JPH11319551A - Adsorbent of hydrocarbon and method for desorption of the hydrocarbon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adsorbent which has high adsorptivity of hydrocarbon and has adsorption performance for adsorbing and holding hydrocarbon at such the temperature that an exhaust gas purification catalyst is actuated even when the adsorbent is used for purification of exhaust gas and also has sufficient heat resistance in its adsorption performance and further to provide a method for desorption of hydrocarbon contained in gas by using the adsorbent. SOLUTION: The adsorbent of hydrocarbon is obtained by containing P into zeolite of MFI structure in which SiO2 /Al2 O3 molar ratio is 20-50, and crystal diameter is 1-5 μm and heat-treating zeolite containing P at temperature of at least 800 deg.C. Further, hydrocarbon contained in gas is desorbed by bringing the adsorbent into contact with gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adsorbent for adsorbing and removing hydrocarbons contained in a gas, particularly an exhaust gas, and to a method for adsorbing and removing hydrocarbons. It can be applied to adsorption and removal of hydrocarbons in exhaust gas.

[0002]

2. Description of the Related Art In purifying exhaust gas containing hydrocarbons discharged from an internal combustion engine of an automobile or the like, a method of contacting the exhaust gas with a three-way catalyst has been put to practical use. It is known that the exhaust gas purifying ability of the three-way catalyst is developed at 300 ° C. or higher. When the exhaust gas temperature at the time of starting the engine is low, hydrocarbons are directly discharged without purifying the catalyst.

[0003] In recent years, environmental issues have been greatly highlighted, and regulations on the emission of pollutants such as hydrocarbons, carbon monoxide, and nitrogen oxides emitted from internal combustion engines such as automobiles have been tightened. For this reason, suppression of hydrocarbon emission at low temperatures is desired. To solve this problem, an adsorbent composed of zeolite and a method of adsorbing and removing hydrocarbons in exhaust gas using an adsorbent composed of zeolite have been proposed. For example, JP-A-6-170234 proposes an adsorbent which is a ZSM-5 zeolite ion-exchanged with at least one metal of Cu and Pd. In addition, JP-A-9-253483 discloses an MFI-type zeolite in which the content of SiOH groups (silanol groups) is 3 × 10 ²⁰ / g or less.
In Japanese Patent Application Laid-Open Publication No. H11-264, an MFI-type zeolite having a hexagonal columnar crystal form is proposed.

In Japanese Patent Application Laid-Open No. 6-63394,
An adsorbent for purifying hydrocarbons prepared using a crystalline aluminosilicate having an MFI structure containing phosphorus has been proposed. Further, Japanese Patent Application Laid-Open No. 9-173827 discloses a hydrocarbon adsorbent which is a molecular sieve, A method for producing an adsorbent, which comprises contacting a substance that modifies an acid site such as a phosphate-containing compound and a super acid,
An acid site-modified adsorbent in which phosphoric acid is contained in ZSM-5 is disclosed. In order to improve the adsorption capacity and durability of hydrocarbons, JP-A-6-63394 discloses SiO
A zeolite having an MFI structure having a ₂ / Al ₂ O ₃ molar ratio of _{30 to} 200 is disclosed in JP-A-9-173827.
iO ₂ / Al ₂ O ₃ molar ratio constitute the adsorbent ZSM-5 of 50 to 250.

[0005] In any of these methods of adsorbing and removing hydrocarbons using an adsorbent, hydrocarbons are once adsorbed to the adsorbent in a low temperature range when the engine is started, and the exhaust gas purification temperature is activated. At a temperature above which the hydrocarbons desorbed from the adsorbent are purified by an exhaust gas purifying catalyst. That is, the adsorption and removal of hydrocarbons by the adsorbent functions effectively, having both adsorption characteristics at low temperatures and adsorption holding power.

[0006]

With the demand for improvement of the technology for removing hydrocarbons, the adsorption characteristics of the adsorbents proposed hitherto are not sufficient and have not been put to practical use.
Further, since the exhaust gas temperature of the internal combustion engine is as high as 600 ° C. or more, even if the adsorbent is exposed to a high temperature, the adsorption performance of hydrocarbons does not decrease, that is, the adsorbent needs to have high heat resistance. is there.

An object of the present invention is to have a high hydrocarbon adsorbing ability,
And even when used for exhaust gas purification, it has an adsorption performance of adsorbing and holding hydrocarbons up to a temperature at which the exhaust gas purification catalyst operates, and an adsorbent having sufficient heat resistance in the adsorption performance and a gas using the adsorbent. It is an object of the present invention to provide a method for adsorbing and removing hydrocarbons contained therein.

[0008]

Means for Solving the Problems In view of these circumstances, the present inventors have made intensive studies especially on the adsorption characteristics of hydrocarbons in exhaust gas.
An adsorbent obtained by adding P to an MFI-structured zeolite having an iO ₂ / Al ₂ O ₃ molar ratio of 20 to less than 50 and a crystal diameter of 1 μm to 5 μm and performing a heat treatment at a temperature of 800 ° C. or more is: The present invention was found to have a high hydrocarbon adsorption property, a strong holding force for the adsorbed hydrocarbon, and no deterioration in the adsorption property even after being exposed to a high temperature, and excellent heat resistance, and completed the present invention. Reached.

That is, according to the present invention, the SiO ₂ / Al ₂ O ₃ molar ratio is from 20 to less than 50, and the crystal diameter is from 1 μm to 5 μm.
An adsorbent for hydrocarbons, wherein P is contained in zeolite having an MFI structure of not more than μm and the P-containing zeolite is heat-treated at a temperature of 800 ° C. or more. The present invention is also a method for adsorbing and removing hydrocarbons in a gas, which comprises contacting the adsorbent with a gas. Less than,
The present invention will be described in detail.

[0010] It is essential that the adsorbent of the present invention is composed of a zeolite having an MFI structure. And generally of MFI _{zeolite, xM n / 2 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 1.5, y Is a number of 20 or more, and z is a number of 0 or more). Regarding the structure, for example,
No. 4771, etc., and are defined as a structure having an X-ray diffraction pattern as shown in Table 1.

[0011]

[Table 1]

The zeolites according to the invention can be produced by known methods. Specifically, US Pat.
No. 86 and the like. The zeolite SiO
_{The 2} / Al ₂ O ₃ molar ratio is 20 or more and less than 50. Si
When the O ₂ / Al ₂ O ₃ molar ratio is less than 20, the heat resistance of the zeolite itself is low, and when the adsorbent is exposed to high temperatures,
Adsorption characteristics decrease. SiO ₂ / Al ₂ O ₃ molar ratio of 50
In the above case, the effect of containing P may not be sufficiently exhibited.

Further, it is essential that the zeolite according to the present invention has a crystal diameter of 1 μm or more and 5 μm or less. The increase in the amount of adsorption of hydrocarbons due to the inclusion of P as described in JP-A-9-173827 is observed even when the crystal diameter is smaller than 1 μm and / or larger than 5 μm. In order to further improve the characteristics (durability), it is necessary that the crystal diameter of zeolite be in the range of 1 μm to 5 μm. In general, the crystal diameter can be determined by a Coulter counter, microtrack measurement, observation with an electron beam microscope (SEM, TEM), or the like. The particle size defined in the present invention is an average primary particle size observed by SEM, and the primary particle size means a minimum unit crystal size of zeolite crystals.

The zeolite according to the present invention is an alkali metal,
It may contain an alkaline earth metal, a rare earth metal or the like.
It is also possible to use an NH ₄ type treated with an ammonium salt or the like, or an H type obtained by an acid treatment with a mineral acid or the like or an NH ₄ type baking treatment. Preferably NH ₄ type,
It is desirable to use the H type.

The hydrocarbon adsorbent of the present invention comprises the above-mentioned MFI
It is produced by incorporating P into a zeolite having a structure. There is no particular limitation on the raw materials used for the inclusion of P, and orthophosphoric acid,
Phosphate compounds such as metaphosphoric acid, pyrophosphoric acid, diammonium hydrogen phosphate, and organic ammonium phosphate, and phosphorous compounds such as trimethyl phosphite may be used, and these phosphorus compounds may be used in combination. The content method is not particularly limited. For example, P can be contained on zeolite by an impregnation-supporting method or an evaporation to dryness method using a solution in which a phosphorus compound is dissolved in a suitable solvent such as water. Further, P can be contained on zeolite by a gas phase treatment method in which a gas containing a phosphorus compound is brought into contact with zeolite.

The content of P contained in the adsorbent produced by these methods is not particularly limited, but in order to sufficiently exhibit the adsorption performance of hydrocarbons, the content of P is 0.1 to 20% by weight based on zeolite. Good in the range. More preferably, it is 0.1 to 15% by weight.

The adsorbent of the present invention is produced by subjecting a zeolite containing P to a heat treatment such as calcination by the above method, and the heat treatment temperature is 800 ° C. or higher. The heat treatment temperature is preferably 850 to 1200 ° C. in order to further enhance the hydrocarbon adsorption performance. The heat treatment time is not particularly limited, and may be in the range of 0.5 to 10 hours, preferably 0.1 to 10 hours.
5 to 5 hours. The atmosphere at the time of the heat treatment is not particularly limited, and the treatment can be performed in an atmosphere in which an inert gas such as air, nitrogen, helium, or the like and a mixture of these gases is used. Further, water, hydrocarbons, nitrogen oxides, and sulfur oxides may be contained in the atmosphere gas. More preferably, an atmosphere containing moisture is desirable. As the heat treatment is performed at a relatively high temperature as in the present invention, the adsorption performance of hydrocarbons is improved, and thus the heat treatment becomes an excellent adsorbent.

As described above, the hydrocarbon adsorbent of the present invention can be produced.

The adsorbent of the present invention can be used by mixing with a binder such as silica, alumina and clay mineral and molding. Examples of the clay mineral include kaolin, attapulgite, montmorillonite, bentonite, allophane, sepiolite and the like. Further, the adsorbent of the present invention can be wash-coated on a cordierite or metal honeycomb substrate and used.

By bringing the adsorbent produced by the above method into contact with a gas containing hydrocarbons, the adsorption and removal of hydrocarbons can be performed. This gas is not particularly limited, and is applicable to a gas phase containing a hydrocarbon, such as an exhaust gas from an internal combustion engine. It is also effective when the gas contains carbon monoxide, carbon dioxide, hydrogen, oxygen, nitrogen, nitrogen oxides, sulfur oxides, and water in addition to hydrocarbons.

The type of hydrocarbon adsorbed on the adsorbent is not particularly limited, and may be an unsaturated hydrocarbon such as ethylene, propylene, decene or 1-hexadecene, or an unsaturated hydrocarbon such as methane, ethane or propane n-decane. And aromatic hydrocarbons such as benzene and toluene; branched hydrocarbons such as 2-methylpropane and isopropylbenzene; and oxygen-containing compounds such as ketones and aldehydes which are derivatives of the above hydrocarbons; and nitrogen-containing compounds such as amines. Compounds are also adsorbed.
That is, the gas targeted by the adsorbent of the present invention contains at least one or more of these hydrocarbons. The adsorbed hydrocarbon is preferably a hydrocarbon having 2 to 5 carbon atoms.

The concentration of the hydrocarbon in the gas is not particularly limited, but is preferably 0.001 to 5% by volume in terms of methane.
More preferably, the content is 0.005 to 3% by volume. The components other than hydrocarbons are not particularly limited.
O 0 to 1 vol%, CO ₂ 0-10 vol%, O ₂ is 0
The range may be 20% by volume, 0 to 1% by volume of nitrogen oxide, 0 to 0.05% by volume of sulfur oxide, and 0 to 15% by volume of water.

The space velocity and temperature at the time of adsorbing and removing the hydrocarbon are not particularly limited, but the space velocity is 100 to 5000.
It is preferable that the temperature is 00 hr ^-1 and the temperature is -30 to 250 ° C.

[0024]

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

Example 1 Preparation of adsorbent 1 MFI structure zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio = 40 and a particle diameter of 4 μm: NH ₄ Cl: 18
g was added to an aqueous solution of ammonium chloride dissolved in 400 g of pure water, and an ion exchange operation was performed at 60 ° C. for 20 hours. After this ion exchange operation is repeated twice, solid-liquid separation is performed, and the resultant is washed with pure water until Cl ions cannot be detected.
After drying at 110 ° C. for 20 hours, ammonium-type MFI
(NH ₄ -MFI-1) was obtained.

NH ₄ -MFI-1: 20 g (anhydrous equivalent)
Was added to an aqueous solution obtained by dissolving 1 g of diammonium hydrogen phosphate in 100 g of pure water, and evaporated to dryness under reduced pressure at 60 ° C. Thereafter, the resultant was dried at 110 ° C. for 20 hours and heat-treated at 850 ° C. for 5 hours in humidified air containing 10% by volume of water to obtain adsorbent 1. The adsorbent 1 was analyzed from ICP emission spectrometry, it had a composition of _{0.48P 2 O 5 · Al 2 O} 3 · 40SiO 2 in oxide-based anhydrous.

Example 2 Preparation of Adsorbent 2 Diammonium hydrogen phosphate: 1 g and orthophosphoric acid: 1 g
The adsorbent 2 was obtained by performing the same operation as in Example 1 except that the adsorbent 2 was changed. The adsorbent 2 was analyzed by ICP emission spectrometry, it had a composition of _{0.47P 2 O 5 · Al 2 O} 3 · 40SiO 2 in oxide-based anhydrous.

<Example 3> Preparation of adsorbent 3 The same operation as in Example 1 was carried out except that diammonium hydrogen phosphate used for containing P on zeolite having an MFI structure was changed to 1 g: 2 g. Adsorbent 3 was obtained. Adsorbent 3
Was analyzed from ICP emission spectrometry, it had a composition of _{0.95P 2 O 5 · Al 2 O} 3 · 40SiO 2 in oxide-based anhydrous.

Example 4 Preparation of Adsorbent 4 A SiO ₂ / Al ₂ O ₃ molar ratio = 30 and a particle diameter of 1.5 μm
Adsorbent 4 was obtained by performing the same operation as in Example 1, except that 40 g of the zeolite having the MFI structure was used. The adsorbent 4 was analyzed from ICP emission spectrometry, it had a composition of _{0.37P 2 O 5 · Al 2 O} 3 · 30SiO 2 in oxide-based anhydrous.

Comparative Example 1 Preparation of Comparative Adsorbent 1 M having a SiO ₂ / Al ₂ O ₃ molar ratio = 26 and a particle diameter of 1 μm
The same operation as in Example 1 was performed using a zeolite having an OR structure to obtain a comparative adsorbent 1. The comparative adsorbent 1 was analyzed from ICP emission spectrometry, it had a composition of _{0.33P 2 O 5 · Al 2 O} 3 · 26SiO 2 in oxide-based anhydrous.

Comparative Example 2 Preparation of Comparative Adsorbent 2 SiO ₂ / Al ₂ O ₃ molar ratio = 27, particle size 0.1 μm
Comparative Adsorbent 2 was obtained by performing the same operation as in Example 1 by using the zeolite having the BEA structure described above. The comparative adsorbent 2 was analyzed from the ICP emission spectrometry, it had a composition of _{0.32P 2 O 5 · Al 2 O} 3 · 27SiO 2 in oxide-based anhydrous.

Comparative Example 3 Preparation of Comparative Adsorbent 3 M _{2 having a} SiO ₂ / Al ₂ O ₃ molar ratio = 70 and a particle diameter of 1 μm
The same operation as in Example 1 was performed using zeolite having the FI structure to obtain comparative adsorbent 3. ICP for comparative adsorbent 3
Analysis from emission analysis, had a composition of _{0.82P 2 O 5 · Al 2 O} 3 · 70SiO 2 in oxide-based anhydrous.

Comparative Example 4 Preparation of Comparative Adsorbent 4 SiO ₂ / Al ₂ O ₃ molar ratio = 40, particle size 0.05 μm
Comparative adsorbent 4 was obtained by performing the same operation as in Example 1 using zeolite having MFI structure of m. The comparative adsorbent 4 was analyzed from ICP emission spectrometry, it had a composition of _{0.47P 2 O 5 · Al 2 O} 3 · 40SiO 2 in oxide-based anhydrous.

Comparative Example 5 Preparation of Comparative Adsorbent 5 A comparative adsorbent 5 was obtained in the same manner as in Example 1 except that the heat treatment at 850 ° C. for 5 hours was performed at 750 ° C. for 5 hours.

<Hydrocarbon Adsorption Removal Test> Examples 1-4
In addition, 1 cc of the adsorbent obtained in Comparative Examples 1 to 5 was filled in a quartz glass atmospheric pressure fixed bed flow-type reaction tube, and subjected to a hydrocarbon adsorption experiment. As pre-treatment, dry air is supplied at 2 L / min.
While flowing, 500 ° C at a heating rate of 20 ° C / min.
And held at 500 ° C. for 1 hour. After cooling to room temperature and completely replacing with nitrogen gas, a model exhaust gas having the composition shown in Table 2 was added to the adsorbent at room temperature at a gas flow rate of 2 L / min.
Contact for an hour. The space velocity (based on volume) at this time is 12
0000 hr ⁻¹ . After confirming that the adsorption of hydrocarbons in the model exhaust gas reached saturation, nitrogen gas was introduced again into the adsorbent to completely remove hydrocarbons remaining in the gas phase.
Subsequently, while flowing the nitrogen gas at 2 L / min and raising the temperature of the adsorbent at 10 ° C./min, hydrocarbons desorbed from the adsorbent are detected by a flame ionization detection (FID) hydrocarbon concentration meter. Continuous quantitative analysis was performed to evaluate the adsorption characteristics of hydrocarbons. Table 3 shows hydrocarbon adsorption characteristics (adsorption amount and desorption peak temperature).

[0036]

[Table 2]

[0037]

[Table 3]

As is clear from Table 3, the adsorbent of the present invention has a large amount of adsorbed hydrocarbons and a high desorption of hydrocarbons, and therefore has a strong ability to retain and adsorb hydrocarbons. Things.

[0039]

Since the adsorbent of the present invention is obtained by heat treatment at a relatively high temperature of 800 ° C. or higher, it is possible to efficiently adsorb and remove hydrocarbons in a gas. Further, since the crystal diameter of the zeolite constituting the adsorbent is 1 μm or more and 5 μm or less, the adsorption performance of hydrocarbons is high even after the adsorbent is exposed to a high temperature. Accordingly, hydrocarbons can be efficiently removed by bringing the adsorbent of the present invention into contact with a gas containing hydrocarbons. Utilizing this property, the adsorbent of the present invention can efficiently adsorb and remove hydrocarbons discharged at the start of an engine of an automobile or the like, and can adsorb and hold the hydrocarbon to a temperature at which the exhaust gas purifying catalyst operates.

[0040]

Claims (3)

[Claims] (1) The molar ratio of SiO ₂ / Al ₂ O ₃ is 20 or more and 50 or more.
A hydrocarbon adsorbent, wherein P is contained in an MFI-structured zeolite having a crystal diameter of less than 1 μm and not more than 5 μm, and the P-containing zeolite is heat-treated at a temperature of 800 ° C. or more. 2. The hydrocarbon to be adsorbed and removed has 2 to 5 carbon atoms.
The hydrocarbon adsorbent according to claim 1, characterized in that: 3. A method for adsorbing and removing hydrocarbons in a gas, comprising contacting the adsorbent according to claim 1 with a gas.