WO2004014553A1 - Ceramic honeycomb structural body - Google Patents

Abstract

A tubular ceramic honeycomb structural body (1) used for catalyst carriers utilizing catalytic action or exhaust gas particulate collecting filters of internal combustion engines, boilers, chemical reaction equipment, and reformers for fuel cells, comprising a plurality of cells (2) forming a fluid flow passage partitioned by partition walls (3), characterized in that the shape of the cells (2) are triangular at the end of the ceramic honeycomb structural body (1), the thickness of the partition walls (3) is 5.5 mil or less, and a cell density is 230 cell/in2 or higher, whereby even when the cell density is increased, the durability of the ceramic structural body against a damage by a thermal stress when the structural body is used can be improved.

Description

 Specification

 Technical field of ceramic honeycomb structure

 The present invention relates to a ceramic honeycomb structure used for a catalyst carrier utilizing a catalytic action or a filter for collecting fine particles in exhaust gas, such as an internal combustion engine, a boiler, a chemical reaction device, and a reformer for a fuel cell. In particular, the present invention relates to a ceramic honeycomb structure having excellent durability (thermal shock resistance) against breakage due to thermal stress during use. Background art

 A catalyst carrier that uses the catalytic action of internal combustion engines, boilers, chemical reaction equipment, fuel cell reformers, etc., or a filter (DPF) that traps particulates in exhaust gas, especially particulate matter in diesel engine exhaust ) Etc. use a ceramic honeycomb structure. As shown in FIG. 5, a conventional ceramic honeycomb structure 1 is generally used in which the cell 2 has a square shape for reasons such as purification performance, mechanical strength, thermal shock resistance, and ease of manufacturing. ing.

With regard to the ceramic honeycomb structure used as a carrier for the catalyst, with the tightening of exhaust gas regulations in recent years, by devising the material and the like of the structure itself, the carbon black (HC) that is discharged from the engine during driving, carbon monoxide (CO), nitrogen oxides (NO _x) hand improvements have been made to reduce the emission of harmful substances such as, for the catalyst supported, an improvement of three-way catalysts are currently the mainstream With both effects, reduction of harmful substance emissions is being achieved.

As such improvements have been made in response to the tightening of exhaust gas regulations, the amount of harmful substances emitted during driving has generally decreased, but the amount of harmful substances emitted immediately after the engine is started is a problem that cannot be ignored. It has been up. For example, in the U.S. regulated driving cycle FTP-75 cycles, the total amount of harmful substances emitted during the entire driving cycle in the 140-second Bag-1 mode immediately after the engine is started 60 to 80% are discharged. This is particularly harmful immediately after engine start (Bag-1 A) because the exhaust gas temperature is low and the catalyst is not sufficiently activated. This was because the substance passed through the catalyst without being purified.

 Also, immediately after the engine is started, the combustion state is not stable, and the air-fuel ratio of the exhaust gas (A / F: Air / Fue 1) is one of the important factors that affect the purification performance of the three-way catalyst. This is because the ratio of the amount of oxygen in the exhaust gas fluctuates due to fluctuations in the air quality. When AZF reaches the stoichiometric air-fuel ratio of 14.7, the catalyst exhibits the most effective purification performance. As the catalyst, T-alumina with a fine pore structure with a high surface area is supported on the surface of the partition walls that partition the cells of the ceramic honeycomb structure, and the alumina carries noble metal components such as platinum, palladium, and rhodium as catalyst components. These are commonly used.

 Therefore, in order to quickly raise the temperature of the catalyst immediately after the engine is started, place the catalyst as close to the engine as possible and place the catalyst in a place where the exhaust gas temperature is high, or install a partition to reduce the heat capacity of the catalyst itself. In order to reduce the thickness of the exhaust gas, quickly absorb the heat of the exhaust gas, and increase the contact area between the catalyst and the exhaust gas, efforts have been made to increase the cell density of the ceramic honeycomb structure as a catalyst carrier.

 However, the ceramic secondary cam structure used for such a purpose has a non-uniform temperature distribution due to a rapid temperature change of exhaust gas or local heat generation, and cracks occur in the ceramic honeycomb structure. There was a problem. In addition, when used as a DPF, it is necessary to burn and remove the accumulated fine particles of carbon, and to regenerate them. There were problems such as easy cracking.

 In particular, in the case of a conventional ceramic honeycomb structure with a square cell at the end face, the thermal shock resistance is remarkable as the partition walls that partition each cell are made thinner and the density of the cells is increased. And exacerbated the problems described above.

The present invention has been made in view of the above-described problems, and has as its object to provide a ceramic honeycomb structure having excellent durability against damage due to thermal stress during use even when the cell density is increased. Aim. Disclosure of the invention The present invention has been studied to solve the above problems, and as a result, when the thickness of the partition walls of the ceramic honeycomb structure having a triangular shape is reduced, the conventional ceramic cell having a rectangular cell is obtained. As with the two-cam structure, the thermal shock resistance decreases, but when the cell density is increased, the thermal shock resistance increases, contrary to the conventional ceramic honeycomb structure with square cells. That is, the present invention has been completed. That is, the ceramic honeycomb structure of the present invention is a cylindrical ceramic honeycomb structure having a plurality of cells serving as a flow path of a fluid partitioned by partition walls, and the shape of the cell at the end face is triangular. The thickness of the partition walls is 5.5 mi 1 or less, and the cell density is 230 cells Z square inches or more. The thickness of the partition wall mentioned above is also called a rib thickness, and lmi 1 is 100 minutes in inches (about 0.025 mm).

 In such a ceramic honeycomb structure having triangular cells, the higher the cell density, the higher the thermal shock resistance, which can be adapted to the higher cell density associated with stricter exhaust gas regulations.

 Further, in the ceramic honeycomb structure of the present invention, the partition wall thickness is preferably 4.5 mi 1 or less, the cell density is preferably 300 cells / square inch or more, and the partition wall thickness is 3.5. It is more preferable that the cell density is not more than mi 1 and the cell density is not less than 400 cells / square inch, and the thickness of the partition wall is not more than 3.5 mi 1 and the cell density is not less than 600 cells / square inch. It is particularly preferred that there is.

 In the ceramic honeycomb structure of the present invention, the cell preferably has at least one shape selected from the group consisting of an equilateral triangle, a right triangle, a right isosceles triangle, and an isosceles triangle. Further, the ceramic honeycomb structure of the present invention is suitably used for purifying automobile exhaust gas and as a filter for collecting diesel particulates.

The main component of the ceramic honeycomb structure of the present invention is preferably at least one compound selected from the group consisting of cordierite, alumina, mullite, aluminum titanate, silicon carbide, silicon nitride, zirconium, and titanium. BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a plan view schematically showing an end face of one embodiment of the ceramic honeycomb structure of the present invention.

 FIG. 2 is a graph showing the relationship between the bulk density of the ceramic honeycomb structure and the safety limit cooling steepness obtained by the Bernard-Solling test in the example of the present invention.

 FIG. 3 is a graph showing the relationship between the cell density of the ceramic honeycomb structure and the safety limit cooling steepness obtained by the Bernard-Solling test in the example of the present invention.

 FIG. 4 is a graph showing the relationship between the thickness of the partition walls of the ceramic honeycomb structure and the safety limit cooling steepness obtained by the burner spalling test in the example of the present invention.

 FIG. 5 is a plan view schematically showing an end face of a conventional ceramic honeycomb structure.

BEST MODE FOR CARRYING OUT THE INVENTION

 Hereinafter, embodiments of the ceramic honeycomb structure of the present invention will be specifically described with reference to the drawings. However, the present invention is not construed as being limited thereto, and does not depart from the scope of the present invention. To the extent possible, various changes, modifications, and improvements can be made based on the knowledge of those skilled in the art.

FIG. 1 is a plan view schematically showing an end face of one embodiment of the ceramic honeycomb structure of the present invention. The ceramic honeycomb structure 1 of the present embodiment is a cylindrical ceramic honeycomb structure 1 having a plurality of cells 2 serving as a flow path of a fluid partitioned by a partition wall 3. The shape of the cell 2 on the end face 1 is triangular, the thickness of the partition wall 3 is 5.5 mi 1 or less, and the cell density is 230 cells / square inch or more. Here, the reason why the thickness of the partition walls 3 is set to 5.5 mi1 or less is that even if the thickness of the partition walls 3 is set to be more than 5.5 mi1, the cells are rectangular in terms of thermal shock resistance. This is because no superiority can be seen, and the reason why the cell density is set to 230 cells Z square inches or more is that if the cell density is less than 230 cells / square inch, it is used as a catalyst carrier or filter. Function Because it cannot be added.

 The ceramic honeycomb structure 1 having triangular cells 2 as shown in Fig. 1 has a higher thermal shock resistance as the cell density increases. Can respond to the high density of cells. Further, the mechanical strength of the ceramic honeycomb structure 1 having the cells 2 having a triangular end surface with respect to the impact from the side peripheral surface is increased.

Further, in the present embodiment, it is preferable that the thickness of the partition wall 3 is 4.5 mi 1 or less, and the cell density is 300 serno square inches or more, and the thickness of the partition wall 3 is 3.5 mi. It is more preferable that the partition wall 3 has a thickness of not more than 3.5 mi 1 and a cell density of 600 cells / square inch. It is particularly preferred that it be greater than inches. As for the thickness and cell density of the partition walls of the ceramic honeycomb structure 1 that can be substantially manufactured for manufacturing reasons, the thickness of the partition walls is 1.0 O 1 or more, and the cell density is 30 It is preferably at most 100 cells / square inch. Further, in the ceramic honeycomb structure of the present embodiment, it is preferable that the ratio between the thickness of the partition and the cell density is 1:70 or more. As described above, the ceramic honeycomb structure 1 in which the shape of the cell 2 is an equilateral triangle is described as an example, but in the ceramic honeycomb structure of the present invention, the shape of the cell 2 is not limited to an equilateral triangle. Instead, any shape of triangle may be used, but the cells 2 can be arranged regularly, and the cell density of the ceramic honeycomb structure 1 can be easily increased. Since the ceramic honeycomb structure 1 can be easily and inexpensively manufactured, a small number of members selected from the group consisting of equilateral triangles, right triangles, right isosceles triangles, and isosceles triangles are provided. Both is preferably one shape. Further, the ceramic honeycomb structure 1 of the present embodiment is suitably used as a catalyst carrier for gas purification or a DPF because the thermal shock resistance increases as the cell density increases. At this time, when used as a filter for collecting and removing particulate matter contained in exhaust gas such as DPF, the cells 2 on the end face of the ceramic honeycomb structure 1 are alternately sealed. Used. The main component of the ceramic honeycomb structure 1 of the present embodiment is at least one compound selected from the group consisting of cordierite, alumina, mullite, aluminum titanate, silicon carbide, silicon nitride, zirconia, and titania. It is preferred. In the present invention, the main component means a component which accounts for 80% by mass or more of the component and becomes a main crystal phase.

 When the ceramic honeycomb structure 1 of the present embodiment is used as a catalyst carrier in an internal combustion engine, a fuel cell, a chemical reaction device, a reformer for a fuel cell, or the like, a metal having catalytic ability in the ceramic 82-cam structure 1 Is carried. Platinum, palladium, rhodium, and the like are typical examples having catalytic ability. It is preferable that at least one of these is supported on the ceramic honeycomb structure 1.

 When exhaust gas containing particulate matter is passed from one end face of such a ceramic honeycomb structure 1, the exhaust gas is discharged from the ceramic honeycomb structure 1 from the unsealed cell 2 on this one end face side. It flows into the inside, passes through a porous partition wall 3 having a filtering ability, and is discharged from an unsealed cell 2 on the other end side. When passing through the partition 3, the particulate matter is captured by the partition 3. As a material for plugging the cell 2 on the end face, a material substantially the same as the material of the ceramic honeycomb structure can be suitably used. When such a ceramic honeycomb structure 1 is installed in an automobile or the like as a filter, if the trapped particulate matter accumulates on the partition wall 3, the pressure loss rises sharply and the load on the engine increases. Since the fuel efficiency and the driver's utility decline, the particulate matter should be burned and removed periodically by a heating means such as a heater to regenerate the filter function. At the time of the combustion regeneration, the ceramic 82-cam structure 1 has the above-mentioned catalytic ability in order to promote the combustion or to substantially continuously regenerate and regenerate the particulate matter trapped in the partition walls 3. A noble metal or the like may be supported. Further, the ceramic honeycomb structure 1 of the present embodiment can be manufactured by the same manufacturing method as the conventional ceramic honeycomb structure having square cells by using a die having a triangular cell shape. .

 Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

The shape of the ceramic honeycomb structure used in all Examples and all Comparative Examples was A cylindrical shape with a diameter of φ106 mm, an axial length of 11.4 mm, and a volume of 1.0 liter, made of talc, alumina, kaolin, etc. It was formed by extruding a honeycomb structure using a mold (base) having a predetermined cell shape, partition wall thickness and cell density, followed by drying and firing. In each example and each comparative example, the cell shape, the partition wall thickness, and the cell density on the end face of the above-described ceramic honeycomb structure were changed as shown in Tables 1 and 2. Further, such a ceramic honeycomb structure, palladium 1 2 0 g Z f ^3, to that carrying the catalyst in Wosshukoto 2 0 0 gZ liters performs burner hate-ring test, a rapid-heated ceramic honeycomb structure The temperature difference at which cracking occurs due to rapid cooling (hereinafter referred to as “cooling steepness”) was determined.

Burner spalling test, the ceramic honeycomb structure Zotai carrying the above-mentioned catalyst, and by Uni holding a surface pressure of about 0. 7 k gZ cm ² in a non-intumescent mat in Metal holder one to the LPG as fuel bar It was attached to a nurse polling tester. The heating conditions were constant in each example and each comparative example, the heating flow rate was 3 Nm ³ Z min, the heating time was 5 minutes, and the heating temperature was 5 mm downstream from the center of the inlet-side end face of the ceramic honeycomb structure. The temperature was set at 100 ° C.

 The cooling condition was the cooling steepness set to the maximum cooling steepness measured at the same position as the heating condition, controlled by the air flow rate at room temperature, and added 10 cycles of heating and cooling. After the test, remove the ceramic honeycomb structure from the metal holder and check for cracks with a stereoscopic microscope.If there are no cracks, heat again under the same conditions and cool under conditions that increase the cooling steepness. This was repeated until cracks occurred in the ceramic honeycomb structure.

 (Examples 1 to 10)

In Examples 1 to 9, the shape of the cell at the end face of the ceramic honeycomb structure was a regular triangle, and in Example 10, the shape of the cell was a right-angled isosceles triangle. A burner spot ring test was performed using a sheet formed to have a thickness and a cell density.

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Right-angled isosceles cell shape equilateral triangle

Triangular cell structure (partition thickness no cell density) 4.5 / 308 4.5 / 400 3.5 / 400 3.5 / 460 3.5 / 600 4.5 / 600 2.5 / 900 3.5 / 900 2.5 / 1200 3.5 / 460 Partition wall thickness (mil) 4.5 4.5 3.5 3.5 3.5 4.5 2.5 3.5 2.5 3.5 Cell density (cells / square inch) 308 400 400 460 600 600 900 900 1200 460 Porosity (%) 35 35 35 35 35 35 35 35 35 35 Cell density (N cm ² ) 47J 62 62 71.3 93 93 139.5 139.5 186 71.3 Rib thickness (mm) 0.1 14 0.1 14 0.089 0.089 0.089 0.1 14 0.064 0.089 0.051 0.089 Geometric surface area (cm ² Zcm ³ ) 28.7 32.2 33 35.2 39J 38.4 49.2 47.4 56 37 Bulk density (gZcm ³ ) 0.296 0.335 0.263 0.281 0.319 0.405 0.281 0.387 0.322 0.295 Safety margin cooling steepness 120 120 85 120 150 180 150 180 180 120

(Comparative Examples 1 to 9)

In Comparative Examples 1 to 8, the shape of the cell at the end face of the ceramic honeycomb structure was a square, and in Comparative Example 9, the cell shape at the end face of the ceramic honeycomb structure was a regular triangle, as shown in Table 2. The above-described personal spalling test was performed using a barrier rib having such a thickness and a cell density.

Comparative Example 1 | Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 l "k sa 5llQ

T-shaped square rectangle il—cell structure (partition wall thickness cell density) 5.5 / 300 6J / 400 3.5 / 400 4.5 / 400 4.5 / 600 3.5 / 600 2.5 / 900 2.5 / 1200 6J / 308 Partition wall thickness (mil) 5.5 6J 3.5 4.5 4.5 3.5 2.5 2.5 6.7 Cell density (cell square inch) 300 400 400 400 600 600 900 1200 308 Porosity (%) 35 35 35 35 35 35 35 35 35 Cell density (N cm ² ) 46.5 62 62 62 93 93 139.5 186 47J Rib thickness (mm) 0.14 0.17 0.089 0.1 14 0.1 14 0.089 0.064 0.051 0.17 Geometric surface area (cm ² / cm ³ ) 24.7 27.3 29.3 28.7 34.3 35.3 43.7 49.8 27.3 Bulk density (gZcm ³ ) 0.31 1 0.43 0.232 0.296 0.358 0.282 0.248 0.284 0.43 Safety cooling steepness 85 120 30 60 60 30 10 10 120

¾) 2 The mass per unit area of the ceramic honeycomb structure, that is, the so-called forcegdensity (gZcm ³ ) was calculated from the thickness of the partition walls and the cell density of the ceramic 82 cam structure in each of the examples and comparative examples. Figure 2 shows the relationship between the bulk density and the critical cooling steepness without cracks (hereinafter referred to as “safety critical cooling steepness”) obtained by the burner spoiling test. Fig. 3 is a graph showing the relationship between the cell density of the ceramic 82-cam structure and the safety limit cooling steepness in each of the examples and comparative examples, and Dalaf is a graph showing the relationship between the partition wall thickness and the safety limit cooling steepness. Is shown in FIG.

 As shown in FIG. 2, the ceramic honeycomb structures having the triangular cells of Examples 1 to 10 are safer at the same bulk density as compared with the ceramic honeycomb structures having the rectangular cells of Comparative Examples 1 to 8. The critical cooling steepness was increased, and the ceramic honeycomb structure of this example had improved thermal shock resistance. In particular, in this example, the ceramic honeycomb structure having a high cell density had a significantly higher safety limit cooling steepness, and the thermal shock resistance was dramatically improved. In addition, the ceramic honeycomb structure having the triangular cells with the partition wall thickness of 6.7 mi 1 of Comparative Example 9 has almost the same result as the ceramic honeycomb structure having the rectangular cells of Comparative Example 2, No difference in cells from the square was observed.

 This can be more clearly understood from the graph shown in Fig. 3, which shows the relationship between the cell density and the safety limit cooling steepness. In the present embodiment, the safety limit cooling steepness increases as the cell density increases, whereas in this comparative example (Comparative Examples 1 to 8), the safety limit cooling steepness increases as the cell density increases. Was getting lower. Thus, the ceramic honeycomb structure having triangular cells (Examples 1 to 8) is similar to the ceramic honeycomb structure having conventional square cells (Comparative Examples 1 to 8) even when the cell density is increased. Since the thermal shock resistance does not decrease and, conversely, the thermal shock resistance increases, the ceramic honeycomb structure can respond to higher definition and higher density.

As shown in Fig. 4, the relationship between the thickness of the partition walls of the ceramic honeycomb structure (cell density of 400 (cells / square inch)) of the present embodiment (Examples 2 and 3) and the cooling limit steepness at the safety limit. And the ceramic honeycomb structure of this comparative example (Comparative Examples 2 to 4) Comparing the approximation line B showing the relationship between the thickness of the partition walls of the body (cell density 400 (cells / square inch)) and the safety critical cooling steepness, the approximation line A shown in the present example is better than the approximation line B. It shows a high safety margin cooling steepness. In addition, an approximation line C indicating the relationship between the thickness of the partition walls of the ceramic honeycomb structure (cell density 600 (cells / square inch)) of the present embodiment (Examples 5 and 6) and the safety limit cooling steepness. And an approximation line D showing the relationship between the thickness of the partition walls of the ceramic eight-unit honeycomb structure (cell density 600 (cell Z square inch)) and the safety critical cooling steepness of the comparative examples (Comparative Examples 5 and 6). In comparison, the approximation line C shown in the present example indicates that the safety limit cooling steepness is higher. Thus, it can be seen from the graph shown in FIG. 4 that the ceramic honeycomb structure having triangular cells has improved thermal shock resistance as the cell density increases. Industrial applicability

 As described above, the present invention can provide a ceramic honeycomb structure excellent in durability against damage due to thermal stress during use, even when the cell density is increased.

Claims

The scope of the claims  1. A cylindrical ceramic honeycomb structure having a plurality of cells serving as a flow path of a fluid partitioned by partition walls, wherein the shape of the cells at the end faces is triangular, and the thickness of the partition walls is A ceramic honeycomb structure characterized by having a cell density of 5.5 mi 1 or less and a cell density of 230 cello square inches or more.  2. The ceramic honeycomb structure according to claim 1, wherein the thickness of the partition walls is 4.5 mi 1 or less, and the cell density is 300 cells / square inch or more. 3. The ceramic honeycomb structure according to claim 1, wherein the thickness of the partition wall is equal to or less than 3.5 mi 1 and the cell density is equal to or more than 400 cells Z square inch. 4. The ceramic honeycomb structure according to claim 1, wherein the thickness of the partition wall is equal to or less than 3.5 mi 1 and the cell density is equal to or greater than 600 cells Z square inch. 5. The ceramic honeycomb structure according to any one of claims 1 to 4, wherein the shape of the cell is an equilateral triangle.  6. The ceramic honeycomb structure according to any one of claims 1 to 4, wherein the shape of the cell is a right triangle.  7. The ceramic honeycomb structure according to any one of claims 1 to 4, wherein the shape of the cell is a right-angled isosceles triangle.  8. The ceramic honeycomb structure according to any one of claims 1 to 4, wherein the shape of the cell is an isosceles triangle. ' 9. The ceramic honeycomb structure according to any one of claims 1 to 8, which is used for purifying automobile exhaust gas.  10. The ceramic honeycomb structure according to any one of claims 1 to 9, which is used as a filter for collecting diesel particulates. 11. The main component is at least one compound selected from the group consisting of cordierite, alumina, mullite, aluminum titanate, silicon carbide, silicon nitride, zirconia and titania. The ceramics described in one item Iu Ma two, / π 0800T0 / C00Zdf / X3d OAV