JP2007002124A - Pitch for impregnation and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pitch for impregnation excellent in permeability into a baked product of graphite and high in a fixed carbon content (FC) and a toluene insolubles content (TI), and its manufacturing method. <P>SOLUTION: A new pitch for impregnation comprises: a quinoline insolubles content of <0.1 mass%; a toluene insolubles content of ≥25 mass%; and a fixed carbon content of ≥55 mass%, and has a softening point of ≤80°C, and a viscosity at 200°C of ≤25 cP. Its manufacturing method comprises heat-treating a coal based tar pitch at 380-450°C, adding, after the heat treatment, 100-25 parts by mass of a tar based heavy oil to 100 parts by mass of the tar pitch and then performing filtration, and subjecting the filtrate to second heat treatment under vacuum or steam at ≤350°C for ≥6 hours. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an impregnation pitch and a method for producing the same, and more particularly to an impregnation pitch effective as a material for a graphite electrode for electric furnace steelmaking and a method for producing the same.

For example, a graphite electrode used for steelmaking in an electric furnace is usually manufactured by kneading aggregate coke and binder pitch, forming into a columnar shape, and then graphitizing by firing. At that time, since the volatile component contained in the binder pitch is evaporated by firing, many voids (voids) are generated in the fired body (hereinafter referred to as a graphite fired body). In order to fill this void and increase the density of the graphite electrode as the final product, increase the strength, and improve the thermal shock resistance, it is usually 100 to 200 MPa (10 to 20 kg / cm ² ) in the void of the graphite fired body. A so-called “impregnation process” is performed in which the pitch is pushed in by a pressure of 10 m. This impregnated pitch is called an impregnation pitch. Then, the “baked-in” graphite fired body is fired again at a temperature of 600 to 800 ° C., and then a screw groove into which a nipple described later is screwed is formed at both ends to be used as a graphite electrode.

  Such a columnar graphite electrode is consumed during use and gradually decreases in length. Therefore, the thread provided at both ends of the nipple is engaged with the thread groove provided at one end of another graphite electrode, and used in the longitudinal direction. Accordingly, the nipple is also made of the same material as the graphite electrode, and is particularly required to have a high strength from the viewpoint of strengthening the engagement. Therefore, the impregnation / firing process described above is also performed during the manufacture of the nipple. Repeated 3-5 times. In this sense, the graphite electrode described below includes not only the electrode body but also such a nipple.

  By the way, the required performance level is increasing more and more as the graphite electrode can cope with recent innovations in electric furnace operation technology such as high power operation and operation in combination with oxygen gas blowing. The demands on the characteristics of the pitches as manufacturing materials are becoming more severe.

Conventionally, the following characteristics have been required for impregnation pitches.
(1) When impregnating the graphite fired body, it easily penetrates into the micropores (micropores) of the graphite fired body. (2) When impregnating the graphite fired body, the micropores of the graphite fired body (3) The amount of carbon remaining in the graphite electrode as the final product (represented by the residual carbon ratio) is large after re-firing the graphite fired body after impregnation. As an index representing the characteristics of such impregnating pitch, the following measured by an industrial analysis method of pitch mainly composed of a solvent splitting method has been well known. Yes.
(A) Softening point (symbol: SP),
(B) viscosity,
(C) content of toluene insoluble matter (symbol: TI),
(D) Fixed carbon content (symbol: FC),
(E) Content of quinoline insoluble (symbol: QI) Here, as the softening point (SP), a measured value by a well-known R & B method (ring and ball method) is used. The softening point and viscosity are properties related to the fluidity of the pitch and the permeability to the graphite fired body, and in any of these, the smaller the value, the better the pitch has the fluidity and permeability. become. Further, toluene-insoluble content (TI) and fixed carbon content (FC) indicate the residual carbon ratio of the pitch, respectively, and improve the density and strength of the product graphite electrode obtained by refiring the graphite fired body after impregnation treatment. It is an indicator related to. The higher these values, the higher the density of the product graphite electrode and the higher the strength. In addition, quinoline insoluble matter (QI) is an important index of impregnation pitch, and is related to the residual carbon ratio, but particularly indicates the solid content in the pitch. If the quinoline insoluble content (QI) is large, the pitch is prevented from penetrating into the micropores of the graphite fired body, as will be described later. Therefore, it is desirable that the quinoline insoluble content (QI) is as close to zero as possible.

  Thus, the characteristics desired as an excellent pitch for impregnation are substantially free of quinoline insoluble matter (QI), have low softening point (SP) and viscosity values, which are indicators of permeability (fluidity), and the remaining The values of toluene insoluble (TI) and fixed carbon (FC), which are indicators of the charcoal rate, are large. However, generally, if the softening point (SP) and the viscosity are lowered, the toluene insoluble matter (TI) and the fixed carbon content (FC) are also reduced, so this permeability (fluidity) and residual carbon ratio are compatible. As a result, the following problems have arisen in the production of the conventional pitch for impregnation.

  First, coal tar is generally used as a raw material for impregnating pitch. In order to remove solid content in the impregnating pitch to be produced, from the raw material coal tar, for example, “gravity sedimentation method” or “filtration method” is used. The pretreatment for removing the quinoline insoluble matter (QI), which is a solid content, is performed in advance (see, for example, Patent Document 1 and Patent Document 2).

  This quinoline insoluble matter (QI) is originally contained in the raw material coal tar, and is quinoline insoluble matter (QI) (hereinafter referred to as “primary quinoline insoluble matter) which is an amorphous fine carbon fine particle having a particle size of 1 μm or less. (Referred to as "primary QI)"), the crystalline quinoline insoluble matter (QI) (secondary quinoline insoluble matter (secondary QI) or Also called “Mesophase”.

  These primary QI and secondary QI are different from each other in crystal structure, but they are the same in that the penetration of the pitch into the graphite fired body is hindered. It is required not to do. Subsequently, the raw material coal tar after removing the quinoline insoluble matter (QI) is subjected to distillation and thermal reforming operation, and the softening point ( SP), toluene insoluble matter (TI), fixed carbon content (FC), etc. are adjusted. This process is the same whether the pitch for impregnation is manufactured or the binder pitch is manufactured.

  However, in the case of producing a pitch for impregnation, a heat treatment that is performed afterwards in order to maintain high permeability of the produced pitch into the graphite fired body, even if the primary QI in the raw coal tar is extremely low. It is necessary to suppress the generation of secondary QI generated during the heat treatment process. Furthermore, the raw material coal tar is removed in the process of removing the quinoline insoluble matter (QI) together with the quinoline insoluble matter (QI) and the heavy component (which becomes a carbon source) in the coal tar. It was difficult to increase the toluene insoluble content (TI) and the fixed carbon content (FC) while keeping the softening point of the impregnation pitch to be low.

In other words, with binder pitches that do not go through the quinoline insoluble (QI) removal step (usually the primary QI removal step), it is easier to fix carbon even if the softening point (SP) of the pitch produced is 80 ° C. or lower. It was possible to achieve a component (FC) of 55% by mass or more and a toluene insoluble component (TI) of 25% by mass or more. However, in the pitch for impregnation containing no quinoline insoluble component (QI), the softening point ( SP) is about 80 ° C., it is hard to obtain a fixed carbon content (FC): 50 mass% or less, toluene insoluble content (TI): 20 mass% or less, and it is difficult to realize a large residual carbon ratio. there were. Therefore, in the impregnation pitch that is currently available, it is possible to produce a graphite electrode that can withstand the operation of a recent electric furnace with a high power load unless the impregnation and firing are repeated many times when impregnating the graphite fired body. There was a problem that it was difficult. On the other hand, when trying to achieve fixed carbon content (FC): 55% by mass or more and toluene insoluble content (TI): 25% by mass or more, not only the softening point (SP) exceeds 80 ° C. but also graphite. There is also a problem that impregnation into the fired body becomes extremely difficult.
JP-A-10-204441 (page 2-6, FIG. 1) Japanese Patent Publication No. 3-54994 (page 2-4, FIG. 1)

  In view of such circumstances, an object of the present invention is to provide a pitch for impregnation excellent in permeability to a graphite fired body and having a high fixed carbon content (FC) and toluene insoluble content (TI), and a method for producing the same. .

  The inventor has intensively studied to achieve the above object, and the results have been embodied in the present invention.

  That is, the present invention relates to quinoline insoluble matter (QI): less than 0.1% by mass, toluene insoluble matter (TI): 25% by mass or more, fixed carbon content (FC): 55% by mass or more, softening point (SP): The pitch for impregnation is characterized by having a viscosity at 80 ° C. or lower and 200 ° C. of 25 centipoise (CP) or lower.

  In addition, the present invention heat-treats coal-based tar pitches at 380 to 450 ° C., and adds 100 to 25 parts by mass of tar-based heavy oil to 100 parts by mass of tar-pitches after heat treatment, followed by filtration. Then, the obtained residual pitch is subjected to a reheat treatment at a temperature of 350 ° C. or lower for 6 hours or more while exposing it to a vacuum or blowing steam into the system.

  According to the present invention, it is possible to obtain a pitch for impregnation not only having a softening point that is equivalent to that of the prior art but also having a high toluene insoluble content (TI) and high fixed carbon content (FC). This impregnating pitch makes it easy to impregnate the graphite fired body, and makes the quality of the graphite electrode and nipple used for metal refining in an electric furnace much better than before.

  The best mode of the present invention will be described below.

  As described above, in order to produce the impregnated pitch, the quinoline insoluble matter (QI) was almost completely removed from the raw coal tar. However, the conventional removal method has a problem that heavier components necessary for the pitch are always removed.

  Therefore, the inventor has conducted earnest research on how much the QI content in the raw coal tar is acceptable in order to minimize the accompanying removal of the heavy components. And if it was the pitch for impregnation with QI content less than 0.1 mass%, it confirmed that the penetration | invasion to a micropore could be performed smoothly, and made this the 1st requirement of this invention.

  Further, the toluene-insoluble content (TI) and the fixed carbon content (FC) of the impregnated pitch are conventionally combined with the quinoline-insoluble content (QI) treatment (that is, the accompanying removal of heavy components occurs). It was difficult to contain more than 50% by mass. Therefore, in the present invention, as will be described later, the “filtration step” is appropriately performed to suppress the amount of quinoline insoluble matter produced, and the toluene insoluble matter (TI) and the fixed carbon content (FC) are each 25% by mass or more, 55%. Since it was able to be made into the mass% or more, this was made into the 2nd requirement of this invention.

  Furthermore, the softening point (SP) and viscosity of the impregnated pitch are factors necessary for easily and stably producing a graphite electrode with a high power load. In order to ensure good permeability, it is desirable to make it as low as possible. In response to this request, the inventors have examined that the softening point is 80 ° C. or lower and the viscosity at 200 ° C. should be 25 centipoise (CP) or lower. As a requirement. This is because impregnation into the graphite fired body cannot be performed smoothly at a pitch outside this condition.

  As described above, the impregnation pitch according to the present invention exhibits the permeability to the graphite fired body superior to the conventional impregnation pitch by simultaneously providing the first to third requirements described above, The fixed carbon content (FC) is 55% by mass or more and the toluene insoluble content (TI) is 25% by mass or more, and the amount of residual carbon is equal to that of the conventional binder pitch.

  Next, since the inventor has also developed a manufacturing method suitable for obtaining the impregnation pitch according to the present invention, the contents thereof will be described.

  The manufacturing method of the pitch for impregnation according to the present invention comprises the following three basic requirements.

That is,
(1) The raw material tar / pitch is heat-treated to produce a small amount of the secondary QI in the raw material tar / pitch (2) The primary QI component originally contained in the raw material tar / pitch is the above (1 ) And the secondary QI produced by heat treatment. At that time, 25 to 100 parts by mass of heavy tar oil is added to 100 parts by mass of the raw material tar and pitch that has been heat-treated in advance. (3) The “filtrate” from which quinoline insoluble matter (QI) has been removed by the above filtration is heat treated again so as not to generate secondary QI, and the softening point of the product (pitch) is adjusted. The heat treatment of the raw material tar / pitch, which is the first basic requirement, is effective for easily and easily removing the primary QI component in the raw material tar / pitch by filtration. An important point in the heat treatment step is to generate a certain amount of secondary QI in the raw material tar pitch during the heat treatment. The reason for this is that when this secondary QI is produced, it is concentrated with the primary QI and impurities originally present in the tar pitch, so that subsequent filtration can be performed efficiently. In addition, the heat treatment temperature necessary to produce secondary QI that acts as a “filter aid” for such primary QI varies depending on the type of raw material tar and pitch, but is 350 to 450 ° C. This is because when the temperature is lower than 350 ° C., the generated amount is small, and when the temperature is higher than 450 ° C., it is excessive. The amount of secondary QI to be generated is sufficient if there is an amount corresponding to 5% by mass of the raw material tar / pitch. Even if the amount is large, the effect of the present invention is not affected. However, if the amount is too large, the product yield of the impregnated pitch decreases, which is economically disadvantageous. Therefore, 5 to 10% by mass is optimal.

  About filtration of raw material tar and pitches after the heat treatment which is the second basic element, 25 to 100 parts by mass (preferably, tar-based heavy oil with respect to 100 parts by mass of the heat-treated tar and pitches in advance) 50 to 75 parts by mass) is essential. This heavy tar oil is added to reduce the viscosity of the heat-treated tar pitch. However, if the addition amount is more than 100 parts by mass with respect to 100 parts by mass of the heat-treated tar / pitch, a heavy component is precipitated from the heat-treated tar / pitch by a poor solvent effect, and the heavy component is being filtered. The quinoline insoluble matter (QI) component remains as a solid substance. As a result, the heavy components governing the residual carbon ratio of the “filtrate” decrease, and then the fixed carbon content (FC) of the impregnated pitch as a product by adjusting the softening point of the product by re-heat treatment of the “filtrate” Since the improvement of toluene insoluble matter (TI) is not recognized, the upper limit is limited to 100 parts by mass. On the other hand, if the amount of the heavy heavy oil added is less than 25% by mass with respect to 100 parts by mass of the heat-treated tar / pitch, the viscosity of the heat-treated tar / pitch becomes too high, and the filtration rate is slow. This is because not only the efficiency is reduced, but also the heavy component remains as a solid together with the quinoline insoluble component (QI), and the amount of the heavy component in the filtrate also decreases in this case.

  In addition, it does not specifically limit in this invention as a kind of tar type heavy oil to add. This is because any desired oil can be obtained as long as it is an oil fractionated from the side of the distillation column when the raw tars and pitches are distilled. However, preferably, an anthracene oil having a boiling point range of 200 ° C to 350 ° C is optimal.

  The re-heat treatment of the “filtrate (hereinafter referred to as“ dequinoline-insoluble tar ”), which is the third basic element, may be performed in the category of operation technology for producing a normal pitch. In other words, the “dequinoline-insoluble matter tar” is distilled at a temperature of 350 ° C. or less for 6 hours or more in order to effectively remove light components while suppressing the regeneration of secondary QI. -A heat treatment operation will be performed.

  Thus, the pitch for impregnation produced by the method constituted by the above three basic requirements contains almost no quinoline insoluble (QI) component, and therefore has excellent permeability to the graphite fired body, and is representative. Taking a typical impregnating pitch as an example, even when the softening point is 80 ° C., it is equivalent to a conventional binder pitch having a toluene insoluble content (TI) of 25 mass% or more and a fixed carbon content (FC) of 55 mass% or more. It has an excellent residual carbon ratio.

Specific examples are shown below.
<Example 1>
Raw material tar pitches containing 1.5 mass% of primary quinoline insoluble (primary QI) component were heat-treated at a temperature of 425 ° C. for 5 minutes. Industrial analysis values of the obtained heat-treated pitch were quinoline insoluble matter (QI) 25 mass% and toluene insoluble content (TI) 52 mass%. 50 parts by mass of “tar heavy oil” (boiling range: 240 to 300 ° C.) is added to 100 parts by mass of the heat-treated tar pitch, and “pressure filtration” is performed on the filter at a temperature of 100 ° C. It was. The pressure of the “pressure filtration” was 30 MPa (3 kg / cm ² ). The “filtrate” was reheated while blowing steam at a temperature of 350 ° C., and the softening point of the pitch obtained after the heat treatment was adjusted to 78 ° C.

  Industrial analysis values of the obtained pitch were as follows.

(1) The quinoline insoluble matter (QI) is 0% by mass,
(2) Toluene insoluble matter (TI) is 26% by mass
(3) Fixed carbon content (fixed carbon content (FC)) is 57% by mass
(4) Softening point (SP) is 78.2 ° C
(5) Viscosity 23 cp (at 200 ° C.)
These characteristics are excellent in that the pitch for impregnation containing no quinoline insoluble component (QI) has a toluene insoluble component (TI) and a fixed carbon component (FC) that are extremely high for the softening point.
<Example 2>
Raw material tar pitches containing 3.0% by mass of primary quinoline insoluble (primary QI) component were heat-treated at a temperature of 430 ° C. for 30 minutes. Industrial analysis values of the obtained heat-treated pitch were 30% by mass for quinoline insoluble matter (QI) and 58% by mass for toluene insoluble content (TI). 50 parts by mass of tar heavy oil (boiling range: 240 to 300 ° C.) was added to 100 parts by mass of the heat treatment pitch, and “pressure filtration” was performed at a temperature of 100 ° C. The pressure of the “pressure filtration” was 30 MPa (3 kg / cm ² ). The “filtrate” was reheated while blowing steam at a temperature of 350 ° C., and the softening point of the pitch obtained after the heat treatment was adjusted to 80 ° C. Industrial analysis values of the obtained pitch were as follows.

(1) The quinoline insoluble matter (QI) is 0% by mass,
(2) Toluene insoluble matter (TI) is 28% by mass
(3) Fixed carbon content (fixed carbon content (FC)) is 59% by mass
(4) Softening point (SP) is 79.9 ° C
(5) Viscosity 20 cp (at 200 ° C.)
These characteristics are excellent because the pitch for impregnation containing no quinoline-insoluble component (QI) has a toluene-insoluble component (TI) and a fixed carbon component (FC) that are extremely high for the softening point.
<Comparative example>
200 parts by mass of tar light oil was added to 100 parts by mass of the raw tar pitch containing 1.5% by mass of the primary quinoline insoluble (primary QI) component, and the mixture was precipitated and separated at a temperature of 35 ° C. After removing the light oil by vacuum distillation of the supernatant liquid, the obtained tar was heat-treated while blowing steam at a temperature of 350 ° C., and two kinds of impregnation pitches (pitch A and pitch A and softening points of 77 ° C. and 80 ° C.) were obtained. Pitch B) was produced. Industrial analysis values of the obtained pitches are shown in Table 1.

  From Table 1, it is clear that both the pitches A and B are lower in toluene insoluble content (TI) and fixed carbon content (FC) than the impregnation pitch obtained in the practice of the present invention.

Claims (2)

    Quinoline insoluble matter (QI): less than 0.1% by mass, toluene insoluble matter (TI): 25% by mass or more, fixed carbon content (FC): 55% by mass or more, softening point (SP) by R & B method: 80 ° C. or less A pitch for impregnation having a viscosity at 200 ° C. of 25 centipoise (CP) or less. The coal-based tar pitches are heat-treated at 380 to 450 ° C., 100 to 25 parts by mass of tar-based heavy oil is added to 100 parts by mass of the tar-pitches after the heat treatment, and the resulting residue is filtered. A method for producing a pitch for impregnation, wherein the pitch is reheated at a temperature of 350 ° C. or less for 6 hours or more while being exposed to vacuum or blowing water vapor into the system.