JPH0269356A - Production of isotropic graphite material having high purity - Google Patents

Abstract

PURPOSE:To easily obtain isotropic graphite material having high purity and a low anisotropy ratio by finely crushing amorphous pitch coke, bringing into contact with an aq. strong acid soln. for a fixed time period to remove ash, thereafter washing, drying, molding, sintering and graphitizing. CONSTITUTION:The amorphous pitch coke produced by carbonizing coal tar pitch, is crushed to <=250mum. Then, the crushed pitch coke is brought into contact with the aq. strong acid soln. (e.g., aq. hydrochloric acid soln.) for >=5min to remove metallic impurities contained in the coke. The coke powder obtd. after washing and drying, as raw material, is molded with or without pitch as binder, sintered and graphitized to obtain the isotropic graphite material having high purity and <=1.05 anisotropy ratio. Thereby, the load for highly purifying when the coke powder is graphitized, can be lightened, because the metallic impurities in the amorphous pitch coke as raw material, have been removed in advance.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to amorphous green pitch coke produced from coal tar pitch and a method for producing isotropic graphite material of high purity from amorphous calcined pitch coke.

Among conventional pitch cokes, amorphous coke is a raw material for isotropic graphite material. Since this coke is produced by carbonizing pitch, which is a distillation residue of coal tar, the ash contained in the coal tar is condensed and contained in the amorphous pitch coke. The ash component is derived from the raw coal of coal tar, and from compounds added as anticorrosive agents during the coal tar door retention process, but mainly contains alkali metals such as sodium, alkaline earth metals such as calcium, and Contains iron, silica, etc.

Isotropic graphite branches with an anisotropy ratio of 1.05 or less are usually manufactured through the following process.

(1) A step of pulverizing amorphous calcined coke to several pm to several tens of lm, (2) A step of mixing the pulverized amorphous coke powder and binder pitch, (3) A step of molding the mixture, (4) (5) graphitizing the fired product; (6) processing the graphite material depending on the purpose.

Furthermore, a method for producing isotropic graphite material using a binderless method has recently been developed. is omitted.

Depending on the application, it is undesirable for isotropic graphite materials to contain metal impurities.Especially, when used as graphite for nuclear reactors, it is undesirable to have trace amounts of impurities mixed in.Furthermore, it is undesirable for isotropic graphite materials to be used in the manufacture of electronic components. In this case, for example, metal impurities are extremely likely to be mixed into isotropic graphite materials used in crucible holder heaters for silicon pulling, as well as jig materials for hermetic sealing.

Therefore, in general, a method for removing metal impurities from isotropic graphite material is to distribute halogen gas as an atmospheric gas in the process of graphitizing the fired product in the manufacturing process of the graphite material to achieve so-called high purity. , a method of vaporizing metal impurities has been used.

Furthermore, as a method for removing alkali metals and alkaline earth metals from carbon materials, Japanese Patent Publication No. 62-45184
It is disclosed in the publication No. This method is a method in which uncarbonized polyacrylonitrile material is brought into contact with acid at a temperature of 37.7°C or higher to convert metals into soluble salts and remove them, and acid treatment is performed before carbonization. is a feature.

With the high purification treatment currently being carried out industrially, it is possible to almost completely remove metal impurities in isotropic graphite materials, but since it uses halogen gas at ultra-high temperatures, it is not safe or
It is difficult to say that it is an economical method because it requires special attention to pollution problems and uses a large amount of halogen gas.

Furthermore, among the isotropic graphite materials used for manufacturing electronic components among the above-mentioned applications, materials with too much graphitization may not be preferable in terms of hardness. However, the current graphitization process uses halogen gas to remove impurities.
Since it is necessary to heat the material to a graphitization temperature, graphitization will definitely proceed. As the graphitization progresses, the hardness of the graphite material decreases, so it is difficult to manufacture an isotropic graphite material with high hardness using current methods.

In addition, a solvent is added to coal tar to reduce the viscosity.
The technology to remove quinoline solubles (QI) from coal tar by sedimentation separation or filtration of insoluble matters has been established, and in this case, the ash content is simultaneously removed by QI removal. Carbonization of the treated, QI-free coal tar pitch produces needle coke suitable for use in graphite electrodes for steelmaking.

Since this coke has a large anisotropy, it is not suitable as a raw material for producing monoisotropic graphite material. Therefore, the above-mentioned method of removing QI and ash from coal tar in advance is It cannot be used when producing amorphous coke, which is a raw material for wood.

Problem to be Solved by the Invention It is an object to reduce metal impurities from amorphous pitch coke, which is a raw material for graphite material, and to provide a high-purity isotropic graphite material using this amorphous pitch coke.

Means for Solving the Problems The present invention involves reacting metal impurities in amorphous pitch coke chains with strong acids to form soluble salts, which are then removed and reduced. The existence form of metals in amorphous pitch coke is not clear.

Metals derived from coal tar are included in the structure of amorphous pitch coke during the pitch carbonization process, and do not easily react with acids.The inventors have conducted extensive research to develop amorphous pitch coke chains using the following method. The present invention was completed based on the discovery that metal impurities in the material can be effectively reduced.

That is, in the present invention, amorphous pitch coke is
Using amorphous pitch coke powder obtained by pulverizing it to 0 g m or less, contacting it with a strong acid aqueous solution for 5 minutes or more, washing with water, and drying it as a raw material, it can be molded, fired, and graphitized with or without binder pitch. This is a method for producing a high-purity isotropic graphite material with a low content of metal impurities.

The amorphous pitch coke used as a raw material in the present invention is amorphous green pitch coke produced from coal tar pitch, and amorphous calcined pitch coke obtained by calcining it.

The manufacturing method of the present invention is as follows.

The raw material pitch coke is pulverized to 2501Lm using a regular crusher such as a jet mill, vibration mill, ball mill, or hammer mill.
Thereafter, the particles are preferably pulverized to 1004 m or less, and the particles are brought into contact with a strong acid aqueous solution. The particle size of amorphous pitch coke powder is 250. If it exceeds g and m, N will not react with metal impurities in the amorphous pitch coke upon contact with a strong acid aqueous solution, and the effect of reducing metal impurities will not be sufficient.

Amorphous pitch coke containing metal impurities was pulverized and divided into coarse powder and fine powder, and the metal impurities contained in each were measured. As a result, it was found that metal impurities were concentrated in the fine powder. therefore.

If the raw material amorphous pitch coke is first coarsely pulverized to remove fine powder, and then the coarse powder is pulverized again to 250 gm or less and the method of the present invention is applied, the effect of removing metal impurities will be increased compared to the case where re-pulverization is not performed. do.

A specific method is described below. For example, amorphous pitch coke powder pulverized to 250 ILm or less and a strong acid aqueous solution are placed in a glass-lined container and stirred.

After stirring for a predetermined time, the slurry is taken out and filtered to remove the amorphous pitch coke powder.Next, the amorphous pitch coke is rinsed with water until no acid is attached to it, and then dried. Since this method can be operated at relatively low temperatures and normal pressure, the equipment and operation are very simple.

An isotropic graphite material having an anisotropy ratio of 1.05 or less is produced using the amorphous pitch coke powder subjected to such treatment as a raw material, and a known method is applied to the production method. In other words, if amorphous pitch coke is green coke containing about 10% volatile matter, it can be molded, fired, and graphitized to produce graphite material, and if amorphous pitch coke is calcined coke, binder pitch can be used as a binder. After addition and kneading, isotropic graphite material is produced by molding, firing, and graphitization.

The acid used in the present invention may be any strong acid, but from an economic standpoint, it is preferable to use inexpensive mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid. The extraction is performed at a concentration, temperature, and time sufficient to effect substantial ion exchange with hydrogen ions to form salts. The acid concentration can be varied from 0.1 to 35% by weight or more depending on the type of acid used, but if the acid concentration is too low, the effect will not be sufficient. Furthermore, if the acid concentration is too high, excess acid must be used to sufficiently wet the pitch coke powder, which is not economical.

Room temperature is fine, but in order to extract metals in a short time, it is desirable to heat it to below the boiling temperature of the acid aqueous solution.The contact time with the acid depends on the particle size of the amorphous pitch coke powder, the processing temperature, and the acid Although it varies depending on the concentration, it is necessary to take 1 ift for at least 5 minutes or more during washing. Also.

As an upper limit of the contact time, about 120 minutes is sufficient.

After extraction with a strong acid aqueous solution, the amorphous pitch coke powder is washed with metal salt and ash-free water. This water washing step is for dissolving and washing off substantially all the residual acid and salts generated by contact with the acid aqueous solution, and must be carried out sufficiently. Therefore, it is necessary to perform this washing with water for a sufficiently long time.

Following water washing, water adhering to the amorphous pitch coke is removed by drying.Drying is carried out at around 100℃.The drying temperature is high if calcined coke is used as the raw material and in a reducing atmosphere vI4 atmosphere. Drying is fine, but when green coke is used as a raw material, drying at high temperatures changes the quality and amount of volatile matter contained in the coke, which is undesirable.If the drying temperature is around 100°C,
Since the quality and quantity of volatile components in green pitch coke do not change, it can be used as is as a raw material for binderless isotropic graphite material.

The method of the present invention uses amorphous pitch coke at 250
After pulverizing to below pm, it is contacted with a strong acid aqueous solution, which may seem uneconomical, but since isotropic graphite material is manufactured from pulverized coke as mentioned above, the pulverization process is Since this step is originally essential, no extra steps were added for the purpose of the present invention, and it does not constitute a disadvantage.

Although the method of the present invention does not remove all the ash in the amorphous pitch coke, the alkali metal,
Alkaline earth metals, iron, etc. are effectively removed. Since silicon and the like are difficult to remove in the present invention, their residual ratio is high.

The amorphous pitch coke powder thus obtained can be used as a raw material for isotropic graphite material as it is, but depending on the use of the graphite material, it can also be re-pulverized and used as a raw material. The graphite material manufacturing process may be the same as the usual method, but
In high purification using halogen gas in the graphitization process, the amount of impurities in the graphite material is reduced even if the graphitization temperature is lower than usual.

Examples Examples 1 to 9, Comparative Example 1.2 Amorphous green pitch coke was used as a raw material. Put 100 g of coke powder crushed in a vibrating ball mill and 150 g of a strong acid aqueous solution into a beaker, and after contacting with the stirred 6 strong acid aqueous solution, filter the acid with a glass filter.
The filtrate was washed with wood until it became neutral. After that, 80℃
It was dried with

Table 1 shows the conditions of contact with the strong acid aqueous solution and the ash content before and after contact.

Both when using hydrochloric acid and when using sulfuric acid.

It can be seen that the ash content has decreased. Furthermore, when the coke particle size was large, as shown in Comparative Example 1, the ash removal rate was low.

For comparison, Comparative Example 2 shows the amount of ash contained in coke when a sample having a particle size of 75 to 45 g, m was not brought into contact with a strong acid aqueous solution and only washed with water.

It can be seen that the ash content in the coke powder is hardly reduced by the water washing process alone.

Example 10, Comparative Example 3 The same treatments as in Examples 1 to 9 were performed using calcined pitch coke. The treatment conditions, ash content, etc. are shown in Table 2.

It can be seen that by reducing the pulverized particle size, ash can be removed even when calcined coke is used as a raw material. Furthermore, as shown in Comparative Example 3, it can be seen that when the particle size is large, the extent to which ash is removed is small.

Example 11. Comparative Example 4 The same amorphous green pitch coke as in Examples 1 to 9 was pulverized using a vibrating ball mill so that the particle size was 74 gm or less. To 100g of this powder, 20g of hydrochloric acid with a concentration of 18%
After adding 0g of the mixture and stirring in a beaker at 50°C for 30 minutes, the mixture was filtered with a 3G glass filter and washed with water until the filtrate became neutral.

Using the obtained coke powder as a raw material, an isotropic graphite material was produced by molding, firing, and graphitization without using binder pitch, and the ash content and physical properties of the graphite material were measured. In addition, as a comparative example, a graphite material was manufactured using the same procedure using a powder that was not treated with hydrochloric acid, and was used as a comparative material. The physical properties of the graphite material are shown in Table 3 together with Comparative Example 4.

The manufacturing conditions for the graphite material are as follows: Molding, Φ, Primary forming: Press molding with a molding pressure of 50 kg/cm2 Secondary molding using a Nirabar press, and molding with a molding pressure of 2 tons/C 2 cm After secondary molding Dimensions: Diameter = 25 layers■, height = 48m■ Firing/Number: Temperature raised to 1100℃ at a temperature increase rate of 3℃/hour Graphitization... Temperature raised to 2500℃ at a temperature increase rate of 10℃/minute As shown in Table 3, the graphite material made from coke powder washed with hydrochloric acid has a low graphitization temperature of 2500° C. and has a low ash content even though it is not purified using halogen gas.

Example 12, Comparative Example 5 The same amorphous calcined pitch coke as in Example 1O was pulverized with a jet mill to a particle size of 50 Bm or less.

Add 200g of hydrochloric acid with a concentration of 18% to 100g of this powder,
After stirring in a beaker at 50°C for 30 minutes, the mixture was filtered through a 3G glass filter and washed with water until the filtrate became neutral. 80 g of binder pitch with a softening point of 90°C was added to the obtained coke powder, mixed at 120°C using a Ni-Goo, molded, fired, and graphitized to produce a graphite material, and the ash content and physical properties of the graphite material were measured. did.

In addition, as a comparative example, a graphite material was manufactured using the same procedure using a powder that was not treated with hydrochloric acid, and was used as a comparative material. The physical properties of the graphite material are shown in Table 4 together with Comparative Example 5.

The manufacturing conditions for the graphite material are as follows: Molding... φ Primary forming: Press molding at a molding pressure of 50 kg/cm2 Secondary molding using a nirabar press, molding at a molding pressure of 2 tons/C2 after secondary molding Dimensions: Diameter = 27mm, Height = 48 ■ Firing - Temperature raised to 1100°C at a heating rate of -3°C/hour Graphitization... Temperature raised to 2600°C at a heating rate of 10°C/min Table 4 As shown in the examples, the content of metal impurities is small even though high purification using halogen gas is not performed.

Table 3 The burden of purification can be reduced.

Claims (1)

[Claims] Amorphous pitch coke is crushed to 250 μm or less, brought into contact with a strong acid aqueous solution for 5 minutes or more, washed with water, and dried. Using the coke powder obtained as a raw material, molding, firing, and graphitization can be performed with or without binder pitch. A method for producing a high-purity isotropic graphite material having an anisotropy ratio of 1.05 or less.