CH621323A5 - Process for the preparation of anthraquinone - Google Patents

Description

The present invention relates to a method for producing anthraquinone.

It has long been known that anthraquinone can be produced by oxidizing anthracene using chromic acid or bi-chromates (see FIAT Final Report No. 1313, Vol. 2, p. 19). This process requires an expensive oxidizing agent, can only be carried out continuously with difficulty and is based on a starting product (anthracene), which is obtained practically exclusively from hard coal and is therefore only available to a limited extent. In recent times, attempts have therefore been made to put the production of anthraquinone on a new raw material basis.

A newer process is based on naphthalene, which is accessible from both coal and petroleum. In this method, naphthalene is first produced from naphthalene by oxidation with oxygen, which is then converted with butadiene in a Diels-Alder reaction to give tetrahydroanthraquinone, which finally gives anthraquinone by oxygen dehydrogenation. Phthalic anhydride is obtained as a by-product. Such a method is described for example in DT-OS 2 245 555.

For the large-scale implementation of such a process, it is necessary that it can be carried out continuously, as little separation and purification as possible

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operations and can be designed in such a way that as many product flows as possible can be circulated so that product losses and environmental pollution are as low as possible. In addition, the formation of deposits, for example in the form of tars or crystalline precipitates, must be largely avoided, since otherwise malfunctions due to blockages can be expected.

The object of the process according to the invention is to provide such a process which enables a technically and economically advantageous preparation of anthraquinone from naphthalene.

A process has now been found for the preparation of anthraquinone, which is characterized in that

(A) Oxidized naphthalene with an oxygen and inert gas in the presence of a vanadium-containing catalyst

(B) from the reaction products from (A) in a quench system, a liquid product essentially containing naphthoquinone, phthalic anhydride and naphthalene and a circulating gas essentially containing oxygen, naphthalene, carbon dioxide and inert are obtained

(C) the liquid from (B) is reacted with butadiene in excess and thus obtains a liquid mixture which essentially contains tetrahydroanthraquinone, phthalic anhydride and naphthalene

(D) feeds the product from (C) to a destijlation system which consists of a column with a strengthening section and stripping section and a bladder, the stripping section and / or the bladder being designed in such a way that the feed mixture is prevented from passing quickly, whereby an oxygen-containing gas is fed into the distillation system in the lower part and a gas containing naphthalene is withdrawn from the distillation system at the top of the column and a liquid mixture essentially containing anthraquinone, phthalic anhydride and naphthalene is withdrawn from the bubble, the naphthalene obtained at the top being partially removed Cooling is liquefied

(E) the liquid mixture from (D) is fed to a column in which a mixture essentially containing phthalic anhydride and anthraquinone is obtained at the top of naphthalene and at the bottom

(F) the liquid mixture from (E) is fed to a column in which a mixture essentially containing phthalic anhydride is obtained at the top and a crude anthraquinone is obtained at the bottom

(G) the top product from (F) is fed to a further column in which impurities boiling more easily than phthalic anhydride are optionally obtained together with phthalic anhydride at the top and phthalic anhydride together with impurities boiling higher than phthalic anhydride at the bottom

(H) feeds the bottom product from (G) to a further column in which virtually pure phthalic anhydride is obtained at the top and a phthalic anhydride containing the high-boiling impurities in an enriched form is obtained at the bottom,

wherein fresh gas containing oxygen is fed into stage (A) and / or (D), fresh naphthalene into stage (B) and fresh butadiene into stage (C), and the following cycles are maintained:

a) Oxygen-containing cycle gas from stage (B) is divided and part, if appropriate after removal of naphthalene and discharge of a partial stream, directly after (A), the rest of the cycle gas from stage (B) via stage (D) after stage (A ) recycled b) gas containing naphthalene from stage (B) is recycled to stage (A) c) naphthalene-containing gas from stage (D) is recycled to stage (A) d) naphthalene from stage (E) is recycled to stage ( A) and / or returned to stage (B) e) Excess butadiene is separated from the product of stage (C) and returned to the feed to stage (C) f) liquefied naphthalene from stage (D) is fed into the inlet -set product returned to stage (C) or before stage (C) g) contaminated phthalic anhydride from stage (F) is partially returned to stage (D) or before stage (D) jh) the top product and / or part of the Bottom product from stage (G) and / or part of the top product of the stage (H) is returned to step (C) in the input product i) the bottom product from step (H) is returned before step (D).

The present invention relates to the combination of the apparatuses A to H and their connection by the returns a to i.

When carrying out the process according to the invention, a molecular oxygen-containing gas mixture can be used for the oxidation of naphthalene to naphthoquinone and phthalic anhydride and for the oxydehydrogenation of tetrahydroanthraquinone, which is circulated under pressure over both reaction stages. This cycle gas usually has to overcome the total system pressure of around 3 bar. The absolute pressure of the reaction can be between 3 and 10 bar. Depending on the oxygen requirement of the two stages, the circulating gas can be divided into the two oxidation stages by normal control measures. In addition to oxygen and naphthalene, various other proportions can be contained in the cycle gas, for example water vapor, carbon dioxide, carbon monoxide, nitrogen and other inerts. In order not to allow the level of the inert components to rise too high, a small partial stream of this gas can be removed from the system, for example by washing. The removal of the discharged products can be by normal combustion or by catalytic post-combustion, e.g. over palladium catalysts. It is advantageous to maintain a level of 1-10% by volume of naphthalene in the cycle gas. The naphthalene oxidation is then usually carried out with an excess of naphthalene, the majority of the naphthalene is returned to the cycle gas from the process and only as much fresh naphthalene is added as corresponds to the chemical consumption.

It may be advantageous to add small amounts of sulfur compounds, for example sulfur dioxide, to the feed gas in the naphtha lin oxidation.

In the process according to the invention, the higher-boiling reactants and reaction products, for example naphthalene, phthalic anhydride and naphthoquinone, are initially not separated, but are passed together through the following reaction stages after the naphthalene oxidation.

The reactor for carrying out the oxidation of naphthalene can be a conventional tubular reactor which contains tubes with lengths between 2 and 12 m, preferably between 3 and 8 m. The gas mixture can with a flow rate of 0.5 to 5 m / sec. and an average residence time of 1-9 seconds are passed through the tube reactor. The exothermic heat of reaction can e.g. be removed by a molten salt with a secondary cooler. In order to heat the reaction gases to the required reaction temperature of, for example, 280-450 ° C., a gas / gas heat exchanger can be installed in front of the reactor. It is also possible to only partially use the tubes in the tube reactor

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Fill catalyst and use the remaining part of the tubes, which can be filled with inert material, as a preheating zone.

The reaction gases emerging from the reactor for the oxidation of naphthalene are advantageously not liquefied by direct cooling, since tar-like products can form here as a result of secondary reactions. The reaction gases are therefore first cooled in a conventional cooler, for example in a boiling cooler, to temperatures of max. 280 ° C or gives these gases directly together with already liquefied reaction product under increased pressure, the reaction gases being cooled below the dew point of naphthoquinone and phthalic anhydride. This cooling system expediently works with a high liquid circulation, in which a large quantity of liquid, already cooled reaction product is brought into close contact with the hot or pre-cooled reaction gases. The heat extracted from the reaction gases can then be removed via a heat exchanger which is in the liquid circulation. It has been shown that deposits on these heat exchanger surfaces can be avoided over long periods of time, for example over several weeks, if the temperature of the cooling medium is set in the range from 80 to 150 ° C.

The gases leaving this condensation system can still contain small proportions of the reaction products, especially naphthoquinone. You are therefore expediently subjected to a countercurrent wash with naphthalene. The fresh naphthalene required in the overall process is advantageously introduced into this laundry and from there reaches the oxidation reactor via various circuits.

Water vapor can also be fed into the feed product in the oxidation reactor. It can also be advantageous to add as much sulfur compounds, for example sulfur dioxide, to the feed gas for naphthalene oxidation that 1-500 ppm sulfur compounds are contained in the feed gas, for example. The product required for further processing to anthraquinone is taken from the liquid circulation of the condensation system. In the following, the combination of the condensation system and the subsequent washing with naphthalene is also referred to as the quench system.

The liquid product withdrawn from the quench system and essentially containing naphthoquinone, phthalic anhydride and naphthalene is then reacted with butadiene to form tetrahydroanthraquinone. With this implementation, due to the strong tendency of butadiene to polymerize, blockages are generally to be expected, in particular immediately behind the butadiene addition point. In addition, a certain proportion of low-volatility residues can form in this reaction due to side reactions. These disadvantages can be avoided if the Diels-Alder reaction is carried out as follows:

Use of the butadiene in an excess of, for example, 2-20 mol per mol of naphthoquinone, temperatures from 90 to 200 ° C., preferably 90 to 1J0 ° C., residence times in the reactor from 10 to 300 minutes, preferably 50 to 100 minutes, additional dilution of the feed mixture with naphthoquinone-containing naphthalene and / or phthalic anhydride, especially in the mixing section. Naphthalene and / or phthalic anhydride containing naphthoquinone suitable for dilution can optionally be obtained at other points in the overall process for the production of anthraquinone. For example, naphthoquinone-containing naphthalene can be obtained at the top of the column in which the oxydehydrogenation of tetrahydroanthraquinones to anthraquinone or the removal of the residual naphthalene takes place. The Diels-Alder reactor can be used in a manner known per se as

Residence tube or boiler cascade or a combination of both. The reaction pressure in this reactor can be between 5 and 50 bar, for example between 10 and 30 bar.

The unreacted butadiene is then separated off from the products leaving the Diels-Alder reactor. This can be done, for example, by heating or applying a vacuum. The butadiene obtained in this way is returned to the reactor, for example, via a corresponding single-stage or multi-stage compressor. When recycled, polymerizations can be largely prevented if small amounts of naphthoquinone are always present. The butadiene consumed in the reaction is replaced by adding fresh butadiene. Since commercial butadiene always contains certain proportions of other hydrocarbons, for example butanes and butenes, it is advantageous to remove a partial stream from the recycle butadiene continuously or discontinuously. In this way, the enrichment of, for example, butenes and butanes can be avoided.

The now available, largely butadiene-free mixture consisting essentially of naphthalene, phthalic anhydride and tetrahydroanthraquinone is subjected to the oxydehydrogenation. The oxydehydrogenation takes place at pressures between 1 and 20 bar, preferably between 5 and 10 bar, and at a temperature at which naphthalene evaporates. The oxydehydrogenation is carried out in a distillation system. The heat of reaction can be used to evaporate the naphthalene. As already mentioned, a partial stream of the oxygen-containing circulating gas can be passed through this distillation system and, with the oxygen contained therein, the oxydehydrogenation of the? Tetrahydroanthraquinones can be carried out to anthraquinone. However, it is also possible to introduce a fresh gas which contains oxygen, for example from 1 to 20% by volume and nitrogen and / or other inerts, into the oxide hydrogenation. The residence times for this reaction are between 15 and 120 minutes, preferably between 30 and 60 minutes. The distillation system generally consists of a column with a rectifying section and stripping section and a bubble, the stripping section and / or the bubble being designed in such a way that there is a residence time in the abovementioned range. For this purpose, bell bottoms, valve trays, sieve trays or eaves trays, which are provided with discharge weirs, can be installed in the stripping section of the column. But you can also use a bubble that consists of several chambers. A reaction cascade is preferably used as the bubble. Naphthalene, which generally still contains small amounts of naphthoquinone, passes over the top of the column. This naphthalene is partially condensed and returned to the Diels-Alder reactor. Another part of the naphthalene is returned with the circulating gas and / or fresh gas passed through the column without prior condensation for the oxidation of naphthalene. A product is obtained in the bubble of the distillation system, which essentially consists of anthraquinone, phthalic anhydride and naphthalene.

The liquid product from the bubble of the distillation system is first fed to a column in which a liquid mixture containing essentially phthalic anhydride and anthraquinone, and possibly also small amounts of naphthalene, is obtained at the top and essentially at the bottom. This column is preferably operated in vacuo. The naphthalene obtained at the top, if appropriate after condensation and evaporation in the presence of the top product or parts of the top product from the distillation system described above, is returned to the naphthalene oxidation. The one that falls on the head

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Naphthalene can also be recycled into the quench system in addition or exclusively.

The bottom product from the column for the partial or complete separation of naphthalene, which contains anthraquinone, phthalic anhydride, optionally small amounts of naphthalene and a certain proportion of high-boiling products, is fed to a further column for the separation of phthalic anhydride and any naphthalene present. This column can be of conventional design and is conveniently operated under vacuum. A crude phthalic anhydride is optionally taken off at the top of the column together with the remaining naphthalene. According to the invention, part of the crude phthalic anhydride obtained in this way is then returned to the distillation system, where the return can be carried out not only directly into the column, but also, if appropriate, in whole or in part into the still. The recycling can also take place before the distillation system. A crude anthraquinone is obtained at the bottom of this column.

The crude phthalic anhydride which is not recycled and which is obtained at the top of this column can be purified in the following manner, for example:

The crude phthalic anhydride is placed in a column which is preferably operated under vacuum. This column can be a conventional rectification column. The low-boiling by-products are optionally discharged via the head together with naphthalene and phthalic anhydride. The top product is returned to the process, suitably before the Diels-Alder reaction. In order to obtain a practically pure phthalic anhydride from the bottom of this column, it is generally necessary to remove residues of quinones, especially naphthoquinone.

To obtain practically pure phthalic anhydride, the bottom product from the column for separating naphthalene and low-boiling by-products from phthalic anhydride is added to a further column, if appropriate using separate apparatus. Practically pure phthalic anhydride is obtained as the top product in this column. The bottom of this column is returned to the oxydehydrogenation.

Any low boilers still present can either be separated off in an upstream column and added to the top product from the low boiler removal of phthalic anhydride, or practically pure phthalic anhydride is taken off as a side stream in the upper part of the last column, and the top product from the last column containing the low boilers is likewise added to the top product added to the previous column.

The purification of the crude anthraquinone obtained in the process according to the invention is not the subject of the present invention. It can also be carried out by distillation. In principle, a large number of evaporator constructions are possible for this distillation, preferably a thin-film evaporator. Gaseous anthraquinone is preferably removed from this distillation under normal pressure or slightly reduced pressure, while the high-boiling impurities occur in practically solid form and are removed from the system using a suitable discharge device, for example a discharge screw. The gaseous anthraquinone can be subjected to rectification for further purification. A thin-film evaporator is preferably used, on which a rectification attachment of the usual type is applied, in which the anthraquinone is rectified under reflux and is taken off in liquid form as the top product.

Part of the anthraquinone can be returned to the column for separating phthalic anhydride from anthraquinone.

Residual anthraquinone can be obtained from the residues at the bottom of the evaporator by sublimation or extraction.

A technical preferred embodiment of the method according to the invention will be explained with reference to the accompanying drawing:

A gas mixture containing 1-5% by volume of naphthalene, 1-10% by volume of oxygen, 1-12% by volume of water vapor, 0-12th is fed via line 10 to a tube reactor 1 at a pressure of 2-10 bar Vol .-% carbon dioxide, 0 - 3 vol .-% carbon monoxide and additionally 100% inert, for example nitrogen. The tube reactor 1 contains tubes with a length of 3 to 12 m and a diameter of 20 to 50 mm, which are completely or partially filled with a vanadium-containing catalyst which is arranged in a sealed manner. The temperature is kept between 250 and 500 ° C. during the oxidation by means of a salt melt. The gas mixture flows at a speed of 0.6 - 5 m / sec. through the tube reactor (based on an empty tube).

The gases leaving the tube reactor are fed to a quench system 2 via line 11, optionally after pre-cooling in a boiling cooler to temperatures above 280 ° C. The quench system 2 consists of 2 stages. In the first stage, the gases fed through line 11 are quenched, so that a liquid mixture essentially containing naphthalene, naphthoquinone and phthalic anhydride at a temperature below 200 ° C., preferably below 150 ° C., is drawn off via line 16 at the bottom of the quencher can be. The uncondensed portions of the gases supplied via line 11 escape at temperatures below 150 ° C. at the top of the quencher. These are fed to a washer and washed there in countercurrent with naphthalene. The fresh naphthalene required in the overall process is fed to this scrubber via line 12. The gases 13 leaving the scrubber are divided into two streams 41 and 15. Part of stream 41 is discharged via line 40.

The naphthalene contained in stream 40 is advantageously separated off, for example by cooling or washing. This recovered naphthalene is preferably added to the feed naphthalene 12. The part of the gas stream 41 which has not been discharged is fed to the tube reactor 1 via the lines 14 and 10.

The liquid product 16 drawn off from the quench system 2 is fed, optionally after adding naphthalene 36 recirculated from the column 6, via lines 17 and 18 to a reactor 3 in which naphthoquinone is reacted with butadiene in a Diels-Alder reaction to give tetrahydroanthraquinone . Fresh butadiene is added via lines 43, 20, 19 and 18, a naphthoquinone-containing naphthalene from the top of distillation system 4 via line 30 and excess butadiene separated off after the Diels-Alder reaction being added via line 22 to this butadiene. The reactor 3 can be designed as a tubular reactor. In dwell times in the range of 0.1 to 5 hours, with laminar flow, temperatures between 60 and 200 ° C, pressures in the range of 3 to 120 bar and in the presence of at least 3 moles of butadiene per mole of naphthoquinone, the reaction of naphthoquinone Tetrahydroanthraquinone performed. The reactor can also be designed as a boiler cascade. The product mixture leaving the reactor 3 is removed via line 21, excess butadiene is separated off, for example by reducing the pressure, and added again to the starting product via line 22. The remaining product stream 23 is fed via line 24 to the reaction of tetrahydroanthraquinone with oxygen in the distillation system 4,

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a partial stream 25 can optionally be fed into the column 6.

The distillation system 4, in which the complete or partial separation of naphthalene from the mixture present after the Diels-Alder reaction and at the same time the conversion of tetrahydroanthraquinone to anthraquinone is carried out, consists of a column with stripping section and rectifying section and a bubble, the stripping section Contains internals that prevent the feed mixture 24 from running quickly and / or the bladder is designed in the form of several chambers. The bladder preferably consists of a cascade of cascades or interconnected chambers. If a boiler cascade is used, it can be connected upstream of the column. In this case, the oxydehydrogenation of tetrahydroanthraquinone takes place practically outside the column, which is then only required essentially for the separation of naphthalene. In any case, the heat released during the oxydehydrogenation is removed by evaporating naphthalene. The oxygen required to convert tetrahydroanthraquinone to anthraquinone is fed in the form of part of the gas (recycle gas) emerging from quench system 2 via lines 15 and 45 into the lower region of the stripping section or into the bubble of column 4. You can also or only fresh gas, for example. an oxygen / nitrogen mixture, feed into the distillation system 4 via lines 46 and 45. The distillation system 4 can be operated at temperatures of 100-300 ° C and pressures 1-20 bar. At the top of the column of the distillation system 4, a gas is removed via line 29, which contains all or part of the naphthalene introduced with the starting product 24, as well as the unreacted parts of the introduced gas 15 and impurities and by-products boiling more easily than phthalic anhydride, for example naphthoquinone. A portion of the naphthalene and naphthoquinone contained in stream 29 is separated off, for example by condensation, and optionally recycled via line 30 to the butadiene 20 and 43 to be used in the Diels-Alder reaction. The portions of stream 29 which have not been separated off are fed via lines 31, 9 and 10 into the; Oxidation reactor 1 returned. A liquid mixture which essentially contains the anthraquinone, phthalic anhydride, impurities and, if appropriate, naphthalene formed is removed from the bubble of the distillation system 4 via line 27.

The anthraquinone-containing stream 27 is fed to column 5, in which crude phthalic anhydride 33 is obtained at the top and crude anthraquinone 32 is obtained at the bottom. The column 5 is operated in a vacuum, for example at 100-900 mbar. The crude anthraquinone 32 obtained at the bottom of column 5 can contain high-boiling impurities and by-products which can be removed by further purification, for example by distillation. The top product of column 5, which consists of crude phthalic anhydride 33, is divided and partly returned via lines 34 and 28 to distillation system 4 and partly fed via lines 35 and 26 into column 6.

A conventional vacuum column is arranged in front of column 5, in which residual naphthalene is separated off. The top product is then evaporated in the cycle gas system and returned to the naphthalene oxidation 1 and / or the quench system 2.

The top product 35 from column 5 is fed into column 6. The column 6 can be operated at temperatures between 200 and 300 ° C and under vacuum. At the top of the column 6, the lower boiling than phthalic anhydride are introduced with the feed stream 26

Compounds, in particular naphthalene, together with certain proportions of phthalic anhydride, obtained and returned via line 36 to the feed product in the reactor 3. At the bottom of column 6, a phthalic anhydride is obtained which still contains small amounts of impurities. This phthalic anhydride is fed via line 37 to a further column 7, in which practically pure phthalic anhydride is taken off as top product (38) and a bottom product 44 which, in addition to phthalic anhydride, may also contain anthraquinone and other impurities. The bottom product from column 7 is returned via lines 44, 39 and 28 to column 4 and / or via lines 44, 42, 20, 19 and 18 into apparatus 3.

An input mixture is fed to the overall system via line 8 and optionally via line 46 to replace the oxygen consumed in FIGS. 1 and 4, via line 12 fresh naphthalene and via line 20 fresh butadiene. A crude anthraquinone is removed from the overall system via line 32, practically pure phthalic anhydride via line 38 and part of the circulating gas via line 40. All other product flows can be circulated.

The technical design of the reaction sequence can partly be carried out in a known manner. For the oxidation of naphthalene e.g. despite the preferred embodiment of a tubular reactor, basically another reaction system, e.g. a fluidized bed or moving bed can be used.

Although the cooling and quenching units described are a preferred embodiment, modified constructions are also conceivable. A residence time tube is preferably used for the Diels-Alder reaction, but this reaction can in principle also be carried out in other apparatus, for example. in stirred tanks. The oxydehydrogenation of tetrahydroanthraquinone is preferably carried out in a rectification column, but bubble columns or other reaction vessels are also conceivable. The subsequent columns for working up the reaction products can be of conventional design, for example as sieve plate, bubble plate, packed or valve plate columns.

Stainless steels and carbon steels provided with coatings on the surface have proven successful as materials for the apparatus and lines to be used according to the invention. For example, plastic or enamel can be used as coatings. When using non-coated carbon steels, a sharp increase in the formation of high-boiling by-products and the formation of deposits was observed.

The process according to the invention permits the production of anthraquinone from naphthalene in a continuous manner, whereby the formation of by-products and the formation of deposits can surprisingly be largely suppressed. In addition, practically all the product streams occurring in the process, with the exception of the end products, are reused by the returns according to the invention. This keeps product losses and environmental pollution low.

Anthraquinone can be used as a starting product for the production of dyes [see, for example, Ulimanns Enzyclopadie der Technische Chemie, Volume 3, p. 662 ff., 3rd edition (1953)]. The phthalic anhydride formed as a by-product can be used as a starting product for the production of plasticizers and many other chemical syntheses [see, for example, Ullmanns Enzyclopadie der Technische Chemie, Volume 18, pp. 556 ff, 3rd edition (1967)].

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The method according to the invention is explained in more detail using the example below, without restricting it to the details in the example.

example

The oxidation of naphthalene to naphthoquinone is carried out in the gas phase by means of molecular oxygen in a conventional type tubular reactor which is cooled with a molten salt via a secondary cooling circuit. The reactor has 48 tubes with a length of 6 m and an inner diameter of 32.8 mm. The contact bed is approx. 3.5 m high, which results in a total catalyst volume of 145 l. The catalyst consists essentially of vanadium pentoxide, silica and potassium sulfates. The pressure at the inlet of the reactor is 6 bar, the temperature of the molten salt is 330 ° C. 300 normal cubic meters of a gas stream containing approx. 2.5 vol.% Naphthalene, approx. 6 vol.% Oxygen and approx. 6 vol.% Water vapor are passed over the catalyst every hour. In addition to these components, nitrogen and CO 2 in addition to smaller amounts of CO and other gaseous components are contained. About 50% of the oxygen is converted in the reaction. The reaction gases are cooled to 280 ° C in a normal tube cooler (evaporative cooling) and then brought into contact with the liquid reaction product in a quench system. Here, the gaseous products are led in countercurrent to the liquid reaction products. The bottom temperature of the quencher is 120 ° C., the circulation of the liquid reaction products to the top of the quencher is conducted through a cooler whose cooling medium has a temperature of 100 ° C. The escaping gases have a temperature of approx. 105 ° C. In order to remove reaction products contained in partial pressure, the gases are fed with fresh naphthalene before being returned to the oxidation reactor. Approx. 20 kg / h of fresh naphthalene are fed into this wash. The gases escaping at the top of the wash contain approx. 3% oxygen and approx. 0.5% naphthalene and are returned to the reactor via a fan. Part of this gas stream is introduced into the reaction stage provided for the dehydrogenation of the tetrahydroanthraquinone and leaves this reaction part via the top of the column located in this reaction part. By adjusting the condensation temperature in the column, this gas is loaded with naphthalene in such a way that the total stream for the oxidation reactor for the oxidation of naphthalene to naphthoquinone contains about 2.5% by volume of naphthalene. The oxygen consumed is introduced into the system in the form of air, the oxygen content in the oxidehydrogenation stage of the tetrahydroanthrachone to anthraquinone being approximately 8.5% by volume by appropriate connection. From the two combined gas circuits, the proportion of the inert substances introduced, especially nitrogen, and the gaseous by-products formed, especially H20, C02 and CO, have to be removed. This is done by accepting a corresponding partial flow that is removed from the process. The two gas circuits are now closed. To maintain the oxidation of naphthalene to naphthoquinone, it is necessary to continuously feed water vapor into the cycle gas upstream of the oxidation reactor, so that the aforementioned value of 6% by volume is obtained. In addition, small amounts of sulfur compounds, preferably SO 2, are added continuously or batchwise to the naphthalene-containing gas to be oxidized, so that their content is between 5 and 50 ppm.

The washed and condensed liquid reaction products are withdrawn together from the quench system. The amount is about 75 kg / h with about 10% naphthoquinone, 7-10% phthalic anhydride as a by-product and excess naphthalene. This crude reaction product is now fed directly to the Diels-Alder reaction with butadiene without any treatment. The reactor used is a 3-chamber stirred tank with a downstream residence tube, which can be heated to temperatures between 100 and 150 ° C. The reaction is carried out at 120 ° C.

Excess butadiene is added in an amount of 10 to 12 kg / h. The reaction is carried out under a pressure of 20 bar and a residence time of approx. 90 minutes. After the reaction, the pressure is released into a container, the excess butadiene largely escaping. This butadiene is compressed again to 20 bar with a compressor and used again in the Diels-Alder reactor, with the amount of butadiene consumed being added again. When the butadiene is recycled, small amounts of crude product from the Diels-Alder reactor are added to the line at one or more points.

Without further intermediate treatment, the product from the Diels-Alder reactor is fed into the third reaction stage, the oxydehydrogenation of tetrahydroanthraquinone to anthraquinone. The amount is about 80 kg / h, the product contains 6 to 7% tetrahydroanthraquinone and 6 to 7% phthalic anhydride, in addition to small amounts of impurities and the large amount of excess naphthalene. The oxide dehydrogenation reactor is designed as a rectification column. The column has a diameter of 300 mm and a height of 8.7 m. The column is equipped with valve trays in the stripping section. The feed product is fed in at the sump. The sump is designed as a 3-stage chamber cascade connected in series.

In addition, about 12 kg / h of phthalic anhydride from the subsequent column for separating phthalic anhydride and anthraquinone are returned to the stripping section. 140 normal cubic meters of the above-mentioned cycle gas are introduced into the bottom of the column. The composition is about 8.5% oxygen and 0.5% by volume naphthalene in addition to the inert gaseous components mentioned above.

The column is operated at a system pressure of 5-7 bar and has a bottom temperature of 200 to 220 ° C. The oxydehydrogenation of tetrahydroanthraquinone is practically quantitative. Crude naphthalene is rectified in the column and essentially separated from phthalic anhydride. At the top of the column, the temperature of the condenser is set so that the gas passed through the column saturates in the desired manner with naphthalene, for example 3-5% by volume, and a sufficient proportion remains for the reflux.

Approx. 60 kg / h of raw product are withdrawn from the top chamber of the 3-stage chamber cascade. This product contains approx. 10-20% anthraquinone, 30-50% naphthalene, approx. 5% higher boiling residues, approx. 1% unknown by-products. The difference to 100 results from the proportion of phthalic anhydride.

In a subsequent column, the reaction product from the chamber cascade is largely freed of naphthalene in vacuo, which is mixed in gaseous form with the cycle gas before the naphthalene oxidation by an evaporator. In total, approximately 42 kg / h of naphthalene are fed to the oxidation reactor for the oxidation of naphthalene.

To separate crude phthalic anhydride as the top product and crude anthraquinone as the bottom product, the reaction mixture is fed into a rectification column which is operated at 400 torr. The column is designed in a conventional design as a packed column. Because of the high temperature required, the sump is heated electrically. The

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621 323

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Bottom temperature is 280 ° C. Crude phthalic anhydride is taken off at the top of the column. An oil ring pump is used to create a vacuum. The amount of phthalic anhydride removed is approximately 22 kg / h. As mentioned above, about 12 kg / h of this are pumped back into the system in which tetrahydroanthraquinone is oxidehydrogenated. At the bottom of the column there is an hourly product which contains about 6 kg of anthraquinone and about 1.5 kg of high-boiling by-products. This bottom product is fed to a conventional thin film evaporator. A discharge screw with cooling is installed for the smooth discharge of the high-boiling by-products. The high-boiling products are obtained in solid or liquid form and are removed from the process. Residual anthraquinone is obtained from the discharged mixture by sublimation or extraction with xylene and subsequent crystallization. The thin film evaporator is operated under normal pressure, the anthraquinone evaporates and is removed in gaseous form. The apparatus is electrically heated in order to reach the high temperatures of around 450 ° C. A 1 m long rectification attachment filled with packing elements is attached above the thin film evaporator. In a manner known per se, anthraquinone is cleaned there under reflux and initially leaves the system in liquid form and is crystallized and discharged in a downstream cooling screw. This completes the synthesis and purification of anthraquinone.

The crude phthalic anhydride obtained as a by-product is now freed of residues of carried-along impurities. The crude phthalic anhydride is fed into a conventional type of column. The column is operated at a vacuum of 150 torr. Low-boiling impurities which are not known in detail are taken off at the top of this column and returned to the process before the Diels-Alder reaction. The bottom product of this column, which, in addition to phthalic anhydride, contains a small amount of unknown by-products, is fed to another column in which most of the phthalic anhydride is taken off as the top product. This phthalic anhydride 10 is now colorless. Any further cleaning which may be necessary can be carried out in a manner known per se. This concludes the isolation of the phthalic anhydride by-product.

Alternatively, the crude phthalic anhydride can also be purified in a known manner by thermal treatment, reaction with sulfur, treatment with sulfuric acid / boric acid or a combination of several of these cuts. Fine fractionation is also possible.

At the bottom of the column, a crude phthalic anhydride is taken off in an amount of about 1 kg and returned to the column for the oxydehydrogenation of tetrahydroanthraquinone.

This closes all cycles. Process 25 thus uses: naphthalene, oxygen (in the form of air), water vapor and butadiene. In addition to the actual reaction product, two streams are discharged from the process, namely the partial stream from the gas circuit and the bottom product of the thin-film evaporator, which contains the 30 high-boiling components.

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1 sheet of drawings

Claims (7)

621 323 1. A process for the preparation of anthraquinone, characterized in that (A) Oxidized naphthalene with an oxygen and inert gas in the presence of a vanadium-containing catalyst (B) from the reaction products from (A) in a quench system, a liquid product essentially containing naphthoquinone, phthalic anhydride and naphthalene is obtained and a cycle gas essentially containing oxygen, naphthalene, carbon dioxide and inert gases (C) the liquid from (B) is reacted with butadiene in excess and thus obtains a liquid mixture which essentially contains tetrahydroanthraquinone, phthalic anhydride and naphthalene (D) feeding the product from (C) to a distillation system consisting of a column with a rectifying section and stripping section and a bubble, the stripping section and / or the bubble being designed in such a way that a rapid passage of the feed mixture is prevented, wherein in the distillation system is fed into the lower part of an oxygen-containing gas and a gas containing naphthalene is withdrawn from the distillation system at the top of the column and a liquid mixture essentially comprising anthraquinone, phthalic anhydride and naphthalene is withdrawn from the bladder, the naphthalene obtained at the top being partially cooled is liquefied (E) the liquid mixture from (D) is fed to a column in which a mixture essentially containing phthalic anhydride and anthraquinone is obtained at the top of naphthalene and at the bottom (F) the liquid mixture from (E) is fed to a column in which a mixture essentially containing phthalic anhydride is obtained at the top and a crude anthraquinone is obtained at the bottom (G) the top product from (F) is fed to a further column in which impurities boiling more easily than phthalic anhydride are optionally obtained together with phthalic anhydride at the top and phthalic anhydride together with impurities boiling higher than phthalic anhydride at the bottom (H) feeding the bottom product from (G) to a further column in which practically pure phthalic anhydride is obtained at the top and a phthalic anhydride containing the high-boiling impurities in enriched form is obtained at the bottom, wherein fresh gas containing oxygen is fed into stage (A) and / or (D), fresh naphthalene into stage (B) and fresh butadiene into stage (C), and the following cycles are maintained: a) Oxygen-containing cycle gas from stage (B) is divided and a part, optionally after removal of naphthalene and discharge of a partial stream, directly after (A), the rest of the cycle gas from stage (B) via stage (D) after stage (A ) recycled b) naphthalene-containing gas from stage (B) is recycled to stage (A) c) naphthalene-containing gas from stage (D) is recycled to stage (A) d) naphthalene from stage (E) is recycled to stage ( A) and / or recycled to stage (B) e) excess butadiene is separated from the product of stage (C) and returned to the feed to stage (C) f) liquefied naphthalene from stage (D) is fed to the feed Stage (C) or before stage (C) g) contaminated phthalic anhydride from stage (F) is partially returned to stage (D) or before stage (D) h) the top product and / or part of the bottom product from the Stage (G) and / or part of the top product of stage (H) is returned to step (C) in the feed product i) the bottom product from step (H) is returned before step (D). 2. The method according to claim 1, characterized in that in (A) a gas mixture is used, the 1-5 vol .-% naphthalene, 1-10 vol .-% oxygen, 1-12 vol .-% water vapor, 0- Contains 12 vol .-% carbon dioxide, 0-3 vol .-% carbon monoxide, 5 to 50 ppm sulfur dioxide and in addition to 100% nitrogen. 2nd PATENT CLAIMS 3. Process according to claims 1 and 2, characterized in that a tube reactor is used in stage (A) through which the gas mixture flows at a flow rate of 0.5-5 m / sec. and is conducted with a dwell time of 1-9 seconds. 4. Process according to Claims 1 to 3, characterized in that stage (A) is carried out at temperatures from 280 to 450 ° C. 5. The method according to claim 1 to 4, characterized in that one uses a quencher with high liquid circulation in stage (B), from which the liquid product is removed at temperatures below 150 ° C and which is followed by a gas scrubber in which the circulating gas in countercurrent is washed with naphthalene. 6. Process according to Claims 1 to 5, characterized in that 2 to 20 moles of butadiene per mole of naphthoquinone are used in stage (C), the reaction at temperatures of 90-200 ° C, residence times of 10-300 minutes, printing of 5- 50 bar and with the addition of naphthoquinone-containing naphthalene and / or phthalic anhydride. 7. The method according to claims 1 to 6, characterized in that in stage (D) a distillation system is used which consists of a column with a rectifying section and stripping section and a bubble, the stripping section and / or the bubble being designed such that the total residence time is 15-120 minutes and this distillation system operates at a pressure between 1 and 20 bar and at a temperature at which naphthalene evaporates.