JPH05279667A - Production of binder pitch - Google Patents

Abstract

PURPOSE:To obtain a binder pitch having low thermal expansion coefficient, high bulk density and excellent strength and thermal shock resistance and useful for graphite electrode, etc., by adding and mixing a specific coke powder to a binder pitch. CONSTITUTION:The objective pitch is produced by mixing a binder pitch with preferably <=10wt.% of coke powder having a volatile material content (VM) of >=2% and an ash content of <=0.5%. The average particle diameter of the coke powder is preferably <=50mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a van inder pitch. More specifically, it relates to a method for producing a binder pitch used for a graphite electrode for steelmaking.

[0002]

2. Description of the Related Art Conventionally, binder pitch is produced by distilling and heat treating coal tar and heavy petroleum oil. In general, a graphite electrode for steelmaking is manufactured by adding coke grains and powder mixed in a predetermined ratio to a suitable amount of binder pitch while heating and mixing, and after extrusion, extrusion molding. After firing this raw electrode,
If necessary, Pichi is impregnated to carry out densification treatment, and after re-baking, graphitization treatment is carried out. Further, this graphitized product is processed to produce a product graphite electrode.

[0003]

In recent years, with the rise in energy costs, efforts have been made in the electric furnace industry to improve energy efficiency by operating at high power. Along with this, graphite electrodes used in electric furnaces have come to be used under severe conditions. Therefore, the appearance of a graphite electrode having higher characteristics is desired, and particularly, a graphite electrode having a low coefficient of thermal expansion (CTE), a high bulk density, and a high strength is desired. That is, since the graphite electrode is used under extremely severe conditions of high temperature and rapid temperature rise in the atmosphere, it is required to have high thermal shock resistance.

It is generally said that a material having a low CTE has high thermal shock resistance, and a graphite electrode having a low CTE is required. Further, when the graphite electrode is used in an electric steelmaking furnace, scrap, which is a raw material, is put in, but at that time, the graphite electrode is subjected to a large impact, and troubles such as breaking of the graphite electrode occur. Also, since graphite electrodes are used at high temperatures of several thousand degrees in an electric steelmaking furnace, they react with gases such as oxygen and carbon dioxide and are consumed, so graphite electrodes with high bulk density, high strength, and few pores are used. Is desired.

As a method therefor, efforts are made such as applying pressure when kneading the aggregate of the needle coke and the binder pitch with a kneader, kneading with strong energy, and changing the particle size of the needle coke to a smaller one. Has been done. However, all of these methods are troublesome, require a large amount of energy at the time of mating and extrusion molding, are costly, and have problems such as the needle coke being destroyed at the time of mating.

[0006]

The inventors of the present invention have made extensive studies in view of the above circumstances, and as a result, by producing a graphite electrode using a specific binder pitch, the coefficient of thermal expansion of the graphite electrode is lowered, The finding that the bulk density can be increased has been completed, and the present invention has been completed. That is, they have found that the bulk density of a graphite lead electrode obtained by adding coke powder having a volatile content of 2% or more and an ash content of 0.5% or less to a binder pitch can be improved, and arrived at the present invention.

It is generally known that when the raw electrode is fired, volatile matter is generated, causing a weight reduction and expanding the volume during firing. If the expansion of the electrode during firing is reduced, the bulk density of the electrode is increased, and the object of the present invention is to reduce the expansion of the electrode during firing.
This improves the bulk density of the product electrode.

The present invention will be described in detail below. First, as the binder pitch in the present invention, coal tar distillation produced by coal tar distillation, heat treatment, petroleum heavy oil, or heat treated product thereof, or hydrogenated product thereof, heat treated product thereof, naphthalene, etc. Pitch obtained by polycondensation of low molecular weight compounds, or heat-treated products thereof, pitches obtained by treating them with a solvent, products obtained by heat-treating these, and the like, including mesophase It may or may not be included.

The softening point of the binder pitch may be such that it can be mixed with needle coke with an existing kneader or the like and can be extruded with an existing extruder. Further, the extruded molded product loses its shape due to its own weight. It is preferable that the softening point is 50 ° C or higher and 150 ° C or lower, more preferably 60 ° C or higher and 130 ° C or lower, most preferably 70 ° C or higher. Yes 120 ° C or less.

The solvent insoluble matter may be the same as the conventional binder pitch. The coke powder added in the present invention must have a volatile content of 2% or more. That is, if the volatile content is less than 2%, the effect of reducing the expansion amount during firing of the raw electrode is small, so the volatile content is 2%.
It is above, more preferably 4% or more, most preferably 6% or more.

Further, if the volatile content is too high, many components volatilize during firing, and the traces that have escaped remain as defects and cause a decrease in bulk density. Therefore, the volatile content is preferably 50% or less. Is preferably 40% or less, and most preferably 30% or less. Further, if the ash content in the coke is high, it causes oxidative consumption, and the traces of ash volatilized during graphitization remain as defects and cause deterioration of characteristics. Therefore, the ash content needs to be 0.5% or less. Yes, and preferably 0.2% or less.

If the particle size of the coke powder is too large, the particles are likely to settle and separate when the binder pitch is melt-preserved, so the particle size is preferably small, and when the binder pitch and the coke powder are mixed, the particle size is large. The average particle size of the coke powder is preferably 200 μm or less, more preferably 100 μm, because it is difficult to settle and uniformly disperse.
The following is preferable, and the most preferable is 50 μm or less.

Examples of the coke powder include petroleum-based or coal tar-based pitch coke and needle coke, which are produced by heat treatment in a coke drum, an autoclave, etc., and calcined in a kiln, an electric furnace, etc. And then crushed to obtain coke powder. Further, raw coke obtained by heat treatment in a coke drum, an autoclave or the like may be pulverized and then calcined.

When the amount of the coke powder added is increased, the viscosity of the binder pitch produced becomes too high, and there are problems that it is difficult to mix with needle coke and a kneader, and it is difficult to perform extrusion molding. The addition amount is preferably 30% by weight or less, more preferably 20% by weight or less, and most preferably 10% by weight or less. The coke powder and the binder pitch can be mixed by heating and melting the binder pitch to mix the coke powder in a liquid state.

Further, the binder pitch can be obtained by dissolving the binder pitch in a solvent, or pulverizing the binder pitch and then dispersing the binder pitch in the solvent, and then adding and mixing coke powder and removing the solvent. The coke powder to be added may be plain, but may be added after being dispersed in a solvent, or may be added after being predispersed with the binder pitch.

The solvent used here may be one that dissolves the binder pitch, one that does not dissolve the binder pitch, or one that partially dissolves the binder pitch, as long as it uniformly disperses the binder pitch and the coke powder. Further, the solvent is one that is removed after mixing the binder pitch and the coke powder, and one that is easily volatilized is preferable. The boiling point of the solvent in order to evaporate and remove the solvent from the mixture,
Alternatively, the 50% distillation temperature is preferably 300 ° C. or lower, more preferably 50 to 250 ° C., and most preferably 70 to
It is 200 ° C.

The solvent used here is toluene,
Aromatic hydrocarbons such as xylene, aliphatic hydrocarbons such as hexane and kerosene, cyclic hydrocarbons such as cyclohexane, alcohols such as ethanol, ethylene glycol and propanol, esters such as ethyl acetate, ketones such as methyl ethyl ketone. Further, distillate oil obtained by distilling coal tar can be used, and one solvent may be used, but several solvents may be mixed and used.

The temperature for mixing may be room temperature when it is dissolved or dispersed in a solvent, but it is also possible to mix it by heating and melting above the softening point of the binder pitch. The temperature for mixing is preferably 50 ° C. or more higher than the softening point of the binder pitch, more preferably 70 ° C. or more, and most preferably 100 ° C. or more in order to uniformly disperse the coke powder.

If the temperature is too high, the binder pitch may deteriorate, so the mixing temperature is 50.
The temperature is preferably 0 ° C. or lower, more preferably 450 ° C. or lower, and most preferably 400 ° C. or lower. As the viscosity to be mixed, the viscosity of the binder pitch or the viscosity of the mixture of the binder pitch and the solvent is 10 centipoise to 3
The mixing is preferably performed under the condition of 000 centipoise, more preferably 30 centipoise to 2000 centipoise, and most preferably 50 centipoise to 1000 centipoise.

The mixing time varies depending on the mixing temperature and the viscosity, but when the temperature is high, the binder pitch may be altered, so the mixing time is preferably short. When the temperature is low and the viscosity is high, it is preferable to thoroughly mix the binder pitch and the coke powder.
Although it depends on the viscosity, it is preferably within 10 hours, more preferably within 5 hours, and most preferably within 2 hours.

The mixing may be carried out under normal pressure, but it is carried out at a high temperature, when the solvent is added and mixed, the binder pitch is prevented from being altered, and the solvent is volatilized under pressure so as to prevent volatilization of the solvent. You may process in a state. The atmosphere may be in the air, but may be in an inert gas such as nitrogen, or under autogenous pressure.

The binder pitch and the coke powder may be mixed in a container such as an autoclave under heating and melting while stirring with a stirrer, ultrasonic waves, etc. When the viscosity is high, it may be kneaded with a kneader or the like. As long as it can be processed in a batch system or continuously mixed, the binder pitch and the coke powder can be sufficiently mixed. The pitch produced in this way can be mixed with a conventional needle coke by an existing kneader or the like, and can be extruded.

That is, the softening point of the binder pitch can be mixed with the needle coke in an existing kneader or the like, can be extruded by an existing extruder, and the formed product after extrusion can be shaped without losing its shape by its own weight. Is preferable, the softening point is 50 ° C or higher, 150 ° C
The following are desirable, and further 60 ° C or higher, 1
It is preferably 30 ° C. or lower, most preferably 70 ° C. or higher and 120 ° C. or lower.

The binder pitch according to the present invention can be mixed with needle coke and extruded without changing the conventional method of use, and can reduce the expansion amount when firing the raw electrode, and thus the product graphite electrode. The bulk density of is improved.

[0025]

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Example-1 Commercially available binder pitch (softening point; 90.5 ° C., toluene insoluble content; 31.4%, quinoline insoluble content; 8.9%) was heated and melted in the atmosphere to give a binder pitch having a viscosity of 5
Coke powder having an volatile content of 6.0% and an ash content of 0.1% or less (average particle diameter;
m) 5% was added and then stirred and mixed for 1 hour to obtain a binder pitch.

The softening point of the produced binder pitch is 9
At 4.7 ° C., the toluene insoluble content was 35.2% and the quinoline insoluble content was 12.8%. Using a commercially available coal tar-based needle coke as an aggregate, after mixing the particle size, 32 parts of binder pitch was added while heating and mixing in a kneader, and after kneading, a molded body was obtained by extrusion molding.

The molded product was placed in a coke breeze, and 1000
It was fired up to ℃ to obtain a fired body. As a result, the expansion coefficient during firing of the green compact was 1.2%. The fired body was graphitized at a temperature rising rate of 20 ° C./min to 2800 ° C. in a Tammann furnace to obtain a graphite molded body. The coefficient of thermal expansion (CTE) from room temperature (25 ° C.) to 125 ° C. of the graphite molded body is 5.7 × 10.
It was ^-7 .

Comparative Example-1 Coke powder containing 0.3% of volatile matter and 0.1% or less of ash (average particle diameter: 30 μm) in the same binder pitch as in Example-1 and in the same manner as in Example-1. 5% was added and mixed to obtain a binder pitch. The generated binder pitch has a softening point of 93.8 ° C. and a toluene insoluble content of 35.0.
%, And the quinoline insoluble content was 12.9%.

A molded body was produced in the same manner as in Example-1. As a result, the expansion amount of the green body when fired was 3.1%.
The coefficient of thermal expansion (CTE) of the graphite molded body from room temperature (25 ° C.) to 125 ° C. was 5.5 × 10 ⁻⁷ . Comparative Example-2 A binder pitch was obtained by heat treatment in the same manner as in Example-1 without adding coke powder to the same binder pitch as in Example-1.

The softening point of the produced binder pitch is 9
At 4.4 ° C., the toluene insoluble content was 32.3% and the quinoline insoluble content was 8.4%. A molded body was manufactured by the same method as in Example-1. As a result, the amount of expansion of the green body when fired was 3.8%, which was 1 at room temperature (25 ° C) of the graphite molded body.
The coefficient of thermal expansion (CTE) up to 25 ° C. was 5.7 × 10 ⁻⁷ .

[0031]

As described above, the binder pitch according to the present invention can be used without any change in the conventional method for producing a graphite electrode, and when the raw electrode is fired without changing the thermal expansion coefficient of the graphite electrode. The expansion amount can be reduced, and thus the bulk density of the product graphite electrode is improved.

Claims (1)

[Claims] 1. A method for producing a binder pitch, wherein coke powder having a volatile content (VM) of 2% or more and an ash content of 0.5% or less is added to and mixed with the binder pitch.