JPH09253484A - Adsorbent for purification of hydrocarbons in exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an adsorbent having a high hydrothermal stability for cleaning off hydrocarbons in exhaust gas by using MFI zeolite having a hexangular-prism-like crystal structure. SOLUTION: MFI zeolite such as ZSM-8, zeta 1 and the like having a crystal structure similar to that of ZSM-5 is used. Crystal structure of the MFI zeolite is a hexangular prism crystal structure, and a crystal size of 1 to 10μm is preferred. Molar ratio of SiO2 /Al2 O3 , of the MFI zeolite is preferably 20 to 500 and in respect of hydrothermal stability and activity a ratio of 30 to 200 is more preferred. The adsorbent thus obtained has a high hydrothermal stability and exhibits a high adsorbent performance of adsorbing hydrocarbons such as methane, benzene and the like even after steaming treatment.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an adsorbent for purifying hydrocarbons in exhaust gas.

[0002]

2. Description of the Related Art In the exhaust gas of automobiles, as hydrocarbons, paraffin hydrocarbons such as methane, ethane, propane, butane, pentane and hexane, ethylene,
It contains olefinic hydrocarbons such as propylene, butene, pentene and hexene, and aromatic hydrocarbons such as benzene, toluene, xylene and trimethylbenzene. The concentration of hydrocarbons in the exhaust gas varies depending on the type of engine and operating conditions, but is generally 500 to 20000 p.
pm.

Conventionally, as such a catalyst for purifying automobile exhaust gas, a three-way catalyst which simultaneously oxidizes hydrocarbons and carbon monoxide and reduces NO _x has been used. This type of three-way catalyst exhibits sufficient catalytic activity at a reaction temperature of a predetermined temperature or higher. Usually, hydrocarbons in exhaust gas of an automobile engine are discharged in a particularly large amount immediately after the engine is started. However, since the temperature of the exhaust gas at this time is not sufficiently high, there is a drawback that hydrocarbons cannot be efficiently purified by the three-way catalyst. Therefore, in order to compensate for such drawbacks of the three-way catalyst, a zeolite is placed upstream of the three-way catalyst to temporarily adsorb hydrocarbons discharged when the three-way catalyst is at a low temperature to this zeolite. After that, a method of burning and removing hydrocarbons with a three-way catalyst has been proposed (JP-A-2-75327, JP-A-2-13512).
However, the adsorption capacity of the zeolite for hydrocarbons was not sufficient. On the other hand, the exhaust gas of an engine contains a large amount of water, and the temperature of the exhaust gas becomes high when the engine is in operation, so the adsorbent for purifying hydrocarbons in the exhaust gas has high hydrothermal stability. Is required.

Of the various zeolites, ZSM-5 is said to have the most excellent hydrothermal stability.
-5 was not sufficiently satisfactory in terms of hydrothermal resistance practically. That is, since it has poor hydrothermal stability, it exhibits sufficient performance in the initial stage, but it has not been practically used because the hydrocarbon adsorption capacity disappears after long-term use.

[0005]

The present invention has been made from the above viewpoint, and provides an adsorbent having high hydrothermal stability and capable of highly efficiently purifying hydrocarbons in exhaust gas. The purpose is.

[0006]

As a result of earnest research, the present inventors have found that the use of MFI type zeolite having a specific crystal form can effectively achieve the above-mentioned object of the present invention. Is completed. That is, the present invention is an adsorbent for purifying hydrocarbons in exhaust gas, characterized by using MFI-type zeolite having a hexagonal columnar crystal morphology.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. The MFI type zeolite used in the present invention is
Zeolite having a crystal structure similar to that of ZSM-5, for example, ZSM-5, ZSM-8, zeta 1, zeta 3, Nu-4, Nu-5, TZ-1, TPZ-1, IS
Zeolites such as I-3, ISI-5 and AZ-1 are applicable. You may use these zeolites in mixture of 2 or more types.

It has been found that the crystal form of the MFI-type zeolite is required to be hexagonal columnar, and the hexagonal columnar one has higher heat resistance than other crystal forms. Among them, those having a crystal size of 1 to 10 μm are particularly excellent. The crystal size here means the longest length of the diagonal line of the hexagon. SiO ₂ / Al ₂ of the MFI-type zeolite
The O ₃ molar ratio is preferably 20-500. From the viewpoint of hydrothermal resistance and activity, 30 to 200 is more preferable. When the molar ratio is less than 20 or 30, the hydrothermal resistance is relatively low and the durability is low. The molar ratio is 200 or 500
If it exceeds, since the Al content is low, the adsorptivity of hydrocarbons becomes weak, and sufficient adsorbability may not be obtained.

The hexagonal columnar MFI-type zeolite can be synthesized by holding a raw material mixture having the following composition (each represents a molar ratio) at 150 to 200 ° C. for 4 hours to 10 days for crystallization. _{SiO 2 / Al 2 O 3 =} 20~500 ( preferably 30
To 300) OH / SiO ₂ = 0.01 to 0.5 (preferably 0.1)
~ 0.4) NaX / SiO ₂ = 0 to 3.5 (preferably 0.2 to
2.0) R / SiO ₂ = 0 to 5.0 (preferably 0 to 3.0) H ₂ O / SiO ₂ = 10 to 300 (preferably 15 to 1)
00) (R: crystallization accelerator, X: inorganic anion ... Cl ⁻ ,
SO ₄ ^2-, NO ₃ ^- etc.) the raw material mixture of silica source, alumina source is prepared by mixing the alkali source. As a mixing method, each component source may be added and mixed at the same time, or one component may be added and mixed with another component. Hexagonal columnar MFI zeolite can be easily obtained by adding a small amount of various zeolites as seed crystals to the raw material mixture under the above reaction conditions.

The synthesized MFI type zeolite is preferably H type or metal exchange type. The H type may be ion-exchanged with hydrochloric acid, ammonium chloride, ammonium nitrate or the like by a usual method. The metal of the metal exchange type is not particularly limited, but Cu, Ag, Pt, Pd, Co, Fe and the like are preferable, and ion exchange may be performed by a usual method. H generated
Type or metal exchange type zeolite is 300-1000 ℃
It is preferable to bake at. At that time, it may be performed in the presence of steam.

Further, the obtained MFI-type zeolite can be used after being appropriately treated with a substance such as acid, alkali, ammonia, halogen, or other non-metal compound. The obtained adsorbent may be molded using a binder such as silica, alumina, silica-alumina, magnesia, zirconia. The shape of the adsorbent obtained in the present invention is arbitrary and can be, for example, pellet, plate, column, or lattice. Further, a lattice-like material such as cordierite, mullite, or alumina, and a base material such as a wire mesh may be coated with an adsorbent.

[0012]

EXAMPLES Next, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. [Example 1] Aluminum sulfate (18-hydrate) 13.5
g, sulfuric acid (97%) 14.5 g, water 330 g (referred to as liquid A), water glass (SiO ₂ 28.5%, N
a ₂ O 9.5%, water 62%) 211 g, water 300 g (referred to as liquid B) and sodium chloride 121 g,
A solution consisting of 200 g of water (referred to as liquid C) was prepared. First, after the liquid C and the liquid A were mixed, this liquid was added dropwise to the liquid B while stirring. After adding 0.3 g of mordenite powder to this raw material mixture, it was put into an autoclave and kept at 180 ° C. for 30 hours while stirring under a closed condition. After cooling, the reaction product was filtered, washed, and dried at 120 ° C.
As a result of X-ray diffraction, the product was a MFI-type zeolite. The crystal morphology by scanning electron microscope (SEM) is shown in Fig. 1.
As shown in FIG. Furthermore, this zeolite was calcined in an air stream at 550 ° C. for 4 hours. The SiO ₂ / Al ₂ O ₃ molar ratio of the zeolite thus obtained was 38.5. This zeolite was subjected to ion exchange with a 1N ammonium nitrate solution, and the obtained ammonium-type zeolite was dried at 120 ° C and then at 550 ° C for 4 hours.
Fired for hours. Quartz reaction tube was filled with 5 g of the produced zeolite, and 2% by volume of air (50 cc /
Steaming (hydrothermal treatment) was performed for 10 hours at 800 ° C.

Next, the adsorption of hydrocarbons was evaluated as follows on the zeolite after steaming. First, this adsorbent was compression-molded to have a uniform particle size of 32 to 64 mesh, and then 0.05 g of this adsorbent was charged into a fixed bed tubular reactor (diameter 7 mm). The reactor was maintained at 120 ° C. for 1 hour while flowing a mixture of air (45 cc / min) and water (5 cc / min) as a carrier gas. next,
As a hydrocarbon, 0.2 cc of propylene was taken in a syringe, and propylene was injected in a pulsed manner into this reactor. Then, the propylene concentration at the reactor outlet was measured to calculate the amount of propylene adsorbed on the adsorbent. As a result, the amount of propylene adsorbed was 0.030 g per 1 g of the adsorbent.

Comparative Example 1 In Example 1, the amount of sulfuric acid was 21.0 g, and tetrapropylammonium bromide 2 was used as a crystallization agent instead of mordenite.
The zeolite of Comparative Example 1 was synthesized in the same manner except that 6.3 g was used. As a result of X-ray diffraction, the product was MFI.
Type of zeolite. The crystal morphology by SEM is shown in FIG.
As shown in Fig. 3, it had a rounded rectangular columnar shape. Furthermore, this zeolite was calcined in an air stream at 550 ° C. for 4 hours. Si of the zeolite thus obtained
O ₂ / Al ₂ O ₃ molar ratio was 37.5. This zeolite was treated in the same manner as in Example 1 to prepare an adsorbent.

Example 2 In Example 1, the amount of aluminum sulfate (18-hydrate) was 7.6 g and the amount of sulfuric acid was 1.
The zeolite of Example 2 was synthesized in the same manner except that 5.1 g, the amount of sodium chloride was 85 g, and the amount of mordenite was 0.5 g. As a result of X-ray diffraction, the product was MF
It was a type I zeolite. The crystal morphology by SEM was a hexagonal columnar shape as shown in FIG. Furthermore, this zeolite was calcined in an air stream at 550 ° C. for 4 hours. SiO ₂ / Al ₂ O ₃ molar ratio of the zeolite was 67.5. This zeolite was treated in the same manner as in Example 1 to prepare an adsorbent.

Example 3 In Example 1, the amount of sulfuric acid was 18.1 g, the amount of sodium chloride was 85 g, and 0.5 g of Y-type zeolite was used as a seed crystal instead of mordenite. Synthesis temperature of 160 ℃,
The zeolite of Example 3 was synthesized in the same manner except that the synthesis time was 70 hours. The product is the result of X-ray diffraction,
It was an MFI type zeolite. The crystal morphology by SEM was a hexagonal column as shown in FIG. Furthermore, this zeolite was calcined in an air stream at 550 ° C. for 4 hours. SiO ₂ / Al ₂ O ₃ molar ratio of the zeolite was 40.2. This zeolite was treated in the same manner as in Example 1 to prepare an adsorbent.

Example 4 The zeolite of Example 4 was synthesized in the same manner as in Example 1 except that 5.2 g of morpholine was used as the crystallization agent instead of mordenite. As a result of X-ray diffraction, the product was a MFI-type zeolite. The crystal morphology by SEM was a hexagonal column as shown in FIG. Furthermore, this zeolite was calcined in an air stream at 550 ° C. for 4 hours. Zeolite SiO ₂ /
The Al ₂ O ₃ molar ratio was 39.1. This zeolite was treated in the same manner as in Example 1 to prepare an adsorbent.

Example 5 In Example 1, the amount of aluminum sulfate (18-hydrate) was 4.2 g and the amount of sulfuric acid was 1 g.
8.1 g, 85 g of sodium chloride, 63 g of water
0 g (200 g of solution A, 230 g of solution B, 200 g of solution C), 55.8 g of butylamine as a crystallization agent instead of mordenite, and a synthesis temperature of 1
The zeolite of Example 5 was synthesized in the same manner except that the temperature was 60 ° C. and the synthesis time was 70 hours. As a result of X-ray diffraction, the product was a MFI-type zeolite. The crystal morphology by SEM was a hexagonal column as shown in FIG. Furthermore,
This zeolite was calcined in an air stream at 550 ° C. for 4 hours. Zeolite has a SiO ₂ / Al ₂ O ₃ molar ratio of 12
0.5. This zeolite was treated in the same manner as in Example 1 to prepare an adsorbent.

Comparative Example 2 In Example 1, the amount of sulfuric acid was 18.1 g, the amount of sodium chloride was 21 g, and the amount of water was 415 g (165 g of liquid A, 150 g of liquid B, 100 of liquid C).
g) and the amount of mordenite was 0.1 g, and the zeolite of Comparative Example 2 was synthesized in the same manner.
As a result of X-ray diffraction, the product was a MFI-type zeolite. The crystal morphology by SEM showed the form of aggregated small square columns as shown in FIG. 7. Furthermore, this zeolite was calcined in an air stream at 550 ° C. for 4 hours. SiO ₂ / Al ₂ O ₃ molar ratio of the zeolite was 40.8.
This zeolite was treated in the same manner as in Example 1 to prepare an adsorbent.

The synthesis conditions and physical properties of the zeolites of Examples 1 to 5 and Comparative Examples 1 and 2 are summarized in Table 1. Next, the adsorbents of Examples 2 to 5 and Comparative Examples 1 and 2 were steamed in the same manner as in Example 1 and then the adsorption performance of propylene was evaluated. The results are shown in Table 1 below.

[0021]

[Table 1]

[0022]

[Table 2]

From Table 1, since the adsorbents according to Examples 1 to 5 are hexagonal columnar MFI-type zeolites, even after the steaming treatment, propylene adsorption is much higher than in Comparative Examples 1 and 2. It can be seen that it has performance.

[0024]

According to the adsorbent for purifying hydrocarbons in exhaust gas of the present invention, the adsorbent for hydrocarbons has a high adsorption performance even after the steaming treatment.

[Brief description of drawings]

FIG. 1 Crystal morphology of the zeolite obtained in Example 1 by SEM (magnification: 10,000 times)

FIG. 2 Crystal morphology of the zeolite obtained in Comparative Example 1 by SEM (magnification: 10,000 times)

FIG. 3 Crystal morphology of the zeolite obtained in Example 2 by SEM (magnification: 10,000 times)

FIG. 4 is a SEM crystal morphology of the zeolite obtained in Example 3 (magnification: 10,000 times).

FIG. 5: Crystal morphology of the zeolite obtained in Example 4 by SEM (magnification: 10,000 times)

FIG. 6 is a crystal morphology of the zeolite obtained in Example 5 by SEM (magnification: 10,000 times).

FIG. 7: Crystal morphology of the zeolite obtained in Comparative Example 2 by SEM (magnification: 10,000 times)

Claims (3)

[Claims] 1. An adsorbent for purifying hydrocarbons in exhaust gas, which comprises using MFI type zeolite having a hexagonal columnar crystal morphology. 2. SiO ₂ / Al ₂ of MFI type zeolite
The adsorbent for purifying hydrocarbons in exhaust gas according to claim 1, having an O ₃ molar ratio of 20 to 500. 3. The adsorbent for purifying hydrocarbons in exhaust gas according to claim 1, wherein the hexagonal columnar crystal size of MFI zeolite is 1 to 10 μm.