JPH08224462A - Reactor - Google Patents

Abstract

(57) [Summary] [Structure] In a reactor equipped with a reactor in which a chemical reaction is performed in a high temperature atmosphere, the reactor is formed of a carbon base material, and the surface of the reactor exposed to high temperature is A reactor characterized by being coated with a silicon carbide film. [Effects] The reactor of the present invention has excellent effects such as heat resistance, high temperature strength, thermal shock resistance, chemical stability with respect to atmospheric gas, and incompatibility with raw material powders, and moreover, can be easily applied to a large molded body. It can be processed and enables long-term continuous stable operation.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a reactor for a high temperature reaction, and particularly to a silicon nitride in a high temperature fluidized bed reaction.
The present invention relates to a reaction apparatus suitably used for producing non-oxide powders of silicon carbide, boron nitride, aluminum nitride, sialon, etc. with stable quality and continuously for a long time.

[0002]

2. Description of the Related Art Conventionally, a production apparatus for producing a non-oxide powder by a high temperature reaction of 1000 ° C. or higher using a fluidized bed, a fluidized bed comprising a silica reactor, a carbon powder and a silicon nitride powder is a carbon reactor. And a silicon nitride powder manufacturing apparatus using a reduction nitriding method in which the reaction is performed with nitrogen gas at 1300 ° C. or more and 1550 ° C. or less (Japanese Patent Publication No. 63-5).
No. 6168) is known.

On the other hand, a reaction tube made of mullite is formed, and a dispersion plate, a raw material supply tube and a product discharge tube are attached to the reaction tube, and silicon nitride powder is preliminarily charged in the reaction tube to form a fluidized bed. There is known a method for producing a silicon nitride powder (Japanese Patent Laid-Open No. 4-240106) in which a mixed gas of nitrogen and hydrogen and a metal silicon powder are continuously supplied and reacted after the temperature is raised to 1000 ° C. or more and 1500 ° C. or less. Further, in a multi-stage synthesis apparatus in which a plurality of fluidized beds are stacked and used as a reaction section, a method for producing a non-oxide powder using carbon, silicon carbide, and silicon nitride as reactor materials (Patent Publication 6-
No. 38911) is also known.

[0004]

However, when the non-oxide powder is produced at a high temperature by using the above-exemplified carbon, mullite, silicon carbide, and silicon nitride as the material of the reactor, there are the following problems. It was (1) Carbon has an advantage that a large material can be processed by machining, but since the hardness of the carbon member is low, the carbon is abraded by the flow of the raw material powder in the flow reaction, and the carbon is mixed into the product. Furthermore, when metallic silicon is used as a raw material powder as in the case of producing silicon nitride, at a reaction temperature of 1200 ° C. or higher, Si (s) + C (s) → SiC
Since the reaction (s) occurs and the metal silicon powder undergoes an adhesive reaction with the reaction tube, it becomes difficult to form and maintain a stable fluidized bed due to unevenness on the surface of the reaction tube. (2) In the mullite, when metal powder is used as the raw material powder, the silica component contained in the mullite is gradually reduced and volatilized as SiO, and the mullite itself becomes brittle. (3) Silicon carbide and silicon nitride are good materials that have no affinity for metal powder, but it is difficult to obtain a large-scale structural material because they are sintered and the residual stress at the time of molding is high. And becomes slightly brittle due to thermal stress.

From these points, it has been desired to develop an excellent reactor material capable of stably operating a high quality non-oxide powder for a long time on an industrial scale.

The present invention has been made in view of the above circumstances, and is a reactor for a high temperature reaction which is effective in the case of producing a non-oxide powder with stable quality and continuously for a long time in a high temperature fluidized bed reaction. The purpose is to provide.

[0007]

In order to achieve the above object, the present invention is a reactor equipped with a reactor in which a chemical reaction is carried out in a high temperature atmosphere, wherein the reactor is formed of a carbon base material. At the same time, there is provided a reactor characterized in that the surface of the reactor exposed to high temperature is coated with a silicon carbide film.

That is, for example, a reaction used in a high temperature reaction such as a fluidized bed reactor for producing a non-oxide powder by fluidizing a raw material powder such as metal silicon with a non-oxidizing reaction gas and performing a reaction at a high temperature of 1000 ° C. or higher. In the apparatus, as the material of the structural material that constitutes such a reaction apparatus, heat resistance, high temperature strength, thermal shock resistance, wear resistance, chemical stability to atmospheric gas, and incompatibility with the raw material powder are required. . 10
Heat resistance at high temperature of 00 ° C or higher, silicon, aluminum,
Examples of the material having a non-affinity with the raw material powder such as boron include silicon carbide, silicon nitride, alumina, aluminum nitride, boron nitride, zirconia, ceramic materials such as sialon, but these ceramic materials are, Residual stress is likely to remain in a large-sized compact due to sintering and may be damaged by thermal stress at high temperature, temperature gradient, or thermal shock, and there is a problem in using it as a reactor for fluid reaction. On the other hand, although carbon is a large-scale structural material and a material suitable for high temperature strength stability, there are problems in abrasion resistance and incompatibility with raw material powder at high temperatures. In consideration of such a point, the present inventor diligently studied the material used for the reactor for high temperature reaction as described above, and as a result, by using a carbon substrate whose surface is coated with a silicon carbide film, Wear resistance is improved compared to the case where a carbon substrate itself is used, for example, it is possible to reliably prevent carbon from being worn due to the flow of raw material powder in a fluidized bed reaction and carbon being mixed into a product. In the case where metallic silicon is used as the raw material powder as in the case, at the reaction temperature of 1200 ° C. or higher, Si (s)
By the reaction of + C (s) → SiC (s), it is possible to reliably prevent the reaction of the surface of the reaction tube due to the adhesion reaction of the metal silicon powder with the reaction tube, thereby forming a stable fluidized bed.
In addition to being able to maintain, because carbon is used as a base,
High-temperature strength stability is sufficiently maintained, production and processing are easy, and problems that occur when a ceramic material is used as a base material are solved. In this case, the silicon carbide film is well compatible with carbon, especially CVR. (Chemical
It was found that the silicon carbide film formed by the Vapor Reaction method is formed to a thickness of 0.3 mm or more and cracks hardly occur even if this film is repeatedly used, and the function of the surface silicon carbide is exerted more effectively. . That is, carbon was conventionally considered to be unusable as a device material particularly in a high temperature region under a hydrogen atmosphere, but it was confirmed that it can be sufficiently used by coating its surface with a silicon carbide film, The present invention has been completed.

The present invention will be described in more detail below. In the reactor of the present invention, a reactor in which a chemical reaction is carried out in a high temperature atmosphere is formed of a carbon base material, and the surface of the reactor exposed to a high temperature is used. Is coated with a silicon carbide film. In this case, the thickness of the silicon carbide film is preferably 0.3 mm or more from the viewpoint of effectively exerting the effect, and the method for forming the silicon carbide film is not particularly limited, but it may be formed by the CVR method. , 0.3
Even when formed to a thickness of not less than mm, cracks are less likely to occur in repeated use as compared with a coating film formed by a CVD method. Therefore, the effect of the silicon carbide film itself can be effectively exhibited, and a protective effect for a carbon substrate is also high, which is preferable. It is a thing.

Here, as the high temperature reaction, a reaction with a high temperature gas, particularly a reaction gas containing a non-oxidizing reaction gas at 1000 ° C. or higher, especially hydrogen gas, is effective,
Specifically, the metal or non-metal powder is fluidized with a non-oxidizing reaction gas, and the reaction is performed at a temperature of 1000 ° C. or higher to obtain the metal or non-metal non-oxide powder such as silicon nitride or silicon carbide. , A fluidized bed reaction for producing powders of boron nitride, aluminum nitride, sialon, etc. is suitable, and therefore, it is effectively used as a reactor in a fluidized bed reactor (reaction tube) used for this kind of reaction.

FIG. 1 shows an example of a reactor equipped with such a fluidized bed reactor (reaction tube). In the figure, 1 is a reaction tube, and this reaction tube 1 has an upper reaction chamber 3 formed by a gas dispersion plate 2 having a large number of reaction gas passage holes inside.
And a lower reaction gas supply chamber 4. A lower gas supply pipe 5 into which a reaction gas is introduced is connected to the bottom wall of the reaction gas supply chamber 4, and the reaction gas is introduced into the supply chamber 4 by this supply pipe 5 and passes through the gas dispersion plate 2. It is adapted to be distributed and supplied to the reaction chamber 4 through the holes. A fluidized bed 6 is formed in the reaction chamber 4 from the supplied reaction gas and raw material powder.

Reference numeral 7 denotes a raw material supply pipe for continuously supplying raw material powder, one end of which is positioned so as to be introduced into the lower part of the fluidized bed 6, and the other end of which is not shown is shown. The raw material powder is connected to a raw material hopper and a constant quantity feeder, the atmosphere of the raw material powder is replaced with a non-oxidizing gas in the raw material hopper, and then introduced into the lower part of the fluidized bed 6 via the constant quantity feeder. In this case, as the raw material powder, silicon, boron,
Metal powder such as aluminum or silicon, boron, metal powder such as aluminum, silicon nitride, boron nitride,
A mixed powder of non-oxide powders such as aluminum nitride and sialon is preferably used.

Reference numeral 8 denotes a product discharge pipe for discharging the non-oxide powder formed in the fluidized bed 6 along with the discharged gas, one end of which is located at the upper end of the fluidized bed 6 and is shown in the drawing. Although the other end is connected to a separator equipped with a collector, the non-oxide powder discharged along with the exhaust gas is separated from the exhaust gas by the separator and collected in the collector. It has become. The exhaust gas from which the non-oxide powder has been removed can be returned to the reaction gas supply chamber 4 of the reaction tube 1. In this case, the height of the fluidized bed 6 is determined by the position of one end of the discharge pipe 8. In addition, 9 is a heater.

Here, in the present invention, the reaction tube 1 is used.
Is formed of a carbon base material, and at least the inner surface thereof is covered with a silicon carbide film. in this case,
It is preferable that the dispersion plate 2, the raw material supply pipe 7, and the product discharge pipe 8 arranged in the reaction tube 1 are also formed of a carbon base material and the surface exposed to the reaction gas is covered with a silicon carbide film. The thickness of this silicon carbide film is 0.
It is 3 mm or more, more preferably 0.5 to 1.5 mm, and this silicon carbide film has a CVR (Chemical V
It is recommended to form it by the apor reaction method. The formation of the silicon carbide film by the CVR method can be performed by a known method.

As the method for producing the non-oxide powder by using the above-mentioned reactor of FIG. 1, a known method depending on the kind of the non-oxide powder can be adopted. Specifically, after charging the non-oxide powder in the reaction chamber 3 of the reaction tube 1,
A reaction gas containing nitrogen gas, hydrogen gas, a mixed gas thereof or ammonia gas is continuously introduced into the reaction gas supply chamber 4 from the reaction gas supply pipe 5, and the reaction gas is supplied from the reaction gas supply chamber 4 through the gas dispersion plate 2. A reaction gas is dispersedly supplied to the chamber 3 to form a fluidized bed 6 composed of the reaction gas and the non-oxide powder, and the reaction tube 1 is heated to 1000 ° C. or higher by an external heater 9. On the other hand, the raw material powder mixed and dispersed with a non-oxidizing gas is jetted from the tip of the raw material powder through the raw material supply pipe 7 to the bottom portion of the fluidized bed 6, whereby the raw material powder is continuously supplied into the fluidized bed 6, React in 6. The non-oxide powder generated in the fluidized bed 6 is discharged together with the exhaust gas from the upper end of the fluidized bed 6 through the exhaust pipe 8 and collected.

FIG. 2 shows another example of a reactor equipped with a fluidized bed reactor (reaction tube). In this example, while FIG. 1 is a continuous reactor, a batch reactor is used. 2, the raw material supply pipe 7 and the product discharge pipe 8 are not provided, and the exhaust pipe 10 is connected to the upper end of the reaction pipe 1, which is the same as the device of FIG. The same reference numerals as those in FIG. 1 are given to the same constituent parts as in FIG. When a non-oxide powder is produced using this reactor, the raw material powder is charged into the reaction tube 1 in advance and heated to 1000 ° C. or higher by the external heater 9, and then nitrogen gas, hydrogen gas, a mixed gas thereof or ammonia. A reaction gas containing a gas is supplied from the lower gas supply pipe 5 through the dispersion plate 2 to form a fluidized bed 6 and react. The reaction exhaust gas generated in the fluidized bed is discharged through the exhaust pipe 10. Although not shown, the other end of the exhaust pipe 10 is separately connected to an exhaust gas treatment chamber so that the exhaust gas does not flow into the atmosphere.

Here, in FIG. 2, the reaction tube 1 is made of carbon, and a silicon carbide film is formed on the inner surface thereof. Further, the dispersion plate 2 is also made of carbon, and the entire surface thereof is carbonized. It is preferable to form a silicon film.

The reaction apparatus of the present invention is the same as that shown in FIGS.
For example, although the discharge pipe 8 is connected to the lower part of the reaction tube 1 in FIG. 1, it may be connected to the upper part of the reaction pipe 1, and the discharge pipe 8 and the supply pipe 8 are not limited to those shown in FIG. Two or more 7 may be provided, and other configurations may be variously modified without departing from the gist of the present invention.

[0019]

Industrial Applicability The reactor of the present invention has excellent effects such as heat resistance, high temperature strength, thermal shock resistance, chemical stability with respect to atmospheric gas, and incompatibility with raw material powder, and is suitable for large-sized compacts. It can be easily processed and enables continuous stable operation for a long time.

[0020]

EXAMPLES The present invention will be described below in detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Example 1 Silicon nitride powder was produced using the reactor shown in FIG. The reaction tube has an inner diameter of 120 mm,
A porous plate is used as the dispersion plate, the inner diameter of the raw material supply pipe and the product discharge pipe is 15 mm, and the entire surface of the reaction pipe, the dispersion plate, the raw material supply pipe, and the product discharge pipe is covered with a carbon carbide film of 1.0 mm. The structural material was made of wood. 4000 g of silicon nitride powder was charged as the initial base material, and the reaction temperature was 1250 ° C.
The reaction gas used was a mixed gas (volume ratio) of nitrogen: hydrogen = 4: 1 and was supplied from a gas supply pipe. The raw material metal silicon powder was supplied at 400 g / hr for continuous operation. The operation time was 300 hours, the flow was stable, and the product powder obtained had a reaction rate of 70% and an α-conversion rate of 97%, and no change with time in quality was observed.

After completion of the operation, the apparatus was disassembled and the inner surface of the reactor was observed, but no abnormality was found.

Example 2 Using the same reactor as in Example 1, silicon nitride powder was produced. 4000 g of silicon nitride powder was charged as an initial base material, and the reaction temperature was set to 1400 ° C. As the reaction gas, a mixed gas (volume ratio) of nitrogen: hydrogen = 4: 1 was used and was supplied from a gas supply pipe. As the feed material, the silicon nitride intermediate produced in Example 1 was fed at 550 g / hr for operation. The operation time was 200 hours and the flow was stable, and the product powder obtained had 0.7% unreacted silicon.
No change with time in quality was observed at a weight percentage and an alpha conversion of 93%.

After completion of the operation, the apparatus was disassembled and the inner surface of the reactor was observed. As a result, no abnormality was found as in the case of Example 1. Furthermore, a part of the reactor was cut out and the cross section was checked. As a result, the surface layer maintained the initial thickness of 1.0 mm.

Comparative Example Silicon nitride powder was produced using the reactor shown in FIG. The reaction tube uses an inner diameter of 120 mm, the dispersion plate uses a perforated plate, and the raw material supply pipe and product discharge pipe have an inner diameter of
It was 5 mm, and each was made of mullite. 4000 g of silicon nitride powder was charged as an initial base material, the reaction temperature was set to 1250 ° C., and the reaction gas was nitrogen: hydrogen = 4: 1.
The mixed gas (volume ratio) of was used and was supplied from a gas supply pipe. The raw material metal silicon powder was supplied at 400 g / hr and continuously operated. After 110 hours of operation, the deposition of metallic silicon powder on the discharge pipe grew and the discharge pipe was blocked, so the operation was interrupted. Further, after the operation time exceeded 100 hours, the flow became unstable due to the deposition of the metal silicon powder on the inner surface of the reaction tube, and the internal temperature fluctuated greatly. The product powder thus obtained has a reaction rate of 58% or more and 70% or less and an α conversion rate of 8
The quality varied between 9% and 97%.

After observing the inside of the reactor after the end of the operation, a large amount of Si and Si ₃ were distributed from the dispersion plate, the supply pipe, the tip of the discharge pipe, the upper part of the flow surface of the main body to the space called the free zone.
Adhesion of N ₄ was observed.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a reaction apparatus of the present invention.

FIG. 2 is a schematic view showing another embodiment of the reaction apparatus of the present invention.

[Explanation of symbols]

 1 Reaction Tube 2 Dispersion Plate 3 Upper Reaction Chamber 4 Lower Reaction Gas Supply Chamber 5 Gas Supply Pipe 6 Fluidized Bed 7 Raw Material Supply Pipe 8 Product Discharge Pipe 9 External Heater 10 Exhaust Pipe

Claims (4)

[Claims] 1. A reactor equipped with a reactor for performing a chemical reaction in a high temperature atmosphere, wherein the reactor is formed of a carbon base material, and a surface of the reactor exposed to a high temperature is formed of a silicon carbide film. A reactor characterized by being coated. 2. The silicon carbide film has a thickness of 0.3 according to the CVR method.
The reactor according to claim 1, which is formed to have a thickness of at least mm. 3. A reactor fluidizes the metal or non-metal powder with a non-oxidizing reaction gas and performs a reaction at a temperature of 1000 ° C. or higher to produce the metal or non-metal non-oxide powder. The reactor according to claim 1 or 2, which is a fluidized bed reactor. 4. A dispersion plate for dispersing and introducing reaction gas into the reactor, a raw material supply pipe for supplying metal or non-metal powder to the reactor, and a product discharge pipe for discharging non-oxide powder from the reactor, respectively. A silicon carbide film is formed on the surface of the dispersion plate, the raw material supply pipe, and the product discharge pipe, which are attached to the reactor and are arranged in the reactor, of a carbon base material, and the surface exposed to the reaction gas. A reactor according to claim 3 coated with.