JPS6152733B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas purification method for a combustion appliance, which is mainly applied to the exhaust system of an open combustion appliance to purify the exhaust gas thereof.

For combustion appliances such as portable kerosene stoves or fan heaters, the ignition,
The CO and HC' generated during fire extinguishing were disliked, and equipment equipped with a catalyst that catalytically oxidizes and purifies this using an oxidation catalyst has begun to appear. These catalysts completely oxidize C and H compounds and convert them into CO ₂ and H ₂ O. A typical oxidation catalyst is a catalyst in which a platinum metal element is supported on a heat-resistant carrier such as ceramic. The temperature required for the oxidation reaction using these catalysts is
When targeting HC′, a temperature of 250°C or higher is required. When a hydrocarbon and an oxidation catalyst are subjected to a contact reaction at 250°C or higher, a dehydrogenation reaction occurs in addition to a complete oxidation reaction, and a phenomenon in which carbon is precipitated on the catalyst surface, a so-called coking phenomenon, occurs. Furthermore, combustion is unstable and soot is often produced if the fuel/air mixture ratio fluctuates for some reason. As a result, as the use of catalysts progresses, this carbon inhibits the catalytic reaction, and
The performance of the catalyst will be significantly reduced. This carbon can be removed by burning it by burning it in the air at high temperatures, but such high-temperature treatment causes sintering, structural changes, and compositional changes in the catalyst and carrier, which often leads to permanent deterioration. There are concerns that

This carbon deposition not only reduces and destroys the catalytic ability, but also increases the pressure in the catalyst layer, affecting the combustion itself, and there is a concern that it may cause unstable combustion. As described above, the application of oxidation catalysts to combustion exhaust systems involves the troublesome problem of carbon deposition.

The present invention is a method characterized by using a catalyst system that almost completely solves such concerns.

The present invention uses an extremely new carrier system as a carrier on which an oxidation catalyst is to be supported.

The present invention deals with the following reaction between water vapor and carbon (1) C+H ₂ O=CO+H ₂ (△H=32Kcal/mo) (2) C+2H ₂ O=CO ₂ +2H ₂ (△H=24Kcal/mo
) is used to gasify carbonaceous matter.

Alkali salts or group transition metal compounds are used as effective catalysts for the above gasification reactions.

The catalytic reaction mechanism by alkali salts (particularly alkali carbonates) is thought to be as follows.

M ₂ CO ₃ + 2C = 2M (g) + 3CO (g) 2M (g) + 2H ₂ O (g) = 2MOH + H ₂ (g) 2MOH + CO (g) = M ₂ CO ₃ + H ₂ (g) It is thought that it contributes to the gasification reaction.

On the other hand, in the case of transition metals, they contribute to reactions such as M+H ₂ O=M-O _a +2M-H _a C+M-O _a = M+CO 2M-H _a =M+H ₂ (where a indicates the adsorbed species). It is thought that then.

The structure of the carrier system of the present invention is carried out as follows. Since catalytic oxidation reactions using oxidation catalysts at high temperatures are often dominated by external diffusion, the shape of the carrier or the state of dispersion of the catalyst on its surface is important. Therefore, the shape of the carrier used in the exhaust system is preferably a honeycomb or a similar shape. Processing metal or
First, a prototype of the carrier is obtained by molding the ceramic.
An inorganic heat-resistant paint in which one or more compounds selected from the group of alkali salts and transition metal compounds are dispersed is sprayed onto the metal or ceramic surface that serves as the prototype of this carrier, and this inorganic paint-based coating is applied. form a layer. Before this coating film dries, powder of an oxidation catalyst supported on a heat-resistant porous carrier is sprayed onto its surface. after that,
Finish by firing the coating at a temperature of 300-400°C.

When a noble metal is used, only the coating may be baked and hardened first, and then immersed in a noble metal chloride aqueous solution to be supported, and then reduced and supported.

As the binder for forming the coating, it is desirable to use an inorganic compound. Examples of inorganic binder systems that provide good physical properties as a coating include systems that use metal phosphoric acid and systems that use alkali metal silicates. If a large amount of alkali salts are dispersed and used, the former system may cause gelation of the binder, so the use of the latter alkali metal silicates provides better effects.

The effects of the present invention will be described below based on Examples. Commercially available honeycomb catalyst 150mmφ, wall thickness
A catalyst with holes of 20mm and 3mmφ formed with a porosity of 60%.This catalyst uses mullite as a carrier and 0.2wt of platinum.
% (sample 1) and the same mullite carrier was used to coat the entire surface with a film thickness of approximately 50μ, and a catalyst with 0.2wt% platinum supported on the coating (sample 2). ) was prepared. For the latter coating condition, Shikoku Kaken Kogyo's Ceramitite SMA-2000 was used as the alkali metal silicate paint.
A paint prepared by adding 5wt% K ₂ CO ₃ , 2wt% Fe ₂ O ₃ , and 1wt% CaO and mixing in a ball mill for 1 hour was sprayed using a spray gun. This was placed on the top plate of a portable kerosene stove. The temperature of this top plate is 320℃ during steady combustion.
It was hot. During steady combustion, the CO concentration in the exhaust from a portable stove without a catalyst was 15 ppm, but with a catalyst, it was 6 ppm, and there was no difference in the effectiveness of samples 1 and 2.
Some effect was observed. In order to quantitatively evaluate the activity of the catalyst, air containing 100 ppm of CO was sent, the catalyst was placed, and the catalyst temperature was set to 150°C.
When a distribution test was carried out under the condition of SV=24000 [h ^-1 ], sample 1 showed a conversion rate of 85% and sample 2 showed a conversion rate of 92%. This catalyst was attached to the aforementioned portable kerosene stove, and its durability was evaluated by repeatedly burning it intermittently in a cycle of 20 hours of combustion and 4 hours of extinguishing. After 100 days, the activity of the catalyst was evaluated by the above flow test, and Sample 1 showed a conversion rate of 58% and Sample 2 showed a conversion rate of 95%.

As seen above, it can be seen that the durability of the catalyst is dramatically improved by the method of the present invention. The effect here is that in the conventional case, coking occurs as a result of dehydrogenation of H/C' and the catalyst gradually deteriorates, whereas in the case of the present invention, the catalyst is gradually deteriorated. It is thought that long-term durability was achieved because this carbon was gasified by the water vapor contained, preventing coking.

Claims (1)

[Claims] 1. At least one compound selected from the group of alkali salts and group transition metal compounds is dispersed in the exhaust gas flow path on a metal or ceramic surface using an inorganic binder as a binder. The catalyst is coated, and the coated body is used as a carrier, and a catalyst characterized in that an oxidation catalyst is supported on the coated body is disposed and brought into contact with the catalyst to purify unresolved gas in exhaust gas. A distinctive method for purifying exhaust gas from combustion appliances. 2. The method for purifying exhaust gas from a combustion appliance according to claim 1, characterized in that a silicate-based binder is used as the inorganic binder.