KR20210094269A - A method for coating multilayer of catalyst slurry on a carrier of purification catalyst for exhaust gas - Google Patents

Abstract

The present invention relates to a method for multi-layer coating the inside of a catalyst carrier for exhaust gas purification with quantitative catalyst slurry, and in detail, to a coating method for improving the productivity of a coating process by coating the inside of a converter or filter, which is the catalyst carrier for exhaust gas purification, in multiple layers with the quantitative catalyst slurry and completing all one layer in a coating step, and when the quantitative catalyst slurry is injected into a carrier channel once to form one layer, the productivity is improved by about 20% compared to a conventional partial-coating method.

Description

A method for coating multilayer of catalyst slurry on a carrier of purification catalyst for exhaust gas

The present invention relates to a method of multi-layer coating the inside of a catalyst carrier for exhaust gas purification with a quantitative catalyst slurry, and more particularly, multi-layer coating the inside of a converter or filter for exhaust gas purification with a quantitative catalyst slurry, one layer being a slurry It relates to a coating method for improving the productivity of the coating process by completing the entire coating step by injection.

The catalytic converter is a structure that converts harmful components of exhaust gas into harmless components by catalysis. In a typical form of a catalytic converter, a slurry on which various catalyst components are supported (hereinafter referred to as catalyst slurry) is coated on a plurality of longitudinal channels of a carrier. In addition, the catalytic filter for exhaust gas purification is a filter technology that collects particulate matter emitted from an internal combustion engine, burns it, regenerates it, and collects particulate matter again for reuse. , Catalyzed soot filter) method may be employed. The carrier or carrier of such a converter or filter is a porous silicon carbide sintered compact, a type of ceramic sintered compact, or a honeycomb structure formed of cotierite, aluminum titania, or the like, and a catalyst material is coated on the carrier cell wall. On the other hand, various methods can be considered as a method of coating a quantitative catalyst slurry on the catalytic converter, but in particular, the so-called PnP (push and pull) method in Korean Patent 10-1271434 and the partial-coating method in US Patent 9,144,796 are the most effective methods. is understood as However, in the case of forming a multilayer catalyst structure by applying the above-mentioned powerful coating methods, each catalyst layer is formed by multiple coatings in two steps, specifically, the first part of the catalyst slurry is partially coated on the first half of the support, and after inverting the support, The second part of the catalyst slurry is partially coated on the second half of the carrier, and by introducing a viscosity improving modifier into the slurry, the first partial coating part can be strengthened to solve the non-uniformity caused by the introduction of the second part of the slurry, so that the first part Although it has the advantage that the drying step can be omitted between the coating and the second partial coating, it takes two or more partial coatings to complete one such layer, with the time burden of viscosity modifier selection and application and the negative impact on catalyst activity. There is a disadvantage of a decrease in productivity due to this.

According to U.S. Patent 10,183,287, a wet multi-layer catalyst layer coating method is disclosed into a carrier, the first catalyst layer is formed by one coating of the initial first catalyst slurry, and the viscosity of the first catalyst layer is higher than that of the initial catalyst slurry. A method is taught in which a second catalyst layer is formed on the first catalyst layer by one-time coating of the second catalyst slurry, but the viscosity of the second catalyst slurry is lower than that of the first catalyst layer. In the 287 patent, a viscosity control process is required to enable such a one-time coating, compared to the improved productivity by one-time coating for one layer, and thus problems of process time and cost are pointed out. Therefore, the development of a coating method for improving productivity is still required.

It is an object of the present invention to provide a catalyst slurry coating method for forming a multi-layer catalyst layer on a catalyst carrier for exhaust gas purification. Another object of the present invention is to provide a catalyst slurry coating method capable of improving productivity by one-time coating for one layer without applying a viscosity modifier and a dispersant to the catalyst slurry. According to the present invention, a catalyst slurry coating method in which a noble metal can be uniformly distributed in a multi-layer catalyst layer is proposed. Another object of the present invention is to provide a catalyst slurry coating method in which productivity is improved by about 20% compared to the conventional partial-coating method.

In order to achieve the above object, the present invention provides a method for forming a multi-layer catalyst layer on a catalyst carrier for exhaust gas purification, the method comprising: forming a first layer by quantitatively injecting a catalyst slurry once into the catalyst carrier from an inlet side; first drying the catalyst carrier; inverting the catalyst carrier; cooling the catalyst; forming a second layer on the first layer by quantitatively injecting the catalyst slurry once into the catalyst carrier from an outlet side; and secondary drying the catalyst carrier. includes Listing the features of the present invention without limitation, the first and second layers are coated with at least 90% of the carrier length, and the first and second layers are configured in a symmetrical shape, and the primary drying rate (water removal level) ) is 90% or more and the second drying rate is 80% or more. According to the present invention, the step of quantitatively injecting the catalyst slurry from the inlet side or the outlet side into the catalyst carrier is the step of putting the catalyst slurry into a metering container whose bottom moves up and down, and the container so that the bottom of the catalyst carrier and the top of the container are horizontal. It includes the steps of moving the upper part to the lower end of the catalyst carrier, sealing the lower end of the catalyst carrier and the upper end of the container from the outside, the step of moving the bottom of the container upward, and the step of applying a vacuum at the same time as releasing the seal. Furthermore, according to the present invention, the catalyst slurry injected from the inlet side and the catalyst slurry injected from the outlet side may be the same or different.

According to the method for quantitative injection of catalyst slurry for forming a multi-layer catalyst layer on the catalyst carrier for exhaust gas purification according to the present invention, the catalyst slurry is quantitatively injected into the carrier internal channel, and since one layer is formed by one injection, conventional partial-coating or Problems caused by adding a viscosity modifier can be solved. When a predetermined amount of the catalyst slurry is injected into the carrier channel once to form one layer, the drying step and/or the firing step can be omitted compared to the conventional partial-coating method, so that the productivity is greatly improved.

The drawings are intended to illustrate embodiments of the present invention and do not limit the invention encompassed by the claims.
1 is a schematic perspective view and a partially enlarged cross-sectional view of a catalyst carrier, in particular a catalyst filter carrier;
2 is a scanning electron microscope (SEM) photograph showing a catalyst component coated on a carrier cell wall.
3 is a schematic flowchart for applying a conventional PnP method or a coating method according to partial-coating to a carrier.
4 shows a process for preparing a two-layer catalyst layer in a conventional partial-coating method.
5 schematically shows a single pass multi-layer coating method according to the present invention.
6 shows schematic cross-sections and specifications of catalyst modules according to Examples and Comparative Examples.

Justice

As used herein, the 'multi-layer' catalyst layer means two or more catalyst layers formed by coating catalyst slurries on the cell walls inside the carrier. A 'one-time' coating or all-coating or single coating refers to a step in which the catalyst slurry is applied once into a carrier cell or channel to form all of one catalyst layer, and a part for forming a part of one catalyst layer- Contrasted with coating or multiple coatings. Single pass coating refers to a cycle coating process in which a catalyst slurry is injected from the catalyst carrier inlet side, dried, the catalyst carrier is turned over, the catalyst slurry is injected from the catalyst carrier outlet side, and the catalyst carrier is dried. If single pass coating is performed twice, it is proceeding to double pass coating.

In the present invention, the term 'quantitation' means that the catalyst slurry of a precisely controlled predetermined amount is almost completely coated on a plurality of channels or cells. By 'nearly' completely coated as used herein, it is meant that only less than 1% of the metered catalyst slurry exits the carrier channels without being coated or loaded. While describing the carrier structure in the description of the present invention, in particular the filter structure is exemplified, it goes without saying that the same applies to a conventional converter structure, and, unless otherwise specified, the 'cross-section' means a cross-section perpendicular to the exhaust gas flow direction, unless otherwise specified. is defined as On the other hand, the 'second half' or 'outlet side' may be understood as the side through which the exhaust gas is discharged to the outside through the carrier, and the 'first half' or 'inlet side' refers to the exhaust gas being discharged from the engine. It is defined as the side where the exhaust gas is introduced. In addition, 'first half' and 'second half' are not necessarily terms that divide the carrier in the longitudinal direction, and may be understood as a part of the first half and a part of the second half according to exhaust gas and engine conditions. The term carrier may be used interchangeably with the term support or carrier. In the present invention, exhaust gas refers to exhaust gas of a comprehensive concept containing harmful components, including exhaust gas generated from a mobile internal combustion engine such as an automobile or a stationary internal combustion engine such as a power plant.

The present invention provides a catalyst slurry coating method for forming a multi-layer catalyst layer on a catalyst carrier for exhaust gas purification, and productivity can be improved by one-time coating for all one layer without adding a viscosity modifier and a dispersant to the catalyst slurry. By proposing a catalyst slurry coating method, a multilayer catalyst layer in which noble metals are uniformly distributed can be prepared by the coating method according to the present invention.

The catalyst carrier is coated with a single catalyst layer or a multi-layer catalyst layer. In particular, for the catalyst coating layer in which the catalyst components have a high dry gain (250g/L or more), a slurry with high %Solid (solids content of 43% or more and viscosity of 1500cP or less) is required, but manufacturing such slurry is difficult. Therefore, although viscosity modifiers or dispersants are sometimes applied to the slurry, there is a need to apply as a multi-layer catalyst layer rather than a single catalyst layer because of the instability with respect to the cost, the time burden for selecting a suitable dispersant, and the negative effect on the catalyst activity. In addition, a multi-layered catalyst layer is sometimes required to fabricate a multi-functional catalyst module, for example, a multi-functional catalyst module for simultaneously or sequentially performing a THC oxidation function and a NOx reduction function. However, the currently implemented coating method has a problem of lowering productivity due to the partial-coating method. Accordingly, the present invention is to improve productivity by avoiding partial-coating and suggesting a single-pass double coating method. As a result of various experiments and vehicle application by the present inventors, it was confirmed that the multi-layer catalyst layer by the proposed single-pass multi-layer coating method has the same effect as the single coating layer.

Hereinafter, the multilayer catalyst layer coating method of the catalyst carrier according to the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments. First, the carrier structure will be described. 1 is a perspective view and a partially enlarged cross-sectional view of a carrier of a cylindrical catalyst filter. In the structure of the honeycomb carrier 10, a plurality of through-cells or channels 12' and 12" having a substantially square cross section are regularly formed along the axial direction, and each of the through-cells 12', 12" ) are partitioned from each other by thin cell walls 13 . Of the plurality of cells, about half are opened at the inlet end face 9a, and the remaining cells are open at the outlet end face 9b. A catalyst material 30 made of platinum group elements or other metal elements and oxides thereof is coated or supported on the surface or inside the pores of the cell walls 13 inside the cells 12' opened at the inlet end face 9a. The opening of each through-cell 12', 12" is sealed by plugging 15 on either end face 9a, 9b side. Therefore, the entire cross-section of the carrier exhibits a checkerboard shape. Cell Density is set to around 200 pieces/inch ^2, and the thickness of the cell wall 13 is set to around 0.3 mm. The exhaust gas entering into the cell 12' opened at the inlet end face 9a passes through the cell wall while particulate matter is After being filtered (trap, deposition), only the remaining gas component is discharged to the outside through the cell 12" opened at the outlet end face 9b through the cell wall pores (or pores). At this time, the gas component is converted into a harmless component by promoting the oxidation-reduction reaction by the catalyst layer coated on the cell wall 13 (FIG. 2), and is discharged outside in the direction of the outflow section 9b. As will be understood from FIG. 1 , since the inlet side and the outlet side have a symmetrical shape, they are separated for convenience and do not indicate an absolute carrier position. For example, although described as the inlet side in the manufacturing process of the carrier, it can be used as the outlet side in the process of mounting and using the carrier, and vice versa.

Among the various coating methods for the surface of the cell walls 13, a so-called PnP method or a partial-coating method is described with reference to FIG. 3 as a method of coating a quantity of catalyst slurry, a. Putting the catalyst slurry into a metering container whose bottom moves up and down, b. moving the top of the container to the bottom of the catalyst support so that the bottom of the catalyst support and the top of the container are horizontal, c. sealing the bottom of the catalyst carrier and the top of the container with the outside; d. moving the bottom of the vessel upward, e. vacuum application step, f. The catalyst slurry may be coated inside the carrier channel, specifically, on the surface of the cell wall through the step of releasing the seal at the bottom of the catalyst carrier and the top of the container. When explaining the operation of the coating method consisting of these steps, after a predetermined amount of the catalyst slurry is filled in the plurality of channels of the catalyst carrier through steps a-d, a vacuum is applied (step e). Until step e, the slurry filled in the channel is not moved to the upper part of the inside of the channel above the filling level, and the next step, that is, f. A step of releasing the sealing of the bottom of the catalyst carrier and the top of the container is followed, and accordingly, the amount of catalyst slurry filled in the channel is moved to the upper part of the inside of the channel, and the catalyst slurry is thinly applied to the inner wall of the channel, that is, the first or the second half of the cell wall. . After the half-coating, if the catalyst carrier is inverted to complete the coating on the catalyst carrier by repeating steps a to f for the remaining part, it is coated on each of the lower and upper parts of the cell wall to obtain a single coating layer. That is, using the PnP method, partially coating the lower part of the cell wall of the carrier, preferably 50% of the total, and turning the carrier over to coat the remaining portion of the upper part of the cell wall remaining uncoated again, partial coating Through this, the slurry is coated differently in the lower and upper portions of the cell wall to obtain one catalyst layer.

A process for preparing a two-layer catalyst layer by a PnP method or a partial-coating method is shown in FIG. 4 . The two catalyst layers (bottom coating layer, B/C and top coating layer, T/C) are completed in two successive single passes, i.e., double passes, of catalyst slurry (CW), and as shown, drying and calcining steps are inevitably Therefore, there was a problem that productivity was lowered. Specifically, in the first single pass process, a first drying step is required after half coating on the first half of B/C, and a second drying step and a first firing step are required after half coating on the second half of B/C. In the second single pass process, a third drying step is required after half-coating of the first half of T/C, and a third drying step and a second firing step are required after half-coating of the second half of T/C.

The present inventors devised a single-pass double coating method to overcome the decrease in productivity caused by conventional partial-coating and manufactured various catalyst structures. It was confirmed that it had the same effect, and it was found that the productivity of the coating process was greatly improved. 5 schematically shows a single pass multi-layer coating method according to the present invention.

A method for forming a multi-layer catalyst layer on a catalyst support according to the present invention comprises: forming a first layer by injecting a catalyst slurry once from an inlet side into a catalyst support; first drying the catalyst carrier; inverting the catalyst carrier; cooling the catalyst; forming a second layer on the first layer by quantitatively injecting the catalyst slurry once into the catalyst carrier from an outlet side; secondary drying of the catalyst carrier; and a calcination step. At this time, the step of quantitatively injecting the catalyst slurry from the inlet side or the outlet side into the carrier is described in the aforementioned prior patents, and thus detailed description is omitted, but as shown in FIG. Putting into the moving quantitative container, moving the upper part of the container to the lower part of the catalyst carrier so that the lower part of the catalyst carrier and the upper part of the container are horizontal, sealing the lower part of the catalyst carrier and the upper part of the container with the outside, moving the bottom of the container upward , and applying a vacuum at the same time as releasing the seal. The single-pass multi-layer coating method according to the present invention forms two catalyst layers, and compared with the PnP or partial coating method, the drying step and the firing step can be reduced by about half, thereby greatly improving the productivity.

In the present invention, the first layer and the second layer are coated at least 90% of the length of the carrier, the first layer and the second layer are configured in a symmetrical shape, the drying rate for the first layer is 90% or more and the second layer It is characterized in that the drying rate is 80% or more. When the length of the first and second coating layers is less than 90%, the uniformity of the catalyst components included in the catalyst coating layer cannot be secured, and symmetry is also an important factor in determining the uniformity of the catalyst components in the catalyst coating layer. In addition, in the process of forming the second layer catalyst layer, in order to prevent movement or deformation and loss due to the concentration of the catalyst material of the first layer, the moisture production ratio for the first layer should be 90% or more, and the drying rate for the second layer should be It is set lower than the first drying rate in consideration of productivity, but it is confirmed that 80% or more is required. Furthermore, the catalyst slurry injected from the inlet side and the catalyst slurry injected from the outlet side may be the same or different, and the slurry forming the first layer and the second layer may be the same or different. When the slurries constituting the first and second layers are the same, the catalyst components are applied to form a catalyst coating layer having a high dry gain (250 g/L or more), and when the slurries constituting the first and second layers are different, double It can be applied to the formation of a catalyst coating layer having a function.

Hereinafter, various catalyst layers having two layers were manufactured by applying the coating method according to the present invention, and adhesion and back pressure evaluation and engine and vehicle evaluation were performed. The physical characteristics of the carrier to be coated were 105.79*115, 600/3, and VIC Mode via Pilot PnP was used as a coating device, and the slurry of the components was usually applied.

Example 1

In the catalyst carrier of 105.79*115, 600/3 specification, a slurry of normal physical properties is injected once from the inlet side of the carrier in the VIC Mode via Pilot PnP method, and the length (103.5mm) corresponding to 90% of the length of the carrier is first layer was formed. After primary drying and inverting the carrier, a slurry having a lower solid content ratio of at least 2% is injected once into the catalyst carrier in a VIC Mode via Pilot PnP method from the outlet side to ensure fluidity compared to the slurry, and the length of the carrier A second layer corresponding to 90% of the was formed on the first layer. This was secondarily dried and calcined to complete a catalyst module (referred to as M1). In the case of insufficient moisture removal during primary drying (less than 90%), the cell is clogged or the back pressure is increased due to the phenomenon that the slurry of the first layer is tilted and deformed and stacked by the vacuum after the slurry is injected during the second layer coating process In order to solve this problem, the primary drying rate (water removal level) must be secured at least 90%. On the other hand, since the second layer coating was the last coating order, it was possible to proceed with minimal moisture removal, and thus the secondary drying rate was sufficient as 80% or more.

Example 2

Catalyst module (M2) in which the first layer and the second layer were coated with different lengths by applying the same as in Example 1, except that only the coating length of the second layer was applied to correspond to 75% of the length of the carrier (86.25 mm) was prepared. However, asymmetric coating layers were formed in the first layer and the second layer, and the distribution of noble metals varied according to the carrier length, which was confirmed as an unsuitable module.

Example 3

The same procedure as in Example 1, except that the coating length of the first layer and the second layer was applied so that 95% of the length of the carrier (105 mm) was applied, and the catalyst module in which the first and second layers were symmetrically coated ( M3) was prepared.

Comparative Example 1

A multi-layer catalyst layer was prepared by a conventional partial-coating method. In the first single pass process, the first half of B/C half-coated with a conventional slurry and then dried, and after half-coated of the second half of B/C, dried and fired again to complete the first layer. In the second single pass process, a comparative module (Ref) was manufactured by drying after half coating of the first half of T/C, drying after half coating of the second half of T/C, and finally firing with a slurry having a solid content of 2% lower than that of the slurry. As such, the comparison module is completed in two successive single passes, i.e., double passes, of the catalyst slurry (W/C, wash coat) in which the two catalyst layers (bottom coating layer, B/C and top coating layer, T/C) are As such, there is a problem in that productivity is lowered due to the drying step and the firing step.

Comparative Example 2

The same procedure as in Example 2 was performed except that the second layer coating slurry was applied with the same slurry as the first layer coating slurry. As will be described below, when the slurry applied to the first layer and the second layer is the same, the fluidity of the slurry in the second layer is not secured, so that asymmetric coating layers are formed.

6 shows schematic cross-sections and specifications of catalyst modules according to Examples and Comparative Examples.

First, adhesion to the catalyst modules and back pressure were evaluated. The adhesion of M1, M2 and M3 is similar to that of the Ref module, and the back pressure is reduced by up to 20% compared to the Ref module. In addition to the advantage of reducing the back pressure, the catalyst module manufactured by the method according to the present invention also has the advantage of improving productivity because the drying and/or calcining step can be omitted. Meanwhile, as a result of engine evaluation (THC, CO, NOx evaluation) for the catalyst modules, catalytic activity equivalent to that of the Ref catalyst was confirmed except for M2.

Claims (6)

A method for forming a multi-layer catalyst layer on a catalyst carrier for exhaust gas purification, the method comprising: forming an entire first layer by quantitatively injecting a catalyst slurry once into a catalyst carrier from an inlet side; first drying the catalyst carrier; inverting the catalyst carrier; forming a second layer entirely on the first layer by quantitatively injecting the catalyst slurry once into the catalyst carrier from an outlet side; and secondary drying the catalyst carrier. A method comprising The method according to claim 1, wherein the first layer and the second layer is coated 90% or more of the length of the carrier, the first and second layers are configured in a symmetrical shape, the primary drying rate is 90% or more and the second drying rate is 80 % or more. The method according to claim 1, wherein the quantitatively injecting the catalyst slurry from the inlet side or the outlet side into the catalyst carrier comprises: injecting the catalyst slurry into a metering container whose bottom moves up and down; A method comprising the steps of moving an upper portion of a vessel to a lower end of the catalyst carrier, sealing the lower end of the catalyst carrier and the upper end of the vessel from the outside, moving the vessel bottom upward, and applying a vacuum at the same time as releasing the seal. The method according to claim 1, wherein the catalyst slurry injected from the inlet side and the catalyst slurry injected from the outlet side are the same or different. 5. The method of claim 4, wherein the catalyst slurry applied to the first layer and the second layer are the same or different. 6. The method of claim 5, wherein when the catalyst slurry applied to the first layer and the second layer are different, the solids proportion of the catalyst slurry applied to the second layer is at least 2% lower than the solids proportion of the catalyst slurry applied to the first layer. Characterized by a method.

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