DE102009009579A1 - Coating the channels of honeycomb body with ceramic based suspension, useful e.g. to catalytic exhaust gas purification, comprises immersing the lower end of honeycomb body in suspension filled vessel, rotating the body and applying vacuum - Google Patents

Abstract

For coating the channels of a honeycomb body (1) with a ceramic-based suspension (4), the honeycomb body (1) is immersed in an impregnation vessel (3) filled with the suspension (4) to form the lower end region (10) of the honeycomb body (1 ) to fill with suspension (4), whereupon the honeycomb body (1) rotated by 180 ° and then applied to the lower end of the thus turned over, in its upper end region (10) with suspension (4) filled honeycomb body (1) abruptly a vacuum is to evenly distributed over the surface of the channels from the upper end region (10) sucked suspension.

Description

The The invention relates to a method and a device for Coating of honeycomb bodies. She also has the use the so coated honeycomb body to the object.

For the removal of pollutants from exhaust gases, thermal, catalytic and sorptive processes are used. Thermal processes lead to high energy costs in exhaust gases with low pollutant concentration. Sorptive processes generate waste that needs to be disposed of or reconditioned. Catalytic processes using coated honeycomb bodies in conjunction with high efficiency honeycomb catalysts, see DE 19 905 733 B4 , enable a highly efficient and energy saving operation.

extruded Honeycomb bodies are ideal carriers for catalytic Coatings, as they have very high geometric surfaces own and the ordered flow through parallel channels only causes low pressure loss.

The extruded honeycomb body itself have a very dense low porous surface, which is an additional porous layer as the carrier of the active catalytic needed effective substance. This usually exists from gamma-alumina suspensions.

To evenly coat such extruded honeycomb body, they are usually completely immersed in the suspension (slurry) such. In US Pat. No. 6,625,976 B1 described. The viscosity of the suspension can be only moderately high, otherwise the channels are not completely filled and the coating remains uneven. Due to the lower viscosity, the thickness of the adhering coating (washcoat) is low and the process of impregnation with slurry must be repeated several times. Due to the surface tension of the aqueous suspension, the corners are more strongly coated, which results in an undesirable rounding of the channels.

To Each dive will be followed by the channels blown free with compressed air. This process also often leads to a non-uniform layer thickness, the coating tends to be in the channel in the direction of gravity and the channel corners to condense.

Another variant will be in EP 0 327 880 described. In this case, the honeycomb body is clamped vertically in a suction device, attached a suction device below, then the suspension-filled channels are released row by row on a mobile top slotted plate and freed in succession. The excess suspension is recycled. The achievable suction speed is limited, which also a tracking of the coating is possible. The recycled pulp suspension has reacted physically through contact with the honeycomb body and also due to evaporation no longer having the same properties as the fresh suspension, which can lead to quality problems for further coatings.

Another embodiment of the coating is in CA 2 324 546 described. A honeycomb body is clamped in a vertical suction device to which vacuum can be applied from below. Above the honeycomb body, a tub is placed with sealing elements, which can be fed from above with the suspension. After the suspension has been applied from above, it can be sucked into the channels with a vacuum. The problem with this arrangement is that the suspension flowing in from above begins to penetrate into the channels and small irregularities in the inflow are intensified by the force of gravity, that is, a channel that is already filled, will draw more liquid by gravity and so reinforce the imbalance of the filling. As a result, it is hardly possible to produce a uniform filling before applying the vacuum. After applying the vacuum, the more heavily filled channels now receive an excess of coating and the less filled channels are deficient in coating. A uniform coating is not achieved.

task The invention is about the channels of a honeycomb body over their entire length with a coating of the same thickness to be provided, so in particular without rounded corners, where for provided the coating of the respective honeycomb body Amount of suspension substantially that for coating the honeycomb body required quantity, ie without a surplus to have to use suspension.

This is according to the invention with the characterized in claim 1 Procedure achieved. In claims 2 to 16 are preferred Embodiments of the invention Process reproduced. Claim 17 has a preferred device for carrying out the inventive Method for the subject matter, which is characterized by the features of the claims 18 to 30 is formed in an advantageous manner while yourself. the claim 31 to a preferred use of the inventive Process produced honeycomb body refers.

Thus, according to the method of the invention, in step a) the honeycomb body with its lower end immersed in a container filled with the suspension pot. Thus, the channels are filled in the lower end of the honeycomb body to the same level, ie to the same height with the suspension.

Preferably is the inner circumference of the watering vessel adapted to the outer periphery of the honeycomb body, that substantially all of the suspension in the drinking vessel in the channels is pressed when the honeycomb body is immersed in the drinking vessel.

By Turning the honeycomb body in step b) is the with the Suspension filled lower area of the honeycomb body turned up. Thus the suspension is in the upper end region of the channels.

in the next step c) is at the bottom of the honeycomb body abruptly applied a vacuum, with the result that the suspension is sucked down from the upper end area, and so, that a uniform coating of the channels over their entire length arises.

These uniform coating is on the thixotropic Attributed to the properties of the suspension. D. H. the slurry usually has a high viscosity, so that when the lower region filled with suspension has been turned upwards, in the upper part of the channels first sticks, so does not drain down.

By the subsequent vacuum surge is through the channels a large amount of air sucked in the shortest possible time, whereby the suspension in the channels high shear forces is exposed, leading to a sudden reduction in viscosity lead the thixotropic suspension. The then thin liquid suspension can do so over the entire surface of the channels evenly distributed. After the vacuum shock is the suspension again thick, so they now over the surface of the channels evenly distributed, adhering to the surface.

According to the invention so that with a precise dosage of the suspension a complete and even coating without loss Suspension possible.

Of the Honeycomb is preferably by an extruded formed ceramic honeycomb body, such as mullite, Cordierite or the like ceramic masses.

The Channels of the honeycomb body can be a hydraulic Diameter of, for example, 1 to 12 mm, wherein below the hydraulic diameter of the quotient of the 4-fold cross-sectional area of the channel is to be provided by the circumference.

The honeycomb body coated with the method according to the invention is preferably intended for catalysts, in particular catalysts for exhaust gas purification. For this purpose, a coating is formed with the suspension on the surface of the channels, which is referred to as a washcoat. For the preparation of the washcoat, an aqueous suspension of a binder and a ceramic powder is preferably used. The binder may, for. Example, colloidal alumina (Al ₂ O ₃ ), silicon oxide (SiO ₂ ) or zirconium oxide (ZrO ₂ ), the ceramic powder Al ₂ O ₃ , in particular gamma-Al ₂ O ₃ , TiO ₂ , SiO ₂ or ZrO ₂ .

Based on the solids content of the suspension (slurry) the binder content preferably 5 to 30 wt .-% and the content of the ceramic powder is preferably 70 to 90% by weight.

The Viscosity of the suspension is preferably with water 0.05 to 1, in particular 0.1 to 0.5 Pa · sec set.

By the high inner surface of the washcoat becomes a very realized large effective area. In the washcoat the catalytically active components are stored. This can the washcoat then provided with the active component become. However, the storage preferably takes place in that the catalytically active component or its precursor of the suspension is added, from which the washcoat is formed.

When Catalytically active component may be a metal oxide or a noble metal be used. As metal oxide copper or manganese oxide can be used, while as precious metals, especially a platinum group metal, So in particular platinum, palladium or rhodium is used.

there the suspension is an aqueous solution of a Salt of the metal of the metal oxide or the precious metal or platinum metal added. The salt may be, for example, a nitrate, chloride, Sulfate, optionally a complex salt.

there becomes the copper or manganese salt of the aqueous suspension in a concentration of 5 to 50 g / l suspension added and the salt of the platinum group metal in one concentration from 0.3 to 3 g / l suspension.

To corresponds to the immersion of the honeycomb body in the drinking vessel the level of suspension in the channels is preferably 10 to 30% of the height or length of the honeycomb body.

The Vacuum, which abruptly at the upper end with suspension filled honeycomb body is applied, at least at the beginning, preferably throughout the coating less than 0.3 bar, in particular less than 0.1 bar absolute.

The Apparatus for carrying out the inventive Method essentially comprises the drinking vessel to Inclusion of the suspension, in which the honeycomb body with its lower end portion is immersed, also a connector, on the outer circumference of the honeycomb body on the immersed end portion opposite end portion can be applied gas-tight, a device to which the honeycomb body is rotatably fixed by 180 °, and a vacuum source, the with the connector for abrupt application of a Vacuum is flexibly connected.

Of the Inner circumference of the watering vessel is included to the outer periphery of the honeycomb body preferably adjusted so that between the drinking vessel and the honeycomb body when dipping the honeycomb body in the drinking vessel a distance of maximum 1 mm, so when immersing the honeycomb body in the drinking vessel essentially the entire Suspension in the drinking vessel in the channels of the honeycomb body is pressed.

The Height of the pot can be between 20 and 40%, in particular 25 to 30% of the height of the honeycomb body be.

In order to the vacuum of the vacuum source abruptly to the honeycomb body can be created, preferably several measures are taken.

So the vacuum source is preferably through an evacuation chamber educated. The evacuation chamber has a large volume preferably 100 to 1,000 times, preferably 200 to 500 times the outer volume of the honeycomb body, So that from the two end faces and the side surfaces corresponds to the volume formed by the honeycomb body.

there the evacuation chamber is preferably at a pressure of at least 0.3 bar absolute, preferably evacuated at least 0.1 bar absolute.

to Connection of the evacuation chamber with the connector is further preferably a vacuum-resistant tube with a large Diameter used, namely a hose with a cross-sectional area, at least 30%, preferably at least 50%, especially 80-100% the cross-sectional area of the honeycomb body corresponds. Of the Hose can be through a metal corrugated hose or the like be formed. By connecting the evacuation chamber with the fitting through a hose, the honeycomb body be rotated in step b).

After all is preferably a quick-closing valve or the like shut-off between the evacuation chamber and the fitting used that has a large opening cross-section and in a short time of preferably less than 0.2 Seconds, especially less than 0.1 seconds completely open leaves. This can z. B. an electropneumatically actuated butterfly valve be used.

to Evacuation of the evacuation chamber is preferably a vacuum pump with a nominal capacity of at least 30 times, preferably 50 to 70 times the outer volume of the honeycomb body used per second. Due to the high flow rate of the Vacuum pump can according to the invention a high production capacity be achieved on coated honeycomb bodies. So can the time for coating a honeycomb body according to the invention only 30 seconds or less.

Around to prevent the abrupt application of the vacuum to the Honeycomb particles of the suspension or other debris in get the vacuum pump, is preferably a shut-off, for example a flap, provided between the evacuation chamber and the vacuum pump. This obturator is closed when the vacuum on the honeycomb body is created.

The mentioned particles can then move by gravity in the evacuation chamber.

Around fine particles, for example droplets of the colloidal Binders of the suspension is also between evacuation chamber and vacuum pump provided a fine filter.

The honeycomb bodies coated according to the invention and provided with a catalytic component can be used, for example, as catalysts for cleaning the exhaust gases of internal combustion engines. A further application is, for example, the regenerative catalytic exhaust gas purification. In this case, the exhaust gas stream flows through at least two honeycomb bodies arranged adjacent to one another with at least one honeycomb body layer being catalytically coated in the hot region according to the invention, while the other honeycomb body layers are uncoated and merely serve as heat accumulators. A facility for regenerative thermal / catalytic exhaust gas purification with such honeycomb bodies is, for example, in EP 0 472 605 B1 and DE 9905733.8 described.

below the invention with reference to the accompanying drawings by way of example described in more detail, whose only figure schematically the Coating of a honeycomb body with an embodiment of the inventive device shows.

Thereafter, the honeycomb body 1 in step a) according to the arrow 2 in a trough shaped as a trough 3 dipped with a predefined amount of an aqueous suspension 4 is filled on a ceramic basis. The predefined amount is the required amount previously determined for complete coating, optionally with a slight excess of at most 5% by weight of the material used. The channels, not shown, of the honeycomb body 1 are perpendicular, so that the openings of the channels at the upper and lower end side of the illustrated honeycomb body 1 are arranged.

The upper end of the honeycomb body 1 is gas-tight on a hood-shaped connection piece 5 attached, via a hose 6 with an evacuation chamber 7 connected is. Between the connection piece 5 and the evacuation chamber 7 is a quick-closing valve 8th intended.

For immersing the lower end portion of the top of the fitting 5 clamped honeycomb body 1 in the drinking vessel 3 an unillustrated linear motor is provided. The connection piece 5 at the same time forms part of the support of the honeycomb body 1 ,

The inner dimensions of the watering vessel 3 are doing to the outer dimensions of the honeycomb body 1 adjusted so that the suspension 4 in the drinking vessel 3 into the channels of the honeycomb body 1 is pressed, as by the arrows 9 indicated when the honeycomb body 1 into the drinking vessel 3 is dipped.

Supported by the force of gravity, the lower range becomes the principle of communicating tubes 10 the channels of the honeycomb body 1 with the suspension 4 to the same level 11 filled.

According to step b), the honeycomb body becomes 1 immediately after its lower end area 10 to the level 11 has been filled to the horizontal axis 12 rotated by 180 °, leaving the filled end area 10 with the drinking vessel 3 is arranged above. The now empty pot 3 is then removed.

According to step c) then the valve 8th opened and thus the connector 5 with the evacuation chamber 7 abruptly connected so that the suspension 4 in the upper end region 10 is subjected to a vacuum shock. This will make the suspension 4 in the upper end area 10 evenly distributed over the surface of the channels. Subsequently, the valve 8th closed and the honeycomb body 1 from the connector 5 away.

To the evacuation vessel 7 is at the top of a line 15 with a fine filter 12 and a vacuum pump 13 connected. Between the fine filter 12 and the evacuation chamber 7 is a shut-off device 14 , For example, a flap provided. Through the vacuum pump 13 can the evacuation chamber 7 , which for example has a volume of 1 cubic meter, within z. B. 30 seconds to an absolute pressure of 0.1 bar.

It It is understood that all the described processes can be performed automatically.

example 1

A suspension of 1.2 kg of Al ₂ O ₃ powder with 2-5 μm grain size and 0.3 kg of Al ₂ O ₃ binder in 1.5 kg of water is prepared in a stirred vessel. The mixture is stirred for 2 h; Subsequently, 15 g of platinum and 15 g of palladium are stirred in the form of 10% nitrate salt solution. Thereafter, the viscosity of the suspension is 0.25 Pa · sec. Then a volume of 0.3 liters of this suspension in the pot 3 submitted with a footprint in the dimensions 152 × 152 mm.

A honeycomb body measuring 150 × 150 × 150 mm and a cell count of 120 csi (cells per square inch) is inserted into the rotatable connector 5 clamped by clamping the suction device, The suction device is a flexible corrugated pipe 6 with 100 mm diameter with the evacuation chamber 7 and the quick-closing valve 8th connected to the same diameter. From the evacuation chamber 7 An overhead connection leads over the fine filter 12 to the vacuum pump 13 with a capacity of 10 m ³ / min.

The honeycomb body 1 is turned 180 ° downwards and vertically by lowering into the filled, exactly fitting pot 4 immersed to the ground.

The Capillary action draws the suspension into the channels.

Thereafter, the honeycomb body 1 with the attached trough 4 180 ° upwards turns and then the drinking vessel 4 away.

Then via the electrically actuated valve 8th the way to the evacuation chamber 7 with 1 m ³ content released for 0.5 sec. The suspension is uniform in the total length of the channels of the honeycomb body 1 sucked, there is no significant excess of slurry that enters the vacuum vessel; ie at most 5 vol .-% at most. Due to the high speed of suction, the channels are evenly coated down to the corners and there is then no detention of the suspension in the channels.

Subsequently The coated honeycomb body is dried and at 400 ° C. conditioned in hot air stream.

The Light-off temperature for octane of the catalyst thus prepared, the temperature at which the octane is replaced by oxygen Air is oxidized, is 240 ° C.

Example 2

A suspension of 0.85 kg of Al ₂ O ₃ powder with 2-5 μm grain size and 0.15 kg of Al ₂ O ₃ binder in 0.88 kg of water is prepared in a stirred vessel. The mixture is stirred for 1 h, then 150 g of copper and 300 g of manganese are stirred in the form of ammonium-stabilized nitrate solution. Thereafter, the viscosity of the suspension is 0.4 Pa · sec.

Of the Honeycomb body is then in the same manner as in the example 1 coated with the suspension. The conditioning of the coated honeycomb body but at 300 ° C.

The Light-off temperature for carbon monoxide (CO) of the so produced Catalyst is 110 ° C.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 19905733 B4 [0002]
• - US 6625976 B1 [0005]
• - EP 0327880 [0007]
• - CA 2324546 [0008]
• EP 0472605 B1 [0041]
• - DE 9905733 [0041]

Claims (33)

Method for coating the channels of a honeycomb body ( 1 ) with a ceramic-based suspension, characterized by the following steps: a) the honeycomb body ( 1 ) with its lower end in one with the suspension ( 4 ) filled drinking vessel ( 3 ) dipped to the channels at the same level ( 11 ) in the lower end region ( 10 ) of the honeycomb body ( 1 ) with suspension ( 4 ) to fill; b) The honeycomb body ( 1 ) is rotated through 180 ° to the suspension (with 4 ) filled end region ( 10 ) to turn up; and c) to the lower end of the so turned over, in its upper end ( 10 ) with suspension ( 4 ) filled honeycomb body ( 1 ), a vacuum is applied abruptly to the upper end region ( 10 ) sucked suspension ( 4 ) evenly over the surface of the channels. Method according to claim 1, characterized in that that as suspension an aqueous suspension of a Binder and a ceramic powder is used. Method according to claim 2, characterized in that that the suspension of 5 to 30 wt .-% of binder and 70 to 90 Wt .-% ceramic powder, based on the solids content, contains. Method according to claim 2 or 3, characterized that the binder of colloidal alumina, silica and / or zirconium oxide. Method according to claim 2 or 3, characterized that the ceramic powder of alumina, titania, silica and / or zirconium oxide. Method according to one of the preceding claims, characterized in that in the coating of the channels a catalytically active component is provided. Method according to Claim 6, characterized the catalytically active component is a metal oxide or a noble metal is. Method according to claim 7, characterized in that that the metal oxide is copper or manganese oxide and the precious metal at least is a platinum group metal. Method according to one of claims 7 or 8, characterized in that the suspension is a solution a salt of the metal oxide or the noble metal added becomes. Method according to claim 8 or 9, characterized that the copper or manganese salt in the suspension in a concentration from 5 to 50 g / l suspension or the salt of the platinum group metal in a concentration of 0.3 to 3 g / l of the suspension. Method according to one of the preceding claims, characterized in that the suspension has a viscosity from 0.05 to 1, preferably 0.2 to 0.5 Pa · sec. A method according to claim 1, characterized in that the inner circumference of the drinking vessel ( 3 ) to the outer periphery of the honeycomb body ( 1 ) is adjusted so that the suspension ( 4 ) in the drinking vessel ( 3 ) into the channels of the honeycomb body ( 1 ) is pressed when the honeycomb body ( 1 ) in the suspension ( 4 ) in the drinking vessel ( 3 ) is dipped. Process according to claim 1 or 12, characterized in that the amount of suspension ( 4 ) in the drinking vessel ( 3 ) before immersing the honeycomb body ( 1 ) the amount necessary for coating the surface of the channels of the honeycomb body ( 1 ) corresponds. Method according to claim 1 or 12, characterized in that the level ( 11 ) of the suspension ( 4 ) in the channels after immersing the honeycomb body ( 1 ) in the drinking vessel ( 3 ) 10 to 30% of the height (H) of the honeycomb body ( 1 ) corresponds. A method according to claim 1, characterized in that after the sudden application of the vacuum at most 5 wt .-% of the suspension from the honeycomb body ( 1 ) exit. Method according to claim 1, characterized in that that at least at the beginning of the sudden application of the vacuum the vacuum has a pressure of less than 0.3, preferably 0.2 to 0.1 bar absolute. Device for carrying out the method according to one of the preceding claims, characterized by an impregnation vessel ( 3 ) for receiving the suspension ( 4 ) into which the honeycomb body ( 1 ), a fitting ( 5 ), which on the outer circumference of the honeycomb body ( 1 ) at which the immersed end region ( 10 ) opposite end portion, a device with which the drinking vessel ( 3 ) about a horizontal axis ( 12 ) is rotatable, and a vacuum source connected to the connector ( 5 ) is connectable to the sudden application of a vacuum. Apparatus according to claim 17, characterized in that the inner circumference of the drinking vessel ( 3 ) on the outer periphery of the honeycomb body ( 1 ) is adjusted so that between the drinking vessel ( 3 ) and the honeycomb body ( 1 ) when dipping the honeycomb body ( 1 ) into the drinking vessel ( 3 ) is a distance of a maximum of one millimeter. Apparatus according to claim 17 or 18, characterized in that the height (h) of the watering vessel between 10 and 50%, preferably between 20 and 30% of the height (H) of the honeycomb body ( 1 ). Apparatus according to claim 17, characterized in that the vacuum source through an evacuation chamber ( 7 ) is formed. Apparatus according to claim 20, characterized in that the evacuation chamber ( 7 ) has a volume which is at least 100 times, preferably 200 to 400 times, the volume of the honeycomb body ( 1 ) corresponds. Apparatus according to claim 20 or 21, characterized in that in the evacuation chamber ( 7 ) is at most 0.3 bar absolute. Device according to one of claims 17 to 22, characterized in that for connecting the vacuum source with the connector ( 3 ) a hose ( 6 ) is provided. Device according to claim 23, characterized in that the hose ( 6 ) has a cross-sectional area which is at least 20%, preferably 50 to 100% of the cross-sectional area of the honeycomb body ( 1 ) corresponds. Apparatus according to claim 17, characterized in that the vacuum source via a quick-closing valve ( 8th ) with the connector ( 5 ) is connectable. Apparatus according to claim 25, characterized in that the quick-closing valve ( 8th ) is designed such that the time for the complete opening of the quick-closing valve ( 8th ) is less than 0.1 to 0.2 seconds. Apparatus according to claim 25 or 28, characterized in that the quick-acting valve ( 8th ) is formed by an electropneumatically operated butterfly valve. Apparatus according to claim 20, characterized in that for evacuation of the evacuation chamber ( 7 ) a vacuum pump ( 13 ) having a nominal delivery capacity of at least 30 times, preferably 50 to 70 times, the volume of the honeycomb body ( 1 ) is provided per second. Apparatus according to claim 28, characterized in that the evacuation chamber ( 7 ) with the vacuum pump ( 13 ) via a shut-off device ( 14 ) connected is. Apparatus according to claim 28 or 29, characterized in that the evacuation chamber ( 7 ) with the vacuum pump ( 13 ) via a fine filter ( 12 ) connected is. Device according to one of claims 17 to 30, characterized in that the steps described fully mechanized for coating or automated can be. Use of the honeycomb body coated according to one of Claims 1 to 16 ( 1 ) for the catalytic emission control Use of according to one of claims 1 to 16 coated honeycomb catalyst, characterized that the catalyst thus prepared as the topmost layer in a honeycomb heat storage elements equipped regenerative catalytic post-combustion plant is used.