JPH07100137B2 - Exhaust gas adsorbent manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an adsorbent for adsorbing hydrocarbons (HC) in exhaust gas of an automobile.

(Prior Art) A pellet-shaped or monolith-type catalyst is used for purifying exhaust gas of an automobile. Of the harmful components (HC, CO, NO _X ) in the exhaust gas, the purification of HC, especially with a catalyst,
Exhaust gas temperature has a strong effect, and a temperature of 300 ° C or higher is generally required even when a precious metal catalyst is used. Therefore, when the exhaust gas temperature is low, such as immediately after the engine is started, the HC
Is hard to be purified by a catalyst. Moreover, since a large amount of HC is discharged immediately after the engine is started, the emission of HC (hereinafter referred to as cold HC) when the temperature of the exhaust gas is low accounts for a large proportion of the total. Therefore, it has been an issue to suppress the emission of cold HC.

As an automobile exhaust gas purifying device for solving the above problems, an exhaust system of an engine is provided with a purifying catalyst for harmful components in exhaust gas, and upstream of the catalyst, adsorption for adsorbing cold HC It is proposed that the materials are arranged (Japanese Patent Application No. 63-226070 and Japanese Patent Application Laid-Open No. 2-75327). In the exhaust gas purification device, HC is trapped in the adsorbent at low temperatures, and HC is desorbed from the adsorbent at high temperatures and purified by a catalyst. As the adsorbent, for example, a monolith carrier coated with zeolite has been proposed because zeolite has excellent adsorption performance.

Conventionally, a ceramic carrier made of a ceramic such as cordierite or a metal carrier made of a high heat resistant stainless steel such as an Fe—Cr—Al alloy has been used as a monolith carrier for supporting an exhaust gas purification catalyst. However, when it is used for an exhaust gas purification system of an automobile, it is necessary to particularly consider mountability, pressure loss and the like, and the metal carrier is more advantageous in these points. Therefore, in recent years, the use of metal carriers as carriers for exhaust gas purification catalysts has been increasing.

Similarly, in the case of a monolith carrier used as an HC adsorbent, a metal carrier is considered to be more advantageous in terms of mountability and pressure loss.

(Problems to be Solved by the Invention) However, since zeolite has poor adhesion to metal, when coated on a metal carrier, there is a problem that the amount of adhesion per coating is extremely small. For this reason, the number of coatings must be increased in order to deposit a sufficient amount to obtain the desired adsorption performance. When the number of coats increases, the time and labor required for production increase, the production cost increases, and the number of firing increases, which causes a problem that zeolite crystals collapse and HC adsorption performance decreases. Therefore, the present invention provides a method capable of excellently coating zeolite when producing an HC adsorbent using a metal carrier having excellent loadability and low pressure loss,
It is an object to produce an HC adsorbent to which a desired amount of zeolite is attached without increasing the number of times of coating.

(Means for Solving the Problem) In order to achieve the above object, the method for producing an exhaust gas adsorbent according to the present invention is such that an alumina slurry is adhered onto the surface of a monolithic metal carrier, dried, and fired. This is characterized in that after the alumina is coated by this, the zeolite slurry is further adhered onto it, dried and calcined to coat the zeolite.

As the monolith-type metal carrier, a generally widely used high heat resistant stainless steel, for example, one made of Fe-Cr-Al alloy can be used.

The coating of alumina and zeolites can be carried out by repeating the operation of immersing the carrier in a washcoat slurry containing alumina or zeolite, drying and firing once or several times.

The coating amount of alumina varies depending on the number of cells of the carrier and the like, but an amount corresponding to 5 to 30 g / volume of the monolith carrier is preferable.

As the zeolite, it is preferable to use H-type mordenite or HY-type zeolite which has particularly excellent adsorption performance. In this case, Na-type mordenite or Na-Y-type zeolite is coated on the carrier, Na ⁺ ions are converted to NH ₄ ⁺ ions, and then heated to H ⁺ ions to form H-type mordenite or H-Y-type zeolite. However, the Na ⁺ ion may be directly converted into the H ⁺ ion by using hydrochloric acid.

(Operation) In the method for producing the HC adsorbent of the present invention, since the adhesion of alumina to the metal carrier is good and the affinity between alumina and zeolite is high, it is possible to apply the alumina to the carrier once after the application. The zeolite coating amount is large, and the zeolite is coated well with a small number of coatings.

(Examples) Hereinafter, the present invention will be described in more detail with reference to Examples. In the examples, “parts” means “parts by weight”, and the coating amount (g /) of alumina or zeolite is 1 volume of the monolith carrier.
Indicates the amount per hit.

Example: 10 parts of γ-alumina powder, 7 parts of alumina sol (10% by weight) and 20 parts of water were mixed and stirred to prepare a slurry. An Fe-Ce-Al alloy monolithic carrier (cell number 400, volume 1) was immersed in this slurry, pulled up, excess slurry was blown off, dried at 100 ° C for 1 hour, and then calcined at 500 ° C for 3 hours. Thereby, the carrier is coated with alumina in an amount of 8 g /.

Na-type mordenite 100 parts, alumina sol (10 wt%) 140
Parts and 30 parts of water are mixed, the pH is adjusted with an Al (NO ₃ ) ₂ aqueous solution, and the alumina-coated monolith carrier obtained above is immersed in a slurry having a viscosity of 150 cps prepared by stirring. After pulling up and blowing off the excess slurry, drying at 100 ° C. for 1 hour and baking at 500 ° C. for 3 hours, Na-type mordenite is coated on the upper surface of the alumina layer at a coating amount of 60 g /.

The above operation, that is, the immersion in the mordenite slurry, the drying and the calcination, is repeated once more. As a result, Na-type mordenite is coated at a total coating amount of 120 g /.

Next, the obtained Na-type mordenite-coated monolith carrier is immersed in a 1N ammonium chloride aqueous solution to convert Na ⁺ ions into NHa ⁺ ions. Then, by heating at 300 ° C. for 1 hour, NH ₄ ⁺ ions are further converted into H ⁺ ions. As a result, an HC adsorbent coated with H-type mordenite at a coating amount of 120 g / is obtained.

Comparative Example 1: The same monolithic carrier as used in Example 1 was dipped in the same Na-type mordenite slurry as used in Example 1, pulled up, excess slurry was blown off, and dried at 100 ° C for 1 hour. After that, it is baked at 500 ° C. for 3 hours. As a result, the carrier is coated with Na-type mordenite at a coating amount of about 5 g /. This coating amount is remarkably lower than the coating amount (60 g /) obtained in one coating in Example 1.

Comparative Example 2 A monolithic carrier made of cordierite (cell number 400, volume 1) was immersed in the same Na-type mordenite slurry as that used in Example 1, pulled up, excess slurry was blown off, and dried at 100 ° C. for 1 hour. After that, it is baked at 500 ° C. for 3 hours, so that the coating amount of Na-type mordenite is 60 g /. The above operation, that is, dipping and blowing of the slurry,
Drying and firing is repeated once more. This gives Na
Type mordenite is coated at a total coating amount of 120 g /. Then, Na ⁺ ions were added to H by the same method as in Example 1.
^When changed to ⁺ ions, an HC adsorbent coated with H-type mordenite at a coating amount of 120 g / is obtained.

Test Example The methods of Example and Comparative Example 2 are performed using a test monolith carrier. As the test monolith carrier, a Fe-Cr-Al alloy monolith carrier (cell number 400, volume 35 cc) and cordierite monolith carrier (cell number 400, volume 35 cc) are used.
Each is coated with Na-type mordenite at a coating amount of 120 g /. The adsorption performance of each of the adsorbents thus obtained (the product of the example and the product of the comparative example) was tested using the test apparatus 1 shown in FIG.

The test uses a model gas consisting of nitrogen gas containing C ₃ H ₆ : 840 ppm and O ₂ : 0.84%, N ₂ : 5.6 / min, space velocity (S.
V): 1.7 hr ⁻¹ , inlet gas temperature: 200 ° C., after passing the model gas through water 2, it is heated by heater 3 and adsorbent 4
(Example product or comparative product)
This is done by measuring the amount of C ₃ H ₆ .

The adsorption performance is evaluated by the C ₃ H ₆ adsorption rate. C ₃ H ₆ adsorption rate is
Detected by the HC meter within 10 minutes after starting the model gas flow using the monolith carrier not coated with zeolite
Obtain the amount of C ₃ H ₆ gas (A) and the amount of C ₃ H ₆ gas (B) detected by the HC meter within 10 minutes after starting to flow the model gas using the example product or the comparative example product, Calculated according to the following formula.

The results are shown in the graph of FIG. As is clear from the graph, the C ₃ H ₆ adsorption rates of the example product and the comparative example product are almost the same, and the adsorption performances of the example product and the comparative example are similar.
Therefore, according to the method of the present invention, the coating amount of the zeolite on the metal carrier per one time becomes almost the same as the coating amount on the cordierite carrier per one time, and the same coating amount and adsorption performance can be obtained even at the same coating times. It is clear that

(Effect of the invention) In the method for producing the HC adsorbent of the present invention, the alumina slurry is deposited on the surface of the monolith-type metal carrier and dried, and after the alumina is coated by firing, the zeolite is further deposited thereon. Since the zeolite is coated by attaching the slurry, drying and firing, the zeolite is well coated, and the same coating amount as the cordierite carrier can be coated with the same coating amount to obtain the same adsorption performance. be able to. Therefore, an HC adsorbent using a metal carrier that has excellent loadability, pressure loss, and good adsorption performance without causing problems such as labor, cost increase, and zeolite crystal destruction due to increasing the number of coatings It can be manufactured.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a test device for measuring the C ₃ H ₆ adsorption rate of the HC adsorbent, and FIG. 2 is a graph showing the adsorption rate of each adsorbent.

Claims (1)

[Claims] 1. A monolith-type metal carrier is coated with alumina slurry by adhering it onto the surface of the monolithic metal carrier, drying and firing to coat the alumina, and then further adhering zeolite slurry onto it to dry and firing. A method for producing an exhaust gas adsorbent, which comprises coating zeolite.