JPH07323215A - Exhaust gas purifying device - Google Patents

Abstract

PURPOSE:To adsorb aliphatic hydrocarbons in an exhaust gas even in the presence of steam by providing a reforming material for reforming the aliphatic hydrocarbon into an aromatic hydrocarbon. CONSTITUTION:The reforming catalyst (reforming material) 3, a ternary catalyst 4 and an adsorbing catalyst (adsorbing material) 5 are arranged in this order from the upstream side in an exhaust gas passage 2 of automobile engine 1. The reforming catalyst 3 is obtained by wash-coating a monolith carrier with a gallium silicate having MFI type structure as the adsorbing material. The ternary catalyst 4 is obtained by wash-coating the monolith carrier with a catalyst powder having Pt, Pd, Rh, ceria or the like carried on gamma-alumina. The adsorbing catalyst 5 is obtained by wash-coating the monolith carrier with a Y-type zeolite having FAU type structure and carrying Pd by impregnation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying device.

[0002]

2. Description of the Related Art It is generally known to provide a three-way catalyst in an exhaust passage of an engine of an automobile for purifying exhaust gas of the engine. However, the function of the three-way catalyst is exhibited only when the exhaust gas temperature reaches or exceeds a predetermined temperature. However, the exhaust gas temperature is low immediately after the engine is started, and HC (hydrocarbon) in the exhaust gas is reduced. Is not decomposed by the catalyst.

On the other hand, a technique is known in which Y-type zeolite is disposed as an HC adsorbent in the exhaust passage upstream of the three-way catalyst (Japanese Patent Laid-Open No. 2-7).
(See Japanese Patent No. 5327). When the exhaust gas temperature is low, the adsorbent adsorbs HC in the exhaust gas, and when the exhaust gas temperature rises, the adsorbent absorbs HC.
Is to be released and decomposed by the three-way catalyst. In addition, Y-type zeolite is used as an HC adsorbent because it has higher C ₃ H ₆ adsorption capacity and higher heat resistance than X-type zeolite.

[0004]

However, although the above Y-type zeolite is certainly suitable as an HC adsorbent from the viewpoint of heat resistance, according to the study of the present inventors, it has a low carbon number of C _{2 to} C _4. The ability to adsorb aliphatic hydrocarbons was not very high, and the ability to adsorb such hydrocarbons was rather inferior to metal-containing silicates having an MFI type structure such as ZSM5. Further, the HC adsorbent has a general problem that the HC adsorbing ability decreases when the amount of water vapor in the exhaust gas is large. Therefore, the above Y-type zeolite is
It was found that even when used as an adsorbent, the desired HC purification cannot be expected when the exhaust gas contains water vapor.

[0005]

Means for Solving the Problem and Its Action The present inventor has conducted detailed experiments on the above-mentioned problems regarding the HC adsorbing ability of various metal-containing silicate crystals having microscopic pores such as the above Y-type zeolite. As a result of research, the Y-type zeolite has a low adsorption capacity for the low carbon number aliphatic hydrocarbons. The Y-type zeolite has a FAU-type structure and its pore size is larger than that of the MFI-type. Due to this, the metal-containing silicate having the FAU type structure adsorbs relatively large molecule hydrocarbons well, and the aliphatic hydrocarbons in the exhaust gas can be reformed to aromatic hydrocarbons. For example, they have found the fact that a relatively large amount of hydrocarbons are adsorbed even in the presence of water vapor, and have completed the present invention.

[0006] Hereinafter, a claim 1 for solving the above problems.
Each invention of 6 to 6 will be specifically described.

<Invention of Claim 1> The present invention is an exhaust gas purifying apparatus for purifying exhaust gas containing aliphatic hydrocarbons, wherein the aliphatic hydrocarbons in the exhaust gas are converted into aromatic hydrocarbons. It is characterized in that it comprises a reforming material for reforming and an adsorbent for adsorbing hydrocarbons in contact with the reforming material.

In the present invention, even if the exhaust gas contains an aliphatic hydrocarbon having a low carbon number, it is reformed into an aromatic hydrocarbon by the reforming agent. The variation is reduced, which is advantageous for the adsorption of hydrocarbons by the adsorbent.

The modifying material and the adsorbent can be separately arranged on the upstream side and the downstream side in the exhaust passage.
It is also possible to mix them with one another and place them in one place.

The type of the modifier is not particularly limited, but gallium silicate described later is suitable, and other aromatization catalysts can be used.
The adsorbent may be of any type as long as it has a property of adsorbing hydrocarbons. However, since the above-mentioned reforming material reforms an aliphatic hydrocarbon into an aromatic hydrocarbon, it is possible to use the adsorbent like the above-mentioned Y-type zeolite. Those having excellent adsorption ability for various aromatic hydrocarbons are preferable.

<Invention of Claim 2> The present invention provides the exhaust gas purifying apparatus as set forth in claim 1 above.
It is characterized in that the modifying material and the adsorbent are separately arranged on an upstream side and a downstream side in an exhaust passage through which the exhaust gas flows.

In the case of the present invention, the exhaust gas passes through the adsorbent after the hydrocarbon is aromatized by the reformer.

<Invention of Claim 3> The present invention is an exhaust gas purification apparatus for purifying exhaust gas of an automobile engine, wherein an aliphatic hydrocarbon contained in the exhaust gas is aromatic in an exhaust passage of the engine. A reforming agent for reforming to hydrocarbons is provided, and the adsorbing ability to adsorb aromatic hydrocarbons is more downstream than the adsorbing ability to adsorb aliphatic hydrocarbons. It is characterized in that a high adsorbent is provided.

The exhaust gas of the engine contains hydrocarbons, nitrogen oxides, carbon monoxide, etc., and the hydrocarbons contain C _2-
A relatively large amount of C ₄ low carbon number aliphatic hydrocarbons is also contained, but in the present invention, such an aliphatic hydrocarbon is to be passed through an adsorbent after being reformed to an aromatic hydrocarbon. become. Since the adsorbent has a high ability to adsorb aromatic hydrocarbons, it is possible to reliably adsorb the hydrocarbons that have been reformed into aromatic hydrocarbons by the reformer.

As an adsorbent having a higher adsorption capacity for adsorbing aromatic hydrocarbons than that for adsorbing aliphatic hydrocarbons, a FAU type structure having a relatively large pore size, such as Y-type zeolite described above, is used. The metal-containing silicates it has are suitable.

<Invention of Claim 4> This invention is the exhaust gas purifying apparatus as set forth in claim 1, claim 2 or claim 3, in which the modifier has a part of a crystal lattice. It is gallium silicate composed of Ga, and the adsorbent is a Y-type zeolite.

In the present invention, since the reforming material is gallium silicate, the aliphatic hydrocarbon is well modified into an aromatic hydrocarbon, and since the adsorbing material is Y-type zeolite, the aromatic hydrocarbon is well adsorbed. . Here, the above-mentioned modification by the gallium silicate is carried out because the gallium silicate has an adsorbing ability for an aliphatic hydrocarbon, and Ga constituting a part of the crystal lattice functions as an aromatization catalyst. It is believed that this is due to increasing Therefore, the gallium silicate is preferably of MFI type in order to enhance the adsorptivity of aliphatic hydrocarbons having a low carbon number.

<Invention of Claim 5> This invention is the exhaust gas purifying apparatus as described in claim 2 or claim 3, in which a three-way catalyst is arranged between the reforming material and the adsorbing material. The modifying material is gallium silicate whose crystal lattice is partially composed of Ga, and the adsorbing material is Y-type zeolite.

In the present invention, the three-way catalyst is not placed downstream of the adsorbent but is placed between the reforming material and the adsorbent because the exhaust gas is discharged from the three-way catalyst. This is to ensure that the hydrocarbon is always supplied and that the catalytic function is immediately exerted when the activation temperature of the three-way catalyst is reached.

That is, the temperature at which the three-way catalyst is activated does not always match the temperature at which the adsorbent releases hydrocarbons. Therefore, if a three-way catalyst is arranged downstream of the adsorbent, even if the three-way catalyst reaches the activation temperature, if the release of hydrocarbons from the adsorbent is delayed, the hydrocarbon is not supplied. The catalyst function cannot be exerted. Conversely, when the three-way catalyst reaches the activation temperature after the start of the release of hydrocarbons from the adsorbent, the three-way catalyst does not work and the hydrocarbons are discharged as it is. In order to prevent such a situation, the above-mentioned arrangement configuration is adopted in the present invention.

<Invention of Claim 6> The present invention is the exhaust gas purifying apparatus according to any one of Claims 1 to 5, wherein the adsorbent promotes a decomposition reaction of hydrocarbons. It is characterized in that a noble metal active species is supported.

In the case of the present invention, even if the temperature at which the adsorbent releases the adsorbed hydrocarbons is reached, the hydrocarbons are decomposed by the noble metal active species carried on the adsorbent, so that the hydrocarbons are It is prevented from being discharged without being decomposed. In this case, the noble metal active species is Pd,
Pt or the like is preferable.

[0023]

According to the first aspect of the present invention, it is provided with the reforming material for reforming the aliphatic hydrocarbon to the aromatic hydrocarbon and the adsorbent for adsorbing the hydrocarbon in contact with the reforming material. Therefore, even if the exhaust gas contains an aliphatic hydrocarbon having a low carbon number, it is possible to reduce the variation in the size of the hydrocarbon molecule by the above reforming, and the adsorbent has, for example, different pore sizes. It is possible to prevent the emission of hydrocarbons by obtaining a relatively high hydrocarbon adsorption rate without using a combination of many types, even with a single adsorbent and in the presence of water vapor.

According to the second aspect of the present invention, since the reforming material and the adsorbent are separately arranged on the upstream side and the downstream side in the exhaust passage through which the exhaust gas flows, The aliphatic hydrocarbon can be reformed into an aromatic hydrocarbon by the reforming agent and then brought into contact with the adsorbent, which is advantageous for adsorption of the hydrocarbon by the adsorbent.

According to the third aspect of the present invention, the reforming material is arranged in the exhaust passage of the engine of the automobile, and the hydrocarbon adsorbing material is arranged downstream of the reforming material. Therefore, it is possible to prevent a large amount of hydrocarbons in the exhaust gas of the engine from being discharged. Particularly, since the adsorbent has a high adsorbing ability for aromatic hydrocarbons, It is advantageous for emission prevention.

According to the invention of claim 4, the modifying material is gallium silicate whose crystal lattice is partially composed of Ga, and the adsorbing material is Y-type zeolite. It is possible to efficiently reform the above-mentioned aliphatic hydrocarbons to aromatic hydrocarbons and surely adsorb them to the adsorbent, and to carry out each of the inventions of the above-mentioned claims 1 to 3 to obtain the desired effect. It will be advantageous in above.

According to the fifth aspect of the invention, the three-way catalyst is arranged between the reforming material and the adsorbent, and the reforming material has a part of the crystal lattice made of Ga. Since it is gallium silicate and the adsorbent is Y-type zeolite, the exhaust gas can be purified by using the three-way catalyst without waste while preventing the release of hydrocarbons in the exhaust gas.

According to the sixth aspect of the present invention, since the adsorbent carries the noble metal active species that accelerates the decomposition reaction of hydrocarbons, the hydrocarbons after the adsorbent reaches the hydrocarbon release temperature. Can be prevented from being discharged as it is.

[0029]

EXAMPLES Examples of the present invention will be described below.

—Structure of Exhaust Gas Purification Device— FIG. 1 shows the arrangement structure of each element of the exhaust gas purification device. In the figure, 1 is an automobile engine, 2 is the engine 1
In this exhaust passage 2, a reforming catalyst (reforming material) 3, a three-way catalyst 4 and an adsorption catalyst (adsorbing material) 5 are arranged in this order from the upstream side. The reforming catalyst 3 is a monolithic carrier (made of cordierite) with wash coat of gallium silicate having an MFI structure as an adsorbent, and the three-way catalyst 4 is γ-alumina containing Pt, Pd, Rh, ceria, etc. Is a catalyst obtained by wash-coating a monolith carrier with a catalyst powder supporting P, and the adsorption catalyst 5 is obtained by wash-coating the Y-type zeolite having a FAU type structure on the monolith carrier and further supporting Pd by impregnation. is there.

-Preparation of modifier (gallium silicate) -NaCl (26.3 g), tetrapropylammonium bromide (7.5 g), deionized water (208 ml), Na
A solution consisting of OH (2.4 g) and sulfuric acid (2.85 g) was vigorously stirred while being ice-cooled, and gallium sulfate (predetermined amount), deionized water (60 ml) and sulfuric acid (6.
Liquid B consisting of 2 g) and liquid C consisting of water glass No. 3 (predetermined amount) and ion-exchanged water (45 ml) were added dropwise over 6 minutes. At that time, the pH of the mixed solution is 9 to 11
NaOH aqueous solution or sulfuric acid aqueous solution was added appropriately so that After the dropping was completed, stirring was continued for about 2 minutes.

The hydrated gel obtained as described above was placed in an autoclave and replaced with nitrogen (nitrogen partial pressure: 4 k
gf / cm ² ), while stirring the gel, the temperature inside the furnace is 16
The hydrothermal synthesis of the gel was carried out by raising the temperature to 0 ° C. in 160 minutes and then to 200 ° C. in 800 minutes. Thereafter, the product is naturally cooled to room temperature, the product is taken out and washed with pure water, and the temperature is 540 to 600 ° C.
A Na-type gallium silicate was obtained by firing for 3 hours.

Next, the Na-type gallium silicate 14 is used.
11.4 g of ammonium nitrate and 700 ml of water were added to g, and the mixture was stirred at 50 ° C. for 8 hours to give Na.
^After ion exchange of ⁺ → H ⁺ , cooling to room temperature, filtration and washing, and baking at 600 ° C for 3 hours to obtain H-type (proton-type) gallium silicate as a modifier. (Cayban ratio 30) was obtained.

-Reforming function of the above H-type gallium silicate- Simulated exhaust gas of the following composition was flowed through the above H-type gallium silicate at various temperatures at SV = 60,000 h ^-1 , and C ₃ H
The conversion of ₆ to benzene was investigated. The results are shown in Figure 2.

(Composition of simulated exhaust gas) NOx: 0.5%, CO: 0.6%, C ₃ H ₆ ; 0.0
55% C, CO ₂ ; 3.0%, O ₂ ; 0.6%, balance N
₂

According to FIG. 2, the gallium silicate has a function as an aromatization catalyst for reforming an aliphatic hydrocarbon into an aromatic hydrocarbon, and the function is exhibited at a relatively low temperature of 200 ° C. It is also understood that the reforming function is relatively high. The reason why gallium silicate is H type is advantageous in terms of heat resistance and reforming performance.

-Hydrocarbon adsorbing ability of adsorbent (Y-type zeolite) -Y-type zeolite with a Cayban ratio of 6 and ZS with a Cayban ratio of 30
M5 was prepared, and the amount of benzene adsorbed on the Y-type zeolite and the amount of C ₃ H ₆ adsorbed on ZSM5 in the presence of water vapor were examined. The results are shown in Figure 3.

According to the figure, the amount of benzene adsorbed on the Y-type zeolite is larger than the amount of C ₃ H ₆ adsorbed on ZSM5. Considering that the Y-type zeolite does not adsorb C ₃ H ₆ and that ZSM5 does not adsorb benzene, the results shown in FIG. 3 indicate that Z does not reform the aliphatic hydrocarbons in the exhaust gas.
It can be seen that reforming this into aromatic hydrocarbon and adsorbing it onto the Y-type zeolite is much more advantageous in preventing hydrocarbon emission than adsorbing onto SM5.

-Exhaust Gas Purification Test-In the configuration of FIG. 1 described above, the Y1 mode (0 to 6)
The HC purification rate in the exhaust gas of the engine 1 up to 0 seconds was 74.3%.

On the other hand, as shown in FIG. 4, the reforming catalyst is not provided and only the three-way catalyst 4 and the adsorption catalyst 6 are used. The adsorption catalyst 6 is a monolith obtained by mixing Y-type zeolite and ZSM5. When the HC purification rate was measured under the same conditions for the apparatus of Comparative Example 1 of the mixed type (with Pd loaded) supported on the carrier (others have the same configuration as that of FIG. 1), 63.
It was 4%. From this, it is understood that the combination of gallium silicate as the modifier shown in FIG. 1 and Y-type zeolite as the adsorbent has a remarkable effect on the improvement of the HC purification rate.

Further, as shown in FIG. 5, the adsorption catalyst 7 is ZS.
The HC purification rate of the apparatus of Example 2 in which M5 was carried on a monolith carrier (other structure is the same as that of FIG. 1) was measured under the same conditions, and it was 53.1%. From this, it can be seen that Y-type zeolite is suitable for adsorbent betting. In addition, in the configuration of FIG. 5, when the same purification test was performed by omitting the reforming catalyst 3, H
The C purification rate was 51.0%.

Further, as shown in FIG. 6, the same applies to the device of Comparative Example 2 in which the adsorption catalyst is not provided and only the reforming catalyst 3 and the three-way catalyst 4 (other configurations are the same as those in FIG. 1). When the HC purification rate was measured under the above condition, it was 43.6%. From this, it is understood that the three-way catalyst 4 does not work as an adsorption catalyst, and the adsorption catalyst 5 using the above Y-type zeolite is required.

As shown in FIG. 7, in the device of Comparative Example 3 using only the three-way catalyst 4, the HC purification rate was 40.1%. Therefore, from the comparison of the HC purification rates in the respective devices of FIG. 6 and FIG. 7, it can be seen that gallium silicate itself has almost no HC adsorbing ability and a combination with an adsorbent is required.

<Others 1> In the following, the invention of a suitable steam removing method and apparatus for increasing the HC purification rate in the presence of water vapor and for increasing the HC purification rate in combination with the previous embodiment Will be explained.

-Conventional Problems-Exhaust gas from an engine usually contains about 10% of water vapor, and this water vapor adversely affects the performance and durability of the exhaust gas purifying catalyst. . For example, Y
In the case of an exhaust gas that does not substantially contain water vapor, the HC adsorbent that uses type zeolite or the like has an adsorbing ability that decreases as the amount of water vapor increases even if the desired HC adsorbing performance is obtained. On the other hand, HC in the exhaust passage of the engine
Although there is a concept of arranging activated carbon on the upstream side of the adsorbent to remove water in the exhaust gas, it cannot withstand long-term use and requires separate regeneration treatment or replacement.

-Structure and Effect of the Invention- The first means for solving the above problems is to supply a hydrocarbon or alcohol into the exhaust gas, and the hydrocarbon or alcohol and the steam in the exhaust gas are steam reforming catalysts. A method for removing water vapor from exhaust gas, which comprises producing carbon dioxide or carbon monoxide and hydrogen by reacting in the presence of

According to this first means, the water vapor in the exhaust gas is removed by the above reaction, and it becomes possible to obtain the exhaust gas with a low water content.

As the above-mentioned hydrocarbon or alcohol, methanol, ethanol, gasoline, light oil, methanol.
Liquid fuels such as gasoline mixed fuel (M85) and gaseous fuels such as natural gas are suitable. As the steam reforming catalyst, Pt, a metal catalyst formed by mixing Cu and Zn
Alternatively, a noble metal / alumina catalyst prepared by supporting a noble metal such as Pd on alumina, or a hydrocarbon steam reforming catalyst may be used. These are used by supporting them on a heat resistant carrier, for example, a cordierite monolith carrier. can do.

A second means for solving the above problem is characterized in that methanol is used as the alcohol in the first means.

In the case of the second means, methanol is easier to handle than hydrocarbons such as methane or naphtha, and the conversion reaction is easy to proceed, so that it is suitable for carrying out the first means. .

A third means for solving the above-mentioned problem is an apparatus for removing water vapor in exhaust gas for carrying out the method of the above-mentioned first means, which is connected to an exhaust passage of an engine and is provided in the exhaust passage. A supply means for supplying a hydrocarbon or alcohol, and the exhaust passage is provided on the downstream side of the connection means for the supply means, and reacts the hydrocarbon or alcohol with water vapor in the exhaust gas to form carbon dioxide or carbon monoxide. And a steam reforming catalyst for generating hydrogen.

A fourth means for solving the above-mentioned problem is the above-mentioned third means, wherein the supply means supplies a tank for storing hydrocarbon or alcohol and a supply device for supplying the hydrocarbon or alcohol in the tank to the exhaust passage. (Pump) and supply amount control means for controlling the operation of the supply device, and the supply amount control means detects the operating state of the engine (engine speed sensor, engine water temperature sensor, engine load sensor). Etc.) and means for detecting the properties of the exhaust gas (air-fuel ratio sensor, exhaust gas temperature sensor, etc.)
And an operation signal to the supply device so as to supply the hydrocarbons or alcohol corresponding to converting the amount of water vapor in the exhaust gas based on the outputs of the both detection means to the exhaust passage. And a computer unit for outputting.

According to the fourth means, hydrocarbons or alcohol can be supplied in an appropriate amount according to the amount of water vapor in the exhaust gas, so that the property of the exhaust gas released into the atmosphere is deteriorated. Without this, it becomes possible to efficiently remove the water vapor in the exhaust gas.

A fifth means for solving the above problem is, in the third means or the fourth means, an HC adsorption for adsorbing hydrocarbons in exhaust gas in an exhaust passage downstream of the steam reforming catalyst. The material is arranged.

According to the fifth means, the exhaust gas from which water vapor has been removed can be sent to the HC adsorbent, and the hydrocarbon adsorbing efficiency of the HC adsorbent can be increased.

A sixth means for solving the above-mentioned problem is the exhaust means, which is arranged in the exhaust passage downstream of the HC adsorbent in the fifth means, for causing a purification reaction of harmful components in the exhaust gas. A gas purifying catalyst, a bypass passage for flowing exhaust gas to the exhaust gas purifying catalyst by bypassing the HC adsorbent from the downstream of the steam reforming catalyst, and provided in the bypass passage for opening and closing the bypass passage. An on-off valve,
The on-off valve is set to the engine temperature (exhaust gas temperature may be used).
And an opening / closing valve control means that operates so that the bypass passage is closed when the engine temperature is below a predetermined value and the bypass passage is opened when the engine temperature exceeds a predetermined value. Is characterized by.

According to the sixth means, the hydrocarbons in the exhaust gas are adsorbed to the HC adsorbent to prevent the exhaust thereof when the engine is cold (when the exhaust gas purifying catalyst does not reach the activation temperature). However, after the engine is warmed up, the exhaust gas can be purified and discharged using the exhaust gas purifying catalyst.

The seventh means for solving the above problem is to fill one side with exhaust gas and the other side with alcohol, which is separated by a porous wall that allows water molecules to pass and alcohol molecules to pass. The method for removing water vapor from exhaust gas is characterized by:

According to this method, the water vapor in the exhaust gas diffuses through the pores of the porous wall, moves to the alcohol side and is captured by the alcohol, and as a result, the water vapor in the exhaust gas decreases. Will be done.

An eighth means for solving the above problem is a device for removing water vapor in exhaust gas for carrying out the method according to the seventh means, which is a porous material which allows water molecules to pass but alcohol molecules not to pass. A double passage having an exhaust passage portion through which the exhaust gas flows and the alcohol passage portion through which alcohol flows, is formed on one side of the quality wall, and liquid alcohol is introduced into the alcohol passage portion from one end thereof. And an alcohol supply means for causing the alcohol to flow out from the other end of the alcohol passage portion.

According to this means, when the exhaust gas is caused to flow from the one end to the exhaust passage portion, the water vapor in the exhaust gas diffuses through the porous wall and moves to the alcohol passage portion, and the alcohol in the alcohol passage portion is discharged. The exhaust gas, which has been captured by the exhaust gas and has a reduced amount of water vapor, can be discharged from the other end of the exhaust passage portion.

Here, the double passage is formed by forming a double pipe structure composed of an inner pipe formed of the porous material and an outer pipe formed of a material that does not allow water molecules to pass therethrough. You can In this case, the inside of the inner pipe can be the alcohol passage part and the outside thereof can be the exhaust passage part, and conversely, the inside of the inner pipe can be the exhaust passage part and the outside can be the alcohol passage part. Further, the alcohol passage portion and the exhaust passage portion may be provided adjacent to and parallel to each other, and the boundary between the both passage portions may be formed by the porous wall.

A ninth means for solving the above-mentioned problem is the above-mentioned eighth means, wherein the alcohol supply means reacts the liquid mixture of liquid alcohol and water flowing out from the downstream end of the alcohol passage portion to generate carbon dioxide. And a hydrogen reforming catalyst reaction tank, a cooler for liquefying the gaseous alcohol in the product obtained by the reforming catalyst reaction tank to remove the residual carbon dioxide and hydrogen, and the cooler A pump for supplying anhydrous alcohol to the obtained liquid alcohol and supplying it to the alcohol passage portion from its upstream end is provided.

According to this means, the alcohol for removing the water vapor in the exhaust gas can be recycled and reused, and the alcohol can be supplied to the alcohol passage portion in a substantially anhydrous state. Therefore, the removal efficiency of water vapor in the exhaust gas is increased.

A tenth means for solving the above-mentioned problems is the above-mentioned eighth means or ninth means, wherein the porous material is formed of a porous metal-containing silicate crystal having a pore diameter of 2 to 4 angstroms. It is characterized by being formed by a first wall forming a wall surface of the alcohol passage portion and a second wall formed by porous alumina having a pore diameter larger than that of the first wall and forming a wall surface of the exhaust passage portion. And

According to this means, it is possible to prevent the movement of alcohol from the alcohol passage portion to the exhaust passage portion while allowing the diffusion of water vapor from the exhaust passage portion to the alcohol passage portion.

Here, as the first wall, Thomsonite (pore size 2.3 to 3.9, 2.2 to 4.0, the above values are Angstroms) and natrolite (pore size 2.6 to 3) are used. 1.9 Angstrom) is preferable.
The molecular size of water is 1.54, the molecular size of methanol is 3.00, and the molecular size of methane is 1.78 (the above values are Angstroms).

-Specific Example 1- Specific examples of the first to sixth means will be described below.

FIG. 8 shows a preferred structure of a device for removing water vapor from exhaust gas. In the figure, reference numeral 11 is an automobile engine, and 12 is an exhaust passage of the engine. In the exhaust passage 12, the steam reforming catalyst 13 and the HC adsorbent 14 are provided.
The exhaust gas purifying catalyst 15 is sequentially arranged from the upstream side, and the bypass passage 16 that bypasses the HC adsorbent 14 and connects the steam reforming catalyst 13 and the exhaust gas purifying catalyst 15 is provided. An opening / closing valve 17 for opening and closing the bypass passage 16 is provided in the bypass passage 16. Further, the steam reforming catalyst 13 in the exhaust passage 12
Fuel tank 1 storing methanol in the upstream
The fuel supply passage 20 extended from 9 is connected,
A fuel supply device (pump) 21 is provided in the fuel supply passage 20.
Is provided.

Further, in the same drawing, 22 is the opening / closing valve 1
7 and the fuel supply device 21 for controlling the operation, and performs the control based on the engine speed, the engine water temperature, the exhaust gas air-fuel ratio, and the exhaust gas temperature. The illustration of these sensors is omitted. In this case, based on the engine water temperature, the computer unit 22 closes the bypass passage 16 when the temperature of the engine is colder than a predetermined value and opens the bypass passage 16 when the temperature exceeds the predetermined value. On-off valve 17
An operation signal is output to the engine, and the amount of water vapor in the exhaust gas is calculated based on the engine speed, the engine water temperature, the air-fuel ratio, and the exhaust gas temperature, and the amount of methanol equivalent to converting the amount of water vapor is exhausted from the exhaust gas. An operation signal is output to the fuel supply device 21 so as to supply to the passage 12.

The steam reforming catalyst 13 is formed by supporting Cu--Zn on a cordierite monolith carrier. The HC adsorbent 14 is a mixture of Y-type zeolite and ZSM5 supported on the same monolith carrier, and the exhaust gas purifying catalyst 15 is a three-way catalyst supported on the same monolith carrier.

The steam reforming reaction by the steam reforming catalyst 13 is as follows, and the steam in the exhaust gas is removed by this reaction. MeOH + H ₂ O → 3H ₂ + CO ₂ ... MeOH is an abbreviation for CH ₃ OH.

FIG. 9 shows the steam reforming catalyst (Cu, Zn).
2 shows the relationship between the reaction temperature and the catalyst outlet gas (product) composition when the above reaction is caused in a fixed flow type reaction apparatus using. According to the figure, the water vapor (H ₂ O) removal effect is obtained even at a relatively low temperature of about 300 ° C., and the water vapor removal effect becomes higher as the temperature rises, and when the exhaust gas temperature reaches about 400 ° C. It can be seen that the water vapor in the gas is almost gone.

The model gas in this case is 10% H ₂ O,
SV = 10000h ^-1 with 10% MeOH and balance N _2.
And This point is the same for each data in FIGS. 10 to 12 described below.

FIG. 10 shows an example in which Pt / Al ₂ O ₃ obtained by supporting Pt on γ-alumina is used as a steam reforming catalyst, and FIG. 11 shows Pd / where Pd is supported on γ-alumina. This is an example when Al ₂ O ₃ is used as the steam reforming catalyst. Even in these cases, the water vapor removing effect is recognized as in the case of the Cu and Zn based catalysts, but the effect is lower than that of FIG. On the other hand, when Pt / MgO obtained by supporting Pt on MgO is used as the steam reforming catalyst, the steam removing effect is recognized as shown in FIG. 12, but the effect is considerably low. . From the above, it can be said that the use of the Cu, Zn-based catalyst is preferable because it has a high effect of removing water vapor and does not generate methane.

Next, the SV dependency of the Cu, Zn based catalyst was tested, and the following results were obtained.
That is, a Cu, Zn-based catalyst was molded into pellets, the catalyst volume was set to 2 liters, and S was added in a fixed flow reactor.
V value of 6000h ^-1 , 10000h ^-1 , 15000h ^-1
The conversion rate of methanol was examined by changing the above three types. Results are shown in FIG. From the figure, SV = 10000h
^It can be seen that ^-1 or less, more preferably 6000 h ^-1 is suitable. The reactor outlet gas (product) composition at SV = 6000 h ⁻¹ is shown in FIG. From the figure, SV = 6
It can be seen that good results are obtained at 000 h ^-1 .

Next, the above steam reforming catalyst (Cu, Zn) is actually introduced into the exhaust passage of the engine of the automobile from the engine 1 to
The amount of H ₂ O in the exhaust gas during steady operation at λ = 1, which was installed 1.5 m away (catalyst capacity was 2 liters), showed that the amount of H ₂ O without the catalyst Was 10% by volume, but it had dropped to 3% by volume.

Further, when the HC purification rate in the Y1 mode was examined, it was 65% in the case where the catalyst was not provided, but it became 70%.

-Specific Example 2- Next, specific examples of the seventh to tenth means will be described.

FIG. 15 shows a preferred structure of a device for removing water vapor from exhaust gas. In the figure, reference numeral 31 denotes a metal exhaust pipe of an automobile engine, and a porous pipe 32 is inserted in the middle thereof, and an inner alcohol passage portion 33 and an outer exhaust passage portion 34 are separated by the porous pipe 32. A double passage 35 is formed. A circulation passage 36 connects the upstream end and the downstream end of the alcohol passage portion 33, and the reforming catalyst reaction tank 37, the cooler 38, the alcohol supply port 39, and the alcohol supply pump are connected to the circulation passage 36. 40 are sequentially arranged from the downstream end side to the upstream end side.

The reforming catalyst reaction tank 37 uses a cordierite monolith carrier as a reforming catalyst for reacting a mixed liquid of liquid alcohol and water flowing out from the downstream end of the alcohol passage portion 33 to generate carbon dioxide and hydrogen. It is carried on the. A heating device 41 for controlling the reaction temperature around 400 ° C. is provided outside the reforming catalyst reaction tank 37. The reforming catalyst is Cu, Zn
System steam reforming catalyst.

The cooler 38 corresponds to the reforming catalyst reaction tank 3
The gaseous alcohol in the product obtained by No. 7 is liquefied, and the remaining reformed gas (carbon monoxide,
It removes carbon dioxide and hydrogen) and is provided with a reformed gas outlet 38a. The reformed gas outlet 38a is connected to the intake system of the engine and supplies the reformed gas to the combustion chamber of the engine.

The alcohol replenishment port 39 is connected to a tank (not shown) that stores anhydrous alcohol so that the anhydrous alcohol is supplied to the circulation passage 36. The amount of this anhydrous alcohol supplied is equal to the amount of alcohol consumed by the reforming catalytic reaction. The pump 40 supplies the liquid alcohol obtained by the cooler 38 and the supplemented anhydrous alcohol to the alcohol passage portion 33. In this case, reforming catalyst; Cu, Zn system, SV = 60000h ^-1 , H ₂ O; 1
Under conditions of 0%, vaporization temperature; 150 ° C., methanol may be supplied by the pump 40 at 120 ml / min or more.

As shown in FIG. 16, the porous tube 32 has a three-layer structure including an inner porous wall 32a, an intermediate porous wall 32b and an outer porous wall 32c. The inner porous wall 32a is made of Thomsonite. The intermediate porous wall 32b and the outer porous wall 32c are made of porous alumina, and both of them are the inner porous wall 3
The pore diameter is larger than 2a, and the outer porous wall 32c is larger than the intermediate porous wall 32b.

Therefore, in the above-described specific example, the exhaust gas containing water vapor flows through the exhaust pipe 31 and the exhaust passage portion 34.
16, the water molecules in the exhaust gas sequentially diffuse and move through the outer porous wall 32c, the intermediate porous wall 32b, and the inner porous wall 32a to enter the alcohol passage portion 33 while the exhaust gas is exhausted. The relatively large molecules in the gas cannot be diffused because they are blocked by the outer porous wall 32c of the porous tube 32. Therefore, the exhaust gas becomes a dry exhaust gas with less water content and is exhausted.

The water molecules that have entered the alcohol passage portion 33 from the exhaust passage portion 34 are sent to the reforming catalyst reaction tank 37 together with methanol. Then, there, the reformed gas (carbon dioxide and hydrogen) is generated by causing the reaction of the above-described equation between the vaporized methanol and water vapor. It is considered that the reaction of (MeOH → 2H ₂ + CO) occurs partially.

Then, the methanol gas and the reformed gas not involved in the above reaction are sent to the cooler 38, and the methanol gas is liquefied and flows into the pump 40, while the unliquefied reformed gas is discharged to the engine. It is sent to the intake system and is supplied to the engine combustion chamber together with fuel. The liquefied methanol is supplied to the alcohol passage portion 33 again together with the supplemented anhydrous alcohol.

FIG. 17 shows the composition of the model gas at the inlet and the outlet of the exhaust passage portion 34 (the upper side shows the gas composition at the inlet, the lower side shows the gas composition at the outlet, and all numerical values are flow rates (mi / min))). According to the figure, the amount of water vapor has decreased from about 9% to about 1.4% of the total gas amount,
It can be seen that the water vapor has been removed.

Therefore, an adsorbent carrying 25 ml of Y-type zeolite is arranged on the downstream side of the apparatus shown in FIG. 15, and a model gas (similar composition to the one on the upper side of FIG. 17) is caused to flow therethrough.
When the C adsorption capacity was evaluated, the propylene adsorption amount of the adsorbent was 10 mg when the water vapor removal device was not provided.
It increased to 126 mg. Furthermore, when an adsorbent made of Y-type zeolite was installed in the exhaust passage of the engine in an actual automobile and the HC purification rate in the Y1 mode was examined, it was found that the water vapor removal device was not installed.
%, The HC purification rate was 74% in the case where the above water vapor removal device was provided. This is because the water vapor was removed and the adsorbability of the adsorbent was increased.

<Others 2> Next, a means for well adsorbing HC in exhaust gas and preventing its discharge even in the presence of water vapor will be described.

(Problem) As shown in FIG.
In the exhaust system 2 of the vehicle, the inside of the catalytic converter arranged at the underfloor position (under the vehicle body floor) of the automobile is divided into two parts, the three-way catalyst 4 in the front stage and the HC adsorption catalyst (HC
When a mixture of an adsorbent and another catalyst) 51 is housed, HC discharge can be prevented. However, the function of the HC adsorbent is greatly reduced when water vapor is present in the exhaust gas, so that the above system is also insufficient.

(Solution Means) In the present proposal, in order to solve the above problems, any one of the following means is provided.

I) An HC adsorbing and purifying system is constructed by using an element having an HC adsorbing ability (Fe, Co, Ni, Mn) added to the ion-exchange site or skeleton structure of zeolite as an HC adsorbent even in the presence of water vapor. To do.

Ii) The system is provided with means for removing water vapor so that the HC adsorbent layer is not adversely affected (for example, a hygroscopic agent and an HC adsorbent are mixed. Alternatively, a condensation trap is placed before the adsorbent layer. To provide).

(Regarding Solution i) Most commercially available zeolites have exchange ions of Na ⁺ or H ⁺ . Therefore, we prototyped MFI-type zeolite (ZSMS) in which various ions other than these were exchanged.
The C adsorption characteristics were evaluated.

[0096]

[Table 1]

As described above, in the cases 1 to 4, comparisons 1 and 2 are made.
On the other hand, it was found that the amount of HC adsorbed in the presence of water vapor was greatly improved. It is considered that this is because the exchanged ions themselves have a certain amount of HC adsorption ability in the presence of water vapor.

Subsequently, an attempt was made to add zeolite into the framework.

By dissolving a metal salt in a synthetic reaction solution before hydrothermally synthesizing MFI-type zeolite, MFI-type metallosilicate (metal-containing silicate) containing Fe, Co, Ni, and Mn in the skeleton structure is dissolved. (Agreement with) was synthesized respectively. By exchanging these with H ⁺ , an H ⁺ exchange metallosilicate was prepared. Then, similarly, the adsorption property of C ₃ H ₆ was evaluated.

[0100]

[Table 2]

As described above, according to the present proposals 5 to 8, it was confirmed that the amount of C ₃ H ₆ adsorbed was improved as compared with Comparative 2. This is because the metal added in the skeletal structure is
With adsorbs C ₃ H _6, for weakening the force for sucking of H ₂ O weaken the acid strength of the entire silicate, a force which inhibits the H ₂ O is considered due to a decrease.

From the above, two types of Fe ³⁺ -MFI zeolite and H ⁺ -Si / Al / Fe metallosilicate were picked up and evaluated in an actual vehicle. The actual vehicle system configuration is exactly the same as in FIG.

Experimental conditions V6 2500cc engine car F
TP mode Actual vehicle running evaluation ・ Catalyst converter configuration First stage: Pt-Rh-based three-way catalyst 900 ℃ × 50h Air-heat treated product
1.0 ■ Second stage: The adsorbent is H ⁺ −FAU (Cayban ratio 8)
0) Equal amount is mixed After adsorbent is coated on the honeycomb, CeO ₂ and Pd are supported CeO ₂ supported amount 50g / ■ Pd supported amount 8g / ■ Adsorbent supported amount 150g / ■ Honeycomb capacity 1.3
■

[Table 3]

As described above, according to the present invention, the HC purification rate in the actual vehicle can be improved.

Besides, as the zeolite structure, MOR, F
The same effect can be obtained by using ER.

(Regarding Solution Means ii) FIG.
Shown by 20. A condensation trap 52 is placed in front of the catalytic converter (three-way catalyst 4, HC adsorption catalyst 51) at the underfloor position, and a throttle valve 53 is provided at the rear of the converter. When the engine is started when it is cold, the throttle valve 53 is throttled for 100 seconds and then completely opened.

For 100 seconds after the start, the trap 52 is
Is sufficiently cold, the water vapor in the exhaust gas is condensed and trapped here. At this time, the throttle valve 53 is further throttled to increase the partial pressure of water vapor, so that the condensation is further promoted. Therefore, the exhaust gas containing less steam flows into the catalytic converters 4, 51. The HC partial pressure in the exhaust gas is also increasing. Therefore, the HC adsorption efficiency is improved due to the synergistic effect of the decrease of the water vapor concentration and the increase of the partial pressure of HC.

The results of evaluation by incorporating this system into an actual vehicle are shown.

Experimental conditions V6 2500cc engine car F
TP mode Actual vehicle running evaluation ・ Catalyst converter configuration First stage: Pt-Rh-based three-way catalyst 900 ℃ × 50h Air-heat treated product
1.0 ■ Second stage: The adsorbents are H ⁺ -MFI (Cayvan ratio 30) and H ⁺ -F
Equal weight mixture of AU (Cayban ratio 80) Loading amount 150g / ■ CeO ₂ and Pd loading CeO ₂ loading amount 50g / ■ Pd loading amount 8g / ■ Honeycomb capacity 1.3 ■ after coating the adsorbent on the honeycomb

[Table 4]

As described above, also in the case of the present invention, the HC purification rate is improved.

Besides, instead of the condensation trap, CaO,
Place a hygroscopic agent such as CaCl ₂ upstream of the converter,
Alternatively, a similar effect can be obtained by mixing a hygroscopic agent in the adsorbent layer.

[Brief description of drawings]

FIG. 1 is a diagram showing an arrangement configuration of respective elements of an exhaust gas purifying apparatus according to an embodiment.

FIG. 2 is a graph showing a benzene conversion rate of propylene by a steam reforming catalyst.

FIG. 3 is a graph showing the HC adsorption amount of ZSM5 and Y-type zeolite.

FIG. 4 is a diagram showing an arrangement configuration of each element of an exhaust gas purification apparatus of Comparative Example 1.

FIG. 5 is a diagram showing an arrangement configuration of each element of the exhaust gas purification apparatus of the second embodiment.

FIG. 6 is a diagram showing an arrangement configuration of each element of an exhaust gas purification device of Comparative Example 2.

FIG. 7 is a diagram showing an arrangement configuration of respective elements of an exhaust gas purification apparatus of Comparative Example 3.

FIG. 8 is a configuration diagram showing an example of a device for removing water vapor from exhaust gas.

FIG. 9 is a graph showing a relationship between a reforming reaction temperature and a gas composition by a Cu, Zn-based reforming catalyst.

FIG. 10 is a graph showing a relationship between a reforming reaction temperature and a gas composition by a Pt / Al ₂ O ₃ based reforming catalyst.

FIG. 11 is a graph showing a relationship between a reforming reaction temperature and a gas composition by a Pd / Al ₂ O ₃ based reforming catalyst.

FIG. 12 is a graph showing a relationship between a reforming reaction temperature and a gas composition by a Pt / MgO based reforming catalyst.

FIG. 13 is a graph showing the SV dependence of Cu and Zn based reforming catalysts.

FIG. 14 is a view similar to FIG. 9 with SV = 6000 h ⁻¹ .

FIG. 15 is a configuration diagram showing another example of a device for removing water vapor in exhaust gas.

FIG. 16 is a diagram showing the relationship between porous partition walls and various molecules.

FIG. 17 is a graph showing the composition change of the model gas at the inlet and outlet of the exhaust passage.

FIG. 18 is a block diagram showing an exhaust purification system.

FIG. 19 is a block diagram showing another example of an exhaust purification system.

FIG. 20 is a schematic step view showing a condensation trap.

[Explanation of symbols]

 1,11 engine 2,12 exhaust passage 3 reforming catalyst 4 three-way catalyst 5 adsorption catalyst 13 steam reforming catalyst 14 HC adsorbent 15 exhaust gas purification catalyst 16 bypass passage 17 on-off valve 19 fuel tank 20 fuel supply passage 21 fuel Supply device 22 Control unit 31 Exhaust pipe 32 Porous pipe 32a Inner porous wall 32b Intermediate porous wall 32c Outer porous wall 33 Alcohol passage portion 34 Exhaust passage portion 35 Double passage 36 Circulation passage 37 Reforming catalyst reaction tank 38 Cooler 39 Alcohol supply port 40 Supply pump 41 Heating device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location B01D 53/86 ZAB B01J 29/87 A B01D 53/36 ZAB (72) Inventor Takahiro Kurokawa Hiroshima Aki 3-1, Shinchi, Fuchu-cho, Municipality of Mazda Co., Ltd. (72) Masahiko Shigets 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture In-house Mazda Co., Ltd. (72) Shuji Iwakuni, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture No. 1 in Mazda Motor Corporation

Claims (6)

[Claims] 1. An exhaust gas purification device for purifying exhaust gas containing aliphatic hydrocarbons, comprising: a reforming material for reforming the aliphatic hydrocarbons in the exhaust gas into aromatic hydrocarbons; An exhaust gas purification device, comprising: an adsorbent that adsorbs hydrocarbons that have come into contact with a quality material. 2. The exhaust gas purifying apparatus according to claim 1, wherein the reforming material and the adsorbing material are separately arranged on an upstream side and a downstream side in an exhaust passage through which the exhaust gas flows. An exhaust gas purification device characterized by the above. 3. An exhaust gas purifying apparatus for purifying exhaust gas of an automobile engine, wherein a reforming material for reforming an aliphatic hydrocarbon in the exhaust gas into an aromatic hydrocarbon is provided in an exhaust passage of the engine. An adsorbent that has a higher adsorbability for adsorbing aromatic hydrocarbons than an adsorbent for adsorbing aliphatic hydrocarbons is disposed downstream of the modifier. Exhaust gas purification device characterized by. 4. The exhaust gas purifying apparatus according to claim 1, claim 2, or claim 3, wherein the modifier is gallium silicate in which a part of a crystal lattice is composed of Ga, An exhaust gas purification device, wherein the adsorbent is Y-type zeolite. 5. The exhaust gas purifying apparatus according to claim 2 or 3, wherein a three-way catalyst is arranged between the reforming material and the adsorbent, and the reforming material is crystallized. An exhaust gas purifying device, characterized in that a part of the lattice is gallium silicate composed of Ga, and the adsorbent is Y-type zeolite. 6. The exhaust gas purifying apparatus according to claim 1, wherein the adsorbent carries a noble metal active species that promotes a hydrocarbon decomposition reaction. A characteristic exhaust gas purification device.