JPH08281036A - Honeycomb structure and manufacture therefor - Google Patents

Abstract

PURPOSE: To provide a honeycomb structure wherein clogging of combustible particulates is hard to be caused, air-flow resistance of exhaust gas is hard to ascend, compact and uniform heating is possible without need for frequent repeated reproduction, and erosion or thermal stress cracking is hard to be caused. CONSTITUTION: The satisfactory honeycomb structure consisting of constitution that ratio occupied by pores having 50-70μm diameter is 30-50 volume % to the all pore volume is porous wall and further porosity or mean pore diameter are >=40% or 5-40μm respectively is provided. Especially, the most satisfactory honeycomb structure is provided through addition of pore forming agent to silicon carbide powder having specified particle size distribution and burning thereof in nonoxidizing atmosphere, and favorable diesel particulates filter is provided by using this honeycomb structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a honeycomb structure which collects combustible fine particles such as soot from exhaust gas, heats and incinerates the same, and particularly collects combustible fine particles discharged from a diesel engine. The present invention relates to a honeycomb structure which is regenerated by heating and incinerating the collected combustible fine particles, and a diesel particulate filter using the honeycomb structure.

[0002]

2. Description of the Related Art Conventionally, a filter for collecting combustible fine particles from exhaust gas such as soot and the like, for example, a filter for collecting combustible fine particles discharged from a diesel engine is a cordierite having a low thermal expansion coefficient. A honeycomb structure having porous walls mainly made of ceramics or silicon carbide ceramics having high thermal conductivity is applied. A filter of such a honeycomb structure has innumerable through-holes connected in a honeycomb shape in the longitudinal direction between the inlet end face and the outlet end face through a porous thin wall, and the inlet end face and the outlet end face of the through holes are alternated. The through hole having the inlet end face sealed is opened at the outlet end face, and the through hole having the inlet end face opened is sealed at the outlet end face. Such a filter having a honeycomb structure is preferably used particularly for collecting combustible fine particles of exhaust gas of a diesel engine, but it is attached as a part of an exhaust gas system, and a through hole of an open inlet end surface is used. Exhaust gas containing combustible particles that flows in from the exhaust gas containing almost no combustible particles because most or all of the combustible particles are collected in the porous wall by completely passing through the porous wall. Flows out of the through hole opened at the outlet end face. Therefore, the pore characteristics of the porous wall through which the exhaust gas passes are such that exhaust gas containing combustible particles can easily flow through the wall, and most or all of the combustible particles can be collected by the porous wall. It must have a suitable pore size and porosity.

In Japanese Patent Publication No. 5-77442, therefore, in the porous wall of the honeycomb structure, the volume of open porosity and the average diameter of the pores forming the open porosity are point 1-G-5-2- on the coordinates. 3-4 (However, point 1; open porosity 58.5%, average pore diameter 1 μm, point G; open porosity 46.8%, average pore diameter 12 μm, point 5; open porosity 39.5%, average pore diameter 15 μm, point 2; open porosity 33.0%, average pore size 15μm, point 3; open porosity 52.5%, average pore size 20μm, point 4; open porosity
90.0%, having an average pore diameter of 1 μm), a particulate filter for a diesel engine exhaust gas system within a zone defined by a boundary line connecting the two is disclosed.

Further, JP-A-61-83689 discloses that in a silicon carbide honeycomb structure in which a large number of through holes are adjacent to each other in the axial direction with thin partition walls, the partition walls have an average aspect ratio.
It is disclosed that the porous body has a three-dimensional network structure mainly composed of plate crystals within the range of 2 to 50.

As described above, since the honeycomb structure has a large effective specific surface area and a large amount of the combustible fine particles collected per unit volume, it is excellent by appropriately selecting the pore diameter and porosity of the porous wall. It has a characteristic of having a collection performance. However, when a certain amount of combustible particles are collected, the porous wall is clogged and the ventilation resistance increases, so it is necessary to incinerate and regenerate the collected combustible particles at regular intervals. This regeneration is mainly performed by injecting burner combustion gas into a filter to incinerate it, combining a nichrome wire heater or a heating metal layer with a filter to heat and incinerate it with an external heater, or applying a material having heater performance to the filter. However, various methods such as a method of uniformly heating and incinerating by energization heat generation of the filter itself are applied.

However, since most of the porous walls of the conventional honeycomb structure are composed of fine pores of 50 μm or less, the combustible fine particles are likely to be clogged, and the ventilation resistance of exhaust gas increases in a short time. , It was necessary to frequently repeat the regeneration by heating and incineration. Therefore, in order to lengthen the collection time, it is unavoidable to increase the porosity excessively or to cope with the filter by enlarging it, resulting in a decrease in strength and an uneven temperature distribution when incinerating combustible particles. There is a problem in that thermal stress cracking or the like is likely to occur due to melting loss of the filter or a heat cycle due to heat incineration.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and it is difficult for porous combustible fine particles to be clogged, exhaust gas ventilation resistance is unlikely to increase, and strength is improved. Therefore, it is an object of the present invention to provide a honeycomb structure that is compact and does not need to be repeatedly regenerated, can be uniformly heated, and is unlikely to cause thermal stress or cracking due to filter melting loss or heat cycle. .

[0008]

That is, a feature of the present invention is a honeycomb structure in which flammable fine particles are collected by a porous wall and the collected combustible fine particles are regenerated by heating and incineration. 50 pore size for the total pore volume of the porous wall
The honeycomb structure has a proportion of pores of ˜70 μm of 30 to 50% by volume. Further, it is more preferable that the porosity of the porous wall of the honeycomb structure is 40% or more and the average pore diameter is 5 to 40 μm, and that the material of the honeycomb structure is mainly composed of silicon carbide. More preferable. The characteristic of the manufacturing method of this honeycomb structure is that the average particle diameter is 5 to
50 μm, 10% diameter (D ₁₀ ) in cumulative particle size distribution
And 50% diameter (D ₅₀ ) particle diameter ratio (D ₁₀ / D ₅₀ ) of 0.2 or more silicon carbide powder with 10% by volume or less of the sintering accelerator added to 100 parts by volume of the average particle diameter 40 to 100 μm pore former
After mixing 15 to 25 parts by volume and molding, it is fired in a non-oxidizing atmosphere at 1600 ° C or higher. Further, a feature of the present invention is a diesel particulate filter using these honeycomb structures.

The present invention will be described in more detail below.

The honeycomb structure of the present invention has a honeycomb structure in which combustible fine particles contained in exhaust gas of, for example, a diesel engine are collected by a porous wall, and the collected combustible fine particles are regenerated by incineration by heating. A body filter with a pore size of 50-70 relative to the total pore volume of the porous wall.
The proportion of pores of μm is 30 to 50% by volume.

The honeycomb structure of the present invention is, for example, in the case of a honeycomb structure for a diesel particulate filter, when the exhaust gas passes through the pores of the porous wall, the combustible fine particles contained in the exhaust gas are contained in the porous wall. The structure is collected by. The ratio of pores with a pore size of 50-70 μm to the total pore volume of the porous wall is 30-50.
The reason why the volume% is necessary is to prevent clogging due to the collection of the combustible particles, and the pores of less than 50 μm are suitable for collecting the combustible particles almost completely. Although it can be increased, there is a problem that combustible fine particles are easily deposited and clogged. Meanwhile, 70
The pores larger than μm can hardly collect the combustible fine particles, so that the collection efficiency is significantly reduced. Therefore, the ratio of pore size 50 to 70 μm that can be included in the porous wall without impairing the collection efficiency is 30 to 30% of the total pore volume.
In the range of 50% by volume, if it is less than 30% by volume, combustible fine particles are likely to be clogged, and the ventilation resistance of exhaust gas increases in a short time.
When it exceeds 50% by volume, the collection efficiency is lowered and the strength of the honeycomb itself is lowered. If more than 5% by volume of pores larger than 100 μm are present, the collection efficiency is also reduced and the strength of the honeycomb itself is reduced. The term "pore size" as used herein refers to that determined by mercury porosimetry, which will be described in detail in the examples.

The porosity of the porous wall of the present invention is 40%.
Or more, preferably 50 to 70%, more preferably 45% to 65%
If it is less than 40%, the ventilation resistance is high, and if it exceeds 70%, the mechanical strength is reduced. The average pore size is 5-40μ.
If the particle size is less than 5 μm in the m range, combustible fine particles are likely to be clogged, and the ventilation resistance of exhaust gas increases in a short time. On the other hand, if the average pore diameter exceeds 40 μm, the collection efficiency is lowered and the filter performance is lowered.

As the material of the honeycomb structure, metal, ceramics, or a composite material thereof can be used.
In order to efficiently collect the combustible fine particles in the exhaust gas passing through the honeycomb structure, it is preferable that the surface roughness of the porous wall surface is rough, and a ceramic material is preferable as the material. In particular, those containing silicon carbide as a main component have a high surface roughness because the gaps between the crystal particles are large, and it is easy to take the exhaust gas into the porous wall, and the pore structure inside the porous wall is complicatedly entangled with the crystal particles. Since the continuous air holes are formed in the gaps in the state, the strength is high, and the inclusion efficiency of the combustible fine particles is high by containing a specific amount of pores of 50 to 70 μm. The term "mainly containing silicon carbide" means that the content of silicon carbide is 80% by weight or more, preferably 90% by weight.
Above, more preferably, 95 wt% or more. Further, as components other than silicon carbide, which is the main component, Al, F
Elementary metals such as e and Cr and other inorganic materials such as oxides, carbides and nitrides thereof may be included.

A diesel particulate filter using a honeycomb structure having such a porous wall is
As described above, in the pore characteristics of the porous wall, the combustible fine particles contained in the exhaust gas of the diesel engine have a specific proportion of pores having a pore diameter of 50 to 70 μm and have an appropriate average pore diameter and porosity. Can be collected by the porous wall, and at this time, increase in ventilation resistance due to clogging of the porous wall due to the collected combustible fine particles can be appropriately suppressed. Further, the material containing silicon carbide as the main component has a high pore strength because the pore structure is pores formed by entangled crystal grains in a complicated state, and exhibits particularly good collection efficiency. Therefore, it is possible to obtain a diesel particulate filter which has a long collection time of the combustible particles and enables the filter to be made compact.

Next, a method for manufacturing the honeycomb structure for a diesel particulate filter of the present invention will be described. First, the average particle size is 5 to 50 μm
A powder of silicon carbide having a particle size distribution of a 10% diameter and a 50% diameter (D ₁₀ / D ₅₀ ) of 0.2 or more, preferably 0.3 or more, more preferably 0.4 or more is used as a main raw material. This particle size ratio (D ₁₀ / D ₅₀ ) is preferably higher as described above,
It is industrially difficult to control the particle size of 5 or more. A sintering accelerator of 10% by volume or less of the total volume after mixing is added to this silicon carbide powder and mixed. As the sintering promoter, Si, A
Various metal powders such as l, Fe and Cr, or oxides of these,
Nitride, carbide, etc. can be used. Since sintering of this silicon carbide powder is possible even without adding a sintering accelerator,
It is not necessary to add these sintering accelerators, but when a sintering accelerator is added, one having higher strength can be obtained.

When the average particle size of silicon carbide is smaller than 5 μm or the particle size ratio (D ₁₀ / D ₅₀ ) of the cumulative particle size distribution is less than 0.2, fine pores having a pore diameter of 5 μm or less are formed on the porous wall. Since the number increases, the average pore diameter decreases. On the other hand, if the average particle diameter of silicon carbide exceeds 50 μm, the sinterability is lowered and the strength of the honeycomb itself is lowered, which is not preferable.

Next, as a method for forming pores, organic resin particles such as polystyrene and polyethylene having an average particle diameter of 40 to 100 μm, or graphite, starch, rice husks, wood chips, etc., which are burned or carbonized by heat treatment, in the raw material powder Is added as a pore-forming agent. The pore diameter and porosity of 50 to 70 μm of the porous wall can be controlled by adjusting the particle size and the filling amount of the pore-forming agent powder. If the average particle size of the pore-forming agent is smaller than 40 μm, it becomes difficult to form pores of 50 μm μm or more, and the average particle size is 100 μm.
If it exceeds μm, the ratio of coarse air holes increases. The amount of the pore-forming agent added is preferably 15 to 25 parts by volume with respect to 100 parts by volume of the silicon carbide powder or the mixture of the silicon carbide powder and the sintering accelerator. Below 15 parts by volume, the porosity is 50 to 70 μm. Is reduced to 25
If it exceeds the volume part, the amount is too large, so that the collection efficiency, the mechanical strength and the like are lowered.

Mixing of these raw material powders can be carried out by dry type, wet type, etc.
Any method can be applied as long as it can be uniformly mixed. Further, in the molding of the mixed raw material, it is possible to add an organic binder such as methyl cellulose or polyvinyl alcohol, and form the honeycomb by extrusion molding or the like.

Next, the through-holes on the inlet end face and the outlet end face of the obtained honeycomb-shaped molded body are alternately plugged with a sealing material containing silicon carbide as a base material as a base material, and the temperature is 1600 ° C. or higher. The firing is preferably performed in a non-oxidizing atmosphere such as Ar, N2, and vacuum at 1700 to 2300 ° C. If the powder to be added as a pore-forming agent is not burned out by firing at a temperature of 1600 ° C or higher in a non-oxidizing atmosphere, the residual carbonaceous component will be removed by 500
It is necessary to perform heat treatment in an oxidizing atmosphere at ℃ to 1000 ℃.

[0020]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples.

(Examples 1 to 5 Comparative Examples 1 to 3) As a starting material, a silicon carbide powder having an average particle size of 5 to 70 μm shown in Table 1 1
Average particle size of 20 to 100μ
m styrene or graphite powder was added as shown in Table 1,
Further, 20% by weight of water and 8.0% by weight of methyl cellulose as a binder were mixed with these mixed powders, and then mixed with a Henschel mixer for 10 minutes. Then, kneading for 30 minutes using a kneader type kneader, using a high-pressure vacuum extrusion molding machine, at a molding pressure of 60 kg / cm ² outer diameter dimension □ 100 mm, cell pitch 2.0 mm,
It was extruded into a honeycomb shape with a wall thickness of 0.4 mm. The obtained compact is cut to a length of 100 mm, and after drying, the inlet end face and the outlet end face are alternately plugged, so a slurry containing silicon carbide powder with an average particle size of 1.0 μm and a solid content of 80% is the main component. Were poured from each end face to a depth of about 10 mm, dried and solidified, and then baked at 2100 ° C. for 1 hr in an Ar atmosphere. Among them, in Examples 3 and 4, Examples 1, 2 and 5, and Comparative Examples 1 and 2, the obtained sintered bodies were further oxidized in the atmosphere at 900 ° C. for 3 hours to incinerate the remaining graphite.

The following characteristics of the honeycomb structure for a diesel particulate filter thus obtained were measured, and the results are shown in Tables 2 and 3. (1) Porosity: Archimedes method. (2) Pore diameter: By mercury porosimetry, assuming that the pores are cylindrical, the average value of the pore diameter and the total pore volume in the total pore volume obtained by dividing the total pore volume by the pore specific surface area. The proportion of pores having a pore diameter of 50 to 70 μm was measured. (3) Mechanical strength: The honeycomb structure was cut into □ 10 × 10 mm, and the compressive strength in the horizontal direction was measured with respect to the through-holes in the inlet end face and the outlet end face of the unsealed portion. (4) Capability of collecting combustible particles: □ 100 × 100 mm diesel particulate filter, exhaust gas components emitted from diesel engine have combustible particle concentration of 0.15 g / Nm ³ , exhaust gas flow rate of 10 Nm ³ / min, temperature 2
A collection test was performed under the condition of 50 ° C, and the time required for the initial pressure loss to reach 150 mm Hg due to collection of combustible particles was measured. Further, a paper filter was attached to the exit end of the honeycomb structure, and the collection efficiency of the filter was calculated from the weight of the combustible fine particles attached.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

(Examples 6 to 8 and Comparative Examples 6 to 8) Silicon carbide powder having an average particle size of 5 to 70 μm was used as a starting material, and 10% by volume or less of a sintering accelerator was added as an internal component. Was blended as shown in Table 4 by the same operation as in Examples 1 to 5 to form a honeycomb shape. Then, both ends were similarly plugged with the silicon carbide slurry, and then 2000 ° C ×
Sintered for 1 hr in Ar atmosphere. Of these, Example 7,
Regarding 8 and Comparative Example 5, the obtained sintered body was further subjected to an oxidation treatment in the atmosphere at 900 ° C. for 3 hours to incinerate the remaining graphite. With respect to the honeycomb structure thus obtained, each physical property was measured by the same method as in Examples 1 to 5. The results are shown in Tables 4, 5, and 6.

[0027]

[Table 4]

[0028]

[Table 5]

[0029]

[Table 6]

(Examples 9 to 11, Comparative Examples 7 to 9) Table 7 shows talc, kaolin, calcined kaolin and alumina as starting materials, and a graphite powder or styrene having a mean particle size of 50 to 100 μm as a pore forming agent. Formulated as described above, Example 1
By the same operation as in 4, extrusion molding was performed into a honeycomb shape. Then, a slurry having the same composition as the starting material of each honeycomb formed body was prepared, whereby both end faces of the honeycomb shape were alternately plugged and sintered in the atmosphere at 1400 ° C. × 1 Hr. The physical properties of the obtained honeycomb structure were measured in the same manner as in Examples 1 to 5. The results are shown in Table 7, Table 8 and Table 9.

[0031]

[Table 7]

[0032]

[Table 8]

[0033]

[Table 9]

As can be seen in Tables 1-9, Examples 1-9
The honeycomb structure of has a high compressive strength, has a good collection efficiency of combustible fine particles contained in the exhaust gas discharged from the diesel engine, and suppresses an increase in ventilation resistance due to the clogging of the porous wall of the honeycomb. Therefore, it was found that the collection time is long and the honeycomb structure is suitable for a diesel particulate filter.

[0035]

EFFECTS OF THE INVENTION The honeycomb structure of the present invention has high strength, the combustible fine particles forming the porous wall are less likely to be clogged, the ventilation resistance of exhaust gas is unlikely to increase, and regeneration is frequently repeated. It is unnecessary and compact and can be heated uniformly, and it is difficult for melt damage of the honeycomb structure and thermal stress cracking due to heat cycle to occur. Therefore, it is excellent as a filter for various kinds of exhaust gas, particularly as a diesel particulate filter.

Claims (5)

[Claims] 1. A honeycomb structure in which flammable fine particles are collected by a porous wall, and the collected combustible fine particles are regenerated by heating and incineration, and a pore diameter of 50 to 70 μm with respect to the total pore volume of the porous wall. 30-50% by volume of pores
And a honeycomb structure. 2. The honeycomb structure according to claim 1, wherein the porous wall of the honeycomb structure has a porosity of 40% or more and an average pore diameter of 5 to 40 μm. 3. The honeycomb structure according to claim 1, wherein the material of the honeycomb structure is mainly composed of silicon carbide. 4. The average particle size is 5 to 50 μm, and the particle size ratio (D ₁₀ ) of the 10% size (D ₁₀ ) and the 50% size (D ₅₀ ) in the cumulative particle size distribution (D
₁₀ / D ₅₀₎ is 10% by volume at an internal split in 0.2 or more silicon carbide powder
Characteristic is that 100 parts by volume of powder containing the following sintering accelerator is mixed with 15 to 25 parts by volume of a pore-forming agent having an average particle size of 40 to 100 μm, molded, and then fired in a non-oxidizing atmosphere at 1600 ° C or higher The method for manufacturing a honeycomb structure according to claim 1, claim 2, or claim 3. 5. A diesel particulate filter using the honeycomb structure according to claim 1, claim 2, or claim 3.