JPS61117109A - Preparation of impregnating pitch for electrode - Google Patents

Abstract

PURPOSE:To prepare an impregnating pitch for electrode having improved impregnability to an electrode and cong. substantially no trace impurities by removing trace amt. of impurity in a pitch freed of quinoline insolubles by filtration, fractional solvent extraction, or centrifuging, etc. CONSTITUTION:Coal tar cong. <0.1% quinoline-insolubles which has been freed of quinoline-insolubles, or pich obtd. from said coal tar is subjected further to the treatment for removing impurities (such as filtration of molten pitch, etc.), thus, purifieid pitch cong. <=0.05% impurity, suitable for impregnating electrode having high bulk density and increasing effect for the strength of the electrode, is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing impregnated pitch for electrodes with improved pitch permeability suitable for use in producing carbon electrodes for electric furnaces.

(Prior art) Conventionally, when producing high-quality artificial graphite electrodes, when producing coal-based needle coke from coal tar or coal tar pitch, a few percent of quinoline coke contained in the tar or pitch was used. It is necessary to remove dissolved substances in advance, and various removal methods have been developed. for example,
Japanese Patent Publication No. 49-11608 describes a method for obtaining tar or pitch with low quinoline insoluble content after mixing with a solvent.
It is described that a trace amount or up to 0.4 inch of insoluble quinoline can be efficiently removed by one step of centrifugation.

JP-A-52-78201 proposes a method in which particles containing insoluble quinoline are coarsened using a mixed solvent and then separated by sedimentation. Furthermore, Japanese Patent Laid-Open No. 52-28501 proposes removing quinoline insolubles by mixing a similar solvent to substantially reduce the quinoline insolubles to less than a trace amount of 0.1%. In the current analytical method for quinoline insoluble matter, a value of less than 0.1.4 is considered to be within the error range as an analytical value.

On the other hand, in the production of carbon electrodes for electrical devices, in order to improve the bulk density and strength, petroleum-based or coal-based pitch coke and pitch as a binder are heated, mixed, and then shaped and fired to form electrodes. The process of softening and melting the pitch, impregnating it into the pores of the electrode at a pressure of 7 to 15 to 9/cnJ, and firing it is repeated 1 to 3 times to lower the porosity at 1 tffi and improve the bulk density. In this case, the step of impregnating the minute pores with the highly viscous molten pitch not only takes a long time for each impregnation process, but also makes it impossible to achieve uniform impregnation of the pores. For this reason, the pitch for impregnation is required to penetrate easily into pores and have a high fixed carbon content during carbonization, that is, to have a high carbonization yield. However, although this carbonization rate is generally higher for high softening point pitches, at the same time, the viscosity increases, resulting in poor impregnating properties.

(Problems to be Solved by the Invention) As described above, when using coal tar or pitch with a quinoline insoluble content of less than 0.1% that has been treated to remove quinoline insoluble content by a conventional method as an impregnated pitch for a carbon electrode, It has poor impregnating properties into electrodes, making it impossible to obtain sufficient density and strength as electrodes. Therefore, the present invention focuses on impregnating electrodes with coal tar or pitch (currently commercialized as QI-free pitch, trade name: rPK-QLJ) with less than 0.1% of quinoline insolubles that has been treated to remove quinoline insolubles. The purpose is to improve

(Means for Solving the Problems) As a result of numerous studies to improve the impregnation properties of pitch impregnated with a carbon electrode layer, the present inventors found that quinoline insolubles of 0.1 % of coal tar or pitch (de-QI pitch), i.e., the substance that remains as P slag when treated with a pore filter (e.g. 0.22μ Teflon @ filter) is impregnable. It was discovered that the impregnating property was significantly improved by removing this residual substance, and the present invention was achieved based on these findings.

The present invention has zero quinoline insoluble content as impregnated pitch for carbon 1 frame.
．． The object of the present invention is to obtain an impregnated pitch that is substantially free of coal tar or trace impurities in the pitch (de-Qed epitaxial).

The method for producing carbon electrode layer-impregnated pitch of the present invention involves removing trace impurities in the de-QI pitch, that is, 7 slag, through an appropriate removal process such as filtration, solvent division, or centrifugation, and remaining in the pitch. The objective is to produce pitch that is substantially free of impurities. Further, by performing this removal treatment on the tar before pitch distillation (but after the Q removal process) in the pitch manufacturing process or on the molten pitch after pitch distillation, the impurities in the product pitch can be removed.

In order to obtain impregnated pitch for carbon electrodes in the present invention, the above-mentioned raw material pitch is heated and melted at a temperature of, for example, 200''C to 320'C, and filtered (average pore size, for example, 0.1
~40μ) and 0.5i9/crl~5 J9/
The quinoline is filtered under pressure at a pressure of c++f so that the amount of quinoline insoluble matter is reduced to a trace amount, for example, 0.05% or less, preferably 0.02% or less, to the extent that the analysis error is considered to be substantially absent.

In fact, the pitch before and after filtering with an o, 22 μ filter has a quinoline insoluble content of about 0.05 in the analysis.
% or less, the value of the pitch before filtration is not necessarily large. From this, it is difficult to conclude that the quinoline-insoluble content in the above-mentioned trace amount (specifically, 10 (approximately 50 ff + 9 slag per liter pitch was obtained) of impurities greatly affects impregnating properties. The reason for this is that even in the case of a high-density fired electrode, as shown in Figure 3, the pore distribution has pores of 10 to 100μ, while the particle size of the quinoline-insoluble matter is usually about 1μ or less. Therefore, it is difficult to say that the size of the pore diameter is a direct inhibiting factor, but rather, it is thought that the combined effect with certain components in the pitch has a large effect on the impregnating property.

In addition, in removing impurities, the removal step can be applied to the pitch production process described above, and in this case, it is preferable that the impurity removal step such as filtration be performed on the sintered pitch after the pitch distillation step. Alternatively, an impurity removal step such as filtration may be provided in the step after removing the quinoline insoluble matter and before the pitch distillation to obtain a sufficient practical effect.

Regarding the average pore size of the filter used for filtration in removing impurities in the present invention, an average pore size in the range of 0.1 to 40μ was experimentally used, but 0.22μ was particularly convenient as a paper that can sufficiently capture fine particles. The average pore diameter of the seven papers exemplified in the present invention is not limited to a specific range.

Examples 1 and 2 specifically illustrate that the impregnating properties of pitch are significantly improved after filtering with filters having average pore sizes of 0.22μ and 10μ.

(Effects of the Invention) As described above, in the present invention, coal tar or pitch containing less than 0.1% of quinoline insolubles, which has been treated to remove quinoline insolubles by a conventional method, is removed by a removal process such as filtration. By removing the remaining impurities, i.e., 7 slag, to obtain an impregnated pitch for electrodes containing impurities of 0.05% or less, the impregnation of the pitch into the electrode is improved, and the bulk density and strength of the electrode are improved. I was able to increase it.

(Example 1) Product name “PK-QLJ de-QI pitch 100g to 210g”
Melt at 219°C using a 0.22μ filter.
When pressure filtration was performed using /c++J, the filtration rate decreased significantly over time as shown in Figure 1.
(0.05%) of F slag was obtained. Next, when this filtered pitch was used to perform filtration under the same conditions, as shown by the upper curve in FIG. 1, the decrease in filtration rate was slight.

Furthermore, using filter plates obtained from low-density fired products (human waste) and high-density fired products (B-waste) of electrodes actually used, the pitch before filtration and the pitch after filtration with a 0.22 μ filter were measured. A transient test was conducted on As shown in Table 1, the results show that the permeability was significantly improved (the filtration rate of raw pitch was set at 1). Note that the qI component content of pitch is approximately 0.0% before and after P slag removal. On~0
．． It was 0.5%.

Table 1 (Example 2) Samples from the same lot as in Example 1 were subjected to a transient test using a 10μ filter. As shown in Fig. 2, the filtration rate of the raw pitch decreased significantly, and the decrease was hardly observed in the pitch after the filtration, showing the same tendency as in Example 1. The re-overspeed was significantly large.

[Brief explanation of drawings]

Figure 1 is a graph showing the filtration characteristics of pitch obtained by filtering with a 0 and 22μ filter according to the method of the present invention. Figure 2 is a graph showing the filtration characteristics of pitch obtained by filtering with a 10μ filter according to the method of the present invention. A graph showing the characteristics, and FIG. 3 is a graph showing the pore size distribution of the filter plate taken from the electrode material. Fig. 1 Fig. 2 Fig. f Running time

Claims (1)

[Claims] 1. Quinoline insoluble content removed by quinoline insoluble content 0.1
1. A method for producing impregnated pitch for electrodes, characterized in that pitch containing less than 0.05% of impurities is obtained by removing impurities from coal tar or pitch obtained therefrom.