JPH04310512A - Production of active silicon carbide - Google Patents

Abstract

PURPOSE:To efficiently produce active silicon carbide having a high specific surface area in a short time by adding a specified crystallization agent to a carbonaceous raw material and subsequently thermally reacting the mixture with silicon monoxide. CONSTITUTION:A carbonaceous raw material such as active carbon or porous carbon having a specific surface area of >=60m<2>/g is mixed with 0.1-3.0wt.% of one kind or more of the single bodies (or compounds) of Be, B, Al, P, Cr, Fe, Ga and Bi as a particle growth-inhibiting agent. On the other hand, silica, etc., is mixed and thermally reacted with a reducing component powder such as silicon powder under vacuum to produce silicon monoxide gas. The above- mentioned carbonaceous raw material mixture is reacted with the silicon monoxide gas at 1400-1800 deg.C to produce active silicon carbide.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing activated silicon carbide having a high specific surface area and useful as a catalyst carrier.

0002

[Prior Art] Silicon carbide, which belongs to ceramic materials, is put into practical use as a variety of components used under high temperature and harsh atmospheric conditions by utilizing its unique properties such as excellent strength, hardness, heat resistance, and chemical stability. However, one of these uses is as a catalyst support. Silicon carbide used as a catalyst carrier is required to have a specific surface area of at least 60 m2/g to exhibit surface activity.

Conventionally, catalyst carriers made of silicon carbide include:
Pore 0.2-2.0ml/g, specific surface area 3m2
Porous silicon carbide sintered body having a three-dimensional network structure with an average compressive strength of 300 kgf/cm3 or more and an average compressive strength of 300 kgf/cm3 or more (Japanese Unexamined Patent Publication No. 62-45344), a porous silicon carbide sintered body manufactured from silicon-integrated biomass such as rice husk or rice straw. quality silicon carbide
(Japanese Unexamined Patent Application Publication No. 64-85142) are known, but all of these have a specific surface area of 50 m2/g or less, which is insufficient as an active surface. Also, SiO
2 and Si is brought into contact with split-state reactive carbon having a specific surface area of at least 200 m2/g at a temperature of 1100 to 1400°C to form silicon carbide fine particles with a specific surface area of 100 m2/g. A method for producing a catalyst carrier has also been proposed (Japanese Unexamined Patent Publication No. 1999-13
Publication No. 1016). However, this method requires a relatively low reaction temperature of 1,100 to 1,400 degrees Celsius, so it takes a long time (4 to 7 hours) to produce silicon carbide, making it difficult for industrial mass production. There are problems with this method.

0004

However, when the above-mentioned method is adopted, if the reaction temperature is increased, the grain growth of the produced silicon carbide progresses and the grains become coarser, resulting in a decrease in the specific surface area.

An object of the present invention is to suppress the grain growth of silicon carbide that accompanies an increase in reaction temperature when silicon carbide is produced by the reaction between carbon and silicon monoxide. An object of the present invention is to provide a method for efficiently producing activated silicon carbide having the following properties.

[0006]

[Means for Solving the Problems] A method for producing activated silicon carbide according to the present invention to achieve the above-mentioned object is to produce silicon carbide with a high specific surface area by subjecting a carbonaceous raw material to a catalytic reaction with silicon monoxide gas at high temperature. In the conversion step, one or more of beryllium, boron, aluminum, phosphorus, chromium, iron, gallium, or bismuth alone or as a compound is added to the carbonaceous raw material in advance as a grain growth inhibitor of silicon carbide.
Added in the range of ~3.0% by weight, 1400~1800
The structural feature is that it reacts with silicon monoxide in the temperature range of °C.

The carbonaceous raw material used in the present invention serves as a base material that will eventually be converted into silicon carbide, and is selected from those having a high specific surface area. For example, 60m2/
Activated carbon, porous carbon, carbon black, etc. having a specific surface area of 100 g or more are preferably used.

Silicon monoxide gas, which is a reaction source for silicon carbide, is prepared by mixing a powder containing a reducing component such as silicon or carbon with a powder containing silicon dioxide such as silica sand or silica gel, and then heating the mixture under reduced pressure for 10 minutes.
It can be produced by a heating reaction at a temperature of 00 to 1500°C.

In the present invention, when the above-mentioned carbonaceous raw material and silicon monoxide gas are subjected to a contact reaction at high temperature, it is important to add and mix a component for suppressing the grain growth of silicon carbide to the carbonaceous raw material in advance. This is a requirement. This grain growth inhibitor is
It is selected from beryllium, boron, aluminum, phosphorus, chromium, iron, gallium, and bismuth alone or as a compound, and is used singly or in combination of two or more. The most suitable component in terms of handling and cost is boron or aluminum. The addition ratio of the grain growth inhibitor is set in the range of 0.1 to 3.0% by weight based on the carbonaceous raw material. If the addition ratio is less than 0.1% by weight, the effect of suppressing the grain growth of silicon carbide will not be achieved, and if it exceeds 3.0% by weight, the added component will remain at the grain boundaries of silicon carbide, which is not preferable.

[0010] The carbonaceous raw material mixed with a grain growth inhibitor is reacted with silicon monoxide gas in a high temperature range of 1400 to 1800°C and converted into silicon carbide. The reaction temperature is 1400
If it is less than 1800°C, it will take a long time to generate silicon carbide, and if it exceeds 1800°C, the effect of the grain growth inhibitor will be diminished and the silicon carbide produced will become coarse.

[0011]

[Function] According to the present invention, the grain growth inhibitor added in advance migrates to the surface of silicon carbide particles generated during the reaction process between the carbonaceous raw material and silicon monoxide, and has the effect of inhibiting surface diffusion of silicon carbide particles. runs a business. 1400-1800℃ due to this action
Even at such high reaction temperatures, the produced silicon carbide does not become coarse and a high level of specific surface area is maintained. Therefore, the high reaction temperature makes it possible to produce activated silicon carbide having an excellent specific surface area within a very short time.

0012

[Examples] Examples of the present invention will be explained below in comparison with comparative examples. Examples 1 to 3, Comparative Examples 1 to 5 Activated carbon powder with a specific surface area of 750 m2/g [Takeda Pharmaceutical Co., Ltd.
Co., Ltd., trade name ``Shirasagi''] was used as a carbonaceous raw material, a grain growth inhibitor was added thereto, and the mixture was thoroughly dry-mixed using a ball mill. As a grain growth inhibitor, the average grain size is 0.9 μm.
boron powder [manufactured by Hermashi C. Stark, amorphous boron] and alumina powder with an average particle size of 0.2 μm [manufactured by Daimei Kagaku Co., Ltd., trade name "Taimicron TMD"]
] was used.

[0013] Next, the above mixed powder was placed in a closed heating furnace, and the temperature was raised to a predetermined temperature while maintaining the inside of the furnace under a reduced pressure of 10 Torr. A silicon monoxide gas produced by reacting a mixed powder of silica sand and silicon at a temperature of 1300° C. in a vacuum atmosphere of 30 Torr was introduced into this furnace in a separate system, and brought into contact with the mixed powder. The reaction conditions applied are shown in Table 1.

[0014]

The product was combusted in air at a temperature of 600° C. to burn off unreacted carbonaceous materials. The specific surface area, SiC conversion rate, and residual rate of grain growth inhibitor of each silicon carbide thus produced were measured, and the results are shown in Table 2. Note that the specific surface area was determined by the nitrogen adsorption method, and the residual rate of the grain growth inhibitor was determined by the fluorescent X-ray quantitative analysis method.

[0016]

From the results in Table 2, the silicon carbide of Examples 1 to 3 that satisfies the reaction conditions of the present invention has a specific surface area of 350 m2/g.
It exhibited a highly active surface that exceeded 100%, and showed a good SiC conversion rate and a small residual rate. On the other hand, in Comparative Example 1, in which no grain growth inhibitor was added, the specific surface area decreased significantly, and on the other hand, in Comparative Example 2, in which the addition rate exceeded 3.0% by weight, an undesirable increase in the residual amount was observed. . Reaction temperature is 1800℃
In Comparative Example 3, which exceeds the above, the specific surface area is significantly reduced. When the reaction temperature is 1300℃ and the reaction time is 30 minutes, SiC
The conversion of was insufficient (Comparative Example 4), and the reaction time was reduced to 18
Even when extended to 0 minutes, both the specific surface area and the SiC conversion rate were lower than in the example (Comparative Example 5).

[0018]

[Effects of the Invention] As described above, according to the present invention, activated silicon carbide having a high specific surface area can be efficiently produced within a short period of time by catalytically reacting silicon monoxide gas with carbonaceous raw materials at high temperatures. can. Therefore, it is extremely useful as a mass production means for manufacturing catalyst carriers used under high temperature and severe conditions.

Claims (1)

[Claims] Claim 1: In the process of converting a carbonaceous raw material into silicon carbide having a high specific surface area through a contact reaction with silicon monoxide gas at high temperatures, beryllium, boron, aluminum, phosphorus, chromium,
It is characterized by adding one or more of iron, gallium, or bismuth alone or as a compound in a range of 0.1 to 3.0% by weight, and reacting with silicon monoxide in a temperature range of 1400 to 1800°C. A method for producing activated silicon carbide.