JP2018192377A - Honeycomb filter - Google Patents

Abstract

To provide a honeycomb filter which can suppress carrying of a catalyst to a ceramic coat layer.SOLUTION: A honeycomb filter 300 includes a columnar porous core part 100 and a porous ceramic coat layer 200 arranged on an outer peripheral surface of the core part 100. The core part 100 includes a porous ceramic honeycomb structure 120 having a plurality of flow passages, and a plurality of sealing parts 130 which close one end of a part of the flow passages out of the plurality of flow passages, and the other end of the other flow passages out of the plurality of flow passages. When a specific surface area and an ignition loss of the ceramic coat layer 200 are respectively Sc(m/g), and Lc(-), an expression (1) is satisfied. Lc/Sc≤100×10g/m(1).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a honeycomb filter.

  Conventionally, as a filter for engine exhaust gas, a honeycomb filter comprising a porous ceramic honeycomb structure and a columnar core portion having a sealing portion, and a porous ceramic coat layer provided on the outer peripheral surface of the core portion It has been known. When the ceramic coat layer is provided, the strength of the honeycomb filter can be improved.

WO2010 / 138500 gazette JP 2008-43851 A JP 2005-199179 A JP 2009-202464 A WO2009 / 073096

In such a honeycomb filter, there is a case of loading a catalyst on pore surfaces of the porous ceramic honeycomb structural body for the purpose of reduction of promoting or NO _x soot combustion. When a catalyst is supported, the filter is often dipped in an aqueous slurry containing a catalyst component (including a precursor) and a catalyst support, and then the slurry is dried.

  However, when a conventional honeycomb filter is used, the catalyst is also carried on the ceramic coat layer. Since the ceramic coat layer does not function as a filter, it is not necessary to support a catalyst from the beginning, and the catalyst often contains relatively expensive raw materials such as noble metals and zeolite, which causes an increase in cost.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a honeycomb filter capable of suppressing catalyst loading on a ceramic coat layer.

The honeycomb filter according to the present invention includes a columnar core portion and a porous ceramic coat layer provided on the outer peripheral surface of the core portion. The core portion includes a porous ceramic honeycomb structure having a plurality of channels, one end of a part of the plurality of channels, and the remaining channel in the plurality of channels. And a plurality of sealing portions for closing the other end.
When the specific surface area and the loss on ignition of the ceramic coat layer are Sc (m ² / g) and Lc (−), the formula (1) is satisfied.
Lc / Sc ≦ 100 × 10 ⁻⁵ g / m ² (1)

  Since the loss on ignition Lc means the amount of mass reduction after the ignition test per unit mass of the ceramic coat layer, and the specific surface area Sc means the surface area per unit mass of the ceramic coat layer, Lc / Sc is the surface area per unit area of the ceramic coat layer. This means the amount of mass reduction after the ignition test. In addition, it is considered that the amount of loss on ignition of the ceramic coat layer has a correlation with the amount of surface hydroxyl groups of the ceramic before the ignition test, and the amount of hydroxyl groups has a correlation with high hydrophilicity. According to the present invention, the expression (1) is satisfied, that is, the loss on ignition per surface area of the ceramic coat layer is sufficiently small, so that the amount of surface hydroxyl groups per surface area of the ceramic coat layer is sufficiently small as compared with the prior art. Therefore, the liquid absorption amount of the aqueous slurry of the ceramic coat layer can be reduced.

Here, when the average pore diameter of the ceramic coat layer is Dc (μm), the expression (2) can also be satisfied.
Dc ≧ 0.05 μm (2)

  Furthermore, the ceramic coat layer may include fused ceramic particles such as fused silica particles and fused alumina particles.

  Furthermore, the ceramic coat layer may include fibrous ceramic particles.

  Furthermore, the honeycomb filter may further include a catalyst supported on the ceramic honeycomb structure.

  According to the present invention, it is possible to suppress the catalyst loading on the ceramic coat layer.

FIG. 1 is a schematic cross-sectional view of a honeycomb filter according to an embodiment of the present invention.

  A honeycomb filter 300 according to an embodiment of the present invention will be described with reference to the drawings. The honeycomb filter 300 includes a core part 100 and a ceramic coat layer 200.

  The core part 100 has a column shape and has an inlet end face (one end face) 100a and an outlet end face (the other end face) 100b. The core part 100 has a porous ceramic honeycomb structure 120 and a plurality of sealing parts 130. The ceramic honeycomb structure 120 includes a plurality of inlet channels (a plurality of first channels) 110a and a plurality of outlet channels (a plurality of second channels) 110b. The cross-sectional shapes of the inlet channel 110a and the outlet channel 110b can be, for example, a circle, an ellipse, a quadrangle, a hexagon, and an octagon. The ceramic honeycomb structure 120 functions as a partition wall that separates the inlet channel 110a and the outlet channel 110b adjacent to each other.

  Each inlet channel 110a is opened at the inlet end surface 100a and sealed by the sealing portion 130 at the outlet end surface 100b. Each outlet channel 110b is opened at the outlet end surface 100b and sealed by the sealing portion 130 at the inlet end surface 100a. In FIG. 1, the sealing portion 130 has a plug shape, but the sealing portion 130 may be formed by deforming a part of the ceramic honeycomb structure 120 (for example, a conical shape portion).

  Examples of the ceramic of the core portion (the ceramic honeycomb structure 120 and the sealing portion 130) are an aluminum titanate ceramic, a silicon carbide ceramic, and a cordierite ceramic. The aluminum titanate-based ceramic can contain magnesium, silicon, and the like. The ceramic may contain trace components derived from raw materials or trace components inevitably contained in the production process.

  The porosity of the ceramic honeycomb structure 120 may be 50 to 75%. The porosity is preferably 55 to 70% and more preferably 55 to 65% in order to maintain the pressure loss performance and improve the catalyst activity. If the porosity exceeds 75%, the strength of the ceramic honeycomb structure 120 may decrease. The porosity can be measured by mercury porosimetry.

The cell density can be, for example, 35 to 80 cells / cm ² .

  The ceramic coat layer 200 is provided on the outer peripheral surface of the core part 100. The ceramic coat layer 200 can be provided over the entire circumference on the outer peripheral surface. The thickness of the ceramic coat layer 200 can be set to 0.2 to 2.0 mm, for example.

  The ceramic coat layer 200 can have ceramic particles and an inorganic binder that binds them. The ceramic coat layer can be porous. The porosity of the ceramic coat layer 200 is smaller than that of the ceramic honeycomb structure and may be 10 to 40%.

  Examples of the ceramic of the ceramic coat layer 200 include alumina, silica, aluminum titanate, cordierite, and the like. It may be the same as or different from the ceramic of the core part 100.

  Examples of the shape of ceramic particles are non-fibrous particles (ratio of major axis to minor axis (aspect ratio) of less than 3 times) and fibrous particles (ratio of major axis to minor axis (aspect ratio) of 3 times). Above). When fibrous ceramic particles are included, mechanical strength (Young's modulus) can be improved.

  An example of the particle size of the non-fibrous particles (D50 of the volume-based particle size distribution by a laser diffraction particle size distribution measuring device) can be 2 to 30 μm.

  Further, the major axis of the fibrous particles can be 10 to 200 μm, and the minor axis can be 2 to 10 μm. The aspect ratio of the fibrous particles can be 3-100.

  The ratio of the mass of fibrous particles to the mass of all ceramic particles can be 5 to 25%.

  The ceramic particles can include, for example, molten ceramic particles such as fused alumina and fused silica as non-fibrous particles. Since the molten ceramic particles are melted at, for example, 2000 ° C. or higher, the amount of surface hydroxyl groups is small.

  Examples of the inorganic binder are colloidal silica, alumina sol, titania sol, water glass, hydraulic alumina, ρ-alumina, boehmite alumina, alumina cement, and Portland cement. The amount of the inorganic binder can be 3 to 30 parts by weight with respect to 100 parts by weight of the ceramic particles.

In this embodiment, when the specific surface area and the loss on ignition of the ceramic coat layer are Sc (m ² / g) and Lc (−), respectively, the ceramic coat layer satisfies the formula (1).
Lc / Sc ≦ 100 × 10 ⁻⁵ g / m ² (1)

The loss on ignition is the rate of decrease in mass before and after the heat treatment of the object, and in this embodiment, there is a correlation with the amount of hydroxyl groups in the object. The conditions for the heat treatment are 2 hours at 1100 ° C. in an air atmosphere.
The specific surface area can be measured by a mercury intrusion method. The measurement conditions can be a maximum pressure of 414 Mpa (60,000 psia).

  Since the loss on ignition Lc means the amount of mass reduction after the ignition test per unit mass of the ceramic coat layer, and the specific surface area Sc means the surface area per unit mass of the ceramic coat layer, Lc / Sc is the surface area per unit area of the ceramic coat layer. This means the amount of mass reduction after the ignition test. The magnitude of the loss on ignition of the ceramic coat layer is correlated with the amount of surface hydroxyl groups of the ceramic before the ignition test, and the amount of hydroxyl groups is considered to correlate with the hydrophilicity.

  According to the present embodiment, the amount of surface hydroxyl groups per surface area of the ceramic coat layer is sufficiently small because the ignition loss per surface area of the ceramic coat layer is sufficiently small that satisfies the formula (1). Therefore, the hydrophilicity of the ceramic coat layer can be reduced, absorption of the aqueous slurry can be suppressed, and catalyst loading on the ceramic coat layer can be suppressed.

Lc / Sc can be 100 × 10 ⁻⁵ g / m ² or less. Further, Lc / Sc can be 1 × 10 ⁻⁵ g / m ² or more.

Further, when the average pore diameter of the ceramic coat layer 200 is Dc (μm), the expression (2) can be satisfied.
Dc ≧ 0.05 μm (2)

Here, as for the average pore diameter, first, the pore diameter distribution in the range of 0.0018 to 100 μm of the object is measured by mercury porosimetry, and the cumulative volume fraction of the pore diameter in the pore diameter distribution is 50%. Obtained by obtaining the pore size. Dc can also be 0.10 μm or more.
When the average pore diameter Dc of the ceramic coat layer 200 is large to some extent, the capillary force may be reduced, which may contribute to a reduction in the suction force of the aqueous slurry.

Further, from the viewpoint of maintaining the strength of the ceramic coat layer 200, Dc can satisfy the formula (2A).
Dc ≦ 5μm (2A)

In addition, the specific surface area, loss on ignition, and average pore diameter of the ceramic honeycomb structure can be appropriately set according to desired filtration characteristics and the like.
When the specific surface area and the loss on ignition of the ceramic honeycomb structure 120 are Sh (m ² / g) and Lh (−), respectively, the ceramic honeycomb structure 120 can satisfy the expression (3).
Lh / Sh ≧ 400 × 10 ⁻⁵ g / m ² (3)

The ignition loss Lh means the mass reduction amount after the ignition test per unit mass of the ceramic honeycomb structure 120, and the specific surface area Sh means the surface area per unit mass of the ceramic honeycomb structure 120, so Lh / Sh is It means the amount of mass reduction after the ignition test per surface area of the ceramic honeycomb structure 120. It is preferable that the ceramic honeycomb structure satisfies the formula (3), that is, if the loss of ignition per surface area of the ceramic honeycomb structure 120 is sufficiently large, the ceramic honeycomb structure can easily absorb the aqueous slurry.
Lh / Sh can be 500 × 10 ⁻⁵ g / m ² or more, can be 600 × 10 ⁻⁵ g / m ² or more, and can be 700 × 10 ⁻⁵ g / m ² or more. And can be 1000 × 10 ⁻⁵ g / m ² or less.

Further, when the average pore diameter of the ceramic honeycomb structure 120 is Dh (μm), the expression (4) can also be satisfied.
Dh ≧ 10 μm (4)
Since Dh is large to some extent, pressure loss can be reduced, and there are advantages of high output and low fuel consumption.
From the viewpoint of improving environmental performance by improving the soot accumulation effect of the ceramic honeycomb structure 120, Dh can satisfy the formula (4A).
Dh ≦ 30μm (4A)

In the present embodiment, when the water Krem absorbency of the ceramic honeycomb structure 120 defined in JIS P8141: 2004 is As and the water Klem absorbency defined in JIS P8141: 2004 of the ceramic coat layer 200 is Ac, Ac / As can be 0.3 or less, can be 0.25 or less, and can be 0.2 or less.
In the experiment, a food red solution was used, and the manufacturer was Ogura Food Chemical Co., Ltd. The product name is a red preparation, which is used by dissolving 0.5 g in 100 g of water.

Then, an example of the manufacturing method of the above honeycomb filters is demonstrated.
First, a green raw material containing a ceramic source, a pore former, an organic binder, a solvent, and an additive added as necessary is prepared to obtain a green ceramic honeycomb structure 120. Subsequently, one end of the flow path is blocked by a known method using the same raw material as the green raw material to form the green sealing portion 130 to obtain the green core portion. Subsequently, the core part 100 made of ceramic is obtained by firing the green core part. Thereafter, if necessary, processing such as cutting and polishing of the outer peripheral surface of the core portion 100 may be performed.

  Subsequently, the ceramic coat layer 200 is formed on the outer peripheral surface of the core portion 100. Specifically, first, a coating paste containing ceramic particles, an inorganic binder, and a solvent such as water is prepared.

  Here, the raw material of a ceramic coat layer is adjusted so that Lc / Sc of the ceramic coat layer 200 may satisfy | fill Formula (1). Specifically, in order to adjust the specific surface area Sc, the weight ratio of the binder to the inorganic substance and the particle size of the binder may be adjusted. For example, to increase the specific surface area, the weight ratio of the binder is increased. Or what is necessary is just to make the particle size of a binder small. In order to adjust the loss on ignition, for example, a raw material having a small surface hydroxyl group can be used as the ceramic particles of the ceramic coat layer. In particular, it is preferable to use at least a part of the ceramic particles whose hydroxyl groups are reduced by passing through a high-temperature process as ceramic particles, but other raw materials having a small amount of hydroxyl groups on the surface can also be used. Further, it is also suitable to further subject the ceramic coat layer using the raw material having a small surface hydroxyl group to a high temperature treatment as described later, and the temperature at that time is usually 400 ° C. or higher, preferably 600 ° C. or higher. More preferably, it is 800 ° C. or higher, and usually 1000 ° C. or lower.

  Further, the average pore diameter Dc of the ceramic coat layer 200 can be adjusted by the particle diameter of the raw material.

  Subsequently, the obtained coating paste is applied to the outer peripheral surface of the core portion 100 over the entire periphery. The application method is not particularly limited, and examples thereof include a brush coating method, a roller brush method, and a doctor blade method.

  Thereafter, the coating film is dried and fired as necessary. Drying can be performed by evaporating the solvent in the coating solution at a relatively low temperature of 40 to 200 ° C. In firing, solvent molecules adsorbed on the surface can be removed by treatment at a relatively high temperature of 400 to 1000 ° C. Thereby, a honeycomb filter provided with a core part and a ceramic coat layer is completed.

Next, a method for supporting a catalyst on the honeycomb filter of the present embodiment will be described.
One method is a method in which a catalyst support material is supported on the surface of the core portion 100 and then a catalyst is supported on the catalyst support material. Another method is a method in which a catalyst support material on which a catalyst is supported is supported on the surface of the core portion 100. Still another method is a method of directly supporting the catalyst on the surface of the core portion without supporting the catalyst support material.

Examples of the catalyst support material are oxides such as alumina, silica, magnesia, titania, zirconia, ceria, La ₂ O ₃ , BaO, and zeolite, or composite oxides containing one or more of these. The particle size D50 of the catalyst support material can be 2 to 5 μm.

  Examples of the catalyst are particles of at least one metal element selected from the group consisting of Pt, Pd, Rh, silver, vanadium, chromium, manganese, iron, cobalt, nickel, copper, or zeolite catalyst. As described above, the catalyst support particles may previously carry the catalyst thereon.

  In order to support the catalyst support material and / or the catalyst on the surface of the core part 100, an aqueous slurry containing the catalyst support material and / or the catalyst is prepared, the honeycomb filter is immersed in the aqueous slurry, and then the filter is heated. The aqueous slurry may be dried. As described above, a honeycomb filter carrying a catalyst can be manufactured.

  When the honeycomb filter according to this embodiment is used, since the expression (1) is satisfied, the amount of catalyst supported on the ceramic coat layer 200 can be reduced. Therefore, the waste of the catalyst can be reduced.

The present invention is not limited to the above embodiment, and various modifications can be made.
For example, there are no particular limitations on the outer shape of the ceramic honeycomb structure and the arrangement of the flow paths. For example, the ceramic honeycomb structure may not be a cylinder but may be a prism such as a quadrangular prism or a hexagonal prism. The arrangement of the flow paths can take various forms such as a triangular arrangement and a square arrangement.

Example 1
A core portion made of aluminum titanate was prepared. The cross section of each flow path was hexagonal, and the cell density was 380 cpsi. The outer diameter was 25.4 mm and the height was 25.4 mm. The porosity of the ceramic honeycomb structure is 59%, the average pore diameter Dh is 18.12 μm, the specific surface area Sh is 0.145 m ² / g, the loss on ignition Lh is 0.12%, and Lh / Sh is 827.6 × 10 ^{− It was 5} g / m ² .

  170 g of fused silica particles having a D50 of 5 μm, 30 g of aluminum titanate particles having a D50 of 25 μm, 20 g of alumina fibers having a major axis of 20 μm and a minor axis of 4-6 μm, 22.5 g of colloidal silica having a particle diameter of 12 nm, and 52.5 g of water Were mixed to obtain a coat paste. The fused silica particles and aluminum titanate particles are non-fibrous particles. The formulation is shown in Table 1.

  This coat paste was applied to the entire outer peripheral surface of the honeycomb structure by a doctor blade method. Thereafter, the coat paste was dried at 150 ° C. and further dried at 1000 ° C. to obtain a honeycomb filter having a core portion and a ceramic coat layer. The weight of the ceramic coat layer adhering to the core portion was 1.46 g.

  Subsequently, a catalyst was supported on the honeycomb filter. Specifically, after stirring 300 g of commercially available β zeolite into 700 g of pure water, this was pulverized to a mean particle size of 3 μm with a ball mill to obtain an aqueous slurry, and then a honeycomb filter was dipped in the slurry, Further, it was dried at 500 ° C.

(Example 2)
The procedure was the same as Example 1 except that the amount of colloidal silica as an inorganic binder was 33.75 g, the amount of water was 78.75 g, and the drying temperature at the second stage was changed from 1000 ° C. to 700 ° C. The weight of the ceramic coat layer formed on the ceramic honeycomb structure was 1.54 g.

Example 3
Example 2 was the same as Example 1 except that the drying temperature in the second stage was changed from 1000 ° C to 700 ° C. The weight of the ceramic coat layer formed on the ceramic honeycomb structure was 0.95 g.

(Example 4)
The same procedure as in Example 1 was performed except that the drying temperature of the second stage was changed from 1000 ° C. to 450 ° C. The weight of the ceramic coat layer formed on the ceramic honeycomb structure was 1.55 g.

(Example 5)
Example 4 was the same as Example 4 except that the thickness of the coat paste applied to the outer peripheral surface of the ceramic honeycomb structure was reduced and the weight of the ceramic coat layer formed on the ceramic honeycomb structure was 0.69 g.

(Comparative Example 1)
Example 5 was repeated except that γ-alumina particles having a D50 of 5 μm were used instead of fused silica. The weight of the ceramic coat layer formed on the ceramic honeycomb structure was 0.81 g. The γ-alumina particles are neither fibrous particles nor fused ceramic particles.
Table 1 shows the composition of the coating paste for forming the ceramic coating layer, the coating amount, and the final drying temperature.

(Evaluation)
(Ease of forming a ceramic coating layer)
The coating property when applying a coating paste for forming a ceramic coat on the outer peripheral surface of the ceramic honeycomb structure was evaluated. Specifically, after the coating paste is applied to the outer peripheral surface of the ceramic honeycomb structure once, the adhesion state of the coating layer to the honeycomb structure is determined. When it exists, it was set as x.

(Pore diameter of ceramic coat layer)
The average pore size is obtained by measuring the pore size distribution in the range of 0.0018 to 100 μm using the mercury intrusion method, and obtaining the pore size at which the cumulative volume fraction of the pore size is 50% in the pore size distribution. Obtained.

(Fire loss of ceramic coating layer)
The mass of the cut sample was measured, and after heat-treating at 1100 ° C. for 2 hours in the air atmosphere, the mass was measured again to determine the mass reduction rate.

(Chem water absorption ratio of ceramic coat layer and honeycomb structure)
Each sample was cut out from the honeycomb filter, the lower end was immersed in water vertically, the height at which the water rose after 10 minutes was measured, and the ratio was determined.

(Strength of ceramic coat layer)
The pencil hardness of the ceramic coat layer was measured based on JIS K 5600-5-4. The case where the pencil hardness was B or less was evaluated as x, and the case where the pencil hardness was 5H or more was evaluated as ◯.

(Amount of catalyst supported on the ceramic coat layer)
The amount of catalyst supported on the ceramic coat layer was obtained by SEM.
Table 2 shows the evaluation results of the ceramic coat layer.

  DESCRIPTION OF SYMBOLS 100 ... Core part, 100a ... Inlet end surface (one end surface), 100b ... Outlet end surface (other end surface), 110a ... Inlet flow path (1st flow path), 110b ... Outlet flow path (2nd flow path), 120 ... Ceramic Honeycomb structure, 200 ... ceramic coat layer, 300 ... honeycomb filter.

Claims (5)

A columnar core part, and a porous ceramic coat layer provided on the outer peripheral surface of the core part,
The core portion is a porous ceramic honeycomb structure having a plurality of flow paths;
One end of a part of the plurality of channels, and a plurality of sealing portions for closing the other end of the remaining channel among the plurality of channels,
A honeycomb filter that satisfies the formula (1) when the specific surface area and the loss on ignition of the ceramic coat layer are Sc (m ² / g) and Lc (−), respectively.
Lc / Sc ≦ 100 × 10 ⁻⁵ g / m ² (1) The honeycomb filter according to claim 1, which satisfies the formula (2) when an average pore diameter of the ceramic coat layer is Dc (µm).
Dc ≧ 0.05 μm (2)   The honeycomb filter according to claim 1 or 2, wherein the ceramic coat layer includes molten ceramic particles.   The honeycomb filter according to any one of claims 1 to 3, wherein the ceramic coat layer includes fibrous ceramic particles.   The honeycomb filter according to any one of claims 1 to 4, further comprising a catalyst supported on the ceramic honeycomb structure.

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