GB2062670A - Process for dissolution of carbonaceous material - Google Patents

Abstract

A process for dissolution of finely ground coal or similar carbon- containing raw material under elevated pressure and elevated temperature is characterised in that the solvent employed is a highest- melting aromatic distillate from the heat/pressure treatment of coal-tar pitch and/or a residue rich in aromatics from the pyrolysis of crude petroleum fractions and has an average boiling point of greater than 380 DEG C.

Description

SPECIFICATION Process for dissolution of carbonaceous material The invention relates to an improved process for putting carbon-containing materials into solution by treating pulverised coal or the like with a solvent and using increased temperature and increased pressure.

Because of the increasing shortage of crude petroleum and natural gas over the long term, coal is becoming increasingly important as a future raw material, particularly since it is widely available in many industrial countries. Private and State authorities in the industrial nations are endeavouring to make it possible to replace crude petroleum and natural gas by coal using new and improved coal refining techniques. A further medium-term direction from which raw materials can be guaranteed is the increased conversion of heavy mineral oil fractions into lighter products by thermal and catalytic processes, partly by using molecular hydrogen.

Because of the expected long-term shortage of mineral oil and the consequent increasing tendency to convert heavy mineral oil fractions into petrol and light fuel oil, there is a strong demand for techniques which make it possible to produce substitute products for residues derived from crude petroleum which are particularly suitable as raw materials for the manufacture of carbon products.

Extraction processes for removing ash from and liquefying coal have been proposed over a considerable time for manufacture such coal-derived products.

In such princesses, the coal is brought into intimate contact with a solvent under increased pressure and increased temperature, as a result of which a large part of the coal goes into solution. The reaction product is separated from the ash-rich residue, and the coal extract weak in ash can then be used as a high-value raw material for producing carbon products such as electrodes or carbon fibres after adjusting it to have suitable flow properties (viscosity, softening point).

Hydrocarbon mixtures with available hydrogen are particularly suggested as the solvents. Solvents such as tetralin or hydrogenated anthracene oil are able to convert large proportions of the coal into soluble form. The solution is then usually described in the specialist literature as the quinoline-soluble part of the coal used (G. O. Davies eft at Journal of the Inst of Fuel, Sept 1 977, page 121).

Accordingly, using 3 parts of solvent and 1 part of coal, and depending on the type of coal, up to 90% of the coal used is transformed into the quinoline-soluble form by using increased pressure and temperature.

However, these processes have the drawback that in order to produce the hydrogenated aromatics, a costly hydrogenation stage must be provided before the actual coal extraction.

With other solvents, such as residues of mineral oil processing or the conventionally used anthracene oil, the extraction yields for hydrogenated aromatic mixtures under the high pressures and temperatures given in the literature are not attained unless molecular hydrogen is used.

For these reasons there is a requirement for solvents the availability of which is ensured for as long a time as possible, and the dissolving capacity of which is as close as possible to the solvation potential of hydrogenated aromatics even under mild conditions.

Consequently, the object of the present invention is to provide a process for dissolving solid carbon-containing materials by using solvents having a high solvation power, in order to produce aromatic raw materials from coal or other carbonaceous material by refining with solvents under particularly mild pressure and temperature conditions. A further object is to extend the solvent range for the said purpose.

According to the invention a process for dissolution of finely ground coal or similar carboncontaining raw materials with an aromatic solvent under increased pressure and increased temperature is characterised in that highest-melting highly aromatic distillates from the heat/pressure treatment of coal-tar pitch and/or residues rich in aromatics from the pyrolysis of crude petroleum fractions with an average boiling point of greater than 3800C are used as the solvent for forming the solution.

In the present process, pulverised coal is mashed together with the highest-boiling mixtures of aromatics having an average boiling point of greater than 3800C, and is dissolved under increased pressure and increased temperature.

For this purpose, the type of coal can vary over a wide range, but pit coals or steam coals are preferred as raw materials. These coal represent the greatest proportion of all coal supplies. They are poorly suitable for producing coal coke.

However, coals with a low volatile content such as lean coals or other carbon-containing raw materials such as brown coals, peat or old tyres or other carbon-type waste materials can also be used.

In the present process, the degree of pulverisation is of secondary importance. According to the invention, distillates from the processing of coal-tar pitch or from the refining of mineral oil residues, such as for example occur in delayed coking plant or thermal crackers are used as the aromatic solvent (see for example German Auslegeschrift 2 129 281 or US Patent 3 547 804).

However, distillates obtain from the heat/pressure treatment of coal-tar pitch or from the coking of hard pitch are preferably used.

Coal-tar pitch occurs in the primary distillation of coal-tar in a quantity of 5055% with a softening point of 6575% (Krämer-Sarnow).

Pitches, which soften in this temperature range, are however not directly suitable for use as primary carbon products such as electrode binders, hard pitch or pitch coke, but can be refined for this purpose by known heat/pressure treatment processes (see for example US Patent 2 985 577 and K.

Raja, A. K. Moitra, Central Fuel Research Inst News, India 19, 1969, 57-63).

High-boiling hydrocarbon mixtures of high aromatics content occur as distillates in these processes. These hydrocarbon mixtures have an average boiling point of greater than 3800C. and thus clearly boil above the anthracene oil fractions normally recommended for coal extraction.

From the earlier tests with anthracene oil fractions, it was originally concluded that the dissolving capacity of tar aromatics should increase mainly with increasing boiling point of the solvent. It was also postulated that hydrogenated aromatics, such as hydrogenated anthracene oil or tetralin as used in the Pott-Broche process (Ullmann, Encyklopädie der techn Chemie, Figure 10, page 570, 1958) have a better dissolving capacity than non-hydrogenated mixtures of aromatics.

However, in further tests it has been sown that the aforesaid trend with regard to dissolving capacity does not generally extend over the anthracene fractions tested by Davies et al, because according to such a hypothesis, coal-tar pitch being the highest-boiling mixture of tar aromatics should have the best dissolving capacity for coal, but this is refuted by the present Comparison Example 1.

However, distillates from the further refining of coal-tar pitch surprisingly show an unusually high dissolving capacity under astoundingly mild conditions (pressure, temperature), to an extent which under the mild conditions according to the invention even exceeds that of hydrogenated tar aromatics with transferable hydrogen.

Preferably, the reaction components are brought into intimate contact in the proportion of 10 to 50% pulverised coal and 90 to 50% high-melting pitch distillate and are converted at preferably 200 to 5000C under and increased pressure of preferably 3 to 30 bars within say 0.5 to 5 hours, whereby a large part of the coal is concerted into quinoline-soluble form.

Particularly preferred reaction conditions are temperatures of around 3400C and pressures of around 10 bars.

The reaction product can be separated by known techniques -- such as filtration, distillation or promoter-accelerated settling -- into a coal extract of low ash content which is suitable for the production of carbon products such as electrode coke, binders and carbon fibres, and a mineral-rich residue.

The flow properties of the reaction product can be adjusted without problem my mixtures of aromatics deriving from tar, such as for example wash oil or anthracene oil.

Examples given hereafter illustrate the process according to the invention comparison Examples are also given.

EXAMPLE 1 1 part of finely groung long-flame gas coal (Westerholt type; ash content 4.6%; water content 1.9%; moisture content waf 38.1%) and 3 parts of pitch distillate from the heat/pressure treatment (i.e.

treatment under hot conditions, possibly with the use of pressure) of coal tar pitch were converted in a heatable stirred autoclave. The pitch distillate was characterised by the following boiling properties: Beginning of boiling: 3050C; 20% at 3870C; 50% at 4160C; 80% at 4550C.

The autoclave was cooled after a reaction time of 3 hours, and the pressure in the reaction vessel was released.

Further parameters and some typical results are given in Table 1.

EXAMPLE 2 The procedure of Example 1 was followed.

The solvent used was a distillate obtained by distilling the pitch coke distillate from the coke of hard pitch for producing pitch coke.

This highly aromatic distillate was characterised by the following boiling analysis.

Beginning of boiling: 3020C; 20% at 3900C; 50% at 4240C; 80% at 46000.

The degree of coal solubilisation which can be attained with this solvent based on several test results is shown in table 2.

Comparison Example I The procedure of Examples 1 and 2 was followed.

The solvent used was a typical coal-tar pitch obtained from the continuous distillation of coal tar.

(Softening point: 730C, Ql: 3.6%).

This comparison test shows that any generally valid conclusion regarding increasing dissolving capacity with increasing boiling point is not admissible (table 3).

Comparison Example 2 This is a Comparison Example which with the Examples 1 and 2 shows that the solvents according to the invention exceed hydrogenated aromatics in terms of their dissolving power under the mild conditions according to the invention.

The procedure of Examples 1 and 2 was followed.

The solvent used was tetralin (tetrahydronaphthalene). The reaction conditions and degree of coal digestion are given in table 4.

It can be seen herein that this coal dissolving medium, which is reputed to have the best coal dissolving capacity, is clearly inferior to the solvents used according to the invention under the mild conditions which are technically easy to attain.

TABLE 1: Reaction conditions and production features of example 1 Reaction Max. reaction Product Product temperature pressure yield characterisation Degree of coal solubilisation (O/o) ( C) (bars) (%) (%) (as quinoline-insoluble matter) Q.l. T.l.

300 7 98 7.2 25.2 73 340 10 98 5.5 23.2 80 TABLE 2: Reaction conditions and production features ot example 2 Reaction Max. reaction Product Product temperature pressure yield characterisation Degree of coal solubilisation (O/o) ( C) (bars) ( /0) (%) (as quinoline-insoluble matter) Q.l. T.l.

300 8 98 7.5 26.1 72 340 11 98 6.5 23.5 76 TABLE 3: Reaction conditions and production features of-Comparison Example 1 Reaction Max. reaction Product Product temperature pressure yield characterisatlon Degree of coal solubilisation (Y0) (etc) (bars) (%) (%) (as quinoline-insoluble matter) Q.l.

300 7 98 11.4 -71 340 14 98 11.5 71 TABLE 4: Reaction conditions and production features of Comparison Example 2 Reaction Max. reaction Product Product temperature pressure yield characterisation Degree of coal solubilisation (%) ( C) (bars) (o/o) (%) (as quinoline-insoluble matter) Q.l.

300 8 98 16.6 34 340 12 98 14.8 41

Claims (3)

1. A process for dissolution of finely ground coal or similar carbon-containing raw material under elevated pressure and elevated temperature, characterised in that the solvent employed is a highest melting aromatic distillate from the heat/pressure treatment of coal-tar pitch and/or a residue rich in aromatics from the pyrolysis of crude petroleum fractions and has an average boiling point of greater than 3800C.

2. A process as claimed in claim 1, characterised in that 10-50% by weight of pulverised coal and 90-50% of high boiling pitch distillate as the solvent are brought into intimate contact and are transformed over 0.5-5 hours at 200-5000C under an increased pressure of between 3 and 30 bars.

3. A process as claimed in claim 1 and 2, characterised in that the transformation is carried out at a temperature of around 3400C and a pressure of around 10 bars.