EP0135943B1 - Process for separating resinous materials from heavy coal oils, and use of the fractions so obtained - Google Patents

Description

The invention relates to a process for separating predominantly dissolved resinous substances from coal-derived heavy oils, in which two fluid fractions are obtained, one of which contains only a small proportion of toluene-insoluble substances (TI), and the other enriches the toluene-insoluble (TI) is, as well as the use of these fractions.

Heavy oils obtained from coal, in particular coal liquefaction products and tars from the gasification or coking of lignite and hard coal, are refined by working up by distillation. This thermal work-up process is limited to the evaporable portion of the heavy oils and is limited by their decomposition temperature. The remaining residue contains all ash, coke and coal components not removed beforehand and the high-molecular solids contained or newly formed from the beginning.

The quinoline-insoluble solids (QI) present in the residues are undesirable for many processing processes and are therefore removed, if necessary, by mechanical separation processes. The separation effect is achieved either due to the particle size as in filtration or primarily due to the higher density of solids as in centrifugation. It is also known to agglomerate the solid particles by adding a promoter liquid so that they can be removed from the residues under the action of gravity by simply letting them settle (DE-PS-2 810 332).

After distilling off the promoter liquid, the almost QI-free residues are mainly used for the production of highly anisotropic carbons. In order to achieve the highest possible carbon yield, the known processes aim to keep the loss of β-resins (TI - QI) as low as possible. This also has the advantage that the 0.1-rich residue is obtained as an easily manageable granulable solid (DE-OS-3 112 004) or as a non-sticky suspension (DE-OS-2 355 606).

The removal of the toluene-insoluble is very difficult to carry out, in particular in the case of a high proportion of β-resins, as are present in high-temperature coal tars. When precipitated with the quinoline-insoluble solids, the β-resins form a sticky, rubber-like mass which settles on the bottom of the settling tank and in the pipes and can only be removed mechanically.

An analytical method for determining the toluene-insoluble is known, which is also suitable for the separation of the β-resins under laboratory conditions. However, it is unsuitable for transfer to a commercially usable process because of the required high solvent excess of approximately 70 parts by weight of solvent per 1 part by weight of heavy oils.

For the production of high-quality electrode binders, pitches with a high content of β-resins are required, which also have a not too low content of quinoline-insoluble.

Additional β-resins can be produced in the heavy oils by a gentle thermal treatment, but a simultaneous generation of QI, which is not desirable, cannot be avoided. In addition, such thermal processes are very complex. Mechanical separation processes for TI concentration are not known.

Hard pitches with a high QI content and a high coking residue are required for the production of abrasion-resistant, hard coke with a high bulk density, as are used, for example, for the carburization of steel and cast iron. Such hard pitches have hitherto been produced from normal pitches by thermal treatment and blowing with air and coked in horizontal chamber furnaces.

On the other hand, it is known that pitches with a low TI content and a high Bureau of Mines Correlation Index are an excellent carbon black oil component. Methods for the production of such carbon black raw materials are described in the patents DE-2 547 679 and DE-2 560 019. The insoluble in toluene is removed in a high-speed centrifuge or with a very fine filter. Apart from the fact that the effectiveness of a centrifuge depends not only on its speed, but at least also on its diameter and the free path length of the particle to be separated, this method appears to be of little use for technical implementation due to the small difference in density between the β-resins and the other pitch components suitable. It is also known that β-resins cannot be obtained by filtration without prior precipitation, such as in the analytical method described. Even the removal of the quinoline-insoluble solids is technically only possible with appropriate filter aids, with the residue being discarded as waste. Although the known processes show that high-quality soot raw materials can be obtained from almost TI-free pitches in a mixture with steam cracker oils or anthracene oil, the processes described for separating the toluene-insoluble are technically not feasible, at least for pitches with a high β-resin content.

Low-viscosity, aromatic residual oils with high coking residues are desired for the production of impregnating agents for carbon moldings. Heavy oils with a low TI content available from coal are also suitable starting products here.

It was therefore the task of separating heavy oils obtainable from coal with solvents or solvent mixtures which can be easily removed by distillation into two fluid fractions, one of which contains only a small proportion of toluene-insoluble constituents (TI) and the other of which the toluene-insoluble constituent is concentrated, and for both Fractions suitable to show possible uses.

This object is achieved according to the invention in that the content of toluene-insoluble (TI) in the heavy oil used, obtained from coal, with an aromatic solvent to less than 10 % By weight, preferably less than 5% by weight, and the mixture is mixed with a non-aromatic, organic solvent in a ratio of 1: 3 to 5: 1 and with stirring the heavy, TI-rich phase which settles with a peripheral speed of the stirrer of 0.5 to 6.0 m / s at a temperature between 50 and 200 ° C, preferably between 50 and 100 ° C under the influence of gravity with a clarification surface load of up to 1 t / m ² h in a TI poor and a TI-rich fraction is separated.

The amount used per unit of time in relation to the clarification area is referred to as the clarification area load.

The aromatic solvent can be added to the heavy oil first or together with the non-aromatic solvent. Mixing is not a problem. For example, a static mixer can be used. Mixing in a centrifugal pump is also sufficient, however, if the solvent is metered in evenly before the pump.

Basically all common organic solvents can be used, the aromatic for diluting the heavy oil and the aromatics poorly dissolving, non-aromatic for the precipitation of the β-resins. However, it is advantageous to use solvents whose boiling point is lower than the start of boiling of the heavy oil, the mixture should preferably have a boiling gap. As a result, almost complete separation of the solvents from the heavy oil fractions is achieved when the solvents are recovered by distillation and the solvent loss is minimized. The recovered solvents are reused.

For heavy oils with an initial boiling point of around 200 ° C., a solvent combination of toluene and methanol has proven particularly effective, the best results being achieved with a ratio of solvent mixture to heavy oil of at least 1: 1 and an excess of methanol. In order to maintain good flowability of the TI-rich fraction, the toluene-insoluble content in the fraction must not exceed 50% by weight.

A solvent combination of methylnaphthalene oil and petrol has proven itself for heavy oils with a boiling point of about 300 ° C and above, but other solvent combinations such as xylene and n-heptane also serve the same purpose. For reasons of cost, however, fractions are preferred to pure substances.

Surprisingly, it has been shown that by slowly stirring the heavy phase, the low peripheral speeds for the preferred stirrers with a large diameter in relation to the container diameter, such as, for example, flat, bar or anchor stirrers, and the higher for stirrers with a small diameter, such as Propeller or turbine stirrers are used, not only the formation of sticky rubber-like substances is avoided, but also the separation of the toluene-insoluble is increased. The separation of resinous components from the slowly moving light phase is supported, and the elimination of the TI-poor fraction from the heavy phase is increased. The stirrer speed must remain well below the critical speed in order to avoid mixing the two phases. ,

It has also been shown that the ratio of the container diameter (d) to the filling height (h) also has an influence on the removal of the toluene-insoluble. A ratio d / h 2 is particularly advantageous.

The inventive method makes it possible to reduce the residues from the reprocessing of coal-derived heavy oils with reasonable effort and to partially process them into valuable products. This opens up new areas of application for these residues that were previously reserved for oils obtained by distillation.

The inventive method is explained in more detail on the basis of a few discontinuous exemplary embodiments, without being limited thereto. The process can also be carried out continuously with the same result, the mixture of heavy oil and solvents preferably being fed into the agitator tank in the region of the phase interface.

Example 1:

40 parts by weight of a topped high-temperature coal tar (boiling point = 224 ° C, TI = 8.1% by weight, QI = 1.9% by weight, ash content 0.1% by weight) are initially at 60 ° C in 30 parts by weight of toluene and mixed with 30 parts by weight of methanol on a static mixer. The mixture is fed into a cylindrical agitator tank with a dished bottom (D / h = 2.5), in which an anchor stirrer rotates at a peripheral speed of 0.8 m / s near the bottom. The sewage treatment area load is 0.15 t / _M ² h. The settling process with stirring at 60 ° C is complete after one hour. After phase separation, the two fractions are discontinuously distilled at a top pressure of 93 mbar up to a top temperature of 90 ° C. in order to recover the solvents. The residues left are 26.3 parts by weight of a low-TI fraction in which there are still 0.2% by weight of toluene but no methanol, and 13.8 parts by weight of a TI-rich fraction in the no solvent residues can be detected. The analysis data are shown in the table.

The TI-poor fraction has a Bureau of Mines Correlation Index of 175 and is used as a soot raw material.

In a furnace reactor, rubber soot of this type is produced in 44.2% yield from this material.

The TI-rich fraction is worked up by distillation in the usual way, like topped tar. Based on the topped tar used, a residue of only 33.8% by weight is obtained compared to 59.3% by weight of the usual purely distillative workup. The residue has a softening point according to Krämer-Sarnow (EP) = 73 ° C (K.-S.).

By blowing, a hard pitch with a softening point of 172 ° C (K.-S.) is produced from this in a yield of 82% by weight, which is coked in a horizontal chamber furnace at 1050 ° C for 24 hours to give a macroscopically almost isotropic coke with a bulk density of 520 kg / m ³ and a Micum drum strength of M ₁₀ = 8.2% by weight.

The coke yield based on the pitch residue (normal pitch) is 62% by weight.

Example 2

10 parts by weight of coal tar pitch (EP = 72 ° C (K.-S.), TI = 19.2% by weight, Ql = 6.5% by weight, ash content 0.18% by weight), are diluted with 10 parts by weight of methylnaphthalene oil (boiling range 235 to 265 ° C), and the mixture with 16 parts by weight of white spirit (boiling range 140 to 170 ° C) via a centrifugal pump into a stirrer tank with a flat bottom (d / h = 3 , 2) promoted. A cross-bar stirrer rotates near the ground at a peripheral speed of 1 m / s. The sewage treatment area load is 0.2 t / m ² h. After being left to sit for 2 hours with stirring at 73 ° C., the mixture separated into a light and a heavy phase. At 100 mbar head pressure and a bottom temperature of up to 288 ° C., 25 parts by weight of the upper phase and 1 part by weight of solvent are distilled off from the lower phase. In this way, 6 parts by weight of a TI-rich and 4 parts by weight of a TI-poor fraction are obtained, the analysis data of which are listed in the table.

The 4 parts by weight of the TI-poor fraction mixed with 4 parts by weight of filtered An _t hracenöl mixed. The Bureau of Mines Correlation Index of this mixture is 179. In a furnace reactor it is used to produce rubber soot in a 45.1% yield.

The 6 parts by weight of the TI-rich fraction are mixed with 3 parts by weight of coal pitch normal pitch with the same analysis data as the pitch to be extracted and processed by gentle helmet distillation to form electrode binders. In 92% yield, a binder with a softening point of 90 ° C. (K.-S.), a QI content of 10.2% by weight, a β-resin content of 25.3% by weight, an ash content of 0.28% by weight and a coking residue (Conradson) of 52.6% by weight.

Example 3

10 parts by weight of a soft pitch from the gasification of brown coal (EP = 34 ° C (K.-S.), TI = 9.8% by weight, QI = 3.1% by weight, ash content 0.1 % By weight) are mixed with a solvent mixture of 7 parts by weight of xylene and 16 parts by weight of n-heptane at 85 ° C. in a pipe section through a bypass circuit with 90% recirculation and placed in a pointed bottom container (i.e. / h = 2.0), in the conical part of which a blade stirrer adapted to the container geometry moves the heavy phase at a peripheral speed of 0.7 m / s. The sewage treatment area load is 0.4 t / m ² h. At 85 ° C the phase separation is completed within one hour. 24 parts by weight of solvent and tar oils are distilled off from the light phase at a top pressure of 100 mbar and a bottom temperature of up to 350 ° C. The remaining 5 parts by weight of distillation residue are almost free of Ql and contain only 1.3% by weight of β-resins. The softening point is 62 ° C (K.-S.) and the coking residue is 43.1% by weight. The residue is used as an impregnating agent in graphite electrodes for steel production.

0.5 part by weight is distilled off from the 4 parts by weight of the heavy phase at a top pressure of 100 mbar and a bottom temperature of up to 370.degree. The residue with a softening point of 90 ° C (K.-S.) and a coking residue (Conradson) of 54.3% by weight has an ash content of 0.3% by weight and a QI content of 9.5 % By weight and a β-resin content of 26.7% by weight and is used as an electrode binder.

A coal-based product from which the ash constituents or the quinoline-insoluble matter has at least partially been removed can also be used as the heavy oil. It is known to reduce the ash content in heavy oils by centrifugation, and to at least partially remove the quinoline-insoluble by filtering, separating or allowing accelerated settling. In particular, methods for removing the quinoline-insoluble by letting the promoter accelerate settling can be combined well with the inventive method.

Example 4

20 parts by weight of normal pitch coal pitch as in Example 2 are mixed with 9 parts by weight of methylnaphthalene oil (boiling range 235 to 245 ° C) and 9 parts by weight of kerosene (boiling range 250 to 300 ° C) in a tip-top container with a reflux condenser for 3 hours with stirring 250 ° C thermally treated. The mixture is then cooled to 180 ° C. by pumping over a cooler. After one hour without stirring, a QI-rich fraction (20% by weight of the mixture) has settled on the bottom and is drained off. The 30.4 parts by weight of the remaining fraction (QI = 0.04% by weight, TI = 7.25% by weight) are mixed with a further 7.5 parts by weight of methylnaphthalene oil and 16.5 parts by weight. Parts of kerosene are mixed by pumping over the cooler and cooled to 75 ° C. The d / h ratio is 2.1 and the blade stirrer rotates at the same speed as in Example 3. After two hours the mixture has separated into a light and a heavy phase. After the solvents have been distilled off, 8 parts by weight of a low-TI fraction with 0.1% by weight of toluene-insoluble, which are used as the carbon black oil component, and 7 parts by weight of a TI-rich fraction with a TI content of 31 3 wt .-% obtained, which are converted by coking in a delayed coker with a yield of 73 wt .-% in a highly anisotropic green coke. After calcining at 1300 ° C, this coke has a thermal expansion coefficient of 3.1 - 10 ^-5 K ^-1 between 25 and 200 ° C.

Example S (comparison)

A normal pitch as in Example 2 is used. The extraction is carried out as in this example, but without stirring. There is no flowable heavy phase. The material that settles out can neither be loosened nor melted completely and must therefore be removed mechanically.

29 parts by weight of the light phase are carefully removed from above. After a short time, resinous constituents already precipitate out due to inadequate separation of the β-resins. The mixture is distilled in a stirrer retort under a pressure of 100 mbar to a bottom temperature of 275 ° C. in order to remove the solvents. The pitch-like residue (4 parts by weight) has the analysis data given in the table. A comparison with the analysis data of Example 2 clearly shows the influence of stirring on the removal of the insoluble in toluene.

Example 6 (comparison)

The test is carried out as described in Example 2, with the exception that only 5 parts by weight of white spirit are used. The TI content of the solvent-free TI-low fraction is 3.9% by weight. The material is not suitable as a soot oil component.

Claims (10)

1. A process for separating resinous materials from coal-derived heavy oils by extraction with aromatic and non-aromatic organic solvents, characterized in that the content of toluene-insolubles (TI) in the heavy oil used is adjusted with an aromatic solvent to less than 10 % by weight, preferably [less] than 5 % by weight, and the mixture is mixed with a non-aromatic organic solvent in a ratio of 1 : 3 to 5 : 1 and is separated into a TI-lean and a TI-rich fraction while stirring the precipitating heavy TI-rich phase at a peripheral speed of the stirrer of 0.5 to 6 m/s at a temperature of between 50 and 200° C, preferably between 50 and 100° C under the action of gravity with a clarification surface charging of up to 1 t/m²h.

2. A process according to Claim 1, characterized in that the content of toluene-insolubles in the TI-rich fraction after distilling off the solvent does not exceed 50 % by weight.

3. A process according to Claim 1, characterized in that in the case of a heavy oil with a boiling point of approximately 200° C toluene is used as the aromatic solvent and methanol as the non-aromatic solvent, the ratio of solvent to heavy oil being equal to or greater than 1 and the ratio of methanol to toluene being greater than or equal to 1.

4. A process according to Claim 1, characterized in that, for a heavy oil with a boiling point of approximately 300°C.or more, methyl-naphthalene oil is used as the aromatic solvent and benzene is used as the non-aromatic solvent.

5. A process according to Claim 1, characterized in that the extraction is carried out in a settling container, the ratio of the container diameter (d) to the filling height (h) being arranged such that it is greater than or equal to 2, and the aromatic and the non-aromatic solvents are added at the same time.

6. A process according to Claim 1, characterized in that the coal-derived heavy oil is a heavy oil from which the ash components or the quinoline-insoluble solids have been removed beforehand in a manner known per se.

7. The use of the Tl-lean fraction obtainable according to Claim 1, after separating the solvents and, where appropriate, distilling off a further oil fraction, as an impregnating agent for moulded carbon bodies.

8. The use of the Ti-lean fraction obtainable according to Claim 1, after separating the solvents alone or as a mixture with aromatic oil fractions obtained by distillation, as soot oil.

9. The use of the TI-rich fraction obtainable according to Claim 1, after separating the solvents and where appropriate distilling off a further oil fraction alone or as a mixture with other aromatic residues, as a binder for moulded carbon bodies.

10. The use of the TI-rich fraction obtainable according to Claim 1, after separating the solvents and where appropriate distilling off a further oil fraction, as a charging product for the production of coke.