JPH0710010Y2 - Exhaust gas purification device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an exhaust gas purifying apparatus for purifying harmful components in exhaust gas.

[Conventional technology]

Exhaust gas from automobiles contains harmful components such as hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx), so a catalyst was provided in the exhaust system to purify them. Purification equipment is used. Exhaust gas purifying catalysts include various types such as pellet type and monolith type, but the catalytic purifying ability is generally affected by temperature. Among the above-mentioned harmful components, the catalyst purification ability, particularly for HC, is strongly influenced by the exhaust gas temperature, and is generally purified by a noble metal catalyst at a temperature of 300 ° C. or higher. For this reason, the catalyst cannot sufficiently purify the exhausted HC when the exhaust gas temperature and the catalyst temperature are still low when the engine is started (at the time of cold start). Since a large amount of this cold HC is emitted, it accounts for a large proportion of the total HC emissions, and there is a strong demand for reducing it.

As described above, it is difficult to purify cold HC by using an exhaust gas purifying device that includes only a purifying catalyst such as a precious metal catalyst. Therefore, an exhaust gas purifying device has been proposed in which measures such as providing an HC trapper on the upstream side of the catalyst are taken. The applicant also proposed in Japanese Utility Model Laid-Open No. 62-6416 an exhaust gas purifying device in which an adsorbent for malodorous components is arranged in the bypass passage and the exhaust gas is caused to flow into the main passage or the bypass passage depending on the exhaust gas temperature. did. Further, in Japanese Patent Application No. 63-226070, an exhaust gas purifying device was proposed in which an HC trapper equipped with zeolite (Y-type zeolite or mordenite) as an HC adsorbent was arranged upstream of a purifying catalyst. In these devices, when the exhaust gas temperature is low, the malodorous components and cold HC are removed by the adsorbent. When the exhaust gas temperature is high, on the contrary, HC is desorbed from the adsorbent, so that the adsorption of HC and the regeneration of the adsorbent can be repeated depending on the temperature of the exhaust gas flowing through the adsorbent.

[Problems to be solved by the device]

However, since the high-temperature exhaust gas flowing to the adsorbent for regeneration also contains HC, even if the flow of the exhaust gas is appropriately changed by a switching valve, etc., regeneration of the HC adsorbent will be completed completely depending on the conventional technology. Some of the HC remained retained on the adsorbent. Furthermore, when high-temperature exhaust gas is passed through the adsorbent, a coking reaction occurs and cokes are generated, clogging the pores of the adsorbent and reducing the surface activity, which reduces the HC adsorbability of the HC adsorbent. It was easy to do.

The present invention is to solve the above-mentioned problems in the prior art. It is an object of the present invention to provide an exhaust gas purifying apparatus equipped with an HC adsorbent which has a high ability to adsorb cold HC, can be sufficiently regenerated, and has excellent durability.

[Means for Solving the Problems]

That is, the exhaust gas purifying apparatus of the present invention includes a temperature measuring unit in the exhaust system, and an operation controlled based on the measured temperature.
And a second switching valve, a hydrocarbon trapper having a hydrocarbon adsorbent and a catalyst adsorbent made of a three-way or oxidation catalyst, and a catalytic converter having a three-way catalyst. The second switching valve and the second switching valve are connected in parallel by a first passage and a second passage having a hydrocarbon trapper arranged in an intermediate portion, and the first switching valve and the second passage are connected to each other. The hydrocarbon trapper and the intermediate portion of the second switching valve are connected by a third passage, and a catalytic converter is connected downstream of the second switching valve.

The temperature measuring means may be a conventional means such as a thermocouple or a temperature sensing resistor. As a place where the temperature measuring means is provided, a place where a representative temperature of the exhaust gas flowing into the exhaust gas purification device can be measured, for example, a passage, is appropriately selected.

As the first and second switching valves, those which can switch the flow path of exhaust gas based on the measured temperature by an electric signal output from a control device such as a computer are used.

The hydrocarbon adsorbent provided in the hydrocarbon trapper may be a zeolite such as mordenite, Y-type zeolite, ZSM-5, etc. coated on a desired carrier such as a cordierite monolith carrier. Similarly, a three-way or oxidation catalyst provided in a hydrocarbon trapper may be prepared by coating a noble metal such as platinum, rhodium, iridium, or palladium with other promoter components, such as cerium or lanthanum, on the monolith carrier, if desired. What is carried in the layer is used. It is practically convenient to use a hydrocarbon adsorbent on one side of one monolithic support and a catalyst adsorbent on the other side of which a three-way or oxidation catalyst is formed. It can be produced in the same manner as the original catalyst.

The passage for connecting the first and second switching valves, the hydrocarbon trapper and the catalytic converter to each other usually uses a pipe having a predetermined property. Then, by connecting the respective constituent elements as described above, it is possible to control the adsorption-desorption of the hydrocarbon relating to the hydrocarbon adsorbent, as described below.

1) When cold HC is adsorbed (when the exhaust gas is at a low temperature), the exhaust gas is caused to flow so that the HC adsorbent of the HC trapper becomes the front flow portion, and the cold HC is adsorbed by the HC adsorbent. Exhaust gas
After passing through the HC adsorbent, it passes through the three-way or oxidation catalyst in the downstream part, and further passes through the downstream catalytic converter to be discharged.

2) The temperature of the exhaust gas rises, and the temperature of the gas entering the HC adsorbent is
At temperatures above 200 ° C, the HC adsorbed on the HC adsorbent begins to desorb. Therefore, the three-way catalyst provided in the catalytic converter is adsorbed by the HC adsorbent until fully activated.
The exhaust gas passage is switched so that the exhaust gas flows only to the catalytic converter so that HC is not desorbed.

3) After the exhaust gas temperature further rises and the three-way catalyst provided in the catalytic converter is sufficiently activated, the HC trapper is regenerated. That is, the exhaust gas passage is switched again so that the three-way or the oxidation catalyst of the adsorbent with a catalyst is in the front flow portion,
Exhaust gas is made to flow so that the HC adsorbent becomes the downstream part. As a result, the HC adsorbed on the HC adsorbent is desorbed / removed by the exhaust gas containing almost no HC component purified by the three-way or oxidation catalyst to regenerate the HC adsorbent.

4) When zeolite having low heat resistance is used as the HC adsorbent, the following operation is further added to prevent the zeolite crystals from collapsing due to heat. Perform operation 3)
After regeneration of the HC adsorbent, if the exhaust gas temperature rises to a temperature that causes thermal degradation of the zeolite crystals, return to the state of 2) and the exhaust gas flows only to the catalytic converter,
Prevent hot exhaust gas from flowing into the HC adsorbent.

[Action]

Depending on the temperature of the exhaust gas, the exhaust gas passage is switched by the switching valve to reverse the flow direction of the exhaust gas passing through the hydrocarbon trapper or prevent the exhaust gas from flowing into the hydrocarbon trapper. Adsorption of HC by the material and regeneration of the HC adsorbent can be conveniently performed.

〔Example〕

The present invention will be described in more detail with reference to the following examples and comparative examples. The present invention is not limited to the following embodiments. Parts indicate parts by weight.

Example 1 1. Production of adsorbent with catalyst Monolith carrier: Cordierite monolith carrier (1.7 l, 4
00 cells / in ² ) i) Application of alumina 100 parts of alumina, 140 parts of alumina sol (10 wt%) and Al
(NO ₃ ) ₃ · aq (14 parts) is ball-milled with water and nitric acid, and one-third of one end of the water-absorbed monolith carrier is immersed in the wash-coat slurry. After pulling up the monolith carrier from the slurry, the excess liquid in the cells of the monolith carrier is blown off with compressed air. The carrier is dried to remove free water and calcined at 500 ° C. for 1 hour to obtain a carrier on which one-third of the monolith carrier is coated with alumina.

ii) Support of Pt and Rh The carrier of the alumina-coated portion was immersed in a nitric acid aqueous solution of dinitrodiammine platinum, dried and calcined at 200 ° C for 1 hour to obtain 1.35 g / l [0.765 g / (1.7 / 3) l ] Platinum is supported on alumina. Then, the platinum catalyst was immersed in an aqueous rhodium chloride solution, dried, and then calcined at 200 ° C. for 1 hour to support 0.15 g / l [0.085 g / 1.7 / 3) l] of rhodium on the alumina, and Pt- The Rh catalyst is prepared in one third part of the monolith support.

iii) Application of HC adsorbent (H / mordenite) 100 parts H / mordenite, 70 parts silica sol (20wt%), water 5
Mix 5 to 70 parts and stir to mix H / H with a viscosity of about 100 cps
Prepare a mordenite slurry. The remaining two-thirds (not coated with the catalyst) of the water-absorbed monolith carrier was immersed in the slurry, pulled up, and the excess slurry was blown off, and after sufficiently drying at 100 ° C. for 5 to 10 hours, 350 ° C
Calcination is performed for 2 to 3 hours. The above operation, that is, the immersion in the slurry, the drying and the calcination are repeated several times. As a result, H / mordenite is coated in a total amount of 100 g / l.

By the above-mentioned operations i) to iii), the adsorbent 3 with a catalyst shown in FIG. 2 and comprising the HC adsorbent 10 and the three-way (oxidation) catalyst 11.
To manufacture.

2. Production of three-way catalyst Monolith carrier: Cordierite monolith carrier (1.3l, 4
00 cells / in ² ) 1. Alumina was applied to the monolithic carrier in the same manner as i) and ii) in the production of the adsorbent with catalyst, and then Pt (1.35 g / l), Rh
(0.15 g / l) is carried to produce a three-way catalyst 5.

3. Exhaust Gas Purification Device (Fig. 1) The adsorbent 3 with catalyst manufactured as described above is housed in a heat-resistant container and fixed by a spring 12 and a holder 13 to obtain an HC trapper 2. Further, the three-way catalyst 5 is housed in a heat resistant container and fixed by the spring 12 and the holder 13 to obtain the catalytic converter 4. These are connected to each other through a pipe 9 together with the switching valves 6 and 7 and the temperature measuring device 8 and are connected to the exhaust system of the engine 1 to obtain the exhaust gas purification device shown in FIG. Incidentally, A to D in the figure show respective states when the switching valves 6 and 7 are switched.

4. Control of HC Adsorption and Desorption (Regeneration) Mechanism of Exhaust Gas Purification Device As shown in FIG. 3, the HC adsorption material is adsorbed and desorbed by controlling the switching valves 6 and 7.

HC trapper inlet gas temperature: Tin (where Tin is the first
The temperature is measured by the temperature measuring device 8 shown in the figure, and the valve switching is controlled according to the output gas temperature during reverse flow regeneration.

i) When Tin <200 ° C. In the valve 6-A, 7-C HC trapper 2, the HC adsorbent 10 in the upstream portion adsorbs cold HC.

ii) When the inlet gas temperature of the HC adsorbent 10 exceeds 200 ° C, HC
Cold HC adsorbed on the adsorbent 10 begins to desorb. However, since the three-way (oxidation) catalyst 11 in the downstream part and the three-way catalyst 5 in the downstream side are not yet sufficiently activated, the desorbed HC cannot be completely purified. Therefore, Tin is 200 ℃
In the temperature range above 500 ° C, the exhaust gas does not flow to the HC trapper 2 and is adsorbed on the HC adsorbent 10.
Since the elimination of HC is prevented and there is almost no heat loss in the HC trapper 2, the three-way catalyst 5 on the downstream side heats up more quickly, so that activation is faster.

iii) When 500 ° C ≤ Tin <650 ° C Valves 6-B, 7-D Up to the temperature at which the downstream three-way catalyst 5 is fully activated and the HC adsorbent 10 can be regenerated (complete removal of adsorbed HC). When the Tin rises, the reverse flow regeneration of the HC adsorbent 10 is performed. By switching the valve 6, the three-way (oxidation) catalyst 11 in the front flow section and the rear flow section in the back flow section
Since it becomes the HC adsorbent 10, the HC adsorbent 10 is regenerated (HC removed) by the gas purified by the three-way (oxidation) catalyst 11 (gas containing almost no HC component). Therefore, HC adsorbent
It is possible to prevent deterioration due to caulking of 10.

iv) When using zeolite with low heat resistance as the HC adsorbent, or when the exhaust gas temperature is high and the Tin is often 800 ° C. or higher and the thermal deterioration of the HC adsorbent 10 is large,
The following control functions may be added.

When 650 ℃ ≦ Tin, the valve 6-A, 7-D high temperature exhaust gas does not flow through the HC adsorbent 10 (HC trapper 2), thus preventing thermal crystal collapse of the HC adsorbent 10 (zeolite). .

Comparative Example 1 (Fig. 4) As shown in Fig. 4, a catalytic converter in which the HC trapper 2 containing the HC adsorbent 10 is arranged on the upstream side of the engine exhaust system and the three-way catalyst 5 is contained on the downstream side. An exhaust gas purifying apparatus in which No. 4 was arranged was obtained in the same manner as in Example 1.

HC adsorbent 10 carrier: 1.13 l, 400 cells / in ² , made of cordierite HC adsorbent: H / mordenite, 100 g / l coated three way catalyst 5 carrier: 1.7 l, 400 cells / in ² , made of cordierite catalyst component : Pt (1.35 g / l), Rh (0.15 g / l) <Performance comparison test> Using the exhaust gas purification apparatus shown in Example 1 and Comparative Example 1, HC purification performance was evaluated on an engine bench.

The evaluation was performed by cold start evaluation (starting → yield → acceleration → 60 km / h steady running). The cold start evaluation was repeated 500 times to investigate the durability along with the initial performance.

The test results are shown in Table 1. (HC adsorption rate-HC trapper gas temperature is less than 200 ℃
C adsorption rate; Cold HC reduction rate-In the cold start evaluation, HC that was adsorbed on the HC adsorbent and desorbed as the temperature of the exhaust gas rose, was not purified by the catalyst and was discharged without purification. (HC adsorption rate calculated including HC that is generated) In Example 1, the durability of the HC adsorbent is improved as compared with Comparative Example 1. This is largely due to the fact that by using the reverse flow regeneration method, regeneration can be performed with a gas containing no HC purified by a catalyst. Also, as shown in FIG.
When HC is adsorbed, a large amount of HC is adsorbed at the inlet of the HC adsorbent of the adsorbent with a catalyst. Therefore, in the forward flow regeneration method, a large amount of HC is desorbed near the inlet, and in order for this desorbed HC to be discharged from the HC trapper, it must pass over the HC adsorbent for a long distance. The probability of a reaction occurring is high. However, in the reverse flow regeneration method, since a large amount of HC is desorbed near the outlet of the HC trapper, the regeneration is efficient and the probability of re-adsorption and coking reaction is low.

[Effect of device]

The exhaust gas purifying apparatus of the present invention has the above-mentioned configuration, and the switching valve switches the exhaust gas passage in accordance with the temperature of the exhaust gas to optimize the flow condition for the HC trapper and the catalytic converter under each temperature condition. Since the exhaust gas can be circulated through, it is possible to prevent the regeneration of the HC adsorbent and the deterioration of the HC adsorbing ability due to coking. or,
Since it can be easily regenerated, it can be regenerated at a lower temperature, and thermal deterioration of the HC adsorbent can be suppressed. Further, by using the bypass system and the reverse flow regeneration method, the exhaust gas does not always flow to the HC adsorbent, and the HC adsorbent may become a downstream portion in the HC trapper. Therefore, deterioration of the HC adsorbent due to poisoning caused by oil ash (P, S, Zn, Ca, etc.) can be suppressed (poisoning is easily received on the upstream side of the engine exhaust system). Zeolites (HC adsorbents), which have a high HC adsorption capacity but low heat resistance, can also be used as HC adsorbents because hot exhaust gas does not flow to the HC adsorbent due to high temperature bypass. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of an exhaust gas purifying device of the present invention, FIG. 2 is an explanatory diagram of an adsorbent with a catalyst used in the device of the present invention, and FIG. 3 is a switching valve in the device of the present invention. FIG. 4 is a schematic configuration diagram of an example of a conventional exhaust gas purifying device, and FIG. 5 is an explanatory diagram of a hydrocarbon adsorption state on a catalyst-containing adsorbent used in the device of the present invention. . In the figure, 1 ... Engine, 2 ... HC trapper, 3 ... Adsorbent with catalyst, 4 ... Catalytic converter, 5 ... Three-way catalyst, 6, 7 ... Switching valve, 8 ... Temperature measuring device, 9 ... Piping, 10 ... HC adsorbent, 11 … Three-way (oxidation) catalyst 12… Spring, 13… Holder

Claims (1)

[Scope of utility model registration request] 1. An exhaust system, a temperature measuring means, first and second switching valves whose operation is controlled based on the measured temperature, a hydrocarbon adsorbent and an adsorbent with a catalyst comprising a three-way or oxidation catalyst. And a catalytic converter having a three-way catalyst are arranged. The first switching valve and the second switching valve have a first passage and a hydrocarbon trapper arranged in an intermediate portion. The first switching valve is connected in parallel with the second passage, and the first switching valve is connected to the hydrocarbon trapper of the second passage and the intermediate portion of the second switching valve by the third passage. An exhaust gas purification device, characterized in that a catalytic converter is connected to the downstream side of the switching valve.