JPH0356600B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a purification treatment method for highly purifying raw material pitch used in the production of carbon fibers and other high-grade carbon materials. It is essential that the raw material pitch for producing high-grade carbon materials such as carbon fiber raw materials, electrode materials, graphite sliding materials, heat-resistant materials, or chemical-resistant materials be highly purified. In general, the method for refining raw material pitch is as follows:
A method of heat treating coal-based or petroleum-based heavy oil at its original concentration, a method of heating a mixed liquid of both heavy oils,
Alternatively, there is a method of diluting with an organic solvent and then heating. The principle of these pitch refining means is to improve the sedimentation properties of solids by making solid fine particles large by utilizing particle agglomeration or adhesion of polymer components to solids. The purpose is to separate and remove solids by utilizing the density difference of heavy oil. Such solids are represented by quinoline insolubles. The quinoline insoluble content represents the amount of coarse solid impurities with a size of 10 μm or more that are insoluble in the quinoline solvent and do not pass through the pores of a glass filter as specified in JIS-K2425 (method for determining quinoline insoluble content). This quinoline insoluble content is not found in carbon fiber raw materials as described in JP-A-57-19878.
The conventional standard is to keep the content below 100ppm, and for other carbon materials below 300ppm. However, the ash in the pitcher is mainly composed of inorganic suspended solids of less than 10 to 5 μm that pass through the glass filter, and can be removed not only by sedimentation but also by existing filtration or centrifugation methods. It forms fine impurities that are difficult to remove. By the way, a special filter (pore diameter
According to the results of measuring the ash content of solid impurities less than 10 μm (quinoline-insoluble matter) collected using 0.45 μm), the ash content accounts for more than 70% (wt) of the impurities. Taking pitch for carbon fiber raw material as an example, if ash or solvent-insoluble solids are present in refined pitch, the heterogeneity of the precursor pitch (precursor material) produced through the modification process will increase, which will impair spinnability. It is said that it not only deteriorates the carbon fiber, but also causes unfavorable results on the strength, elastic modulus, etc. of the carbon fiber. In conventional purification methods, the solid content in the raw material pitch is made large by flocculation, and even if it is separated and removed by increasing the sedimentation rate, it is not possible to remove the ash content, and it is not possible to achieve as high a purity as expected. cannot be achieved. For example, JP-A No. 57-47384 discloses a method of obtaining purified pitch by pre-mixing raw pitch with an aromatic solvent and an aliphatic solvent and separating and collecting the precipitated insoluble phase. The content of impurities remaining in pitch is 0.02 ~
It only drops to 0.03%. Furthermore, such conventional separation methods require high-temperature heating for long periods of time to maintain the low viscosity of the stock solution, which increases operating costs.Additionally, the use of expensive organic solvents increases, so many In this case, it is necessary to recover and reuse the material, which makes the equipment complicated and has major economical problems. In any case, the various conventional processing methods for refining pituti involve the use of large amounts of organic solvents in petroleum-based heavy oils such as coal tar, which is produced as a by-product during coal carbonization, or residual oil under normal pressure or vacuum pressure. Although the aim is to purify to a high purity by simply performing a primary treatment, the above-described operation of agglomerating fine particles to make them large has the drawback that the desired purity cannot be achieved. The purpose of the present invention is to inexpensively refine high-purity pitch with a residual ash content of 30 ppm or less, which could not be achieved using conventional pitch refining methods, and to obtain excellent raw material pitch for carbon fibers. It is. The present inventors have confirmed through microscopic observation that the behavior of the anisotropic phase generated in the process of thermally reforming coal pitch is greatly influenced by the amount and degree of coexisting impurities. The present invention was made based on this knowledge,
First, a crude pitch is produced, and this crude pitch is appropriately heat-treated without using an organic solvent or the like to generate an anisotropic phase in the pitch.
The purpose of the present invention is to provide a method for purifying high-purity pitcher which can reduce the ash content in pitcher to 30 ppm or less. The present invention will be explained in detail below. The present invention is useful in the production of carbon material products.
When producing refined high-purity raw material pitch (hereinafter referred to as refined pitch), by directly heat-treating the primary treated pitch (hereinafter referred to as crude pitch) that has been pretreated using an existing method, Utilizing the formation of an anisotropic phase in the pitch and the adsorption of fine suspended solids on the surface of the spheres constituting this phase, the impurities can be easily separated and removed, thereby increasing the pitch. It is in the purification process of pitchchi to purify it. In the present invention, the anisotropic phase is a phase that is generated in the pitch by heating and has optical anisotropy.
Refers to a phase that exhibits a fine spherical shape. This anisotropic phase is generally a layered arrangement of planar molecules of a certain size that are formed as aromatic molecules undergo thermal polymerization during the heating process, and the more regular they are, the more optically oriented they are. It is said to have a strong degree of anisotropy. The possibility that pitches will form this anisotropic phase is highly dependent on various factors. Further, the chemical structure, softening point, viscosity, and other physical properties of the anisotropic phase formed largely depend on the properties of the pitch used as a raw material. When a few percent (weight) or less of insoluble quinoline is present in the crude pitch, it has the effect of suppressing the formation of spheres that form the above-mentioned anisotropic phase and the growth of spheres due to their coalescence, and at the same time uniformizing the particle size of the substance. There is. The present invention utilizes this phenomenon to control the total amount of anisotropic phase produced and its particle size by appropriately controlling the heating temperature and treatment time. That is, the present invention first produces a crude pitch containing a certain amount of quinoline insoluble matter through a conventional primary treatment using existing heat treatment equipment, and then processes this crude pitch at a temperature range of 430 to 450°C without using a solvent. The mixture is maintained for 1 to 3 hours with continued slow stirring to generate 25% by volume or more of an anisotropic phase consisting of spheres with an average particle size in the range of 40 to 60 μm. This amount of production is calculated by considering the yield described below.
25-35% by volume is most preferred. In this case, stirring is started soon after the pitch is melted, and after reaching a predetermined temperature, slow stirring at 60 rpm or less is continued to allow fine particles of several μm or less to be adsorbed onto the surface of the grown sphere. Excessive stirring is undesirable because it promotes detachment of adsorbed substances or collapse of aggregated particles. If the heating temperature is lower than 430°C, the particle size of the spheres produced becomes significantly smaller and at the same time the amount of produced spheres also decreases. If the average particle size of the generated spheres becomes too small, the anisotropic phase will be incorporated into the impurity particles, reducing the adsorption effect, so the heating temperature should be 430°C or higher.
The average particle size of the particles produced must be 40 μm or more. In a temperature range where the heating temperature exceeds 450°C, coalescence due to fusion between anisotropic phases locally progresses, resulting in large and uneven distribution of coarse amorphous phases, or polycondensation of aromatic compositions. proceed. Therefore, the viscosity of the anisotropic phase becomes high, making it difficult for the impurity particles to move, and as a result, the adsorption ability is not exhibited, so the upper limit of the temperature is set at 450°C. The above operations may be performed under normal pressure, reduced pressure, or increased pressure. The average particle size of the spherical particles of the anisotropic phase is also influenced by the temperature increase rate, but when the temperature increase rate is fixed, it largely depends on the heating temperature and the holding time. As a result of repeated research, the present inventors confirmed the following three points. (1) The total amount of anisotropic phase produced was controlled within a certain range, and the influence of the difference in particle size of the spheres constituting the anisotropic phase, that is, the difference in total surface area, on the impurity removal effect was investigated. , average particle size 40μm to 60μm
Up to this point, it was observed that there was no significant change in the adsorption capacity of the anisotropic phase. (2) The heating conditions for maintaining the average particle diameter and particle size within the required range are as follows: For pitches containing 5% by weight or less of quinoline insoluble matter, heating conditions for maintaining the average particle diameter and particle size within the required range are as follows:
Holding for ~3 hours is effective. That is, under these conditions, an anisotropic phase can be appropriately generated, its abnormal growth can be suppressed, and the grain size can be averaged. (3) Excessively increasing the total production rate of the anisotropic phase will extremely reduce the recovery yield of purified pitch in the subsequent process, since the anisotropic phase that has adsorbed impurities will be separated and discarded. It is desirable to reduce the anisotropic phase as much as possible. The lower limit can be determined from FIG. Figure 1 shows the amount of ash remaining in the refining pitch when the amount of anisotropic phase produced was varied within the range of average particle size of 40 to 60 μm. Viewed from a different perspective, this figure shows changes in impurity adsorption capacity. From Figure 1,
It is clear that if the amount of anisotropic phase produced is 25% or more, it is possible to reduce the amount of ash remaining in the refining pitch to 30 ppm or less. The anisotropic phase generated as described above can be easily separated and removed using existing filtration equipment or centrifugation equipment, and the amount of ash remaining in the refining pitch can be reduced to 30 ppm or less. Is possible. The method of highly purifying raw material pitch by efficiently removing fine particulate solid impurities according to the present invention not only makes it possible to reduce the cost of products such as carbon fibers, but also makes it possible to reduce the cost of products such as carbon fibers. It is also possible to make the characteristics of the product more sophisticated and increase added value.
This greatly contributes to expanding the uses of such high-grade carbon materials. Hereinafter, the present invention will be explained in more detail based on Examples. Example 1 After pulverizing coal tar pitch to a total amount of 1 mm or less, it was filled into a cylindrical container without adding any solvent, and the anisotropic phase production reaction was continued while maintaining it at a predetermined temperature using an existing heat treatment device. That is, approximately 10 g of crude coal tar pitch with a quinoline insoluble content of 3.89% having the properties shown in Table 1 was filled into an aluminum cylindrical container (inner diameter 15 mm) purged with inert gas, and heated at 435°C under a low degree of vacuum. The temperature was raised at a temperature increase rate of 2° C./min until the temperature reached 2° C./min, and then maintained for 1 to 3 hours while continuing slow stirring to generate anisotropic phases of various vol%. Next, this heat-treated pitch is dissolved using 1 to 2 times the amount of solvent, and the entire amount of undissolved residue is separated and removed using an existing vacuum filtration device.The filtrate is then subjected to solvent removal treatment, and the purified pitch is recovered. Measure the amount of ash remaining in the
The results shown in Table 2 were obtained. Example 2 The same crude pitch as in Example 1 was charged into an autoclave (capacity 1000 ml), and the temperature was maintained at a predetermined temperature with slow stirring without adding any solvent to continue the reaction to generate an anisotropic phase. . That is about 400 pitches
g was charged into an autoclave, and after purging with inert gas, the temperature was raised from 200°C to 445°C at a rate of 3°C/min. The mixture was held for a period of time to generate anisotropic phases of various vol%. Next, the same operation as in Example 1 was carried out to measure the amount of ash remaining in the recovery pitch, and the results shown in Table 3 were obtained. From the above results, according to the method of the present invention, by treating crude pitch under certain conditions using existing equipment, it is easy to refine more highly purified pitch without any problems. It has been proven that it can be done.

【table】

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the total amount of anisotropic phase produced by heat treatment and the amount of ash remaining in the refining pitch.

Claims (1)

[Claims] 1. Produce a crude pitch by removing coarse solid impurities from coal-based or petroleum-based heavy oil, hold the crude pitch at a heating temperature of 430 to 450°C for 1 to 3 hours while continuing to stir slowly, and At least 25% by volume of an anisotropic phase having optical anisotropy and exhibiting a spherical shape with an average particle size of 40 to 60 μm is generated in the pitch, and then the anisotropic phase is separated and removed, and the anisotropic phase is separated and removed. A method for refining pituti, which is characterized by adjusting the residual amount of ash to 30 ppm or less.