JP2012240007A - Multiple-pipe filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multiple-pipe filter capable of effectively purifying particulates while suppressing consumption of a catalyst material.SOLUTION: The multiple-pipe filter includes a plurality of inflow cells 36 in which pipe shafts are arranged along with gas passages and outlet parts 35 located downstream of gas flow are closed, a plurality of outflow cells 34 in which pipe shafts are arranged along with gas passages and inlet parts 33 located upstream of gas flow are closed, and partition walls 38 which partition the inflow cells 36 and the outflow cells 34 and have micropores for capturing fine particles by passing through a gas 40, and also includes a catalyst material which is supported so as to reduce the supported amount in accordance with the direction from the inlet parts 33 toward the outlet parts 35 in inflow layers 42 which are layers of the inflow cells 36 of the partition walls 38.

Description

  The present invention relates to a filter that collects and burns particulates (solid carbon fine particles, liquid or solid high molecular weight hydrocarbon fine particles) contained in exhaust gas such as a diesel engine, and purifies the exhaust gas. The present invention relates to a catalyst support structure of a filter.

  Particulates (hereinafter referred to as “PM”) contained in the exhaust gas discharged from the diesel engine have a particle size of approximately 1 μm or less. Such PM tends to float in the atmosphere and is easily taken into the human body during breathing. In addition, since PM contains carcinogenic substances, regulations on PM discharged from diesel engines are being strengthened.

  As an exhaust gas purification filter for removing PM in exhaust gas, a diesel particulate filter (hereinafter referred to as “DPF”) is known.

  Conventional catalyst support structures for DPF include the following. Hereinafter, a conventional DPF catalyst carrier structure will be described with reference to FIGS. 8, 9 and 10. FIG.

  The DPF 10 is a filter disposed in an exhaust gas passage of a diesel engine, and includes a large number of tubular cells having tube axes aligned in a direction along the exhaust gas passage (Y-axis direction in the drawing). Of the many cells, half of the outflow cells 14 have the exhaust gas inlet portion 13 closed by the plug 12 and open at the outlet portion 15, and the other half of the inflow cells 16 have the exhaust gas outlet portion 15 plug 12. And is opened at the inlet 13. And the outflow cell 14 and the inflow cell 16 are arrange | positioned in the state bundled alternately. The partition wall 18 forming the cell is provided with pores through which the exhaust gas 20 can pass but PM can be collected. That is, in this case, the DPF 10 has a wall flow type porous multi-tubular structure.

  Here, the layer on the side of the partition wall 18 where the exhaust gas flows (the layer on the side of the inflow cell 16) is referred to as the inflow layer 22, and the layer on the side of the partition wall 18 where the exhaust gas flows out (the layer on the side of the outflow cell 14). To do. The exhaust gas 20 containing a large amount of PM flows into the inflow cell 16 of the DPF 10, passes through the partition wall 18 of the porous material from the inflow layer 22 toward the outflow layer 28, and PM is collected. The collected PM is purified by the action of a catalyst previously supported on the partition wall 18 of the DPF 10. Thereby, it becomes possible to continuously collect and purify PM discharged from the engine.

  As a conventional exhaust gas filter, the catalyst is uniformly supported on the entire partition wall 18 of the DPF 10, and therefore has the same PM purification ability regardless of where PM is collected.

JP 2009-106922 A

  However, in the inlet portion 13 of the DPF 10, a part of the exhaust gas 20 that has flowed into the inflow cell 16 of the DPF 10 passes through the partition wall 18 of the inlet portion 13 and flows into the outflow cell 14. It flows toward the part 15. The exhaust gas flowing in the inflow cell 16 toward the outlet flows while in contact with the inflow layer 22 which is the inner wall of the inflow cell 16.

  As a result, PM is particularly easily collected in the inflow layer 22 of the inlet portion 13. Further, the collected PM adheres to the pores of the partition walls 18 and narrows the pores, so that the amount of the exhaust gas 20 passing through the partition walls 18 decreases with time. Therefore, PM is not easily collected in the outflow layer 28 of the inlet portion 13.

  However, in the conventional configuration, the inflow layer 22 of the inlet portion 13 where PM is easily collected and high catalytic action is required, and the outflow layer 28 of the outlet portion 15 where PM is extremely difficult to collect and catalytic action is not required. There is a problem that the catalyst is uniformly supported and the purification efficiency of PM is limited.

  Further, most of the exhaust gas flowing through the inflow cell 16 at the outlet 15 of the DPF 10 passes through the partition wall 18 and flows into the outflow cell 14. The exhaust gas 20 passing through the partition wall 18 in this portion flows from the inlet portion 13 to the outlet portion 15 and contacts and flows inside the partition wall 18. Accordingly, the amount of PM contained in the exhaust gas attenuates from the inlet portion 13 side toward the outlet portion 15 side, so that PM is more easily collected by the partition wall 18 on the outlet portion 15 side than the inlet portion 13 side. Furthermore, when the collected PM adheres to the pores of the partition wall 18 on the inlet 13 side and narrows the pores, most of the PM is collected on the inlet 13 side, and almost collected on the outlet 15 side. It will not be collected.

  As described above, when PM is collected in the inflow layer 22 and is not collected in the outflow layer 28, the surface area where the PM contacts the catalyst decreases.

  In such a conventional configuration, since the catalyst is uniformly supported throughout the DPF, the pore diameters of the partition walls on the inflow side and the outflow side are the same size, and PM does not easily penetrate into the outflow side. There is a problem that there is a limit to the purification efficiency.

  The present invention solves the above-described conventional problems, and efficiently disperses the catalyst in a location where a large amount of PM is collected, and further collects the PM in the entire partition wall, so that the PM and the catalyst are in contact with each other. An object of the present invention is to provide a multi-tube filter capable of expanding the surface area to be improved, improving the PM purification effect by the catalyst, and further reducing the amount of catalyst supported.

  In order to achieve the above object, a multi-tube filter according to the present invention includes a plurality of inflow cells in which a tube axis is disposed along a gas flow path and an outlet side that is downstream of the gas flow is closed, and a gas flow path. A plurality of outflow cells arranged along the tube axis, the inlet side being upstream of the gas flow is blocked, and the inflow cells and the outflow cells, and pores through which gas is collected to collect fine particles. A multi-tubular filter having a partition wall having a catalytic substance supported so that a supported amount decreases in an inflow layer as a layer on the inflow cell side of the partition wall from an inlet portion toward an outlet portion. It is characterized by.

  With such a configuration, a large amount of catalyst material is disposed in a place where a large amount of PM is collected, so that the PM purification efficiency can be improved.

  Furthermore, in the outflow layer, which is the layer on the outflow cell side of the partition wall, the catalyst material supported so that the supported amount increases from the inlet portion toward the outlet portion may be provided.

  With such a configuration, a large amount of PM is collected in the inflow layer and the pores are blocked, so that the catalyst material is reduced in the outflow layer of the inlet portion where PM is difficult to collect, and the outflow of the outlet portion where PM is easily collected to the inside of the partition wall. The layer carries more catalyst material. Thereby, PM purification efficiency can be improved even with a small amount of catalyst material as a whole.

  Moreover, it is preferable that the amount of the catalyst material supported on the inflow layer is larger than the amount of the catalyst material supported on the outflow layer at the inlet portion.

  With this configuration, the catalyst material is supported in a place where PM is collected and the catalyst material in a place where PM is not collected is reduced, so that the PM purification efficiency can be improved even with a small amount of catalyst material as a whole of the multi-tube filter. it can.

  Moreover, it is preferable that the amount of the catalyst material supported on the inflow layer is smaller than the amount of the catalyst material supported on the outflow layer at the outlet.

  With this configuration, the PM becomes larger in the outflow layer than in the inflow layer, so that PM passes through the inflow layer of the partition wall and is sufficiently collected in the outflow layer. For this reason, since PM is collected on the inflow side of the partition wall and the contact probability between the PM and the catalyst substance caused by blocking the pores of the partition wall can be prevented, the PM purification efficiency is improved.

  Here, the average pore diameter of the inflow layer is preferably 10 to 20 μm, and the average pore diameter of the outflow layer is preferably 5 to 15 μm.

  In addition, the amount of the catalyst substance supported in the inflow layer at the inlet portion is A, the amount of the catalyst material supported in the outflow layer is B, and the catalyst of the inflow layer is intermediate between the inlet portion and the outlet portion. When the loading amount of the substance is C and the loading amount of the catalyst substance in the outflow layer is D, the following formula 1 may be satisfied.

  (A / B) / (C / D) = α (1.5 ≦ α ≦ 5.5) Equation 1

  In addition, in the outlet portion, the loading amount of the catalytic material in the inflow layer is E, the loading amount of the catalytic material in the outflow layer is F, and the catalyst of the inflow layer is intermediate between the inlet portion and the outlet portion. When the loading amount of the substance is C and the loading amount of the catalyst substance in the outflow layer is D, the following formula 2 may be satisfied.

  (C / D) / (E / F) = β (1.5 ≦ β ≦ 5.5) Equation 2

  With this configuration, it is possible to improve the PM purification efficiency with a small amount of catalyst.

  As described above, according to the multi-tubular filter of the present invention, the portion of the partition wall where the catalyst can be efficiently supported on the partition wall and the PM can be effectively collected in accordance with the trapped state of the PM. By spreading to the outflow side, it is possible to increase the contact probability between the PM and the catalyst material, and to achieve highly efficient PM purification while keeping the amount of the catalyst material low.

FIG. 1 is a side sectional view showing the structure of the DPF of the present invention. FIG. 2A is a conceptual diagram illustrating a distribution state of the catalytic substance in the inflow layer viewed from the ii direction in the DPF illustrated in FIG. FIG. 2b is a graph showing a change in the amount of the catalyst substance supported in the inflow layer as viewed from the ii direction in the DPF shown in FIG. FIG. 3A is a conceptual diagram illustrating a distribution state of the catalytic substance in the outflow layer as viewed from the ii-ii direction in the DPF illustrated in FIG. FIG. 3B is a graph showing a change in the amount of the catalyst substance supported in the outflow layer as viewed from the ii-ii direction in the DPF shown in FIG. FIG. 4A is a conceptual diagram showing a distribution state of the catalyst substance inside the partition wall at the entrance of the iii-iii portion in the DPF shown in FIG. FIG. 4B is a graph showing a change in the amount of the catalyst material supported inside the partition wall at the inlet of the iii-iii portion in the DPF shown in FIG. FIG. 5a is a conceptual diagram showing a distribution state of the catalyst substance inside the partition wall at the outlet of the iv-iv portion in the DPF shown in FIG. FIG. 5B is a graph showing a change in the amount of the catalyst substance supported in the partition wall at the outlet of the iv-iv portion of the DPF shown in FIG. FIG. 6 is a conceptual diagram showing a distribution state of the catalyst substance inside the partition wall in the DPF shown in FIG. FIG. 7 is a graph showing the correlation between catalyst loading and purification characteristics in the DPF. FIG. 8 is a front view showing the structure of a conventional DPF. FIG. 9 is a side sectional view showing the structure of a conventional DPF. FIG. 10 is a conceptual diagram showing a distribution state of a catalyst substance inside a partition wall of a conventional DPF.

  Embodiments of the present invention will be described below with reference to the drawings. In these drawings, common elements are given the same reference numerals. However, the following embodiment is merely an example, and it goes without saying that the present invention is not limited to this embodiment.

(First embodiment)
The multi-tube filter according to the first embodiment will be described below. In the following description and claims, the words are defined as follows.

  The “inlet portion 33” is an upstream side of the flow of exhaust gas inside the DPF 30, and when the distance of the portion excluding the plug 32 from the inlet to the outlet of the DPF 30 is L, L / 12 to L / 4 part.

  The “exit portion 35” is the downstream side of the exhaust gas inside the DPF 30, and is a portion of 3L / 4 to 11L / 12 from the inlet.

  The “inflow layer 42” is a layer on the side where the exhaust gas flows in the partition wall 38 of the DPF 30, and is a layer of the partition wall 38 having a depth of about 50 to 150 μm from the surface of the partition wall 38.

  The “outflow layer 48” is a layer on the side from which the exhaust gas flows out in the partition wall 38 of the DPF 30, and is a layer of the partition wall 38 having a depth of about 50 to 150 μm from the surface of the partition wall 38.

  FIG. 1 is a side sectional view showing the structure of the DPF of the present invention.

  In FIG. 1, a DPF 30 is a filter disposed in the exhaust gas 40 passage of the diesel engine, and is configured by a number of tubular cells that are arranged with the tube axes aligned along the flow direction of the exhaust gas 40. In the DPF 30, the tube axis of the cell is arranged along the gas flow path (Y-axis direction in FIG. 1). When the end portion is viewed from the Y-axis direction, the rectangular annular cell is matrixed in the XZ plane as shown in FIG. The structure is bundled in a shape. The cross-sectional shape of the tubular cell may be not only a rectangle but also a hexagon. When the cross-sectional shape of the cell is a hexagon, the DPF 30 has a honeycomb structure.

  Among these cells, the cell in which the inlet portion 33 is blocked and the outlet portion 35 is opened is the outflow cell 34. Conversely, the cell that is opened at the inlet 33 and the outlet 35 is closed is the inflow cell 36. The inflow cell 36 and the outflow cell 34 are disposed adjacent to each other. The partition wall 38 that partitions the inflow cell 36 and the outflow cell 34 is formed of a porous material provided with a large number of pores through which the exhaust gas 40 can pass and PM can be collected. The DPF 30 has a wall flow type porous multi-tubular structure.

  When the exhaust gas 40 flows into the DPF 30 from the inlet 33, the exhaust gas 40 flowing into the inflow cell 36 always passes through the partition wall 38 made of a porous material, so that PM is collected by the partition wall 38. The collected PM is purified by the action of the catalyst material previously supported on the partition wall 38 of the DPF 30. Thereby, the DPF 30 can continuously collect and purify PM discharged from the engine.

  Here, the inflow layer 42 of the inlet 33 is a region LA, the outflow layer 48 of the inlet 33 is a region LB, the inflow layer 42 of the outlet 35 is a region LE, and the outflow layer 48 of the outlet 35 is a region LF. The amount of the catalyst material in the region LB is A, the amount of the catalyst material in the region LB is B, the amount of the catalyst material in the region LE is E, and the amount of the catalyst material in the region LF is F.

  Here, the supported amount is the amount of the catalyst material supported per unit volume of the partition wall 38. Further, the amount of the catalyst substance is any one of the number of particles of the catalyst substance, the total weight, the total volume, and the total surface area.

  The material of the porous multitubular structure of the DPF 30 is preferably a metal or a ceramic. In particular, when the partition wall 38 is metallic, a relatively inexpensive and high melting point simple metal such as iron, copper, nickel, chromium, titanium, or an alloy thereof can be used as a material. In addition, the material of the partition 38 is not limited to these. When the partition wall 38 is a ceramic porous body, mullite, cordierite, aluminum titanate, silica, alumina, silica alumina, silicon carbide, silicon nitride, or the like can be used. In addition, the material of the partition 38 is not limited to these.

  Although there is no restriction | limiting in particular in the shape and magnitude | size of DPF30, It is preferable to set it as the circular pipe shape of diameter 1-30cm and height 2-30cm.

  As the catalyst material supported on the partition wall 38 of the DPF, at least one selected from metal oxides, noble metals such as platinum, alkali metals, alkaline earths, and rare earths can be used. Examples of the noble metal contained in the catalyst material include rhodium, palladium, iridium, and platinum. Examples of the metal oxide contained in the catalyst material include one containing copper, one containing vanadium or molybdenum, one containing both copper and vanadium, and one containing both copper and molybdenum. Examples of the alkali metal contained in the catalyst substance include lithium, sodium, potassium, and cesium. Examples of the alkaline earth metal contained in the catalyst material include calcium, strontium, and barium. Examples of the rare earth include lanthanum and yttrium.

  2a is a conceptual diagram showing a distribution state of the catalyst substance in the inflow layer 42 as seen from the ii direction in the DPF 30 shown in FIG. 1 according to Embodiment 1 of the present invention.

  FIG. 2B is a graph showing a change in the amount of the catalyst substance supported in the inflow layer 42 as viewed from the ii direction in the DPF 30 shown in FIG. 1 according to Embodiment 1 of the present invention.

  FIG. 3A is a conceptual diagram showing a distribution state of the catalyst material in the outflow layer 48 as viewed from the ii-ii direction in the DPF 30 shown in FIG. 1 according to Embodiment 1 of the present invention.

  FIG. 3B is a graph showing a change in the amount of the catalyst substance supported in the outflow layer 48 as viewed from the ii-ii direction in the DPF 30 shown in FIG. 1 according to Embodiment 1 of the present invention.

  FIG. 4A is a conceptual diagram showing a distribution state of the catalytic substance in the partition wall 38 of the inlet 33 of the iii-iii portion in the DPF 30 shown in FIG. 1 according to Embodiment 1 of the present invention.

  FIG. 4b is a graph showing a change in the amount of the catalyst substance supported in the partition wall 38 of the inlet 33 of the iii-iii portion in the DPF 30 shown in FIG. 1 according to Embodiment 1 of the present invention.

  FIG. 5A is a conceptual diagram showing a distribution state of the catalyst substance in the partition wall 38 of the outlet portion 35 of the iV-iV portion in the DPF 30 shown in FIG. 1 according to Embodiment 1 of the present invention.

  FIG. 5B is a graph showing a change in the amount of the catalyst substance supported in the partition wall 38 of the outlet portion 35 of the iV-iV portion in the DPF 30 shown in FIG. 1 according to Embodiment 1 of the present invention.

  As shown in these drawings, the exhaust gas 40 that has flowed into the inflow cell 36 of the DPF 30 becomes the exhaust gas 401 that flows almost in parallel with the partition wall 38 in the inflow cell 36 toward the outlet portion 33 in the inlet portion 33. Part of the exhaust gas 402 passes through the partition wall 38 of the inlet 33 and flows into the outflow cell 34. The exhaust gas 401 flows in contact with the inflow layer 42 region LA which is the inner wall of the inflow cell 36. Further, the exhaust gas 402 flows in contact with the inner surfaces of the pores of the partition wall 38 from the region LA of the inflow layer 42 toward the region LB of the outflow layer 48.

  Since the exhaust gas 401 passes through the partition wall 38 between the inlet portion 33 and the outlet portion 35, the exhaust gas flowing in the inflow cell 36 toward the outlet portion 35 gradually decreases as the outlet portion 35 is approached. .

  In the outlet portion 35, the exhaust gas 403 that passes through the partition wall 38 of the outlet portion 35 and flows into the outflow cell 34 flows in contact with the inner surface of the pores of the partition wall 38 from the region LE of the inflow layer 42 toward the outflow layer 48 region LF. .

  Since the PM contained in the exhaust gas 401 has a very small particle diameter of about 1 μm or less and causes an irregular Brownian motion, a part of the PM is also generated when the exhaust gas 401 flows in the inflow cell 36 toward the outlet portion 35. It is collected in the area LA of the inflow layer 42.

  The exhaust gas flowing in the inflow cell 36 from the inlet portion 33 to the outlet portion 35 toward the outlet portion 33 substantially in parallel with the partition wall 38 decreases, and accordingly, the collection rate of PM in the inflow layer 42 also increases. It decreases from 33 area | region LA to the exit part 35 area | region LE.

  When PM is collected in the inflow layer 42, PM adheres to the pores of the partition wall 38, the average pore diameter becomes small, and PM becomes difficult to be collected in the outflow layer 48. Therefore, the collection rate of PM in the outflow layer 48 increases from the region LB of the inlet portion 33 to the region 35 LF of the outlet portion.

  Further, PM contained in the exhaust gas 402 is collected so as to gradually decrease from the region LA of the inflow layer 42 to the outflow layer 48 region LB while passing through the inside of the partition wall 38. Here, when PM is collected in the region LA of the inflow layer 42 and the pore diameter is narrowed, PM is more likely to be collected in the region LA of the inflow layer 42, and therefore PM is particularly captured in the region LB of the outflow layer 48. It becomes difficult to be collected. Further, the amount of exhaust gas 402 flowing through the partition wall 38 is reduced.

  In addition, PM contained in the exhaust gas 403 is collected so as to gradually decrease from the region LE of the inflow layer 42 to the region LF of the outflow layer 48 while passing through the inside of the partition wall 38. Here, when PM is collected in the region LE of the inflow layer 42 and the pore diameter is narrowed, the PM is more easily collected in the region LE of the inflow layer 42, so that more PM is captured in the region LF of the outflow layer 48. It becomes difficult to be collected. Thus, when PM is collected in the inflow layer 42 and is not collected in the outflow layer 48, the area where the PM and the catalyst come into contact with each other and the PM can be purified decreases.

  As shown in FIGS. 2a and 2b, A and E, which are the loading amounts of the catalyst substance in the inflow layer 42, are distributed so as to decrease from the inlet portion 33 to the outlet portion 35 of the DPF 30.

  Further, B and F, which are the loadings of the catalyst substance in the outflow layer 48, are distributed so as to increase from the inlet portion 33 to the outlet portion 35 of the DPF 30, as shown in FIGS. 3a and 3b.

  Further, as shown in FIGS. 4 a and 4 b, the outflow layer 48 is smaller in the outflow layer 48 than the inflow layer 42.

  In addition, as shown in FIGS. 5 a and 5 b, the outflow layer 48 has a larger amount of the catalyst material loaded E and F at the outlet portion 35 than the inflow layer 42.

  With such a configuration, a large amount of catalyst material is supported in a place where PM is easily collected, and the amount of catalyst material in the entire DPF 30 is the same as that of the conventional DPF by reducing the amount of catalyst material in a place where PM is difficult to collect. PM purification efficiency about 1.1 to 1.2 times higher than that of DPF can be obtained. That is, the PM purification efficiency can be improved more efficiently even with a small amount of catalyst material.

  Further, since the average pore diameter of the partition wall 38 is larger in the inflow layer 42 than in the outflow layer 48 of the outlet portion 35, PM can be further permeated into the outflow layer 48. That is, since the catalyst substance and PM can be brought into contact in a wider range, the PM purification efficiency can be improved.

  The loading amount of the catalyst substance at the inlet portion 33 is preferably 1.5 to 5.5 times in the inflow layer 42 as compared with the outflow layer 48. If it is less than 1.5, the PM purification ability is weak, and PM that is easily collected in the inflow layer 42 cannot be removed efficiently. On the other hand, if it is larger than 5.5, the pore diameter of the partition wall is narrowed, and the PM tends to block the pores of the inflow layer 42 and prevents the PM from penetrating into the outflow layer 48. And PM purification efficiency falls.

  Further, the catalyst material of the outlet portion 35 is preferably 1.5 to 5.5 times in the outflow layer 48 as compared with the inflow layer 42. If it is less than 1.5, the PM closes the pores of the inflow layer 42 and is easily collected, and prevents the PM from penetrating into the outflow layer 48. Therefore, the surface area where the PM and the catalyst come into contact is reduced, and the PM purification efficiency is improved. descend. If it is larger than 5.5, it is considered that the PM purification action of the inflow layer 42 is reduced, PM is easily collected in the inflow layer 42, and the PM purification efficiency is lowered.

  The cell size is preferably a rectangle having a side of 0.5 to 2 mm.

  The average pore diameter of the region LE of the inflow layer 42 of the outlet portion 35 is preferably 7 to 15 μm, and the average pore diameter of the partition wall of the region LF of the outlet layer 48 of the outlet portion is preferably 5 to 13 μm. This average pore diameter is not particularly limited.

(Embodiment 2)
FIG. 6 is a conceptual diagram showing a distribution state of the catalyst substance in the partition wall 38 in the DPF shown in FIG. 1 according to Embodiment 2 of the present invention.

  Here, it is assumed that the inflow layer 42 in the central portion 50 is the region LC, the outflow layer 48 in the central portion 50 is the region LD, the loading amount of the catalytic material in the region LC is C, and the loading amount of the catalytic material in the region LD is D.

  Here, the “central portion 50” is the upstream side of the exhaust gas inside the DPF 30 and is 5/12 from the inlet when the distance of the portion excluding the plug 32 from the DPF inlet to the outlet is L. ~ 7/12 part.

  The exhaust gas 40 that has flowed into the inflow cell 36 of the DPF 30 passes through the partition wall 38 of the central portion 50 and the exhaust gas 401 that flows in the central portion 50 almost in parallel with the partition wall 38 toward the outlet portion 33. The exhaust gas 406 flows into the outflow cell 34. The exhaust gas 401 flows in contact with the region LC of the inflow layer 42 that is the inner wall of the inflow cell 36. Further, the exhaust gas 406 flows in contact with the inside of the partition wall 38 from the region LC of the inflow layer 42 toward the region LD of the outflow layer 48.

  Since the PM contained in the exhaust gas 401 has a very small particle diameter of about 1 μm or less and causes an irregular Brownian motion, a part of the PM is also generated when the exhaust gas 401 flows in the inflow cell 36 toward the outlet portion 35. It is collected in the region LC of the inflow layer 42.

  Further, PM contained in the exhaust gas 406 is collected so as to gradually decrease from the region LC of the inflow layer 42 to the region LD of the outflow layer 48 while passing through the inside of the partition wall 38. Here, when PM is collected in the region LC of the inflow layer 42 and the pores are narrowed, PM is more easily collected in the inflow layer 42 region LC. Therefore, PM is more collected in the region LD of the outflow layer 48. It becomes difficult to be done. Thus, when PM is collected in the inflow layer 42 and is not collected in the outflow layer 48, the area where the PM and the catalyst come into contact with each other and the PM can be purified decreases.

  The loading amounts A to F of the catalyst material in the partition wall 38 of the DPF are as shown in FIG. That is, in the area LA of the inflow layer 42 of the inlet 33, A is particularly larger than other areas. In the region LB of the outflow layer 48 of the inlet portion 33, B is particularly less than other regions. In the region LC of the inflow layer 42 in the central portion 50, C is an average amount. In the region LD of the outflow layer 48 in the central portion 50, D is an average amount. In the region LE of the inflow layer 42 of the outlet portion 35, E is smaller than other regions. In the region LF of the outflow layer 48 of the outlet portion 35, F is larger than other regions.

  With this configuration, a large amount of catalyst material is supported in the area LA where PM is easily collected, and the amount of catalyst material is reduced in the area LB where PM is difficult to be collected. The purification efficiency can be improved.

  Further, the region LE of the inflow layer 42 carries less catalyst material than the region LF of the outflow layer 48 of the outlet portion 35, and the average pore diameter of the partition wall 38 is increased, so that PM is further transferred to the outflow layer 48. Can penetrate. That is, since the surface area where the catalyst material and the PM come into contact can be increased, the PM purification efficiency can be improved.

  In the central portion 50, in order to satisfy both of the functions of supporting a large amount of catalyst in a region where PM is easily collected and increasing the surface area where the PM and the catalyst are in contact with each other and improving the PM purification capability, In the region LC and the region LD, a catalyst substance is supported on average, and the PM purification efficiency can be improved.

  The partition wall 38 of the DPF 30 is preferably made of SiC. The diameter of the DPF 30 as a whole is 2 to 30 cm, the length is 5 to 30 cm, the partition wall 38 has a thickness of 250 to 400 μm, and the porosity is 30. ~ 50% is preferred.

  The present invention is not limited to the above embodiment. For example, another embodiment realized by arbitrarily combining the components described in this specification and excluding some of the components may be used as an embodiment of the present invention. In addition, the present invention includes modifications obtained by making various modifications conceivable by those skilled in the art without departing from the gist of the present invention, that is, the meaning described in the claims. It is.

  For example, the catalyst material inside the partition wall 38 of the multi-tube filter may be supported more in the central portion of the multi-tube filter than in the outer peripheral portion of the multi-tube filter.

  With such a configuration, the PM purification efficiency can be improved by supporting more catalyst material at the center of the DPF 30 where the exhaust gas amount is large and the PM amount is collected.

  FIG. 7 is a graph showing a correlation between catalyst dispersibility and PM purification ability in the DPF 30 according to Embodiment 2 of the present invention.

  The PM purification capacity was determined from the following experiment.

  First, a predetermined amount of PM is collected in a DPF 30 that previously supports a catalyst substance so as to have a predetermined catalyst dispersibility. Next, heat treatment is performed on the DPF 30 that has collected PM to supply hot air having a predetermined air volume at a predetermined temperature to the inside of the DPF 30 for a predetermined time. Here, the amount of weight change before and after the heat treatment was defined as the PM purification amount of the DPF 30. The PM purification capacity of the DPF 30 is a value obtained by dividing the PM purification amount of the DPF 30 by the reference PM purification amount of the reference DPF 30 in which the catalyst material is supported on the partition wall 38 substantially uniformly.

  Moreover, catalyst dispersibility (alpha) and (beta) are shown. The catalyst dispersibility α and β are defined as follows.

  α = (A ÷ B) ÷ (C ÷ D), β = (C ÷ D) ÷ (E ÷ F)

  Further, the catalyst substance loadings A, B, C, D, E, and F are average values in the corresponding region.

  In this case, a fluorescent X-ray analyzer (XRF) manufactured by HORIBA was used to determine the loadings A to F of the catalyst substance. In addition, the catalytic substance can be quantified by a scanning analytical electron microscope (EM-EDX) or ICP emission analysis.

  As shown in FIG. 7, it can be seen that when the catalyst dispersibility value is in the range of 1.5 ≦ α ≦ 5.5 and 1.5 ≦ β ≦ 5.5, it has a high PM purification capacity.

  When the value of the catalyst dispersibility α is less than 1.5, PM that is easily collected in the inflow layer 42 of the inlet portion 33 of the DPF 30 is efficiently removed without much difference from the conventional case where the catalyst is uniformly dispersed over the entire surface of the DPF. It is not possible to efficiently disperse the catalyst material at a location where a large amount of PM of the present invention is collected, and to further penetrate the PM into the partition wall 38, thereby increasing the contact area between the PM and the catalyst material. This is probably because the effect of improving the purification effect was not obtained.

  If the value of the catalyst dispersibility β is less than 1.5, PM is collected in the inflow layer 42 of the outlet portion 35 of the DPF 30 without much difference from the case where the catalyst substance is uniformly dispersed over the entire surface of the conventional DPF. Since 40 closed the pores of the inflow layer 42 and the contact area between the PM and the catalytic material was reduced, it is considered that the PM purification effect was reduced.

  Further, when the value of the catalyst dispersibility α exceeds 5.5, PM closes the pores of the inflow layer 42 at the inlet 33 of the DPF 30 and is easily collected, so that the PM penetrates into the outflow layer 48. Therefore, the surface area of contact between the PM and the catalyst substance is reduced, and the PM purification efficiency is reduced. Further, the inflow layer 42 and the outflow layer 48 of the partition wall 38 can extremely bias the catalyst, and the exhaust gas 40 flowing through the partition wall 38 is extremely reduced at the inlet portion 33 of the DPF 30, and from the central portion 50 to the outlet portion 35 of the DPF 30. Since a lot of exhaust gas flowed, more PM was purified relatively from the central part 50 to the outlet part 35 of the DPF 30, and it is considered that the PM purification efficiency deteriorated.

  Further, when the value of the catalyst dispersibility β exceeds 5.5, the PM purification ability of the inflow layer 42 is reduced at the outlet portion 35 of the DPF 30, so that PM is easily collected in the inflow layer 42, and PM is outflow layer. It is considered that the contact area between the PM and the catalytic substance is reduced and the PM purification efficiency is reduced because the penetration into the 48 is prevented.

  As described above, by satisfying the following expression 1 or expression 2, it is possible to obtain the DPF 30 having a high PM purification efficiency with a small amount of catalyst.

(A / B) / (C / D) = α (1.5 ≦ α ≦ 5.5) Equation 1
(C / D) / (E / F) = β (1.5 ≦ β ≦ 5.5) Equation 2

  The multi-tube filter of the present invention can be used as an exhaust gas purification filter capable of purifying PM with high efficiency with a small amount of catalyst material.

10 DPF
12 Plug 13 Inlet part 14 Outflow cell 15 Outlet part 16 Inflow cell 18 Bulkhead 20 Exhaust gas 22 Inflow layer 28 Outflow layer 30 DPF
32 Plug 33 Inlet part 34 Outflow cell 35 Outlet part 36 Inflow cell 38 Bulkhead 40 Exhaust gas 42 Inflow layer 48 Outflow layer 50 Center part

Claims (6)

A pipe axis is arranged along the gas flow path, and a plurality of inflow cells in which the outlet part side downstream of the gas flow is closed; a pipe axis is arranged along the gas flow path; A multi-tubular filter having a plurality of outflow cells to be closed, a partition wall having pores that partition the inflow cell and the outflow cell and allow gas to pass through to collect particulates,
In the inflow layer that is the layer on the inflow cell side of the partition wall,
A multi-tubular filter comprising a catalytic material supported so that the amount of support decreases from the inlet portion toward the outlet portion. further,
In the outflow layer that is the layer on the outflow cell side of the partition wall,
The multi-tubular filter according to claim 1, further comprising the catalyst material supported so that a supported amount increases from the inlet portion toward the outlet portion. At the entrance,
3. The multi-tube filter according to claim 1, wherein an amount of the catalyst material supported on the inflow layer is larger than an amount of the catalyst material supported on the outflow layer. At the exit,
3. The multi-tubular filter according to claim 1, wherein an amount of the catalyst material supported on the inflow layer is smaller than an amount of the catalyst material supported on the outflow layer. At the entrance,
A loading amount of the catalyst material in the inflow layer is A,
The loading amount of the catalyst material in the outflow layer is B,
In the middle part between the entrance and exit,
The amount of the catalyst substance supported in the inflow layer is C,
When the loading amount of the catalyst substance in the outflow layer is D,
The multi-tubular filter according to claim 1, wherein the following formula 1 is satisfied.
(A / B) / (C / D) = α (1.5 ≦ α ≦ 5.5) Equation 1 At the exit,
E, the loading of the catalyst material in the inflow layer,
The loading amount of the catalyst substance in the outflow layer is F,
In the middle part between the entrance and exit,
The amount of the catalyst substance supported in the inflow layer is C,
When the loading amount of the catalyst substance in the outflow layer is D,
The multi-tubular filter according to claim 1, wherein the following formula 2 is satisfied.
(C / D) / (E / F) = β (1.5 ≦ β ≦ 5.5) Equation 2

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