MXPA99002322A - Process for the coating of the flow channels of a catalytic converter conduit in the form of a bee nest with a dispers cover - Google Patents

Abstract

The present invention relates to a process for the coating of a monolithic, cylindrical catalyst agent, in the form of a honeycomb with a coating dispersion, the agent has axially aligned flow channels arranged in a grid over a cross-sectional area, the agent has a top and bottom face and the process is characterized in that it comprises the steps of: a) leading the agent to a straight position so as to direct the flow channels vertically, b) filling the flow channels through the bottom face with a volume of This coating dispersion, which is 10% larger than the empty volume of the flow channels, so that after finishing the filling cycle, the coating dispersion floods the upper face, c) remove the excess dispersion of the coating. coating of the upper face of the agent, d) emptying and cleaning by extraction the flow channels through an extraction impulse, which is generated by m The connection of a vacuum tank by means of an extraction duct, with the underside of the catalytic agent, means that the time between the start of the filling cycle and the end of the emptying and the cleaning by extraction does not exceed 5 seconds. and optionally drying and calcining the coated catalyst agent after emptying and flushing the fluids.

Description

PROCESS FOR THE COATING OF CHANNELS OF FLOW OF A CATALYST CONVERTER DUCT IN SHAPE OF BEES NEST WITH A COVER OF DISPERSION Field of the Invention The present invention relates to a process for coating the flow channels of a catalyst conduit in the form of a honeycomb with a dispersion coating.

Background of the Invention The honeycomb catalytic converter ducts are largely used for the creation of automobile exhaust catalytic converters. They can have a cylindrical shape and are replete with a multitude of flow channels parallel to the axis of the exhaust cylinder of internal combustion engines. The shape of the transverse profile of the catalytic conduit depends on the design requirements of the vehicle. In general, catalytic converters with transverse profile are used REF .: 29769 of round, elliptical or triangular shape. The flow channels have, for the most part, a square cross-sectional profile and are arranged in a tight lattice over the entire cross-section of the catalytic converter. According to the circumstances of each specific application, the cell density of the flow channels varies between 10 and 120 cm-2. Beehive ducts are being developed with cell densities up to 250 cm "2 and more.

Those that are used predominantly for the purification of automobile exhaust gases are the catalytic conduits that are obtained by the extrusion of ceramic masses. On the other hand, there are catalytic ducts made of corrugated and rolled metal sheets. Ceramic catalytic converters with cell densities of 62 cm 2 are still predominantly used for the purification of passenger vehicle emissions, and the cross-sectional dimensions of the flow channels amount, in this case, to 1, 27 x 1.27 mm-2 The wall thicknesses of these catalytic ducts are in the range of 0.1 to 0.2 mm.

In general, metals of the platinum group finely distributed are used, which can be modified in their catalytic effect by means of base metal compounds, for the conversion of the pollutants contained in the exhaust of automobiles - such as carbon monoxide, hydrocarbons and oxide. of nitrogen - to obtain harmless compounds. These catalytically active components must be deposited in the catalytic ducts. However, it is not possible to guarantee the necessary fine distribution of the catalytically active components by means of the deposition of these components on the geometric surfaces of the catalysts. just applies equally to non-porous metal catalysts, as well as porous ceramic catalysts. Only a sufficiently large surface area for the catalytically active components can be obtained by the application of a support coating of fine particle materials with large surface area.

Description of the invention.

Accordingly, the present invention relates to a process for applying said type of support coating on the internal surfaces of the flow channels of the honeycomb catalysts. In the context of the present invention, the support retention for the catalytically active components is designated as a dispersion coating. The dispersion coating consists of fine particle materials with a large surface area and is produced under the application of a so-called dispersion resistor. The coating dispersion consists largely of a mixture of the fine particle materials in water.

Various processes for the deposition of the dispersion coating are known in the prior art. After the coating process, the catalysts are dried and then calcined to consolidate the coating in dispersion. Long the catalytically active components in the dispersion coating are introduced by impregnation with mostly aqueous solutions of precursor compounds of the catalytically active components. On the other hand, the catalytically active components can be added to the coating itself. In this case, another impregnation of the dispersion coating prepared with the catalytically active components is no longer necessary.

For efficient purification of exhaust gases from internal combustion engines, the volume of catalytic ducts must be of an adequate dimension. Usually, a displacement ratio of the engine cylinders to the volume of the catalytic duct is chosen from 1: 2 to 2: 1. This is how a typical automobile catalytic converter has a volume of approximately 1 liter with a diameter of 100 mm (4 inches) and a length of 152 mm (6 inches). The dry weight of the dispersion coating of these catalyst ducts is 50 to 200 g / 1 volume of the catalyst duct. With a cell density of 62 cm-2, this corresponds to a calculated coating thickness of the dispersion coating from 20 to 80 μm. However, because of the capillary forces, the dispersion coating is generally distributed irregularly over the cross section of the flow channels, with heavy accumulations of coating material in the channel bends and coating thicknesses. thin in the middle part of the walls of the channels.

The processes for the application of the coating in dispersion to the catalytic ducts must have a high productivity with low amounts of waste. Therefore, it should be possible to apply the total amount of coating on the catalyst conduit in a single cycle of action. Multiple coatings should be avoided to obtain the necessary coating thickness. Moreover, the coating processes must ensure that the coating material does not obstruct the flute channels. In addition, generally such coating processes require to avoid coating the outer covering of the catalyst conduit. By doing so, you can economize on the expensive coating material and potentially expensive catalytically active components.

GB 1 515 733 describes a reversing process for ceramic catalyst ducts. The porous catalyst ducts are inserted in the upright position, that is, with the vertically oriented flow channels, in a coating tank adjusted to pressure and degassed by means of the application of a partial vacuum of 0.84 bar (8.40 kPa). ) (25-inch (60 cm) mercury column). The coating dispersion is then poured onto the upper face of the catalyst conduit inside the coating tank and compressed into the porous of the catalyst conduit by the application of overpressure. After removing the overpressure and opening the discharge valve at the base of the coating tank, the excess coating dispersion leaves the flow channels of the catalyst conduit. Finally, the channels that may be blocked by the coating dispersion are opened with compressed air blown from top to bottom. The cycle time of this coating process amounts to less than 1 to 2 minutes.

U.S. Patent No. 4,208,454 also describes a process for coating porous ceramic catalyst ducts. The catalytic ducts to be coated are placed with their lower face on the opening of a collecting tank in which the pressure is reduced by means of a high volume blower through a water column of 5 to 16 inches (12 to 38.3 cm) ) in relation to atmospheric pressure. This partial vacuum remains constant throughout the coating period. A predetermined volume of the coating dispersion is distributed over the upper face of the catalyst conduit and is constantly run through the flow channels to the collector tank. The aspiration cycle is maintained for approximately 30 seconds. After the first 5 seconds, the total amount of coating is run through the catalyst conduit. For the rest of the time, the air that flows through the Flow channels guarantee the opening of the 'channels that may be blocked by the coating dispersion. The amount of coating remaining in the catalyst conduit can be affected by the total solution time duration and by the partial vacuum level. The axial uniformity of the condensate on the catalyst conduit can be improved by rotating the catalyst conduit after approximately half the aspiration time and then aspirating in the opposite direction. With this process, coating dispersions with a solids content of 30 to 45% as well as a viscosity of 60 to 3000 cps can be processed. The preferred solids content is 37% by weight and the preferred viscosity is 400 cps. The possibility of reproduction of the coating quantity is +/- 5% in this process.

EP 0157 651 also describes a process for coating ceramic catalyst conduits with a predetermined amount of a coating dispersion. For this purpose, the pre-weighed amount of the coating dispersion is poured into a well-open tank and the lower face of the catalyst conduit is submerged. The dispersion is then aspirated into the flow channels by the application of a slight partial vacuum. To improve the axial uniformity of the coating, it is recommended, also in this case, that the coating process be carried out in two stages.

In the first step, only about 50 to 85% of the total amount of coating in the tank is poured and aspirated into the catalyst conduit. Next, the catalyst conduit is rotated and the remaining amount of coating is drawn in the opposite direction. This coating process does not require a separate passage for the opening of the flow channels. The cycle duration of this process amounts to less than one minute. With this process, coating dispersions with a solids content of 35 to 52% as well as a viscosity of between 15 and 300 cps can be processed.

U.S. Patent No. 5,182,140 discloses a process for coating ceramic and metallic catalyst ducts. In this process, the coating dispersion is pumped from below into the catalyst conduit placed in a vertical position until the dispersion reaches a level completely above the upper face of the catalyst conduit. The coating dispersion of the substrate is then removed by the application of compressed air on the upper face of the catalyst conduit. In this way, the flow channels that can still be closed are opened by insufflation. In accordance with Example 1 of this patent document, a level of the coating dispersion 2 cm above the upper face of the catalyst conduit is used. Compressed air is introduced for the ejection of the coating dispersion from the flow channels in two successive pressure stages. During the first 2 seconds after the filling of the catalyst duct, the coating dispersion is operated with compressed air at 3.7 bar (370 kPa). This high pressure is sufficient to expel the coating dispersion completely from the flow channels for the 2 seconds available. Next, the compressed air is reduced to 0.37 bar ^ and the catalyst conduit is operated twice with this pressure for 0.5 seconds at a time. With this process, coating dispersions with a specific density of between 1 and 2 g / ml and a viscosity of between 100 and 500 cps can be processed.

Similarly, DE 40 40 150 C2 describes a process for the uniform coating of a honeycomb duct made of ceramic or metal. For this process, the honeycomb duct is submerged in an immersion barrel and filled with the coating dispersion from the bottom. Then the honeycomb duct is also evacuated by means of insufflation or aspiration. The honeycomb duct is then removed from the dip barrel and cleaned with suction or insufflation in a separate arrangement to avoid blockage of the flow channels. With this process, dispersions of condensation can be processed with a solids content of 48 to 64% and viscosities of 50 to more than 100 cps.

The catalytic converters of exhaust emissions for internal combustion engines are subject to constantly increasing regulatory requirements with respect to their ability to convert pollutants and their useful life. An increase in the useful life of the catalytic converters can be obtained by means of an improved catalyst make, as well as by an increase in the amount of catalytically active components on the catalyst. Nevertheless, a greater quantity of catalytically active components also requires a higher loading of the catalyst conduit with the coating dispersion. A better conversion of contaminants can also be obtained by means of catalyst ducts with higher cell densities. In both cases - with the increase in the coating concentration as well as with the increase in cell density - the danger of the coating process clogging the flow channels with the coating dispersion increases.

Therefore, one of the objectives of the present invention is to present a new coating process for metallic or ceramic honeycomb-shaped catalyst ducts that is distinguished by exhibiting the following characteristics: - Reproducible load of the catalyst duct of a production batch with the same amount of coating dispersion.

- Coating of the catalyst duct with more than 200 g of dry mass per liter of the volume of the catalyst duct.

- Coating of catalytic ducts with cell densities of up to 250 cm "2.

- The radial and axial thickness of the coating as uniform as possible to obtain.

Safely prevent blockage of flow channels - The greatest possible independence between the process and the reollogical characteristics of the coating dispersion.

The aforementioned and other objects are obtained according to the present invention by means of a process for coating the flow channels of a cylindrical catalyst duct with honeycomb conformation, with a coating dispersion, filling the oriented flow channels in a vertical position with a dosed amount of the coating dispersion through the lower face of the catalyst conduit and then emptying in the downward direction and cleaning of the flow channels, as well as drying and calcining the catalyst conduit. The process is characterized by understanding the following steps: a) Filling the flow channels with a dosed amount that is approximately 10% higher than the capacity of the flow channels, so that the coating dispersion overflows the top of the catalyst duct after the filling cycle is completed, b) Elimination of excess coating dispersion in the upper part before evacuating the flow channels, and c) Evacuation and cleaning by extraction of the flow channels by means of an extraction impulse, which is generated by connecting a tank vacuum with the underside of the catalytic converter, therefore, the time between the beginning of the filling cycle and the end of the evacuation and cleaning by extraction is not greater than 5 seconds.

Brief Description of the Drawings.

The present invention will be understood more clearly with reference to the accompanying drawing in which: Figure 1 is a schematic representation of the apparatus used to carry out the process.

Detailed description of the invention.

According to the present invention, the filling, evacuation and cleaning by extraction of the flow channels of the catalytic converter are carried out very quickly. The flow rate of the coating dispersion inside the flow channels is 0.1 to 1 m / s. The filling of the coating dispersion from the bottom continues until the softening dispersion exits the upper face of the catalyst conduit and is submerged to the upper face. In this way, it is ensured that all the flow channels of the catalyst conduit are filled with the coating dispersion. This is the case, then, if the required coating dispersion volume is approximately 10% higher than the capacity of all the honeycomb-shaped duct flow channels as a whole. Preferably, this excess coating dispersion is adjusted to 1 to 5% of the capacity of the flow channels. On the one hand, this excess must be kept as low as possible, although, on the other hand, it must be sufficient to guarantee the complete filling of all the flow channels. Too large an excess of coating dispersion leads to a washing effect of the flow channels and, thereby, to the reduction of the amount of coating remaining on the catalyst conduit.

The filling of the flow channels can occur in various ways. There is the possibility of pumping the coating dispersion into the catalyst conduit from the bottom or, otherwise, aspirating it into the catalyst conduit by means of the application of a partial vacuum on its upper face. Preferably, the coating dispersion is introduced by pumping.

The second measure - according to which the excess coating dispersion is removed by the upper part before the evacuation and cleaning by extraction of the flow channels - of the process according to the present invention also serves to prevent said effect of washing. This can happen, for example, by means of the application of suction on the upper face of the catalytic conduit from the side or from above. The omission of the removal of excess coating dispersion before the evacuation would result in that this excess excess coating dispersion has to be extracted also by the flow channels. The consequent washing effect would reduce the amount of coating deposited on the catalyst conduit.

Tests have shown that by pre-removing the excess coating dispersion, the amount of coating collected in the catalyst conduit can be increased by approximately 20 g dry mass per liter volume of the catalytic converter.

The rapid evacuation and safe prevention of blockage of the flow channels are obtained by applying an extraction pulse on the underside of the catalytic channel. The short span of less than 1 second between filling and evacuation leads to a situation in which the flow limit of thixotropic to intrinsically viscous dispersions can not be increased. The extraction pulse is generated by means of a vacuum tank, which is connected to the lower face of the catalyst conduit. Preferably, the vacuum tank is evacuated with a partial vacuum of at least 150 mbar (15 kPa). By creating the connection between the underside of the catalyst conduit and the vacuum tank, the coating dispersion is removed from the flow channels in a short time of 1 to 1.5 seconds. The incoming air opens the flow channels that may still be blocked, which, in the context of the present invention, is characterized as extraction cleaning, and leads to the reduction of the partial vacuum in the vacuum tank and, consequently, to a continuous decrease in the flow rate of air in the flow channels.

The characteristics of the evaluation can be affected by four parameters. Consequently, it implies the initial partial vacuum in the vacuum tank, the power required in the suction blower, the capacity of the vacuum tank in relation to the capacity of the catalytic converter and the open cross-sectional profile between the lower face of the catalytic converter and the vacuum tank.

The fastest possible removal of the coating dispersion from the flow channels is obtained by means of a partial vacuum in the vacuum tank of at least 150 mbar (15 kPa). Subsequently, the partial vacuum, as a driving force for the removal of the coating dispersion from the flow channels and for the subsequent air flow, must be constantly reduced to prevent the release of a large part of the coating material from the flow channels. . This can happen by means of the correct dimension of the volume of the vacuum tank and the power of the blower, and by means of the adjustment - between 0 and a maximum value equal to the cross section of the duct chosen between the catalyst duct and the tank of vacuum - by means of a reducing register, with an open transverse profile between the catalytic converter and the tank.

During extraction cleaning, the air flow rate in the flow channels is more than 5 m / s. The maximum value of the flow index at the beginning of the extraction is greater than 40 m / s. These flow rates can be adjusted by the corresponding regulation of the reduction register and the power of the blower.

The dried ceramic catalyst ducts can produce a considerable suction capacity for the fluid phase of the coating dispersion. In the coating of catalytic ducts with high cell density, which have cell densities of 120 cm "2 and more, this already leads to a solidification of the coating dispersion *, and in turn to an obstruction of the flow channels during the filling of the catalyst conduit. catalyst ducts by means of the process described, the catalytic ducts must be moistened before the coating.In this wetting, a previous impregnation with acids, bases or saline solutions can be used.The previous impregnation facilitates the formation of the coating on the walls of the channels according to the with the sol-gel method By contacting the coating dispersion with the walls of the pre-impregnated channels, the pH value of the dispersion is modified, in this way, the dispersion becomes a gel.

The concentration of the coating dispersion on the catalyst conduit can be increased, in another advantageous embodiment of the process according to the present invention, by flowing preheated air through the catalyst conduit at temperatures of 20 to 150 ° C and speeds greater than 4, preferably 7-10 m / s, against the gravitational force during the 5 to 20 seconds after the removal of the coating apparatus from the bottom. By means of this type of drying prior to the actual calcination of the catalyst ducts, a tapering of the flow channels - or a narrowing of the channel at the lower end of the catalytic ducts - often observed with very high loads can be avoided. . This additional measurement makes it possible to load the catalyst duct with a larger amount of coating than usual, without the danger that the flow channels will become narrowed or narrow during the drying and calcination cycle.

Next, the invention will be explained in more detail with reference to some examples.

According to Figure 1, the coating apparatus consists of: the catalyst conduit 1 to be coated, a receptacle 17 for the catalyst conduit with a lower rubber collar 2 and a rubber upper collar 2 ', - an extraction funnel 3 under the receptacle for the catalytic converter, - an extraction duct 4 connecting the extraction funnel 3 to the vacuum tank 5 by means of the regulating vane 12, - a steam extractor 6 with the vacuum tank, as well as a suction blower 7, which maintains a partial vacuum of approximately 150 to 500 mbar in the empty tank, - a recirculation duct 8, as well as a pump 9, for the recirculation of the excess coating dispersion, - tank 10 for coating dispersion 19, - a pump 11 for pumping the coating dispersion towards the catalyst conduit, - a cover cap 13 with a relief valve 16 and a suction line 15 entering the extraction line 4, whereby the cover cover can be lifted by rotating around the pivot axis 14, and - a suction valve 18 in the suction line 15.

- With this coating apparatus, the coating of a honeycomb-shaped duct is carried out in the following manner: 1. The regulating fin 12 and the suction valve 18, 2 are closed. The catalyst conduit 1 is loaded in the receptacle 2, 3. The cover cap 13 is placed on the upper rubber collar of the catalyst conduit, opening the relief valve 16, 4. An amount is pumped to fill the coating dispersion approximately 10% higher than the capacity of the flow channels (excess coating dispersion), into the catalyst conduit from the bottom with the pump 11, . The suction valve 18 is opened and the excess coating dispersion from the upper face towards the vacuum tank 5 is sucked from the upper part, 6. The suction valve 18 is closed, the lid is opened and then the regulating flap 12 is opened - up to a predetermined value to extract the excess coating dispersion from the catalyst duct (extraction cleaning), 7. Subsequent extraction is carried out of air to open the flow channels that may still be blocked, 8. The catalytic channel is removed, and in some cases hot air is blown through the catalyst conduit in the opposite direction to that of evacuation in a separate apparatus.

In the vacuum tank, the extracted coating dispersion is collected and transferred back to the storage tank 10 by means of the pump 9 through the return pipe With the described apparatus, the following series of tests was carried out: Comparative Example 1 A catalytic coating was applied to a series of 100 ceramic honeycomb ducts. All the dispersions were strongly thixotropic (the definition of thixotropy is taken according to DIN 13342).

Data of honeycomb ducts Density of cells 62 cm "2 Wall thickness 0.16 mm Diameter 101.6 mm Length 152.4 mm Capacity 1, 24 1 Data of the dispersion of withdrawal Solids content of the mixed dispersion of oxides A1203 60% by weight vis eosity 400 mPa. s Process parameters Filling time 1.5 s Excess of coating dispersion Suction time for excess coating no suction "empty container /" honeycomb UU partial vacuum pi 350 mbar (35 kPa) position of the regulating fin 27% evacuation time (extraction time) 0.5 s time after extraction (cleaning by extraction) 1 s With these coating parameters, a coating concentration of 210 g of dry mass per liter of catalyst catalyst capacity was obtained with a standard deviation of s = 8 g.

Example 1 The restoring sequence of the Comparative Example 1. However, the excess amount of coating dispersion was removed by suction in a lapse within 1 second, this time before evacuation.

The concentration of the coating obtained in this way amounted to 235 g of dry mass per liter of capacity of the catalyst condjuct with a standard deviation of s = 5 g.

E j us 2.

The coating sequence of Example 1 was repeated with a setting of the regulating fin at 25% (25% opening of the maximum flow cross section). The channels were still blocked after the extraction cleaning. Then there was an air flow heated to 80 ° C through the flow channels of the catalytic converter from the bottom at a speed of 5 m / s for a duration of 10 seconds. The channels opened and, after 10 minutes, they were still open.

The coating concentration obtained in this manner amounted to 263 g of dry mass per liter of catalyst catalyst capacity with a standard deviation of s = 6 g.

Example 3 Another series of 100 honeycomb ducts was coated as in Example 1. The honeycomb ducts were moistened before applying the coating by immersion in a solution of ammonia in water (pH = 8, 5) . All other parameters were the same as those used in Example 1.

The absorbed dry product obtained from the honeycomb conduits amounted to 252 g / 1 with a standard deviation of s = 3 g.

E j us 4 A catalytic coating was applied to a series of 100 ceramic conduits "in honeycomb with high density of cells.

Data of honeycomb ducts Density of cells 120 cm "Wall thickness 0, 1 mm Diameter 152.2 mm Length 50.8 mm Capacity 0.93 1 Data of the coating dispersion: Solids content of the mixed dispersion of oxides l2? 3 50 in weight viscosity 300 mPa. s Process parameters Filling time 1.0 s Excess of coating dispersion 5% Suction time for the excess coating 1 s "empty container /" honeycomb 500 partial vacuum pi 400 mbar (40 kPa) position of the regulating fin 30% time evacuation (extraction time) 0.5 s time after extraction (cleaning by extraction) 3 s With these coating parameters, a coating concentration of 315 g dry mass per liter of catalyst catalyst capacity was obtained with a standard deviation of s = 10 g.

As in the preceding examples, by means of the application of the measures according to the present invention, especially the elimination of the upper excess of coating dispersion before the evacuation of the honeycomb ducts and the circulation of hot air through them in the opposite direction to the evacuation, you can significantly increase the concentrations of coating that is possible to obtain. Accordingly, by removing the excess excess coating dispersion, the increase in the coating concentration of Example 1 reaches +12% relative to Comparative Example 1. Another increase in coating concentration of + 12% was obtained. (+25% in relation to Comparative Example 1) by reducing the cross-sectional profile of open flow in the extraction cleaning and subsequent circulation.

The possibility of reproducing the coating by means of impregnation of the honeycomb ducts with a solution of ammonia in water can be considerably improved.

The present result was obtained in the apparatus of Figure 1. The process can, however, be carried out with differently configured apparatuses, completely following the steps described in the process.

Further variations and modifications of the foregoing will be clear to those skilled in the art and are thought to be encompassed by the claims added to this.

The German priority document 198 10 260.7 is taken as a basis, which is incorporated herein by reference.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, the content of the following is claimed as property.

Claims (8)

Claims

1. A process for coating the flow channels of a honeycomb-shaped cylindrical catalyst duct with a dispersion coating by filling the vertical flow channels of said duct with a filling amount of the dispersion of coating on a lower face of the catalytic channel and the subsequent evacuation in the downward direction and cleaning by extraction of the flow channels, characterized in that it consists of the following steps: a) filling of the flow channels with a dosed quantity that is approximately 10% higher than the capacity of the flow channels, so that the coating dispersion overflows the top of the catalytic converter once the filling cycle is completed, b) elimination of excess coating dispersion in the upper part before evacuating the flow channels, and c) evacuation and cleaning by extraction of the flow channels by means of an extraction impulse, which is generated by connecting a tank vacuum with the underside of the catalyst duct, and optionally the drying and calcination, whereby the time elapsed between the beginning of the filling cycle and the end of the evacuation and cleaning by extraction does not exceed 5 seconds.

2. The process according to claim 1, characterized in that the vacuum tank has an initial partial vacuum of at least 150 mbar (15 kPa) and a volume that adds 100 to 1000 times the volume of the catalyst conduit.

3. The process according to claim 2, characterized in that, during extraction cleaning, a minimum air flow rate of 5 m / s is maintained in the flow channels.

4. The process according to claim 3, characterized in that the transverse flow profile open to the vacuum tank can be adjusted between 0 and a maximum volume.

5. The process according to the claim 4, characterized in that the time elapsed between filling and evacuation is so short that the flow limit of the thixotropic or intrinsically viscous dispersions can not be developed.

6. The process according to the claim 5, characterized in that the catalyst conduit is moistened before proceeding to the application of the coating.

7. The process according to claim 5, characterized in that the catalyst conduit is previously impregnated with acid, bases or salt solutions before proceeding to the application of the coating.

8. The process according to the rei indication 1, characterized in that, after evacuating the flow channels and before the calcination of the catalyst conduit, a flow of air is run by heating to a temperature of 40 to 80 ° C through the flow channels, in the opposite direction to the direction of evacuation at a speed of more than 2 to 10 m / s during a period of 2 to 60 seconds. Summary of the Invention A process for coating the flow channels of a honeycomb-shaped cylindrical catalyst conduit with a dispersion coating is described by filling the vertical flow channels of said conduit with a filling amount of the coating dispersion on the underside of the catalyst duct and the subsequent evacuation in the downward direction and cleaning by extraction of the flow channels, as well as the drying and calcination of the catalyst duct, which is characterized by the following steps: a) Filling the flow channels with a dosed amount that is approximately 10% higher than the capacity of the flow channels, so that the coating dispersion overflows the top of the catalyst duct after the filling cycle is completed, b) Elimination of excess coating dispersion in the upper part before evacuating the flow channels, and c) Evacuation and cleaning by extraction of the flow channels by means of an extraction impulse, which is generated by connecting a tank vacuum with the underside of the catalytic converter, therefore, the time elapsed between the beginning of the filling cycle and the end of the evacuation and cleaning by extraction does not exceed 5 seconds.