JPH0217911A - Combustible waste removing apparatus of internal combustion engine - Google Patents

Abstract

PURPOSE:To efficiently remove combustible particles by forming a porous layer of composite oxide represented by general formula A1-xA'xB1-yB'yO3 (wherein A is a rare earth metal element, and B and B' are Cr, Mn, Fe, Co or Cu) on the surface of carrier. CONSTITUTION:A porous layer of perovskite composite oxide represented by general formula A1-xA'xB1-yB'yO3 (wherein A is a rare earth metal element, A' is an alkaline earth element, x is 0<=x<=1 and y is 0<=y<=1) such as La0.8Sr0.2 CoO3 is formed to the surface of a carrier having filter function and a particulate in exhaust gas is collected by the carrier. By heating this carrier, the particulate is burnt and the carrier is regenerated.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a device for removing combustible emissions from an internal combustion engine.

In order to suppress and prevent the filter function from being degraded due to blockage of particulates, which are mainly made up of fine carbon particles, various catalysts are supported on the filter to burn the particulates at a lower temperature and improve the regeneration performance of the filter. is known.

Various catalysts such as platinum group metals and base metals have been proposed to improve the regeneration performance of this filter. Platinum (Pt) is a platinum group metal, and copper (Cu) is a base metal that has relatively good regeneration performance. It is said that it has.

Although it is not primarily intended for particulate combustion,
As composite oxide catalysts, Cr5CuN11.4010, which is found in Japanese Patent Publication No. 54-38598, and Japanese Patent Publication No. 56-1989
Co, ~8Mn1~2Cu found in Publication No. 52619
O. etc. have also been proposed. Furthermore, as a means for regenerating the filter, a method using an external ignition means such as a heater/burner, a method of raising the exhaust gas temperature to a temperature higher than the combustion temperature of particulates by using an intake/exhaust throttle, etc. are also adopted.

[Conventional technology]

For filters for collecting diesel particulates [Problems to be Solved by the Invention] However, none of the above-mentioned catalysts has yet achieved satisfactory effects in terms of ignitability and particulate combustibility. Furthermore, during regeneration, the filter material is exposed to high temperatures of about 1000° C. or higher due to the heat of combustion of particulates, and there is a problem in that all of the above-mentioned catalysts deteriorate significantly under such high temperature conditions.

Therefore, in order to solve the above problems, the present inventor first developed the general formula A, -, xA'xB1 , B, -, B', 0
3 (wherein A is one or more elements selected from rare earth elements, A' is one or more elements selected from alkaline earth elements, B, B' are Cr, Mn, Fe, Co, Ni
, Cu, and 0≦x≦1.0≦y≦1. ) has been disclosed (Japanese Patent Application No. 62-300147), which is characterized by coating a carrier having a filter function with a perovskite-type composite oxide represented by the following.

Perovskite-based composite oxides have high basic oxidation activity; for example, the most active one can be ignited at 270° C. when particulates and perovskite powder are mixed and thermally analyzed. However, when a honeycomb filter is coated and the gas temperature is raised at a constant rate, the temperature reaches 420°C, and when the gas temperature is kept constant at 200°C and heated with an electric heater installed on the upstream end of the filter. In order to obtain a high combustion rate, a thermal gradient is generated within the filter, so it is necessary to heat the end face of the filter to 475°C, and its high activity cannot be fully demonstrated.

This is thought to be because when thermal analysis was performed, perovskite and particulates were uniformly mixed in a mortar, and the contact efficiency with the particulates was close to ideal, so ignition was possible at a low temperature. On the other hand, in experiments in which a honeycomb filter was coated with perovskite and particulates were collected, the degree of contact between the particulates and perovskite was insufficient, and sufficient oxidation activity did not seem to be exhibited. Furthermore, in a regeneration method using an external heater as a regeneration means, since the heater is normally energized at a low flow rate, a thermal gradient is created within the filter, making regeneration more difficult.

Therefore, an object of the present invention is to develop an improved combustion removal device for combustible waste so that the high oxidation activity of perovskite-based composite oxides can be fully exhibited.

[Means to solve the problem]

In order to achieve the above object, the present invention provides general formulas A, -,
xA'xB1, BI-, B' y03 (wherein A is one or more elements selected from rare earth elements, A' is one or more elements selected from alkaline earth elements, B, B' are Cr
.

One or more elements selected from Mn, Fe, Co, Ni, and Cu, and 0≦x≦1.0≦y≦1. Provided is a device for removing combustible exhaust from an internal combustion engine, characterized in that a porous layer of a perovskite complex oxide represented by the following formula is formed on the surface of a carrier having a filter function.

The carrier having a filter function may be any of the carriers of conventional particulate collection filters, such as ceramics such as cordierite, alumina, mullite, and aluminum titanate, or metal honeycomb structures, porous structures, metal meshes, and wires. In addition to meshes, in filters that are simply filled with particles, the particles are also carriers.

General formula A, -, xA'xB1, B, -, B', 0.
The perovskite complex oxide represented by A, xA
'xB1, B, B' in a desired composition by adding an alkali to a solution, usually an acidic solution, typically a nitric acid solution -A,
It can be obtained by co-precipitating the hydroxides of xA'xB1, B, and B', drying, and then firing.

In order to form a porous layer of the perovskite composite oxide obtained in this manner on the surface of the carrier, a solvent, an organic binder, and additives as necessary are used to form a perovskite composite oxide powder and a particle size of 1 to 30J. ! m1 preferably 5-
~15- combustible substances may be mixed to form a slurry, coated on a carrier, and then dried and fired. The combustible substance may be any substance that is completely destroyed by combustion at the firing temperature (approximately 400 to 1000°C), but for example, amorphous carbon, resin powder such as nylon, polypropylene, coal fine powder, etc. can be preferably used. . If the particle size of the combustible substance is smaller than one line, the degree of contact between the particulate and the composite oxide cannot be improved satisfactorily, and if it is larger than 30 pm, the composite oxide layer is divided and the degree of contact decreases. do.

Further, the mixing ratio of the combustible substance to the composite oxide powder is preferably within the range of 10 to 5 Qwt%. If the mixing ratio of the combustible substance is less than 1Qwt%, sufficient porosity to increase the oxidation activity of the catalyst will not be obtained, while if it exceeds 5Qwt%, the strength of the porous catalyst layer will be insufficient, and the composite will be damaged during calcination. The oxide layer may peel off.

The amount of composite oxide supported on the filter carrier is 25 to 15
0g (per filter volume 11), preferably 75~
About 125g is good.

Further, it is preferable to disperse and support a platinum group metal, particularly palladium, in the composite oxide because it lowers the ignition temperature and peak temperature. Platinum group metals can be supported on the filter by impregnating, drying, and firing the composite oxide after forming a composite oxide porous layer on the filter carrier. It's okay.

Furthermore, if a voltage can be supplied by connecting an external connection lead wire to this perovskite-based composite oxide, it is possible to generate heat because the perovskite-based composite oxide has appropriate conductivity (electrical resistance). This has the advantage of eliminating the need for an external heater to burn the particulates collected in the filter (Japanese Patent Application No. 63-6982).
(See Specification No. 6).

[For production]

A filter carrying a composite oxide represented by the above general formula has excellent regeneration properties (ignition temperature, peak temperature), and because it is an oxide, high-temperature durability is improved. The improvement in reproducibility is thought to be due to the high oxidation activity of this composite oxide. Furthermore, by making the composite oxide layer porous, contact with combustible waste (particulates) is improved, and as a result, the inherent high oxidation activity of the composite oxide is exhibited more than on the preceding side. Became.

〔Example〕

Example 1 A mixed solution of nitrates of lanthanum, strontium, and cobalt was prepared and the concentration was adjusted to the desired composition. Next, this mixed solution was carbonated while stirring.
A Jium aqueous solution was gradually added dropwise to co-precipitate these elements as hydroxides. The obtained precipitate was thoroughly washed with water, filtered, dried, pulverized, and calcined at 800°C in the atmosphere to obtain La
A perovskite powder having a composition of olSro and aco03 was obtained.

Next, this Lao9. Sro, 2Co mouth. 90 parts by weight of perovskite powder of the composition, 10 parts by weight of amorphous carbon with an average diameter of about 1 rho as a combustible material, 0.5 parts by weight of polyvinyl alcohol as a binder, 1 part by weight of a surfactant, and 50 parts by weight of distilled water, The mixture was thoroughly stirred to form a slurry.

Next, a commercially available cordierite honeycomb filter (φ30
The slurry was coated on a cylindrical body (X50 cylinder) by a suction method, dried at 120°C for 2 hours, and fired at 1000°C for 3 hours to form a porous perovskite layer on the collected surface.

In addition, the amount of perovskite supported at this time is the filter volume 1
It was about 95g per portion.

Example 2゜Same ao-esro, 2COO3 powder 7 as Example 1
0 parts by weight, 30 parts by weight of the same carbon powder as the combustible material,
A slurry having the same composition as in Example 1 was otherwise prepared, and a porous perovskite layer was formed on the honeycomb filter described above using the same method. The amount of perovskite supported at this time was about 80 g per filter volume 1β.

Example 3 A porous perovskite layer of about 90 g per filter volume lβ was formed in the same manner as in Example 1, except that a slurry was prepared using 40 parts by weight of Lao, asroo, CoO, powder, and 60 parts by weight of carbon powder. did. Here, since the proportion of combustible substances was high, coating was performed twice to match the amount of perovskite supported.

Comparative Example 1 Lao, 1lsro, 2C in the same manner as Example 1
A perovskite with an OO3 composition was prepared and made into a slurry using distilled water and polyvinyl alcohol. Next, a commercially available honeycomb filter (same as Example 1) was coated with this slurry, and after drying and firing, a relatively dense perovskite layer was formed on the collected surface. Note that the amount of perovskite supported at this time was about 100 g per filter volume 11.

Comparative Example 2 A filter in which 90 g of perovskite was supported per 11 filter volumes was obtained in the same manner as in Example 1, except that 95 parts by weight of perovskite powder and 5 parts by weight of carbon powder were used.

Comparative Example 3 A perovskite layer was formed using the same operations as in Example 1, except for using 20 parts by weight of the same perovskite powder, 80 parts by weight of carbon powder, and the like. However, the perovskite peeled off during handling of the filter after firing, so testing at this mixing ratio was discontinued.

Test Example 1 The filters of Examples 1 to 3 and Comparative Examples 1 to 3 were attached to the exhaust system of a turbocharged diesel engine, and 0.55 to 0.65 g of particulates were collected per filter. Next, these filters were assembled into the evaluation apparatus shown in FIG. 1, and the filter end face heating temperature (regeneration temperature) at which a particulate combustion rate of 70% or more was obtained was investigated. In Fig. 1, 1 is a reaction tube, 2 is an exhaust pipe, and 3 is a reaction tube.
is N2-〇□ gas introduction pipe, 4 is filter, 5 is rectifier,
6 is an electric furnace.

Test Example 2゜In order to examine the adhesion strength of the perovskite layer formed on the surface of the honeycomb filter, Examples 1 to 3 and Comparative Example 1.
Immerse the filter in step 2 in distilled water and rinse it in an ultrasonic cleaner.
It was left for 0 minutes. Next, the filter was taken out, and after sufficiently drying, the amount of peeling of the perovskite layer was determined from the change in filter weight. The results of Test Example 1.2 are summarized in Table 1.

Table 1 Table 1 shows that compared to Comparative Example 1, where the perovskite layer is relatively dense, the regeneration performance is improved in all cases where combustible materials are mixed, and the one with a mixture of around 30% has the highest activity. I understand that. In principle, the more porous the perovskite layer is, the larger its geometric surface area should be, and the more active it should be. However, in Example 3, coating was performed twice because the amount supported was small. The first porous layer is replaced with the second porous layer.
It seems that the activity has decreased slightly because it is blocked by the second coating. Note that it is not preferable to increase the amount of combustible material too much since the perovskite layer begins to peel when the combustible material reaches 60%.

Note that here, La is used as a perovskite-type composite oxide.
Although an example is shown in which amorphous carbon is used as combustible materials, the composition of the composite oxide is not limited to this in principle, and other combustible materials include nylon, It is clear that powdered coal powders of polypropylene and other resins can also be used.

In addition, it was said that the particle size of combustible material should be 1 to 30μ, but 1-30μ is preferable.
If the grain size is below, the degree of contact between the particulates and the perovskite cannot be improved satisfactorily, and if the grain size exceeds 307, the perovskite layer will be divided and the degree of contact will be reduced. Therefore, the particle size is preferably 5J, although it depends on the amount of perovskite supported (thickness of the perovskite layer).
It is in the range of I11 to 15μ.

〔Effect of the invention〕

According to the present invention, the inherently high oxidation activity of a specific perovskite-type composite oxide is fully exhibited, the regeneration properties of the filter (particulate ignition temperature, etc.) are further improved, and the durability is excellent. Additionally, a combustible exhaust combustion removal device is provided.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an apparatus for evaluating characteristics of a filter according to an embodiment. ■...Reaction tube, 2...Exhaust pipe, 3
...N2-0□Gas introduction pipe, 4...Filter 5.
... Rectifier, 6... Electric furnace.

Claims (1)

[Claims] 1. General formula A_1_-_xA'_xB_1_-_yB'
_yO_3 (wherein A is one or more elements selected from rare earth elements, A' is one or more elements selected from alkaline earth elements, B, B' are Cr, Mn, Fe, Co, Ni,
One or more elements selected from Cu, 0≦x≦1, 0≦y
≦1. 1. A device for removing combustible exhaust from an internal combustion engine, characterized in that a porous layer of a perovskite complex oxide represented by the following formula is formed on the surface of a carrier having a filter function.