JPH03213610A - Diesel particulate filter - Google Patents

Abstract

PURPOSE:To prevent particles from being re-splashed at the time of changeover of an operation, delay an increase in back pressure and reduce a filter in size by providing many pores, each diameter of which becomes smaller from the surface toward the inside, in a wash coat layer formed integrally with a base. CONSTITUTION:The essential part of a filter is constituted of a honeycomb structure 1 as a base, a wall part 10 of which provides numerous cells 11, and a wash coat layer 2 covering the wall 10. Innumerable pore groups 10a are formed in the wall 10. Numberless small, middle and large size pore groups 2a, 2b and 2c are respectively formed of fine slits in crystals in the wash coat layer 2. The wash coat layer 2 is coated, for example, with a first layer 21 made of gamma-alumina of 50g/l or more, and second and third layers 22, 23 made of beta-alumina of 20g/l or more. Therefore, particles in exhaust gas can be deposited on pores in sequence from the outermost surface.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a diesel particulate filter (hereinafter referred to as DPF), and more specifically, the present invention relates to a diesel particulate filter (hereinafter referred to as DPF). Regarding the DPF that collects the data.

[Prior Art] As a conventional DPF, one having a honeycomb structure and a wash coat layer coated on the honeycomb structure is known. The honeycomb structure is mainly made of cordierite, and has walls with countless pores forming countless cells that serve as gas passages. The wall of this honeycomb structure is coated with a t-tush coat layer, which is mainly made of γ-alumina and has pore groups smaller in diameter than the pores in the wall. In general, each cell of the DPF is alternately closed with plugs at the end face on the inlet side or the end face on the outlet side of the exhaust gas, and the exhaust gas is guided into the cell from the end face on the inlet side that is not blocked by the plug material. is moved from the cell to the adjacent cell by the plug material that closes the outlet side of the cell, and at that time, particulates are collected as they pass through the pores in the wall and the pores in the washcoat layer. be purified.

By the way, when this DPF is installed in a jacket, there are known exhaust gas purification devices that combine a DPF with fine cells and a DPF with coarse cells, and exhaust gas purification devices that are equipped with a coarse ceramic foam on the inlet side ( Unexamined Japanese Patent Publication 1986-10
No. 1214, No. 171814, No. 171814, No. 171814, No. 171814, No. 62
-180619). With these exhaust gas purification devices,
Particulates are collected at a low collection rate in the upstream DPF or filter of the exhaust gas, and the particulates are collected in the downstream DPF.
By collecting the particulates at a high collection rate, the particulates that have been previously collected will not escape from the downstream DPF that has a high collection rate, so particulates can be prevented from being re-dispersed during operational fluctuations, and Since particulates are freely allowed to enter from the pore group of the upstream DPF to the pore group of the downstream DPF, the rise in back pressure can be delayed while particulate collection efficiency is maintained.

[Problems to be Solved by the Invention] However, if the above conventional exhaust gas purification device using a DPF is not to achieve these objectives, it is necessary to equip a jacket with a plurality of DPFs, or to install other filters together with the DPF. It is also necessary to equip the jacket with
Exhaust gas purification devices have become larger, which is contrary to the desire to reduce the weight of vehicles.

The present invention aims to prevent particulates from being re-dispersed during operating fluctuations, and to delay the increase in back pressure while maintaining particulate collection efficiency, while also making the exhaust gas purification device of a day cell engine more compact. This is a technical issue that should be addressed.

[Means for Solving the Problems] In order to solve the above problems, the diesel particulate filter of the present invention includes a base body in which countless gas passages are formed by a wall portion having countless pores, and a coating on the wall portion. , a novel method is adopted in which the washcoat layer has a countless number of pores that change from large to small diameter from the surface to the inside.

As the base, a commercially available honeycomb structure made of ceramic such as cordierite or mullite, or a fiber honeycomb can be used. These are countless pores (Φ=0
．． 5-50μm) (t=0.3-0.5mm)
＞ Yotte Myriad (7) t? A gas passage such as /L/ can be used. Note that the pores do not exist independently, but communicate with each other through slits that exist in the grain boundaries of the ceramic powder.

The wash coat layer consists of γ-alumina, titania, β-
It can be obtained by coating with heat-resistant ceramic powder or ceramic fiber such as alumina. β
- It is preferable to use alumina in terms of heat resistance. This washcoat layer also has numerous pores that do not exist independently, but are interconnected through slits that exist at the boundaries of the grain boundaries and fibers of the powder. In order to obtain a washcoat layer in which the pore group changes from a large diameter to a small diameter from the surface to the inside, multiple layers may be coated while gradually increasing the particle size of the ceramic powder and the diameter of the ceramic fiber. Alternatively, it can also be obtained by coating a plurality of layers of foaming components or vanishing components whose diameters are gradually increased together with ceramic powder or ceramic fibers, and firing them. In terms of collection efficiency, it is preferable that the pore group on the side closer to the wall in the washcoat layer be formed to have a smaller diameter than the pore group in the wall. Further, it is preferable that the pore group on the side far from the wall in the washcoat layer be formed to have a diameter larger than that of the pore group in the wall, from the viewpoint of delaying the increase in back pressure. Furthermore, when the base body is a honeycomb structure and each cell is alternately closed with plug material at the end face on the exhaust gas inlet side or the end face on the outlet side, the inlet side is not closed by the plug material. It is also possible to coat the washcoat layer only on the side of the wall on the cell side that is not covered. In order to coat only one side of the wall with a washcoat layer, it is possible to apply a method using suction filtration, and remove components such as PVA coat (PVA coat).
Possible methods include blocking the other side with polyvinyl alcohol). Note that an active substance or the like can also be supported on this washcoat layer.

[Function] In the DPF of the present invention, the washcoat layer has a group of pores whose diameter changes from large to small from the surface to the inside. Therefore, particulates in the exhaust gas preferentially adhere to the pore group of the washcoat layer on the surface side due to inertial collision, but from the pore group of the washcoat layer on the surface side with a large diameter to the wall part with a small diameter. It is allowed to freely penetrate into the pores of the washcoat layer. Since this washcoat layer is integrated with the substrate, there is no need to equip the jacket with another DPF or other filter to obtain this effect.

[Example] Hereinafter, an example embodying the present invention will be described with reference to the drawings.

As shown in FIG. 1, the DPF of this embodiment includes a honeycomb structure 1 in which countless cells 11 are formed by a wall portion 10;
As shown in FIG. 2, it consists of a wash coat layer 2 coated on a wall portion 1°.

The wall portion 10 of the honeycomb structure 1 has a thickness of t=0.3 to 0.5 mm.
, and this wall 10 has countless pore groups 10a (Φ-0
, 5 to 50 μm).

The wash coat layer 2 has countless small pore groups 2a (Φ-5 to 1000X), medium pore groups 2b (Φ=50 to 500 μm), and large pore groups 2c (Φ
= 100 to 10 ooμm) is formed. This DP
F is equipped on the jacket 3 as shown in FIG.
Used as an exhaust gas purification device for diesel engines.

Such a DPF could be obtained as follows.

First, honeycomb structure 1 (manufactured by NGK Insulators) was used as a base.
prepared. This honeycomb structure 1 is made of cordierite. In this honeycomb structure 1, each cell 11 is alternately closed with plug members 12a and 12b made of cordierite at the end face on the exhaust gas inlet side or the end face on the outlet side.

In addition, in order to coat the wash coat layer 2, γ-alumina powder (manufactured by Cataler Industries) with an average particle size of 2 μm,
β-alumina powder (BaO 6A
12o3, manufactured by Toyo CCI) and β with an average particle size of 150 μm.
- Alumina powder (same as above) was prepared. Average particle size 2μm
γ-alumina powder, β-alumina powder with an average particle size of 100 μm, and β-alumina powder with an average particle size of 150 μm were stirred with distilled water, and each was mixed with distilled water so that the viscosity was about 50 CpS using a B-type viscometer. Adjusted the seed slurry.

The honeycomb structure 1 was impregnated with a slurry containing γ-alumina powder, and the excess slurry was blown off by air blowing to uniformly coat the wall portion 10 with the slurry. At this time, the slurry has entered the pore group 10a of the wall portion 10. This was fired in an atmosphere of about 600' C1. thus,
The wall portion 10 of the honeycomb structure 1 has a T- of 50C1/ρ or more.
A first wash coat layer 21 made of alumina was coated.

Next, on the honeycomb structure 1 coated with the first wash coat layer 21, an average particle size of 100/j77? The slurry containing β-alumina powder is suction filtered, and the inlet side is plugged with plug material 12.
The slurry was coated only on the surface of the wall portion 10 on the side of the cell 11 that was not blocked by a.

This was fired in an atmosphere of about 1000'C1. In this way, a second wash coat layer 22 made of β-alumina of 20 CI/.1) or more was coated.

Furthermore, on the honeycomb structure 1 coated with the second wash coat layer 22, a slurry containing β-alumina powder with an average particle size of 150 μm was suction-filtered, and 20 g/1
Third wash coat layer 2 made of the above β-alumina
3 was coated. 1st to 3rd wash coat layers 21 to 2
The wash coat layer 2 consisting of the honeycomb structure 1 was integrated with the honeycomb structure 1 without being able to visually confirm each layer. Further, the wash coat layer 2 is applied to the wall portion 10 by the plug material 12b.
The sides were coated a little thicker.

Note that these second and third wash coat layers 22 and 23
As another manufacturing method, coating with an alkoxide slurry may be performed by dipping, but in this case, care should be taken that a large amount of alcohol as a by-product is generated and that particle size control is controlled by curing time.

In this way, the DPF of the example was obtained.

(Evaluation) The DPF of the example was installed in a stainless steel jacket 3 as shown in FIG. 1, and an exhaust gas purification device was assembled.

This exhaust gas purification device was then installed on each forklift truck equipped with a 3fJ direct injection diesel engine. Particulates in the exhaust gas preferentially adhere to the large pore group 20 of the third washcoat layer 23 due to inertial collision. It is allowed to freely penetrate into the small pore group 2a of the washcoat layer 21. Therefore, the exhaust gas purification device equipped with the DPF of this embodiment can prevent particulates from being re-dispersed during operational fluctuations and delay the increase in back pressure while maintaining particulate collection efficiency. Ta.

This DPF also eliminates soluble organic matter (SOF) unique to direct injection diesel engines, which was difficult to purify with conventional DPFs.
= Soluble QrganCFraction)
Since the particles were able to collide with the plurality of first to third wash coat layers 21 to 23, they were able to be sufficiently adsorbed and purified.

Furthermore, in this DPF, since the first to third wash coat layers 21 to 23 are coated somewhat thickly on the plug material 12b side with respect to the wall portion 10, the difference in back pressure gradient between the inlet side and the outlet side Particulates adhered uniformly to the inlet side, and particulates did not adhere thickly to the outlet side as in conventional DPFs. Therefore, the combustion heat of the regeneration process was effectively transmitted to this DPF, and the purification performance could be easily and sufficiently restored through maintenance.

This DPF is the first to third wash coat layers 21.
Since the wash coat layer 2 consisting of ~23 is integrated with the honeycomb structure 1, if this DPF is used, there is no need to install other DPFs or other filters at the same time.
It becomes possible to assemble the exhaust gas purification device compactly.

In addition, in the DPF of the present invention, if the pore group of the wash coat layer is varied by selecting the particle size of the ceramic powder and the particle size of the vanishing component, it becomes possible to purify particulates by size.

[Effects of the Invention] As detailed above, in the DPF of the present invention, the washcoat layer integrated with the base has countless pores whose diameter changes from large to small from the surface to the inside. Therefore, this D
By equipping the jacket with a PF, the exhaust gas purification device can be made more compact while preventing particulates from being re-dispersed during operational fluctuations and delaying the increase in back pressure while maintaining particulate collection efficiency.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an exhaust gas purification device equipped with a DPF according to an embodiment, and FIG. 2 is an enlarged sectional view of the DPF according to an embodiment. 1... Honeycomb structure (substrate) 10... Wall portion 10a... Pore 11...
Cell (gas passage) 12a, b...Plug material 2...Wash coat layer 21...First wash coat layer 22...Second wash coat layer 23...Third wash coat layer 2a...・Small pore 2b...middle pore 2C...
large pore

Claims (1)

[Claims] (1) A base body with countless gas passages formed by a wall with countless pores, and a washcoat coated on the wall with countless pores that change from large to small diameter from the surface to the inside. A diesel particulate filter characterized by having a layer.