JP4428394B2 - Exhaust gas purification filter - Google Patents

Description

  The present invention relates to an exhaust gas purification filter that collects particulates in exhaust gas discharged from an internal combustion engine and purifies the exhaust gas.

  Conventionally, there is an exhaust gas purification filter that collects particulates in exhaust gas discharged from an internal combustion engine and purifies the exhaust gas. The exhaust gas purification filter has a honeycomb structure having partition walls having a large number of pores and cells partitioned by the partition walls.

  When purifying the exhaust gas using the exhaust gas purification filter, the exhaust gas is introduced into the cell and moved to the adjacent cell through the partition wall. At this time, the particulates in the exhaust gas are collected in the partition wall, and the exhaust gas is purified. Further, for example, by collecting a catalyst on the partition wall, the collected particulate can be decomposed and removed by a catalytic reaction.

  As the performance of the exhaust gas purification filter, it is important that the exhaust gas purification efficiency is high and the pressure loss of the exhaust gas to be passed is small. Therefore, as disclosed in Japanese Patent No. 2726616, there has been proposed an exhaust gas purification filter in which the porosity, the hole diameter, etc. are regulated within a predetermined range to improve the performance.

  However, in recent years when a higher performance exhaust gas purification filter is required, it is difficult to sufficiently improve exhaust gas purification efficiency and reduce exhaust gas pressure loss even with the conventional exhaust gas purification filter.

  That is, as shown in FIG. 6, each pore 93 in the partition wall 91 of the exhaust gas purification filter has a nonuniform surface opening diameter and pore diameter. Therefore, a phenomenon occurs in which particulates accumulate on the surface 911 of the partition wall 91 and block the opening 931 of the pore 93, or the particulate is discharged without being collected by the partition wall 91. As a result, it is difficult to sufficiently improve the purification efficiency and reduce the pressure loss.

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide an exhaust gas purification filter having high purification efficiency and low pressure loss.

  The present invention relates to an exhaust gas purification filter that collects particulates in exhaust gas discharged from an internal combustion engine and purifies the exhaust gas. The exhaust gas purification filter is partitioned by a partition wall having a large number of pores and the partition wall. And a plug portion is provided in one of the opening portions of the cell, and the opening portion of the cell in which the plug portion is provided on the end surface of the honeycomb structure. And the openings of the cells not provided with the plugs are alternately arranged, and the partition wall has a surface opening area ratio of 20 μm or less of the surface opening diameter of the whole surface opening area ratio. The partition wall has a surface opening area ratio due to pores having a surface opening diameter of 70 μm or more, and is 40% or less of the entire surface opening area ratio, and the partition wall has pores having a pore diameter of less than 10 μm. Due to pores Is 10% or less, and the porosity of pores having a pore diameter exceeding 70 μm is 10% or less. The surface opening diameters of all the pores formed in the partition walls are measured with a laser depth microscope and averaged. The exhaust gas purification filter is characterized in that the measured value is 1.5 times or more the average value of the surface opening diameters of all the pores formed in the partition walls measured with a mercury intrusion porosimeter ( Claim 1).

  The partition wall has a surface opening area ratio due to pores having a surface opening diameter of 10 μm or less being 20% or less of the entire surface opening area ratio. That is, there are few “pores whose surface opening diameter is too small” where the particulates are likely to be clogged in the opening. Therefore, it is possible to prevent particulates from clogging the pore openings and depositing on the partition walls. Thereby, exhaust gas can be sufficiently introduced into the pores. Therefore, the exhaust gas purification efficiency can be sufficiently increased. Further, the pressure loss of the exhaust gas introduced into the exhaust gas purification filter can be reduced.

  The partition wall has a surface opening area ratio of 40% or less of the entire surface opening area ratio due to pores having a surface opening diameter of 70 μm or more.

  The partition wall has a porosity of 10% or less due to pores having a pore diameter of less than 10 μm. That is, there are few “pores having too small pore diameters” that cause an increase in pressure loss of exhaust gas introduced into the exhaust gas purification filter. Therefore, the pressure loss of exhaust gas can be reduced. In addition, since there are few “pores having too small pore diameters” in which the particulates are likely to clog the pores, it is possible to prevent the particulates from being deposited on the partition walls. Therefore, exhaust gas can be sufficiently introduced into the pores, and the purification efficiency can be increased.

  Further, the porosity due to the pores having a pore diameter exceeding 70 μm is 10% or less. That is, there are few “pores with too large pore diameters” that are relatively difficult to collect particulates. Therefore, the partition can sufficiently collect particulates. Therefore, the exhaust gas purification filter can sufficiently increase the purification efficiency.

  Moreover, the said partition has an average surface opening diameter larger than an average pore diameter.

Therefore, an exhaust gas purification filter having high purification efficiency and low pressure loss is provided. The average surface opening diameter is an average of the surface opening diameters of the pores formed in the partition wall. The average pore diameter is an average of the pore diameters of all the pores formed in the partition wall.

  That is, that the average surface opening diameter is larger than the average pore diameter means that pores having a surface opening diameter larger than the pore diameter exist in a certain ratio or more. And the pore whose surface opening diameter is larger than the pore diameter is relatively difficult for the particulates to be deposited in the opening portion, and the particulates are easily collected inside. Therefore, the pores can be prevented from being blocked and the purification efficiency can be improved. Therefore, the presence of such pores at a sufficient ratio as described above can sufficiently increase the purification efficiency and sufficiently reduce the pressure loss. As described above, the surface opening diameter is measured using a laser depth microscope, and the pore diameter is measured using a mercury intrusion porosimeter.

  Further, the partition wall has an average surface opening diameter of 1.5 times or more of the average pore diameter. Therefore, it is possible to provide an exhaust gas purification filter with high purification efficiency and low pressure loss.

  According to the present invention, it is possible to provide an exhaust gas purification filter having high purification efficiency and low pressure loss.

  In the present invention (Claim 1), the internal combustion engine includes, for example, a diesel engine (the same applies hereinafter). The “surface opening diameter” refers to the diameter of the opening of the pores on the surface of the partition wall. The surface opening diameter is measured using a laser depth microscope. That is, an enlarged image 200 times larger than the surface of the partition wall is processed by the laser depth microscope. As a result, a portion having a depth greater than a predetermined value can be detected as an opening of the pore on the surface of the partition wall, and the surface opening diameter can be calculated.

  The “surface opening area ratio due to pores having a surface opening diameter of 10 μm or less” is, for example, the ratio of the area of all pores having a surface opening diameter of 10 μm or less to the area of the partition wall measured by a laser depth microscope. (The same applies hereinafter). The exhaust gas purification filter is preferably formed by supporting a catalyst on the partition including the inner wall of the pore. Thereby, the particulates collected by the partition walls can be decomposed and removed by the action of the catalyst.

  The pore diameter is obtained by measuring with a mercury intrusion porosimeter. The porosity is a value obtained by measuring with a mercury intrusion porosimeter, for example, and is the volume of pores per unit volume of the partition wall. Preferably, the partition wall has a porosity of 10% or less due to pores having a pore diameter exceeding 50 μm.

  The partition wall preferably has a porosity of 5% or less due to pores having a pore diameter exceeding 70 μm. In this case, the partition can collect the particulates more sufficiently. Therefore, the exhaust gas purification filter can further increase the purification efficiency. Preferably, the porosity of pores having a pore diameter exceeding 50 μm is 5% or less.

  Next, the honeycomb structure is preferably made of cordierite, silicon carbide, aluminum titanate, or zirconium phosphate (Claim 3). In this case, a partition having a desired surface opening diameter, pore diameter, and porosity can be easily formed.

  The overall porosity of the partition walls is preferably 55 to 75%. Thereby, it is possible to provide an exhaust gas purification filter with higher purification efficiency and smaller pressure loss. If the porosity is less than 55%, the pressure loss may increase. On the other hand, when the porosity exceeds 75%, the strength of the exhaust gas purification filter may be reduced.

Further, the exhaust gas purification filter is provided with a plug portion at one of the opening portions of the cell, and at the end face of the honeycomb structure, the opening portion of the cell provided with the plug portion and the plug portion are provided. Preferably, the openings of the cells not provided are arranged alternately, and the area of the openings of the cells is 0.6 to 2.25 mm ² .

  Also in this case, it is possible to provide an exhaust gas purification filter with high purification efficiency and low pressure loss. When the exhaust gas purification filter is used, the exhaust gas is introduced into the cell from an opening where the plug portion is not provided on one end face of the honeycomb structure. The introduced exhaust gas passes through the partition wall, moves to an adjacent cell, and is discharged from an opening portion where the plug portion of the cell is not provided. And when the said exhaust gas passes a partition, purification | cleaning of exhaust gas is performed.

  As described above, since the openings of the cells provided with the plugs and the openings of the cells not provided with the plugs are alternately arranged on the end face of the honeycomb structure, exhaust gas is introduced. The cells and the cells to be discharged are arranged next to each other. Therefore, the exhaust gas efficiently passes through the partition wall. Therefore, an exhaust gas purification filter having excellent purification efficiency can be obtained.

Moreover, since the area of the opening of the cell is 0.6 to 2.25 mm ^2, it is possible to provide an exhaust gas purification filter with higher purification efficiency and lower pressure loss. When the area of the opening of the cell is less than 0.6 mm ² , the pressure loss may increase. On the other hand, when the area exceeds 2.25 mm ² , there is a possibility that sufficient purification efficiency cannot be obtained.

  Further, the partition wall preferably has an average surface opening diameter of 1.5 to 2 times the average pore diameter. This is because it is possible to prevent a reduction in purification efficiency by defining the average surface opening diameter to be not more than twice the average pore diameter.

Example 1
An exhaust gas purification filter according to an embodiment of the present invention will be described with reference to FIGS. The exhaust gas purification filter 1 of the present example collects particulates in exhaust gas discharged from a diesel engine as an internal combustion engine, and purifies the exhaust gas.

  As shown in FIGS. 1 to 3, the exhaust gas purification filter 1 has a honeycomb structure 10 having partition walls 11 having a large number of pores 13 and cells 12 partitioned by the partition walls 11. In the partition wall 11, the surface opening area ratio due to the pores 13 having the surface opening diameter A of 10 μm or less shown in FIG. Further, the partition wall 11 has a surface opening area ratio due to the pores 13 having a surface opening diameter A of 70 μm or more of 40% or less of the entire surface opening area ratio.

  The “surface opening diameter” refers to the diameter of the opening 131 of the pore 13 on the surface 111 of the partition wall 11. The surface opening diameter A is measured using a laser depth microscope. That is, a 200 times magnified image of the surface 111 of the partition wall 11 is processed by the laser depth microscope. As a result, a portion having a depth greater than a predetermined value is detected as the opening 131 of the pore 13 in the surface 111 of the partition wall 11, and the surface opening diameter A is calculated. The surface opening area ratio is a value obtained by measurement with a laser depth microscope, and is the surface opening area of the pores 13 existing per unit area of the partition wall 11.

  The “surface opening area ratio by the pores 13 having a surface opening diameter of 10 μm or less” is the cumulative area occupied by the pores having a surface opening diameter of 10 μm or less in the unit area of the partition wall 11 (the same applies hereinafter). . Further, the exhaust gas purification filter 1 has a catalyst supported on the partition wall 11 including the inner wall of the pore 13 (not shown). Thereby, the particulates collected by the partition wall 11 can be decomposed and removed by the action of the catalyst. The honeycomb structure 10 is made of cordierite. In place of this cordierite, silicon carbide, aluminum titanate, or zirconium phosphate may be employed. The overall porosity of the partition wall 11 is 55 to 75%.

  As shown in FIGS. 1 and 2, the exhaust gas purification filter 1 is provided with a plug portion 14 in one of the openings 121 and 122 of the cell 12. On the end surfaces 191 and 192 of the honeycomb structure 10, the openings 121 and 122 of the cells 12 provided with the plug portions 14 and the openings 121 and 122 of the cells 12 not provided with the plug portions 14 are alternately arranged. Has been placed. That is, as shown in FIG. 1, the plug portion 14 is arranged so as to have a so-called checkered pattern when the honeycomb structure 10 is viewed from the end surfaces 191 and 192. The area of the openings 121 and 122 of the cell 12 is 0.6 to 2.25 mm2.

  Further, the partition wall 11 has an average surface opening diameter larger than the average pore diameter. That is, many pores 13 having a wide opening 131 and a narrow inside as shown in FIG. 4 are formed. Specifically, the average surface opening diameter is 1.5 to 2 times the average pore diameter. The average surface opening diameter is an average of the surface opening diameters of all the pores 13 formed in the partition wall 11. The average pore diameter is an average of the pore diameters of all the pores 13 formed in the partition wall 11.

  When the exhaust gas purification filter 1 is used, as shown in FIG. 2, the exhaust gas 2 is introduced into the cell 12 from the opening 121 where the plug portion 14 is not provided on one end surface 191 of the honeycomb structure 10. To do. The introduced exhaust gas 2 passes through the partition wall 11, moves to the adjacent cell 12, and is discharged from the opening 122 where the plug portion 14 of the cell 12 is not provided. When the exhaust gas 2 passes through the partition wall 11, the exhaust gas 2 is purified.

In manufacturing the exhaust gas purification filter 1, a cordierite raw material comprising the following SiO ₂ raw material, MgO · SiO ₂ raw material, and Al ₂ O ₃ raw material is prepared. That is, in the SiO ₂ raw material and the MgO · SiO ₂ raw material, the particles of 40 μm or more are made 20% by weight or less of the whole, and the particles of 10 μm or less are made 20% by weight or less of the whole. The Al ₂ O ₃ raw material contains 70 μm or more of particles at 10% by weight or less and 5 μm or less of particles at 10% by weight or less.

  Water is added to the cordierite raw material, kneaded and extruded to obtain a honeycomb formed body. After forming, drying and firing are performed. After that, slurry that becomes plug portions 14 in a so-called checkered pattern is applied to the openings of predetermined cells in the honeycomb formed body, and then fired. Thereby, the honeycomb structure 10 provided with the plug portion 14 is manufactured. A catalyst such as platinum is supported on the ceramic structure 10 to obtain an exhaust gas purification filter 1 (FIG. 1).

  Next, the effect of this example will be described. The partition wall 11 has a surface opening area ratio due to pores 13 having a surface opening diameter of 10 μm or less, which is 20% or less of the entire surface opening area ratio. That is, there are few “pores whose surface opening diameter is too small”, in which the particulates are relatively easily clogged in the opening 131. Therefore, it is possible to prevent particulates from clogging in the opening 131 of the pore 13 and depositing on the partition wall 11.

  Thereby, the exhaust gas 2 can be sufficiently introduced into the pores 13. Therefore, the purification efficiency of the exhaust gas 2 can be sufficiently increased. Further, the pressure loss of the exhaust gas 2 introduced into the exhaust gas purification filter 1 can be reduced.

  Further, the partition wall 11 can further improve the purification efficiency because the surface opening area ratio due to the pores 13 having a surface opening diameter of 70 μm or more is 40% or less of the entire surface opening area ratio.

  Next, the honeycomb structure 10 is made of cordierite, silicon carbide, aluminum titanate, or zirconium phosphate. Therefore, it is possible to easily form a partition having a desired surface opening diameter, pore diameter, and porosity. Moreover, since the porosity of the whole partition wall 11 is 55 to 75%, it is possible to provide the exhaust gas purification filter 1 with a smaller pressure loss.

  Further, on the end faces 191 and 192 of the honeycomb structure 10, the openings 121 and 122 of the cell 12 provided with the plug 14 and the openings 121 and 122 of the cell 12 not provided with the plug 14 are provided. Alternatingly arranged. Therefore, the cell 12 for introducing the exhaust gas 2 and the cell 12 for discharging the exhaust gas 2 are arranged next to each other. Therefore, the exhaust gas 2 efficiently passes through the partition wall 11. Therefore, the exhaust gas purification filter 1 having excellent purification efficiency can be obtained.

Moreover, since the area of the openings 121 and 122 of the cell 12 is 0.6 to 2.25 mm ^2, it is possible to provide the exhaust gas purification filter 1 with higher purification efficiency and lower pressure loss.

  Moreover, the said partition 11 has an average surface opening diameter larger than an average pore diameter (FIG. 4). Therefore, the purification efficiency can be further increased and the pressure loss can be reduced. That is, that the average surface opening diameter is larger than the average pore diameter means that the pores 13 having the surface opening diameter larger than the pore diameter exist in a certain ratio or more. And the pore 13 whose surface opening diameter is larger than the pore diameter is relatively difficult to deposit the particulates in the opening 131 and easily collect the particulates inside. Therefore, the pore 13 can be prevented from being blocked and the purification efficiency can be improved.

Therefore, the presence of such pores 13 at a sufficient ratio as described above can sufficiently increase the purification efficiency and sufficiently reduce the pressure loss.
As described above, according to this example, it is possible to provide an exhaust gas purification filter with high purification efficiency and low pressure loss.

(Example 2)
This example is an example of the exhaust gas purification filter 1 in which the pore diameter of the partition wall 11 is defined. That is, the partition wall 11 has a porosity of 10% or less due to the pores 13 having a pore diameter of less than 10 μm. And the porosity by the pore 13 in which a pore diameter exceeds 70 micrometers is 10% or less. More preferably, the porosity due to pores having a pore diameter exceeding 70 μm is 5% or less.

  The pore diameter can be obtained by measuring with a mercury intrusion porosimeter. The porosity is a value obtained by measurement with a mercury intrusion porosimeter, and is the volume of pores per unit volume of the partition wall 11. In this example, the average surface opening diameter of the pores 13 of the partition wall 11 is not particularly defined. Others are the same as in the first embodiment.

  The partition wall 11 has a porosity of 10% or less due to the pores 13 having a pore diameter of less than 10 μm. That is, there are few “pores with too small pore diameters” that cause an increase in pressure loss of the exhaust gas 2 introduced into the exhaust gas purification filter 1. Therefore, the pressure loss of the exhaust gas 2 can be reduced. Further, since there are few “pores having too small pore diameters” where the particulates are likely to clog the pores 13, it is possible to prevent the particulates from being deposited on the partition walls 11. Therefore, the exhaust gas 2 can be sufficiently introduced into the pores 13 and the purification efficiency can be increased.

  Further, the porosity of the pores 13 having a pore diameter exceeding 70 μm is 10% or less. That is, there are few “pores with too large pore diameters” that are relatively difficult to collect particulates. Therefore, the partition wall 11 can sufficiently collect particulates. Therefore, the exhaust gas purification filter 1 can sufficiently increase the purification efficiency.

  As described above, according to this example, it is possible to provide an exhaust gas purification filter with high purification efficiency and low pressure loss.

(Example 3)
In this example, as shown in FIG. 5, the relationship between the average surface opening diameter in the partition wall of the exhaust gas purification filter and the pressure loss of the exhaust gas was measured. Specifically, the pressure loss in nine kinds of pores having an average surface opening diameter in the range of 3 μm to 65 μm was measured by changing the particle diameters of the SiO 2 raw material, Mg · SiO 2 raw material, and Al 2 O 3 raw material. The measurement results are shown in FIG.

  As can be seen from FIG. 5, the pressure loss is particularly large when the average surface opening diameter is 10 μm or less. From this example, it can be seen that the presence of many pores having a surface opening diameter of 10 μm or less is a major cause of a decrease in pressure loss. Therefore, it can be seen that the pressure loss can be reduced by reducing the number of pores having a surface opening diameter of 10 μm or less.

Example 4
In this example, as shown in Table 1, the relationship between the pore size distribution in the partition wall of the exhaust gas purification filter and the pressure loss of the exhaust gas and the particulate collection rate was measured. That is, as shown in Table 1, the ratio of the porosity due to pores with a pore diameter of less than 10 μm to the total porosity, and the ratio of the porosity due to pores with a pore diameter greater than 70 μm with respect to the overall porosity are different. An exhaust gas purification filter was prepared. These were designated as Sample 1 to Sample 4, respectively, as shown in Table 1.

The pore diameter is measured by first injecting mercury into the pores using a mercury intrusion porosimeter on a 10 × 10 × 15 mm sample cut out from the exhaust gas purification filter. The porosity due to the pores was measured. Further, exhaust gas containing particulates was allowed to flow into each exhaust gas purification filter at a flow rate of ² m ² / min. And the pressure loss before and after the exhaust gas purification filter was measured using a manometer. The results are shown in Table 1. In Table 1, the pressure loss ratio is a ratio with respect to the pressure loss value of Sample 1 with reference to (100).

Further, the masses M1 and M2 of the exhaust gas purification filter before and after the exhaust gas was introduced were measured, and the mass N of the particulates that passed through the exhaust gas purification filter was measured. Based on the masses M1, M2, and N, the calculation formula P = (M2−M1) / (M2−M1 + N)
The particulate collection rate P was calculated by calculating by The calculation results are shown in Table 1.

表１より分かるように，細孔径１０μｍ未満の細孔による気孔率が大きいほど，圧力損失は高くなり，細孔径１０μｍ未満の細孔による気孔率が小さいほど，圧力損失は低くなる。一方，細孔径７０μｍを超える細孔による気孔率が大きいほど，捕集率Ｐは低くなり，細孔径７０μｍを超える細孔による気孔率が小さいほど，捕集率は高くなる。

As can be seen from Table 1, the pressure loss increases as the porosity of pores having a pore diameter of less than 10 μm increases, and the pressure loss decreases as the porosity of pores having a pore diameter of less than 10 μm decreases. On the other hand, the larger the porosity due to pores having a pore diameter exceeding 70 μm, the lower the collection rate P, and the smaller the porosity due to pores having a pore diameter exceeding 70 μm, the higher the collection rate.

  And, the ratio of the porosity due to the pores having a pore diameter of less than 10 μm is 10% or less, and the ratio of the porosity due to the pores having a pore diameter exceeding 70 μm is also 10% or less, the sample 4 has a low pressure loss ratio (80 ), High collection rate (96%). From this result, the pressure loss is reduced by setting the ratio of porosity due to pores having a pore diameter of less than 10 μm to 10% or less and the ratio of porosity due to pores having a pore diameter exceeding 70 μm being set to 10% or less. It can be seen that the concentration can be increased.

1 is a perspective view of an exhaust gas purification filter in Example 1. FIG. BRIEF DESCRIPTION OF THE DRAWINGS FIG. Sectional drawing of the partition in Example 1. FIG. 3 is a schematic diagram of pores formed in a partition wall in Example 1. FIG. The diagram showing the relationship between the surface opening diameter in a partition in Example 3, and the pressure loss of waste gas. Sectional drawing of the partition in a prior art example.

Explanation of symbols

1. . . Exhaust gas purification filter,
10. . . Honeycomb structure,
11. . . Bulkhead,
12 . . cell,
13. . . pore,
14 . . Stopper part,
2. . . Exhaust gas,

Claims (6)

In an exhaust gas purification filter that collects particulates in exhaust gas discharged from an internal combustion engine and purifies the exhaust gas,
The exhaust gas purification filter has a honeycomb structure having partition walls having a large number of pores and cells partitioned by the partition walls,
A plug portion is provided in one of the opening portions of the cell, and at the end surface of the honeycomb structure, an opening portion of the cell provided with the plug portion, and an opening portion of a cell not provided with the plug portion are provided. Are arranged alternately,
The partition wall has a surface opening area ratio due to pores having a surface opening diameter of 10 μm or less, which is 20% or less of the entire surface opening area ratio,
The partition wall has a surface opening area ratio due to pores having a surface opening diameter of 70 μm or more, which is 40% or less of the entire surface opening area ratio.
The partition wall has a porosity of 10% or less due to pores having a pore diameter of less than 10 μm, and a porosity of pores having a pore diameter exceeding 70 μm is not more than 10%,
The average value obtained by measuring the surface opening diameter of the pores formed in the partition walls with a laser depth microscope is 1 of the average value obtained by measuring all the pore diameters formed in the partition walls with a mercury intrusion porosimeter. An exhaust gas purification filter characterized by being 5 times or more. 2. The exhaust gas purification filter according to claim 1, wherein the partition wall has a porosity of 5% or less due to pores having a pore diameter exceeding 70 μm. The exhaust gas purification filter according to claim 1, wherein the honeycomb structure is made of any one of cordierite, silicon carbide, aluminum titanate, or zirconium phosphate. The exhaust gas purification filter according to any one of claims 1 and 2, wherein the whole porosity of the partition wall is 55 to 75%. 4. The exhaust gas purification filter according to claim 1, wherein an area of the opening of the cell of the exhaust gas purification filter is 0.6 to 2.25 mm ² . The exhaust gas purification filter according to claim 1, wherein the partition wall has an average surface opening diameter of 1.5 to 2 times an average pore diameter.

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