EP0138235B1 - Process for preparing a thermal-stable pitch and oil from aromatic petrochemical residues and its use - Google Patents

Description

Process for the production of thermally stable pitches and oils from highly aromatic petrochemical residues and their use.

The invention relates to a method for producing thermally stable pitches from highly aromatic, unsaturated compounds containing petrochemical residues with an increased yield of distillable aromatic oils.

Pitches are usually stored in liquid form for a long time before they are processed, generally at temperatures around 200 ° C. In the case of hard coal tar pitches, no change in the properties is to be expected at these temperatures, but in the case of pitch-like residues from the petrochemical workup, such as. B. from unsaturated compounds containing aromatic residues from high-temperature pyrolysis and aromatic extraction of mineral oil-derived fractions.

From DE-C1815568 by the applicant it is known to subject aromatic residues containing unsaturated compounds to heat treatment under pressure in order to obtain a thermally stable aromatic mixture which can be worked up by distillation without difficulty. The distillation residue is given as 42%. The disadvantage of this process is that part of the valuable oils is converted into pitch by polymerization.

It is also known to subject the gasoline fraction of a pyrolysis residue from the steam cracking of petroleum fractions to a selective hydrogenation in order to prevent the polymerization (gum formation), in particular of the diolefins. The hydrogenation is carried out in the presence of a catalyst at temperatures of about 177 ° C. and a pressure of 21 to 42 bar (Selective Hydrogenation; British Petroleum Company Ltd.).

In other hydrogenation processes for saturating the olefins, pressures of up to 100 bar and temperatures of up to 427 ° C. are customary, depending on the catalyst. All these processes have in common that a catalyst and gaseous hydrogen are required. This makes these processes so complex that they are only carried out on the more valuable distillates, but not on residues.

From the patent US-A 3 238 118 a method is known to mix residues from the hydrogenative splitting of gas oil with residues from crude oil distillation in a ratio of 0.3: 1 to 4 1 and in a temperature range from 371 to 538 ° C under one Treat pressure from 48 to 69 bar thermally to obtain a higher yield of gas oil and other lower boiling oils. The residue mixture treated in this way is fed back to the crude oil distillation, the gas oil fraction boiling between 200 and 400 ° C. is split hydrogenatingly into gasoline with the addition of a catalyst. The residue boiling above 220 ° C is used as a hydrogen donor for the thermal treatment of crude oil residues.

A similar process using hydrogenated aromatic residues from various processes of mineral oil processing as a hydrogen donor is described in US Pat. No. 2,953,513. The boiling range of the residues used is between 371 and 593 ° C.

However, the hydrogenated residues with a relatively low aromatic content of about 40% used in this process have a high boiling point and therefore cannot be separated from the residues by distillation. In addition, they would reduce the aromatic content of highly aromatic pitches.

The object was therefore to treat highly aromatic, unsaturated compound-containing residues of the petrochemical workup by a simple process, avoiding the disadvantages of the processes mentioned, so that a thermally stable pitch and aromatic mixtures are obtained from them in high yield by distillation.

The object is achieved in that the highly aromatic residues containing unsaturated compounds from mineral oil processing are mixed with residues boiling between 150 and 280 ° C. from the hydrogenating refining of aromatic oils in a ratio of 1: 0.02 to 1: 0.25 and are heated to a temperature between 350 and 400 ° C under the autogenous pressure which is formed, and the reaction product is rectified under atmospheric or reduced pressure in order to obtain aromatic fractions and a pitch with a Krämer-Sarnow softening point of 50 ° C and higher.

Aromatic extracts and residues from the high-temperature pyrolysis of mineral oil fractions with an initial boiling point of 200 ° C. and higher, in particular from the steam pyrolysis of gasoline, are used as highly aromatic residues for the production of olefins. The aromatic fractions obtained can be formed into pure aromatics such as, for example, without the formation of polymerization residues in the same way as coal tar tractions. B. naphthalene and valuable aromatic mixtures such. B. Work up soot oil. The pitch obtained by the process according to the invention is distinguished by a low content of quinoline-insoluble constituents (QI) and a high coking residue. It is therefore suitable for the production of highly anistropic coke for graphite electrodes and carbon fibers as well as for use as an electrode binder and impregnating agent for carbon molded articles.

The process according to the invention is explained in more detail in the example below, without being restricted thereto.

example

95 parts by weight of a residual oil topped up to 200 ° C from pyrolysis for the production of olefins are mixed with 5 parts by weight of a pressure raffinate residue (boiling range: from 188 to 235 ° C / tetralin = 38.2%, naphthalene = 12.5 %) heated to 400 ° C in an agitator autoclave within one hour. A pressure of 13 bar is established. The reaction product is then immediately cooled to 120 ° C. and rectified at a head pressure of 30 mbar. At the end of the distillation, the top temperature is 275 ° C. As a residue, a pitch (A) with a softening point (Krämer-Sarnow) of 110 ° C remains in 27% yield. The analysis data of the feed mixture and the reaction mixture are shown in Table 1. A comparison shows the clear decrease in unsaturated, polymerizable compounds (resin formers) and the proportion in the reaction mixture that cannot be evaporated in the gas chromatograph.

On the other hand, there is also a significant increase in distillable aromatics. The hydrogen produced during the dehydrogenation of the hydroaromatics has therefore specifically brought about saturation of the polymerizable compounds and a hydrolytic cleavage of the thermally labile polymers.

To investigate the thermal stability, the pitch (A) was treated under extreme conditions at 250 ° C. in the presence of air for one week (168 h). As a comparison, a commercially available impregnating pitch of petro origin (B) and a pitch (C) which were obtained in the same way as the pitch (A), but without the addition of hydroaromatics, were subjected to the same thermal aging. The results of the analyzes are shown in Table 2.

For impregnation pitches, in addition to a Conradson coking residue of more than 45% by weight, the lowest possible viscosity and a low quinoline-insoluble content (01) are required in order to achieve quick and complete impregnation of the carbon moldings. Unaged, the pitch produced according to the invention has a desired low viscosity at application temperatures with sufficient coking residue. The petrochemical reference pitch has similar data, with the slightly higher coking residue and the slightly higher viscosity resulting from the higher softening point, which can be freely adjusted for all pitches by distillation. Compared to the non-hydrogenated pitch (C), pitch (A) has a significantly higher coking residue. In the case of hydrogenated stabilized pitch, obviously smaller amounts of slightly cracking components remain in the impregnating agent, so that less escapes from the impregnated material during the firing process and the impregnating effect is improved.

After aging in air, the weight loss was less than 0.6% in any case, so that the change in material data can be attributed to chemical changes in pitch. The hydrogenated pitch (A) shows pitch (C) a tolerable increase in viscosity and insolubility, while pitch (B) increases in viscosity so much that satisfactory processability can no longer be expected.

It has been shown that a relationship between species and. There is an amount of the quinoline-insoluble and the viscosity with regard to its influence on the impregnation properties, so that it is not possible to make a statement about this solely from these analysis data. A filtration test was therefore also carried out.

30 g of pitch were pressed at 200 ° C. with a pressure of 5 bar through a standardized sintered disc made of stainless steel W. No. 1 4404 with a pore diameter of 3 μm, a thickness of 25 mm and a diameter of 19 mm, and the reciprocal filter performance F. T / m determined as a function of the area-specific amount of filtrate M / F (F = filter area; m = filter amount; t = flow time).

The figure shows the filtration curves for the pitch (A) produced by the process according to the invention and the pitch (C) produced without addition of hydroaromatics. The pitch (B) had reciprocal filter capacities of at least 50 cm ² min / g, aged 90 cm ² min / g when the filter was quickly blocked.

Both untreated and aged, the values for pitch (A) are more favorable than for pitch (C). In particular, the filter in the aged pitch (C) is blocked after 6.5 g / cm ² flow, while larger amounts can be filtered by pitch (A).

As the most important result of the comparative investigation, it can be stated that the pitch (A) produced according to the invention has significant advantages over the comparative pitch (B) in terms of thermal resistance and filterability, as well as over the comparative pitch (C) in terms of coking residue and filterability after aging.

Claims (5)

1. A process for the production of thermally stable pitches from residues of the petrochemical processing containing highly aromatic, unsaturated compounds, characterised by mixing the highly aromatic residues with residues from the hydrogenation refining boiling between 150 and 280 °C at a ratio of 1 : 0,02 to 1 : 0,25 and heating to a temperature between 350 and 400 °C under the pressure which develops during said heating, and rectifying the reaction product under atmospheric or reduced pressure to obtain fractions of aromatics and a pifch with a softening point of at least 50 °C, measured according to Kraemer-Sarnow.

2. A process as in claim 1, characterised by employing the residue boiling above 200 °C obtained from the vapor pyrolysis of naphtha in the production of olefins as highly aromatic residue.

3. A process as in claim 1, characterised by employing a pressure refining residue with a tetralin content of at least 30 % by weight as a residue obtained from the hydrogenation refining of aromatic oils.

4. The use of the pitch obtained according to claim 1 as a binder or impregnation medium for carbon shaped bodies.

5. The use of the aromatic fraction obtained according to claim 1 for obtaining pure aromatics.

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