Coating station

Abstract

The present invention relates to a coating device for producing catalytically coated flow-through monoliths for automotive exhaust treatment, wherein a vertically oriented flow-through substrate is coated from the upper and the lower sides, wherein less than 20% of the length of the through-flow monolith is coated from the lower side, and then the excess wash coat is sucked away downwards.

Description

[0001] Coating station

[0002] Description

[0003] The present invention is directed to a coating apparatus for producing catalytically coated flow-through monoliths for automotive exhaust treatment.

[0004] The exhaust gases from combustion engines in motor vehicles, for example, typically contain the harmful gases carbon monoxide (CO) and hydrocarbons (HC), nitrogen oxides (NO X ) and possibly sulfur oxides (SO X), as well as particles, which consist predominantly of soot residues and any adhering organic agglomerates. These are referred to as primary emissions. CO, HC, and particulates are products of the incomplete combustion of fuel in the engine's combustion chamber. Nitrogen oxides are formed in the cylinder from nitrogen and oxygen in the intake air when combustion temperatures locally exceed 1400°C. Sulfur oxides result from the combustion of organic sulfur compounds, which are always present in small quantities in non-synthetic fuels.To remove these environmentally and health-damaging emissions from motor vehicle exhaust gases, a variety of catalytic exhaust gas purification technologies have been developed. Their basic principle is typically based on passing the exhaust gas to be purified over a catalyst consisting of a flow-through or wall-flow honeycomb structure (wall-flow filter) and a catalytically active coating applied to and / or within it. The catalyst promotes the chemical reaction of various exhaust gas components, forming harmless products such as carbon dioxide and water.

[0005] The flow-through or wall-flow monoliths described above are therefore also referred to as catalyst supports, carriers, or even substrate monoliths, as they carry the catalytically active coating on their surface or in the pores of the wall that form this surface. The catalytically active coating is often applied to the catalyst support in a so-called coating process in the form of a coating suspension (washcoat).

[0006] An important aspect of the production of these heterogeneous catalysts is the precise coating of substrates with a washcoat, especially with regard to, for example, coating length of the channels of the substrate, applied coating amount, uniformity of the coating layer, uniformity of the coating length and coating gradients along the longitudinal axis of the catalyst support as well as in the production of layered or zoned coating designs - in short, coating quality.

[0007] There are two basic groups of manufacturing processes for producing these catalytically active catalyst bodies. Both process groups have in common that the coating suspension is introduced into the substrate monolith by applying a pressure difference, i.e., by creating different pressures at the two end faces. The coating suspension then moves through the channels of the substrate monolith toward the lower pressure.

[0008] The first group additionally works with an excess of coating suspension, which is introduced into the filter substrate by a pressure difference and where the excess coating suspension is removed from the channels by a subsequent pressure difference reversal. In this case, an excess of coating suspension means that the amount of suspension used for the coating process is significantly higher than the value required for the desired loading of the filter with catalytically active material. The excess of coating suspension is to be removed from the substrate monolith by appropriate measures, e.g. a pressure difference reversal. In the context of the invention, pressure difference reversal is understood to mean that a pressure difference present at the respective ends of the wall-flow filter is reversed, thus changing its sign. This pressure difference reversal therefore acts counter to the original coating direction.

[0009] The second group works without a pressure difference reversal and a washcoat excess, ie the entire amount of suspension intended and provided for the coating remains essentially, ie > 97% of the solid content of the coating suspension, in the substrate monolith.

[0010] EP2533901 B1 presents a coating technique for substrate monoliths that allows for a particularly precise, zoned coating. Using a special coating system, an excess amount of coating suspension is pumped into an upright substrate monolith from below. The excess coating suspension in the channels is then sucked downwards. It is particularly important that a precisely specified amount of coating medium remains on the substrate monolith. Since the coating suspensions often contain expensive precious metals such as platinum, palladium, and / or rhodium, too much suspension would result in a waste of expensive precious metal. Too little, however, can lead to the catalyst no longer achieving the required catalytic activity.

[0011] EP2415522B1 also shows a coating process in which a coating medium is applied to a substrate from above – so-called top-down coating. Using a plunger, the coating medium is fed into a cavity via a feed line and then applied to the substrate via openings in a base plate – similar to a shower head. The coating suspension is then sucked into the substrate by applying a vacuum on the other side of the substrate monolith.

[0012] The processes just discussed are all carried out using specifically designed coating devices or coating stations. Therefore, there is still a need for optimized coating equipment for the production of catalytically active substrate monoliths, especially flow-through monoliths, which set new standards in the requirements triangle of cycle time, robustness, and coating quality.

[0013] These and other objects familiar to the person skilled in the art are achieved by a coating station according to the features of claim 1. Claim 2-x is directed to preferred embodiments of the coating device according to the invention.

[0014] By specifying a coating device (1) for producing catalytically coated flow-through monoliths (2) for exhaust gas catalysis, wherein the flow-through monoliths (2) have two end faces, a lateral surface of length L and flow channels which ensure a gas flow from one end face to the other, comprising: a first unit (3) for receiving the flow-through monolith (2) in a vertical orientation; a second unit (4) for applying a coating suspension (7) to the upper end face of the flow-through monolith (2); and a third unit (5) for applying a coating suspension (7') through the lower end face of the flow-through monolith; and a fourth unit (6) for sucking excess coating suspension downwards from the flow channels of the flow-through monolith, wherein the coating device (1) is designed such thatBy ensuring that the third unit (5) contacts less than 20% of the length L of the flow-through monolith with the coating suspension (7'), and by applying the second unit (4) in such a quantity of coating suspension (7) that, upon a subsequent suction pulse by the fourth unit (6), all the flow channels come into contact with the coating suspension (7, 7') over the entire length L, the stated problem is solved quite simply, but no less advantageously. With the present coating device, it is possible to obtain more uniform values ​​over the entire coating campaign, particularly with regard to the coating quantities remaining on the flow-through monolith after coating. Likewise, the coating cycle time can be further reduced.Compared to the state of the art, there is no need to completely pump a large excess of coating suspension into the flow-through monolith, and on the other hand, two separate coating processes, possibly involving rotation of the flow-through monolith, are no longer required. Likewise, a more uniform coating length is achieved compared to designs where the coating is to be applied exclusively over the entire length of the flow-through monolith. This was by no means to be expected given the known state of the art.

[0015] Flow-through monoliths are conventional catalyst supports in the state of the art and can be made of metal (e.g., corrugated carriers, WO17153239A1, WO16057285A1, WO15121910A1 and literature cited therein) or ceramic materials. Refractory ceramics such as corderite, silicon carbide, or aluminum titanate, etc., are preferred. The number of channels per unit area is characterized by the cell density, which is typically between 200 and 900 cells per square inch (cpsi). The wall thickness of the channel walls for ceramics is between 0.5 and 0.05 mm. Further details can be found in the literature (Catalytic Air Pollution Control, Heck et al., John Wiley & Sons, Inc. 2009, p. 176ff.).

[0016] In this case, the catalytically active mass or coating is applied in the form of a suspension to the channels of the flow-through monolith using the coating device according to the invention. The coating suspension is generally a slurry of insoluble oxidic components and optionally soluble metal compounds, e.g., precious metal compounds in water. The coating suspension exhibits a desired rheology, which can be specifically adjusted to meet requirements by adding surfactants, thickeners, or acids / bases, etc. Those skilled in the art know how to proceed. The coated flow-through monolith is then dried and, if necessary, tempered and / or calcined. The finished flow-through monolith is then installed in appropriate exhaust systems.

[0017] The catalytically active coatings (7, 7') can be selected from the group consisting of three-way catalyst, SCR catalyst, ammonia oxidation catalyst, nitrogen oxide storage catalyst, oxidation catalyst, and hydrocarbon storage. Combinations are also possible. The catalytically active coatings used can be located in the pores and / or on the surfaces of the channel walls of the flow-through monolith. It is possible to coat the flow-through monolith with two different coating suspensions using the coating device according to the invention. However, using the device according to the invention, the flow-through monolith can be coated particularly well over its entire length L with a uniform coating suspension.

[0018] The production of coating suspensions for the intended purpose is well known to those skilled in the art. For stoichiometrically combustion engines, for example, so-called three-way catalysts are used to reduce exhaust emissions. Three-way catalysts (TWCs) are well known to those skilled in the art and have been legally required since the 1980s. The actual catalyst mass usually consists of a high-surface-area metal compound, particularly an oxide support material, on which the catalytically active components are deposited in extremely fine distribution. Particularly suitable catalytically active components for purifying stoichiometrically composed exhaust gases are the precious metals of the platinum group, platinum, palladium, and / or rhodium. Suitable support materials include, for example, aluminum oxide, silicon dioxide, titanium oxide, zirconium oxide, cerium oxide, and their mixed oxides and zeolites.So-called active aluminum oxides with a specific surface area (BET surface area measured according to DIN 66132 - latest version on the date of application) of more than 10 m are preferred. 2 / g. To improve dynamic conversion, three-way catalysts also contain oxygen-storing components. These include cerium / zirconium mixed oxides, which may be provided with lanthanum oxide, praseodymium oxide, and / or yttrium oxide. Zoned and multi-layer systems with three-way activity are now also known (US8557204; US8394348). For the field of lean-burn diesel and direct-injection gasoline engines, reference is made to the relevant literature (Catalytic Air Pollution Control, Heck et al., John Wiley & Sons, Inc. 2009, pp. 238ff.). In a preferred embodiment, the coating device (1) according to the invention has a second unit (4) with which the coating suspension (7') can be applied to the upper end face of the flow-through monolith (2). The second unit (4) has a shower head through which the coating suspension is applied.Other application devices are also conceivable (EP application EP22181902.2).

[0019] In a further preferred embodiment, the coating device (1) comprises a container (8) that helps prevent the coating suspension (7') from running down the outer shell of the flow-through monolith (e.g., DE202022000455U1). The container (8) can be attached to the second unit (4). However, it is also possible to attach the container (8) to the first unit (3). Those skilled in the art will know how to accomplish this in terms of equipment.

[0020] The coating device according to the invention is part of a coating station in which the flow-through monoliths to be coated are transported to the coating device, for example via belt conveyor systems. Once they have arrived there, an initial weighing step can take place in order to determine the gross weight of the flow-through monolith. The flow-through monoliths are then picked up in the first unit. The coating suspension is then applied by the coating device. The coating device, which is controlled by digital process control, can be designed such that the coating is first applied and sucked away by the third and fourth units before the coating suspension is applied and sucked through by the second and fourth units. However, according to the invention, the coating device is set up such that only one suction pulse is required.To this end, the control unit controls the coating device in such a way that the coating is first applied by the third unit from below. Then, or simultaneously, the coating suspension is applied from above by the second unit. The subsequent suction pulse by the fourth unit then conveys excess coating suspension out of the channels of the flow-through monolith and also conveys the coating suspension applied from above into the flow-through monolith. The result is a complete, preferably homogeneous coating of the channels of the flow-through monolith with extremely good wet pick-up accuracy, which can subsequently be determined by a further weighing step. Examples of a first unit can be found in the following documents, for example: WO2011098450A1; EP3887063A1; EP3865211A1; EP3285936A1.

[0021] Examples of a second unit can be found in the following documents: US9227184B2; EP1900442B1 ; JP5925101B; JP2015039672A; Examples of a third unit can be found in the following documents: DE102017122254A1 ; EP3122458B1; US2021170386AA

[0022] Examples of a fourth unit can be found in the following documents: EP3386642A1 ; CN114289253A; CN112756190A; EP3865211A1; CN208839891U; EP3285936A1 ; WO16143811 A1; JP2014233713A2

Claims

Patent claims 1. Coating device (1) for producing catalytically coated flow-through monoliths (2) for exhaust gas catalysis, wherein the flow-through monoliths (2) have two end faces, a lateral surface of length L and flow channels which ensure a gas flow from one end face to the other, comprising: a first unit (3) for receiving the flow-through monolith (2) in a vertical orientation; a second unit (4) for applying a coating suspension (7) to the upper end face of the flow-through monolith (2); and a third unit (5) for applying a coating suspension (7') through the lower end face of the flow-through monolith;and a fourth unit (6) for sucking excess coating suspension downwards from the flow channels of the flow monolith, characterized in that the coating device (1) is designed such that the third unit (5) contacts less than 20% of the length L of the flow monolith with the coating suspension (7') and the second unit (4) applies so much coating suspension (7) that, in a subsequent suction pulse by the fourth unit (6), all of the flow channels come into contact with coating suspension (7, 7') over the entire length L.; 2. Coating device according to claim 1, characterized in that the second unit (4) has a shower head through which the coating suspension (6) is applied.

3. Coating device according to claim 1, characterized in that it has a container (8) which prevents the coating suspension (7) from running down the outer shell of the flow-through monolith.

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