JPS6278104A - Production of needle coke - Google Patents

Abstract

PURPOSE:To improve the crystallinity of coke and produce a high-quality needle coke, by adding a phenolic compound to pitch, heat-treating the mixture and calcining the obtained raw coke. CONSTITUTION:Pitch having a softening point of >=25 deg.C and obtained by removing light oil components such as phenols and naphthalenes from bitumen such as heavy liquefied coal oil, distillation residue of petroleum, cracked residue of petroleum, coal tar, etc., is added with >=1wt% phenols and, if necessary, a basic substance (e.g. NaOH). The mixture is heat-treated under pressure at >=250 deg.C for >=5min to obtain mesophase pitch. After removing unreacted phenol from the mesophase pitch, the pitch is converted to raw coke and calcined to obtain the objective needle coke.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing needle coke suitable for electrode materials and the like by modifying pitches.

BACKGROUND OF THE INVENTION Needle coke is widely used as a raw material for artificial graphite electrodes. In recent years, the electric steel industry, which uses graphite electrodes, has adopted large electric furnaces and U)IP to improve productivity.
C Ultra High Power) operations are now being carried out, and the conditions of use are becoming increasingly severe. Therefore, there is a demand for graphite electrodes with even better performance.

One particularly important performance of graphite electrodes is the coefficient of thermal expansion (Co
eNcient of thermal expan
sion (hereinafter abbreviated as C, T, E), C, T
, E are related to the durability and spalling resistance (thermal shock resistance) when graphite electrodes are used, and those with large C, T, and E tend to crack easily, resulting in troubles due to electrode falling off or electrode wear. This causes important problems such as deterioration of basic unit.

Generally, artificial graphite electrodes are manufactured by kneading coke and binder pitch, extrusion molding, first firing, impregnating with impregnated pitch after firing if necessary, firing again, and graphitizing.

In order to obtain an artificial graphite electrode with good performance, it is necessary that the coke used as a raw material be high-quality needle coke. In the process of manufacturing needle coke using pitch as a raw material, as the pitch is heated, optically anisotropic liquid crystalline so-called membrane spherulites are generated from the isotropic liquid, and they grow. , the amount of membrane increases as it coalesces and deforms, and at 500 to 600°C it passes through a state of accumulation of graphite-like microcrystallites with a stack of carbon hexagonal networks.
As the material is further treated at high temperatures, the net surface develops and it grows into giant crystals.

Menface plays a very important role in the development of crystals of the structural components that make up needle coke.

During the memface formation process, if the memface has low viscosity and easily coalesces and grows, it will show a good flow structure under a polarizing microscope and will have a needle-like appearance. If the viscosity of the produced memface is high, even if the memface spherules coalesce, they will not grow sufficiently and will show a mosaic-like appearance under a polarizing microscope, and will have a lump-like appearance, making it impossible to obtain needle coke. .

So far, among the conventional techniques for producing needle coke, the following techniques related to raw materials have been known.

(1) In the coking process, select a raw oil type that has low membrane viscosity, easily coalesces and grows, and forms a good flow structure.

(2) Remove from the raw materials substances that inhibit the coalescence and growth of menface during the coking process, or substances that change into substances that inhibit the coalescence and growth of menface during the coking process.

(3) The raw material is modified so that the viscosity of the membrane during the coking process is low and it coalesces and grows easily.

Regarding the first method, for example,
No. 35802, JP-A-53-34801, JP-A-54
The method shown in No.-122301 can be pointed out. In this method, only a very limited amount of pitch or heavy oil becomes the raw material for needle coke.

Regarding the second method, for example, JP-A-53-
No. 88901, JP-A-54-148191, JP-A-5
The method shown in No. 5-138111 can be pointed out. In this method, the problem is how to efficiently remove the very fine non-melting solid components contained in the pitch, known as quinolinous components. However, this method does not reduce the viscosity of the mesophase produced, and its effectiveness is limited.

Regarding the third method, for example, 1.
No. 11802, JP-A-59-122585, Special Publication No. 4
The method shown in Japanese Patent Publication No. 9-11442 and Japanese Patent Publication No. 51-4112!3 can be pointed out. These methods generally use catalysts, but they have problems such as short lifespan and high cost.

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 have an undesirable effect.

Problems to be Solved by the Invention The present inventors have arrived at the present invention as a result of various studies on the modification of raw materials for producing needle coke based on the above-mentioned prior art.

The purpose of the present invention is to provide a method for producing needle coke of better quality by improving the crystallinity of coke produced by modifying raw material pitch and lowering the viscosity of membrane during the coking process. It is something to do.

Means for Solving the Problems The structure of the present invention is to add phenols to pitches.
It consists of heat treatment at a temperature of 50° C. or higher for 5 minutes or more, followed by green coke formation and then calcination to produce needle coke, and includes the following embodiments.

(+) The heat treatment performed by adding phenols is performed under pressure.

(2) Phenols are added in an amount of 1% by weight or more based on the pitches, and the heat treatment is carried out at a temperature of 300° C. or higher and under pressure for 5 minutes or more.

(3) The heat treatment of pitches and phenols is performed in the presence of a basic substance.

The content of the present invention will be explained in detail below.

Until now, there has been no research on the reaction between phenols and pitches or on heat treatment. Phenols are contained in coal tar and coal liquefied oil, which are raw materials for pitch.
When producing pitches, which are these heavy residues, the conventional method is to remove these phenols in advance using chemicals such as caustic soda, or to drive them out to the light oil side during the distillation process. Therefore, there are almost no phenols in the pitch.

Pitches are used exclusively as raw materials for carbon products, but the oxygen in the raw materials is thought to inhibit the graphitization of carbon products, along with sulfur, and from this point of view, phenols are intentionally removed. This is the usual method for producing pitch for carbon products.

As an extreme example, phenol-formaldehyde resin, which is synthesized from phenols as a raw material, is said to be a typical raw material for non-graphitizable carbon (Sugibe Otani, Yuzo Sanada Fundamentals of Carbon Engineering) 2゜117, Ohmsha, 1980).

As described above, heat treatment with phenols is completely unthinkable in common sense as a means of producing raw materials for carbon products that require a structure similar to graphite.

Contrary to such common sense, the present inventors have repeatedly studied in detail the heat treatment of pitches and various compounds, and as a result, by adding phenols to pitches and heat-treating them,
The present invention was completed by discovering that it can be modified into a raw material suitable for producing needle coke.

Pitch as used in the present invention refers to pitch fractions produced from bituminous materials such as heavy coal liquefied oil, petroleum distillation residue oil, petroleum cracking residue oil, and coal tar. Pitch with a softening point of about 25° C. or higher is produced by removing light oils such as naphthalenes and naphthalenes.

The phenols referred to in the present invention are compounds having a phenolic hydroxyl group, such as phenol, monohydric phenols such as cresol and xylenol, dihydric phenols such as resorcinol and hydroquinone, and polyhydric phenols such as hydroxyhydroquinone.

Heat treatment by adding phenols to pitches is
This is carried out by heating at 250°C or higher, preferably between 300°C and 550°C for 5 minutes or more. It is not effective at temperatures lower than 250°C. Moreover, if the temperature becomes high, the coking reaction of pitches will be intense, which is not preferable.

Heat treatment performed with the addition of phenols requires that the phenols be contained, and therefore is carried out under pressure higher than the autogenous pressure. This pressure is the phenol used.
If the boiling point of the group is low, the critical pressure may be exceeded.

In the process of heating pitch and turning it into raw coke via membrane phase, and then calcining it to produce needle coke, the microstructural structure of needle coke is preliminarily determined at the raw coke stage, and the microstructural structure changes. heavily dominated. Furthermore, the structural structure of raw coke is largely controlled by the fluidity of the generated membrane, and the higher the fluidity, the larger the domains, resulting in better quality needle coke.

Therefore, one method for determining the effect of heat treatment performed by adding phenols to pitches is as follows.

After adding phenols to pitches as raw materials and performing heat treatment, when the pitches are further heat-treated, memphasis is generated in the pitches.

In the present invention, mesoface refers to a structure that exhibits optical anisotropy, which can be determined by polishing the surface of cooled and solidified pitch and observing it using a reflective polarization microscope.
The memface content in the memface pitch refers to the proportion of anisotropic structure observed in this way.
As described in 4), it is a "liquid crystal state in which the molecular groups are regularly oriented but have fluidity and are capable of reversible phase changes such as melting and re-precipitation."

Therefore, it is possible that part or all of mesophase pitch transforms into an isotropic structure at high temperatures, but it is not clear that it is very difficult to observe the structure at high temperatures.

In the present invention, as the heat treatment described above is intensified, the amount of memphasis increases and eventually coke is formed. During this period, as the content of memphis increases, the softening point of memphis pitch increases.

The softening point of the pitch obtained from the pitch heat-treated with the addition of phenols is about 10°C or more for pitches heat-treated with the addition of phenols for the same memphase content. Microstructure observation using a reflective polarizing microscope of membrane-faced pitch' in which membrane-phase formed a continuous phase was conducted at 60°C lower and with and without heat treatment with the addition of phenols. The membrane obtained from the pitch heat-treated in this way has fewer domains in the membrane when compared with the same membrane content.

In other words, it can be seen that there are few lamination defects.

From the above, the mesophase produced by further heat-treating pitch that has been heat-treated with the addition of phenols is
It can be seen that the fluidity is higher than that of the membrane produced by heat-treating pitch that has not been heat-treated with the addition of phenols.

The reason why heat treatment of pitches with the addition of phenols has the above-mentioned effect is that the heating reaction of pitches is unique due to the presence of phenols. , it's still not clear.

After adding phenols to pitches and heat-treating them, the decrease in the softening point of menface pitch obtained by heat treatment is as follows:
It varies depending on the addition ratio of phenols.

Based on pitches heat-treated with varying phenol addition ratios to coal tar pitch, softening points at 70% membrane content were compared by changing subsequent heat treatment conditions. It was confirmed that a considerable decrease in the softening point occurred.

In order to produce such an effect, the amount of phenol added should be at least 1% by weight (wt), preferably at least 2% by weight (wt), based on the pitch, and the heat treatment should be carried out under pressure at 5% by weight (wt) or more. Minutes or more is preferable.

It is even more effective to add a basic substance to the heat treatment performed by adding phenols to pitches. As the basic substance, caustic alkali, alkali carbonate, tar bases, etc. are effective. Lowering the processing temperature and processing time of heat treatment to obtain the same effect by using basic substances,
The addition ratio of phenols can be reduced.

Further, coking to obtain needle coke after heat treatment by adding phenols to pitch is carried out after removing unreacted phenols.

Distillation and extraction methods are available for this purpose, but distillation is generally advantageous due to the large difference in boiling point between phenols and pitches.

Quinoline-soluble substances, etc. in the raw material pitch generally reduce the quality of the produced coke.In the present invention, it is more effective to remove the quinoline-soluble substances, etc. in the pitch, which is the crude raw material, as necessary. However, the removal treatment can be performed either before adding phenols and heat treatment, or after adding phenols and heat treatment. Removal can be done by solvent extraction using quinoline or various solvents, melt filtration,
Known methods such as centrifugation can be used.

Examples are shown below, and the mesophase content is based on surface m, and unless otherwise specified, parts and percentages are expressed on a weight basis.

Example 100 parts of coal tar pitch with a softening point of 82°C, T of 111%, and QI of 0% and 100 parts of phenol were placed in an autoclave, and after replacing the air inside with N2 gas, the autoclave was sealed and heated at 375°C for 90 minutes in the presence of phenol. The following heat treatment was performed. The pressure at this time was 20 kg/Cm2G. After the heat treatment was completed, the light oil was distilled off at 300° C. and 10 Torr to obtain modified pitch (A).

This modified pitch (A) was taken out, heat treated to make it into raw coke, taken out during the process of making it into raw coke, and observed with a reflective polarizing microscope.
It was confirmed that the domain of menface was larger than that shown in the comparative example described later.

Furthermore, the modified pitch (A) was charged into an autoclave, and after replacing the air inside with N2 gas, it was heated at 550°C for 2 hours.
．． Raw coke was obtained by heat treatment at 5 kg/cm2G. Next, it was calcined in an electric furnace at approximately 1400°C to obtain needle coke. Furthermore, after pulverizing needle coke and blending the particle size (50% of 20-70 mesh pulverized product and 50% of 100 mesh under pulverized product), binder pitch was added and kneaded, and a raw test piece was made by extrusion molding. Molded. Approximately 800 pieces of this raw test piece were heated in an electric furnace.
C. and then graphitized at a temperature of 2600.degree. C. to produce a graphitized piece.

The C, T, and E of the graphitized piece were measured using a diradometer between room temperature and 50 Pff, and it was 1.18X.
10″6deg-’te, good value.

Comparative Example 1 The same coal tar pitch used in the example was placed in a test tube without heat treatment in the presence of phenol, and other conditions were the same as in the example, and the treatment time was changed to obtain various menface pitches. Ta.

Among them, one having a mesophase content comparable to that of the example was observed using a reflective polarization microscope.

The results are as described above.

Furthermore, raw coke was obtained by coking in an autoclave under the same conditions as in the example. Next, it was calcined under the same conditions as in the example to create a green test piece in the same manner, and then fired and graphitized to obtain a graphitized piece. It was created. This thing's C, T,
E is t, 2ex when measured under the same conditions as in the example.
io″@, 1e, −1.

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

Next, it was calcined under the same conditions as in the example to create a green test piece using the same procedure, and then fired and graphitized to create a graphitized piece.

This thing's C, T,! , was measured under the same conditions as in the example and was 1.80×10′ deg −′.

Comparative Example 1 using coal tar pitch that does not contain Ql as a raw material showed smaller C0〒,E than Comparative Example 2 using coal tar pitch containing Ql as raw material.

In the example using coal tar pitch heat-treated with the addition of phenol, C and T were even smaller than in Comparative Example 1.
, E, and it is clear that C, T, and E are improved when phenol is added and heat treated.

Effects of the Invention As detailed above, the present invention improves the pitch by adding phenols to pitch and heat-treating it, which was completely unthinkable in the past, and producing needle coke with excellent performance. It provides a method to do this, and has extremely great industrial value.

Claims (4)

[Claims] (1) Phenols are added to pitches, heat treated at a temperature of 250°C or higher for 5 minutes or more, and then converted into raw coke,
A method for producing needle coke, which comprises then calcination. (2) The manufacturing method according to claim (1), wherein the heat treatment performed by adding phenols is performed under pressure. (3) The manufacturing method according to claim (1), wherein 1% by weight or more of phenol is added to the pitch, and the heat treatment is carried out at 300° C. or more under pressure for 5 minutes or more. (4) The manufacturing method according to claim (1), wherein the heat treatment of pitches and phenols is performed in the presence of a basic substance.