DE102005054946B4 - Process for coating or impregnating the surfaces of a catalyst support - Google Patents

Abstract

A method of coating or impregnating a catalyst carrier (30) having internal cavities having internal surfaces, comprising the following steps:
a) introducing the catalyst support (30) having inner surfaces in a chamber (20) in which a by suction of the chamber (20) caused turbulent flow and a negative pressure prevails;
b) introducing a coating dispersion or an impregnating solution into the chamber (20).
c) forming a mixture of air / coating dispersion or air / impregnation solution
d) Continuously passing the mixture from step c) through the catalyst support (30).

Description

The The present invention relates to a method of coating or for impregnation the inner surfaces a catalyst carrier.

Methods for coating or impregnating the inner surfaces of catalyst supports are known in the art. For example, this describes DE 29 02 073 C2 a process for coating ceramic monolithic catalyst supports in which the catalyst support is exposed to a vacuum and treated with a high surface area alumina coating washcoat, then the excess slurry is removed and the catalyst support is subsequently dried and calcined to form the alumina coating either immersing the catalyst support in the alumina coating slurry or sucking the slurry applied to an upper end of the catalyst support through the catalyst support under applied vacuum pressure, thereby continuing the applied vacuum to remove blockages in blocking passage, with the vacuum of the required height is maintained when the number of blocked passageways during the vacuum treatment increases more and more.

The EP 0 980 710 B1 describes a method for coating the inner flow channels of a monolithic, cylindrically shaped catalyst support with a coating dispersion, wherein the support has two end faces which are interconnected by flow channels arranged parallel to the cylinder axis. In the method, the catalyst support is oriented vertically, a predetermined amount of the coating dispersion is applied to the upper end surface of the support body, ie the channels are completely filled and sucked through the flow channels, wherein excess coating dispersion is removed from the flow channels by suction of the flow channels. The coating dispersion is drawn through the flow channels at a flow rate of 0.1 to 1 m / s, and after completion of the suction suction, excess coating dispersion is removed from the flow channels by applying a suction pulse from below, the suction air flowing at a flow rate between 40 and 1 m / s sucked through the flow channels and the discharged with the air flow excess coating dispersion within a time of less than 100 ms after leaving the catalyst support body is separated from the air flow.

The EP 0 941 763 B1 relates to a method for coating the flow channels of a cylindrically shaped, honeycomb catalyst body with a dispersion coating by filling the vertically oriented flow channels with a filling amount of the coating dispersion through the lower end face of the catalyst body and then draining and sucking down the flow channels and drying and calcining the catalyst body. In this method, the flow channels are filled with a filling amount that is up to 10% greater than the void volume of the flow channels, so that the coating dispersion after completion of the filling process exceeds the upper end face of the catalyst. Thereafter, the supernatant coating dispersion is removed prior to emptying the flow channels, and then the flow channels are emptied and vacuumed by a suction pulse generated by connecting a vacuum container to the lower face of the catalyst body, the time between the start of the filling operation and the end of the Emptying is not more than 5 seconds.

The in the prior art method for coating of Catalyst supports is mean that first in a first process step, the internal cavities in the catalyst body as z. As pores, channels etc. completely be filled with the coating dispersion. In a second Step is the excess coating dispersion blown or sucked from one side of the catalyst carrier. Continuous coating or loading of the inner surfaces of the Catalyst support, more precisely, the surfaces the internal cavities in the catalyst body is not possible.

One Another disadvantage of the method of the prior art in that, for example, during suction, the suction force on the Dimensions of the catalyst carrier decreases. It remains in the inner cavities, the relatively far away from the suction side of the catalyst support, a size Amount of excess coating dispersion, while relatively close located on the suction side cavities due to high suction may even be exposed by the coating dispersion. by virtue of this circumstance have the according to the in the prior art be written Method coated catalyst support a Schichtdickegradienten on, wherein the layer thickness at the inner surfaces of the catalyst support tapers in the direction of the suction side.

Moreover, when applying the suction device to the catalyst carrier, coating dispersion is transferred to the suction device, which dries due to the air flow. Will the Suction device is not cleaned after each suction, so that over time, the so-called "tree cake effect" occurs, in which the dried coating dispersion deposited layer by layer on components of the suction device and so this tapers also the loading of the catalyst support with coating dispersion.

Farther leads the Deposition of the coating material of the coating dispersion on the suction device to a loss of coating dispersion, there once off or dried coating dispersion no longer for the rest Be returned to use can.

task The object of the present invention was therefore to provide a method with which catalyst charges, the inner surfaces exhibit with one as possible low loss of coating dispersion or impregnation solution, in particular a precious metal solution, and also evenly coated or impregnated can be.

• a) Einbringen der Katalysatorträger, die innere Oberflächen aufweisen in eine Kammer, in der eine durch eine Besaugung der Kammer bewirkte Strömung sowie ein Unterdruck herrscht;
• b) Einleiten einer Beschichtungsdispersion oder einer Imprägnierlösung in die Kammer.
• c) Bilden eines Gemisches Luft/Beschichtungsdispersion bzw. Luft/Imprägnierlösung
• d) Kontinuierliches Durchführen des Gemisches aus Schritt c) durch den Katalysatorträger

This object is achieved according to the invention by a method for coating or impregnating a catalyst support having internal cavities with internal surfaces, the method comprising the following steps:

• a) introducing the catalyst support having inner surfaces in a chamber in which there is a caused by a suction of the chamber flow and a negative pressure;
• b) introducing a coating dispersion or an impregnating solution into the chamber.
• c) forming a mixture of air / coating dispersion or air / impregnation solution
• d) Continuously passing the mixture from step c) through the catalyst support

Surprisingly It was found that the inner surfaces in the inner cavities of the Catalyst support ,, in a chamber, in through a through a suction of the chamber, d. H. by a continuously applied negative pressure, caused turbulent flow prevails, from a introduced into the chamber coating dispersion or Impregnation solution largely evenly coated or impregnated become. Both the inner and - provided the desired - the outer surface of the catalyst support be over the dimensions of the catalyst support largely uniformly coated away or substantially uniformly impregnated. It is important in this context that the internal cavities at least partially communicate with each other, so that passing through of fluids through the catalyst body is possible.

The inventive method can be either in batch mode, ie batchwise or continuously operate. It is particularly advantageous if the method is continuously operated in a continuous process. This will ensure that the catalyst carrier in big Numbers, example, for the emission control in motor vehicles, and thus as possible economical can be produced.

Of the Term "catalyst carrier with inner surface (s) denotes in this case known from the prior art geometric Body, as a carrier for catalysts can serve or themselves can be constructed of catalytically active material, the inner, mostly interconnected cavities, such as Pores, channels, Have fiber structures etc, so that the cavities have so-called inner surfaces. This z. B. catalyst support meant, usually in chemical engineering or in automotive engineering be used. The catalyst support is preferably catalyst support molding, preferably to foams, in particular Metal foams, Nonwovens or structured honeycomb bodies, such as As monoliths, for example, from alumina, silica Titanium dioxide, metals and metal alloys are formed.

One Another advantage of the method according to the invention is that the inner cavities in contrast to the prior art methods by the permanently applied negative pressure during the coating / impregnation step remain free and thus the two process steps of the state of Technology, namely the filling the internal cavities and emptying in a single step.

Of the Term "negative pressure" refers to any pressure which is below the normal standard pressure of 1013 mbar. The while the method according to the invention applied negative pressure hangs from the catalyst bodies to be coated. At a monolith with z. 200 cpsi (cells per square inch) and laminar continuous Channels lies the negative pressure at 50 mbar, d. H. it corresponds to a pressure of 963 mbar. In a foam structure, however, with pores with an average diameter of 500 μm is the negative pressure about 100-250 mbar, d. H. it corresponds to a pressure of 763-913 mbar.

The The coating dispersion or the impregnation / impregnation solution is introduced via the coating dispersion Person skilled in the known means, such as nozzles, pumps, slots, pipes Etc.

The inventive implementation of the mixture in step d) depends on the one from the spatial density of the internal cavities (in the case of pores, this refers to the porosity) and their geometry (elongated channels, curved channels, fiber structures, etc.), the viscosity of the coating dispersion / impregnation solution, and, if the process is carried out continuously the rate of transport of the shaped catalyst bodies through the chamber.

The inventive solution further the advantage that the loss of coating dispersion or impregnation solution extremely low is. For example, the process is at room temperature with water as a solvent for the Coating dispersion or for the impregnating solution carried out, so Due to the reduced pressure in the chamber, the process is closer to the corresponding dew point of the solvent operated as at normal pressure, resulting in increased solvent vapor pressure in the Chamber entails. In the chamber introduced coating dispersion or impregnation solution, the For example, on the inner surfaces of the Chamber or on surfaces precipitates the aspirator loses due to the increased solvent vapor pressure in the chamber relatively little Solvent, does not dry on the corresponding surfaces and can over the Capture collected, separated and used again.

Typical values for the volume of coating dispersion (often also called "washcoat") or impregnation / impregnation solution are 30-70 l / min. The suction power for producing the continuous volume is typically 1000-3000 m ³ / h, resulting in a volume ratio for the mixture of washcoat / air or impregnation / impregnation solution / air of 1: 100 to 1: 5000, which also ensures a continuous and complete wetting and thus coating of the inner surfaces.

The in the chamber introduced coating dispersion or impregnation solution, the not on the inner surfaces of the catalyst carrier adheres or does not adhere to inner surfaces of the device for carrying out the Process separates, gets directly into the suction and can also be deposited again used.

To impregnating or coating, the catalyst support is preferably dried or dried and calcined.

Prefers it is when the inventive method at or slightly below the dew point of the solvent of the coating dispersion or is performed at or slightly below the dew point of the solvent of the impregnating solution. The term "dew point" refers to it the temperature T in a gas / vapor mixture in which the gas with just saturated with the steam is. At a cooling beats under the dew point The steam usually settles down as fog or dew.

The Working at or slightly below the dew point of the particular solvent As a result, within the chamber largely saturation vapor pressure of the particular solvent prevails, so on inside surfaces a device for implementation the method according to the invention precipitated coating dispersion or impregnation solution The air entering the chamber dries very slowly. This will ensure that the tree-cake effect described above largely does not occur and that the precipitated coating dispersion or impregnation solution collected and for the purposes of the coating method of the invention or impregnation method fed this again can be.

According to one further preferred embodiment the method according to the invention the method is performed in a device, one or more of which Component components on a dew point or underlying Temperature of the solvent the coating dispersion or at the dew point or below lying temperature of the solvent the impregnation solution corresponding Temperature are tempered. It is usually crucial that the surfaces of the Component components to a temperature corresponding to the dew point tempered with the sprayed into the chamber coating dispersion or with the sprayed Impregnating solution in Contact can come.

During operation of the method according to the invention, component components of a device for carrying out the method according to the invention, for example by the ambient temperature or by the waste heat from units such as pumps or fans, can be heated. Coating dispersion or impregnating solution deposited on the respective component components can give off solvent due to the heating to the air which is constantly entering the chamber, so that an increased coating or impregnation of the corresponding component components can occur. A temperature of one or more component components of a device for carrying out the method according to the invention to a temperature corresponding to the dew point counteracts Ver evaporation of the deposited on the corresponding component components solvent of the coating dispersion or the impregnating solution, so that counteracts a coating or impregnation of the component components and the Beschich tion dispersion or impregnation solution, in particular precious metal solution, can be recovered.

Around a coating or impregnation of Component components of a device for carrying out the method according to the invention particularly effective counteract, according to a particularly preferred embodiment the method according to the invention the method is performed in a device, one or more of which several component components to a temperature of more than 1 ° C below the dew point of the solvent the coating dispersion or below the dew point of the solvent the impregnation solution tempered are, preferably to a temperature of more than 2 ° C below the dew point, more preferably to a temperature of more than 3 ° C below the dew point, more preferably at a temperature of more as 4 ° C below the dew point, more preferably at a temperature of more than 5 ° C below the dew point, most preferably at a temperature of more than 6 ° C below the dew point.

Especially it is preferred if the aforementioned component components of the device the chamber walls or components of a device for carrying out the suction, preferably the suction shaft.

According to one further preferred embodiment the method according to the invention the method is performed in a device, one or more of which Component components are formed tempered. This can be up ensures a particularly simple and therefore cost-effective manner be that or the corresponding component components on Dew point temperature or at a temperature below the dew point tempered can be. At the same time the chamber walls become or the suction shaft, for example in the form of a double mantle formed, within which a cooling liquid can circulate.

It it was found that the lower the pressure or the larger the Underpressure in the chamber is the lower the coating thickness or the extent of Impregnation. According to one further preferred embodiment the method according to the invention can therefore be provided that by the aspiration of the chamber caused reduced pressure in the chamber is less than 950 mbar, preferably less than 800 mbar, and more preferably less than 600 mbar.

According to one further preferred embodiment the method according to the invention the process is at a pressure between 950 mbar to 150 mbar carried out. In other embodiments, especially when using nonwovens as catalyst support, the pressure is even less than 150 mbar. It was found that in this Pressure range particularly uniform coating thicknesses or uniform impregnations of the porous one catalyst support achieve.

to execution the method according to the invention is a turbulent flow required within the chamber. Especially with the use of catalyst supports with relatively large dimensions It may be necessary, the introduced in the chamber coating dispersion or impregnation solution especially to swirl strongly, so that also relatively low-lying cavities with the coating dispersion or wetted with the impregnating solution.

Corresponding a further preferred embodiment the method according to the invention is the porous one catalyst support a foam, a structured honeycomb body, such as. B. a monolith or a fleece. Especially foams, such as nickel foams, Nickel-alloyed foams, Monoliths, structured metal monoliths, for example, with continuous channels, as for example in automotive technology for cleaning used by exhaust gases, or nonwovens are to carry out the inventive method particularly suitable. In this case, for example, the monolith of metal, Titanium dioxide, silicon carbide, aluminum titanate of an alumina or a silica material, a mixture containing silica, alumina and a compound of the aforementioned oxides.

Preferably shows the vast majority Part of the cavities of the porous one catalyst support a diameter of 20 microns to 1.2 mm. Catalyst carrier with a corresponding proportion of corresponding cavities are in the process according to the invention from the sprayed Coating dispersion or the impregnation solution particularly well penetrated, resulting in a largely uniform coating or impregnation of the catalyst carrier also over a relatively large thickness of the catalyst carrier ensured can be.

According to a further preferred embodiment of the method according to the invention, droplets having an average diameter of between 5 micrometers and 2000 micrometers are formed when the coating dispersion or the impregnating solution is introduced into the chamber. Drops with a mean diameter of the aforementioned size are correspondingly strongly swirled in the chamber under the appropriate conditions, so that even very low-lying inner cavities of the catalyst carrier uniformly coated or in the can be stamped.

Preferably the coating dispersion is a so-called washcoat dispersion. Washcoat dispersions are known in the art. They contain usually water as a solvent and extremely fine-grained metal oxides, such as titanium dioxide or aluminum oxides, with which the porous catalyst support to coat is. This may be in particular sol-gel Systems act.

In particularly preferred embodiments The washcoat can also be further catalytically active Metal compounds such as subgroup metal or noble metal compounds such as Compounds of Mo, V, W, Pt, Pd, Rh, Ni, etc., alone or in mixture, so that if these catalytically active metals are required, another impregnation step be avoided after applying and calcining the washcoats in the "one-step process" can. Naturally can the latter, here also "two-step process" be used although it is opposite the "one-step Process "consuming is.

Possibly Washcoat dispersions also contain dispersants to washcoat dispersion to stabilize. It was found that washcoat dispersions despite their relatively high Solids content by the method according to the invention particularly simple and evenly on a porous one catalyst support let raise.

in the Within the scope of the present invention, the term "impregnating solution" is understood to mean a solution in particular a soluble metal compound of a catalytically active metal, a binder or a coupling agent is included.

For example can by means of the method according to the invention on the porous catalyst support first a a bonding agent for The impregnation solution containing the coating can be applied. After this the solvent has been removed, for example by evaporation, can by means of inventive method for example, a Washcoatdispersion as a coating dispersion on the porous catalyst support be applied.

After this the solvent the coating dispersion, for example by evaporation in Vacuum was removed and the coating was calcined the coated catalyst support by the method according to the invention either directly with a catalytically active metal containing Impregnating be impregnated or also previously with a binder or an adhesion promoter for the corresponding Metal-containing impregnation solution.

According to one further preferred embodiment the method according to the invention contains the impregnation solution Binder or a primer. Particularly preferably, the binder contains or the bonding agent is an organic or an inorganic component. It has been found that such impregnating solutions are particularly suitable for carrying out the inventive method suitable.

The following description of a preferred embodiment of the method according to the invention used in conjunction with the description of the explanation the invention. It shows:

1 schematic representation of an apparatus for carrying out the method according to the invention in longitudinal section.

In the 1 is an overall reference numeral 10 proven negative pressure passage coating apparatus for performing the method according to the invention shown. The device comprises a chamber 20 with an entry template 22 at the catalyst carrier inlet side and an outlet template 24 at the catalyst carrier exit side. Both templates 22 . 24 are the cross-sectional shape of the porous catalyst supports 30 are closely approximated but have a certain excess, so that between the template edges and the catalyst supports 30 a narrow gap remains, the ambient air as leakage current entering the chamber 20 allowed.

To the chamber 20 connected is a suction device 40 , The high suction of the chamber 20 With an air flow of 1000-3000 m ³ / h causes the inlet side as the exit side not thombenförmiger formed in the drawing, composed of numerous individual eddy currents and turbulence on the inlet side or outlet side air curtain forms.

About the nozzles 50 For example, an aqueous washcoat dispersion as a coating dispersion is added to the chamber in an amount of 30 to 60 l / min 20 brought in. The Washcoatdispersion passes from a storage container 70 by means of a pump 60 under pressure to the nozzles 50 , Here is the reservoir 70 with a supply line 75 provided for the supply of Washcoatdispersion.

The in the chamber 20 sprayed Washcoatdispersion is strongly swirled by the turbulent air currents prevailing there, whereby the porous catalyst support is uniformly coated or impregnated, ie, both its outer as well as its inner surface.

The Washcoatdispersion is in a high excess by means of the nozzles 50 in the chamber 20 sprayed. The excess Washcoatdispersion passes through the strong suction of the chamber 20 in the suction device 40 in which the Washcoatdispersion is separated from the sucked air. The separated Washcoatdispersion is by means of a derivative 42 in an intermediate container 80 promoted.

In the intermediate container 80 the composition of the Washcoatdispersion is determined by means of a not shown in the drawing, but known per se probe. Should that in the intermediate container 80 Trapped Washcoatdispersion not have the desired composition, so on the feed 82 corresponding components in the intermediate container 80 introduced until the Washcoatdispersion has the desired composition.

Indicates that in the intermediate container 80 Washcoatdispersion collected the desired composition, it is by means of a transfer 84 in the reservoir 70 from where they turn by means of the pump 60 the nozzles 50 can be supplied.

The device 10 further comprises a conveyor belt 90 on which the porous catalyst supports 30 be launched one after the other. After the catalyst support 30 the chamber 20 have passed through the exit template 24 have passed through, they can from the conveyor belt 90 be removed for drying or can be conveyed on the conveyor belt in the drying.

The walls of the chamber 20 and the exhaust duct of the suction device 40 are designed double-walled, wherein within the double wall, a cooling liquid with a temperature of 8 ° C circulates. This serves to ensure that on the inner walls of the chamber 20 or on the inner walls of the exhaust duct of the suction device 40 precipitated Washcoatdispersion to a temperature at the dew point or below the dew point is tempered. This ensures that precipitated Washcoatdispersion is not dried on the corresponding inner walls of the steady stream of air and the corresponding surfaces not coated, but that the dispersion, for example, in the exhaust duct of the suction device 40 can get.

In further preferred embodiments by capillary forces inside the soaked Shaped catalyst body withheld small Part of the washcoat or impregnation solution Create an additional short-term vacuum at the end of the device are removed.

After the catalyst support 30 were coated with the Washcoatdispersion, they are dried and then calcined.

After calcination, the catalyst supports 30 by means of in the 1 illustrated device for carrying out the method according to the invention, for example impregnated with a platinum solution or a palladium solution.

Claims (17)

Process for coating or impregnating a catalyst support ( 30 ) having internal cavities having internal surfaces, comprising the following steps: a) introduction of the catalyst support ( 30 ) having inner surfaces in a chamber ( 20 ), in which one by a suction of the chamber ( 20 ) caused turbulent flow and a negative pressure prevails; b) introducing a coating dispersion or an impregnating solution into the chamber ( 20 ). c) forming a mixture air / coating dispersion or air / impregnation solution d) continuously passing the mixture from step c) through the catalyst support ( 30 ). Method according to claim 1, characterized in that that the process is operated continuously in a continuous process. Method according to one of the preceding claims, characterized characterized in that the method is in a at or below the Dew point of the solvent the coating dispersion or at or below the dew point of the solvent Impregnating solution is performed. Method according to one of the preceding claims, characterized in that the method in a device ( 10 ) is carried out, of which one or more component components are heated to a temperature corresponding to the dew point of the solvent of the coating dispersion or to a temperature corresponding to the dew point of the solvent of the impregnating solution. Method according to one of the preceding claims, characterized in that the method in a device ( 10 ) is carried out, of which one or more component components are tempered at a temperature of more than 1 ° C below the dew point of the solvent of the coating dispersion or below the dew point of the solvent of the impregnating solution. Method according to one of the preceding claims, characterized in that the method in a device ( 10 ) is performed, of which one or more component components are formed tempered. Method according to one of the preceding claims, characterized in that by the suction of the chamber ( 20 ) caused negative pressure in the chamber ( 20 ) is less than 800 mbar. Method according to one of the preceding claims, characterized characterized in that the method at a pressure between 500 mbar to 300 mbar becomes. Method according to one of the preceding claims, characterized in that the porous catalyst support ( 30 ) is a foam, a monolith or a nonwoven. Method according to one of the preceding claims, characterized in that the predominant part of the inner cavities of the catalyst support ( 30 ) has a diameter of 200 microns to 1.2 mm. Method according to one of the preceding claims, characterized in that when introducing the coating dispersion or the impregnating solution into the chamber ( 20 ) Drops with a mean diameter of between 50 microns to 900 microns can be formed. Method according to one of the preceding claims, characterized in that the coating dispersion is a washcoat dispersion is. Method according to claim 12, characterized in that that the Wahcoatdispersion continues to be a compound of a catalytic contains active metal. Method according to claim 12 or 13, characterized that the impregnation solution a Contains binder or a primer. Method according to claim 14, characterized in that that the binder or the adhesion promoter is an organic or contains an inorganic component. Use of the method according to one of the preceding claims for producing a shaped catalyst body for the purification of gases. Use of the method according to one of the preceding claims 1 to 15 for the preparation of a shaped catalyst body for the purification of exhaust gases from internal combustion engines.