates, wherein the ceramic member is made of a material containing silicon carbide, silicon and silicon nitride. In the present invention, the content of silicon nitride contained in the porous ceramic member is preferably about 0.1 to 30% by weight, and more preferably 1.0 to 18% by weight. More preferred, 3 to 13 weight. / ₀ is more preferable. Preferably, the ceramic member has a catalyst applied to a part or the whole of the partition wall surface.

Further, in the present invention, the silicon powder and the organic binder are kneaded with the silicon carbide powder, and the obtained kneaded material is formed as a ceramic member having a honeycomb structure, and provided along the axial direction of the ceramic member. Only one end of many cells is plugged, then calcined to remove the organic binder, and then calcined. Thereafter, the calcined ceramic member and 800-1400 ° C. in a nitrogen atmosphere. A method for producing a honeycomb filter for purifying exhaust gas, characterized by obtaining a porous ceramic filter containing silicon carbide, silicon and silicon nitride by heat-treating in a temperature range of C to nitride silicon carbide and silicon. Suggest.

The content of silicon nitride contained in the porous ceramic filter is preferably 0.1 to 30% by weight, more preferably 1.0 to 18% by weight, and 3 to 13% by weight. Most preferably. Brief Description of Drawings

FIG. 1 is a perspective view showing an example of an exhaust gas purifying honeycomb filter according to the present invention.

FIG. ² is a perspective view showing an example of a porous ceramic member constituting the honeycomb filter shown in FIG. 1. FIG. ² (b) is a perspective view of the porous ceramic member shown in FIG. It is line sectional drawing.

3A is a perspective view showing another example of the honeycomb filter according to the present invention, and FIG. 3B is a cross-sectional view taken along line BB of the honeycomb filter shown in FIG. FIG. 4 is a graph plotting a change in strength (M Pa) with respect to an amount (% by weight) of silicon nitride contained in an exhaust gas purifying honeycomb filter.

FIG. 5 is an SEM photograph (100,000 magnification) of a cross section of the honeycomb filter according to Example 1 taken by a scanning electron microscope.

FIG. 6 is a cross-sectional view schematically showing one example of an exhaust gas purifying apparatus using the honeycomb filter according to the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to these embodiments, and may be appropriately determined based on ordinary knowledge of a person skilled in the art without departing from the spirit of the present invention. It should be understood that design changes, improvements, etc. are made.

FIG. 1 is a perspective view schematically showing a specific example of an aggregated honeycomb filter showing an example of the honeycomb filter of the present invention. FIG. 2 (a) is a perspective view showing a porous filter constituting the honeycomb filter shown in FIG. FIG. 2B is a perspective view showing an example of the ceramic member, and FIG. 2B is a cross-sectional view taken along line AA of the porous ceramic member shown in FIG. As shown in FIGS. 1 and 2, the honeycomb filter 10 is a ceramic block formed by assembling a plurality of columnar porous ceramic members 20 into a cylindrical shape via a sealing material layer 14. The ceramic block 15 is surrounded by a sinole material layer 13 as necessary to prevent leakage of exhaust gas or to adjust its shape. ing.

Each of the porous ceramic members 20 constituting the cylindrical ceramic block 15 has a prismatic shape in this embodiment, and a large number of cells 21 are juxtaposed in the longitudinal direction thereof through partition walls 23. In each cell 21, only one of the ends is sealed by the sealing material 22. It is separated into a gas inflow side and a gas outflow side.

With such a configuration, the exhaust gas that has flowed into the cell 21 a on the exhaust gas inflow side passes through the partition wall 23 that separates these cells 21, and then flows out from the adjacent cell 21 b on the gas outflow side. The partition wall 23 that separates the cells 21a and 2 lb functions as a filter for collecting particles.

FIG. 3 (a) is a perspective view schematically showing a specific example of an integrated honeycomb filter showing another example of the honeycomb filter of the present invention, and FIG. It is a line sectional view.

As shown in FIG. 3 (a), the honeycomb filter 30 is made up of a cylindrical ceramic block 35 made of porous ceramic in which a number of cells 31 are juxtaposed in the longitudinal direction across a partition wall 33. It is configured.

As shown in FIG. 3 (b), the ceramic block 35 of the honeycomb filter 30 is adjacent to the cell 31a whose one end is sealed with a partition wall 33 interposed therebetween. The other end of the cell 31b is sealed with a sealing material 32, and at each end of the ceramic block 35, a honeycomb structure is formed in which openings and closing portions are alternately formed. I have.

With such a configuration, the exhaust gas flowing into the cell 31a on the exhaust gas inflow side passes through the partition wall 33 separating the cell 31a, and then flows out from the cell 31b on the adjacent exhaust gas outflow side. The partition wall 33 that separates these cells 31a, 3lb functions as a filter for collecting particles.

Although not shown in FIG. 3, a sealing material layer may be formed around the ceramic block 35, similarly to the honeycomb filter 10 shown in FIG.

That is, the basic form of the honeycomb filter for purifying exhaust gas of the present invention is a porous filter in which a large number of cells are regularly formed (arranged) along the axial direction (longitudinal direction) across a partition wall. The cross section of the ceramic sintered body (ceramic block) is formed in a polygonal or circular shape such as a triangle, an ellipse, or various columnar shapes, and consists of a simple substance or an aggregate thereof. . The cells are separated from each other by a partition wall that is a filtration wall, and the opening of each cell is sealed at one end side with a sealing body (filling material). The ends are open, and as a whole, each end is plugged with alternating open and closed portions, for example, in a checkered pattern.

The ceramic block composed of an aggregate of one or more ceramic members has a honeycomb structure in which a large number of cells having a substantially square cross section are formed.

According to the above honeycomb structure, the exhaust gas that has flowed into one cell always flows through a partition wall that separates another adjacent cell, that is, a filtration wall, and then flows out through another adjacent cell. The walls separating these cells function as a filter for collecting particles.

It is more preferable to use the same type of porous ceramic as the ceramic member as the filler for sealing. With such a configuration, the adhesion strength between the two can be increased, and the thermal expansion of the filler and the thermal expansion of the ceramic member can be matched. Accordingly, it is possible to prevent a gap from being formed between the filler and the wall portion, and to prevent cracks from being generated on the wall portion of the filler or the portion in contact with the filler.

The density of the cells is preferably about 100 to 400 square inches, more preferably about 200 to 300 cells / square inch, and most preferably about 200 cells / square inch. The reason is that if the number of pieces is less than 100 square inches, the effective area that can collect soot is small, so the soot layer thickness after collecting soot increases, and as a result, the pressure drop On the other hand, if it exceeds 400 square inches, soot will be clogged inside the through-hole, soot filtering function will be lost, and pressure loss will increase. .

About half of the above cells are open at the upstream end face, and the rest are open at the downstream end face, and the thickness of the cell wall separating each cell is about 0.1 to 0.8 mm. Degree is preferable, it is preferably set to about 0.2 to 0.6 mm, and 0.25 to 0.45 mm The degree is most preferred.

The reason is that if it is less than 0.1 mm, soot in the exhaust gas easily passes through the cell wall, and soot collection efficiency is reduced. On the other hand, if it exceeds 0.8 h, the resistance when the exhaust gas passes through the cell wall increases, and the pressure loss increases.

As described above, the filter made of a porous ceramic sintered body having a honeycomb structure has a structure partitioned by porous partition walls, and the pores of the porous partition walls are measured by a mercury intrusion method. The average value of the measured pore diameters was adjusted to be in the range of about 5 to 40111, and the standard deviation value in the pore diameter distribution when the pore diameters were expressed in common logarithm was 0.40 or less. Those are preferred.

If the average pore diameter of the cell wall is within the above-mentioned range, it is suitable for collecting fine diesel particulates. That is, by setting the average pore diameter of the partition walls within the above range, it is possible to reliably collect diesel particulates. On the other hand, if the average value of the pore diameter of the partition is less than 5 / im, the pressure loss when the exhaust gas passes through the inner wall becomes extremely large, which may cause the engine to stop. On the other hand, when the average diameter of the pores exceeds 40 / m, it is not possible to efficiently collect fine particulates.

The porosity of the ceramic block constituting the honeycomb structure of the present invention is preferably 30 to 80%, more preferably 35 to 70%, and most preferably 40 to 60%. If the porosity is less than 30%, the pressure loss becomes too large. On the other hand, if the porosity exceeds 80%, the specified strength cannot be maintained, and the patilla may leak.

The porosity can be measured by a conventionally known method such as a mercury intrusion method, an Archimedes method, and a measurement using a scanning electron microscope (SEM). As the particle size of the raw material particles used in producing such a ceramic block, those having a small shrinkage in the subsequent firing step are desirable, for example, ceramic particles having an average particle size of about 0.5 to 100 / xm. It is desirable to use (silicon carbide) and silicon (metallic silicon) having an average particle size of about 0.5 to 20 / zm. Ceramics of the above particle size This is because the use of the black particle powder enables the production of a ceramic block composed of the porous ceramic having the above-mentioned porosity and average pore diameter.

The “silicon” constituting the ceramic member in the present invention is a concept including metallic silicon, crystalline silicon, and amorphous silicon, but is an embodiment in which metallic silicon is preferably used.

By the way, the feature of the present invention is that the ceramic member made of the ceramic sintered body is made of a porous sintered body mainly made of silicon carbide, silicon and silicon nitride. The determination of silicon carbide, silicon nitride, silicon, etc. can be confirmed by X-ray diffraction (JIS K0131-1996).

The above-mentioned porous sintered body can be fired even at a relatively low temperature during production by using metallic silicon for bonding of silicon carbide powder as refractory particles, thereby suppressing production costs. This is advantageous in that it is possible to improve the yield. With such a configuration, higher thermal conductivity can be obtained as compared with the case where the binder is made of vitreous. Therefore, when used as a DPF, the particulates deposited for filter regeneration are burned. However, it is possible to prevent a local temperature rise that may damage the filter.

That is, the honeycomb filter according to the present invention contains silicon nitride in addition to the silicon carbide powder and the metal silicon powder, and is formed by forming a film of the silicon nitride on the surface of the silicon carbide powder or the metal silicon powder. There is a feature in the point.

When a filter having such a configuration is used as a DPF, even if the filter is exposed to an acid gas generated by combustion of sulfur contained in fuel or the like, destruction or the like caused by dissolution of metallic silicon occurs. Nothing. Moreover, when this is used as a catalyst carrier, even if a catalyst which is an alkali component is supported, no destruction or the like is caused by the dissolution of metallic silicon. Furthermore, since the strength is improved, there is no possibility that breakage or the like will occur due to vibration or the like during traveling.

The porous sintered body constituting the exhaust gas purifying filter according to the present invention (the ceramic member contains silicon nitride as described above, but the content is 0.1%). 3030% by weight¾g, more preferably 1.0-18% by weight, and most preferably 3-13% by weight.

If the amount of silicon nitride is less than 0.1% by weight, there is almost no silicon nitride film, and the above effects cannot be obtained. On the other hand, if the amount of silicon nitride exceeds 30% by weight, most of the silicon in the bonding portion is nitrided, or a large amount of silicon nitride force is generated, and the density of the bonding portion is reduced. It is not preferable because it causes a decrease in conductivity and a decrease in thermal shock resistance, and further, a decrease in strength.

In the present invention, the amount of silicon nitride in the ceramic member is determined by pressurized acid decomposition, steam distillation separation, and medium pressure in accordance with “Chemical analysis method of silicon nitride fine powder for fine ceramics” specified in JIS R1603-1994. The amount of nitrogen was measured by the sum titration method, and silicon nitride (Si ₃ N

₄ ).

The nitrogen component is present on or around the surfaces of the silicon carbide powder and the metal silicon powder in the form of a Si ₃ N ₄ or] 3 Si ₃ N ₄ singly or in a mixed state. Alternatively, a fibrous substance exists in a partially formed form, and as a result, it has an effect of being excellent in oxidation resistance and alkali resistance, and improving the chemical stability as a catalyst carrier.

Honeycomb Filter Force According to the Present Invention In the case of the aggregated honeycomb filter shown in FIG. 1, the sealing material layers 13 and 14 are formed between the porous ceramic members 20 and on the outer periphery of the ceramic block 15. ing. The sealing material layer 14 formed between the porous ceramic members 20 functions as an adhesive for binding the plurality of porous ceramic members 20 together, and is formed on the outer periphery of the ceramic block 15. When the honeycomb filter of the present invention is installed in an exhaust passage of an internal combustion engine and used as an exhaust gas purifying device, the sealing material layer 13 prevents exhaust gas from leaking from the outer periphery of the ceramic block 15. Functions as a sealing material for prevention.

As described above, in the honeycomb filter of the present invention, the sealing material layer is formed between the porous ceramic members and on the outer periphery of the ceramic block. These sealing material layers may be made of the same material, or may be made of different materials. Further, when the sealing material layers are made of the same material, the compounding ratio of the materials may be the same or different.

As a material constituting the sealing material layer in the collective honeycomb filter, for example, a material comprising at least one selected from an inorganic binder, an organic binder, inorganic fibers, and / or inorganic particles can be used. . The sealing material layer is formed between the porous ceramic member and the porous ceramic sintered body, in particular, these sealing material layers may be made of the same material. However, they may be made of different materials. Further, when the sealing material layers are made of the same material, the compounding ratio of the materials may be the same or different.

As the inorganic binder, for example, silica sol, alumina sol and the like can be used. These may be used alone or as a mixture of two or more. Among the above inorganic binders, it is desirable to use silica sol. As the organic binder, for example, polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose and the like can be used. These may be used alone or as a mixture of two or more. It is particularly desirable to use carboxymethyl cellulose among the above organic binders.

As the inorganic fiber, for example, silica-alumina, ceramic fiber made of mullite, alumina, silica or the like can be used. These may be used alone or in combination of two or more. Among the above inorganic fibers, silica alumina fibers are desirable.

As the inorganic particles, for example, a carbide, a nitride, or the like can be used. Specifically, an inorganic powder made of silicon carbide, silicon nitride, boron nitride, or the like, a whisker, or the like can be used. These may be used alone or in combination of two or more. Among the above-mentioned inorganic particles, silicon carbide having excellent thermal conductivity is particularly desirable. The sealing material layer may be made of a dense body or a porous body.However, when the filter of the present invention is installed in an exhaust passage of an internal combustion engine, it is necessary to prevent the exhaust gas from leaking from the outer periphery of the ceramic block. Since it is necessary to prevent this, it is preferable to use a dense body layer.

By making the honeycomb filter of the present invention an aggregate-type honeycomb filter, any size can be easily manufactured by combining members.

By the way, in the case of DPF, if the power S for collecting and regenerating soot, and the amount of soot that can be collected at a time increases, the period until soot regeneration increases, leading to better fuel efficiency. Therefore, a filter capable of collecting a large amount of soot at a time is desired.

However, when a large amount of soot is regenerated at a time, the temperature becomes high due to rapid combustion of the soot, and cracks may occur in the filter block. The soot collection at this time is called the soot limit. Therefore, preliminary experiments on filter strength were repeated to raise the conventional soot limit value.The filter block strength to satisfy the soot limit of 7 g / 1 or more was mainly determined by silicon carbide, silicon, and nitride. In the case of a filter made of silicon, it has been found that the filter should be at least 13 MPa. That is, in the honeycomb filter according to the present invention, it has been found that by setting the strength of the ceramic block to 13 MPa ag or more, the soot limit can be increased.

In particular, in the case of an aggregate type honeycomb filter, since the bonding is made of a different material as described above, the bonding surface of the sealing material and the strength itself of the sealing material are weakened, and compared with the integrated honeycomb filter. It was found that the overall strength was reduced. Even in such a case, it is necessary to provide the same strength as the integrated honeycomb filter, and for that purpose, the strength of each ceramic member can be increased to improve the overall strength. Gawakatsu.

Therefore, in the present invention, if the strength of each ceramic member is set to 13 MPa or more and a plurality of ceramic members having such a range of strength are bundled to form an aggregated honeycomb filter, the same as an integrated honeycomb filter is obtained. Filter with a strength of I found that.

In order to increase the strength of the ceramic member to 13 Mpa or more, the content of silicon nitride needs to be about 0.1 to 30% by weight, and more preferably about 1 to 18% by weight. Range.

As described with reference to FIGS. 1 to 3, the honeycomb filter according to the present invention is sealed in a predetermined through-hole at one end of the ceramic block constituting the honeycomb filter with a sealing material. When the exhaust gas is exhausted from an internal combustion engine such as a diesel engine, it can be suitably used as a honeycomb filter for exhaust gas purification that collects particulates in exhaust gas.

Further, when the honeycomb filter of the present invention is used as the honeycomb filter for purifying exhaust gas, Pt for promoting the combustion of particulates when the regeneration process is performed on the honeycomb filter is provided on the wall of the ceramic block. A catalyst such as Rh and Pd may be supported.

In addition, the honeycomb filter of the present invention is supported on a ceramic block of the honeycomb filter of the present invention, for example, by supporting a catalyst such as a precious metal such as Pt and RhPd or an alloy thereof, thereby making the honeycomb filter of the present invention a heat engine such as an internal combustion engine or the like. It can be used as a catalyst carrier for purifying HC, CO and NOX in exhaust gas discharged from combustion equipment such as boilers, and for reforming liquid fuel or gaseous fuel.

When the honeycomb filter of the present invention is used as the catalyst carrier, the sealing material is not always necessary.

Next, a method for manufacturing a honeycomb filter for purifying exhaust gas of the present invention will be described. When the honeycomb filter according to the present invention is applied to the aggregated honeycomb structure shown in FIG. Extrusion molding is performed using a raw material paste mainly composed of silicon and metallic silicon to produce a ceramic molded body having substantially the same shape (honeycomb shape) as the porous ceramic member 20 shown in FIG.

In addition, when applied to an integral honeycomb structure integrally formed as a whole as shown in FIG. 3, the above-described ceramic particles and metal silicon Extrusion molding is carried out using a raw material paste mainly composed of ceramics and a ceramic molded body having substantially the same shape as the honeycomb filter 30 shown in FIG.

It is desirable that the above-mentioned raw material has a porosity of 30 to 80% of the ceramic block after production. For example, silicon carbide particle powder (average particle size 0.5 to 100 / im) and metallic silicon A mixture of powder (average particle diameter of about 0.5 to 20111) and a binder, a pore-forming agent for increasing porosity if necessary, and a dispersion medium are used. Is done.

In addition, silicon carbide powder raw materials and metallic silicon raw materials may contain trace impurities such as Fe, Al, and Ca, but may be used as they are, and may be used for chemical treatment such as chemical cleaning. And purified.

The metal silicon powder melts during the firing process after the degreasing process described later, wets the surface of the ceramic particles, and plays a role as a bonding material for bonding the ceramic particles.

The amount of the metal silicon powder varies depending on the particle size and shape of the ceramic particle powder, but is preferably about 5 to 50 parts by weight based on 100 parts by weight of the mixed powder. , More preferably 10 to 40 parts by weight, most preferably 15 to 30 parts by weight.

If the amount is less than 5 parts by weight, the amount of the metal silicon powder is too small to function sufficiently as a bonding material for bonding the ceramic particles, and the strength of the obtained honeycomb ceramic (ceramic block) is insufficient. It may be.

On the other hand, if it exceeds 50 parts by weight, the obtained honeycomb ceramic becomes too dense, the porosity becomes low, and the above-mentioned effect of the present invention may not be sufficiently obtained. Further, for example, when the honeycomb ceramic of the present invention is used as the filter, the pressure loss due to the concentration of the particulates becomes large immediately, and there is a possibility that the filter cannot function sufficiently as a filter.

Examples of the binder include methylcellulose, carboxymethylcellulose, hydroxyshethylcellulose, polyethylene glycol, and phenol resin. Epoxy resin or the like is used.

Usually, the amount of the binder is preferably about 1 to 10 parts by weight based on 100 parts by weight of the ceramic particle powder.

As the dispersion medium liquid, for example, an organic solvent such as benzene, an alcohol such as methanol, or water can be used.

The dispersion medium liquid is mixed in an appropriate amount so that the viscosity of the raw material paste falls within a certain range.

The mixed powder, the binder and the dispersion medium are mixed with an attritor or the like, sufficiently kneaded with an abrader or the like to obtain a raw material paste, and the raw material paste is extruded to form the ceramic molded body. I do.

Further, a molding aid may be added to the raw material paste as needed.

As the molding aid, for example, ethylene glycol, dextrin, fatty acid stone, polyalcohol and the like are used.

Further, the raw material paste may be added, if necessary, with a pore-forming agent such as a balloon, which is a fine hollow sphere containing an oxide-based ceramic as a component, spherical acrylic particles, and graphite.

As the above-mentioned balloon, for example, alumina balloon, glass microballoon, shirasu vanolane, fly ash van (FFbanolane), muratononoren and the like are used. Of these, fly ash balloons are preferred. Then, the ceramic molded body is dried using a microwave dryer, a hot air dryer, a dielectric dryer, a vacuum dryer, a vacuum dryer, a freeze dryer, or the like to form a ceramic dry body, which is then sealed in a predetermined through hole. A sealing material paste serving as a material is filled, and a sealing process is performed to plug the through hole.

As the sealing material paste, for example, the same paste as the above-mentioned raw material paste can be used.

Next, the dried ceramic body sealed with the sealing material paste is heated to about 150 to 700 ° C. to remove the binder contained in the dried ceramic body, and the ceramic is removed. A degreasing treatment for forming a fat body is performed.

The degreasing treatment is desirably performed at a temperature lower than the temperature at which the metal silicon melts. The degreasing atmosphere may be an oxidizing atmosphere, and may be an inert gas such as nitrogen or argon. It may be an atmosphere. As the degreasing atmosphere, an optimum atmosphere is appropriately selected in consideration of the amount of the binder used, the type of the ceramic particles, and the like.

Next, the ceramic degreased body is heated to about 1500 ° C. in an argon atmosphere, and subjected to main firing for 1 to 30 minutes. Then, the metallic silicon powder is softened (melted), and the ceramic particles are bonded via silicon to form a porous ceramic, which produces a honeycomb structure (ceramic block) formed integrally as a whole. That's a thing.

Further, it is possible to produce a honeycomb filter for purifying exhaust gas comprising a silicon carbide porous body having a phase of silicon nitride on or around the surfaces of silicon carbide powder and metal silicon powder by heat treatment in a nitrogen atmosphere. it can.

What is important in the production of the purification honeycomb filter of the present invention is that the heat treatment in a nitrogen atmosphere is preferably performed in a temperature range of 800 to 1400 ° C, and is preferably performed in a range of 1000 to 1350 ° C. More preferred. When the temperature is lower than 800 ° C, the formation of the silicon nitride phase is insufficient, and when the temperature is higher than 1400 ° C, the melting point of the silicon metal becomes close to the predetermined shape. It is not preferable because there is. Therefore, according to the purification honeycomb filter manufacturing method of the present invention in which the heat treatment is performed in the above temperature range, it is possible to effectively form a phase of 0.1 to 30% by weight of nitrogen silicon in terms of nitrogen. it can.

The heat treatment time in a nitrogen atmosphere is preferably not more than 5 hours, more preferably 0.5 to 4 hours, and more preferably 1 to 3 hours. Is more preferred. If the time is less than 0.5 hours, the formation of the silicon nitride phase may be insufficient. On the other hand, if the time exceeds 4 hours, the nitridation of the metallic silicon may progress too much, which is not preferable. Therefore, heat treatment in the above temperature range According to the method for manufacturing a honeycomb filter for purifying exhaust gas of the present invention, a phase of 0.1 to 30% by weight of nitrogen silicon in terms of nitrogen can be effectively formed.

In Patent Document 7 of the prior art, since the metal silicon was completely converted to silicon nitride because it was kept at 1600 ° C. for 5 hours in a nitrogen atmosphere, the honeycomb filter was made of only silicon nitride and silicon carbide. Among them, it is a nitrogen silicon phase of 31% by weight or more in terms of nitrogen amount.

The heat treatment may be performed continuously from the main firing, or may be performed after cooling once after the main firing.

The honeycomb structure of the present invention manufactured as described above has a structure in which a sealing material is filled at one end of a predetermined through-hole of a ceramic block, and can be suitably used as the above-described honeycomb filter. In this case, a catalyst such as Pt for promoting the combustion of particulates may be carried on the wall of the ceramic block when the honeycomb filter is subjected to the regeneration treatment.

In addition, the honeycomb filter according to the present invention can be used to purify HC, CO and NOX in exhaust gas discharged from a heat engine such as an internal combustion engine or a combustion device such as a boiler, or to reform a liquid fuel or a gaseous fuel. When used as a catalyst carrier for carrying out the above, a catalyst such as a noble metal such as Pt, Rh, or Pd or an alloy thereof may be supported on the wall of the ceramic block. In this case, the sealing treatment for filling the above-mentioned filler is not always necessary.

When the structure of the honeycomb filter according to the present invention is an aggregate-type honeycomb structure formed by binding a plurality of porous ceramic members via a sealing material layer as shown in FIG. In this way, a porous ceramic member is manufactured. Next, a process of applying a sealing material paste to be a sealing material layer 14 with a uniform thickness on the side surface of the porous ceramic member 20 and sequentially laminating another porous ceramic member 20 was repeated, A laminate of a prismatic porous ceramic member 20 of a predetermined size is produced.

In addition, as a material constituting the above-mentioned scenery material paste, Since the description has been made with respect to the system filter, its description is omitted here.

Next, the laminate of the porous ceramic members 20 is heated to dry and solidify the sealing material paste layer 51 to form a sealing material layer 14. Thereafter, for example, using a diamond force cutter or the like, The outer peripheral portion is cut into the shape shown in FIG. 1 to produce the ceramic block 15.

The present invention in which a plurality of porous ceramic members are bound together via the sealing material layer by forming a ceramic material layer 13 on the outer periphery of the ceramic block 15 using the sealing material paste described above. The honeycomb filter according to (1) can be manufactured.

The manufactured honeycomb structure is obtained by filling one end of a predetermined cell of a ceramic block (porous ceramic member) with a sealing material, and can be suitably used as the above-described honeycomb filter. Also, in this case, a catalyst such as Pt for promoting the burning of particulates is carried on the honeycomb filter wall (partition wall of the porous ceramic member) when the honeycomb filter is subjected to the regeneration treatment. You may.

In addition, the above-mentioned collective honeycomb structure can be used as a catalyst carrier similarly to the one-piece and two-cam structures, and in that case, Pt, Rh, P A catalyst such as a noble metal such as d or an alloy thereof may be supported. Also in this case, the sealing treatment for filling the above-mentioned filler is not necessarily required.

Next, an exhaust gas purifying apparatus using the honeycomb filter according to the present invention will be described.

When the honeycomb filter of the present invention is used as the above-described filter, it is desirable to install the honeycomb filter in the vehicle exhaust gas purification device shown in FIG.

Figure 6 is a cross-sectional view schematically showing one example of an exhaust gas purifying device for a vehicle which the honeycomb filter is installed in the present invention _p

As shown in FIG. 6, the exhaust gas purifying apparatus 600 mainly includes a honeycomb filter 60 according to the present invention, a casing 630 covering the outside of the honeycomb filter 60, and It is composed of a holding sealing material 62 arranged between the honeycomb filter 60 and the casing 63 0, and an end of the casing 63 0 on the side where exhaust gas is introduced is provided with an internal combustion engine such as an engine. An introduction pipe 640 connected to the engine is connected, and a discharge pipe 650 connected to the outside is connected to the other end of the casing 630. The arrows in FIG. 6 indicate the flow of exhaust gas.

Further, in FIG. 6, the structure of the honeycomb filter 60 may be the same as the honeycomb filter 10 shown in FIG. 1 or the same as the honeycomb filter 30 shown in FIG.

Further, on the wall of the honeycomb filter 60, a catalyst such as Pt for promoting the combustion of the particulates is supported via a catalyst support material (not shown) made of γ-alumina or the like.

In the exhaust gas purifying apparatus 600 having such a configuration, exhaust gas exhausted from the power of an internal combustion engine such as an engine is introduced into the casing 630 through the introduction pipe 640, and the honeycomb filter After passing through the partition from the cell 0, the particulates are collected and purified by the partition, and then discharged to the outside through the discharge pipe 65.

In addition, the regeneration treatment for burning and removing the particulates collected by the partition walls of the honeycomb filter 60 is performed continuously using the catalyst supported on the wall portion, or periodically after the catalyst is deposited to some extent. Will be

In the regeneration process, a heating means such as a heater is provided on the exhaust gas inflow side, and the gas heated using the heating means is caused to flow into the inside of the through-hole of the honeycomb filter 60. Alternatively, the honeycomb filter 60 may be heated to burn and remove the particulates deposited on the partition walls.

Alternatively, the particulates may be burned and removed by raising the temperature of the exhaust gas using a post-injection method.

In the exhaust gas purifying apparatus 600 described above, the honeycomb filter 60 according to the present invention has a casing 6330 in a state where the holding sealing material 620 is wound around the outer periphery thereof. It is installed so as to be pushed inside. At this time, a considerable compressive load is applied to the honeycomb filter 60 according to the present invention, and a large internal stress is generated therein. However, as described above, the honeycomb filter 60 according to the present invention has excellent strength. Therefore, it can be installed in the casing 630 without generating cracks or the like. Example

Hereinafter, the honeycomb filter according to the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

(Example 1)

First, the average particle size 30 silicon carbide raw material powder 80 weight ^_0/0 xm, blended with an average particle diameter of 4/20 wt% metal silicon powder xm, as an organic binder to the obtained powder to 100 parts by weight 10 parts by weight of methylcellulose, 2 parts by weight of a plasticizer, 4 parts by weight of a lubricant, and 20 parts by weight of water were added and uniformly mixed and kneaded to obtain a kneaded product for molding. The obtained kneaded product was formed into a honeycomb shape having an outer shape of 35 sleep, a length of 150 hidden, a partition wall thickness of 0.3 mm, a senor density of 300 cells_square inch by an extruder.

Next, the molded body is dried using microwave drying; ^, and then a paste having the same composition as that of the formed molded body is filled in predetermined ends of the through holes and sealed, and then dried again. And dried. This dried body was calcined at 400 ° C for 30 minutes for degreasing, and calcined at 1500 ° C for 15 minutes in an argon atmosphere at normal pressure.

Next, the above sintered body was subjected to a heat treatment at 800 ° C for 3 hours in a nitrogen atmosphere. When confirmed by X-ray diffraction, a phase of silicon nitride was found on or around the surfaces of the silicon carbide powder and the metal silicon powder. A porous honeycomb filter for purifying exhaust gas having a porosity of 60% was manufactured.

Fig. 5 shows an SEM photograph of a cross section of such a honeycomb filter taken with a scanning electron microscope (SE).

(Example 2) The sintering was performed in the same manner as in Example 1 above, and the sintered body was subjected to a heat treatment at 900 ° C. for 3 hours in a nitrogen atmosphere to have a silicon nitride phase on or around the surfaces of the silicon carbide powder and the metal silicon powder A porous exhaust gas purifying honeycomb filter was fabricated.

(Example 3)

The process up to sintering is performed in the same manner as in Example 1, and the sintered body is subjected to a heat treatment at 1000 ° C. for 3 hours in a nitrogen atmosphere to have a silicon nitride phase on or around the surfaces of the silicon carbide powder and the metal silicon powder. A porous exhaust gas purifying honeycomb filter was fabricated.

(Example 4)

The sintering was performed in the same manner as in Example 1 above, and the sintered body was subjected to a heat treatment at 1200 ° C. for 1 hour in a nitrogen atmosphere to form a phase of silicon nitride on or around the surfaces of the silicon carbide powder and the metal silicon powder. A honeycomb filter for purifying exhaust gas having a porous structure was prepared.

(Example 5)

The sintering is performed in the same manner as in Example 1 above, and the sintered body is subjected to a heat treatment at 1200 ° C. for 3 hours in a nitrogen atmosphere to have a silicon nitride phase on or around the surfaces of the silicon carbide powder and the metal silicon powder. A porous exhaust gas purifying honeycomb filter was fabricated.

(Example 6)

The process up to sintering is performed in the same manner as in Example 1, and the sintered body is subjected to a heat treatment at 1300 ° C. for 1 hour in a nitrogen atmosphere to have a silicon nitride phase on or around the surfaces of the silicon carbide powder and the metal silicon powder. A porous exhaust gas purifying honeycomb filter was fabricated.

(Example 7)

The sintering was performed in the same manner as in Example 1 above, and the sintered body was subjected to a heat treatment at 1300 ° C. for 3 hours in a nitrogen atmosphere, and the surface of the silicon carbide powder and the metal silicon powder or the vicinity thereof A porous honeycomb exhaust gas purifying filter having a silicon nitride phase was manufactured.

(Example 8)

The sintering was performed in the same manner as in Example 1 above, and the sintered body was subjected to a heat treatment at 1400 ° C. for 1 hour in a nitrogen atmosphere to have a silicon nitride phase on or around the surfaces of the silicon carbide powder and the metal silicon powder. A porous exhaust gas purifying honeycomb filter was fabricated.

(Reference Example 1)

The sintering was performed in the same manner as in Example 1 above, and the sintered body was subjected to a heat treatment at 750 ° C. for 3 hours in a nitrogen atmosphere, and silicon nitride was formed on or around the surfaces of the silicon carbide powder and the metal silicon powder. A porous exhaust gas purifying honeycomb filter having a phase was prepared.

(Reference Example 2)

The sintering was performed in the same manner as in Example 1 above, and the sintered body was subjected to a heat treatment at 1450 ° C. for 3 hours in a nitrogen atmosphere to have a phase of silicon nitride on or around the surfaces of the silicon carbide powder and the metal silicon powder. A porous exhaust gas purifying honeycomb filter was fabricated.

(Reference Example 3)

80% by weight of a silicon carbide powder with an average particle size of 50 μm and 20% by weight of a metal silicon powder with an average particle size of 10 / im 100 parts by weight of an ataryl resin-based sphere with an average particle size of 20/2 m Add 20 parts by weight of particles, add 10 parts by weight of methylcellulose as an organic binder, 2 parts by weight of plasticizer, 4 parts by weight of lubricant, and 20 parts by weight of water, and uniformly mix and knead for molding Was obtained. The obtained kneaded product was formed into a honeycomb shape having an outer shape of 35 mm, a length of 150 mra, a partition wall thickness of 0.3 mm, and a senore density of 300 sele / square inch by an extruder.

Next, the molded body is dried using a microwave drier, and thereafter, a paste having the same composition as that of the generated molded body is filled in predetermined through holes and sealed, and then dried using a drier. Let dry again. The dried body is calcined for degreasing at 400 for 30 minutes, heated to 1000 ° C at 400 ° C / h in a nitrogen atmosphere, and then heated to 1400 ° C at 400 ° Oh, Further, firing was performed at 1400 ° C. for 10 hours to produce a porous sintered body having a honeycomb structure having a phase of silicon carbide mononitride. When the porous sintered body was examined by X-ray diffraction, no peak corresponding to silicon could be found.

(Comparative Example 1)

The process up to the firing was performed in the same manner as in Example 1, and the subsequent heat treatment was not performed. Thus, a porous exhaust gas purifying honeycomb filter mainly composed of silicon carbide powder and metal silicon powder was produced.

(Comparative Example 2)

The sintering was performed in the same manner as in Example 1 above, and the sintered body was subjected to a heat treatment in the air at 1200 ° C. for 3 hours to form a phase of silicon oxide on or around the surfaces of the silicon carbide powder and the metal silicon powder. A porous honeycomb filter for exhaust gas purification having the following was prepared.

(Comparative Example 3)

60% by weight of silicon carbide raw material powder having an average particle size of 5 μm and 40% by weight of silicon carbide raw material powder having an average particle size of 0.5 μm are used as an organic binder with respect to 100 parts by weight of the obtained powder. 5 parts by weight of methylcellulose, 1 part by weight of a plasticizer, 2 parts by weight of a lubricant, and 10 parts by weight of water were added and uniformly mixed and kneaded to obtain a kneaded product for molding. The obtained kneaded product was formed into a honeycomb shape having an outer shape of 35 mm, a length of 150 mm, a partition wall thickness of 0.3 mra, and a cell density of 300 cen // sq. Inch by an extruder.

Next, the molded body is dried using microwave drying, and then a paste having the same composition as that of the formed molded body is filled in predetermined through holes and sealed, and then dried again using a dryer. Let it. 400 dried body. Then, calcining was performed for 30 minutes for degreasing, followed by baking at 2200 ° C for 3 hours in an atmosphere of argon at normal pressure to produce a porous silicon carbide sintered body having a honeycomb structure.

(Physical property test)

Fabricated according to the above Examples 1 to 8, Reference Examples 1 to 3, and Comparative Examples 1 to 3. A test piece was cut out from each sintered body, and the amount of nitrogen was measured by pressure acid decomposition, steam distillation separation, and neutralization titration, and then converted to the amount of silicon nitride.

In addition, for each sintered body (honeycomb structure) before cutting out the test piece, a three-point bending test (in accordance with JIS R1601-1995) was performed at room temperature using a material testing machine (Instron INSTR0N 5582). ) Was used to calculate the intensity.

In addition, a corrosion test was performed on acid and aluminum oxide using a 6N sulfuric acid solution and a 6N sodium hydroxide solution, and the results are shown in Table 1.

The evaluation of acid resistance and alkali resistance in Table 1 is as follows: X: weight loss at room temperature for 24 hours immersion, △: boiling state, weight loss by 24 hours immersion, 〇: boiling state There was no weight loss by immersion for 24 hours.

【table 1】

FIG. 4 is a graph plotting the change in strength with respect to the amount of silicon nitride contained in the honeycomb filter.

As can be seen from Table 1, the ceramic finoleta according to Example 1 has a low silicon nitride content. The ceramic filters according to Examples 2 to 8 in which the amount of silicon nitride is in the range of 1.0 to 27.8% by weight are slightly lower in acid resistance and alkali resistance because they are relatively small at 0.1% by weight. By having a phase of silicon nitride on or around the surface of silicon carbide powder and metal silicon powder, acid resistance and alkali resistance are improved. As can be seen from Table 1 and FIG. 1, when the amount of silicon nitride is in the range of 0.1 to 30% by weight, the strength of the ceramic filter is relatively large, and in particular, when the amount of silicon nitride is 1 to 15% by weight. In the range, the strength is significantly improved.

On the other hand, when the amount of silicon nitride was less than 0.1% by weight (Reference Example 1), it was confirmed that the film had little silicon nitride film, so that the acid resistance and the alkali resistance were weak. It was also found that there was no improvement in strength in this case. Conversely, when the amount of silicon nitride exceeded 30% by weight (Reference Examples 2 and 3), it was found that the strength which was excellent in acid resistance and alkali resistance was extremely small. This is considered to be due to the fact that metal silicon, which is the bonding portion of silicon carbide, is completely nitrided, or that a large amount of whiskers of silicon nitride are generated. Industrial applicability

The honeycomb filter for purifying exhaust gas according to the present invention is used as a filter for removing particulates and the like in exhaust gas discharged from an internal combustion engine such as a diesel engine, as a catalyst carrier, and the like.

As described above, the exhaust gas purifying honeycomb filter of the present invention can be sintered at a relatively low temperature at the time of its production even though it contains refractory particles such as silicon carbide, so that the production cost is reduced. The yield can be reduced and the cost can be reduced.

In addition, since a silicon nitride phase is formed on or around the surface of silicon carbide powder and silicon powder, it has high thermal conductivity, and has improved acid resistance, alkali resistance, and strength. It can be suitably used as an exhaust gas purifying filter and a catalyst carrier. Further, in the method for manufacturing a honeycomb filter for purifying exhaust gas of the present invention, it is possible to reliably form a phase of silicon nitride on or around the surfaces of the silicon carbide powder and the silicon powder by predetermined steps and conditions. it can.

Claims

The scope of the claims

1. A large number of cells are provided along the axial direction, and a part of these cells is sealed at one end and opened at the other end, Exhaust gas purification comprising one or more aggregates of porous ceramic members having a honeycomb structure, in which some or all of the partition walls separating adjacent cells function as a filter for collecting particles. A honeycomb filter for exhaust gas purification, characterized in that the honeycomb filter includes a ceramic member containing silicon carbide, silicon and silicon nitride.

2. The honeycomb filter for purifying exhaust gas according to claim 1, wherein the content of silicon nitride contained in the ceramic member is 0.1 to 30% by weight.

3. The honeycomb filter for purifying exhaust gas according to claim 1, wherein a catalyst is applied to a part or the whole of the partition wall of the ceramic member.

4. The silicon powder and the organic binder are kneaded with the silicon carbide powder, and the obtained kneaded material is formed into a ceramic member having a honeycomb structure, and a large number of cells provided along the axial direction of the ceramic member are formed. Only one of the ends is plugged, and then calcined to remove the organic binder, and then calcined. A porous ceramic filter containing silicon carbide, silicon nitride, and silicon nitride by nitriding silicon carbide and silicon by heat treatment with a honeycomb filter. .

5. The method for producing a honeycomb filter for purifying exhaust gas according to claim 4, wherein the content of silicon nitride contained in the porous ceramic filter is 0.1 to 30% by weight.