JPH02296894A - Production of needle coke - Google Patents

Abstract

PURPOSE:To decrease the content of nitrogen compds., lower the coefficient of thermal expansion, and prevent the puffing by coking a coal tar-derived raw material freed from quinoline insolubles and lower alcohol solubles. CONSTITUTION:A coal tar-derived raw material pref. comprising a tar pitch with a softening point of 70 deg.C or lower is freed from quinoline insolubles and lower alcohol solubles, and converted into a raw coke in a delayed coker under a pressure of 1-10kg/cm<2> at 450-550 deg.C. The resulting raw coke is calcined at 1200-1500 deg.C to give a needle coke, which is ground and the grain size is adjusted. Then, the adjusted needle coke is mixed with a binder pitch, molded, baked, and graphitized at 2500 deg.C or higher to give a graphite electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing graphite raw material, particularly needle coke, which is mainly used as a raw material for graphite electrodes for electrical steel manufacturing. More specifically, the present invention relates to a method for producing needle coke with low CTE and puffing from a raw material obtained by removing methanol-soluble components from coal tar-based raw material oil that does not contain quinoline-insoluble components.

[Conventional technology]

Needle coke is mainly used as a raw material for electric steelmaking electrodes, but in the electric steelmaking industry, electric furnaces are becoming larger and UH
P (Ultra High Power) operations and operating conditions are becoming increasingly harsh, and graphite electrodes with better performance,
Furthermore, there is a demand for high-grade two-dollar coke.

Especially the CTE (coefficient of thermal expansion). Related to thermal shock resistance during electrode use, lower CTE improves electrode consumption rate, so electrodes and coke with low CTE are desired.

On the other hand, manufacturers of graphite electrodes are also trying to shorten the graphitization time to save energy during graphitization.
A problem is the irreversible thermal expansion phenomenon (puffing) that occurs when the electrode graphitizes.

Puffing becomes larger as the graphitization time becomes shorter, and in extreme cases, graphitization becomes impossible.

Further, if the puffing is large, problems such as a decrease in the bulk density of the electrode obtained after graphitization occur. Therefore, not only the CTE of the graphite electrode but also the puffing during graphitization is an important indicator of needle coke quality.

It has been thought that puffing occurs because the sulfur compounds contained in needle coke rapidly decompose and gasify when heated to high temperatures, pushing the coke structure and expanding it.

Therefore, as a measure to prevent puffing, a method has been proposed in which a metal compound that forms a compound with sulfur (for example, iron oxide) is added to trap sulfur in the temperature range where puffing occurs.

However, even though this method is effective for petroleum-based needle coke obtained from petroleum-based raw materials containing many sulfur compounds, it is not effective for coal-based needle coke obtained from coal-tar-based raw materials, and is not effective as a measure to prevent puffing. It is enough.

In recent years, a detailed investigation into the causes of puffing in coal-based needle coke has revealed that the cause of puffing is not only sulfur but also nitrogen.

Therefore, reducing nitrogen in needle coke is an important point in reducing puffing.

It has been well known that in order to produce needle coke from coal tar-based raw materials, it is necessary to remove several percent of quinoline insoluble content (abbreviated as 01 min) contained in the coal-tar raw materials. Therefore, at least before coking, it is necessary to reduce the content of 01 min to 0.5% by weight or less.

Needle coke obtained from Ql-depleted coal tar-based raw materials has relatively little visceral yellow content, but has a high nitrogen content, so
Anti-puffing agents have little effect, and reducing puffing has become a major challenge.

On the other hand, although the CTE level is lower than that of petroleum-based needle coke, there is an inverse correlation between CTE and puffing, and it has been difficult to reduce CTE without reducing puffing using normal means.

However, a method for denitrifying coal tar-based raw materials,
For example, it has been shown that CTE and puffing can be reduced at the same time by the hydrogenation method disclosed in JP-A-60-149690. This method has the disadvantage of requiring large equipment and cost.

In Japanese Patent Publication No. 62-45916, ordinary coke■
A method has been proposed in which coke is obtained by heating at a temperature range of 1430 to 1.500° C., which is higher than the calcination temperature, for a long time to diffuse the nitrogen content in the coke. This method also has the disadvantage of requiring energy costs.

Japanese Patent Publication No. 57-47125 discloses that coal tar-based heavy oil is mixed with alcohol and a solvent with a boiling point of 200°C or less that is soluble in both the coal heavy oil and the alcohol, and the insoluble gas produced in the mixed liquid is A method has been proposed in which quinoline insolubles are removed by separating and removing the precipitate. This method is a method for removing insoluble components of quinoline, and the raw materials for coking are alcohols, coal-based heavy oil, solvents that are soluble in both alcohols, and soluble in acetone, benzene, toluene, etc. It is a heavy oil component.

Japanese Patent Publication No. 62-28110 discloses that coal tar pitch is dissolved in quinoline, pyridine, etc., the Ql component is removed, and then dissolved in an intermediate solvent such as benzene, toluene, n-hexane, etc., and ethanol, methanol, acetone, etc. A precipitated solid is obtained by mixing with a poor solvent, and this is used as a binder for coke. The solid that precipitates here can also be found in alcohols such as methanol in the de-Ql coal tar pitch.
- It is a precipitated solid that is insoluble in intermediate solvents such as hexane and the initial solvent such as quinoline, and is not a raw material for needle coke, that is, the problem of solving puffing by reducing nitrogen compounds has not been noticed.

[Problem to be solved by the invention]

Based on the technological trends described in the conventional method, the current method for needle coke can be improved without using hydrogenation methods that require large-scale equipment and costs, and without incurring energy costs such as heating coke at high temperatures and for long periods of time. Measures to reduce the nitrogen content from coal tar-based raw materials are eagerly awaited.

An object of the present invention is to provide a method for producing needle coke that is excellent in both CTE and puffing by removing quinoline-insoluble components from a coal tar-based raw material and using a raw material with reduced nitrogen content. .

[Means to solve the problem]

The present inventors have conducted extensive research to solve the above problems, and have found that nitrogen compounds are concentrated in the lower alcohol-soluble content of coal tar-based raw materials, and that this lower alcohol-soluble content is Focusing on the fact that it has a negative effect on the flow structure of coke, we have adopted a simple method of removing lower alcohol soluble content from coal tar-based raw materials.
C.T.E.

The present invention was completed by discovering that needle coke with excellent puffing properties could be obtained.

That is, the present invention is a method for producing needle coke, which comprises removing quinoline-insoluble components and lower alcohol-soluble components from a coal tar-based raw material, and then converting the raw material into coke.

Coal tar-based raw materials include coal tar produced when coal is carbonized, high boiling point tar oil and cool pitch separated from coal tar, and preferably tar pitch.

Cool pitch includes soft pitch with a softening point of 70°C or lower, medium pitch with a softening point of 70 to 85°C, and high pitch with a softening point of 85°C or higher. All of them can be used, but soft pitch is difficult to handle. It is advantageous to use It may also be a mixture of two or three of tar pitch, coal tar, or high boiling point tar oil.

Many documents have already been published regarding methods for removing 01 min from coal tar-based raw materials, but it is also possible to remove it by mechanical methods such as filtration and centrifugation.
Since the particle size of Q1 is extremely small, the separation rate is slow and the separation efficiency is low, such as clogging during filtration, and it cannot be implemented industrially. The same thing can be done even if a solvent is added to lower the viscosity. A method that can be implemented industrially is
As disclosed in Publication No. 0159 and Japanese Patent Application Laid-open No. 53-66901, coal tar-based raw materials are combined with aliphatic solvents such as hexane, octane, kerosene, naphtha, butanol, and benzene, toluene, xylene, methylnaphthalene, An effective method is to add and mix a mixed solvent with an aromatic solvent such as phenol to form an insoluble product around the Q1 particles, increase the size of the particles, and then settle and remove the particles.

An important point in the present invention is that nitrogen compounds are subsequently reduced.

It is generally known that coal tar-based raw materials contain phenolic oxygen and pyrrole nitrogen. The present inventors found that these components can be easily separated using lower alcohols such as methanol, and as a result of detailed research, they found that pyrrolic nitrogen is the main source of nitrogen in needle coke. They discovered that phenolic oxygen and pyrrole nitrogen are components that inhibit the flow structure of needle coke.

Figure 3 shows the infrared absorption spectra of C82 diluted solutions of the methanol-insoluble fraction (Ml), methanol-soluble hexane-insoluble fraction (MS-Hl), methanol-soluble, and hexane-soluble components (MS-H3). show.

It can be seen that phenolic oxygen 1 and pyrrole nitrogen 2 are not included in Ml but are concentrated in MS.

Based on these facts, by coking a coal tar-based raw material from which lower alcohol-soluble components including phenolic oxygen and pyrrole nitrogen have been removed, CTE1 can be achieved.
It has become possible to produce needle coke with excellent puffing properties.

In the present invention, the lower alcohol-soluble content may be removed from the coal tar-based raw material from which the Q1 component has been removed as described above, but the lower alcohol-soluble content may also be removed from the lower alcohol-insoluble coal tar-based raw material from which the lower alcohol-soluble content has been removed. Of course, Q1 minutes may be removed.

Considering the use of the lower alcohol soluble content, it is preferable to first remove the 01 minute content.

Examples of the lower alcohol include methanol, ethanol, propatool, butanol, and ethylene glycol, but methanol is most preferred in terms of cost.

A known method can be used to remove the lower alcohol soluble content. For example, a liquid in which lower alcohol is mixed and stirred with coal tar-based raw material oil, and then left to stand and separated to separate the alcohol layer.
A liquid extraction method is common, and methods such as supercritical extraction may also be used.

Known methods can also be used to coke the raw material from which Ql has been removed and alcohol-soluble components have been removed. For example, under pressure in a delayed coker (1 to 10 kg/cJG)
), produce raw coke at 450 to 550°C, and then heat the raw coke in a rotary kiln, shaft furnace, etc.
It is baked at 00 to 1,500°C to produce needle coke.

Needle coke obtained by the method of the present invention can be crushed,
After adjusting the particle size, it is mixed with binder pitch and molded. If this is fired and then graphitized at a temperature of 2500° C. or higher, a graphite electrode with excellent performance can be efficiently obtained.

That is, the graphite electrode made from the needle coke obtained by the method of the present invention has a small CTE and is less prone to puffing during manufacturing, so it has excellent strength.

〔Example〕

EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to the same extent by these Examples.

(Example) 42. 100 g of coal tar pitch from which the Ql content had been removed in advance was extracted with methanol using a Soxhlet extractor for 30 minutes to remove the methanol soluble content. I got the pitch.

The obtained pitch was coked in a small reactor at 500°C for 8 hours to produce raw coke, and then heated to 100°C.
Baking was performed at 0° C. for 1 hour in an argon atmosphere.

Regarding the obtained coke, CTE, nitrogen content in the coke, etc. were determined by n1.

The results are shown in Table 1, and a polarized light micrograph of the coke obtained is shown in FIG.

(Comparative Example) The same coal tar pitch from which Ql was removed as that used in the example was coked at 500° C. for 8 hours in a small reactor without methanol extraction to obtain raw coke. This raw coke is heated under an argon atmosphere.
Coke was produced by calcining at 1000°C for 1 hour.

Regarding this coke, CTE, nitrogen content in the coke, etc. were measured. The results are shown in Table 1, and a polarized light micrograph of the coke obtained is shown in FIG.

Table 1 shows. It can also be seen from the polarized light micrograph that the structure of the example has better orientation than that of the comparative example.

〔Effect of the invention〕

According to the method of the present invention, nitrogen compounds that cause puffing of coke can be removed by extraction with a lower alcohol such as methanol, without requiring energy costs such as hydrogenation of coal tar-based feedstock oil or high-temperature long-term baking of coke. Since it can be reduced to large +11, it is possible to eliminate Ql.
Coupled with the government's CTE policy, needle coke with excellent CTE and puffing properties can be obtained at low cost.

This invention greatly contributed to the coke industry.

As is clear from Table 1, needle coke made from pitch from which methanol-soluble content has been removed has improved CTE and reduced nitrogen content compared to the comparative example, and puffing has been improved.

[Brief explanation of the drawing]

FIG. 1 is a polarized light micrograph showing the structure of carbon crystals in needle coke according to an example of the present invention. FIG. 2 is a polarized light micrograph showing the structure of carbon crystals in coke in a comparative example without methanol extraction. Figure 3 shows the methanol-insoluble content (Ml) obtained by removing the methanol-soluble content from coal tar pitch, the methanol-soluble and hexane-insoluble content (MS-Hl), and the hexane-soluble content (MS-H3). ) shows the infrared absorption spectra of each cs diluted solution.

Claims (1)

[Claims] A method for producing needle coke, which comprises removing quinoline-insoluble components and lower alcohol-soluble components from coal tar-based raw materials, and then converting the raw materials into coke.