JP2002089237A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system using only one filter since exhaust emission control and regeneration of the filter are performed concurrently and having low manufacturing and running costs since no heating device is needed for regenerating the filter. SOLUTION: In this exhaust emission control system, the filter carrying an oxidation catalyst is installed in an exhaust passage of an internal combustion engine. It is characterized by that it is provided with a dripping nozzle or an injection injector feeding hydrocarbonic liquid to an exhaust gas inflow side of the filter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an exhaust gas purification system.

[0002]

2. Description of the Related Art Exhaust gas purifying filters are used to remove CO (carbon monoxide), HC (hydrocarbon) and the like discharged from an internal combustion engine such as a diesel engine. In addition, this filter removes CO, HC, etc. and, at the same time, collects PM (particulate matter) such as black smoke and SOF contained in the exhaust gas. , The passage resistance increases.

Therefore, in order to cope with the deposition of PM, usually, a heating device such as a heater is provided in the filter, and the filter is regenerated by burning and removing PM by heating. Specifically, trapping of PM and the like and regeneration of the filter are performed by an exhaust gas purification system as shown in FIG. FIG. 5 is a schematic diagram showing an example of a conventional exhaust gas purification system.

[0005] As shown in FIG. 5, in a conventional exhaust gas purification system 100, filters 101 and 101 ′ each having a heater 105 are installed in exhaust passages 104 and 104 ′ of an internal combustion engine 103. Further, valves 106 and 106 'for switching the flow path of the exhaust gas are provided in the exhaust passages 104 and 104'.

In such an exhaust gas purification system 100, the exhaust gas discharged from the internal combustion engine 103 passes through the exhaust passage 104 and the valve 106 and passes through the filter 10.
After being introduced into the filter 101 or the filter 101 ', it is purified and then discharged to the atmosphere through an exhaust passage 104' and a valve 106 '.

The exhaust gas is controlled by the valve 106 so as to flow into only one of the filter 101 and the filter 101 '. At this time, the other filter without the flow of the exhaust gas is subjected to the regeneration treatment. Is controlled to be performed. The above playback process
This is a process for burning and removing PM accumulated in the filter.
By heating the inside of the filter 101 using the 05, PM such as black smoke can be burned and removed.

As described above, in the conventional exhaust gas purifying apparatus, every time a certain amount of PM accumulates in the filters, the flow of the exhaust gas is switched between at least two filters, and the collection and the regeneration are repeated. Needed. Also,
When regenerating the filter, it is necessary to heat the inside of the filter to the combustion temperature of PM, and therefore, it is necessary to provide a heating device such as a heater.

[0008]

In an exhaust gas purifying apparatus having such a structure, at least two filters are usually required, and each filter needs to be provided with a heating device such as an electric heater. In addition, there is a problem that the manufacturing cost is increased and the regeneration cost of the filter requires external heating, thereby increasing the running cost. Further, in the exhaust gas purifying device having such a configuration, there is a problem that the device itself becomes large and the mounting place is restricted when the device is mounted on a vehicle. Further, even in the case of a single filter, a heating device or the like is required, and the above-described problem cannot be sufficiently solved.

The present invention has been made in order to solve such a problem, and an object of the present invention is to simultaneously perform purification of exhaust gas and regeneration of a filter. Another object of the present invention is to provide an exhaust gas purification system in which the production cost and the running cost are low because a heating device is not required for regeneration of the filter.

[0010]

That is, an exhaust gas purification system of the present invention is an exhaust gas purification system in which a filter carrying an oxidation catalyst is installed in an exhaust passage of an internal combustion engine. It is characterized by comprising a dripping nozzle or injection injector for supplying a hydrocarbon-based liquid to the inflow side.

Since the exhaust gas purifying system of the present invention is provided with a drip nozzle or an injection injector for supplying a hydrocarbon liquid on the exhaust gas inflow side of the filter, the hydrocarbon liquid is supplied into the filter together with the exhaust gas. can do. In the filter into which the hydrocarbon liquid has flowed, the filter carries an oxidation catalyst, so that the reaction represented by the following reaction formula (1) proceeds, and the hydrocarbon is decomposed into carbon dioxide and water.

[0012]

Embedded image

Here, the reaction shown in the above reaction formula (1) is as follows:
It is an exothermic reaction and generates a large amount of heat during the reaction. Therefore, PM such as black smoke deposited in the filter is burned and removed by the heat generated by this reaction, and the filter is regenerated in parallel with the purification of the exhaust gas.

In the exhaust gas purifying system of the present invention, the temperature of the exhaust gas introduced into the filter is increased by supplying the hydrocarbon-based liquid. In addition, the temperature of the exhaust gas can be maintained at a high temperature. During the operation of the internal combustion engine, the supply of the hydrocarbon-based liquid may be performed continuously, or may be selectively performed in consideration of the back pressure of the filter or the like.

In the exhaust gas purifying system of the present invention, the hydrocarbon-based liquid supplied by a drip nosole or the like is:
When using a diesel engine as the internal combustion engine,
Preferably, it is light oil. The reason is that the fuel of the diesel engine is light oil, and a fuel supply device attached to the diesel engine can be a supply source of the hydrocarbon liquid.

A specific example of the fuel supply device is, for example, a common rail type fuel injection device. The common rail type fuel injection device is a device that stores fuel at a high pressure by a fuel transport pump at a high pressure in a common rail, and performs fuel injection by opening and closing a needle valve of a nozzle with an electromagnetic valve by electronic control. In this fuel injection device,
By electrical signal, individually for each cylinder,
The fuel injection amount and the injection timing can be freely selected.

Therefore, at least one of the injection nosols of the common rail type fuel injection device is used as a drip nozzle or an injection injector for supplying a hydrocarbon-based liquid to the exhaust gas inflow side of the filter, thereby being attached to the diesel engine. The fuel supply device may be a supply source of the hydrocarbon liquid. For these reasons, the internal combustion engine using the exhaust gas purification system of the present invention is preferably a diesel engine having a common rail fuel injection device.

When a diesel engine is used as the internal combustion engine, it is desirable that the diesel engine be of a post-injection type. The post-injection method is a method of injecting a small amount of fuel after the expansion stroke of the cylinder is started by the main injection of the fuel and before the cylinder is switched to the compression stroke.In a diesel engine using this method, The temperature of the exhaust gas can be raised to 450 ° C. or higher.

Therefore, the exhaust gas discharged from the post-injection type diesel engine has a high temperature when flowing into the filter, and reliably reaches the black smoke combustion start temperature (about 600 ° C.) in a shorter time. It will be.

In the exhaust gas purifying system, an oxidation catalyst is disposed in the exhaust passage upstream of the filter, and the hydrocarbon liquid is disposed between the filter and the oxidation catalyst and / or the oxidation catalyst. It is desirable that the catalyst be supplied to the exhaust gas inflow side of the catalyst. By arranging the oxidation catalyst upstream of the filter, carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gas can be obtained.
Can be removed by oxidation. In addition, since the reaction for oxidizing and removing carbon monoxide and hydrocarbons is also an exothermic reaction, the temperature of the exhaust gas flowing into the filter together with the PM can be increased by arranging the oxidation catalyst. In particular, when a hydrocarbon-based liquid is supplied from the dropping nozzle or the like to the exhaust gas inflow side of the oxidation catalyst, the exhaust gas temperature can be made higher.

Examples of the oxidation catalyst include Pt and Pt.
Examples include metals such as d, Rh, Ce, Cu, V, Fe, Tu, and Ag, alloys of these metals, and compounds thereof. These may be used alone or in combination of two or more. Among these, Pt / Pd binary alloys,
Pt / Pd / Rh ternary alloys are desirable. further,
In addition to the oxidation catalyst made of these alloys, a rare earth oxide such as cerium oxide (CeO ₂ ) may be supported as a co-catalyst. The catalyst having such a configuration includes lead,
This is because deterioration due to catalyst poisons such as phosphorus and sulfur is small, and heat resistance is excellent because heat deterioration is small.

In such an exhaust gas purification system of the present invention, purification of the exhaust gas and regeneration of the filter can be performed at the same time, so that it is sufficient if at least one filter is provided. Since a heating device is not required at this time, manufacturing costs and running costs are low, and the size of the exhaust gas purification system itself is compact, so that when mounted on a vehicle, there are almost no restrictions on the mounting location. Absent. Hereinafter, an embodiment of an exhaust gas purification system of the present invention will be described in detail with reference to the drawings.

[0023]

FIG. 1 is a schematic view showing an embodiment of an exhaust gas purifying system according to the present invention. As shown in FIG. 1, in the exhaust gas purification system 10, the filter 1
1 is an exhaust passage 14, 14 ′ of the diesel engine 13.
And the exhaust gas inflow side 1 of the filter 11
1a is provided with a dripping nozzle 12 for supplying light oil. An oxidation catalyst 1 is provided upstream of the filter 11.
7 are arranged. Therefore, the diesel engine 13
The exhaust gas exhausted from the exhaust passage 14 and the oxidation catalyst 1
7 and is introduced into the filter 11 and purified, and then discharged to the exhaust passage 14 '. In addition, in the exhaust gas purification system 10, although the dripping nozzle 12 is provided in order to supply light oil, an injection injector may be provided instead of the dripping nozzle 12. Further, the drip nozzle may be provided on the exhaust gas inflow side of the oxidation catalyst 17 instead of the exhaust gas inflow side of the filter 11,
Both may be provided.

In order to supply light oil, a drip nozzle 1
Reference numeral 2 is connected to a common rail 18 that supplies fuel to the diesel engine 13, and is configured so that light oil is supplied from the common rail 18.

The filter 11 carries an oxidation catalyst. Therefore, the hydrocarbon-based liquid supplied from the dropping nozzle 12 becomes carbon dioxide and water and generates a large amount of heat by the reaction represented by the reaction formula (1) in the filter 11. Etc. can be removed by burning. Further, the carbon monoxide (C) which could not be oxidized and removed by the oxidation catalyst 17 disposed upstream of the filter 11 due to the oxidation catalyst carried by the filter 11.
O) and hydrocarbons (HC) can be completely oxidized and removed.

It is desirable that the filter 11 be made of a porous ceramic member having the following configuration. FIG. 2 is a perspective view schematically showing a honeycomb filter made of a porous ceramic member, and FIG.
FIGS. 1A and 1B are perspective views schematically showing a porous ceramic member constituting a honeycomb filter. FIG.
FIG. 4 is a cross-sectional view taken along a line A.

As shown in FIG. 3, the honeycomb filter 2
The porous ceramic member 25 of the first embodiment has a large number of through-holes 26 formed in parallel with the longitudinal direction. One end of the porous ceramic member 25 having the through-holes 26 has a filler 27 in a checkered pattern. Is filled. At another end (not shown), the filler is filled in the through hole 26 in which one end is not filled with the filler.

In the honeycomb filter 21 shown in FIG.
A large number of porous ceramic members 25 having such a structure are bound via a heat-resistant adhesive layer 22 and processed into a cylindrical shape, and the outer peripheral portion is coated with a sealing material 23.

Therefore, in this honeycomb filter 21,
As shown in FIG. 3B, one open through-hole 2
Exhaust gas flowing from one end of the adjacent through hole 2
The exhaust gas passes through the porous partition wall 28 that separates the partition wall 6 and flows out through the other through-holes 26, so that the exhaust gas passes through the partition wall 28.
When passing through the portion, PM in the exhaust gas is captured, and functions as a filter.

The ceramic forming the porous ceramic member 25 is not particularly limited. For example, non-oxide ceramics such as silicon carbide, silicon nitride, aluminum nitride, boron nitride, titanium nitride, titanium carbide, alumina, cordierite, Examples thereof include oxide ceramics such as mullite, silica, zirconia, and titania. Among these, silicon carbide, silicon nitride, aluminum nitride, and the like having excellent heat resistance are preferable.

The oxidation catalyst supported on the filter 11 is, for example, Pt, Pd, Rh, Ce, Cu,
Examples include metals such as V, Fe, Tu, and Ag, alloys thereof, and compounds thereof. These may be used alone or in combination of two or more. Furthermore, a rare earth oxide such as cerium oxide (CeO ₂ ) may be supported as a promoter in addition to the oxidation catalyst made of these alloys.
This is because a catalyst having such a configuration is less deteriorated by catalyst poisons such as lead, phosphorus, and sulfur, and is excellent in heat resistance due to small thermal deterioration.

As a method for supporting the oxidation catalyst on the filter, for example, a catalyst support layer made of alumina is formed on the inner wall surface of the filter by a wash coat method, a sol-gel method or the like, and then the catalyst support layer is formed. For supporting the above-mentioned oxidation catalyst. Of these, it is desirable to form a catalyst supporting layer made of alumina by a sol-gel method or the like, and then to carry an oxidation catalyst on the catalyst supporting layer. This is because a filter supporting an oxidation catalyst by such a method has a small pressure loss, is excellent in heat resistance, and is excellent in combustion characteristics such as black smoke.

Therefore, a catalyst filter made of alumina is formed on a partition wall of a through-hole of the honeycomb filter by a sol-gel method or the like using a honeycomb filter made of silicon carbide. The method of carrying the carrier will be described in detail. Of course, the filter supporting the oxidation catalyst used in the exhaust gas purification system of the present invention is not limited to a filter obtained by such a manufacturing method, nor is it limited to a honeycomb filter.

(1) First, a preliminary treatment is performed on a honeycomb filter made of a silicon carbide sintered body. In this preliminary process,
An oxidation treatment is performed on the through-hole wall surface of the honeycomb filter to add Si for promoting chemical bonding with alumina. This process is unnecessary when a sufficient oxide film is formed on the surface of the ceramic particles constituting the honeycomb filter. Also, in this pretreatment, SiO ₂
By increasing the amount, the heat resistance of the honeycomb filter can be improved.

In the preliminary processing, the honeycomb filter is set to 80
It is desirable to carry out by heating at a temperature of 0 to 1600 ° C. for 5 to 100 hours. If the temperature is lower than 800 ° C., the oxidation reaction is unlikely to occur, while if it is higher than 1600 ° C., the oxidation reaction proceeds too much and the strength of the filter may be reduced. A more desirable pretreatment condition is heating at a temperature of 1000 to 1500 ° C. for 5 to 20 hours. Within this range, enough S to supply Si
This is because the iO ₂ film can be formed on the surface of the ceramic particles, the porosity and the pore diameter of the honeycomb filter are hardly changed, and the pressure loss characteristics are not impaired.

(2) Next, a surface of each ceramic particle constituting the honeycomb filter is impregnated with a solution of an aluminum-containing metal compound by a sol-gel method to coat a thin alumina film. The solution of the aluminum-containing metal compound can be prepared using a metal inorganic compound or a metal organic compound as a starting material.

As the above-mentioned metal inorganic compound, for example, A
l (NO ₃ ) ₃ , AlCl ₃ , AlOCl, AlPO
₄ , Al ₂ (SO ₄ ) ₃ , Al ₂ O ₃ , Al (OH)
₃ , Al and the like. Among these, Al (NO ₃ ) ₃ and AlCl ₃ are preferable because they are easily dissolved in a solvent such as alcohol or water and are easy to handle.

Examples of the above-mentioned metal organic compounds include metal alkoxides, metal acetylacetonates, metal carboxylates, and the like.
(OCH ₃ ) ₃ , Al (OC ₂ H ₅ ) ₃ , Al (iso
—OC ₃ H ₇ ) _{3 and the} like. Examples of the solvent for dissolving these metal compounds include water, alcohol, diol, polyhydric alcohol, ethylene glycol, ethylene oxide, triethanolamine, and xylene. These may be appropriately used in consideration of the solubility of each metal compound and the like, and may be used alone or in combination of two or more.

In preparing the solution of the aluminum-containing metal compound, hydrochloric acid, sulfuric acid, nitric acid, acetic acid, hydrofluoric acid and the like may be added as a catalyst. In order to improve the heat resistance of alumina, Li, K, Ca, Sr, Ba, L
A simple substance or a compound of a, Pr, Nd, Si, and Zr may be added to the starting material.

In preparing a solution of an aluminum-containing metal compound, it is desirable to use Al (NO ₃ ) ₃ as the metal compound. This is because they are dissolved in the solvent at a relatively low temperature. It is desirable to use 1,3-butanediol as the solvent. The first reason is that the viscosity is appropriate, and it is possible to form a gel film having an appropriate thickness on SiC particles in a gel state. The second reason is that 1,3-butanediol is used. This is because, since a metal alkoxide is formed in a solution, a metal oxide polymer composed of an oxygen-metal-oxygen bond, that is, a precursor of a metal oxide gel can be formed.

In this case, the amount of Al (NO ₃ ) ₃ is 10
It is desirably about 50% by volume. If the amount is less than 10% by volume, the catalyst cannot support an amount of alumina having a surface area enough to maintain the activity for a long time, while the amount of 50% by volume cannot be supported.
This is because, when it exceeds, a large amount of heat is generated at the time of dissolution, and gelation is likely to occur.

The temperature for preparing the solution of the aluminum-containing metal compound is preferably from 50 to 130 ° C. 5
If the temperature is lower than 0 ° C., the solubility of the solute is low. On the other hand, if the temperature is higher than 130 ° C., the reaction proceeds rapidly, leading to gelation, which may not be used as a coating solution. In addition, the stirring time in this case is desirably 1 to 9 hours. This is because the viscosity of the solution is stable in this range.

As a method for distributing the thus prepared solution of the metal compound in all the pores which are the gaps between the ceramic particles constituting the through-hole partition walls, for example,
After the honeycomb filter is put in the container, a method of filling the solution of the metal compound and degassing, or a method of pouring the metal compound solution from one end of the honeycomb filter and degassing from the other end of the honeycomb filter is used. Can be.
In this case, an aspirator, a vacuum pump, or the like can be used as the deaerator. As described above, by removing air from the pores of the through-hole partition walls, the solution of the metal compound can be evenly distributed on the surface of each ceramic particle.

(3) Next, by evaporating and removing volatile components such as NO ₂ , the solution of the metal compound is gelled and fixed on the surfaces of the ceramic particles, and the excess solution of the metal compound is removed. This processing is performed for 120 to 17
It is desirable to carry out the heating at a temperature of 0 ° C. for about 2 hours. If the heating temperature is lower than 120 ° C., the volatile components may be difficult to evaporate.
The thickness of the gelled film may be non-uniform.

(4) Next, by performing a calcination treatment, residual components are removed and an amorphous alumina film is formed. This process is desirably performed by heating at 300 to 500. If the heating temperature is lower than 300 ° C., it is difficult to remove the residual organic substances, while
If the temperature is higher than 00 ° C., Al ₂ O ₃ is crystallized, and it may not be possible to form small fiber projection boehmite by the subsequent hot water treatment.

(5) Next, the pre-baked honeycomb filter is immersed in hot water. By this treatment, the particles on the surface of the amorphous alumina thin film are peptized and released in a sol state into the solution, and the boehmite particles generated by hydration are condensed as small fibrous projections, It becomes a stable state.

That is, by this hot water treatment, the alumina thin film which individually adheres to the surface of each ceramic particle and forms a thin film is formed into small fibers (needle-like particles), and stands, and exhibits a so-called flocking structure and is coarse. It becomes a thin film on the surface. Therefore, a thin film having a high specific surface area is obtained. Generally, in sintering of alumina, the surface diffusion mainly progresses, and the specific surface area sharply decreases at the time of phase transition to α-alumina. However, when the silica is incorporated into the alumina particles, it is considered that the silica fills the pore sites of the alumina during the heat treatment process or moves to the surface of the acicular particles to suppress surface diffusion and sintering between the particles. Therefore, in the early stage of sintering of the support layer, the viscous flow mechanism due to sintering from the contact point between the acicular particles is dominant, but in the latter stage, in order to block the mass transfer path between the acicular particles of silica It is considered that the transition to α-alumina is inhibited, and a high specific surface area is maintained without further sintering.

In this treatment, the temperature of the hot water is from 50 to
100 ° C. is desirable. If the temperature is lower than 50 ° C., the hydration of the amorphous alumina thin film does not progress, and the fibril-shaped boehmite may not be formed. On the other hand, if the temperature exceeds 100 ° C., water evaporates, and this treatment step is maintained for a long time. Becomes difficult. Further, the processing time in this processing is desirably 1 hour or more. If the time is shorter than 1 hour, the hydration of the amorphous alumina may be insufficient.

(6) Next, a final baking treatment is performed in which the boehmite produced by the hydration is made into membrane water to form alumina crystals.
This main baking treatment is performed at a temperature of 500 to 1000 ° C and a temperature of 5 to 1000 ° C.
It is desirable to carry out by heating for 20 hours. If the heating temperature is lower than 500 ° C., crystallization may not proceed. On the other hand, if it is higher than 1000 ° C., sintering proceeds too much and the surface area tends to decrease.

The shape of the alumina crystal formed here has a diameter of 2 to 50 nm and a length of 20 to 300 nm.
nm, and the length / diameter ratio is preferably 5 to 50. If the diameter is less than 2 nm, the size of the catalyst such as Pt is equal to or smaller than that of the catalyst, so that it is difficult to function as a catalyst supporting layer. If the diameter exceeds 50 nm, a sufficient ratio required for the catalyst supporting layer is obtained. It becomes difficult to secure the surface area. More preferably, the diameter is 5 to 20 nm.

When the length is less than 20 nm, it is difficult to secure a sufficient surface area required for the catalyst supporting layer. On the other hand, when the length exceeds 300 nm, the structure may be brittle. If the ratio of the total length / diameter is less than 5, it is difficult to secure a sufficient surface area required for the catalyst supporting layer. The length / diameter ratio is 10 to 3
More preferably, it is 0.

The alumina crystal has a thickness of 0.5
It is preferable that the specific surface area is 50 μm or less and the specific surface area is 50 to 300 m ² / g. Here, the thickness of the alumina crystal is defined as the small fiber projection of alumina Si from the surface of the SiC particles.
The average of the distance from the surface of the C particle to the farthest part. In the above specific surface area is less than 50 m ² / g, there may be poor in durability because the sintering of the fibrils protruding alumina proceeds excessively, on the other hand, if the specific surface area exceeds 300 meters ² / g, fibril protruding Since the alumina becomes too fine, it may not function as a so-called catalyst supporting layer and may be brittle in structure. Through the processes (1) to (6), an alumina thin film (catalyst supporting layer) can be formed on the surface of the partition wall of the through hole of the honeycomb filter.

(7) Next, Pt is applied to the surface of the catalyst supporting layer.
And the like. Specifically, the evaporative drying method,
The oxidation catalyst is supported by an impregnation method such as an equilibrium adsorption method, an incipient wetness method, or a spray method. Among these, the incipient wetness method is desirable.

The incipient wetness method refers to a state in which an aqueous solution containing a predetermined amount of a catalyst component is dripped little by little onto a catalyst-supporting layer, and the surface of the catalyst-supporting layer starts to be slightly wet uniformly (incipient: ), The impregnation of the aqueous solution containing the catalyst component into the pores of the catalyst support layer is stopped, followed by drying and calcining to support the catalyst. Here, the dropping of the aqueous solution containing the catalyst component is usually performed using a burette or a syringe, and the adjustment of the amount of the catalyst to be supported is performed by adjusting the concentration of the aqueous solution containing the catalyst component.

The drying after dropping of the aqueous solution may be performed, for example, by adding 1
The treatment is carried out at a temperature of about 10 ° C. for about 2 hours to remove water, and then left in a desiccator for about 1 hour. After the drying is completed, under a nitrogen atmosphere,
Baking is performed by heating at a temperature of about 500 ° C. for about 1 hour, and metalization of Pt or the like is performed. Such (1) ~
Through the step (7), it is possible to manufacture a honeycomb filter in which an oxidation catalyst is supported on a catalyst support layer made of alumina. This honeycomb filter is a filter that supports an oxidation catalyst in the exhaust gas purification system of the present invention. Can be suitably used.

The exhaust gas purifying system having such a configuration can be suitably used as an exhaust gas purifying system for exhaust gas from a gasoline engine or a diesel engine, and is particularly suitable as an exhaust gas purifying system for a diesel engine. . Further, in the above exhaust gas purification system, the _the NO _X selective reducing catalyst and吸臓type catalyst capable of reducing NO _X even in an acidic atmosphere, or further supported on the filter, placing the upstream part of the filter By disposing it, it is also possible to reduce NO _x in the exhaust gas.

[0057]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 A. Manufacture of honeycomb filter After adding an organic binder, water, and the like to silicon carbide powder and kneading the resulting mixture, extrusion molding is performed to produce a honeycomb-shaped formed body, and then drying, degreasing, and firing are performed. The average pore system as shown is 5-20 μm and 1 cm ²
A porous silicon carbide sintered body 25 having 31 cells per unit and a partition wall thickness of 0.3 mm was produced.

Next, this porous silicon carbide sintered body 25 is
By bundling a large number using a heat-resistant adhesive containing inorganic fibers such as ceramic fibers or inorganic particles such as silicon carbide, and then cutting using a diamond cutter, the diameter as shown in FIG. The honeycomb filter 11 having a length of 165 mm and a length of 150 mm was formed, and a layer of the sealing material 23 having the same composition as the heat-resistant adhesive was formed on the outer peripheral portion.

B. Loading of Oxidation Catalyst on Honeycomb Filter (1) First, pretreatment was performed at 1100 ° C. for 20 hours to form an SiO ₂ oxide film of a honeycomb filter made of SiC. The amount of SiO ₂ in the honeycomb filter after the pretreatment was 3.0%.

(2) Next, a treatment for forming a catalyst supporting layer made of alumina on the partition walls of the honeycomb filter was performed. Specifically, first, Al (NO ₃ ) ₃ was added at a concentration of 30.
The solution was dissolved in 1,3-butanediol at 100 ° C. with stirring for 5 hours to obtain an Al (NO ₃ ) ₃ solution so as to have a volume%. Next, the pre-treated honeycomb filter is immersed in a container filled with the Al (NO ₃ ) ₃ solution, and then evacuated by a vacuum pump, thereby removing air from the honeycomb filter and removing each ceramic. The Al (NO ₃ ) ₃ solution was spread evenly over the surface of the particles.

(3) Next, the honeycomb filter was taken out of the container and dried at 150 ° C. for 2 hours to obtain Al (NO ₃ )
_{The three} solutions were gelled and fixed on the partition wall surface of the honeycomb filter. (4) Thereafter, the honeycomb filter was calcined at 400 ° C. to remove residual components and to form amorphous alumina.

(5) Next, the temporarily fired honeycomb filter was immersed in hot water at 70 ° C. for 3 hours to form small fiber projection boehmite on the surface of the partition wall of the honeycomb filter. (6) Further, the honeycomb filter on which the boehmite was formed was fully fired at 800 ° C. for 10 hours, so that alumina crystals were formed on the partition wall surface of the honeycomb filter. Here, the amount of alumina in the honeycomb filter was 8 g / l, and the shape was an average diameter of 6 nm and an average length of 120 n.
m, total length / diameter was 20.

(7) Next, through the above steps (1) to (6), Pt was supported as a catalyst on the honeycomb filter having the catalyst supporting layer made of alumina. Specifically, first, a dinitroamine platinum nitrate solution ([Pt (NH
After preparing ₃ ) ₂ (NO ₂ ) ₂ ] HNO), this solution is dropped at regular intervals on both end surfaces of the honeycomb filter with a pipette to uniformly disperse and fix Pt on the surface of the catalyst support layer made of alumina. Let it. Next, the honeycomb filter to which the dinitroamine platinum nitrate solution was dropped was placed at 110 ° C. for 2 hours.
The honeycomb filter was transferred to a desiccator and left for 1 hour, and then fired at 500 ° C. for 1 hour in an N ₂ atmosphere to metallize Pt. As a result, a honeycomb filter carrying a Pt catalyst was obtained.

C. Test of Exhaust Gas Purification System The regenerating ability of the honeycomb filter prepared in B above was evaluated by the following method. That is, first, a thermocouple for measuring the temperature in the honeycomb filter was attached to a portion 10 mm from the end face of the honeycomb filter on the exhaust gas inflow side. Next, the honeycomb filter was housed in a housing, and a dripping nozzle was attached to an exhaust gas inflow side of the honeycomb filter to produce an exhaust gas purification system.

Next, pipes and the like are arranged in the diesel engine having the common rail type fuel injection device and the above exhaust gas purification system, and further attached to one of the injection nosol of the common rail type fuel injection device and the exhaust gas purification system. An evaluation device was manufactured by arranging a pipe between the dropping sol and the mist. In addition, a pressure sensor was installed in the pipe that led the exhaust gas from the diesel engine to the exhaust gas purification system.

Next, this diesel engine was set to 50 N ·
m, the engine speed is 3000 min ^-1
The operation set at (rpm) was performed for 8 hours to collect PM in the honeycomb filter. Here, when the back pressure was measured by the pressure sensor, it was 15 kPa. Next, the operation of the diesel engine was switched to the post-injection method, and after 30 seconds, the supply of light oil from the dropping nozzle was started, and the temperature change in the honeycomb filter at this time was measured by a thermocouple. The results are shown in the graph of FIG.
FIG. 4 is a graph showing the change over time of the temperature in the filter. The vertical axis shows the temperature in the Hanium filter, and the horizontal axis shows time. The time when the operation of the diesel engine is switched to the post-injection method is set to 0 min.

When the back pressure was measured by a pressure sensor 10 minutes after the start of the supply of light oil, the back pressure was 4 kPa, and returned to the initial value before the start of the collection of PM. From these facts, in the exhaust gas purifying system of the present embodiment, the temperature in the honeycomb filter quickly rises to 600 ° C., which is the combustion start temperature of black smoke, after the supply of light oil is started, and the regeneration of the ceramic filter is performed. It has been found that this has been performed sufficiently.

Comparative Example 1 In the same manner as in Examples 1 and 2 except that a filter carrying an oxidation catalyst was produced, and a dripping nozzle was not attached to the exhaust gas inflow side of the honeycomb filter, the same procedure as in Example 1 was carried out. An evaluation device was produced in the same manner. Next, the operation of the diesel engine was performed for 8 hours under the same conditions as in Example 1,
PM was trapped in the honeycomb filter. Next, the operation of the diesel engine was switched to the post-injection system, and the temperature change in the honeycomb filter at this time was measured. The results are shown in the graph of FIG. When the back pressure was measured by a pressure sensor 10 minutes after switching to the post-injection method, the back pressure was 12 kPa. From these facts, it became clear that in the exhaust gas purification system of this comparative example, the temperature inside the honeycomb filter could not be sufficiently increased, and the regeneration of the ceramic filter was not sufficiently performed.

[0070]

Since the exhaust gas purification system of the present invention has the above-described structure, it is possible to simultaneously purify the exhaust gas and regenerate the filter, so that the exhaust gas purification system only needs to have at least one filter. Further, since a heating device is not required for regeneration of the filter, the manufacturing cost and the running cost are low, and the size of the exhaust gas purification system itself is compact. Hardly any restrictions.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of an exhaust gas purification system of the present invention.

FIG. 2 is a perspective view schematically showing a honeycomb filter made of a porous ceramic member.

FIG. 3A is a perspective view schematically showing a porous ceramic member constituting a honeycomb filter, and FIG.
FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 4 is a graph showing the change over time in the temperature inside the honeycomb filter in Example 1 and Comparative Example 1.

FIG. 5 is a schematic view showing an example of a conventional exhaust gas purification system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Exhaust gas purification system 11 Filter 12 Dripping nozzle 13 Diesel engine 14, 14 'Exhaust passage 21 Honeycomb filter 22 Adhesive layer 23 Sealing material 25 Porous ceramic member 26 Through hole 27 Filler 28 Partition

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) F01N 3/24 B01D 53/36 103C F-term (Reference) 3G090 AA03 BA01 EA01 EA02 3G091 AA18 AB02 AB13 BA07 BA13 BA15 BA19 CA18 FC01 GB01W GB04W GB05W GB06W GB07W HA15 4D048 AA13 AA14 AA18 AB01 AB05 AC02 BA03X BA06X BA10X BA19Y BA23Y BA30X BA31Y BA33Y BA34Y BA35Y BA36Y BA41X BB02 BB14 BB17 CC33 CC38 CC61 CD05 DA01 DA02 DA07 DA10

Claims (6)

[Claims] An exhaust gas purification system in which a filter carrying an oxidation catalyst is installed in an exhaust passage of an internal combustion engine, wherein a dropping nozzle or injection injector for supplying a hydrocarbon-based liquid to an exhaust gas inflow side of the filter. An exhaust gas purification system comprising: 2. The exhaust gas purification system according to claim 1, wherein the hydrocarbon-based liquid is light oil. 3. An oxidation catalyst is disposed upstream of the filter in the exhaust passage, and the drip nozzle or the injection injector is provided between the filter and the oxidation catalyst and / or the oxidation catalyst. The exhaust gas purification system according to claim 1, wherein a hydrocarbon liquid is supplied to an exhaust gas inflow side. 4. The internal combustion engine is a diesel engine having a common rail fuel injection device.
An exhaust gas purification system according to any one of the preceding claims. 5. The exhaust gas purification system according to claim 1, wherein the hydrocarbon-based liquid is supplied from a common rail fuel injection device attached to an internal combustion engine. 6. The filter supporting the oxidation catalyst,
A plurality of porous ceramic members in the form of prisms in which a large number of through holes are juxtaposed in the longitudinal direction across the partition walls are bound together via an adhesive layer to form a ceramic block, and the partition walls separating the through holes are used for collecting particles. The exhaust gas purification system according to any one of claims 1 to 5, wherein the exhaust gas purification system is a ceramic structure configured to function as a filter.