CS261881B2 - Process for preparing binder for electrodes - Google Patents

Abstract

The invention relates to a process for preparing an electrode binder having a high proportion of primary quinoline-insolubles. Standard coal tar pitch is mixed with pitch coke oil in a ratio from 1:3 to 3:1 and the mixture is distilled under normal or reduced pressure up to a softening point (Kraemer-Sarnow) from 90 to 130 DEG C. The residue obtained in high yield is optionally mixed with a high-boiling butuminous coal tar fraction to set the desired characteristics.

Description

The present invention relates to a process for preparing a binder for electrodes with a high proportion of primary quinoline-insoluble substances. Normal pitch of coal tar is mixed with pitch carbonation oil in a weight ratio of 1: 3 to 3: 1 and co-distilled under normal pressure or vacuum until a softening point of 90-130 ^° C is reached for the distillation residue. The residue obtained is optionally mixed with a coal tar fraction having a mean boiling point above 350 ^DEG C. in a weight ratio of 1: 0 to 4: 1.

BACKGROUND OF THE INVENTION The present invention relates to a process for producing a binder for electrodes from coal tar products. Coke-bonding binders are required to produce carbonaceous moldings such as carbon and graphite electrodes from special coke. For this purpose, it is suitable to use binders which are derived from coal tar.

The requirements for binders for electrodes are constantly increasing over time. At first, particular importance was given to the high coking residue, later the binder quality was seen in addition to the high proportion of beta-resins in the difference between the toluene-insoluble fraction (TI) and the quinoline-insoluble fraction (QI). The significance of the quinoline-insoluble fraction (QI) has been assessed differently over time. It should be considered in conjunction with existing electrode and anode fabrication techniques.

It has previously been known that the coking residue of hard resins can be increased by thermal post-treatment following distillation (DE-PS 670 187). Since the increase in the collatable residue also leads to an increase in the insoluble fractions (QI, TI) at the same time, it has been proposed to mix again the vacuum distilled hard resin with the high-boiling tar oil (DE-PS 11 82 247).

When the importance of beta-resin for bonding properties was clarified, binders with a high proportion of beta-resins but with a low quinoline-insoluble (QI) content were sought. DE-AS No. 12 82 655 describes a continuous process for the production of an electrode binder, in which normal coal pitch is heat treated in several stages at an increasing temperature, wherein the resulting pitch distillate is always fed to the previous treatment stage.

Through the discovery of coke-forming processes in conjunction with the careful choice of raw materials, high-purity coke with high conductivity is now available for electrode production. In these coke, a graphite structure is already formed.

However, the low strength of said coke is disadvantageous. Therefore, it is necessary to incorporate these coke into a solid binder framework so that the electrodes do not lose their strength.

DE-OS No. 19 29 508 discloses a process for the production of a high-pressure refractory material. A mixture of coal tar and a heat-treated pyrolysis residue of mineral oil fractions is proposed as a binder. This binder should also be suitable for the production of electrode material. However, an increase in compressive strength has only been demonstrated for a dolomite-based refractory material. In addition, mineral oil binders are known to be less suitable for the production of electrodes than coal tar binders.

All known thermal processes are common in that, together with increasing the proportion of beta-resins in the binder, the content of insoluble quinoline is also increased. Accordingly, it has been proposed to add high-boiling oils to the pitch which can be partially thermally polymerized to beta-resins. However, this newly formed quinoline-insoluble fraction (QI) differs from that originally present.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a process for producing a binder for electrodes from coal tar products, wherein the binder produced has a sufficient quinoline-insoluble (QI) content with a high C / H ratio in addition to the high coking residue.

According to the present invention, this is achieved by mixing normal coal tar pitch with a Kramer-Sarnow softening temperature in the range 60-80 ° C in liquid form with a coal tar tar distillate pyrolysis distillation at a temperature above 800 ° C. , in a weight ratio of 3: 1 to 1: 3, and this mixture is distilled under normal pressure or under vacuum until the distillation residue has reached a Kramer-Sarnow softening temperature of 90-130 ° C and the distillation residue is optionally mixed with the fraction coal with a boiling point above 350 ° C in a weight ratio of 1: 0 to 4: 1.

As the distillate from the coal tar pitch pyrolysis, one which is preferably produced when coking the hard pitch in a horizontal chamber furnace at a temperature of about 1000 ° C is preferably used. Surprisingly, it has been shown that, unlike other mixtures of coal tar pitch and high-boiling coal tar distillates, using a mixture according to the present invention, a high Cl content binder can be obtained with a substantially higher yield by simple distillation under normal pressure or vacuum. The C / H ratio of the quinoline-insoluble fraction is also higher than in other known mixtures.

The process according to the invention is explained in more detail on the basis of the following examples.

Example 1

At 150 ^° C, 50 parts by weight of normal coal tar pitch are mixed in the retort with the following values: softening point (K.-S.) 72.5 ° C

TI 24.1% by weight

QI 6.2% by weight with 50 parts by weight of horizontal coke pitch coke oil, characterized by the following values:

TI

QI start of boiling residue after boiling at 360 ° C

8.6% by weight

7.0% by weight 272 ° C

The mixture is distilled at a pressure of 12 kPa to a softening point (K.-S.) of 99.5 ° C. The maximum temperature in the digester is 360 ^° C. In 68% yield a hard pitch is obtained with the following values:

density at 20 ° C

TI

QI carbonization residue (Conradson)

C / H in QI

1.32 g / ciri ³

32.5% by weight

12.1% by weight

59.2% by weight

4.06

Metallographic cut shows no anisotropic structures. The pitch may be directly used as a binder for the electrodes.

Example 2

It melts and mixes 50 parts by weight of normal tar pitch of coal tar, characterized by the following values:

softening temperature

(K.-S.) 71.5 ° C TI 19.6% by weight Q 7.3% by weight and 50 wt parts of coking oil pitch, characterized by the following values. TI 7.0% by weight QI 6.3% by weight the beginning of boiling 262 ° C residue at 350 ° S 91% by weight

The mixture was distilled at atmospheric pressure to a maximum pot temperature is 490 ^Q C. Yield 68.3% was hard pitch having a softening point (K.-S.) of 116 ° C, which is characterized by the following values:

% by weight

TI 36.9 % weight QI 15.6 % weight carbonization residue 62.7 % weight C / H in QI 3.90

100 parts by weight of the hard pitch thus obtained are mixed with 5 parts by weight of high boiling coal tar oil (boiling point 183 ^DEG C., residue at 350 DEG C., 62.5% by weight) per type binder for electrodes having the following values:

softening temperature

(K.-S.) 99.5 Noc: 2 ° C TI 35.7 % by weight QI 14.9 % by weight carbonization residue (Condrason) 58.4 % by weight C / H in QI 3.69 Example 3 (comparative)

Under the same conditions, Example 2 was repeated using a high boiling coal tar distillate (boiling point 240 ° C, residue at 350 ° S 85% by weight) instead of pitch coke oil. A hard pitch is obtained in 53% yield with a softening point of 114.5 ° C, characterized by the following values:

TI 38.1 % weight QI 12.5 % weight carbonization residue (Conradson) 61.8 % weight C / H in QI 3.37

At about the same softening point and carbonization residue, this pitch has a low content of QI and a low C / H ratio in the quinoline-insoluble fraction compared to the hard pitch produced according to the present invention. In metallographic sections, mesophases with a diameter of more than 60 μηι are present. In addition, the yield is lower.

Claims (4)

OBJECT OF THE INVENTION 1. A process for producing a binder for an electrode of products from coal tar, characterized in that in a liquid state mixed normal coal tar pitch with a softening point according to Kraemer Sarnow and in the range of 60-80 ^q C pyrolysis distillate from coal tar pitch at a temperature in excess of 800 ° C, in a weight ratio of 3: 1 to 1: 3, and the mixture is distilled under normal pressure or vacuum until the distillation residue has reached a Kraemer and Sarnow softening point of 90-130 ^° C; the distillation residue is optionally mixed with a coal tar fraction having a mean boiling point above 350 ° C in a weight ratio of 1: 0 to 4: 1. 2. A process according to claim 1, characterized in that as the distillate from coal tar pitch pyrolysis, pitch coke oil produced during the carbonization of hard coal tar pitch at a temperature of 1000 ^° C. 3. The process according to claim 1, wherein the normal pitch of coal tar and the distillate of the coal tar pitch pyrolysis are mixed in a 1: 1 weight ratio. 4. Process according to claim 1, characterized in that the distillation is carried out as a simple distillation without condensate recirculation.