EP1885495A2

EP1885495A2 - Method and device for applying washcoat suspensions to a molded article

Info

Publication number: EP1885495A2
Application number: EP06753870A
Authority: EP
Inventors: Hans-Jürgen EBERLE; Olaf Helmer; Jörg SPENGLER
Original assignee: Sued Chemie AG
Current assignee: Sued Chemie AG
Priority date: 2005-05-25
Filing date: 2006-05-24
Publication date: 2008-02-13
Also published as: WO2006125649A3; US20080200328A1; WO2006125649A2; CA2605289A1; DE102005024124A1

Abstract

The invention relates to a method for removing an excess of a liquid from a molded article that comprises two opposite planar faces and interior cavities and/or channels to be coated with the liquid. The inventive method is characterized by removing in a first removal step, once the liquid has been introduced into the interior cavities and/or channels, the major portion of the excess liquid under the influence of an external force, and removing in a second removal step the excess liquid remaining in the molded article after the first removal step by contacting the molded article with a porous and/or channel-bearing support on the very face where the excess was removed. The pore and/or channel diameter of the support is smaller or equal the diameter of the interior cavities and/or channels of the molded article.

Description

Method and device for applying washcoat suspensions to a molded article

The invention relates to a method and an apparatus for the production of supported catalysts by applying a Washcoat suspension on a ducts or pores having shaped body as a carrier and the use of the thus obtained supported catalysts in the purification of exhaust gases, in particular exhaust gases of internal combustion engines.

Catalysts based on coated moldings, for example so-called monoliths or metal foams for the purification of exhaust gases, such as the oxidation of CO or hydrocarbons to CO ₂ and water or the reduction of NO _x with ammonia or urea to N ₂ and water or the decomposition Of urea or its thermal decomposition product, the isocyanic acid, to ammonia and CO ₂ , have long been known.

As a rule, these catalysts are constructed in such a way that a monolithic carrier material ("honeycomb" in the case of channels or ceramic or metal foam in the case of pores) traversed by channels or pores has a high surface area (high-surface area). Metal oxide coating (washcoat), for example of Al ₂ O ₃ , SiO ₂ or TiO ₂ , or their mixed oxides is coated and on these metal oxide surfaces the actually catalytically active metals or metal compounds, such as precious metals or transition metal oxides, and optionally additional promoter compounds / However, there are also applications in which the metal oxide coatings alone are catalytically active, a typical example being the hydrolysis of isocyanic acid to ammonia on TiO ₂ coated moldings.

Monoliths, often called "honeycombs", for example, consist of a honeycomb body, which consists of a honeycomb sheath and a carrier used therein, for example, a partially structured and wound sheet metal foil, can put together. Another possibility is, for example, that the honeycomb consists entirely of a purely ceramic shaped body. The honeycomb is essentially traversed by running parallel to the main axis of the honeycomb channels.

Metal or ceramic foam are highly porous moldings that can assume any geometric shapes.

In both of the above cases, cylindrical shapes are most preferred.

The channels passing through a monolithic carrier (honeycomb) can have an ordered or disordered channel structure, and furthermore the essentially parallel channels can also be interconnected (so-called open channel structures), for example also through porous channel walls. With open channel structures, a radial gas distribution within the honeycomb body is also made possible. The size of the honeycomb as well as the dimensioning of the channels is determined mainly by the dimension of the exhaust pipe systems, the required pressure losses and the required residence times of the exhaust gas. The same applies mutatis mutandis to the corresponding highly porous metallic and ceramic sponge or foam structures.

The so-called cell density, namely the number of channels or pores per shaped body or surface of an end face of the shaped body, also depends on the requirements. As a rule, these are between 50 and 1000 channels / pores per inch ² (= cells per square mch, cpsi). In individual cases or for special applications, these cell densities may be undershot or exceeded. The higher this cell density of the shaped body, the higher is the reaction available surface; but in the same way the pressure loss increases with increasing cell density.

For example, materials such as Cordient, Steatite, Duranit® or silicon carbide or shaped bodies of silicon dioxide, aluminum oxides, aluminates or even metals and metal alloys are used as material for moldings which can be used according to the invention. The use of metals and metal alloys makes it possible, in particular, to produce complex structured shaped bodies, such as, for example, honeycombs with open channel structures or ceramic or metal foams whose pore structure has a particularly high internal surface area.

The preparation of a catalyst based on a moldable body which can be used according to the invention is generally carried out by applying a washcoat (WC) to the surface of its internal cavities, that is to say, for example. As its channel walls, pores, etc. (coating), followed by drying followed by calcination at higher temperatures for solidification and final surface design of the washcoat. Thereafter, the catalytically active components are applied to the washcoat by impregnation steps, mostly from the aqueous solutions of their precursors. However, it is also possible to apply the active components or their precursor compounds directly with the coating process.

The coating of an inner hollow body or channel-containing shaped body (hereinafter referred to simply as "shaped body") with the inorganic high-surface-area materials is possible by various methods. [In In] As a rule, a suspension of the inorganic carrier oxide in water is prepared first, if appropriate with the addition of additives, such as inorganic or organic binders, surfactants, catalytic active components, pore formers, rheology aids and other additives. 05001

4 dipping, sucking or pumping process is filled with this so-called washcoat suspension.

In the prior art, methods are described in which only the exactly calculated amount of washcoat suspension remaining in the shaped body is introduced into the shaped body and this amount is distributed as uniformly as possible over the channel walls or pore walls.

Other processes introduce an excess into the shaped body (eg flooding of the shaped body) and carry out a subsequent emptying process, with which excess washcoat suspension is discharged. Often, a purge is carried out by means of an air flow for emptying.

In DE 19837731 Al several of these process variants are disclosed. The emptying of the excess washcoat from a honeycomb body by means of a centrifuge unit is described, for example, in GB 1504060.

The constantly increasing legal requirements with regard to the purification of exhaust gases, in particular engine exhaust gases, require the development of new catalysts with significantly higher efficiencies. In addition to improving the catalytic coating, the efficiency of catalysts can also be significantly increased by optimized carrier materials.

For this purpose, on the one hand, the cell density can be increased, but it is also possible to use so-called complex structured shaped bodies. In the case of honeycomb bodies, honeycombs are understood to mean honeycombs with complex structured honeycombs, in which the channels have elevations or depressions or blades. As a result, turbulences are generated in the gas stream passing through the shaped body in a targeted manner, which also leads to better mass transfer and thus higher activities. Open structures are also part of this type of support. In open structures are - P2006 / 005001

5 as already described above - the channels connected by corresponding perforations (holes, pores). As a result, in addition to a vertical direction of flow (parallel to the channel axis), a more or less horizontal (radially to the axis of the honeycomb or channels) gas flow is possible. With complex structures, it is possible to produce catalysts which simultaneously have a mixing effect. Furthermore, of course, combinations of purely plane-parallel and complex structured honeycomb are conceivable. Metal foams are structurally complex per se, but easier to produce.

Honeycomb or porous shaped body with high cell densities as well as honeycomb with complex structured and perforated channels (open structures) can not be coated by the previously known methods without undesirably great expense. In particular, blowing out the excess washcoat suspension with air is no longer possible with open channel structures or pore structures.

The reason for this is that the air used for blowing (blow-out air) basically takes the path of least resistance (path of least pressure loss). As soon as individual open channels or pore structures have arisen between the two end faces of the shaped body, the blow-out air used in the sequence is discharged through the holes of the open structures into those already open channels or pore structures and the pressure of the blow-out air used is insufficient. to blow down the washcoat suspension from still partially filled channels or pores, in which the washcoat suspension is held by capillary forces. Even a few channels or pore structures completely emptied by purging lead to the described effect, so that only a few channels are to be emptied by blowing out alone. This effect, which is particularly noticeable in honeycombs with open structures or porous ceramic and metal foams, is illustrated in FIG. 1:

Fig. 1 shows a partial view of two parallel channels of a honeycomb, which are interconnected via a perforation (open structure). While the channel shown on the right already has been freed of excess washcoat by the blow-off air (the flow direction of the air is illustrated by the arrows), this is no longer possible in the channel shown on the left for the reason described above, so that blow-out alone is no longer possible Remaining and held by the capillary rest of washcoat in the lower region of the channel remains. The same applies z. For example, for cylindrical metal foam moldings.

For coating complex-structured moldings, in particular of honeycomb and foams, therefore more and more complicated processes are necessary. Thus, the application of vibrations is described in DE 10114328 Al when applying the washcoat. On the one hand, this should improve the flowability of the washcoat suspension, and on the other hand, the washcoat application should be as uniform as possible. But even this process no longer allows complete removal of the excess washcoat suspension used.

It is an object of the present invention to provide a method for coating shaped articles, in particular for coating the inner surfaces of such shaped bodies with open and / or complex structures, the inner regions which are interconnected in some areas and essentially pass through the shaped body, i. For example, have channels or pore structures, to provide that solves the above problems.

Another object was a method for emptying such moldings, in particular with open and / or To provide complex channel or pore structures of excess used Washcoat suspension that solves the problems mentioned.

In particular, the solution should be characterized by measures that can be easily implemented.

The object has been inventively solved by the fact that in a first emptying step, the majority of excess liquid is removed by the action of an external force and in a second emptying step of remaining in Formkorper after the first emptying residual amount of excess liquid by contacting the Formkorpers of that End face, at which the excess was discharged in the first emptying step, is removed with a porous and / or channels bearing pad, wherein the pore and / or channel diameter of the support is less than or equal to the diameter of the inner cavities and / or channels of the Shaped body.

If there is a pore distribution in the overlay, which does not have exclusively pores or channels whose diameter is smaller than the diameter of the pores or the channels of the molded article, it should be ensured according to the invention that about 70%, preferably 80%, and most preferably 90% of the pores of the overlay have a smaller diameter than the pores or channels of the molded article to achieve substantially complete purging.

In general, of course, in addition to washcoat suspensions, other suspensions, dispersions, slurries and viscous and non-viscous liquids according to the invention can be used.

The geometrical shape of the shaped body is in principle arbitrary, but it should have two substantially parallel flanges to each other. EP2006 / 005001

8, so-called "end faces." Cylindrical shaped bodies are preferably used.

The shaped body used in the method according to the invention is preferably a ceramic or a metallic shaped body.

The effect of the porous support according to the invention in the emptying process according to the invention is not bound to the used emptying principle. In principle, the measure according to the invention can be used in conjunction with all known to those skilled in the art emptying measures. It can be used in conjunction with a blow-out method, with a centrifuging method as well as with the various other emptying methods. However, the use of a special suction device, as in DE 3803579 A1, or the application of a negative pressure can be dispensed with. Therefore, the automation of the discharge process by the inventive method is significantly favored.

Preferably, the porous or ducted support according to the invention for removing the excess Washcoat- suspension from the channels or pores of the molded article to be coated in connection with the application of a directed to the channels or pores air flow (blowing) and / or by application of Centrifugal forces used.

The inventively used porous or channels traversed support should, in order to achieve the most complete emptying, as completely as possible plane-parallel to the end face of the mold body completely. It is not absolutely necessary for the porous support used according to the invention to be in direct contact with the end face of the shaped body to be emptied. Rather, in the method according to the invention for compensating any unevenness, a flexible porosity can be achieved. se intermediate layer, in particular a flexible network can be used. In this way, a complete production of the contact between the outlet side of the molded article and the porous support used according to the invention is achieved, which lead to optimal results of the inventive method even with not completely planar end faces of molded articles and porous support to be emptied.

For an optimal result of the inventive method, it is therefore appropriate to produce by appropriate measures over the entire end face (exit surface) of the excess of the washcoat suspension to be emptied molding, present and thus continuous contact with a porous support.

An essential feature of the invention is, inter alia, the fact that the diameter of the channels or pores of the porous support used is on average less than or equal to the diameter of the inner cavities of the shaped body to be emptied, in particular the diameter of the hollow body to be emptied on the front side of the mold body to be emptied Channels or pores. The mean pore diameter or the individual pore cross-sectional area of the porous support calculated therefrom should therefore not be greater than the single-channel cross-sectional area or the average pore diameter at the front-outlet side of the shaped body to be emptied.

The composition of the porous support is not bound to a specific material. It can be made of metal, ceramic, plastic or any other suitable to those skilled appear material. Combinations of various porous and / or channeled materials are also conceivable.

In order to achieve an optimal effect of the porous support must, as already explained, preferably the direct contact of the can be achieved according to opposite surfaces of Formkorper and support, in particular over the entire surface of the zα emptying Formkoroers.

Furthermore, the possibility of permeation of the overlay with the coating suspension, dispersion, caustic slurry or solution must be ensured: the diameter of the smallest pore of the overlay should not be less than the diameter of the largest particle of the coating suspension, dispersion or slurry. Otherwise, these components can no longer flow through the pores of the pad and there is a clogging of the porous pad. This requirement restricts the pore diameter of the porous support by means of a minimum pore diameter, which is expediently to be selected as a function of, for example, the washcoat suspension.

In a preferred embodiment of the method according to the invention, a second shaped body, preferably of the same type as the shaped body to be emptied, or even a second shaped body with the same or smaller channel diameter or pore diameter, based on the channel diameter, is used as porous or channel-covered support according to the invention or pore diameter of the emptied molding, used. In this case, the length of such a second shaped body can be significantly shorter than that of the shaped body to be emptied. However, the length or the height of the porous support used according to the invention or of the mold body used for the emptying should be at least high enough that the capillary force of the support or molded body resulting from the cross section or diameter and the pore length or channel length is capable to overcome in the Trager- or pore channels to be emptied acting capillary forces that prevent the outflow of the excess Washcoat- suspension.

If the shaped article to be emptied is a metallic shaped article, then the molding article used for emptying according to the invention is 006/005001

11 preferably also metallic nature and has in the case of a honeycomb plane-parallel channels. Of course, if appropriate, a ceramic shaped body may also be used instead of a metallic shaped body.

In a particularly preferred embodiment of the method according to the invention, a honeycomb of the same type is used for emptying a metallic or ceramic honeycomb, the honeycomb body being emptied of the honeycomb body being emptied in the upper part in order to emptying it honeycomb to reach the front surface of the honeycomb to be emptied.

Further possible embodiments of the invention for porous overlays are open-pored sponges, nets, nonwovens (porous fleece) or comparable materials. The direct and complete contact of the porous support with the emptying surface of the molded body over the entire surface leads to a complete leakage of the excess washcoat in the mold.

Possible embodiments for the porous support are also combinations of a metallic or ceramic honeycomb with a fleece and / or a net and / or a sponge.

An advantage of the inventive method is the simple technical feasibility. Furthermore, the process according to the invention effectively avoids the undesirable formation of bubbles at the channel or pore outlet side, which is often observed when using surfactant-containing coating suspensions.

In one possible embodiment of the method according to the invention, the shaped articles can first be partially emptied by means of another functional principle, in particular by suction, blowing out, centrifuging or simply flowing out. In a further embodiment, the abovementioned possibilities for partial emptying can also be used in combination with the emptying method according to the invention, in particular successively or simultaneously.

The emptying process according to the invention can be used, in particular, as part of a complete coating process of moldings which are interconnected in regions and are essentially continuous through the mold body and have inner cavities.

Thus, a further subject of the invention, a method for coating a partially interconnected, substantially continuous by a mold body, having inner cavities Formkorpers, in particular a channels or pore structures having honeycomb or a porous metal foam with a washcoat suspension comprising the following steps

A) aspirating a washcoat suspension through the inner cavities of the shaped body to be coated by applying a negative pressure on the upper end face of the shaped body, while on the lower end side washcoat suspension is supplied,

B) partial emptying of the excess washcoat suspension from the inner cavities of the molded body to be coated by applying an overpressure on the upper end face of the shaped body,

C) removing the excess of washcoat suspension remaining after step B) from the inner cavities of the shaped body to be coated by means of a porous support which is mounted on the end face of the shaped body on which the excess is to be removed mean pore diameter of the porous support less than or equal the average diameter of the channels of the molding is.

The complete removal of the excess in step C) can be used in combination with any method known to those skilled in the art for emptying such molded articles.

Preferably, the measure according to the invention according to step C) is used in connection with the application of centrifugal forces or inertial forces. By centrifugal forces is meant those forces which are e.g. arise during acceleration or deceleration of the moldings and act on him.

A variant of step B) may be that the partial emptying of the molded article takes place exclusively by the outflow of the excess washcoat suspension, due to its own weight, and then the emptying is carried out by the inventive emptying method using the porous support.

In a preferred embodiment of the coating process according to the invention, steps A) and B) are carried out several times in succession before step C) is carried out. In particular, steps A) and B) are each run through three times in order to ensure that all channels or pores of the molded body with washcoat suspension have been completely filled at least once.

Optionally, the filling after step A) and / or the partial emptying step B) can be carried out by the action of vibrations, in order to increase the flow properties of the washcoat suspension to be aspirated or expelled.

In a further, particularly preferred embodiment of the coating method according to the invention, the steps A) and B) are already carried out in the presence of the porous support, in which case the partial emptying B) is carried out simultaneously 01

14

Application of the inventive emptying principle according to step C) is carried out. The above also applies mutatis mutandis to dispersions, slurries or solutions for the coating of the inner cavities or channels or pore structures of a molded article.

Another object of the invention is a device used for filling and partial emptying of partially interconnected, substantially through a mold body continuous internal cavities of a molded article used apparatus (Kolbenzy- linderanlage), with the inventive coating method can be performed.

The device according to the invention according to FIG. 2 is explained on the basis of a honeycomb body. Of course, what is said also applies to all other Formkorper such. Ceramic or metal foam. The device comprises a piston cylinder (a) for sucking in or emptying the washcoat suspension or dispersion, sludge or solution, a connecting plate (b) which is fixedly connected to the lower end of the piston cylinder and with the upper end side to be coated Can be tightly connected honeycomb, a receiving plate (c), which can be tightly connected on its upper side with the lower end face of the honeycomb to be coated, optionally one or more vibration units, which are fixed to the receiving plate (c), a hydraulically movable suspension ( f) with which the cylinder unit (a), the connecting plate (b) and the receiving plate (c) can be moved together horizontally (up and down movement), an intake / outlet pipe (d), on the lower side of the receiving plate ( c) and a storage trough (e) in which the washcoat suspension is presented.

The tight connection of the honeycomb to be coated with the connecting plate (b) and the receiving plate (c) is preferred way by pressing the end faces of the honeycomb to corresponding sealing devices on the plates (b) and

The connecting plate (b) and the receiving plate (c) are in each case in the area in which they are to receive the honeycomb to be filled, broken so that on the one hand on the KoI- benzylmder (a) a pressure or negative pressure can be established and on the other hand, the washcoat suspension can be sucked or pressed out through the suction / discharge pipe (d).

By means of the coating method according to the invention or the emptying method according to the invention, in particular monolithic catalysts or catalysts based on metal foams which are based on a washcoat consisting essentially of TIO ₂ or similar metal oxides such as SiO ₂ , Al ₂ O ₃ , ZrO ₂ or mixtures thereof, produce.

The catalysts obtainable by the processes according to the invention can be used in particular as catalysts in the purification of exhaust gases, in particular those of internal combustion engines.

Possible uses of the catalysts obtainable by the process according to the invention are, in particular, the purification of automobile and diesel exhaust gases. Furthermore, the catalysts prepared by the process according to the invention can be used as decomposition catalysts for ammonia precursor compounds, as oxidation catalysts, as catalysts for the removal of nitrogen oxides and as catalysts for the reduction of nitrogen oxides.

The novel processes can be used in particular for the preparation of catalysts in which washcoat suspensions consisting of support oxides or support oxide combinations selected from the group comprising TiO ₂ , Al ₂ O ₃ , SiO ₂ , CeO ₂ , ZrO ₂ or Zeolites, are used. The mentioned 6 005001

16

Trageroxide or Trageroxidkombinationen can in turn be doped or coated with metal oxides. It is also possible to use catalytically active compositions or compositions which directly catalytically active coatings are used directly.

Preferably, the active composition contains as additional components one or more metal oxide compounds selected from the group comprising the oxides of vanadium, tungsten, molybdenum, in particular V ₂ O ₅ , WO ₃ , M0O ₃ or noble metal salts, in particular those of palladium, platinum, Rhenium or rhodium.

However, the catalytically active components can also be applied only in a subsequent step after the shaped body which has been coated and emptied according to the invention has been subjected to a temperature treatment.

The washcoat suspensions, dispersions or slurries which can be used in the process according to the invention may contain, in addition to inorganic carrier oxides, water, additives and catalytic active components.

The washcoat suspensions used in the process according to the invention can be inorganic sols or gels, in particular SiO ₂ , TiO ₂ , Al ₂ O _3, sols or gels for improving the adhesion of the resulting coating, additives such as organic mono- and polymers, in particular cellulose derivatives or acrylates as pore formers as well as adhesion promoters and / or surfactants as rheological aids.

Moldings made of materials selected from the group consisting of cordierite, silicates, zeolites, silicon dioxide, silicon carbide, aluminum oxide and aluminates or mixtures of these substances are particularly suitable for the moldings to be emptied or coated by the novel processes as well as metals or metal alloys. Particularly preferred are metallic support structures.

Preference is given to metallic shaped bodies, particularly preferred are complex-structured metal carriers and metal foams. But ceramic honeycomb or Keramikschaume are used. The metal or Keramikformkorper used according to the invention can be pretreated by a thermal or chemical process in such a way that a later applied layer is improved in their adhesion. With the method according to the invention, molded articles with a high to very high cell or pore density can also be emptied.

The catalysts prepared in this way can still undergo a drying step and subsequent calcining step. The further application of catalytically active compounds, such as noble metal compounds, is possible. The catalysts prepared in this way are used especially in gas purification processes, in particular in the purification of automobile exhaust gases. However, they can also be used in other catalytic processes, such as in the chemical industry or power generation.

In summary, the present invention relates to a process for coating catalyst supports by means of a charging step of a support body which [Def. Al] on the outside with a washcoat suspension and a subsequent emptying step to remove the excess washcoat suspension.

At least at the end of the emptying step, the filled or partially filled mold body with its outlet end face is brought into contact with a porous support, with the proviso that the average pore diameter or the calculated individual pore cross-sectional area of the support is not greater than the single cross-sectional area of a representative one Ka nal or pore channels at the front exit side of the catalyst carrier. The catalyst supports coated in this way can be used as supported catalysts, in particular for the purification of automobile exhaust gases.

Explanation of the figures:

Figure 1 is an illustration of the air flow (arrows) for blowing out the excess washcoat suspension in open structures. The illustration shows two adjacent channels connected by perforations as a section of a honeycomb body. The air flow in the perforated channels follows that of the lowest pressure loss, after which, in such a case, a complete emptying of all channels becomes impossible due to the sole blowing out. The excess washcoat suspension is held in the channels by the capillary forces.

FIG. 2 is a schematic representation of a piston-cylinder system according to the invention. FIG.

Fig. 3 shows a honeycomb immediately after removal from the Kozy- benzylinderanlage according to Comparative Example 3. The channels are on the side of the exit surface (lower end face) still completely filled with excess washcoat suspension.

4 shows a honeycomb according to Comparative Example 3 after the action of an air flow (blowing out).

5a shows the view of a honeycomb to be coated, which is subsequently to be freed of excess washcoat (top) with attached second auxiliary honeycomb or support honeycomb (below) for the purpose of complete emptying according to Example 4.

FIG. 5b shows a detailed view of the attachable auxiliary or supporting honeycomb according to example 4, wherein it can be seen that to ensure full coverage of the lower exit surface of the honeycomb to be emptied (not shown) with the upper end surface of the auxiliary honeycomb a small part of the honeycomb envelope Abrasion was removed.

6 is a view of the lower exit surface of a coated honeycomb completely freed from excess washcoat according to Example 4. FIG.

7 is a view of the lower exit surface of a honeycomb exclusively treated by centrifugation according to Comparative Example 5 without the use of an auxiliary honeycomb.

Fig. 8 is a view of the lower exit surface of a honeycomb treated according to Example 6 by centrifugation in the presence of an auxiliary honeycomb.

Fig. 9 is a view of the lower exit surface of a honeycomb treated according to Example 7 (blowout), whereby channels are not completely empty due to incomplete abutment of the auxiliary honeycomb over the entire surface of the exit surface of the honeycomb to be liberated by excess washcoat.

10 is a view of the lower exit surface of a honeycomb treated according to Example 8, wherein the unevenness on the upper end side of the auxiliary honeycomb, which prevent a complete plane-parallel resting of the auxiliary honeycomb over the entire exit surface, by introducing a flexible network between the exit surface of the excess washcoat to be liberated honeycomb and the upper end surface of the auxiliary honeycomb be compensated.

The following examples are intended to explain the invention in more detail and are in no way to be considered as limiting.

Example 1: Preparation of a typical washcoat suspension

100 g of TiO ₂ with a BET surface area of 80 m ² / g are stirred into 80 g of water, then 40 g of an aqueous SiO ₂ sol (content of SiO ₂ : 40%) are added as binder and then the suspension in homogenized with a gear colloid mill. The resulting washcoat suspension has a viscosity of about 4100 mpa * s.

Example 2: Filling and Partial Emptying of Honeycombs

2.1 Description of the filling and part discharge system:

The filling as well as partial emptying of the honeycomb bodies were carried out with the aid of a piston-cylinder system according to FIG. 2.

The plant consists essentially of a piston cylinder (a) for sucking or emptying the washcoat suspension, a connecting plate (b), which is connected at the lower end of the suction fixed to the suction cylinder and which is dimensioned in its underside so that exactly the upper end side of the honeycomb with the suction cylinder by pressing a receiving plate (c) can be tightly connected. Optionally, one or more vibration units can be attached to the receiving plate (c). This fixture (plates (c) and (b)) can move together with the cylinder unit (a) hydraulically up and down over the suspension (f).

On the receiving plate (c), whose upper side is designed so that the lower end side of the honeycomb can be accommodated, on the lower side of an intake / outlet pipe (d) is flanged. The pilot plant is supplemented by a storage tank (e), in which the washcoat suspension is filled.

2.2 General implementation of the filling or partial emptying of a honeycomb body

The washcoat suspension from Example 1 is in the storage tank

(e) presented at least so much that during the later Befullvorganges the intake pipe (d) is always completely immersed in the washcoat suspension. Then, the honeycomb is sealed into the holding device comprising the plates (b) and (c) by hydraulically pressing the honeycomb receiving plate (c) onto the connecting plate (b), and the piston-cylinder unit (a) together with the holding device comprising the plates (b ) and (c) hydraulically downwards over the suspension (f) so that the immersion tube (d) dips into the washcoat suspension. Subsequently, the cylinder piston (a) (also hydraulically) is moved upwards, whereby the washcoat suspension is sucked into the honeycomb via the suction pipe (d). The piston stroke is adjusted so that the washcoat suspension is sucked in at least to the extent that the upper end surface of the honeycomb is completely covered. By quickly lowering the piston (a), a large part of the excess washcoat suspension is printed out again into the storage trough (e). This process is repeated at least twice, which ensures that all channels have been fully filled (flooded) at least once.

For better filling / emptying of the honeycomb, the vibra- tion attached to the receiving plate (c) will be carried out during the entire process. 6 005001

22 rator commissioned (compressed air vibrator: Fa. Netter, NFP 18s, rated frequency at 6 bar = 7700min " ¹ , centrifugal force at 6 bar = 128 M) to improve the flow properties of the washcoat suspension by applying a vibration frequency.

After three pumping and printing operations, the piston is held down for one minute after the last printing operation. Thereafter, the cylinder piston (a) together with the holding device comprising the plates (b) and (c) pneumatically over the suspension (f) moves back up, and finally the outlet pipe (d) is no longer immersed in the washcoat suspension. The honeycomb can be removed after appropriate pressure relief (relax the hydraulic system on the holding device) for further processing (emptying).

Comparative Example 3 Coating of a Metallic Carrier Body (Honeycomb) with a Mixing Function Using a Vibration Unit and Emptying of Remnants with an Air Stream

A complex structured metal honeycomb with mixer function (from Emitec, Type:. MI) cm with a length of 7.5, a diameter of 7 cm and a cell density of 200 cpsi is pretreated h at 750 ⁰ C in a calcining furnace under air atmosphere thermally. 4 The cooled to room temperature honeycomb is then filled by the procedure described in Example 2.2. Thereafter, the test swab was removed. In Fig. 3, the lower end side of the experimental honeycomb is shown. It can be clearly seen that the entire lower end surface of the honeycomb is still covered with washcoat suspension.

Immediately thereafter, an air flow (approx., 200 m ³ / h) is blown through the honeycomb for a period of 1 minute (emptying). However, as can be seen in FIG. 4, this measure also does not lead to a satisfactory result. Only a small proportion of the channels is completely emptied by the air flow. EXAMPLE 4 Coating of a Metallic Carrier Body with a Mixing Function Using a Vibration Unit and a Porous Underlay in the Form of a Second Carrier Honeycomb

The experiment described in Comparative Example 3 was repeated with the difference that a second honeycomb is attached to the underside of the honeycomb to be emptied as a porous base (compare Fig. 5a) and the blowing is dispensed with. So that a direct contact between the surface to be emptied honeycomb and plugged auxiliary honeycomb is made, a small part of the honeycomb shell of the auxiliary honeycomb is cut off (see Fig. 5b). With this combination (Fig. 5a) the same filling and emptying procedure was then carried out.

The result of the emptying process can be seen in FIG. It can be clearly seen that all channels of the honeycomb to be emptied could be completely freed of excess washcoat by using the second auxiliary honeycomb and the complete contact of the support surfaces of both honeycomb.

Comparative Example 5 Coating of a Metallic Carrier Body with a Mixing Function Using a Vibration Unit and a Subsequent Centrifugation Step for Emptying the Remainder

The experiment described in Comparative Example 3 is repeated with the exception that for the purpose of emptying, the test honeycomb was introduced into a centrifuge (d = 600 mm) and centrifuged there for a period of 0.5 min at a speed of 140 rpm.

In Fig. 7, the result can be seen: Although a large part of the remaining washcoat suspension was removed from the metal honeycomb after centrifuging, the exit surface was still almost completely closed with excess washcoat suspension. A use of such a honeycomb without further Aftercare for residual removal of the washcoat would not be possible.

Example 6 Coating of a Metallic Carrier Body with Mixing Function Using a Vibrating Unit and a Subsequent Centrifugation Step Using a Porous Pad

The experiment described in Comparative Example 5 is repeated, with the difference that prior to the centrifuging step, a second auxiliary honeycomb is placed, in which, in order to ensure a direct contact surface, a part of the upper honeycomb shell is removed. As can be seen from FIG. 8, the entire exit surface of the honeycomb is now free of washcoat suspension.

EXAMPLE 7 Coating of a Metallic Carrier Body with a Mixing Function Using a Vibration Unit and a Porous Underlay in the Form of a Second Carrier Honeycomb, in Which, however, the End Surfaces Only Partially Have a Direct Contact with each Other

The experiment described in Example 4 is repeated, with the difference that the mutually facing surfaces of the honeycomb to be emptied and the auxiliary honeycomb (support honeycomb) had no complete, over the entire exit surface extending contact. This is provoked by the deliberate use of a honeycomb with a not quite planar frontal surface.

FIG. 9 shows the exit side of the experimental honeycomb after the coating test. Even a small disturbance of the flat contact leads to an incomplete emptying and thus partial blockage of the channels. Example 8: Coating of a metallic carrier body with mixer function using a vibration unit and a combination of honeycomb and mesh as porous support

The experiment described in Example 7 is repeated, with the difference that between the opposite not completely plane-parallel surfaces additionally a layer of a flexible network (thread thickness: 0.3 mm, mesh size: 1.2 mm * 1.2 mm) placed becomes. In contrast to the experiment according to Example 7, all channels were now free of washcoat suspension after the coating process in the honeycomb to be coated and emptied (to be liberated from excess washcoat) (FIG. 10).

Claims

claims

A method for removing an excess of a liquid from a molded article having two opposing planar faces, the inner cavities and / or channels to be coated with the liquid, after introducing the liquid into the inner cavities and / or channels in a first evacuation step the predominant proportion of excess liquid is removed by the action of an external force, and in a second emptying step the residual portion of excess liquid remaining in the shaped body after the first emptying step is brought into contact with the molding surface at the end face at which the excess has been removed a porous and / or channels bearing pad is removed, wherein the pore and / or channel diameter of the support is less than or equal to the diameter of the inner cavities and / or channels of the molded article.

2. The method of claim 1, wherein the liquid is a solution, suspension, dispersion or slurry.

3. The method of claim 2, wherein the suspension is a washcoat suspension and the introduction of the washcoat suspension by sucking the washcoat suspension through the inner cavities and / or channels of the molded article to be coated by applying a ünterdruckes on the upper end face of the molded body, while on the lower end surface washcoat suspension is supplied.

4. The method of claim 3, wherein the first emptying step of the excess washcoat suspension is performed by applying an overpressure on the upper end side of the molded article.

5. The method according to any one of the preceding claims, characterized in that the removal of the remaining excess in the second emptying step in conjunction with the application of a directed to the inner cavities and / or channels of the molded body Luftstroir.es and / or dhr application centrifugal forces and / or by sole outflow of the u- excess washcoat suspension, due to their own weight, is performed.

6. The method according to any one of the preceding claims, characterized in that the porous and / or channels comprising support is selected from the group containing open-pored sponges, nets, nonwovens, and still untreated Formkorper the same kind as the emptied Formkorper.

7. The method according to claim 6, characterized in that the shaped body to be coated or to be emptied consists of a material which is selected from the group consisting of cordierite, silicates, zeolites, silicon dioxide, silicon carbide, aluminum oxide and aluminates or mixtures of these substances and Metals or metal alloys.

8. The method according to any one of the preceding claims, characterized in that the shaped body to be coated or to be emptied open and / or complex structures.

9. The method according to any one of the preceding claims, characterized in that the moldings to be coated or to be emptied have perforated channels or pore structures.

10. Use of a shaped article obtainable according to one of the preceding claims as a catalyst.

11. A device for carrying out the method according to any one of the preceding claims 1 to 9, comprising a piston cylinder (a) for sucking or emptying a washcoat suspension, a connecting plate (b), which is fixedly connected to the lower end of the piston cylinder and a sealing plate (c) which can be tightly connected on its upper side to the lower end face of the shaped body to be coated, optionally one or more vibration units attached to the receiving plate (11). c) are mounted, a hydraulically movable suspension (f) with which the cylinder unit (a), the connecting plate (b) and the receiving plate (c) can be moved horizontally upwards and downwards, an intake / outlet pipe (d) , which is attached to the lower side of the receiving plate (c) and a storage trough (s), in which the Washcoat suspension is presented.