JP2001293368A - Hydrocarbon adsorbent and method for adsorbing and removing hydrocarbon - Google Patents

Abstract

(57) [Problem] To provide a highly heat-resistant hydrocarbon adsorbent which is excellent in hydrocarbon adsorption capacity and adsorption holding power and whose hydrocarbon adsorption performance is not affected by the atmosphere of the processing gas. provide. SOLUTION: A hydrocarbon adsorbent comprising zeolite containing an alkali metal and not containing an alkaline earth metal and a transition metal is brought into contact with a processing gas to adsorb and remove the hydrocarbon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adsorbent for purifying hydrocarbons (hereinafter referred to as HC) contained in a processing gas, for example, exhaust gas discharged from an internal combustion engine, and a method for adsorbing and removing HC. For example, the present invention can be applied to, for example, adsorption and removal of HC in exhaust gas discharged from an internal combustion engine such as an automobile.

[0002]

2. Description of the Related Art HC emitted from an internal combustion engine of an automobile or the like
In the purification of exhaust gas containing, using a three-way catalyst,
A method of contacting with exhaust gas has been put to practical use. But,
When the engine is started, HC is discharged without being purified because the HC concentration in the exhaust gas is high and the temperature does not reach the temperature at which the three-way catalyst operates.

For the purpose of purifying HC from exhaust gas at low temperatures, Japanese Patent Application Laid-Open No. Hei 2-135126 discloses one type of monolithic carrier coated with Y-type zeolite and mordenite zeolite for the purpose of adsorbing and purifying HC. An exhaust gas purifying apparatus using the HC adsorbent carrying the above-mentioned metals has been proposed. Many other HC adsorbents containing zeolite as a component have been proposed. For example, Japanese Unexamined Patent Publication
JP-126165 proposes a molecular sieve carrying Ag, and JP-A-7-185326 proposes an HC adsorbent composed of Ag and a molecular sieve, one or more of an alkali metal and an alkaline earth metal. I have. JP-A-6-210165 discloses an adsorbent composed of Pd and zeolite, and JP-A-6-210163 discloses C-adsorbent.
zeolite containing u, in JP-A 5-31359 discloses SiO ₂ / Al ₂ O ₃ molar ratio has been proposed more than 40 zeolite. Further, JP-A-11-192427 discloses a ZS having a SiO ₂ / Al ₂ O ₃ molar ratio of 500 or more.
A first zeolite composed of M-5 and SiO ₂ / Al ₂ O ₃
An HC adsorbent composed of a second zeolite composed of a Y-type zeolite having a molar ratio of 200 or more has been proposed.

[0004]

In recent years, environmental problems have been greatly highlighted, and there has been a demand for an improved technique for reducing the amount of HC emission. In the case of purifying the exhaust gas discharged from an internal combustion engine of an automobile or the like using an HC adsorbent, it is necessary to purify the adsorbed HC. In order to directly purify the adsorbed HC with the three-way catalyst, an adsorbent capable of adsorbing and holding the HC in the exhaust gas up to the operating temperature of the three-way catalyst is required. Had insufficient adsorption holding power.

Further, the exhaust gas of the internal combustion engine takes a wide range from an oxidizing atmosphere (lean) to a reducing atmosphere (rich) depending on the operating conditions, and the temperature of the exhaust gas reaches 600 ° C. or more. Therefore, it is necessary that the adsorbent is not affected by the atmosphere of the exhaust gas, has a sufficient adsorption capacity even after being exposed to a high temperature, and has a sufficient adsorption holding power. That is, the adsorbent must have high heat-resistant adsorption performance in any exhaust gas atmosphere.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and is excellent in the HC adsorption capacity and adsorption holding power, and the HC adsorption performance of the process gas. An object of the present invention is to provide a highly heat-resistant adsorbent which is not affected by the atmosphere, and a method for adsorbing and removing HC contained in a processing gas using the adsorbent.

[0007]

In order to solve the above-mentioned problems, the present inventors have intensively studied the adsorption-desorption characteristics of HC. As a result, the present invention was found to be excellent in the ability to retain and adsorb HC, and to have high adsorption performance even after being exposed to a high temperature, without being affected by the atmosphere of the processing gas.

[0008] That is, the present invention is a hydrocarbon adsorbent comprising a zeolite containing an alkali metal and not containing an alkaline earth metal and a transition metal. The present invention is also a method for adsorbing and removing hydrocarbons, which comprises contacting such a hydrocarbon adsorbent with a processing gas. Hereinafter, the present invention will be described in detail.

It is essential that the adsorbent of the present invention is a zeolite containing an alkali metal and not containing an alkaline earth metal and a transition metal. Typically _{zeolites, xM 2 / n O · Al} 2 O 3 · ySiO 2 · zH 2 O ( where, n is the valence of the cation M, x is a number in the range of 0 to 2.5, y is 2 The above number, z is a number of 0 or more), and can be obtained as natural products and synthetic products. In addition, zeolite can be classified and specified based on the crystal structure observed by X-ray diffraction or the like, the pore diameter, the pore structure, and the like.

[0010] The zeolite of the present invention is SiO ₂ / Al ₂
The O ₃ molar ratio is not particularly limited, but is preferably 10 or more, more preferably 20 or more, in order to sufficiently increase the heat resistance of the adsorbent.

Although the structure of the zeolite used in the present invention is not particularly limited, known FER, MFI, MOR, B
It is preferable to use a zeolite having an EA or FAU structure. More preferably, MFI and BEA are good. Further, the zeolite is not limited to a single-structure zeolite, and two or more zeolites may be used in combination.

The method for producing the zeolite is not particularly limited, either.
A commonly known method of dispersing a silica source and an alumina source in an alkaline solution and performing hydrothermal synthesis can be employed. Further, it can be produced by adding an organic curing agent or the like to the production raw material.

The adsorbent of the present invention comprises a zeolite containing an alkali metal and not containing an alkaline earth metal and a transition metal. The alkali metal contained in the zeolite is not particularly limited, but includes, for example, K, Rb, Cs and the like. It is sufficient that at least one of these alkali metals is contained, and a plurality of these may be contained. H
In order to sufficiently increase the adsorption and holding power of C, preferably Cs
Is good. There are no particular restrictions on the raw materials used to contain the alkali metal, and nitrates, sulfates, acetates, chlorides, and the like of alkali metals can be used. As a method for allowing the zeolite to contain an alkali metal, a known ion exchange method, impregnation-supporting method, evaporation to dryness method, and physical mixing method can be adopted. When synthesizing the zeolite, an alkali metal raw material may be added and contained. In order to sufficiently enhance the adsorption performance of the adsorbent of the present invention, it is desirable that the contained alkali metal is in an ion-exchanged state. Therefore, it is preferable that the alkali metal be contained by an ion-exchange method. The content of the alkali metal contained in the zeolite is not particularly limited. However, in order to sufficiently increase the HC adsorption capacity and adsorption holding power, the content of the alkali metal atom in the zeolite is in the range of 0.1 to 30% by weight based on the zeolite. And more preferably in the range of 2 to 20% by weight.

The zeolite containing an alkali metal by the above method may be used after heat treatment (calcination). The heat treatment conditions are not particularly limited. Usually 400 to 1000
The treatment can be carried out at a temperature in the range of ° C and a time in the range of 0.5 to 10 hours.

As described above, the HC adsorbent of the present invention can be produced. The adsorbent of the present invention can be mixed with a binder such as silica, alumina, and clay minerals and then molded and used. Examples of the clay mineral include kaolin, attapulgite, montmorillonite, bentonite, allophane, sepiolite and the like. Further, it can be used by wash-coating a cordierite or metal honeycomb substrate. In the case of wash coating, a method of coating a honeycomb substrate with zeolite and then containing an alkali metal, a method of preliminarily adding zeolite to an alkali metal and then coating the honeycomb substrate with the zeolite can be employed.

By bringing the treatment gas into contact with the HC adsorbent of the present invention as described above, the HC in the treatment gas can be adsorbed and removed. Specific examples of the processing gas include exhaust gas from internal combustion engines such as gasoline engine vehicles and diesel engine vehicles. Further, the processing gas includes H
In addition to C, carbon monoxide, carbon dioxide, hydrogen, nitrogen, oxygen,
It may contain sulfur compounds, nitrogen oxides, water and the like.

The type of HC contained in the gas to be treated in the present invention is not particularly limited, and examples thereof include paraffin, olefin, and aromatic compound. Examples of paraffin and olefin include linear and branched HC having 1 to 20 carbon atoms, and examples of aromatic compounds include benzene, toluene, naphthalene and derivatives thereof. Also, oxygen-containing organic compounds such as ketones and aldehydes and nitrogen-containing compounds such as amines may be used. Further, it is effective even in a state where two or more HCs selected from the above-mentioned HCs are mixed.

The HC concentration in the exhaust gas is not particularly limited, but is preferably 0.001 to 10% by volume in terms of methane.
More preferably, the content is 0.001 to 5% by volume.

The space velocity and temperature at the time of adsorbing and removing HC in the exhaust gas are not particularly limited.
Preferably, the temperature is 500,000 hr ^-1 and the temperature is -30 to 200 ° C.

[0020]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited to these Examples.

Example 1 Preparation of Adsorbent 1 NH ₄ type ZS manufactured by Tosoh having a SiO ₂ / Al ₂ O ₃ molar ratio of 40
M-5 (trade name: HSZ-840NHA) was added to the cesium chloride aqueous solution, and the ion exchange operation at 80 ° C. was performed twice. After ion exchange, solid-liquid separation was performed, and the solid was washed with a sufficient amount of pure water.
When the Cs content of the adsorbent 1 was analyzed by atomic absorption spectroscopy, it was 9.6% by weight based on zeolite.

Example 2 Preparation of Adsorbent 2 β-zeolite (trade name: HSZ-940NHA) manufactured by Tosoh having a molar ratio of SiO ₂ / Al ₂ O ₃ of 37 was calcined at 600 ° C. to obtain H-type β (BEA). -1) was obtained.

Except that the NH ₄ type ZSM-5 was changed to BEA-1, the same operation as in Example 1 was performed to obtain adsorbent 2
I got When the Cs content of the adsorbent 2 was analyzed by atomic absorption analysis, it was 10.3% by weight with respect to the zeolite.

<Example 3> Preparation of adsorbent 3 Na type ZS manufactured by Tosoh having a SiO ₂ / Al ₂ O ₃ molar ratio of 23
M-5 (trade name: HSZ-820NAA) was ion-exchanged in an aqueous ammonium chloride solution, followed by solid-liquid separation, washing and drying to obtain NH ₄ type ZSM-5 (MFI-1). An adsorbent 3 was obtained by performing the same operation as in Example 1 except that the NH ₄ type ZSM-5 in Example 1 was changed to MFI-1. When the Cs content of the adsorbent 3 was analyzed by atomic absorption spectroscopy, it was 15.2% by weight based on zeolite.
Met.

Example 4 Preparation of Adsorbent 4 NH ₄ type ZSM-5 was prepared by mixing SiO ₂ / Al ₂ O _{3 at a} molar ratio of 72.
Tosoh H type ZSM-5 (trade name: HSZ-860H)
Adsorbent 4 was obtained by performing the same operation as in Example 1 except that OA) was used. The Cs content of the adsorbent 4 was analyzed by atomic absorption spectroscopy.
7% by weight.

<Example 5> Preparation of adsorbent 5 K exchange was performed in the same manner as in Example 1 except that the aqueous solution of cesium chloride was changed to an aqueous solution of potassium nitrate. After ion exchange, solid-liquid separation, washing with a sufficient amount of pure water, 110 ° C
For 20 hours to obtain the adsorbent 5. When the K content of the adsorbent 5 was analyzed by atomic absorption spectroscopy, it was 3.0% by weight with respect to the zeolite.

Comparative Example 1 Preparation of Comparative Adsorbent 1 The NH ₄ type ZSM-5 used in Example 1 was calcined in air at 500 ° C. for 1 hour to obtain H type ZSM-5, which was used as Comparative Adsorbent 1.

<Comparative Example 2> Preparation of Comparative Adsorbent 2 Tosoh H-type Z having a SiO ₂ / Al ₂ O ₃ molar ratio of 2100
SM-5 (trade name: HSZ-890HOA), 600
The mixture was calcined in air at 1 ° C. for 1 hour to obtain Comparative Adsorbent 2.

<Comparative Example 3> Preparation of Comparative Adsorbent 3 H-type and Y-type zeolite (trade name: HSZ-390HUA) manufactured by Tosoh having a SiO ₂ / Al ₂ O ₃ molar ratio of 360
The resultant was calcined in air at 0 ° C. for 1 hour to obtain Comparative Adsorbent 3.

<Comparative Example 4> Preparation of Comparative Adsorbent 4 Except that the cesium chloride aqueous solution was changed to a silver nitrate aqueous solution,
Ag exchange was performed by the same ion exchange operation as in Example 1.
After ion exchange, solid-liquid separation, washing with a sufficient amount of pure water,
After drying at 10 ° C. for 20 hours, Comparative Adsorbent 4 was obtained. The Ag content of the comparative adsorbent 4 was analyzed by ICP emission spectrometry, and it was 5.2% by weight based on zeolite.

Comparative Example 5 Preparation of Comparative Adsorbent 5 NH ₄ type ZS manufactured by Tosoh having a SiO ₂ / Al ₂ O ₃ molar ratio of 40
M-5 (trade name: HSZ-840NHA) was added to an aqueous copper acetate solution, and subsequently, aqueous ammonia was added to the slurry to adjust the pH to 10.5. Then, at 30 ° C, 2
Cu exchange was performed by an ion exchange operation for 0 hours. C above
After performing u exchange twice, solid-liquid separation was performed, washed with a sufficient amount of pure water, and dried at 110 ° C. for 20 hours to obtain Comparative Adsorbent 5. When the Cu content of the comparative adsorbent 5 was analyzed by ICP emission spectrometry, it was 2.6% by weight based on the zeolite.

Comparative Example 6 Preparation of Comparative Adsorbent 6 The procedure of Example 1 was repeated except that the aqueous solution of cesium chloride was replaced with an aqueous solution of magnesium nitrate.
After ion exchange, solid-liquid separation, washing with a sufficient amount of pure water,
After drying at 10 ° C. for 20 hours, Comparative Adsorbent 6 was obtained. When the Mg content of the comparative adsorbent 6 was analyzed by ICP emission analysis, it was 0.2% by weight based on the zeolite.

<Comparative Example 7> Preparation of Comparative Adsorbent 7 Ca exchange was performed in the same manner as in Example 1 except that the aqueous cesium chloride solution was changed to an aqueous calcium acetate solution. After ion exchange, solid-liquid separation, washing with a sufficient amount of pure water,
After drying at 0 ° C. for 20 hours, Comparative Adsorbent 7 was obtained. When the Ca content of the comparative adsorbent 7 was analyzed by ICP emission analysis, it was 0.3% by weight with respect to the zeolite.

Comparative Example 8 Preparation of Comparative Adsorbent 8 Zn exchange was carried out in the same manner as in Example 1 except that the aqueous solution of cesium chloride was changed to an aqueous solution of zinc acetate. After ion exchange, solid-liquid separation, washing with a sufficient amount of pure water, 110 ° C
For 20 hours to obtain Comparative Adsorbent 8. When the Zn content of the comparative adsorbent 8 was analyzed by ICP emission spectrometry, it was 2.0% by weight based on zeolite.

Comparative Example 9 Preparation of Comparative Adsorbent The NH ₄ type ZSM-5 used in Example 1 was added to an aqueous solution of ammonium molybdate such that molybdenum was 2% by weight based on zeolite, and evaporated. Mo was supported by a drying method. After carrying Mo, it was dried at 110 ° C. for 20 hours to obtain Comparative Adsorbent 9.

Comparative Example 10 Preparation of Comparative Adsorbent 10 The NH ₄ type ZSM-5 used in Example 1 was added to an aqueous solution of ammonium tungstate so that the amount of tungsten was 2% by weight based on zeolite. W was carried by the evaporation to dryness method. After supporting W, dried at 110 ° C. for 20 hours,
Comparative adsorbent 10 was obtained.

Comparative Example 11 Preparation of Comparative Adsorbent 11 NH ₄ type ZSM-5 was replaced with Na type ZSM-5 (SiO ₂ / Al
Except that instead of the ₂ O ₃ = 40), were Ag exchanged by the same procedure as Comparative Example 4. After ion exchange, solid-liquid separation was performed, washed with a sufficient amount of pure water, and dried at 110 ° C. for 20 hours to obtain Comparative Adsorbent 11. When the Ag and Na contents of the comparative adsorbent 11 were analyzed by ICP emission spectrometry, Ag was 4.7% by weight and Na was 0.7% by weight with respect to the zeolite.
there were.

Comparative Example 12 Preparation of Comparative Adsorbent 12 NH ₄ type ZSM-5 was converted to Na type β zeolite (SiO ₂ / A).
Ag exchange was carried out in the same manner as in Comparative Example 4, except that (I ₂ O ₃ = 37). After ion exchange, solid-liquid separation
After washing with a sufficient amount of pure water, drying at 110 ° C. for 20 hours,
Comparative adsorbent 12 was obtained. Ag and Na of comparative adsorbent 12
When the contents were analyzed by ICP emission spectrometry, Ag was 4.5% by weight and Na was 0.9% by weight based on the zeolite.

<HC adsorption removal test> The HC adsorption removal characteristics of the adsorbents 1 to 5 and the comparative adsorbents 1 to 12 were evaluated by the following method. A predetermined sample was pretreated at 500 ° C. in a flowing air and cooled to room temperature. Next, the model exhaust gas having the composition shown in Table 1 was brought into contact with the adsorbent at room temperature at a gas flow rate of 2000 ml / min. The space velocity at this time is 120,000 hr
It was ^-1 . After the adsorption of HC in the model exhaust gas was saturated, a gas obtained by removing only HC from the model exhaust gas in Table 1 was introduced into the adsorbent to remove HC remaining in the gas phase. Thereafter, the adsorbent was heated at a rate of 10 ° C./min while contacting a gas obtained by removing only HC from the model exhaust gas shown in Table 2 with the adsorbent, and HC desorbed from the adsorbent was detected by flame ionization. Quantitative analysis is continuously performed by a gas chromatograph equipped with a FID, and HC
Was evaluated for adsorption performance.

The adsorption performance of HC can be evaluated from the above desorption spectrum as follows. The HC adsorption capacity can be estimated from the HC desorption amount obtained by integrating the desorption spectrum, and the adsorption retention power can be estimated from the desorption peak temperature and / or the desorption amount at a predetermined temperature or higher. Table 2 shows the amount of desorbed toluene (μmol / g) at 200 ° C. or more per adsorbent weight and the desorption peak temperature (° C.).

[0041]

[Table 1]

<Durability test of adsorbent> Adsorbents 1 to 5 and comparative adsorbents 1 to 12 were each molded under pressure and then pulverized to 12 to 2
It was sized to 0 mesh. The granulated adsorbent, mixed gas containing of H ₂ O in Air gas such that 10% by volume: and H ₂ O (10 vol%) propylene (5000PpmC) to (durable -A oxidizing atmosphere) or nitrogen Was processed at 850 ° C. for 5 hours while flowing a mixed gas containing (A-B: reducing atmosphere). The adsorbents subjected to these durability treatments were evaluated for HC adsorption performance under the same pretreatment and evaluation conditions as in the <HC adsorption removal test>. After endurance, the amount of desorbed toluene at 200 ° C or more per adsorbent weight (μmol /
g) and desorption peak temperature (° C.) are shown in Table 2.

[0043]

[Table 2]

[0044]

The HC adsorbent of the present invention has a large amount of adsorbed HC desorbed at a high temperature and has a high desorbing temperature.
Has adsorption performance. Furthermore, even after endurance treatment in an oxidizing atmosphere and a reducing atmosphere, high HC adsorption performance is maintained, and even when the adsorbent is exposed to high temperatures in any atmosphere, excellent H is obtained.
Shows C adsorption characteristics. Therefore, by bringing the adsorbent of the present invention into contact with the treatment gas containing HC, HC in the exhaust gas can be adsorbed and removed more efficiently than the adsorbent disclosed in the related art. Further, the adsorbent of the present invention can be applied to removal of nitrogen oxides using adsorbed HC in combination with an exhaust gas purifying catalyst.

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Claims (8)

[Claims] 1. A hydrocarbon adsorbent comprising a zeolite containing an alkali metal and not containing an alkaline earth metal and a transition metal. 2. The hydrocarbon adsorbent according to claim 1, wherein the alkali metal is at least one selected from the group consisting of K, Rb and Cs. 3. The hydrocarbon adsorbent according to claim 1, wherein the alkali metal is Cs. 4. The zeolite according to claim 1, wherein the molar ratio of SiO ₂ / Al ₂ O ₃ is at least 10.
The hydrocarbon adsorbent according to any one of the above. 5. The hydrocarbon adsorbent according to claim 1, wherein the alkali metal is contained by ion exchange. 6. The hydrocarbon adsorbent according to claim 1, wherein the content of the alkali metal is 0.1 to 30% by weight based on the zeolite. 7. The method according to claim 1, wherein the zeolite is FER, MFI, MOR, B
The hydrocarbon adsorbent according to any one of claims 1 to 6, wherein the hydrocarbon adsorbent is at least one member selected from the group consisting of EA and FAU. 8. A method for adsorbing and removing hydrocarbons, comprising bringing the hydrocarbon adsorbent according to claim 1 into contact with a processing gas.