JPH072949B2 - Method for manufacturing needle-shaped coke - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a needle-like coke suitable for an electrode material by modifying heavy bituminous materials such as pitches.

2. Description of the Related Art Needle-like coke is widely used as a raw material for artificial graphite electrodes. In recent years, in the electric steelmaking industry using graphite electrodes,
In order to improve productivity, large electric furnaces have been adopted and UHP (ultra high power) operation has been carried out, and the operating conditions are becoming more and more severe. Therefore, there is a demand for a graphite electrode having higher performance.

One of the most important graphite electrode performances is the coefficient of thermal expansion (Coef
ficient of thermal expansion (hereinafter abbreviated as CTE)
Is. CTE is related to durability spalling resistance (thermal shock resistance) when using a graphite electrode, and one with a large CTE is prone to cracking, and as a result, problems such as electrode dislodgement or deterioration of electrode consumption unit are important. Cause problems.

Generally, an artificial graphite electrode is manufactured by kneading coke and binder pitch, extruding, firing, optionally impregnating the impregnated pitch after firing, then secondary firing, and then graphitizing.

In order to obtain a high-performance artificial graphite electrode, it is necessary that the coke, which is a raw material, be good-quality needle coke.

In the process of producing needle-shaped coke from heavy bituminous material, generally, when the heavy bituminous material is heated, a so-called mesophase sphere of optically anisotropic liquid crystal is selected from the isotropic liquid. A crystal is generated, the amount of mesophase increases as it grows, coalesces, and deforms, and through a state of accumulation of graphite-like microcrystallites having a carbon hexagonal network stack at 500 to 600 ° C,
As it reacts at a higher temperature, a network develops and grows into a giant crystal.

The mesophase plays a very important role in the development of crystals of the tissue constituents of coke.

In the process of forming mesophase, the viscosity of mesophase is low, and if they are easily coalesced and grown, they show a good flow structure under a polarization microscope, and the appearance of the obtained coke becomes needle-like in appearance. When the generated mesophase has a high viscosity, even if the mesophase spherules coalesce, the growth is insufficient and the mesophase spheres show a mosaic shape under a polarizing microscope.

The following methods have hitherto been known as methods for producing needle coke.

(1) In the coking process, a raw material oil type is selected so that the viscosity of the mesophase is low, coalesces and grows easily, and has a good flow structure.

(2) Mesophase coalescence in the coking process,
A substance that inhibits growth, or a substance that changes into a substance that coalesces or grows mesophase in the coking process is removed from the raw material.

(3) The raw material is modified such that the viscosity of the mesophase in the coking process is low and the coalescence and growth can be easily performed.

Regarding the first method, for example, Japanese Examined Patent Publication Sho 53-358.
The methods shown in No. 02, JP-A-53-34801 and JP-A-54-122301 can be pointed out. In this method, very limited heavy bituminous material is the only raw material for needle coke.

Examples of the second method include, for example, JP-A-53-669.
01, JP-A-54-148191 and JP-A-55-136111. The problem with this method is how to efficiently remove very fine non-melting solid components known as quinoline insoluble matter contained in heavy bituminous matter.
However, this method does not reduce the viscosity of the generated mesophase, and its effect is limited.

As for the third method, for example, Japanese Patent Publication No. Sho 49-116.
02, JP-A-59-122585, JP-B-49-11442, JP-B-5
The method shown in 1-41129 is mentioned. In these methods, a catalyst is generally used, but there is a problem that its life is short and it is expensive.

Further, JP-A-59-182214 discloses a method in which the second and third methods are used in combination, but the sulfur used in the catalyst may dissolve in the pitch and may have an unfavorable effect.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present inventors have made various studies on the modification of the raw material for needle-like coke production, which is an alternative to the above-mentioned conventional technique, and as a result, added alcohols to heavy bituminous substances such as pitches. The present inventors have found that the raw material suitable for the production of needle-shaped coke can be reformed by the thermal reaction, and have reached the present invention.

The object of the present invention is to improve the crystallinity of the coke to be produced by modifying the heavy bituminous material as a raw material and lowering the viscosity of the mesophase in the coking process, and to obtain higher quality acicular coke. A manufacturing method is provided.

Means for Solving the Problems The present invention is based on the addition of alcohols to heavy bituminous substances.
A method for producing needle-like coke, which comprises heat-reacting at a temperature of ℃ or more, forming raw coke, and then calcining.

Conventionally, the relationship between alcohols and heavy bituminous substances has been considered as an extractant for excluding inappropriate components from heavy bituminous substances as seen in, for example, JP-A-55-136111. The treatment agent was completely unrelated.

In addition, it is generally known that oxygen (O), sulfur (S), etc. in the raw materials inhibit graphitization in the process of obtaining a product through the carbonization process, and the reaction with alcohols , O may be added, and it is completely unthinkable as a means for modifying the raw material for producing needle-shaped coke.

Contrary to such common sense, the present inventors have studied in detail the thermal reaction between heavy bituminous substances and various compounds, and by thermally reacting the heavy bituminous substances with alcohols, acicular coke The present invention has been found to be capable of being modified into a more suitable raw material in the production, and has reached the present invention.

The heavy bituminous substances referred to in the present invention refer to coal tar, heavy coal liquefied oil, petroleum distillation residual oil, petroleum cracked residual oil, and pitch fractions produced from it. Considered from the yield of needle coke pitch. Thus, a so-called pitch fraction obtained by cutting light components is preferable.

The alcohols referred to in the present invention, methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, saturated alcohols such as octanol, unsaturated alcohols such as allyl alcohol, halogeno alcohols such as ethylene chlorohydrin, ethylene glycol, It is a compound having an alcoholic hydroxyl group, such as a polyhydric alcohol such as diethylene glycol, triethylene glycol or glycerin, or an amino alcohol such as ethanolamine.

The thermal reaction between heavy bituminous substances and alcohols is carried out by heating at 250 ° C or higher, preferably between 300 ° C and 550 ° C for 5 minutes or longer. No reaction occurs below 250 ° C. Further, when the temperature becomes high, the coking reaction of heavy bituminous substances becomes intense, which is not preferable.

The thermal reaction needs to contain alcohols, and therefore is carried out under a pressure higher than the autogenous pressure. This pressure may exceed the critical pressure if the alcohol used has a low boiling point.

The effect of thermal reaction can be known as follows. That is,
After the thermal reaction, the heavy bituminous material is then heat-treated to generate mesophases in the heavy bituminous material.

The mesophase referred to in the present invention refers to a structure exhibiting optical anisotropy that can be determined by polishing the surface of the cooled and solidified pitch and observing it using a reflection polarization microscope. or,
The mesophase content in the mesophase pitch refers to the proportion of anisotropic structure observed in this way. Mesophase is “carbon”, as described in NO.116, P35 (1984), “Molecular group has regular orientation but fluidity, and reversible phase such as melting solution and reprecipitation. It is a changeable liquid crystal state. "

Therefore, it is possible that some or all of the mesophase pitch is converted to an isotropic structure at high temperature, but it is very difficult to clearly observe the structure at high temperature, and it is not clear.

Further, as the heat treatment is strengthened, the amount of mesophase increases, and finally it becomes coke. During this period, as the content of mesophase increases, the softening point of the mesophase pitch increases, but the softening point of the mesophase pitch obtained from the heavy bituminous materials thermally reacted with alcohols has the same mesophase content. The ones that have been thermally reacted with alcohols are several degrees Celsius to several tens of degrees Celsius lower.

In addition, the microstructure of the mesophase pitch in which the mesophases formed a continuous phase with and without thermal reaction with alcohols were observed by a reflection polarization microscope. When the mesophases obtained from the bituminous substances are compared with the same mesophase content, the domains in the mesophases are larger.

In other words, it can be seen that there are few stacking faults.

From the above, the mesophase produced by further heat-treating the heavy bituminous material obtained by thermally reacting alcohols is more fluid than the mesophase produced by heat-treating the heavy bituminous material not thermally reacted with alcohols. You can see that it is expensive.

In the process of heat-treating pitches to form raw coke via mesophase and then calcining to produce needle coke, the structure of needle coke is predominantly determined at the stage of raw coke and largely governed by that structure. To be done. Furthermore, the texture structure of raw coke is largely controlled by the fluidity of the generated mesophase, and the higher the fluidity, the larger the domain, resulting in the provision of good quality needle coke.

The mechanism of the thermal reaction between heavy bituminous substances and alcohols is considered as follows.

A peak peculiar to acetone was observed in the nuclear magnetic resonance (NMR) spectrum of the light fraction distilled from the reaction product after thermal reaction of coal tar pitch and isopropanol.
In addition, after thermal reaction of coal tar pitch with normal butanol and secondary butanol, the infrared absorption (IR) spectrum of the light fraction distilled off from the reaction product showed absorption of carbonyl which was not present in the raw material.

Therefore, it is conceivable that the hydrogen of the alcohol moved to coal tar pitch and changed from itself to a carbonyl compound, but the formation of carbonyl is a part of the added alcohol, and a considerable amount remains as the alcohol. However, it is possible that the heating reaction of the pitch is unique due to the presence of alcohol, and the details are not clear.

The lowering of the softening point of the mesophase pitch obtained by heat-treating heavy bituminous substances with alcohols and then heat-treating depends on the addition ratio of alcohols.

The mesophase pitch with different mesophase content is manufactured by heat treating the coal tar pitch that has undergone thermal reaction by changing the addition ratio of alcohol by changing the processing temperature, the processing time and the degree of pressure reduction. When the relationship between the softening point and the content of mesophase was determined and the softening point was compared when the mesophase content was 70%, the softening point was considerably lowered even with a slight addition amount of alcohol.

In order to exert such effects, the amount of alcohols added is preferably 1 wt% or more, and more preferably 2 wt% or more, with respect to heavy bituminous substances. Further, the thermal reaction is preferably carried out for 5 minutes or more under pressure.

In the thermal reaction between heavy bituminous substances and alcohols, it is effective to use a basic substance such as caustic alkali, alkali carbonate, tar bases or the like to further accelerate the reaction.
By using a basic substance, it is possible to reduce the temperature of the thermal reaction for obtaining the same effect, shorten the reaction time, and reduce the addition ratio of alcohols.

For example, 100 parts by weight of isopropanol is added to 100 parts by weight of coal tar pitch, and 1 part by weight of caustic potassium (KOH) is further added as a basic substance, and a thermal reaction is performed under pressure at 320 ° C. for 90 minutes, and after the reaction, it is light. After distilling off the fractions and measuring the NMR spectrum to compare the amount of acetone produced, it was found that about 3 times the amount of acetone was produced compared to the case without addition, and the heat-treated pitch and KOH were not used. The softening point was about 20 ° C lower when KOH was used for heat-treated and heat-treated pitch under the same conditions.

After the heavy bituminous substance and alcohol are reacted with each other by heat, they are heat-treated to form coke, and raw coke is obtained. Further, it is calcined to obtain needle-like coke. A known method such as a batch method using an autoclave or a delayed coking method can be adopted for forming raw coke. Then, in the calcination for producing the needle-shaped coke, a known method such as an electric furnace or a rotary kiln can be adopted.

The heat treatment is performed by removing unreacted alcohols and the generated carbonyl compound. Although there are methods such as distillation, static separation, and centrifugation, the heat treatment is usually performed under a high temperature of 400 ° C or higher and a pressure of 10 kg / cm ² G. Even if it is not necessary, the coke can be distilled off naturally, so that it is possible to directly shift to raw coke following the thermal reaction. Or alcohols have poor compatibility with heavy bitumen, so by leaving the reaction system after thermal reaction,
Phase separation can also occur and be separated. Further, when the alcohol and the carbonyl compound produced are water-soluble, they can be transferred to the aqueous phase by extraction and separated.

Quinoline-insoluble substances and the like in heavy bituminous substances generally deteriorate the quality of the modified pitch. Also in the present invention, it is preferable to remove the quinoline-insoluble substance in the heavy bituminous substance which is a raw material.

The quinoline-insoluble substance may be removed either before the thermal reaction with the alcohol or after the thermal reaction. For removal, known methods such as solvent extraction using quinoline or various solvents, melt filtration, centrifugation can be used.

Examples are shown below, but the mesophase content is based on area, and the number of parts and percentages are based on weight unless otherwise specified.

Example Coal tar pitch 100 with softening point 82 ° C, TI 11%, QI 0%
Parts and 50 parts of isopropanol are charged into an autoclave,
After replacing the internal air with N ₂ gas, seal it at 90 ° C at 320 ° C.
A thermal reaction was performed for a minute. The pressure at this time was 80 kg / cm ² G.

After the completion of the thermal reaction, the mixture was cooled and the supernatant containing unreacted isopropanol was separated by decantation to obtain a thermally reacted pitch (A). Sort this pitch (A),
When heat treatment for making raw coke was carried out, it was taken out in the process of making raw coke, and it was observed with a reflection polarization microscope.It was confirmed that the domain of the mesophase was larger than that of the comparative example described later. .

Further, the pitch (A) was charged into an autoclave, the air inside was replaced with N ₂ gas, and then heat treatment was performed at 550 ° C. for 2 hours at 2.5 kg / cm ² G to obtain raw coke.

Then, it was calcined in an electric furnace at about 1400 ° C. to obtain needle coke. Furthermore, the needle-shaped coke is crushed and the particle size blended (20 ~
After crushing 70 mesh crushed product 50% and 100 mesh under crushed product 50%), binder pitch was added and kneaded, and a raw test piece was prepared by an extrusion molding method. This raw test piece is fired in an electric furnace at about 800 ° C and then 260
Graphitization was performed at a temperature of 0 ° C. to prepare a graphitized piece.

The CTE of the graphitized piece was 1.15 × 10 ^-6 deg ^-1 when measured using a dilatometer between room temperature and 500 ° C.

Comparative Example 1 The same coal tar pitch as that used in the example was taken in a test tube without thermal reaction, and various treatment conditions were changed under the same conditions as in the example to obtain various mesophase pitches. Among them, those having the same mesophase content as those of Examples were observed by a reflection polarization microscope. The results are as described above.

Further, heat treatment was carried out in an autoclave under the same conditions as in the example to obtain raw coke. Then, calcining under the same conditions as in the example,
A raw test piece was prepared by the same procedure and then fired and graphitized to prepare a graphitized piece. When the CTE of this product was measured under the same conditions as in the Example, it was 1.25 × 10 ⁻⁶ deg ⁻¹ .

Comparative Example 2 Coal tar pitch having a softening point of 36 ° C., TI of 11% and QI of 2.5% was coked in an autoclave under the same conditions as in Example to obtain raw coke. The raw coke obtained was lumpy.

Then, calcination was carried out under the same conditions as in the example, and a raw test piece was prepared by the same procedure, followed by firing and graphitization to prepare a graphitized piece.

The CTE of this product was measured under the same conditions as in the example 1.
It was 80 × 10 ^-6 deg ^-1 .

Comparative Example 1 using a coal tar pitch containing no QI as a raw material showed a CTE smaller than that of Comparative Example 2 using a coal tar pitch containing QI as a raw material.

In the example using coal tar pitch, which was subjected to a thermal reaction by adding alcohol, as a raw material, it was smaller than that in Comparative Example 1.
CTE is shown, and it is well understood that CTE is improved when alcohol is added and the reaction is carried out by heat.

EFFECTS OF THE INVENTION As described in detail above, the present invention provides a method for producing needle-like coke having excellent performance, which has not been considered at all in the past, by subjecting heavy bituminous materials to thermal reaction with alcohols for modification. It has a great industrial value.

Claims (4)

[Claims] 1. An alcohol is added to heavy bituminous substances,
After heat reaction at a temperature of 250 ℃ or more, raw coke,
A method for producing needle-shaped coke, which comprises calcination. 2. The production method according to claim 1, wherein the thermal reaction between the heavy bituminous substances and the alcohols is carried out under pressure. 3. The production according to claim 1, wherein the alcohol is added in an amount of 1% by weight or more with respect to the heavy bituminous substance, and the thermal reaction is carried out at 300 ° C. or more under pressure for 5 minutes or more. Method. 4. The method according to claim 1, wherein the thermal reaction between the heavy bituminous substance and the alcohol is carried out in the presence of a basic substance.