JP3460364B2 - Method for producing hydrocarbon adsorbent - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hydrocarbon adsorbent, and more particularly to a method for producing a hydrocarbon adsorbent used in a device for purifying exhaust gas discharged from an internal combustion engine such as an automobile.

Conventionally, as an exhaust gas purifying catalyst for an internal combustion engine of an automobile or the like, three catalysts capable of simultaneously oxidizing carbon monoxide (CO) and hydrocarbons (HC) and reducing nitrogen oxides (NOx) have been proposed. The original catalyst is widely used. Such a catalyst is disclosed in, for example, Japanese Patent Publication No. 58-20307, for example, a noble metal such as palladium, platinum and rhodium in an alumina coat layer on a refractory carrier, and optionally cerium or a cocatalyst component. In most cases, a rare earth metal such as lanthanum or a base metal oxide such as nickel is added.

Such a conventional catalyst is strongly affected by the exhaust gas temperature and the set air-fuel ratio of the engine. The exhaust gas temperature at which the automobile catalyst can exert its purifying ability generally needs to be 300 ° C. or higher, and the air-fuel ratio is H.
The catalyst works effectively near the stoichiometric air-fuel ratio where the oxidation of C and CO and the reduction of NOx are balanced. Therefore, a conventional automobile equipped with an exhaust gas purification device that uses a three-way catalyst is installed at a position where the three-way catalyst works effectively, and the oxygen concentration in the exhaust system is detected to create a theoretical air-fuel mixture. Feedback control is performed so that the fuel ratio is maintained near the fuel ratio.

However, even if the conventional three-way catalyst is installed immediately after the exhaust manifold, the activity is low immediately after the engine start when the exhaust gas temperature is low (300 ° C. or less), and HC is exhausted immediately after start (cold start). Could be discharged as is without being purified.

As an exhaust gas purifying apparatus for solving the above-mentioned problems, there has been proposed one in which an HC trapper containing an adsorbent for adsorbing cold HC is arranged on the exhaust gas upstream side of a catalytic converter (Japanese Patent Laid-Open No. Hei 10-1999) 2-21124
No. 5).

[0006]

However, in the adsorbent disclosed in Japanese Unexamined Patent Publication (Kokai) No. Hei 2-212145, a foaming agent is used to form small pores in the zeolite layer. The agent has a drawback that it is apt to be clogged during honeycomb coating and has poor coating properties.

Therefore, the present invention has been made by paying attention to such a conventional problem, and by using silica sol having an elongated shape as an inorganic binder used in the zeolite slurry, a good coating property is ensured. , It is intended to provide a method for producing a hydrocarbon adsorbent capable of forming small pores in a zeolite layer, improving the diffusivity of hydrocarbons into zeolite pores, and improving adsorption performance. To do.

[0008]

The above objects of the present invention are as follows.
Zeolite powder and silica sol having an elongated shape with a ratio D1 / D2 of the particle size measured by the dynamic light scattering method (D1 nm) and the particle size measured by the nitrogen gas adsorption method (D2 nm) of 5 or more as an inorganic binder are added to zeolite powder. In addition, a method for producing a hydrocarbon adsorbent characterized in that a slurry is formed, and then the slurry is applied to a honeycomb-shaped monolith carrier, dried, and then fired to form a coat layer, is achieved.

The elongated silica sol of the present invention is described in JP-A-1-317115.
"Ratio D1 / D2 of particle size measured by dynamic light scattering method (D1 nm) and particle size measured by nitrogen gas adsorption method (D2 nm)
Is 5 or more, the D1 is 40 to 500 nanometers, and a non-elongated shape having a uniform thickness in the range of 5 to 40 nanometers by electron microscopy and an extension only in one plane. It means "a stable silica sol of 0.5 to 30% by weight of SiO ₂ in which crystalline colloidal silica is dispersed in a liquid solvent" and is commercially available.

In the present invention, the proportion of silica sol is preferably in the range of 5 to 30% by weight of SiO ₂ as a solid content in the coating amount. If the SiO ₂ content is less than 5% by weight, the coating layer will be easily peeled off.
Sufficient adsorption performance cannot be obtained.

The zeolite used in the present invention can be appropriately selected from known zeolites and used, for example, at least one selected from the group consisting of mordenite, USY, β-zeolite and ZSM-5. And the silica / alumina molar ratio is 50
It is preferable to use a zeolite in the range of up to 2000.

Next, the operation of the present invention will be described. According to the method for producing a hydrocarbon adsorbent of the present invention, the adsorbent is provided with small pores in the zeolite layer so that the hydrocarbon can be efficiently diffused into the coat layer. Therefore, a long and narrow silica sol is used as an inorganic binder in the zeolite slurry and applied to the honeycomb carrier. By using such an elongated silica sol, when the zeolites are bound to each other in the major axis direction of the sol, the bonding distance between the zeolite particles is wider than in the case of using a spherical silica sol, and the zeolites are bound to each other in the minor axis direction of the sol. When bonded with each other, the bonding distance between the zeolite particles is shortened and small holes of various diameters are generated, so that the gas diffusibility in the zeolite coat layer can be improved.

Japanese Unexamined Patent Publication (Kokai) No. 1-317115 describes a catalyst carrier, an adsorbent and the like which are preferably formed by molding into a catalyst carrier component and an adsorbent component using such a modified silica sol. When molding a product using a modified sol, attention is paid only to the point that the moldability is improved, but in the present invention, without performing molding, a zeolite powder and a modified sol and water are slurried into a honeycomb shape. It was newly found that the size of the voids between the zeolite powders can be controlled by applying it to the monolith carrier.

Further, since the silica sol has an elongated shape as described in JP-A-1-317115, it is difficult to form a smooth surface even in the contact portion between the zeolite layer and the honeycomb carrier, and conversely. An uneven surface is easily formed, and the adhesion between the honeycomb carrier and the zeolite layer can be improved.

[0015]

EXAMPLES The present invention will now be described in more detail by way of examples, which should not be construed as limiting the invention. Unless otherwise specified, the parts and percentages described below
Indicates parts by weight and% by weight, respectively.

Example 1 100 parts of USY (SiO ₂ / Al ₂ O ₃ = 50), an elongated silica sol (trade name: Snowtex OUP, manufactured by Nissan Chemical Industries, Ltd., specific gravity 1.099, pH 3.
1, viscosity 8.4 mPa.s. s, particle size 55 nm measured by dynamic light scattering method, particle size 12 n measured by nitrogen gas adsorption method
m, particle diameter 12 nm by observation with an electron microscope, SiO ₂ 1
45 parts by weight (5.6% by weight) and 85 parts of water were put into a magnetic pot, and mixed and ground for 40 minutes with a vibration mill device or for 6.5 hours with a universal ball mill device to produce a washcoat slurry. After the monolithic carrier of cordierite product was subjected to water absorption treatment by a suction coating method, the slurry prepared above was uniformly added to the entire cross section of the carrier and the excess slurry was removed by a suction coating method. Then, dry it at 400 ℃
It was calcined for about 1 hour.

As a result, about 60 g of USY zeolite /
The carrier is coated with a coating amount of L. Repeat the above wash coat, drying and baking twice more to obtain a total of about 1
Coated with 50 g / L of zeolite, 6 in air atmosphere
The adsorbent-1 was obtained by firing at 50 ° C for 4 hours.

Example 2 100 parts of β-zeolite (SiO ₂ / Al ₂ O ₃ = 100) powder, 65 parts of silica sol similar to Example 1 and 6 parts of water
Except for using 5 parts, the adsorbent was prepared in the same manner as in Example 1.
Got 2.

Example 3 ZSM-5 (SiO ₂ / Al ₂ O ₃ =) instead of 100 parts of β-zeolite (SiO ₂ / Al ₂ O ₃ = 100) powder
700) An adsorbent-3 was obtained in the same manner as in Example 2 except that 100 parts of powder was used.

[0020] Example 4 beta-zeolite (SiO ₂ / Al ₂ O ₃ = 100) instead of 100 parts of powdered mordenite (SiO ₂ / Al ₂ O ₃
= 200) Adsorbent-4 was obtained in exactly the same manner as in Example 2 except that 100 parts of powder was used.

Example 5 β-zeolite (SiO₂/ Al₂O₃= 100) powder
USY (SiO₂/ Al₂O₃= 5
0) 50 parts powder and ZSM-5 (SiO₂/ Al ₂O₃
= 700) The same as Example 2 except that 50 parts of powder was used.
Thus, Adsorbent-5 was obtained.

Example 6 USY (SiO ₂ / Al ₂ O ₃ = 5) was used in place of 100 parts of β-zeolite (SiO ₂ / Al ₂ O ₃ = 100) powder.
0) 50 parts of powder and β-zeolite (SiO ₂ / Al ₂
O ₃ = 50) Adsorbent-6 was obtained in the same manner as in Example 2 except that 50 parts of powder was used.

Example 7 100 parts of USY (SiO ₂ / Al ₂ O ₃ = 50) powder,
Elongated silica sol (trade name of Nissan Chemical Industries, Ltd .: Snowtex UP, specific gravity 1.132, pH 1
0.2, viscosity 17.0 mPa.s. s, particle diameter measured by dynamic light scattering method 55 nm, particle diameter measured by nitrogen gas adsorption method 12 nm, particle diameter 12 nm by electron microscope observation, Si
O ₂ 20.3% by weight) was used 35 parts and 95 parts of water to give the adsorbent -7 in the same manner as in Example 1.

Comparative Example 1 100 parts of USY (SiO ₂ / Al ₂ O ₃ = 50) powder,
Acidic silica sol (trade name of Nissan Chemical Industries: Snowtex-O, specific gravity 1.128, pH 2.61, viscosity 1.6 cp, SiO ₂ 20.4% by weight, particle size 12 n
m) Adsorbent-R1 was obtained in the same manner as in Example 1 except that 65 parts of water and 65 parts of water were used.

Comparative Example 2 β-zeolite (SiO ₂ / Al ₂ O ₃ = 50) was used instead of 100 parts of USY (SiO ₂ / Al ₂ O ₃ = 50) powder.
An adsorbent-R2 was obtained in exactly the same manner as in Comparative Example 1 except that 100 parts of the powder was used.

[0026] Comparative Example _{3 USY (SiO 2 / Al 2} O 3 = 50) ZSM-5 zeolite in place of 100 parts of the powder _{(SiO 2 / Al 2 O 3} =
700) Adsorbent-R3 was obtained in exactly the same manner as in Comparative Example 1 except that 100 parts of powder was used.

Using the adsorbents obtained in Examples 1 to 7 and Comparative Examples 1 to 3, the HC adsorption performance was evaluated under the following evaluation conditions. The results are shown in Table 1.

[0028]

[Table 1]

1) Catalyst capacity 60 cc 2) Model gas evaluation SV: 40000 / h HC 2000 ppm (C ₇ H ₈ ) N ₂ balance H ₂ O 10% addition The HC adsorption rate for the first 2 minutes was evaluated.

[0030]

As described above, according to the method for producing a hydrocarbon adsorbent of the present invention, a silica sol having an elongated shape is used as an inorganic binder when slurry is prepared by adding an inorganic binder and water to zeolite powder. By using them, the distance between the zeolite particles is expanded, the diffusibility of the exhaust gas is improved, and the hydrocarbon adsorbing ability can be efficiently performed.

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-5-57183 (JP, A) JP-A-4-284827 (JP, A) JP-A-4-210235 (JP, A) JP-A-4- 65314 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) B01J 20/18 B01D 53/04 F01N 3/24

Claims (3)

(57) [Claims] 1. The ratio D1 / D of the particle size (D1 nm) measured by the dynamic light scattering method and the particle size (D2 nm) measured by the nitrogen gas adsorption method to the zeolite powder as an inorganic binder.
Carbonization characterized by adding a silica sol having an elongated shape in which 2 is 5 or more and water to form a slurry, and then applying the slurry to a honeycomb-shaped monolith carrier, drying and firing to form a coat layer. Method for manufacturing hydrogen adsorbent. 2. The zeolite is mordenite, USY, β
-The method for producing a hydrocarbon adsorbent according to claim 1, which is at least one selected from the group consisting of zeolite and ZSM-5. 3. A silica / alumina molar ratio of 50 to 20.
The method for producing a hydrocarbon adsorbent according to claim 1 or 2, characterized in that zeolite in the range of 00 is used.