CN117299461A

CN117299461A - Coating apparatus

Info

Publication number: CN117299461A
Application number: CN202310772180.4A
Authority: CN
Inventors: S·马松; W·哈塞尔曼
Original assignee: Umicore AG and Co KG
Current assignee: Umicore AG and Co KG
Priority date: 2022-06-29
Filing date: 2023-06-28
Publication date: 2023-12-29
Also published as: EP4299194A1

Abstract

The present invention relates to an apparatus and a corresponding method that can be used for producing exhaust gas catalysts. In particular, the apparatus of the present invention is used to supply a liquid coating slurry into a substrate (e.g., a honeycomb monolith).

Description

Coating apparatus

With the dramatic increase in the number of automobiles, it is important to reduce the exhaust emissions of motor vehicles, particularly in the east asian countries. Several clean air actions around the world attempt to keep the pollution of air by motor vehicles at a correspondingly low level. As a result, increasingly stringent regulations have forced automotive manufacturers and suppliers to apply technologies that reduce the harmful pollutants produced by the internal combustion engines of vehicles. One area of these technologies involves the catalytic combustion of exhaust gas pollutants on or in so-called flow-through or wall-flow honeycomb monoliths.

Typically, such monolith bodies (so-called substrates) are made of, for example, metal or cordierite and must be coated with an active layer that catalytically destroys harmful pollutants in the exhaust gas under driving conditions. Great advances have been made by chemically modifying the catalytically active layer relative to the primary reaction of the contaminants in the stoichiometric, oxidizing or reducing exhaust environment. The second approach is to apply certain coating strategies to achieve as high an activity as possible for the existing materials. Thus, several patent applications have been directed to standard processes and apparatus/tools for coating the monolithic supports. For example, the following matters respectively selected from the patent publications focus on various aspects of such a process, such as a coating apparatus, a coating method or a special unit of a coating station etc. (WO 9947260A1; US4550034; US4039482; WO9748500A1; US6478874B1; US20020178707A1; DE19781838T1; WO2011080525A1; US4191126; US6627257B1; US6548105B2; US20080107806A1; US6149973; US6753294B 1).

In principle, coating techniques can be divided into two general categories. The first category relates to a coating strategy in which a liquid coating slurry is applied from below onto a vertically oriented substrate (i.e., a support or monolith support). The second type of coating technique discusses the application of a liquid coating slurry to the top of a vertically oriented substrate.

In WO9947260A1 a top down coating technique is disclosed, wherein a substrate coating apparatus comprises: means for dosing a predetermined amount of the liquid component, said amount being such that it remains substantially entirely within the intended support; a liquid component containment device positionable on top of the substrate to receive the quantity of liquid component; and a pressure device capable of withdrawing the liquid component from the containment device into at least a portion of the substrate. Other techniques working in this way can be found in US9144796B1, WO2015145122A2, EP1900442A1 or EP2415522 A1.

In particular, EP1900442A1 and EP2415522A1 relate to the problem of applying a uniform liquid washcoat slurry on top of a substrate monolith. This is important because after the pumping step, the uneven distribution of the liquid slurry (washcoat) will result in an uneven distribution of washcoat within the channels of the substrates. This problem is said to be solved in these patent applications by rotating the substrate monolith or by applying special nozzle techniques.

The invention also relates to the following problems: the liquid coating slurry on the top end surface of the monolith substrate is metered in such a way that the liquid coating slurry is uniformly distributed over a region of the top end surface of the substrate and is then drawn into and/or forced into the substrate by applying a pressure differential across the channels of the respective substrate. From an economic and/or ecological point of view, the apparatus and method involved should be advantageous in view of the prior art.

These objects are solved by providing a device as claimed in claim 1. Preferred devices are set out in the claims depending on claim 1. In claim 8 and below, a method for performing the coating according to the invention is presented.

The object of the present invention has been solved in that an apparatus for coating a substrate with a catalytically active liquid coating slurry is established, wherein the substrate has two end faces, a circumferential surface and an axial length, and is traversed by a plurality of channels from a first end face to a second end face,

the apparatus comprises

-a holding unit for reversibly vertically holding a substrate;

-a dosing unit for supplying a liquid coating slurry to be applied onto the substrate, the liquid coating slurry eventually providing catalytic activity;

-a unit for applying a pressure differential relative to the substrate to introduce the liquid coating slurry into the unit;

a receiving device located at a distance above the top end surface of the substrate for collecting the liquid coating slurry supplied by the dosing unit,

wherein the receiving means has a bottom plate comprising a flap for reversibly opening and closing. The present apparatus allows for uniform distribution of the liquid coating slurry over the area of the top end surface of the substrate. When the slurry is introduced into the substrate by applying a pressure differential against the substrate, the liquid coating slurry does enter the substrate channels uniformly, which results in a uniform distribution of the slurry within the substrate, both in terms of length and in terms of concentration gradients. It is furthermore advantageous that with the apparatus, a liquid coating paste having a low viscosity can also be applied to the substrate in a sufficient manner, for example,

to provide excellent in-wall coated wall-flow filters.

The device according to the invention comprises a receiving means. The containment device is used to hold the liquid coating slurry (i.e., washcoat) supplied by the dosing unit for a period of time while simultaneously supplying substantially all of the washcoat slurry instantaneously onto the top end surface of the substrate. This serves for a good distribution of the washcoat over the end surfaces, which in turn leads to a uniform distribution of the washcoat in the substrate passages when a pressure differential is established with respect to the substrate passages.

For this purpose, the receiving means preferably have a pot-like design with a collar and a bottom plate, the latter being capable of being reversibly opened and closed as specified above. In a further preferred manner, the apparatus is designed such that the distance between the top end face of the substrate and the bottom plate of the receiving means is between 2cm and 20cm (measured from the bottom plate with the closing flap to the top end face of the substrate; see fig. 1). If the distance is too great, the speed of the descending washcoat will be too high and it will have invaded the channels by striking the top end surface of the substrate, eventually leading to an uneven distribution of washcoat within the substrate. If the distance is too small, the flaps may not open accordingly because they may strike the top end surface of the substrate.

In order to open and close the flaps, it is preferable to arrange them so that they can rotate about the axis of rotation. The tabs at the end points of the rotation axis are fixed to the collar of the receiving means in such a way that they can rotate around the rotation axis. Rotation may be achieved by means known to those skilled in the art, such as pneumatic, electric or mechanical triggers.

In another preferred form, the tab has a tab-like profile of length (L) and is reversible about an axis arranged parallel to length (L). More preferably, the axis of rotation of the tabs is positioned such that in the open mode operating point, a majority of the profile of each tab perpendicular to the axis of rotation is located between the axis of rotation and the top end face of the substrate (see fig. 1). This serves to better pour the washcoat slurry onto the top end surface of the substrate without causing many of the washcoat to spring off by the quick-opening tabs. Instead, the liquid coating slurry in the holding device should preferably fall exactly onto the top end face of the substrate, with other momentum being minimized as much as possible.

It is advantageous if substantially all of the liquid coating slurry residing in the holding means is supplied to the top end surface of the substrate. This aspect may be enhanced if the surface of the airfoil is at least partially provided with a hydrophobic surface. The liquid coating slurry is typically based on an aqueous suspension. In the case of hydrophobic surfaces, substantially no water and insoluble components of the suspension adhere to the tab. Even better hydrophobic surfaces (https:// de. Wikipedia. Org/wiki/Lotoseffekt)) can be achieved using the so-called lotus effect on the surface of the airfoil. It is therefore considered to be very advantageous if the airfoil at least partially comprises a surface showing said lotus effect.

Coating of the substrate typically begins with the substrate being engaged in the holding unit, i.e. in a vertically oriented coating chamber, the substrate now having a top end face and a bottom end face. The holding unit may be any holding unit known to a person skilled in the art. Some examples are shown in the cited documents. Typically, the holding unit comprises an inflatable bladder to engage the substrate. The dosing unit supplies the liquid coating slurry into a receiving device having a closing flap. The dosing unit may be any known to the person skilled in the art, such as a shower head, a nozzle or those mentioned in the cited documents. The accommodating device is positioned right above the substrate. After the slurry has been filled into the containment device, the tabs snap open and the slurry falls onto the top end surface of the substrate. Finally, a unit for applying a pressure differential relative to the substrate is used to force the slurry into the channels of the substrate. After coating, the substrate is removed from the holding unit by deflating the balloon and further processed, for example by drying and optionally calcining it. In a very preferred case, the slurry in the containment device may be leveled by vibration or agitation via air flow or ultrasound.

It must be acknowledged that, as the case may be, the introduction of slurry into the substrate begins when the descending slurry impinges on the substrate. This is particularly advantageous for thin carrier coatings having a low viscosity (measured according to DIN ISO 1652-effective on application day) of 1mPas to 1000mPas, preferably 10mPas to 600mPas, respectively, at 20℃and a shear rate of 20 s-1. In these cases, it is advantageous that a pressure differential with respect to the substrate has been established before the slurry impinges on the top end surface of the substrate. On the other hand, for slurries having higher viscosities of 600mPas to 10000mPas, preferably 600mPas to 2000mPas, respectively, at 20 ℃ and a shear rate of 20s-1, it is entirely possible that the washcoat may first be applied entirely to the top end face of the substrate and only thereafter the means for applying a pressure differential relative to the substrate is used to force the slurry into the channels of the substrate. Those skilled in the art will find the best mode for their coating problem.

The apparatus of the present invention may also be provided with means for inverting the substrate within the apparatus. After the first coating step, the substrate can be turned over and can be coated again in the same way and with the same equipment from the other side, now the top end face. Preferably, this can be done by means known to the person skilled in the art, such as a robotic arm or the like or even manually, when turning the substrate. In an even more preferred manner, the holding unit of the apparatus of the invention is arranged in a rotating carousel device. Thus, by moving the turntable around the rotation axis, the substrate can be moved towards and away from the dosing unit and the receiving means. By preferably using an apparatus with a turntable comprising several holding units, several process steps can be performed in parallel, such as turning the substrate, providing slurry onto the top end surface and introducing slurry into the substrate.

The unit for applying a pressure difference with respect to the substrate is preferably a suction unit. Thus, after the liquid coating slurry is applied to the top end surface of the substrate, the slurry is introduced by sucking the slurry from the bottom end of the substrate through its channels. In a preferred embodiment, no liquid coating slurry leaves the substrate, meaning that the amount of washcoat and the vacuum applied is such that all washcoat remains in the substrate.

In another aspect, the invention relates to a method for coating a substrate with a liquid coating slurry providing catalytic activity, wherein the substrate has two end faces, a circumferential surface and an axial length, and is traversed from a first end face to a second end face by a plurality of channels, wherein each substrate is oriented vertically, and a dosing unit supplies the liquid coating slurry into a receiving device and applies a pressure differential with respect to said substrate, wherein an apparatus as defined above is used.

It is contemplated that the washcoat may be placed on top of each other, preferably without any drying or calcination therebetween. This can be achieved by using a slurry of a specific viscosity in use (EP 3648885 A1). In another preferred embodiment, the method according to the invention is performed twice on a substrate. Here, the method comprises the following steps:

-performing a first coating step according to the invention;

-inverting the substrate within the apparatus;

-performing a second coating step according to the invention.

The process may be carried out with or without any drying of the substrate in between. In view of the better cycle time, no drying step is performed between the coating steps. Those skilled in the art know how to set up the corresponding means to perform the process. The information presented by the device is applicable to the method of the invention mutatis mutandis.

Preferably, for one or both coating steps, the washcoat may be introduced as a slurry under predetermined conditions to form a washcoat layer along the length of the substrate passages, which is up to but preferably less than 100% of the total length of the monolith support; more preferably, the length is equal to or greater than about 50% and less than 80%; and more preferably equal to or greater than about 55% and equal to or less than about 70% in length, any length less than 100% is desirable based on the application. The goal of less than 100% of the total length of the carrier provides further benefits including, but not limited to, reducing accidental spillage of the washcoat slurry through the opposite end surfaces of the substrate; and suppressing particle size and composition drift problems (e.g., forming gradients) to promote a uniform surface of the applied catalyst layer.

Preferably, the substrate coated according to the invention is a flow-through or wall-flow monolith. The flow-through substrate has thin, parallel gas flow channels extending from an inlet face to an outlet face of the substrate such that the channels are open to fluid flow therethrough. The passageway, which is a substantially straight path from the fluid inlet to the fluid outlet, is defined by walls on or in which the catalytic material is coated as a washcoat such that the gas flowing through the passageway contacts the catalytic material. The flow passages of the monolithic substrate are thin-walled channels that may have any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, oval, circular, etc. Such structures may comprise about 400-900 or more gas inlet openings (i.e., cells) per square inch of cross-section (62-140 cells/cm) ² ). The wall thickness (i.e., the thickness of the walls separating the channels of the substrate from one another) is typically about 0.005cm to about 0.25cm.

The substrate to be coated according to the invention may preferably also be a honeycomb wall-flow filter. The wall flow substrate for supporting the coating composition has a plurality of fine, substantially parallel gas flow passages extending along the longitudinal axis of the substrate. Typically, each channel is blocked at one end of the substrate body, with alternating channels blocked at opposite end faces. Particular wall-flow substrates for use in the methods of the invention include thin porous wall honeycomb structures through which fluid flow passes without causing a significant increase in back pressure or pressure drop across the article. Typically, the presence of a clean wall-flow article will create a back pressure of 0.036psi to 10 psi.

The substrate is preferably a metal or ceramic monolith made of any suitable refractory material, such as cordierite, cordierite alumina, silicon nitride, zircon mullite, spodumene, aluminum silico-magnesium, zirconium silicate, sillimanite, magnesium silicate, zircon, petalite, alumina, aluminum silicate and the like. Considering, for example, flow-through monoliths suitable for the production of exhaust gas catalysts for motor vehicles according to the process of the invention, their porosity prior to coating is preferably greater than 20%, generally from 20% to 70%, in particular from 35% to 65% [ measured on the filing date according to DIN 66133 ]. The average pore size is at least 1 μm, for example from 1.5 μm to 25 μm, preferably more than 3 μm, in particular from 5 μm to 18 μm, measured on the filing date according to DIN 66134, before coating. The finished substrates suitable for the exhaust catalysis of motor vehicles initially have an average pore size of from 5 μm to 18 μm and a porosity of from 25% to 65% are particularly advantageous. Considering, for example, ceramic wall-flow filter substrates suitable for the production of exhaust gas filters for motor vehicles according to the method of the invention, their porosity is preferably greater than 40%, generally from 40% to 75%, in particular from 45% to 70% [ measured on the filing date according to DIN 66133 ]. The average pore size is at least 7. Mu.m, for example from 7 μm to 34. Mu.m, preferably greater than 10. Mu.m, in particular from 10 μm to 20. Mu.m [ measured on the filing date according to DIN 66134 ]. The finished substrates suitable for the exhaust catalysis of motor vehicles have an average pore size of from 10 μm to 33 μm and a porosity of from 45% to 65% are particularly advantageous.

When a substrate having the above-described porosity and average pore size is coated with a washcoat, a sufficient amount of the coating composition may be loaded onto and/or into the pores of the substrate to achieve excellent contaminant conversion efficiency and burn off soot in view of the filter. Regardless of the catalyst loading, these substrates are still capable of maintaining adequate exhaust flow characteristics, i.e., acceptable backpressure. In a very preferred embodiment, the substrate is a wall-flow filter.

The expression "coating/to be coated" is understood to mean that the catalytically active material and/or the storage component for the harmful exhaust gas pollutants is applied to a substantially inert substrate, which may be constructed in the manner described above for the wall-flow filter or the flow-through monolith. After drying and calcination, the established coating performs the actual catalytic function and contains storage material and/or catalytically active metal deposited, typically in highly dispersed form, on a temperature stable high surface area metal oxide (see below). Coating is typically performed by applying a liquid coating slurry (also known as a washcoat) of the storage material and/or the catalytically active component onto and/or into the walls (pores of the walls) of the inert substrate. After the liquid coating slurry is applied, the support is dried and calcined at elevated temperature, where appropriate. The coating may be composed of one layer or of a plurality of layers applied to the substrate one above the other (in the form of multiple layers) and/or offset relative to each other (in the form of areas).

The liquid coating medium/slurry is, for example, a suspension or dispersion ("washcoat") for coating an exhaust gas catalyst (flow-through monolith or filter) of a motor vehicle, which comprises a storage material and/or a catalytically active material or precursor thereof, and/or an inorganic oxide such as a zeolite (e.g., CHA, AEI, AFX or similar 8-ring zeolite), or a refractory oxide (e.g., alumina, titania, zirconia, or a combination thereof), which may be doped with, for example, silicon or lanthanum. The zeolite may be exchanged with metal cations such as Fe and/or Cu. Oxides of vanadium, chromium, manganese, iron, cobalt, copper, zinc, nickel, or rare earth metals (such as lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium) or combinations of these oxides may be used as the catalytically active component. Noble metals such as platinum, palladium, gold, rhodium, iridium, osmium, ruthenium, and combinations thereof may also be used as the catalytically active component. These metals may also be present as alloys with each other or with other metals or as oxides. The metal may also be present as a precursor, such as a nitrate, sulfite or organic group of the noble metal, and mixtures thereof; in particular palladium nitrate, palladium sulphite, platinum nitrate, platinum sulphite or Pt (NH) ₃ ) ₄ (NO ₃ ) ₂ Can be used in liquid coating media. The catalytically active component may then be obtained from the precursor by calcination at a temperature of from about 400 ℃ to about 700 ℃. To coat a substrate for the production of automotive exhaust gas catalysts, the coating may first be carried out using a suspension or dispersion of an inorganic oxide, and then in a subsequent coating step, a suspension or dispersion containing one or more catalytically active components may be applied. However, it is also possible for the liquid coating medium to contain two components. In a very preferred embodiment, the liquid coating slurry has a viscosity of 10mPas to 2000mPas at 20℃and a shear rate of 20 s-1.

The preferred embodiment of the initial apparatus is mutatis mutandis in detail according to the method, and vice versa. In another preferred aspect, the invention may cover a coating station comprising an apparatus according to the invention. The preferred embodiments of the methods and/or apparatus disclosed herein are applicable to the coating station mutatis mutandis. This is especially true for more mechanical aspects discussed in connection with the above-described methods and/or apparatus, such as rotating turntables, robots for loading and unloading or turning substrates in a holding unit, and the possibility of coating substrate monoliths from both sides.

The present invention allows for an advantageous top-down coating process. The present invention can be used with liquid coating slurries for exhaust catalyst production, which slurries have a wide range of viscosities. The low viscosity as well as high viscosity washcoat can be very uniformly coated on a flow-through or wall-flow substrate (fig. 2). The uniform distribution of washcoat within such substrates results in optimized backpressure, filtration efficiency, and catalytic performance. This is not obvious to a person skilled in the art before carrying out the present invention.

Description of the drawings:

fig. 1: the holding unit (2) and the receiving means (3) comprising the tabs (4) and the substrate (1) to be coated are shown.

Fig. 2: the coated open monolith according to the present invention shows little variation in the coating length from channel to channel.

Experimental part：

Example 1：

The flow-through substrate (cordierite, 4.66 "diameter 4.5" length, 600/4 pores per square inch/mil) was coated with an alumina-containing washcoat having a viscosity of 1200mPas at 20s-1 using a dosing unit. The monolith was vertically engaged into the coating station and a corresponding amount of washcoat was applied to the top end surface by means of the apparatus according to the invention with the receiving means. After the washcoat is applied, it is drawn into the monolith from below, and the monolith is then dried and calcined under normal conditions.

Claims

1. An apparatus for coating a substrate with a catalytically active liquid coating slurry, wherein the substrate has two end faces, a circumferential surface and an axial length, and is traversed by a plurality of channels from a first end face to a second end face,

the apparatus comprises

-a holding unit for reversibly vertically holding the substrate;

-a dosing unit for supplying a liquid coating slurry to be applied onto the substrate;

it is characterized in that the method comprises the steps of,

the containment device has a bottom panel that includes a reversibly openable and closable flap.

2. The apparatus according to claim 1,

it is characterized in that the method comprises the steps of,

the distance is 2cm-20cm (measured from the bottom panel to the top end face with the closing flap).

3. The apparatus according to claim 1 and/or 2,

it is characterized in that the method comprises the steps of,

the tab has a tab-like profile of length (L) and is capable of being turned around an axis arranged parallel to length (L).

4. The apparatus according to one of the preceding claims,

it is characterized in that the method comprises the steps of,

the surface of the airfoil has at least partially a hydrophobic surface.

5. The apparatus according to one of the preceding claims,

it is characterized in that the method comprises the steps of,

the apparatus includes means for inverting the substrate within the apparatus.

6. The apparatus according to one of the preceding claims,

it is characterized in that the method comprises the steps of,

the holding unit is arranged in a rotary turret device.

7. The apparatus according to one of the preceding claims,

it is characterized in that the method comprises the steps of,

the unit for applying a pressure differential relative to the substrate is a suction unit.

8. A method for coating a substrate with a liquid coating slurry, wherein the substrate has two end faces, a circumferential surface and an axial length, and is traversed from the first end face to the second end face by a plurality of channels, wherein each substrate is oriented vertically, and a dosing unit supplies the liquid coating slurry into a receiving device and applies a pressure differential with respect to the substrate,

wherein the device as defined in one of the preceding claims is used.

9. The method according to claim 8, comprising the steps of:

-performing a first coating step according to claim 8;

-inverting the substrate within the apparatus;

-performing a second coating step according to claim 8.

10. The method according to one of the claims 8-9,

it is characterized in that the method comprises the steps of,

the substrate is a wall-flow filter.

11. The method according to one of the claims 8-10,

it is characterized in that the method comprises the steps of,

the liquid coating slurry was at 20℃and 20s ^-1 The viscosity at shear rate is 0,01pa s-10pa s.