JPS6055463B2 - Manufacturing method of cordierite-based honeycomb for exhaust gas purification - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for producing an exhaust gas purifying honeycomb containing cordierite as a main component.

In general, cordierite (2MgOI beats) 203.
5SiO, ) exhibits a very low coefficient of linear thermal expansion over a wide temperature range, and has excellent resistance to thermal shock when sudden temperature changes are applied. For this reason, cordierite, which has good heat resistance, is formed into a honeycomb shape and used as a catalyst carrier for automobile exhaust gas purification devices. In recent years, increasing the number of honeycomb cells has been studied with the aim of improving catalyst efficiency and downsizing purification equipment. The aim is to increase the specific surface area and achieve miniaturization by increasing the density, but with the conventional cell thickness of 3 m, increasing the density reduces the porosity and increases the pressure loss. arise. Therefore, it is necessary to reduce the cell thickness, but
When made thinner, the strength of conventional materials decreases significantly, and there is a risk of cracking due to vibrations, etc. when installed in a purification device or during use.
I couldn't make it too thin. The purpose of the present invention is to provide a method for manufacturing a cordierite-based honeycomb for exhaust gas purification that is thin but has sufficient mechanical strength and eliminates the above-mentioned drawbacks. 5 to 15 parts by weight of aluminum titanate having an average particle size of 2 to 30 μm are added and mixed to 95 to 85 parts by weight of the cordierite preparation prepared as follows, and then formed into a honeycomb structure. 1430
This is achieved by sintering at 0c to obtain a sintered body.

The sintered body obtained as described above has a water absorption rate of 15 to 25.
%, the coefficient of linear thermal expansion from room temperature to 10 degrees Celsius is 1.2
10-'/°C or less, making it preferable as a honeycomb for exhaust gas purification.

That is, the honeycomb for exhaust gas purification needs to have a water absorption rate of 15% or more because it needs to support catalysts etc. in the subsequent process, and also needs to have a water absorption rate of 25% or less from the viewpoint of strength.
Furthermore, as thermal shock resistance, the linear thermal expansion coefficient is 1.2×1.
It is necessary that the temperature be 0-6/°C. To explain the present invention in more detail below, the blending composition for obtaining cordierite is as close as possible to the theoretical composition of cordierite, which is MgO-71d203-SiO2 and is in the production range of mullite or corundum. It is known that the coefficient of thermal expansion of the obtained sintered body becomes smaller,
A formulation with a high cordierite content has a narrow temperature range suitable for firing. For formulations with a high cordierite content, if the firing temperature is low (below 135 degrees), cordierite will not be produced, and on the other hand, if the firing temperature is high, overfired (1450°C or higher), The fired product decomposes to produce mullite, glass, etc. However, the cordierite that can be used in the present invention has a composition range of MgOll to 16 parts by weight, which is generally considered to be good.
The composition is not limited to a composition with a ratio of 33 to 41 parts by weight of Al2O3 and 43 to 56 parts by weight of SiO2, but MgO may be even lower than the lower limit of the above composition range, and SiO) may be lower than the upper limit of the above composition range. It is OK even if the value is higher than the value.Furthermore, cordierite has a
It may be a green cordierite preparation prepared by blending kaolin, Kibushi clay, etc. so as to have the composition A1203'-゛5Si02, or a cordierite preparation synthesized by calcining this. But it doesn't matter. The above-mentioned cordierite or cordierite preparation is referred to as cordierite C. ) is added with aluminum titanate. The amount of aluminum titanate added must be 5 to 15 parts by weight based on 95 to 85 parts by weight of cordierite. If the amount added is less than 5 parts by weight, no improvement will be seen in mechanical strength and thermal shock resistance, and the effect will not be exhibited. If the amount exceeds 15 parts by weight, the coefficient of linear thermal expansion (room temperature to 10,000C) will be 1.2, 0-6.
/°C, and the thermal shock resistance becomes lower than that without additives. In addition, the average particle size of aluminum titanate is 2~
It is 30 μm. If this average particle size is smaller than 2 μm, the aluminum titanate decomposes quickly during firing, and the titanium produced by the decomposition reacts with the raw material of cordierite, resulting in a water absorption rate of less than 15% and porous Moreover, due to the same reason, the coefficient of linear thermal expansion mentioned above becomes larger than 1.2×10 1 /° C., making it difficult to maintain low expansion properties. Moreover, when the diameter is larger than 30 μm, no increase in strength is observed even if it is added.
Furthermore, if the width of the discharge groove of the extrusion die is less than 0.20 m, discontinuous portions are likely to occur in the thin wall, making molding substantially difficult. As mentioned above, the smaller the average particle size of aluminum titanate, the lower the water absorption rate. For example, when aluminum titanate is added to cordierite as fine particles by grinding, etc., it becomes extremely dense, that is, water absorption. It is known that it is possible to obtain sintered bodies with almost no porosity. After aluminum titanate is added to cordierite, it is mixed by an appropriate means and pressurized appropriately to form it into a honeycomb shape. After molding, it is fired at 1350 to 1430°C. The reason for firing within this temperature range is as follows. That is, if the temperature is lower than 1350°C, the formation of cordierite is not sufficiently promoted, and excellent mechanical strength and thermal shock resistance cannot be obtained. Moreover, if the temperature is higher than 1430C, a part of the cordierite once generated will decompose and form a glassy layer, making it impossible to obtain a honeycomb structure with sufficient porosity.

The firing time is not particularly limited, but ・If the temperature is high, it will be short (usually 0.5 to 1 hour), and if the temperature is low, it will be long (usually 0.5 to 1 hour).
Usually takes 1 to 1 hour). When sintered as described above, a sintered body having a water absorption rate of 15 to 25% and a linear thermal expansion coefficient of 1.2/0-6/°C or less from room temperature to 1000°C can be obtained.

This sintered body differs from conventional cordierite honeycombs in which sintering between particles is not sufficiently performed to make the body porous, but sintering between particles is sufficient. The water absorption rate of this sintered body is
This reflects the pores formed in the wall by adjusting the particle size of the molding binder and aluminum titanate, and it also reflects the pores formed between particles due to insufficient sintering. It's not. This sintered body has improved mechanical strength, particularly thermal shock resistance, by 30 to 50%. The reason for this is thought to be as follows. In other words, the occurrence of cracking due to thermal shock is caused by the temperature difference between the inside of the honeycomb and the outer periphery and end faces that occur during rapid heating or cooling, but the addition of aluminum titanate increases the specific gravity and increases the heat capacity. to reduce this temperature difference. In addition, the thermal shock resistance coefficient R of the honeycomb structure is R=KS/Eα (K thermal conductivity, S
It is generally well known that improving strength improves thermal shock resistance, as shown by mechanical strength, E-modulus, α-ray thermal expansion coefficient, and the synergistic effect of these improves thermal shock resistance. This is expected to be improved. As described above, the honeycomb obtained by the present invention has a high strength due to sufficient bonding between particles, and also has excellent thermal shock resistance.
n, which was said to be the limit for thinness, can now be reduced to 0.13.

Therefore, even if the number of cells is increased to a higher density, the porosity will not decrease much, and the pressure loss will not decrease accordingly. Therefore, the present invention can be said to be a method for producing cordierite-based exhaust gas purifying honeycombs that is extremely suitable for industrial implementation. In addition, because conventional honeycombs do not have sufficient sintering between particles, they have holes that communicate from one side of the wall of the honeycomb structure to the other, which prevents gas passing inside the honeycomb from leaking through the wall of the honeycomb structure. It was. On the other hand, in the honeycomb manufactured by the present invention, the particles are sufficiently sintered, so there are no holes communicating from one side of the wall of the honeycomb structure to the other side, and the holes passing through the inside of the honeycomb form a honeycomb structure. It will not leak through the walls of your body.
Therefore, when the honeycomb produced according to the present invention is used as a heat exchanger, even high pressure gas can be used.
Examples will be described below.

Example 1 Each raw material with the chemical components shown in Table 1 was prepared, and these were mixed into the composition of cordierite (2Mg0-2A1203/5S1
02).

In this example, 51 parts of Korean kaolin (mizuhimono), 37 parts of talc (produced in Oishibashi), and a converted part of α-alumina (A-16 manufactured by Alcoa) were mixed in order to form a raw cordierite preparation. . On the other hand, 69.3 parts of Kongo kaolin, 10.8 parts of frog's eye clay, and 13 parts of talcum. (2), 2Mg0 of Mg(0H)26J part
- Prepared the 3A1203 IO2. The mixture was then placed in an electric furnace with a SiC heating element and calcined at 1300° C. for 1 hour to synthesize cordierite.

On the other hand, aluminum titanate is highly pure (over 99% purity).
γ-Al2O3 and primary reagent TiO2 (anatase type) were prepared in a molar ratio of 1:1, placed in a pot mill, water added, and mixed and ground for an hour.

After that, the ground material was filtered through a filter paper, the filtrate was removed, the fixed material was dried as appropriate, this dried material was placed in the electric furnace, and calcined at 1450° C. for 1 hour, and a part of this calcined material was used. It was confirmed by X-ray analysis that aluminum betitanate was synthesized. Therefore, 50% of the calcined material that became aluminum titanate was added to the calcined material that became cordierite.
, 10,115% by weight, respectively, a molding binder was added to this base material, and after thorough kneading, it was molded into a honeycomb shape. After drying, it was fired at 1390°C for 6 hours, and the diameter was 95%.
× Length 120Tfn (600 cells/i-kaku H2, cell thickness 0
．． 14wn) was obtained. 1 of this structure
Tables 2 and 3 show the linear thermal expansion coefficient α at 000°C, the strength in the gas flow direction, and the water absorption rate. In Table 2, when aluminum titanate (AT) was contained in an amount of 10% by weight, sintered bodies were produced with various average particle diameters ranging from 1.2 to 30 μm, and the respective physical property values were measured. *1: Method for measuring strength Samples were cut into 20m x 2i x 2 pieces, and measured by applying a load in the direction of gas flow until the sample broke using a material testing machine.

*2: Method for measuring water absorption A sample (diameter 95 x length 120?) whose dry weight has been measured in advance is submerged under water and allowed to absorb water in a vacuum for 1 hour, and excess water is removed by compression. Ah (2k9/
Measure the saturated water weight by blowing it off.

Calculate from this dry weight and saturated water weight. *3: Thermal shock cracking temperature measurement method Using an exhaust gas simulator, 800°C combustion gas (18@) and 25°C cold air (120 seconds) are passed through the honeycomb structure repeatedly over a fixed period of time. Repeat the test 5 times at the same temperature and if it does not break, raise the temperature to 50C and repeat the test until it breaks. As is clear from Tables 2 and 3, adding aluminum titanate (AT) increases the strength, and α remains the same or increases slightly.

7 In addition, a honeycomb structure manufactured with 1% AT (average particle size 8 μm) and a honeycomb structure manufactured without additives were respectively heated and cooled and the temperature change at the center was measured, as shown in Figure 1. I got similar results.

In the same figure, the temperature gradient of the specimen with AT added is gentler than that of the specimen without the addition of AT, which is due to the difference in heat capacity. It is well known that heat capacity is expressed by the following formula. Heat capacity = specific heat x bulk density x volume Since the specific heat and volume are the same for both, the difference in heat capacity is thought to be due to bulk density, and the bulk density of both was measured.

The results are shown in Table 4.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the temperature change during heating and cooling of the honeycomb structure obtained in the example.

Claims (1)

[Claims] 1 Cordierite or cordierite formulation 95-8 prepared to have the composition of cordierite
5 to 15 parts by weight of aluminum titanate having an average particle size of 2 to 30 μm are added and mixed to 5 parts by weight, and then formed into a honeycomb structure and sintered at 1350 to 1430 ° C.
A method for producing a cordierite-based honeycomb for purifying exhaust gas, which is characterized by obtaining a sintered body.