JPH02102315A - Particulate oxidation catalyst filter and catalyst device - Google Patents

Abstract

PURPOSE:To secure a high opportunity of contact between particulate and catalyst and improve the exhaust purification performance by forming a particulate oxidation catalyst filter of a thin metal gauze or metal plate having a number of pores along its thickness carrying catalyst. CONSTITUTION:A particulate oxidation catalyst filter 3 is composed of a thin metal gauze or metal plate having a number of pores of a diameter of more than 30mum along its thickness carrying catalyst. A particulate oxidation catalyst device 1 is composed of a plurality of such particulate oxidation catalyst filters disposed in a casing 2 for eliminating particulate by forcing exhaust gas through them. For letting a single metal or metal oxide carried in this oxidation catalyst filter 3, metal gauze of stainless steel wire is heated, the surface layer of the steel wire is oxidized by air, and catalyst is carried on it, for example.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a particulate oxidation catalyst filter and an oxidation catalyst equipped with such a filter.

Specifically, the present invention ensures a high contact opportunity between the particulates and the catalyst, and does not allow unreacted particulates to remain in the catalyst filter, so there is no increase in pressure loss due to this, and thus, The present invention relates to a particulate oxidation catalyst filter that operates stably over a long period of time, and an oxidation catalyst equipped with such a filter.

The exhaust gas emitted from the diesel engine contains soot as fine particles, and the exhaust gas containing such fine particles is recognized as so-called exhaust gas black smoke.

The above-mentioned fine particles are also called particulates, and usually contain carbon and heavy hydrocarbons ranging from soft hydrocarbons to polycyclic aromatic hydrocarbons, and some liquid substances. Although the particle size may reach several thousand particles, it is usually in the range of 100 to 1000 particles, and the average particle size is said to be approximately 300 to 500 particles.

Such particulates are generated by the incomplete combustion of light oil, which is the fuel, in diesel engines, and in recent years, from the perspective of preventing air pollution, efforts have been made to reduce their release into the atmosphere along with nitrogen oxides. It is strongly requested.

Therefore, various oxidation catalyst filters and catalyst devices have been proposed in which a catalyst filter carrying an oxidation catalyst is installed in the exhaust system of a diesel engine to catalytically oxidize particulates.

A typical example is to have a catalyst supported on a ceramic honeycomb structure in which half of the honeycomb pores on the exhaust gas inlet side are closed and the remaining honeycomb pores on the exhaust gas outlet side, and the catalyst is passed from the inlet side to the catalyst filter. A so-called catalyst wall-passing type catalyst device is known in which the introduced exhaust gas is forced to pass through a honeycomb wall and is discharged to the outlet side. The number of pores in the honeycomb wall is usually about 1000 because the honeycomb structure is made of ceramic.

According to this catalytic filter, particulates are captured on the honeycomb walls and are oxidized and decomposed by the catalyst contained in the honeycomb walls.

However, in such a catalytic converter, when the diesel engine rotates at low speed or is idling, the exhaust gas temperature is low, only around 300°C, and as a result, the catalytic oxidation of particulates is not carried out sufficiently in the catalytic converter. Curates accumulate in the honeycomb walls.

In this way, when particulates accumulate on the honeycomb walls and increase the pressure loss of the exhaust gas through the catalytic converter, the back pressure from the catalytic filter deteriorates the combustion condition of the fuel in the combustion chamber of a diesel engine. As the production of curates increases, so does the accumulation on the honeycomb walls, until the combustion of the fuel becomes impossible in the engine.

To solve this problem, it is possible to heat the catalytic converter externally and allow catalytic oxidation of particulates to proceed even when the diesel engine is running at low speed or idling, but this requires the installation of an external heater and the It requires a heat source and is not cost-effective.

In addition to the above, the catalytic converter may also include, for example, a catalyst filter made of a ceramic foam supporting a catalyst or a honeycomb structure made of a ceramic fiber sheet, which is placed inside a cylindrical casing. Catalysts filled with ceramic foam have also been proposed, but they all have the same problems as above, and in particular, in catalysts that use ceramic foam as a catalyst filter, the decomposition rate of particulates is generally lower than that of the honeycomb structure. In addition to being low compared to , the pressure loss is large. Furthermore, since the exhaust gas flow path of a catalyst filter made of ceramic foam is complicatedly curved, pressure loss is large during rapid acceleration of the engine. In addition to the above problems, honeycomb structures made of sheets of ceramic fibers have low strength and are not practical.

On the other hand, honeycomb catalysts used in gasoline engine vehicles have through-holes along the exhaust system, so although there is no increase in pressure loss, the chances of contact between solid particulates and the catalyst are significantly reduced. Since the oxidation rate of particulates is extremely poor, it cannot be used to remove particulates from diesel engine exhaust gas.

The present invention has been made in order to solve the above-mentioned problems in conventional oxidation catalyst filters and catalysts for removing particulates contained in exhaust gas from diesel engines. This ensures a high contact opportunity between the catalyst and the catalyst, and prevents unreacted particulates from remaining in the catalyst filter.Therefore, there is no increase in pressure loss due to this, and thus the fuel consumption can be maintained for a long period of time without deterioration of fuel efficiency. An object of the present invention is to provide a particulate oxidation catalyst filter that can stably oxidize and remove particulates over a long period of time, and a catalytic device equipped with such a filter.

The particulate oxidation catalyst filter according to the present invention for reducing the amount of
It is characterized in that the catalyst is supported on a thin wire mesh or metal plate having a large number of pores with a diameter of 30 μm or more in the thickness direction.

Furthermore, the particulate oxidation catalytic device according to the present invention is characterized in that it is equipped with a plurality of such particulate oxidation catalyst filters, and the exhaust gas of a diesel engine is forced to pass through them.

In the present invention, a wire mesh made of metal wire is preferably used as the base material for the catalyst filter, but a base material obtained by perforating a thin metal plate by a method such as etching may also be used. Therefore, such a substrate has a large number of pores parallel to each other in the direction of its thickness. Moreover, such pores are extremely short and substantially straight.

The pores are preferably 30 μm or more in consideration of the maximum particle size of particulates and pressure loss.

The oxidation catalyst filter according to the present invention is made by supporting any conventionally known oxidation catalyst on the base material as described above. As described below, various simple metals and metal oxides are known to be effective as catalysts.

In the present invention, the method for supporting the catalyst is as follows:
For example, a method of heating a wire mesh made of stainless steel wire to air oxidize the surface layer of the steel wire and supporting a catalyst on it;
Methods include spraying alumina onto a wire mesh made of stainless steel wire and supporting the catalyst thereon, or eluting a portion of the steel wire to make it porous, supporting alumina, etc. thereon, and further supporting the catalyst. be able to.

However, in the present invention, supporting the catalyst on the substrate shall be interpreted in a broad sense according to the present invention, and therefore, for example, heating a wire mesh made of stainless steel wire and air oxidizing the surface layer of the steel wire. When using iron oxide, this method is also included in the method of supporting a catalyst called iron oxide on a substrate. Furthermore, for example, a method of replacing a portion of the iron constituting the steel wire with platinum, palladium, or the like, which is active as a catalyst, by an electrochemical method is also included in the method of supporting a catalyst on a base material.

In the present invention, metals as catalyst filter base materials include, for example, simple metals such as iron, cobalt, molybdenum, titanium, zirconium, chromium, silver, gold, copper, nickel, and tin, and various iron alloys including stainless steel mesh. Various alloys such as copper alloy, nickel alloy, tin alloy, and chromium alloy can be used.

In the present invention, the base metal is not limited in any way, but from the viewpoint of workability, heat resistance, etc., 5U
Stainless steel such as S304 is preferred. However, especially
When heat resistance is required, for example, chrome-nickel steel, manganese-chrome steel, chrome-aluminum steel,
Nickel, chromium, cobalt steel, etc. are used.

Further, as particulate oxidation catalysts, various simple metals and metal oxides have been already known, and the catalyst used in the present invention is not limited in any way. Examples of such catalysts include simple metals such as platinum and palladium, manganese oxide, chromium oxide, copper chromate, and iron oxide.

The particulate oxidation catalyst filter according to the present invention comprises:
By processing or combining the above-mentioned catalyst-supported wire meshes and thin metal plates, various forms and structures can be obtained. Further, by using such a filter, catalysts having various structural forms can be manufactured.

Some embodiments of a particulate oxidation catalyst equipped with a catalyst filter according to the present invention as described above will be described below with reference to the drawings.

FIG. 1 shows an example of such a catalyst 1 according to the present invention,
Catalyst filters made of wire mesh 3 carrying the catalyst are loaded in parallel at intervals in a cylindrical casing 2 that is open at both ends, and is used by being installed in the exhaust gas system of a diesel engine. The exhaust gas is forced to pass through a wire mesh supporting a plurality of the catalysts.

FIG. 2 shows an example of another catalytic converter 1, which is formed by stacking wire meshes 3 carrying a catalyst in a coaxial conical shape, with the exhaust gas inlet side open and the rear end a wall that does not allow exhaust gas to pass through. 4, and the exhaust gas is forced to pass through the wire mesh to oxidize the particulates. If necessary, connect a plurality of such catalysts in series to the exhaust gas system,
May be arranged.

Furthermore, as shown in FIG. 3, the metal mesh 3 carrying the catalyst is fixed in a corrugated shape between suitable supports through which exhaust gas can easily pass, such as wire mesh 5 with large openings, and corrugated 6 As shown in FIG.
A catalyst can be obtained by processing the cylinder into a cylinder whose rear end is closed with a wall 4 that does not allow exhaust gas to pass through, and by loading this into a suitable casing (not shown). In this catalytic converter as well, exhaust gas is introduced into the catalytic converter from the inlet side and forced to pass through a wire mesh carrying a catalyst. If necessary, a catalyst can be constructed by coaxially arranging a plurality of the cylinders.

Furthermore, as mentioned above, even when configuring a catalytic converter by loading a plurality of wire meshes carrying catalysts into a casing, the shape of the wire meshes and the angle relative to the exhaust gas flow can be changed as necessary. can do. For example, as shown in FIG. 5, the wire mesh 3 may be bent almost at right angles and loaded in parallel at intervals in the casing 2, or as shown in FIG. It may be loaded into the casing 2 by changing the angle in a zigzag manner.

Alternatively, the wire mesh 3 may be formed into a long length, bent in a zigzag pattern, and then loaded into the casing 2.

As described above, the particulate oxidation catalyst filter according to the present invention is made by carrying a catalyst on a thin wire mesh or metal plate having many pores in the thickness direction, and is suitable for filtering diesel engine exhaust gas. Since the particulates are forced to pass through, a high chance of contact between the particulates and the catalyst is ensured, and unlike filters that use honeycomb structures made of ceramic foam or ceramic fibers as catalyst carriers, unreacted particulates are eliminated. No residue remains in the catalyst filter.

Therefore, according to the catalyst filter of the present invention, even during long-term operation of a diesel engine, there is no increase in filter pressure loss due to particulates remaining in the catalyst filter, and particulates are removed stably over a long period of time. can do.

Further, according to the present invention, a plurality of catalyst filters made of wire mesh or metal plates carrying the catalyst as described above are arranged,
Alternatively, particulates can be effectively removed by oxidation by forming a plurality of wire meshes or metal plates into coaxial cones or cylinders and forcing the exhaust gas to pass through them one after another.

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way.

Example 1 (Diesel engine operation and exhaust gas composition) A catalytic converter equipped with a catalytic filter as described later was installed in the downstream part of the exhaust system of a diesel engine with a displacement of 12ffi and an exhaust gas amount of 70ONn (7 o'clock). An oxidation test was conducted on Curate.The operating conditions of the diesel engine were as follows.
Engine speed 20oorpm, torque 100kg-m
And so. Under such operating conditions, the engine exhaust gas composition was NO 1500 ppm Sow 150 ppm 0□ 5χ FI20 10χ. Further, the average concentration of particulates in the exhaust gas was 1.0 g/Nrrr. The reaction temperature was adjusted by externally heating the catalyst filter.

(Preparation of catalyst-supported wire mesh) (1) Preparation of platinum-supported wire mesh A wire mesh made of 5US304 with a wire diameter of 35 μm and an opening of 44 μm was cut into a disk shape with a diameter of 150 nm+m.
After degreasing this at 400°C for 30 minutes, 25g/
The wire mesh was immersed in a chloroplatinic acid aqueous solution having an ffi concentration for 1 minute, dried, and 0.05 g of platinum was supported on the surface of the wire mesh to prepare a platinum-supported wire mesh.

(2) Preparation of alumina-platinum supported wire mesh After spraying 50 g of alumina onto the same wire mesh as in (1) above,
20g/I! It was immersed in a concentrated chloroplatinic acid aqueous solution for 1 minute and dried. Next, after firing at 500°C for 1 hour, reduction treatment was performed at 400°C in a hydrogen-nitrogen mixed gas flow for 1 hour to obtain an alumina-platinum-supported wire mesh in which 0.1% by weight of platinum was supported on alumina. Prepared.

(3) Manufacturing method of Cu0-CrzO+-MnO2-supported wire mesh After thermally spraying 50 g of alumina onto the same wire mesh as in (1) above, it was sequentially immersed in an aqueous solution of copper nitrate, chromium nitrate, and manganese nitrate, and then heated at 500°C for 1 hour. After baking for a time, the metal oxide was made into a metal oxide having a weight ratio Cub/Cr gos/Mn0z of 37.
5/3671.8, an alumina-metal oxide supported wire mesh was prepared in which a total amount of 5% by weight of alumina was supported on the alumina.

(4) Preparation of alumina-palladium supported wire mesh (1) above
After spraying 50 g of alumina on the same wire mesh, 120 g
/42 concentration palladium chloride aqueous solution and dried. Then, after baking at 500°C for 1 hour, 400°C
C for 1 hour in a hydrogen-nitrogen mixed gas flow to prepare an alumina-palladium-supported wire mesh in which 1% by weight of palladium was supported on alumina.

(Production of catalyst) As shown in Figure 1, 25 sheets of catalyst-supporting wire mesh obtained as described above were placed in a cylindrical casing at intervals of 5 mm.
A catalytic converter was manufactured by loading 5 catalysts.

Comparative Example 1 Ceramic foam with a diameter of 150 mm and a thickness of 30 mm (
Pridestone Tire Ceramic Foam #20,
It has a porosity of 87.5% and is composed of cordierite and alumina. ) was immersed in alumina slurry, excess alumina was removed, dried, and calcined at 500°C for 1 hour.
674 g of alumina was supported.

Then 20g/I! It was immersed in a concentrated aqueous solution of chloroplatinic acid and dried. Next, it was baked at 500″C for 1 hour, and
An alumina-platinum-supported ceramic foam in which 0.1% by weight of platinum was supported on alumina was prepared by reduction treatment at 00°C for 1 hour in a hydrogen-nitrogen mixed gas flow.

Two sheets of the catalyst-supported ceramic foam were stacked and loaded into a cylindrical casing similar to that shown in FIG.
I made a catalyst.

Comparative Example 2 Chias #281 on ceramic fiber sheet
A honeycomb structure with a diameter of 150 mm and a length of 300 mm consisting of 3) was immersed in alumina slurry, excess alumina was removed, dried, and fired at 500 ° C for 1 hour.
1060 g of alumina was supported.

Next, it was immersed in a chloroplatinic acid aqueous solution with a concentration of 20 g/l, dried, and then baked at 500°C for 1 hour.
A honeycomb structure made of alumina-platinum-supported ceramic fibers in which 0.1% by weight of platinum was supported on alumina was produced by reduction treatment with C for 1 hour in a hydrogen-nitrogen mixed gas flow.

In this honeycomb structure, half of the honeycomb holes on the exhaust gas inlet side were closed, and the remaining half of the honeycomb holes on the exhaust gas outlet side were closed to create a catalyst filter that forced the honeycomb to pass through the honeycomb wall.

This catalyst filter was loaded into a cylindrical casing similar to that shown in FIG. 1 to produce a catalyst.

A diesel engine was operated using the catalyst filters according to the above Examples and Comparative Examples under the conditions described above, and the particulate removal rate and pressure loss were examined immediately, 1 hour later, and 24 hours later. The pressure drop was determined by measuring the static pressure between the inlet and outlet of the catalyst. Also,
47 μm at the outlet side of the catalyst using the dilution tunnel method.
The particulates collected by the filter were weighed to obtain the particulate amount, and the particulate removal rate was determined based on this. The results are shown in Table 1.

With the catalytic filter according to the invention, the particulate removal rate and pressure drop are substantially the same. In contrast, with the catalyst filter of the comparative example, the pressure loss became significantly large one hour after the engine started operating, and fuel combustion in the engine stopped before 24 hours of operation.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of a particulate oxidation catalyst according to the present invention, FIG. 2 is a sectional view showing another embodiment of a catalyst, and FIG. 3 is a wire mesh supporting a catalyst. 4 is a cross-sectional view showing an embodiment of a catalytic converter according to the present invention formed using such a corrugate, and FIGS. 5 and 6 are shown in FIG. 1. FIG. 3 is a cross-sectional view showing a modification of the catalytic device. DESCRIPTION OF SYMBOLS 1... Particulate oxidation catalyst, 2... Casing, 3... Wire mesh supporting catalyst as a catalyst filter, 4... Wall body, 5... Support with large openings, 6 ... Corrugate containing a wire mesh carrying a catalyst, 7
...Support with large openings. Patent applicant Sakai Chemical Industry Co., Ltd. Agent Patent attorney Itsube Makino

Claims (3)

[Claims] (1) A particulate oxidation catalyst filter characterized in that a catalyst is supported on a thin wire mesh or metal plate having a large number of pores with a diameter of 30 μm or more in the thickness direction. (2) The particulate oxidation catalyst filter according to claim 1, wherein the wire or the metal plate is made of stainless steel. (3) Equipped with a plurality of particulate oxidation catalyst filters, each of which has a catalyst supported on a thin wire mesh or metal plate having many pores with a diameter of 30 μm or more in the thickness direction, so that the exhaust gas of the diesel engine is forced to pass through them. A particulate oxidation catalyst characterized by: