JP2002242655A - Filter for collecting particulate in exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease a pressure loss and improve a trap efficiency. SOLUTION: In this filter for collecting particulate in the exhaust gas, an average value m1 of a gas cavity diameter measured by a method of mercury penetration is within 20 μm to 60 μm, and a value SD1 of standard deviation in a gas cavity diameter distribution in a case where the gas cavity diameter is presented by a common logarithm is 0.20 or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter for collecting particulates contained in exhaust gas of a diesel engine.

[0002]

2. Description of the Related Art The number of automobiles has increased exponentially since the turn of the century, and the amount of exhaust gas emitted from internal combustion engines of automobiles has been increasing rapidly.
In particular, various substances contained in exhaust gas emitted from a diesel engine cause pollution, and are now seriously affecting the world environment. Also,
Recently, studies have reported that particulate matter (diesel particulates) in exhaust gas sometimes causes allergic disorders and a reduction in sperm count.
In other words, it is considered that taking measures to remove particulates in exhaust gas is an urgent task for humanity.

Under such circumstances, various types of exhaust gas purifying devices have been proposed. A general exhaust gas purifying apparatus has a structure in which a casing is provided on an exhaust pipe connected to an exhaust manifold of an engine, and a particulate collection filter in exhaust gas having fine holes is disposed therein. I have. Materials for forming the filter include ceramics in addition to metals and alloys. As a typical example of a filter made of ceramic, a filter made of a cordierite honeycomb structure is known.
An oxidation catalyst is supported on such a honeycomb filter.

[0004] A honeycomb filter has a number of cells extending along its own axial direction. As the exhaust gas passes through the filter, particulates are trapped by its cell walls. As a result, fine particles are removed from the exhaust gas. The trapped fine particles are burned and removed by the oxidizing action of the catalyst.

[0005] In this type of honeycomb filter, if the pore diameter is set too small, the pressure loss when exhaust gas passes through the filter inner wall becomes extremely large, and the engine may be stopped. Therefore, at the time of manufacturing a general cordierite honeycomb filter, a pore-forming agent is added in order to reduce pressure loss, thereby forming pores of several tens μm to one hundred and several tens μm.

[0006]

However, in such a filter in which small pores and large pores are mixed and the pore diameter distribution varies, the number of pores having a size suitable for collecting particulates is small. , Will be relatively small. Therefore, a reduction in the particulate collection efficiency was inevitable.

When a filter having a small pore size is manufactured without using a pore-forming agent, there is a sign that the filter regeneration performance deteriorates with time. Therefore, in order to complete the reproduction completely, there is an inconvenience that the required reproduction time must be set gradually longer. Also, if you want to play with a fixed playback time from the beginning,
There has been a drawback in that after long-term use, unburned fine particles tend to gradually occur.

[0008]

The inventors of the present invention have conducted intensive studies. As a result, if the pore diameter is distributed within a limited narrow range, a size suitable for collecting and oxidizing particulates is obtained. It has been found that the number of pores is relatively large, and the collection efficiency and oxidation can be improved. At the same time, it was newly found that the deterioration of the filter regeneration performance over time was caused by the average pore size. And the inventor of the present application conducted further intensive research based on the above findings, and finally came to the following invention.

That is, a first object of the present invention is to provide a filter for collecting particulates in exhaust gas which has a small pressure loss and a high collection efficiency. A second object of the present invention is to provide a filter for collecting particulates in exhaust gas, which is unlikely to deteriorate with time in filter regeneration performance.

In order to solve the above-mentioned problem, according to the first aspect of the present invention, the average value of the pore diameters measured by the mercury intrusion method is in the range of 20 μm to 60 μm, and the pore diameters are commonly used. The gist is that the value of the standard deviation in the pore diameter distribution when expressed in logarithm is 0.20 or less.

According to a second aspect of the present invention, in the first aspect, a catalyst is supported on the surface of the porous ceramic material constituting the filter. According to a third aspect of the present invention, in the second aspect, the porous ceramic material is a honeycomb structure made of porous silicon carbide.

The "action" of the present invention will be described below. According to the first aspect of the present invention, since the pore diameter of this size is suitable for collecting particulates,
By setting the average pore diameter within the above range, particulates can be reliably collected. If the average value of the pore diameter is less than 20 μm, soot does not enter the inside of the wall, so that the oxidizing performance is reduced, the pressure loss when the exhaust gas passes through the inner wall becomes extremely large, and the engine may be stopped. On the other hand, when the average value of the pore diameter exceeds 60 μm, it becomes impossible to efficiently collect fine particulates. Further, when the value of the standard deviation in the pore size distribution is 0.20 or less, that is, when the pore size is distributed within a limited narrow range, the number of pores in the trapping suitable range is relatively small. More. Therefore, the filter has a low pressure loss and a high collection efficiency and high oxidizing property.

According to the second aspect of the present invention, since the catalyst is carried on the surface of the porous ceramic material having pores having a relatively large diameter, even when the engine is operated for a long time, the catalyst is deposited. Catalyst is less likely to be buried in the reduced particulates. Therefore, as a result of maintaining the state where the catalyst is exposed on the outer surface, a reduction in reaction efficiency is prevented. Therefore, it is difficult for the filter regeneration performance to deteriorate with time.

According to the third aspect of the present invention, by using the honeycomb structure as the porous ceramic material, the particulate trapping capacity is increased and the pressure loss is hardly increased. Moreover, if such a honeycomb structure is formed of silicon carbide,
As described above, even when the average value of the pore diameters is set to be relatively large, a decrease in mechanical strength can be avoided.
Therefore, it is possible to make the filter hard to break.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention applied to an exhaust gas purifying apparatus will be described below in detail with reference to FIGS.

As shown in FIG. 1, the exhaust gas purifying apparatus 1 includes a casing 2 made of a metal pipe.
Is connected to the exhaust pipe Ea of the diesel engine E. In the casing 2, a particulate collection filter 3 for purifying exhaust gas emitted from the diesel engine E is provided. Further, a burner 4 for regeneration processing is mounted in the exhaust pipe Ea.

As shown in FIG. 2, the filter 3 is formed in a honeycomb shape by a porous sintered body such as a silicon carbide sintered body, and has a columnar shape as a whole. A plurality of hollow portions 5a and 5b are formed in the axial direction of the filter 3, and each hollow portion 5a and 5b is open at both ends of the filter 3. Either end opening of each of the hollow portions 5a and 5b on the exhaust gas inflow side and the outflow side is closed by a sealing piece 6 made of a porous sintered body and having a thickness of 5 mm. Due to the closing of the sealing piece 6, a cell 7a opening to the inflow side and a cell 7b opening to the outflow side are formed. The cells 7a and 7b are adjacent to each other via an inner wall 8, and an outer surface of the inner wall 8 carries an oxidation catalyst composed of a platinum group element, other metal elements, and oxides thereof.

As shown by the curve C1 in the graph of FIG. 3, the filter 3 of the present embodiment has an average pore diameter m1 measured by the mercury intrusion method of 20 μm to 60 μm.
m. The average value m1 is 3
More preferably, it is 0 μm to 50 μm.

Here, if the average value m1 of the pore diameter is less than 20 μm, the pressure loss when the exhaust gas passes through the inner wall of the cell becomes extremely large, which may cause the stop of the diesel engine E. Further, when the average value m1 of the pore diameter exceeds 60 μm, it becomes impossible to efficiently collect fine particulates.

Further, the standard deviation value SD1 in the pore diameter distribution when the pore diameter is represented by a common logarithm must be 0.2 or less. The standard deviation value SD1
Is more preferably 0.18 or less, particularly preferably 0.16 or less.

When the value of the standard deviation SD1 exceeds 0.20, that is, when the pore diameters are not distributed within a limited narrow range and vary in size, the pores within the preferable collection range are collected. It cannot be said that the number is relatively large. Therefore, it is difficult to realize the filter 3 having a low pressure loss and a high collection efficiency.

Next, the filter 3 configured as described above is used.
Exhaust gas purifying action and regeneration of the filter 3 will be described. A filter 3 is disposed in the casing 2 to allow exhaust gas to flow. Then, the exhaust gas first flows into each cell 7a through each end opening on the inflow side, and is discharged from the adjacent cell 7b opening to the outflow side through the inner wall 8. The particulates in the exhaust gas are trapped when the exhaust gas passes through the inner wall 8, thereby purifying the exhaust gas. When the amount of trapped particulates in the filter 3 reaches a certain value, the burner 4 is ignited and the filter 3 starts heating. Then, due to the oxidizing action of the catalyst carried on the filter 3, the particulates accumulated in the filter 3 are burned and removed, and the filter 3 is regenerated to its original state.

Then, in order to examine the characteristics of the filter 3 of the present embodiment, an example and a comparative example were manufactured by the following method.

[0024]

EXAMPLES AND COMPARATIVE EXAMPLES (Example) Average particle size is 15 μm
20 parts by weight of α-type silicon carbide powder having an average particle diameter of 30 μ
80 parts by weight of β-type silicon carbide powder, 6 parts by weight of methylcellulose as a binder, 1 part by weight of a lubricant and 20 parts by weight of water
A mixture of parts by weight was used as a starting material. After sufficiently kneading this mixture, a cylindrical molded product having a honeycomb structure was obtained by an extrusion molding method. After drying and degreasing the molded product, the molded product is dried at 1700 ° C. in an argon atmosphere.
For 4 hours. Thereafter, hollow portions 5a and 5b in the calcined body were sealed in a checkered pattern using a sealing piece forming ceramic paste containing silicon carbide. At this time, the thickness was set so that the thickness of a portion to be the sealing piece 6 later was about 5 mm. And, under nitrogen atmosphere, 200
The main baking was performed at 0 ° C. for 4 hours to complete the filter 3 of the example (length 150 mm, outer diameter 140 mm, cell wall thickness 0.43 μm, cell density 170 cells / in 2).

In this embodiment, the average pore diameter m1 measured by the mercury intrusion method is 35 μm, and the standard deviation SD1 in the pore diameter distribution when the pore diameter is represented by a common logarithm is 0.16. (Curve C in the graph of FIG. 3)
1). (Comparative Example) As a comparative example with respect to this embodiment, a filter made of cordierite and having the same shape and the same size as those of the embodiment was manufactured. Here, a pore-forming agent was added to the starting material. As shown by the curve C2 in the graph of FIG.
In this cordierite filter, the average value m2 of the pore diameter measured by the mercury intrusion method is 50 μm,
The value SD2 of the standard deviation in the pore diameter distribution when the pore diameter was represented by a common logarithm was 0.40. (Comparative test and its result) Next, the collection rate of particulates and the pressure loss were investigated.

Regarding the collection rate of the particulates, before and after the filter 3 is mounted, the particulates contained in the exhaust gas passing through the mounting position of the filter 3 are adsorbed on the filter paper, and the reflectance (%) of the filter paper is obtained. To JIS D
According to 1101, measurement was performed optically using a smoke tester. With respect to the pressure loss, the pressure difference (mmHg) between the exhaust gas inflow side and the outflow side of the filter 3 in the filter mounted state was measured 60 minutes after the start of collection.

As a result, the reflectance of the filter paper measured in a state where all the particulates in the exhaust gas were discharged without mounting the filter in the casing 2 was 40%. Next, the reflectance in the filter mounted state was 0% in the example, whereas it was 10% in the comparative example. As is clear from the results, according to the filter 3 of the example, it was possible to completely remove the particulates. Also from this, it was found that the filter 3 of the example had a better collecting ability than the filter of the comparative example.

The pressure difference between the exhaust gas inflow side and the outflow side of each filter was as low as 60 mmHg in the example, while it was as large as 120 mmHg in the comparative example. . As described above, the filter 3 of the present embodiment also has a smaller pressure loss than the comparative example.
The result was proved to be excellent.

The filter 3 of the embodiment was used for a long period of time while repeating the regeneration, and the change in the required regeneration time at that time was measured over time. As a result, there was no particular change in the required regeneration time, and no sign that the filter regeneration performance deteriorated with time was observed.

Therefore, according to the present embodiment, the following effects can be obtained. (1) In the filter 3 of the present embodiment, the average pore diameter m1 measured by the mercury intrusion method is 20 μm to 60 μm.
Is set within the range. Further, the value SD of the standard deviation in the pore diameter distribution when the pore diameter is represented by a common logarithm
1 is set to 0.20 or less. Accordingly, the filter 3 has a large number of pores having a size suitable for trapping particulates therein, and particulates can be trapped reliably. Therefore, it is possible to realize the filter 3 having a low pressure loss and a high collection efficiency.

(2) In the filter 3 of the present embodiment, the catalyst is carried on the surface of a porous ceramic material having pores having a relatively large diameter. Therefore, even when the engine E is operated for a long time, the catalyst is not easily buried in the accumulated particulates. Therefore, the state where the catalyst is exposed on the outer surface is maintained. As a result, the reduction of the surface area due to the burying of the catalyst is prevented, and as a result, the reduction of the reaction efficiency is prevented. Therefore, it is difficult for the filter regeneration performance to deteriorate with time. Therefore, it is possible to avoid problems such as a long required reproduction time.

(3) In the filter 3 of the present embodiment, a honeycomb structure is used as the porous ceramic material.
Therefore, as compared with the case where another structure is used, the allowable amount of particulate collection is increased, and the pressure loss is hardly reduced. Moreover, since such a honeycomb structure is formed of silicon carbide, a decrease in mechanical strength can be avoided even when the average value of the pore diameter is set to a relatively large value as described above. Therefore, it is possible to realize the highly reliable filter 3 which is hard to break and can be used for a long time.

The embodiment of the present invention may be modified as follows. The ceramic material constituting the filter 3 does not necessarily have to be a porous body as in the embodiment, and need not be a honeycomb structure. That is, it is possible to select a network aggregate of ceramic fibers, a ceramic foam, or the like as a filter constituent material.

The ceramic material forming the filter 3 is not necessarily limited to silicon carbide as in the embodiment.
For example, it is possible to select silicon nitride, cordierite, sialon, or the like.

The catalyst may not be supported on the surface of the porous ceramic material constituting the filter 3.
Next, in addition to the technical ideas described in the claims, technical ideas grasped by the above-described embodiments will be listed below.

(1) The value of the standard deviation in the pore diameter distribution when the average value (m1) of the pore diameters measured by the mercury intrusion method is in the range of 30 μm to 50 μm, and the pore diameters are represented by common logarithms. A filter for collecting particulates in exhaust gas, wherein (SD1) is 0.18 or less.

(2) An exhaust gas purifying apparatus in which a casing connected to an exhaust pipe of a diesel engine contains the filter according to any one of claims 1 to 3 and the technical idea 1.

[0038]

As described in detail above, according to the first aspect of the present invention, it is possible to provide a filter for collecting particulates in exhaust gas having a small pressure loss and a high collection efficiency.

According to the second aspect of the present invention, it is possible to provide a filter in which the reproduction performance hardly deteriorates with time. According to the third aspect of the present invention, it is possible to provide a filter that is not easily broken.

[Brief description of the drawings]

FIG. 1 is a partial front sectional view showing a mounted state of a filter for collecting particulates in exhaust gas according to an embodiment of the present invention.

FIG. 2 is a partially enlarged sectional view of a filter for collecting particulates in exhaust gas of FIG. 1;

FIG. 3 is a graph showing pore size distribution states of filters of an example and a comparative example.

[Explanation of symbols]

m1 average value of pore diameter measured by mercury intrusion method,
SD1: The value of the standard deviation in the pore size distribution when the pore size is represented by a common logarithm.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) B01D 53/94 F01N 3/24 E F01N 3/24 B01D 46/42 B // B01D 46/42 53/36 103C F term (Reference) 3G090 AA02 BA02 CA01 3G091 AA02 AA18 AB02 AB13 BA00 CA02 GA06 GB01W GB05W GB06W GB10W GB17X 4D019 AA01 BA05 BB06 BC07 BD01 CA01 CB04 CB06 4D048 AA14 AB01 BA30X BA31X BA32X BA33X4B08 MA01 CD01

Claims (3)

[Claims] An average value (m1) of pore diameters measured by a mercury intrusion method is in a range of 20 μm to 60 μm, and a standard deviation value in a pore diameter distribution when the pore diameter is represented by a common logarithm ( SD1) is 0.20 or less, a particulate trap filter in exhaust gas. 2. A filter for collecting particulates in exhaust gas according to claim 1, wherein a catalyst is supported on the surface of the porous ceramic material constituting said filter. 3. The filter for collecting particulates in exhaust gas according to claim 2, wherein said porous ceramic material is a honeycomb structure made of porous silicon carbide.