JPS63302946A - Carrier for catalyst - Google Patents

Abstract

PURPOSE:To increase the specific surface area of a carrier for a catalyst and to improve the strength by using specified amts. of calcium aluminate, molten silica, hydraulic alumina and LiO2.Al2O3.XSiO2 each having a specified particle size to form the carrier. CONSTITUTION:20-40wt.% calcium aluminate is mixed with 40-70wt.% molten silica, 5-20wt.% hydraulic alumina or activated alumina and 1-10wt.% Li2 O.Al2O3.XSiO2 (X=2 or 4). The mixture is kneaded with a prescribed amt. of water, molded, dried and heat treated to form a heat resistant carrier for a catalyst. The pref. average particle size of the calcium aluminate is 5-30mum, that of the molten silica is 5-50mum, that of the hydraulic alumina or activated alumina is 1-10mum and that of the Li2O.Al2O3.XSiO2 is 1-10mum.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a carrier used in a catalyst for purifying exhaust gas of a combustion device using gaseous fuel such as natural gas and propane, and liquid fuel such as petroleum.

Conventional technology Conventionally, an inorganic oxide containing lime aluminate as the main component, fused silica as an aggregate, and titania as a component is mixed with a forming aid, etc., and the mixture is kneaded with water and then added to a porous body. Press and mold. Thereafter, it was solidified, cured, and dried to obtain a catalyst carrier.

Thereafter, for exhaust gas purification, the catalyst was further immersed in a palladium salt solution to support a catalyst, and then heat treated in air at 900°C for 1 hour.

Problems to be Solved by the Invention Catalyst carriers obtained from such conventional structures have a relatively small specific surface area, and when exposed to air at high temperatures for long periods of time, the specific surface area gradually decreases. It's coming down. Therefore, when used as a catalyst for purifying exhaust gas in combustion equipment, the initial performance is excellent, but the catalyst activity deteriorates over time.

- There was a problem in that the ability to purify carbon oxide etc. decreased. Therefore, we proposed removing titania, which has low heat resistance above 900°C, and adding alumina, which has a large specific surface area. Although we were able to improve the specific surface area, the compressive strength tended to decrease slightly, making it practical for practical use. From this point of view, even stronger compressive strength is required. The present invention aims to solve these problems.

Means for solving the problem In order to solve this problem, the present invention mainly uses lime aluminate, fused silica, hydraulic alumina or activated alumina, and Li2O-A7J205 ・X5i02 (where X = 2.4) system. A heat-resistant inorganic oxide composed of a composite oxide, the above-mentioned lime aluminate, fused silica, hydraulic alumina or activated alumina, and Li2O-
AJ203- The composition of the XSiO2-based composite oxide is 2.
0-40 weight%: 40-To weight%: 6-20 weight%:
1 to 10% by weight, and preferably each average particle size is 5 to 30 μm = 5 to 601 tm: 1 to 101
tm: 1 to 1011 m as a catalyst carrier.

Function: With this structure, Li2O・Li is formed in the catalyst carrier.
By containing 2O5・X5i (h, this Li
2O-L71203 ・XSiO2t7) Fine particles and alumina fine particles with a large specific surface area are partially sintered together by heat treatment at high temperatures, forming a strong bond within the carrier, increasing the compressive strength of the carrier without reducing the specific surface area. is improving. Generally Li2O・Aj! 205・2si02 is β-
Eucryptite, Li2O・Al2O5・4si0
2 has a subodumene crystal structure and has the function of reducing the coefficient of thermal expansion. At the same time, in order to improve the compressive strength, fine particle alumina with a large specific surface area and Li2O・A12os・2,
The fine particles of 4Si02 are entangled within the carrier, making it possible to significantly improve the compressive strength.

Furthermore, by supporting a palladium catalyst or the like, it is possible to efficiently purify exhaust gas from combustion equipment without being destroyed even at high temperatures for a long time.

The constituent elements of the carrier for the catalyst in the examples were lime aluminate with an average particle size of 1611 m, fused silica with an average particle size of 30 μm, hydraulic alumina or activated alumina with an average particle size of 5 μm, and Li2O・with an average particle size of 6 μm. Al2O5・2si02(
Crystal structure: β・eucryptite) and Li2O・L
i2O5.4si02 (crystal structure: spodumene) was blended in various composition ratios, and an appropriate amount of water was added and kneaded together with an organic binder such as carboxymethyl cellulose to this mixture. This carrier material was extruded using a honeycomb molding machine, solidified and cured, dried at ioooC to remove moisture, and then heat-treated in air at 1oooC for about 20 minutes. Various types of carriers were obtained.

A carrier with a conventional composition is also shown as a comparative example.

However, 6% by weight of carboxymethyl cellulose was added to all samples as an organic binder based on the total amount. Various carriers were evaluated by examining their specific surface area, compressive strength, and thermal tensile coefficient as physical properties of the catalyst carrier. On the other hand, the durability of the carrier is 10% in an air atmosphere at 1000°C.
The specific surface areas after exposure for 00 hours were investigated and compared.

(Margin below) In these sample carriers, A, B, C, D.

The carriers for K, F, and G are of the present invention type, and the carriers for J and N are L.
i2O・muIhO5・2Si02, Li2O・Al
If the content of 2O3/asi02 is too large, L
The carrier contains too much lime aluminate and too little fused silica. The M carrier contains too little lime aluminate and too much fused silica. The N carrier is a case where the total alumina content is too high. The carriers for H and I are conventional carriers;
The former contains hydraulic alumina, titania and Li2O.
Aj! 205・(2,4) This is the case that does not contain Si02, and the latter contains titania, various aluminas and Li2
This is the case where O.Al2O5(2,4)Si02 is not contained.

For these various carriers, the specific surface area <rrfyg>
.

Thermal expansion coefficient (x 1o-6/aag), mechanical strength (
Table 2 shows the results of measuring kg/7c+4). however,
Specific surface area values are based on exposure to an oxidizing atmosphere for 1000 hours at a temperature of 1000°C. Mechanical strength was measured as compressive strength.

Table 2 As shown in Table 2, catalyst carriers of the present invention, B, C
, D, E, F, G, the specific surface area is s, o ~ 6.5 doors/, 9, and the mechanical strength is 290 ~ 310 kg /
cA, and the thermal expansion coefficient is 2.4 to 2.6X10'/'
It is C. On the other hand, the specific surface area of conventional catalyst carriers H and I is s-4.2.5 wl/g, the mechanical strength is 150 and 170 kg/(:4 te), and the thermal expansion coefficient is 2. 9, 2.5. Therefore, compared to the conventional carrier H, the specific surface area of the present invention type is almost the same, but the mechanical strength is approximately twice as high, and the thermal expansion coefficient is approximately 20. %.Also, compared to conventional carrier materials, there is almost no difference in the coefficient of thermal expansion, but the specific surface area is more than doubled, and the mechanical strength is improved by about 1.8 times. are doing.

Since the present invention type contains 6 to 20% by weight of hydraulic alumina or activated alumina, which has a large specific surface area, the specific surface area of the carrier itself is large, and the average particle size in the carrier is 1 to 10 μm.
Fine hydraulic alumina and activated alumina, which are m, are homogeneously dispersed together with large particles of lime aluminate and fused silica, and Li2O, which has an average particle size of 1 to 1011 m, is 7!2
It is bonded to each other through fine particles of J.2 to 45i02, increasing mechanical strength and retaining a large specific surface area even after long-term exposure in a high-temperature, oxidizing atmosphere. Furthermore, the increase in the coefficient of thermal expansion is suppressed by the action of fused silica having an average particle size of 6 to 5 Q p m.

Furthermore, the mechanical strength is improved by the hardening effect of lime aluminate having an average particle size of 5 to 3071 m.

On the other hand, conventional carrier I gradually undergoes a sintering phenomenon at high temperatures, and its specific surface area decreases. Further, although the conventional carrier H has little sintering phenomenon at high temperatures and has a large specific surface area, it has low mechanical strength. Therefore, damage may occur during the manufacturing process or after being installed in hot smoking equipment. Naturally, even if a carrier with a small specific surface area supports a catalyst and is used in combustion equipment, its exhaust gas purification ability will be poor.

For catalyst carrier J, Li2O・Aj1203・2,
This is an example containing a large amount of asi02, and no significant improvement in mechanical strength and coefficient of thermal expansion is observed. Li2O・People 7!
When compared with the content of 2ch/2.4si02 of 1 to 10% by weight, a phenomenon occurs in which the mechanical strength decreases,
It is not preferable to contain too much.

The catalyst carrier is an example of a large amount of lime aluminate and a small amount of fused silica, which improves mechanical strength but significantly increases the coefficient of thermal expansion, and the degree of expansion and contraction of the carrier itself during the manufacturing process causes cracks. This may cause problems such as

The catalyst carrier M is an example in which the amount of lime aluminate is small and the amount of fused silica is large, and the coefficient of thermal expansion becomes small, but the specific surface area and mechanical strength are significantly reduced.

Catalyst carrier N is an example in which the amounts of hydraulic alumina and activated alumina are increased, and although the specific surface area increases, the mechanical strength decreases significantly and the coefficient of thermal expansion increases.

From this, lime aluminate has mechanical strength, melting strength causes cracks, etc., and alumina has specific surface area, L work 20・Aj
! 203.2-4si02 is related to mechanical strength, and the optimal composition of the catalyst carrier is lime aluminate, fused silica, hydraulic alumina or activated alumina, Li2O
In -Al2O2.2,4si02, 20 to 40% by weight: 40 to 7% by weight: 6 to 20% by weight: 1 to 10% by weight.

Furthermore, the physical properties of the catalyst carrier vary depending on the particle size of these materials. As a result of many experiments, it has been found that the average particle size of lime aluminate is optimally in the range of 6 to 3 Q p m, and when the average particle size of lime aluminate increases by 9 Q p m above this maximum value, the strength of the carrier tends to decrease.

If it is smaller than this minimum value, it will lead to an increase in material cost and cause a practical problem. The average particle size of fused silica is 6-60
The range of μm is optimal, and if it exceeds this maximum value, the strength of the carrier tends to decrease, which also causes a decrease in the specific surface area. If it is smaller than this minimum value, the material cost will increase, causing a practical problem, and the degree of expansion and contraction of the carrier will also increase, causing cracks and the like. The average particle diameter of hydraulic alumina or activated alumina is optimally in the range of 1 to 10 μm, and as it becomes larger than this maximum value, the specific surface area of the carrier tends to decrease. If it is smaller than this minimum value, the material cost will increase, causing a practical problem, and the degree of expansion and contraction of the phase body will also increase, causing cracks and the like. Li2O・
The average particle diameter of Al2O2・2,4Si02 is 1 to 10μ
The range of m is optimal; if it is larger than this maximum value, the mechanical strength tends to decrease, and if it is smaller than this minimum value, it will lead to an increase in material cost, which is not preferable.

In any case, by selecting the optimal composition and particle size, the particles of the various constituent materials are tightly intertwined and bonded, improving mechanical strength, increasing specific surface area, and suppressing the coefficient of thermal expansion. ing. In particular, the effects of Li2O.1ho3.2sio2 having a β-eucryptite structure and Li2O.17!205.4Sl○2 having a spodumene structure are very large, as they maintain a high specific surface area and greatly improve mechanical strength.

In this example, lime aluminate, fused silica, hydraulic alumina, activated alumina, Li2O・k120s・2.4
For Si02, β-eucryptite and spodumene were used alone or in a mixture, but other metal oxides such as F82Q3゜MgO, Li were used as impurity materials.
2O, NaO, NiO, BaO, MnO2, CuO.

No significant difference was observed in the physical properties of the carrier even when a small amount of Coo was contained. Hydraulic alumina is a gamma-type alumina powder, and when water is added, a rewatering reaction occurs, particles aggregate and harden, so it is also called rewaterable alumina. Shows excellent properties.

Effects of the Invention As described above, according to the present invention, the mechanical strength of the catalyst carrier having a large specific surface area and a small coefficient of thermal expansion can be greatly increased, which can prevent cracks during the manufacturing process and improve the catalyst when installed in combustion equipment. This has the effect of preventing damage to the carrier and provides an excellent catalyst carrier.

Claims (2)

[Claims] (1) Mainly lime aluminate, fused silica, hydraulic alumina or activated alumina, and Li_2O・Al_2
A heat-resistant inorganic oxide composed of O_3・XSiO_2 (X=2, 4)-based composite oxide, including the above-mentioned lime aluminate, fused silica, hydraulic alumina or activated alumina, Li_2O・Al_2O_3・XSiO_2-based composite Mixing composition of oxide: 20-40% by weight: 40-70% by weight
: 5 to 20% by weight: 1 to 10% by weight. (2) Lime aluminate, fused silica, hydraulic alumina or activated alumina, Li_2 constituting the heat-resistant inorganic oxide
Each average particle size of O・Al_2O_3・XSiO_2-based composite oxide is 5 to 30 μM: 5 to 50 μm: 1 to 10 μm:
Claim 1 characterized in that the diameter is 1 to 10 μm.
Catalyst carrier as described in Section 1.