GB2067589A - Process for producing carbon black raw materials - Google Patents

Abstract

Comminuted coal is disintegrated using a mixture of aromatised petroleum-based and coal- based solvents having a middle boiling point above 350 DEG C using elevated temperature and pressure conditions to produce a pitch-like material from which 10 to 40% of a fraction boiling between 220 to 480 DEG C is obtained as carbon black raw material by distillation from the pitch-like material which can have been topped to remove up to 5% of constituents boiling up to an end boiling point of 260 DEG C.

Description

SPECIFICATION Process for producing carbon black raw materials The present invention relates to the production of a raw material for producing carbon black, in particular a raw material for use in the oil furnace method.

Carbon black is an important raw material in the rubber and dye-stuffs industries. The most important method by far for producing carbon black is the oil furnace method. In this process a suitable hydrocarbon mixture is pyrolysed in a furnace into carbon black and hydrogen.

It has been found that not all hydrocarbon mixtures are equally suitable for producing carbon black; liquid hydrocarbon mixtures having a high aromaticity have however proved to be particuiarly suitable raw materials. At the present time, coal-based and petroleum-based hydrocarbon mixtures of this kind are used for producing carbon black. Cat-cracker residues (aromatic concentrates) and oils obtained from the steam cracking of petrol (naphtha) serve in particular as petroleum-based raw materials; coal-based materials for use include suitable fractions formed in the processing of coal-tar pitch.

Important preconditions for the suitability of an aromatic hydrocarbon mixture as a carbon black raw material are the boiling point, density (or the Bureau of Mines correlation index obtained from these two factors), atomic C/H ratio as a measure of the aromatisation, and also a sulphur content of at most 2% (see K.Zimmer, Erdol und Kohle, Erdgas, Petrolchem. 22, 1969, 742). From this it follows that a carbon black raw material having a correlation index of above 1 20 is a good starting material for carbon black production.

A corresponding quality gradation of carbon black raw materials is given in German Offenlegungsschrift 2547697, and can be seen in Table 1.

Table 1 Density, elementary analysis and C/H atomic ratio of carbon black raw materials.

Density Elementary analysis at 20 C (g/ml) in % by weight C/H atomic ratio Aromatic Concentrate C H S (Catalytic cracker residues) 0.976 87.2 9.2 1.8 0.79 Light steam cracker oil 1.035 91.1 8.4 0.1 0.91 Heavy steam cracker oil 1.070 92.1 7.0 0.1 1.10 increasing carbon Light anthracene oil 1.085 91.0 6.2 0.6 1.22 black raw material Heavy anthracene oil 1.136 91.4 5.8 0.7 1.31 quality.

The afore-mentioned high grade carbon black raw materials are unfortunately available only in limited amounts. This is true both as regards the hitherto used raw materials based on coai-tar, which on account of their high aromaticity must be considered the best carbon black raw materials, and as regards the petroleum-based raw materials formed as coupling products in the production of olefins or in catalytic cracking processes.

On account of this scarcity, attempts have not been lacking to broaden the raw material basis for high grade carbon black raw materials.

Thus, for example, in German Offenlegungsschrift 2547679 a process is described in which coal-tar pitch is mixed in suitable proportions with pyrolysis oil obtained from the cracking of petrol in order to obtain the required viscosity.

The disadvantage of this method however is that coal-tar pitch is only limitedly available for this purpose since it is used, as a high grade raw material, in particular as a binder for producing other coal products. Also, the interfering suspended substances (ash, etc.) must be removed from the pitch-pyrolysis oil mixture by a mechanically complex method.

For this reason there is thus an urgent need for a method according to which carbon black raw materials can be produced on a secure and guaranteed raw material basis.

The object of the present invention was thus to develop a carbon black raw material whose raw material basis principally depends on the long-term guaranteed coal reserves.

According to the invention, this objective can be achieved if optionally up to 5% of low boiling constituents up to an end boiling point of 260"C are topped (ie. distilled off) from a pitch-like by-product itself obtained by disintegrating comminuted coal and/or similar carbonaceous raw material having a high or low volatile content, the disintegration being effected using a mixture of aromatised petroleum-based and coal-based solvents having a middle boiling point above 350"C and elevated temperature and pressure conditions, and 10 to 40% of a fraction boiling between 220 to 480"C is produced as carbon black raw material by distillation from the optionally topped residue.

The production of high aromatic content hydrocarbons as the starting pitch-like by-product is the subject of our earlier patent application entitled: "Process for preparing highly atomatic pitch-like Hydrocarbons", which claimed priority from German Patent Application P 29 35 039.8. The process involves disintegrating coal having a high or low volatiles content, or a like carbonaceous material. using an aromatised residue obtained from the steam pyrolysis of petroleum fractions in admixture with coal-based aromatic mixtures having a middle boiling point above 350"C as complementary solvent, optionally with the addition of further solvent. In practice, the petroleum-derived residue also has an average boiling point above 350"C.

To obtain the carbon black raw materials of the invention, a fraction of 10 to 40%, preferably 1 5 to 35%, in the boiling point range 220 to 480"C, preferably 250 to 450"C, is distilled off from the optionally topped residue and can be used as carbon black raw material.

Coal is normally used as the principal component in the production of the carbon black raw material according to the invention. Despite extensive investigations, the structure of coal was, up to a few years ago, more a matter of speculation than of exact scientific foundation. The degree of aromaticity of coal, ie. the fractional distribution between aliphatic and aromatic carbon, was especially in dispute. It had earlier been assumed that coal is principally built up from highly aromatic clusters. However, quite another picture has been obtained by applying 1 3 C nuclear resonance spectroscopy to solid coal.Thus, for coals that are particularly suitable for disintegration, an aromatic fraction of only 60-65% was found (see S.K.Chakrabartty, The Structure and Chemistry of Coal, Paper read on the occasion of the World Conference on Future Sources of Organic Raw Materials, Toronto, Canada, 10th-13th July, 1978).

Other investigations have also shown that the highly volatile, low molecular weight coal constituents contain a large proportion of aliphatic compounds (M.Vahrman, Chem. in Britain, 1972, 8,16).

When using a simple mixture of tar-based, high aromatic fractions with partially aromatised pyrolysis oils and partially aromatised, solvent-extractable coal constituents in the appropriate ratios, it would be expected that an oil would be obtained having an average degree of aromatisation and density and thus an average correlation index.

Surprisingly, it has been found that the- oils from the aforementioned sources, namely pryolysis oil, coal-tar oils and extractable coal constituents, that have been modified by the coal distintegration process, have experienced a significant aromatisation on account of the disintegration, with the result that an oil fraction having an extremely high correlation index can be obtained.

The present invention is illustrated by the following non-limiting examples.

Example 1 30 parts by weight of Westerholt coal (volatiles content 37 to 38%) was disintegrated at 370"C and for a reaction time of 3 hours with a mixture of 1 5 parts by weight of pitch distillate, 20 parts by weight of pitch distillate from the heat/pressure treatment of coal-tar pitch, and 35 parts by weight of pyrolysis oil (average boiling point 358"C) from the steam cracking of crude petrol. The maximum reaction pressure was 25 bars. An oil distillate having an initial boiling point of 255'C and a boiling point (95%) of 435"C was obtained by distillation from this coal by-product, after topping off 3 parts by weight of the more highly volatile constituents. The amount of oil distillate was 28%.

The oil was investigated for its quality as a carbon black raw material, in accordance with the specifications given in Table 2. A comparison with the criteria mentioned in German Offenlegungsschrift 25 47 679 shows that the oil according to the invention is an excellent raw material for carbon black.

Example 2 The procedure of Example 1 was adopted, but the following solvent mixture was-used for the disintegration: 1 5 parts by weight of the pitch distillate, 20 parts by weight of pitch distillate obtained from the heat/pressure treatment of coal-tar pitch, and 35 parts by weight of pyrolysis residue (average boiling point 366"C) from the cracking of gas oil. From the coal by-product obtained in this way, a fraction boiling in the range 270 to 430"C and comprising 31% of the coal by-product was obtained by distilling the residue after topping.

An investigation of this fraction as regards the requirements for a carbon black raw material for the furnace method shows that it is an extremely good carbon black raw material, see Table 2.

Table 2 Density Elementary analysis C/H atomic at 20 C (g/ml) in % by weight ratio Correlation index C H S Carbon black raw material according to Example 1. produced by distilling a coal byproduct 1.136 91.40 6.19 0.46 1.23 159 Carbon black raw material according to Example 1, produced by distilling a coal byproduct 1.131 89.44 6.32 1.43 1.17 156 Tar-based carbon black oil according to German Offenlegungsschrift 25 47 679 1.136 91.0 6.20 0.60 1.22 155

Claims (7)

1. A process for producing carbon black raw material wherein optionally up to 5% of low boiling constituents up to an end boiling point of 260"C are topped from a pitch-like coal byproduct obtained by disintegrating comminuted coal and/or like carbonaceous raw material, the disintegration being effected using a mixture of aromatised petroleum-based and coal-based solvents having a middle boiling point above 350 C using elevated temperature and pressure conditions, and 10 to 40% of a fraction boiling between 220 and 480"C is obtained as carbon black raw material by distillation from the optionally topped by-product.

2. A process according to claim 1, wherein the pitch-like coal by-product is obined by disintegrating coal with an aromatised residue from the steam pyrolysis of a petroleum fraction and with a coal-based aromatic mixture as complementary solvent, together with the addition of further aromatic solvents.

3. A process according to claim 1 or 2, wherein the fraction obtained as carbon black raw material boils between 250 and 450"C.

4. A process according to claim 1, 2 or 3, wherein low boiling constituents are distilled from the by-product.

5. A process for producing carbon black raw material substantia!ly as described herein in the Examples 1 and 2.

6. A method for preparing carbon black by heating a raw material, wherein the raw material is produced by a process according to any of claims 1 to 5.

7. Carbon black made by a method as defined in claim 6.