JP2827546B2 - Exhaust gas purification device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently reducing HC in exhaust gas when the temperature of the exhaust gas is low and when the exhaust gas reaches a high temperature of 300 ° C. or more from the low temperature, such as when starting the engine in a cold state. The present invention relates to an exhaust gas purifying apparatus capable of adsorbing well and purifying exhaust gas.

[0002]

2. Description of the Related Art Conventionally, a pellet-type catalyst or a monolith-type catalyst has been used as an exhaust gas purifying device for purifying exhaust gas from automobiles. Here, when purifying the exhaust gas by the exhaust gas purifying device, the harmful component HC in the exhaust gas,
Of the CO and NOx, the performance of purifying HC is particularly strongly affected by the temperature of the exhaust gas.

That is, the purification performance of the conventional exhaust gas purifying catalyst is such that the catalytic function is sufficiently exhibited when the exhaust gas temperature is 300 ° C. or higher, for example. For this reason, when the temperature of the exhaust gas is low and when the temperature of the exhaust gas shifts to a high temperature of 300 ° C. or more from the low temperature, the HC (hereinafter referred to as cold HC) component in the low-temperature exhaust gas is sufficiently reduced by the catalyst. May be released to the atmosphere without purification.

[0004] In general, an air-fuel mixture having a higher concentration than in normal operation is supplied to the engine at the start in a cold state, and the amount of HC contained in the exhaust gas is larger than in the warm-up operation. ing. For this reason, it is desired to efficiently purify cold HC particularly at the time of start-up, etc., and measures such as providing an HC trapper for adsorbing cold HC upstream of the catalyst are taken in addition to the catalyst. An exhaust gas purification device has been proposed. For example, Japanese Patent Laid-Open No. 2-7
As disclosed in Japanese Patent No. 5327, there has been proposed an exhaust gas purifying apparatus in which an HC trapper having a zeolite such as Y-type zeolite or mordenite as an HC adsorbent is arranged upstream of an exhaust gas purifying catalyst in an exhaust gas system. .

[0005]

However, Japanese Patent Application Laid-Open No. Hei.
The HC adsorption performance of various zeolites used in the exhaust gas purifying apparatus disclosed in Japanese Patent No. 75327 is highest at an exhaust gas temperature of 200 ° C. as shown in FIG.
The temperature decreased as the temperature rose to ° C. For this reason, in the exhaust gas purifying apparatus, during the transition until the exhaust gas temperature reaches a high temperature of 300 ° C. or higher at which the catalytic function of the exhaust gas purifying catalyst is sufficiently exhibited, the adsorption rate of HC in the exhaust gas is poor and the exhaust gas is exhausted. It cannot be purified.

[0006] The chemical adsorption power of HC on zeolite used as an adsorbent for cold HC in the HC trapper of the conventional exhaust gas purifying apparatus is affected by its acid strength. That is, in the case of zeolite having a low silica / alumina ratio, the solid acid content is large, but almost all of the weak acid sites do not have an adsorbing power capable of adsorbing and holding HC as a chemical adsorption point. It has the property of adsorbing a large amount of water, and the amount of cold HC adsorbed is small. Conversely, in the case of zeolite having a high silica / alumina ratio, the acid strength is high, but the adsorption point (the amount of acid sites) is small, so that the adsorption amount is small. Therefore, as a zeolite used as an adsorbent for cold HC, a zeolite having an intermediate silica / alumina ratio has been used.

Therefore, an exhaust gas purifying apparatus having an HC adsorbent is capable of adsorbing cold HC contained in exhaust gas more efficiently both when the exhaust gas temperature is low and when the exhaust gas is shifted to a high temperature. Is a challenge. An object of the present invention is to provide an exhaust gas purifying apparatus that solves the above problems.

[0008]

SUMMARY OF THE INVENTION The present invention relates to an exhaust gas purifying apparatus having an HC adsorbent disposed upstream of the exhaust gas purifying catalyst in an exhaust gas system having an exhaust gas purifying catalyst. , A zeolite that has been heat treated in an H ₂ S atmosphere.

As the zeolite, a conventionally used Y-type zeolite, mordenite, ZSM-5 or the like can be used. The silica / alumina ratio constituting the zeolite can be in a wide range from high to low. The condition for the heat treatment of the zeolite is temperature: 300
５００500 ° C., time: 2-5 H, H ₂ S flow rate: space velocity number + h ⁻¹ . The zeolite that has been heat-treated under the above-mentioned conditions has an increased solid acid strength and a stronger HC chemical adsorption power.

[0010] Specific forms of use of the above-mentioned zeolite include pellet-shaped zeolite, pellet-shaped core material coated with zeolite, and cordierite carrier substrate and metal carrier substrate. Those coated with zeolite can be used. A three-way catalyst can be used as an exhaust gas purifying catalyst provided downstream of the HC adsorbent. The three-way catalyst includes a catalyst noble metal such as Pt, Rh, and Pd as a catalyst component in a catalyst supporting layer formed on a surface of a pellet-shaped core material, a surface of a cordierite carrier substrate and a surface of a metal carrier substrate, or the like. Is preferably used.

[0011]

According to the exhaust gas purifying apparatus of the present invention,
H ₂ S atmosphere zeolite heat treated in is used as the HC adsorbent. The zeolite as the HC adsorbent has an increased acid strength by the heat treatment,
The C adsorption force and the holding amount are increased, and the so-called adsorption function is improved. That is, in the zeolite whose acid strength has been increased by the heat treatment, the HC adsorption ability does not become weak as in the case where the heat treatment is not performed with the increase in the exhaust gas temperature (increase in the kinetic energy of HC molecules), Since the maximum temperature at which the adsorbed HC is desorbed is also increased, the previously adsorbed HC is desorbed until the temperature shifts to a high temperature at which the exhaust gas purifying catalyst function is sufficiently exhibited ( Release). For this reason, when an HC adsorbent is disposed and used upstream of the exhaust gas purifying catalyst in an exhaust gas system equipped with the exhaust gas purifying catalyst, HC contained in low-temperature exhaust gas at the time of starting the engine and exhaust gas purifying Exhaust gas temperature 30 at which the catalytic function of the catalyst for use is fully exhibited
HC contained in the exhaust gas during the transition until the temperature reaches 0 ° C. or higher can be efficiently adsorbed, and HC desorption can be prevented.

After the exhaust gas temperature has shifted to a high temperature,
The HC desorbed from the HC adsorbent is oxidized by an exhaust gas purifying catalyst arranged downstream of the HC adsorbent and whose catalytic function is sufficiently enhanced by high temperature to be converted into H ₂ O or CO ₂ , and the exhaust gas is purified. can do. Therefore, according to the exhaust gas purifying apparatus of the present invention, the HC contained therein is efficiently adsorbed by the HC adsorbent in the low-temperature exhaust gas and the exhaust gas before the transition to the high temperature, in which the purification efficiency is low in the past. , Can be purified.

[0013]

(Embodiment 1) An exhaust gas purifying apparatus according to Embodiment 1 of the present invention will be described below with reference to FIGS. The exhaust gas purifying apparatus of the embodiment is disposed in an exhaust gas system E1 that purifies exhaust gas discharged from the engine E and then discharges the exhaust gas to the atmosphere. That is, the exhaust gas system EI includes a first catalytic converter 1, a second catalytic converter 2, and a second catalytic converter 2, which are disposed at a predetermined interval from the upstream side to the downstream side of the exhaust gas passage E10 connected to the engine E. And an HC trapper 3 disposed upstream of the HC trapper 3.

The exhaust gas passage E10 has a bypass passage E11 connecting the upstream side and the downstream side of the HC trapper 3.
Is provided. A first switching valve 4 is provided at each of the upstream connection position and the downstream connection position.
The first and second switching valves 42 are arranged. In the exhaust gas passage E10 between the first switching valve 41 and the first catalytic converter 1, the first and second switching valves 41,
A temperature sensor 43 for detecting the switching timing of 42 based on the level of the exhaust gas temperature and performing the switching operation is disposed. The first catalytic converter 1 has a conical cylindrical end portion 102 having a cylindrical central portion 100 and flange-shaped mounting portions 101 formed on both sides thereof.
And a three-way catalyst 13 housed in the container 10 and fixed by the holder 11 and the wire net 12. This three-way catalyst 13 is a commercially available core
Gelite monolith carrier (capacity: 0.7 l, number of cells:
400 cells / in ² ) and Pt (1.5
g / l-cat) and Rh (0.3 g / l-cat)
Is carried.

The second catalytic converter 2 has a cylindrical central part 2.
00 and a conical cylindrical end 202 formed on both sides thereof and having a flange-shaped mounting portion 201;
And a three-way catalyst 23 housed therein and fixed by a holder 21 and a wire net 22. This three-way catalyst 2
3 is a commercially available cordierite monolithic carrier (capacity:
1.3 l, the number of cells: 400 cells / in ² ), and Pt (1.5 g / l-cat) and Rh (0.
3 g / l-cat).

The HC trapper 3 has a cylindrical central portion 300.
And a conical tubular end 302 formed on both sides thereof and having a conical mounting portion 301, and an HC adsorbent 33 accommodated in the container 30 and fixed by a holder 31 and a wire net 32. . This HC adsorbent 33
Discloses a heat treatment of zeolite supported on a cordierite monolithic carrier in an H ₂ S atmosphere to form an HC adsorbent having an enhanced HC adsorption function.

The HC adsorbent 33 is formed as follows. That is, a commercially available Na—H / Y type zeolite (silica / alumina molar ratio: 30, Na ₂ O: 0.2 w
100%, silica sol (20 wt%) 35
Parts and 50 to 70 parts of water are added and mixed and stirred to prepare a washcoat slurry. Then, in the slurry, a commercially available cordierite monolithic carrier (capacity: 1.0
l, 400 cells / in ² ), after immersion,
After a certain period of time, lift up and blow off excess slurry, 10
After drying at 0 ° C., calcination was performed at 350 ° C. After the calcination, the wash coat is further repeated on the surface to obtain a total of 100 g / l-cat of Na-H.
/ Y-type zeolite-coated washcoat product is calcined at 500 ° C for 3 hours to produce intermediate HC before final heat treatment.
An adsorbent was obtained.

Next, the intermediate HC adsorbent is heated at a temperature of 350
HC adsorbent 33 having, as a coat layer, an HC adsorbent made of zeolite whose solid acid strength has been increased by heat treatment under H ₂ S flow (1.0 l / min) at 3 ° C. for 3 hours.
was gotten. HC adsorbent 33 manufactured as described above
Are stored in the container 30 and fixed by the holder 31 and the wire-net 32 to form the HC trapper-3.

As described above, the HC trapper 3 is connected to the exhaust gas passage E10 on the upstream side of the second catalytic converter 2.
It is arranged in. Next, the exhaust gas purifying apparatus of the present embodiment configured as described above moves the first switching valve 41 to the A and B positions as shown in FIG. 2 according to the exhaust gas temperature T detected by the temperature sensor -43. By switching the second switching valve 42 between the C and D positions, the exhaust gas flow is controlled in either the S1 direction or the S2 direction, and the HC
It performs an adsorbing action, a desorbing (releasing) action of adsorbed HC, a regeneration of the HC adsorbing ability, a thermal deterioration prevention, a desorption prevention at a high temperature of H ₂ S, and the like. Then, i) when T ≦ 200 ° C., the first switching valve 41 is controlled to be in the A position, and the second switching valve 42 is controlled to be in the C position. Then, the exhaust gas discharged from the engine E passes through the first catalytic converter 1, and then is introduced into the HC trapper-3 through the exhaust gas passage E10, and the HC adsorbent 33 reduces the cold HC in the exhaust gas by about 53%. Adsorbed. The exhaust gas having a reduced content of cold HC is introduced from the HC trapper 3 to the second catalytic converter 2 as shown by an arrow S1, and is purified by the three-way catalyst 23.

Ii) When 200 ° C. <T ≦ 300 ° C.,
The first switching valve 41 is in the B position, and the second switching valve 42 is in the D position.
It is controlled to be at the position. Then, the exhaust gas discharged from the engine E passes through the first catalytic converter 1,
It is introduced into the second catalyst converter 2 from the bypass passage E11 as indicated by the arrow S2. That is, during this control,
Assuming that exhaust gas having a temperature higher than 200 ° C. is introduced into the HC trapper 3, the HC adsorbed by the HC adsorbent 33 starts to desorb. However, since the three-way catalyst 23 of the second catalytic converter 2 on the downstream side has not yet been sufficiently activated, the desorbed HC cannot be completely purified. Therefore, in the temperature range from 200 ° C. to 300 ° C., the exhaust gas is prevented from flowing into the HC trapper-3. As a result, the desorption of HC adsorbed on the HC adsorbent 33 is prevented, and since the exhaust gas flows through the bypass E11, there is almost no loss of heat, so that the three-way catalyst 23 of the second catalytic converter 2 on the downstream side is Since the temperature rises more quickly, the activation becomes faster.

Iii) When 300 ° C. <T ≦ 400 ° C., the first switching valve 41 is in the A position, and the second switching valve 42
Is controlled to be the C position. Then, the exhaust gas discharged from the engine E is purified when passing through the first catalytic converter 1 in which the three-way catalyst 13 is sufficiently activated by the high temperature,
With almost no HC component, the exhaust gas passage E10
The HC is introduced into the HC trapper 3 and the HC that has been adsorbed by the HC adsorbent 33 is desorbed at a high temperature within 400 ° C., and the HC is contained in the second catalyst converter as indicated by an arrow S1. 2 and purified by the three-way catalyst 23.

In this case, since the HC adsorbed so far is removed from the HC adsorbent 33 of the HC trapper 3, the HC adsorbing performance of the HC adsorbent 33 is regenerated and the HC adsorbent 33 is coked. Deterioration is prevented. . Also in the second catalytic converter 2 on the downstream side, the three-way catalyst 23 is sufficiently activated by the high temperature, and the exhaust gas containing HC accompanying the regeneration of the HC adsorbent 33 is purified.

Iv) When 400 ° C. <T, the first switching valve 41 is controlled to the B position and the second switching valve 42 is controlled to the D position. Then, the exhaust gas discharged from the engine E passes through the first catalyst converter 1 and then passes through the bypass passage E11 as indicated by the arrow S2 in the second catalyst converter 2.
To be introduced. That is, in this control, if high exhaust gas having a temperature of 400 ° C. or more is introduced into the HC trapper 3, H ₂ S (sulfided) adsorbed on the zeolite of the HC adsorbent 33 by the heat treatment at the time of the production is assumed. Hydrogen) begins to desorb, preventing this, and
To prevent the HC adsorbent 33 from deteriorating due to hydrothermal energy, H
The C trapper-3 is bypassed so that high-temperature exhaust gas exceeding 400 ° C. does not flow. (Comparative Example) In order to confirm the effect of the HC adsorbent of the above example, the HC adsorbent of Comparative Example 1 and the HC adsorbent of Comparative Example 2 were formed. (Comparative Example 1) The HC adsorbent of Comparative Example 1 is the same as the example except that the heat treatment in the H ₂ S atmosphere is not performed unlike the HC adsorbent of the example. (Comparative Example 2) The HC adsorbent of Comparative Example 2 used Na-H / Y-type zeolite (silica / alumina molar ratio: 100) as the zeolite, and used an H ₂ S atmosphere like the HC adsorbent of Example. It is the same as the example except that the heat treatment in the inside is not performed.

(Performance Comparison Test) The HC adsorbent of the example, the HC adsorbent of Comparative Example 1, and the adsorbent of Comparative Example 2 were incorporated in the HC trapper 3 of the exhaust gas purifying apparatus shown in FIG. did. The evaluation was performed by cold start evaluation (starting → idle → acceleration → steady running at 60 km / h).

Table 1 shows the evaluation results. As is clear from Table 1, in the case of the example, a cold HC reduction rate superior to that of the comparative examples 1 and 2 is obtained. This is because the exhaust gas temperature reaches 200 ° C before the HC
It is considered that the adsorbed HC is securely adsorbed and the adsorbed HC is not desorbed.

As described above, the HC adsorbent using the zeolite heat-treated in the H ₂ S atmosphere as the HC adsorbent has an improved HC adsorbing ability. In addition, H of the HC adsorbent
It is presumed that the reason why the C adsorbing ability was improved was that the strength of solid acid sites such as zeolite was increased and the adsorbing power of HC was increased. Also, in an exhaust gas purifying apparatus for an alcohol fueled vehicle, when a performance evaluation test is performed on a zeolite that has been heat-treated in an H ₂ S atmosphere using an HC adsorbent serving as an HC adsorbent, it is found that the zeolite has a formaldehyde adsorption capacity. It was found that the HC adsorption ability was improved.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing an example of use of an exhaust gas purifying apparatus according to an embodiment.

FIG. 2 is an explanatory diagram showing control states of a first switching valve and a second switching valve in the exhaust gas purifying apparatus of the embodiment.

[Explanation of symbols]

1 ... first catalyst converter - motor 2 ... second catalytic converter - motor 3 ... HC trapper 33 ... zeolites heat-treated in H ₂ S atmosphere HC
HC adsorbent used as adsorbent

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01J 20/28 B01D 53/34 B 20/34 120D F01N 3/24

Claims (1)

(57) [Claims] In an exhaust gas purifying apparatus having an HC adsorbent disposed upstream of the exhaust gas purifying catalyst in an exhaust gas system having an exhaust gas purifying catalyst, the HC adsorbent is heat-treated in an H ₂ S atmosphere. An exhaust gas purifying device, which is a zeolite.