JPH01141812A - Production of carbon-based fine hollow body - Google Patents

Abstract

PURPOSE:To obtain carbon-based fine hollow bodies having superior compressive strength and widely utilizable as a heat insulating lightweight filler at high temp. by thermally decomposing a gaseous hydrocarbon to form carbon coating layers on the surfaces of porous oxide granules and by carrying out heat treatment. CONSTITUTION:A gaseous hydrocarbon such as methane or propane is blown into a hot fluidized bed packed with porous granules of an oxide such as SiO2 or CuO as a heat medium. In the bed, the hydrocarbon is thermally decomposed to deposit carbon on the granules. The resulting carbon coated fine spheres are heat treated at a temp. above the m.p. of the oxide or the carbon-oxide reaction temp. in an inert atmosphere. The porous oxide granules in the spheres shrink owing to melting or are reduced by the coating carbon and hollow fine spheres of carbon and/or carbide are continuously obtd. The carbon-based fine hollow bodies have >=200kg/cm<2> compressive strength, are produced at a low cost and can be used as the above-mentioned filler.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a method for producing carbon-based micro hollow bodies such as carbon or carbide used as fillers in composite materials, and in particular to a method for producing carbon-based micro hollow bodies such as carbon or carbide used as fillers in composite materials. The present invention relates to a manufacturing method that allows hollow bodies with desired characteristics to be obtained at low cost by using particles.

<Prior art and its problems> Conventionally manufactured carbon micro hollow bodies are manufactured using coal tar pitch generated in coke ovens, etc. as a raw material, for example, as disclosed in JP-A-61-14110; It is produced using toluene as a solvent and is used as a filler in composite materials.

The carbon micro hollow body consists of (1) carbon material, (2) hollow body, (
3) It has characteristics as a microsphere.

That is, (1) the carbon material has heat resistance, electrical conductivity,
Chemical resistance, etc. (2) As a hollow body, lightweight material,
It is characterized by its heat insulation properties, workability, etc. (3) and isotropy as a microsphere.

Therefore, it is being considered that it can be mixed into various materials and used as a composite material for high-temperature insulation materials, buoyancy materials, etc.

For example, according to the manufacturing method disclosed in Japanese Patent Publication No. 48-28776, a mechanical strength of 170 kgf/cm or more is obtained by compounding or compounding with phenol resin, etc. Strength is also 1 f Okgf/cm'
This has improved.

Also, as disclosed in Japanese Patent Publication No. 58-42215,
There are also attempts to promote weight reduction.

However, the carbon microhollow bodies produced by conventional manufacturing methods do not necessarily satisfy the conditions required for various composite materials, and the current situation is that even more excellent properties are required.

In particular, in terms of mechanical strength, when used as a conductive heat insulating material by press molding, the compressive strength is 200 kgf/cm2 or more,
The electrical resistance value is 0.1Ω・Cm or less, and the insulation property is 0.5 kcal/m- at 1000°C.
Although it is desired that the temperature is hr.° C. or lower, no product has yet been obtained that fully satisfies these characteristics.

Conventionally, micro hollow carbon bodies manufactured by the carbonization process of coal tar pitch have had the disadvantage of having holes in the carbon membrane.

Furthermore, the carbon microhollow bodies manufactured by the conventional method of carbonizing coal tar pitch are expensive to manufacture, which is a factor that hinders the expansion of their uses.

<Object of the Invention> The object of the present invention is to solve the problems in the prior art, to provide a compressive strength of 200 kg/cm2 or more, to be inexpensive to produce, and to be a heat insulating and lightweight filler at high temperatures. The object of the present invention is to provide a method for manufacturing carbon-based micro hollow bodies that can be widely used.

<Structure of the Invention> The present inventors focused on a high-temperature fluidized bed, and when a hydrocarbon gas is blown into a high-temperature fluidized bed filled with porous oxide particles as a heat medium, carbon generated by thermal decomposition of hydrocarbons is attached. When deposited carbon-coated microspheres are obtained and heat treated in an inert gas atmosphere at a temperature higher than the melting point of the oxide or the reaction temperature with carbon, the porous oxide inside the spheres shrinks due to melting. Alternatively, it has been found that hollow carbon and/or carbide microspheres can be obtained continuously by reduction with coated carbon.

That is, in the first aspect of the present invention, a hydrocarbon gas is brought into contact with porous oxide particles in a fluidized state under heating, and a carbon coating layer is formed on the surface of the oxide particles by thermal decomposition of the hydrocarbon gas. A method for producing carbon-based microhollow bodies is provided, which comprises subsequently heat-treating the oxide particles having the carbon coating layer.

Here, a method for manufacturing a carbon-based micro hollow body in which the porous oxide particles are SiO2 is preferable.

Furthermore, it is preferable to carry out the carbon coating layer forming step and the first heat treatment step continuously using separate reaction vessels.

The present invention will be explained in detail below.

FIG. 1 is a flow sheet of the manufacturing method of the present invention.

(Carbon coating process) Using porous oxide particles as a heating medium, an inert gas is flowed at a flow rate higher than the fluidization start speed of the porous oxide particles to form a high-temperature fluidized bed, and the practical thermal decomposition temperature of hydrocarbon gas is achieved. When hydrocarbon gas is blown in while maintaining the above temperature, pyrolytic carbon adheres and deposits on the surface of the porous oxide particles, which are heat transfer particles.
Carbon-coated porous oxide particles are produced.

The porous oxide used as a heat medium may be any material as long as the surface is coated with carbon and then heat-treated to reduce the material, and the constituent elements increase the mechanical strength of the carbon material, depending on the purpose. S f 02 , Cu O, V203
can be used.

Argon, helium, nitrogen, etc. are used as the inert gas.

Any hydrocarbon gas may be used as the coating carbon raw material, but methane, propane, butane, etc. are preferable.

In other words, the requirements for the production method of the present invention are that the fluidized bed using porous oxide particles as a heat medium is at a practical temperature necessary for thermal decomposition of hydrocarbons, and at a temperature below the melting point of the particles or the reaction temperature with carbon. and, in the heat treatment step, to maintain the temperature necessary for the melting and shrinkage or carbonization reaction of the porous oxide inside the coated sphere in an inert gas atmosphere.

If the oxide particles serving as a heat medium are reduced before carbon is precipitated in the high-temperature fluidized bed, the carbon-based hollow body of the present invention cannot be obtained. It is preferable that the inert gas temperature is lower than the thermal decomposition temperature of hydrocarbons.

In the carbon coating process, by adjusting the treatment time and treatment temperature, the amount of coated carbon can be set to a desired value, and the composition ratio of oxides, carbon, and carbides in the generated micro hollow bodies can be set to a desired value. Can be done.

(Heat treatment step) The carbon-coated particles of the present invention are heated at a temperature higher than the melting point of the porous oxide or the reaction temperature with carbon while flowing the carbon-coated particles in an inert gas atmosphere as a high-temperature fluidized bed. A hollow body is obtained.

The carbon coating step and the heat treatment step may be carried out using the same reaction tank as explained later in FIG. 2, or may be carried out continuously using separate reaction tanks as explained in FIG. Good too.

Next, among the manufacturing methods of the present invention, a case in which porous SiO2 particles are particularly used will be described as an example.

(Carbon coating process) A is used as an inert gas to keep the heat medium in a fluidized state.
r, He%N2, etc. can be used. When the heat medium particles are 5 in 2 , the particle size is suitably in the range of 300 to 500 μm.

If the particle size is below this range, fluidization becomes difficult, and if the particle size is above this range, the efficiency of the pyrolysis 4 reaction will decrease.

Methane (CH4) is a hydrocarbon gas that serves as a carbon raw material.
, propane (Cs Ha ), butane (C4H+o), etc., are heated to 800 to 1500°C to generate pyrolytic carbon.

The reaction when the hydrocarbon is propane is as follows.

C3Ha →3 C+ 4 H2... (1) (Heat treatment step) As in the carbon coating step, the carbon coated particles are brought into a fluidized state with an inert gas, the temperature is adjusted, and heat treatment is performed.

The melting point of porous S i 02 particles is 1500-170
The temperature is about 0℃, and the reaction temperature in an inert gas atmosphere is 1700℃.
At temperatures above ℃, the following occurs.

5i02 +3C-=SiC+2CO... (2) After considering these temperatures, the heat treatment conditions for the carbon-coated particles are determined.

In this way, in order to produce carbon and/or carbide micro hollow bodies using porous 5i02 particles as a heat medium and hydrocarbon raw material as Cj H51, the particle size should be set to 300 to 500μ.
m, and the carbon coating step is preferably carried out at a temperature range of aOO to 1500°C, and the heat treatment step is carried out at a temperature of 1500°C or higher. Heat treatment temperature is 1500-1700℃
When the temperature is 1700° C. or higher, mainly carbon hollow bodies are formed, and when the temperature is 1700° C. or higher, mainly carbide hollow bodies are formed. At this time, the CO gas generated by the reaction between the porous oxide and carbon is
Since the amount of carbon is released outside through the fine pores of the carbon film, the carbon film will not crack.

In addition, although these fine pores do not impede the passage of gas at high temperatures, they are large enough to prevent such plastics from entering at room temperature or at the temperature used to fill and mold plastics, which poses a problem in use. It is not.

Next, a preferred apparatus for carrying out the method of the present invention will be explained based on the drawings. The apparatus used to carry out the method of the present invention is not limited to this.

The above-mentioned high-temperature fluidized bed is used in the carbon coating process. The heat treatment step can also use the same or separate high temperature fluidized bed as the carbon coating step, but other types of heat treatment furnaces can also be used.

FIG. 2 is a schematic diagram showing an example of a high temperature fluidized bed type device.

The high-temperature fluidized bed device 100 includes a device body 10 that has heat medium particles inside, a gas supply device 20 that supplies a gas flow that causes the heat medium particles to flow and form a fluidized bed, and a heating device 30 that heats the heat medium particles. It is composed of etc.

The device body 10 preferably has a fluidizing gas supply port 1 at the lower end.
9, has an exhaust gas outlet 25 at the upper end communicating with the exhaust gas pipe 13, and has a reaction tube 11 in the center.

The reaction tube 11 is provided with a sieve-shaped dispersion plate 17 at an appropriate position above the fluidizing gas supply port 19, and is configured such that the porous oxide particles are held above the dispersion plate 17.

A particle supply port 15 is provided at the top of the reaction tube, and a dispersion plate 1
A particle outlet 18 is provided near the hole 7 for taking out particles such as the manufactured carbon-based micro hollow bodies.

The fluidizing gas supply port 19 passes through the gas flow rate regulator 24,
It is communicated with the inert gas cylinder 23. The inert gas for fluidization is supplied from the inert gas cylinder 23 to the gas flow regulator 2.
In step 4, the gas is introduced into the reaction tube 11 at an appropriate flow rate and discharged from the exhaust gas outlet 25.

A heating element 32 is provided at an appropriate position inside the reaction tube 11 and is connected to an external heating power source to heat the inside of the reaction tube 11 to a predetermined temperature.

This temperature is measured by thermocouple 12.

A hydrocarbon gas supply port 16 is provided near the dispersion plate 17 of the reaction tube 11, and raw material gas is supplied from a hydrocarbon gas cylinder 21 located outside the reaction tube 11 via a gas flow rate regulator 21.

Porous oxide particles are charged into the reaction tube 11 through the particle supply port 15 and held on the dispersion plate 17, and fluidized gas is supplied to the particles from the fluidized inert gas cylinder 23 through the gas flow regulator 24.
By blowing in through the fluidizing gas supply pipe 19 and the dispersion plate 17, the porous oxide particles are fluidized by the inert gas flow and a fluidized bed 14 is formed.

The porous oxide particle fluidized bed 14 is heated by a heating power source 31 and a heating element 32 to a temperature of about 800 to 1500° C. required for thermal decomposition of the raw material hydrocarbon gas 21 . The raw material hydrocarbon is supplied by supplying the raw material gas from the raw material hydrocarbon gas cylinder 21 to the heated porous oxide particle fluidized bed 14 via the gas flow rate regulator 22 and the raw material hydrocarbon gas supply port 16. The gas is precipitated as carbon by thermal decomposition, and this precipitated carbon adheres and deposits on the surface of the porous oxide particles forming the fluidized bed 14. The oxide particles gradually become carbon-coated spheres.

After the carbon coating is completed, the supply of the raw material hydrocarbon gas is stopped, and the flow rate of the fluidizing inert gas is adjusted with the gas flow rate regulator 24 to correct the fluidized state, and the particle-encapsulated oxide and the coated carbon undergo a reduction reaction. The temperature inside the reaction tube 11 is raised by the heating element 32 to the temperature required to carry out the reaction. When the particles forming the coated particle fluidized bed 14 reach the reaction temperature, the oxide melts inside the particles and causes a reduction reaction with the coated carbon.

As a result of the reduction reaction, the coated carbon becomes a shell of a carbon compound and forms a hollow sphere. The produced carbide micro hollow bodies are taken out from the apparatus main body 10 through the particle outlet 18.

In order to improve the efficiency of the manufacturing process, the carbon coating process and the heat treatment process can be performed separately using the apparatus shown in FIG. FIG. 3 shows another example of an apparatus suitably used in the manufacturing method of the present invention.

The apparatus shown in FIG. 3 does not perform the carbon coating process and the heat treatment process in the same reaction tube 11, but instead uses a carbon coating tank 40 and a heat treatment tank 50.
This is done separately.

The configurations of the carbon coating tank 40 and the heat treatment tank 50 are similar to those of the apparatus main body 10 described above, but the particle discharge port 48 of the carbon coating tank 40 and the particle supply port 55 of the heat treatment tank 50 are preferably connected to each other. When the carbon-coated particles produced in the carbon-coating tank 40 are discharged from the particle discharge port 48, they naturally fall into the particle supply port 55 and are filled into the heat treatment tank 50.

The carbon-coated particles, which have been coated with carbon in the carbon-coating tank 40 and have increased in weight, settle to the lower part of the porous oxide particle fluidized bed 44 and are taken out from the particle outlet 48. The extracted particles are
The particles are charged into the heat treatment tank 50 via the particle supply port 55, and heat treatment is performed. After the heat treatment, the carbide microhollow bodies are taken out from the particle outlet 57 as the carbon-based microhollow bodies of the present invention.

<Example> The present invention will be specifically explained below using Examples.

Particle size range is 297-500μm (average particle size 395μm)
Porous Sin, 2000g particles with an inner diameter of 98mm
was filled in a graphite reaction tube, heated to 1200°C, and thermally decomposed for 16 hours at a flow rate of argon as a fluidizing gas and a flow rate of propane as a raw material gas of 1.0 J2/win. Carbon was attached and deposited on.

Then, the argon flow rate of the fluidizing gas is 3. OL, temperature 20
Heat treatment was performed at 00° C. for 6 hours to produce silicon carbide micro hollow bodies.

As a result, the coated carbon weight was 1206 g, the total weight of the produced micro hollow bodies was 1607 g, the average particle diameter was 505 μm, and the compressive strength was 20
It was 4 kg/cm'.

The compressive strength was 1.2 to 8 times higher than that of the conventional high-strength microscopic hollow spheres produced by the conventional coal tar pitch carbonization method, and excellent properties were obtained.

In addition, the elemental analysis results of the produced micro hollow bodies show that silicon carbide 89
．． 3wt%, carbon 10.1wt%, silica (S i 0
2) 0. It was 5wt%. This is because the reduction reaction in the heat treatment of the carbon-coated particles is almost complete, and by controlling the amount of coated carbon, the composition ratio of oxides, carbon, and carbides in the micro hollow bodies to be produced can be arbitrarily selected. shows.

Furthermore, as a result of observing the appearance of the produced carbon and carbide micro hollow bodies, it was found that while the carbon micro hollow spheres produced by the conventional coal tar pitch carbonization method have holes in the shell during the manufacturing process, the production method of the present invention has holes. is not possible, has high strength,
Carbon-based microhollow bodies with excellent properties as fillers for composite materials were obtained.

<Effects of the Invention> The carbon-based micro hollow bodies produced by the production method of the present invention have no shell defects caused by the production method, and by appropriately selecting the porous oxide used as the heat transfer medium particles, a variety of It is possible to produce micro hollow bodies made of carbide material and having arbitrary particle sizes, making them suitable as fillers for lightweight and high-strength composite materials.

The manufacturing method of the present invention has a simple manufacturing process and can be easily scaled up by selecting the types of porous oxide and hydrocarbon as raw materials, so that carbon-based microhollow bodies with the above characteristics can be manufactured at low cost. .

In particular, if the carbon coating step and the heat treatment step are performed continuously using separate reaction vessels, mass production is possible and manufacturing is possible at a lower cost.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet of the method of the present invention. FIG. 2 is a schematic diagram showing an example of an apparatus used in the method of the present invention. FIG. 3 is a schematic diagram showing another example of the apparatus used in the method of the present invention. Explanation of symbols 100--High temperature fluidized bed device, 10...High temperature fluidized bed device main body, 11...Reaction tube, 12...Thermocouple, 13...Exhaust gas piping, 14...Fluidized bed 15--Particle supply port, 16--Raw material hydrocarbon gas supply port, 17--Dispersion plate, 18--Particle discharge port, 19---Fluidization gas supply port, 20--Gas supply Apparatus, 21... Hydrocarbon gas cylinder, 22... Gas flow rate regulator, 23... Inert gas cylinder, 24... Gas flow rate regulator, 25... Exhaust gas outlet, 26... Gas flow rate Regulator, 30... Heating device, 31... Power source for heating, 32... Heating element, 40... Carbon coated tank body, 42... Thermocouple for temperature measurement, 43... Exhaust gas piping , 44... Porous oxide particle fluidized bed, 45... Particle supply port, 46... Raw material hydrocarbon gas supply port, 47... Dispersion plate, 48... Particle discharge port, 49... - Fluidization gas supply port, 50... Heat treatment tank, 52... Thermocouple for temperature measurement, 53... Exhaust gas piping, 54... Carbon coated particle fluidized bed, 55... Particle supply port, 56 ...Dispersion plate, 57...Particle discharge port, 58...Fluidization gas supply port, 61...Heating power source, 62...Heating element, 63...Heating power source, 64...・Heating element

Claims (3)

[Claims] (1) A hydrocarbon gas is brought into contact with porous oxide particles in a fluidized state under heating, and a carbon coating layer is formed on the surface of the oxide particle by thermal decomposition of the hydrocarbon gas, and then the carbon coating layer is formed on the surface of the oxide particle. 1. A method for producing a carbon-based micro hollow body, comprising heat-treating oxide particles having the following properties. (2) The method for producing a carbon-based micro hollow body according to claim 1, wherein the porous oxide particles are SiO_2. (3) The carbon coating layer forming step and the first heat treatment step,
Claim 1: Continuously carried out using separate reaction vessels
A method for producing a carbon-based micro hollow body according to item 1 or 2.