DE1643733A1 - Process for the preparation of benzene carboxylic acids - Google Patents

Description

Process for the preparation of benzenecarboxylic acids is the subject of this Invention is a process for the preparation of benzenecarboxylic acids by oxidation of appropriately substituted benzenes with relaxation, fractional distillation and recycling a portion of the liquid reaction mixture.

Various methods are known, according to which by alkyl, hydroxyalkyl and / or formyl groups substituted w benzenes in the liquid phase in counterpart more suitable Catalysts and solvents with oxygen-containing gases to corresponding benzene carboxylic acids be oxidized (German Patent 1 008 279, US Patent 3 089 907, 3 240 803, Belgian patent specification 670 307) 0 In general, serve as solvents low molecular weight fatty acids, as catalysts heavy metal salts such as cobalt manganese or cerium compounds, usually together with bromine ion-yielding compounds or with activators such as peroxides, ozone or peroxide-forming compounds. the Oxidation of the substituted benzenes can, depending on the relative concentrations to each other and v-om partial pressure of oxygen, in a wide range of temperature and Printing conditions be performed. The large-scale implementation the reaction that generates high sales with a minimum of input materials and energy consumption and should enable yields, but raises significant problems.

As with any oxidation reaction, considerable amounts of heat have to be dissipated will. It has already been proposed that the heat of reaction through the reactor wall and to be discharged via cooling surfaces arranged inside and outside the reactor.

A part of the liquid reaction mixture can under the reaction pressure also routed via a corresponding cooling circuit (cooled lines, cooling surfaces) will. All such processes require expensive ones on an industrial scale Cooling devices. If solid end products occur in the reaction, e.g. B. in the case of Terephthalic acid, so there are incrustations in the cooled zones and considerable Operational disruptions.

In order to avoid these difficulties it has been suggested that Remove heat of reaction by evaporative cooling.

During this process, some of the volatile components of the reaction mixture are used evaporated within the reaction room and together with the gaseous components (z. B. Sauerals waste gas, nitrogen, carbon dioxide) of the mixture discharged.

In the case of evaporative cooling, however, for reasons of operational safety the selection of reaction temperature and pressure as well as the composition of the exhaust gas mixture certain There are limits. So z. B. not worked with pure oxygen at elevated pressure will. The exhaust gas must not contain more than 8 volOXtO oxygen. At low At reaction temperatures, evaporative cooling cannot or at least not be carried out uneconomical; water of reaction formed occurs only in small quantities with the Exhaust gas. On the other hand, with regard to yield losses, the water of reaction Do not exceed an amount of up to 10% by weight in the mixture, based on alkanecarboxylic acid should, in such cases, an additional separation of the water, z. 13. through Distillation. If air is used as an oxidizing agent, it occurs an increased amount of exhaust gas due to the nitrogen, the increased amounts of highly volatile Activators, e.g. 13. methyl ethyl ketone, hydrogen bromide, butane or solvents, z. B. acetic acid, carries with it. These components are difficult on an industrial scale recover and thus affect the economy of the process. In addition, the pollution of the atmosphere, e.g. B. by hydrogen bromide, a undesirable side effect.

It has now been found that benzenecarboxylic acids can be reacted of benzenes substituted by alkyl, hydroxyalkyl and / or formyl groups with Oxygen in the liquid phase in the presence of heavy metal catalysts with bromides and / or peroxides or peroxide-forming compounds and in the presence of alkanecarboxylic acids at increased Temperature and at elevated Pressure is advantageously obtained if one part of the liquid is below the reaction pressure standing reaction mixture withdraws from the reaction chamber, to a pressure of 0.1 relaxed to 1 atm, the vapors produced during the relaxation by distillation fractionated and the portion that does not evaporate during the relaxation completely or partially fed to the reaction, with the fractionation resulting Water is separated off and the remaining condensate, if appropriate, the reaction again is fed.

The process of the invention provides a large number of benzenecarboxylic acids in good yield and in a simple way.

Compared to the aforementioned method, the method requires no expensive cooling equipment and allows a wider range of reaction conditions. The water of reaction formed can be up to an amount of total%, based on alkanecarboxylic acid, be withdrawn from the reaction.

In the case of solid end products, encrustations, blockages and thus avoiding operational disruptions. A particular advantage is that the Solids, especially terephthalic acid, are obtained in an easily filterable form. Compared to the methods with evaporative cooling, there are far lower losses of volatile solvents or activators, especially when used of air as an oxidizing agent. Nitrogen and other inert gases are in the liquid Phase barely contain the amount of exhaust gas from the in relaxation The vapors produced are therefore low, the volatile compounds mentioned can thus practically without significant losses in the fractional distillation are recovered, undesirable volatile components, e.g. B. formic acid, Water, however, can be removed. The advantages outlined are based on the procedure the invention achieved by utilizing the heat of reaction, the heat of reaction is therefore in a particularly economical manner compared to the known processes discharged.

The starting materials are alkyl, hydroxyalkyl and / or formyl groups substituted benzenes are used, the alkyl or hydroxyalkyl groups being preferred each have 1 to 4 carbon atoms. Preferred starting materials are with alkyl, Glydroxyalkyl and / or formyl groups triple or, in particular, double substituted benzenes.

The following substituted benzenes can be used as starting materials are: Xylenes, cymene, methyl-ethylbenzenes substituted in the o- or p-position, Diisopropylbenzenes, ethylbutylbenzenes, toluylaldehydes; Pseudecumene, toluene, durol, Mesitylene, hemimellitol -, - 1, 3, 5, triethylbenzene, di-tert.-butylbenzenes, benzaldehyde, Xylenols, benzyl alcohol.

The starting materials are used alone or in a mixture with oxygen gases inert under the reaction conditions, e.g. B. in the form of air, implemented, where the oxygen is usually dependent on the number of substituents Ratio of 1 mole of oxygen to 0.02 to 2 moles of starting material used. at As with all known methods, the present method is chosen for safety reasons the reaction conditions so that the oxygen content in the exhaust gas is critical Value, which depends on the composition of the exhaust gas, does not exceed.

In general, this value is about 5 to 7 vol.% Oxygen, based on exhaust gas.

The reaction is carried out in the presence of heavy metal catalysts in many cases of compounds of metals of the 7th or 8th group of the periodic Systems.

Preferred catalysts are salts of iron, nickel, chromium, tin, Vanadium, molybdenum, cadmium, uli, cerium, palladium and especially cobalt or manganese. Such metal salts can be inorganic or organic in nature, e.g. B. perchlorates, Chlorides, bromates, propionates, butyrates, phthalates, naphthenates or in particular Bromides or acetates. You can also use mixtures of the catalysts mentioned, z. B. manganese bromide or acetate together with ammonium molybdate, tungstic acid or Cobalt acetate. Generally, the catalyst is used in an amount from 0.1 to 50% Mol.0a1, based on the starting material, applied.

In addition to the heavy metal catalyst, bromides are also used in many cases as activators for use. Such bromides are e.g. B. sodium, aluminum, ammonium, Calcium, barium, antimony, tin, aluminum, magnesium bromide or in particular Cobalt, lead, or manganese bromide. You can also use their mixtures or compounds, which form such bromides during the reaction with the heavy metal catalyst, use, e.g. B. hydrogen bromide. or tetrabromoethane. Generally the reaction will In the presence of 0 to 100 mol., Of bromide, based on the starting material.

Peroxides or perfoxide-forming compounds can be used as activators present in the reaction in addition to heavy metal catalysts and optionally bromides be e.g. B. cobalt acetate and acetaldehyde or cobalt bromide, manganese bromide and methyl ethyl ketone.

Preferred peroxides are e.g. 13. Ozone, xylene hydroperoxide, perbenic acid are zoe, preferred peroxide-forming compounds z. B. methyl ethyl ketone, acetaldehyde, Cyclohexanone, propionaldehyde, butyraldehyde, methyl-n-propyl ketone, diethyl ketone, 2,4-pentanedione, 2,5-usually hexanedione, toluyldehyde, butanols, butane. One uses they in an amount of 0 to 100 mol.%, Based on the starting material.

The reaction is discontinuous or, preferably, continuous at elevated temperature, generally between 50 and 250 OC, preferably between 80 OC and 200 OC, and at increased pressure, generally at 1 to 100, preferably at 1.3 to 25 atm. Alkanecarboxylic acids, preferably with 2 to 4 carbon atoms, e.g. 13. Acetic acid, used in general in an amount of 100 to 10,000 molar, based on the starting material.

According to the method of the invention, part of the liquid, under The reaction mixture under the reaction pressure is withdrawn from the reaction space (I). The reaction space, the exit point of the mixture part and the beginning of the exit can be chosen arbitrarily. The reaction is expediently allowed to start for a while, before part of the mixture, preferably at one point in the reaction space where most of the oxygen used has already been consumed.

You can see the reaction z. B. start as follows: In a vertical Reactor are starting material, solvent and the mentioned catalysts and Activators are filled in, then oxygen is introduced from below, e.g. B. introduced via a nozzle and the reaction takes some time, e.g. B. 0.1 hours performed.

Then you take from the upper third of the reactor, but still below an optionally formed exhaust gas cushion, part of the liquid mixture. As a rule, this part is an amount of 1 to 10,000 per hour, preferably from 100 to 5,000% by weight, based on the reaction mixture in the reaction space.

The withdrawn part of the liquid mixture (I) is then from his Reaction pressure relaxed to a pressure of 0.1 to 1 at, z. B. by means of a controllable Valve. When the pressure is released, some of the more volatile components (II) evaporate and the non-evaporated part (III) cools down. It is useful to relax that Mixture (I) in the bottom of a distillation column, which is via a condenser part possibly connected to a vacuum pump.

The resulting vaporous fractions (11) contain the water of reaction, dissolved gases, e.g. B. carbon monoxide and carbon dioxide, and volatile components of the starting mixture (in), e.g.

X, methyl ethyl ketone, hydrogen bromide, acetic acid, alkylbenzenes.

They are fractionated in the column by distillation.

Water, exhaust gas and some of the volatile components (IV) are after Exit from the column passed through a condenser. From the condensate formed is water that is still z. B. acetic acid or methyl ethyl ketone, separated. An organic layer that remains, especially when tolunene and xylenes are oxidized, which contains traces of water in addition to volatile components (IV) can be discarded or more expediently fed back to the column.

In the manner described is in the column by fractionation and condensation exhaust gas and water from the incoming gas mixture (I) withdrawn. Simultaneously The water content in the reaction mixture can thereby be reduced to <1% by weight mixed reaction to be diminished. bies is an essential Advantage of the process, since a higher water content, e.g. B. over 10 trades Oxidation of p-xylene to terephthalic acid, which worsens the yield of the end product.

The cooled portion (III) that does not evaporate during the expansion, possibly together with the condensate (1V) of the fractionation, becomes whole again or partially fed to the reaction. He can next to the liquid, not separated Components of the mixture (I) also include solid fractions, e.g. B. crystallized terephthalic acid, contain.

In a preferred embodiment of the process, the solid end product from the return. The solid external substances, e.g. B. terephthalic acid, Benzoesre, isophthalic acid, fall under the conditions mentioned in easily filterable, coarsely crystalline form, clogging or encrustation of the parts of the apparatus occurs does not contribute to any significant degree, which is another advantage of the method.

The cooled mixture (I) is transferred to the reaction chamber via a compression pump expediently injected with high impulse, z. 13. together with oxygen via a Two-substance nozzle with impulse tube for quick and good mixing with the reaction mixture to ensure. The introduction of the mixture thus also brings one at the same time thorough mixing of the reactor contents with itself. Also in the reactor are after Procedure of the Invention Encrustations and other B-instinct disorders avoided also known process features, e.g. B. insulation or heating of the Apparatus walls, are used. can.

The returned mixture (1) increases the temperature in the reaction space regulated, and the entire circuit of the withdrawn part of the mixture leads out of the reaction chamber ongoing heat of reaction from. If appropriate, the mixture (I) can be used during the cycle additional cooling. Part of the mixture (I) can also be discarded continuously or, e.g. B. with several reaction stages, a subsequent or preceding reactor are fed. Starting materials and other components of the reaction mixture can also be used to the mixture (I) after the fractionation, instead of adding it directly to the reaction space to feed.

The compounds preparable by the process of the invention are valuable intermediate products for the production of synthetic resins, fibers and plasticizers.

The parts given in the examples are parts by weight.

They are related to parts by volume like kg to 1.

Example 1 A corrosion-resistant steel oxidation reactor is provided with Provide feed lines for oxygen, p-xylene, acetic acid and methyl ethyl ketone. From the The top of the reactor is continuously fed into the reaction solution (reaction pressure 4 at) Relaxed bottom of a vacuum distillation column. The column has an effect of about 20 theoretical trays. The vacuum is created by the condenser Downstream column ring liquid pump set so that the bottom temperature is about 70 OC (about 100 Torr). The reaction solution becomes the bottom of the column pumped back into the reactor with a pump. At the bottom of the column is an overflow connected to a filter device. The backmixing the cooled reaction solution in the reactor takes place in a two-fluid nozzle together with oxygen. For better mixing of the reactor contents, the two-substance nozzle is used another circulation pipe set.

There is a solution of 45 parts of acetic acid, 5 parts per hour p-xylene, 1 part cobalt acetate tetrahydrate, 1 part methyl ethyl ketone and 160 parts by volume Oxygen supplied at 4 at. From the overflow mentioned one obtains in addition to 45.8 Parts acetic acid and 1 part cobalt acetate 7 parts (89 afo of theory) terephthalic acid, 0.14 part of toluic acid and 0.1 part of carboxylbenzaldehyde per hour. From the head of the About 1.5 parts of water, 0.1 part of acetic acid and 0.2 parts are added to the vacuum column every hour p-xylene and 0.1 part of methyl ethyl ketone are drawn off. At a reaction temperature from 130 to 135 ° C and a total pressure of 4 at are hourly at 50 parts Reaction solution 500 parts of reaction solution circulated in the reaction chamber by the relaxation. the Apparatus shows no incrustations when opened after 100 hours of operation Clogging due to deposits of terephthalic acid.

Example 2 In an apparatus analogous to Example 1, the reactor hourly a solution of 90 parts of acetic acid, 10 parts of p-xylene, 0.2 part of cobalt acetate tetrahydrate, 0.04 part of manganese acetate and 0.12 part of barium bromide dihydrate and 142r Parts by volume of air supplied below 21 at. To achieve a reaction temperature in the reactor of approx. 188 ° is obtained every hour from its liquid content of approx.

50 parts about ~ 440 parts solid-containing liquid phase through a drain valve in the sump of a distillation column of approx.

20 theoretical trays drained and approx. 335 parts of them back into the reactor pumped back. When draining into the bottom of the distillation column, which is at normal pressure is operated, the superheated reaction solution relaxes and cools down approx. 118 OC. The escaping vapors are fractionated in the column; man can about 2.9 parts of water and 0.1 parts per hour overhead from an aqueous phase Remove acetic acid and about 0.14 part of xylene from an organic phase. Because only about 335 parts of the distillation sump are pumped back into the reactor an hourly overflow of 89.9 parts of acetic acid, 12.6 parts of terephthalic acid, 2 parts of toluic acid and carboxybenzaldehyde and a catalyst similar to that of a second -ly built reactor is fed for post-oxidation.

Unused air and inert gases are refluxed through a condenser cooled to approx. 35 ° and relaxed. There is a loss of about 0.1 part of acetic acid when releasing the reaction gases.

Claims (1)

Process for the production of 13enzenecarboxylic acids by reaction of substituted by alkyl-1-hydroxyalkyl and / or formyl groups Benzene with oxygen in liquid gas in the presence of full heavy metal catalysts together with Bromideii ulld / odei peroxides or peroxide-forming compounds and in the presence of A alkanecarboxylic acids at an elevated temperature and at an elevated temperature Pressure, characterized in that one part of the liquid, under the reaction pressure standing reaction mixture withdraws from the reaction chamber, to a pressure of 0.1 relaxed to 1 atm, the vapors produced during the relaxation by distillation iractions and the part that does not evaporate during relaxation again completely or partially fed to the reaction, with the fractionation resulting Water is separated off and the remaining condensate, if appropriate, of the reaction again supplied wrd