DE2202483B2 - PROCESS FOR THE PRODUCTION OF TRIMELLITIC ANHYDRIDE FROM PSEUDOCUMOL - Google Patents

Description

of polymers that contaminate the end product would be prevented.

The subsequent dehydration of the separated crystals of crude trimellitic acid takes place in a manner known per se (igt US Pat. No. 2,971,011). in pseudocumene as the solvent at a pressure above atmospheric pressure and below 4 atmospheres, the temperature being kept below 240 ^° C. and the water formed being driven off azeotropically together with the solvent. The formation of intermolecular trimellitic anhydride and the declining hydration of the resulting intramolecular anhydride to trimellitic acid remain limited

The remaining as a precipitate dicarboxylic acids are separated by filtration at a temperature from 60 to 170 ⁰ C. The obtained after dehydration Reaktionsgemiscb The residual in Fütrat trimellitic anhydride is further purified by fractional distillation as usual

A post-oxidation of all products of the incomplete oxidation of pseudocumene, which one after Separation of the trimellitic acid (aldehyde products) or after carrying out the dehydration (dicarboxylic acids) receives increases the total yield of 2s end product This is done in the example; in the Post-oxidation are likely to use the aldehyde products as promoters for the oxidation of those used at the same time Dicarboxylic acids are used.

According to the invention, the conversion of pseudocumene to trimellitic acid is as follows carried out:

Pseudocumene is bar acetate at a temperature from 160 to 210 ⁰ C, preferably at a temperature of about 190 ° C, in the presence of heavy metal salts, preferably cobalt (II) and manganese (H) acetate in the liquid phase under a pressure not more than 30 as Catalyst, and in the presence of intermediate products of the oxidation reaction of pseudocumene, preferably aldehydes and aldehydic acids, oxidized as initiating agent. The first batch of the products of incomplete oxidation, which is used as an initiating agent in the process according to the invention, is prepared beforehand by known methods

The oxidation continues until the pseudocumene is completely consumed and until a yield is achieved Trimellitic acid of over 50% continued About 50% of the amount used is made up of the reaction mixture Acetic acid and water of reaction driven off; pseudocumene is added to the residue, and the Crude trimellitic acid crystals precipitated together with dicarboxylic acid are centrifuged off. That Centrifugate (precipitate) is washed with pseudocumene and passed to the dehydration in the filtrate as well as in the washing solutions remain as products of incomplete oxidation z. B. aldehydes, aldehydic acids and monocarboxylic acids, as well as the metal salt catalysts.

These compounds are used as initiators in the oxidation reaction of pseudocumene to trimellitic acid used, the amount of these compounds being enough to initiate a few batches or just being some of these compounds are used as initiators and the rest is a post-oxidation subject. These compounds are not only post-oxidized to trimellitic acid themselves for 6s, but also initiate at the same time also the post-oxidation of mono- and dicarboxylic acids, as well as the oxidation of Pseudocumene, which was introduced with the mother liquor and with the washing solutions.

The dehydration of trimellitic acid to anhydride is carried out in pseudocumene as a solvent in Presence of inert gas at a temperature of 180 to 240 ° C, preferably at ISO to 200 ° C, below 1.5 to 4 bar pressure, preferably below 1.5 to 2 pounds bar, carried out. The water formed is carried out together with Pseudocumene driven off as an azeotrope. The further processing (filtration in the heat, distillation) takes place as you can read above.

The advantages of the method according to the invention can be summarized as follows:

a) Very pure trimellitic anhydride is obtained, which only contains trace amounts of the intermolecular Contains trimellitic anhydride, whereby the yield is not lowered (the yield of the Product is over 80 mol percent based on the pseudocumene used).

b) The chemical products introduced into the reaction are optimally used

c) The amount of waste water, just by washing out the apparatus and by driving off The water of reaction obtained is very little.

d) There is no need for regeneration or separate processing of initiators (promoters) the products of incomplete oxidation used as initiating agents, which in the course of the Trimellitic acid deposition automatically accrue, in turn are oxidized to trimellitic acid. With regard to the use of promoters, that on which the invention is based is obtained Oxidation process to a certain extent by itself

e) The temperature at which the oxidation reaction is carried out is because of the initiation low and the medium less corrosive, which is beneficial for any chemical process

f) Pseudocumene is used as a raw material as well as a solvent or medium in all stages of the Process such as dehydration of acetic acid, crystallization, washing of polycarboxylic acids, Dehydration and expulsion of water from the dehydration vessel, ve.-turns

The following exemplary embodiment explains the invention in more detail.

example

A mixture of 800 g of 98.3% pseudocumene and 28 (10 g of glacial acetic acid was in the presence of a catalyst consisting of 5 g of manganese (I!) Acetate, 5 g of cobalt (H) acetate and 100 g of tiltrate with products of incomplete oxidation of pseudocumene, which preferably contains aldehydes and aldehydic acids, was obtained by a known process and is used as a promoter in an autoclave with air at a temperature of 190 ^° C. and under a pressure of up to 30 bar Reactor passed at a flow rate of 1200 liters per hour Thereafter, 22QOg of liquid - a mixture consisting mainly of acetic acid and water - was distilled off from the reaction mixture. 200 g of pseudocumene were added to the distillation residue, the crystallized precipitate was filtered off and washed with 200 g of pseudocumene.

In this way there was 1130 g of precipitate obtained, which consists of 840 g of trimellitic acid and 290 g of dicarboxylic acid. The filtrate in an amount of 1220 g mainly contained monocarboxylic acids, aromatic

matic aldehydes and aldehydic acids, the rest of the Acetic acid and pseudocuirioL

The 1130 g were Niederschliig dehydration at a temperature of <; twa subjected to 190 ⁰ C under a Drude of 2 bar in a Pseudocumolmedium under inert gas. The produced water were used as water-pseudocumene azeotrope abdestiBlert by filtration at a temperature of 120 to 150 ⁰ C 280 g dicarboxylic acids, ie, nearly the whole amount separated from the Mtrat was distilled off pseudocumene, thereby obtaining 780 g of crude trimellitic anhydride.

The 1220 g ritrat mentioned above, plus the 280 g Dicarboxylic acids and 2000 g acetic acid, 5 g cobalt (H) acetate and 5 g of manganese (II) acetate were added to the reactor and with air at a temperature of 190 ° C and at up to 30 bar pressure post-oxidized in this way 1020 g of precipitate was obtained, which was mainly trimellitic acid and about 140 g Contained dicarboxylic acids, from which, after dehydration, 830 g of crude trimellitic anhydride was obtained.

The crude trimellitic anhydride, which from the oxidation and the post-oxidation thus m one Total amount of 1610 g was obtained, fractional distillation under a pressure of 10 to Subject to 20 torr; 40 g of first runnings, 1500 g of pure trimellitic anhydride and 50 g of residue were obtained. the The yield of pure trimellitic anhydride was over 80 mole percent without taking into account the Possibility to use the advance.

The purity parameters of the anhydride obtained were compared with corresponding parameters of commercial products obtained by oxidation of pseudocumene. The results are compiled in the following table. The TÄG values in Hazen degrees were also determined using the following procedure: 2 g of trimellitic anhydride and 14 ^ ml of triethylene glycol (chemically pure) were ^{heated to 260 °} C. in a nitrogen atmosphere, then cooled to room temperature and diluted with isopropyl alcohol in a ratio of 1: 1. The solution prepared in this way was ^{poured into a 5 cm 3} cell and the extinction with a colorimeter (available in Poland under the designation "KP3") in relation to distilled water, which is in a second Cell is read. The absorbance read was then converted into Hazen degrees using a calibration curve. The results are also given in the table.

Tabel

Purity parameters of trimellitic anhydrides

Purity parameters

Product after the
invention

Products according to the known processes

Amoco
3

Koch-Leight

Fluka

Percentage of trimellitic anhydride, determined by:

1. dynamic cryoscopy

2. Chromatography

3. polarography

4. Infrared spectroscopy
Melting temperature ( ⁰ C, determined
with Mettier device)

Acid number (theoretical: 875)
Aldehyde content (% by weight)
DAY in Hazen degrees

96.5 mol% 96.4 mol% 94.2 mol% 88.9 mol% 98.2% by weight 97.2% by weight 96.5% by weight 91.6% by weight 92.2% by weight 92.2% by weight 90.5% by weight 83.0% by weight 81.5% by weight 166.8 166.3 165.3 164 876 865 845 832 0.008 0.020 0.048 0.025 125 240 125 170

Claims (2)

the bromine content corrosive to the manufacturing claims: layers acts The yields were due to a later 1. Process for the production of trimellitic acid advancement by introducing a two-stage anhydride increased by oxidation of pseudocumene with 5 process, whereby in the first stage initially in molecular oxygen to trimhydric acid in the presence of a catalyst, which cobalt and cerium Temperature of 160 to 21O ° C and a pressure contains bromine compounds and reacted in the not above 30 bar in acetic acid as the second stage oxidation in the presence of a solvent and in the presence of initiating agents: n <i manganese catalyst is completed. Through this However, the problem of obtaining the ßende dehydration of the trimellitic acid, since trimellitic acid has not yet been removed from the reaction mixture by indicating that the oxyda is satisfactorily solved; it was a separate catalysis on the contrary at least part of the dej from the - gate work-up including the promoter required vorhergaenden Oxidation cycle borrowed, and those with the corrosiveness of the reaction medium Mother liquor performs as an initiating agent, with 15 associated disadvantages not being eliminated the mother liquor has been obtained in that the known processes also solve the problem of From the crude deposition of trimhydric acid obtained in the oxidation, only an insufficient mixture of initially water and part of the proportions. Because of the considerable solubility aer acetic the Rücksund in distilled off under trimellitic acid in the reaction medium comprising water 100 ⁰ C is added pseudocumene and contains the trimellitic 20 and acetic acid remain about 30% in solution. In order to achieve a high yield containing acid and other polycarboxylic acids, the solid is separated off after; that the separated process of US Pat. No. 3,261,846 contains the lead solid in boiling pseudocumene under a bend reaction medium together with the still dissolved · pressure of 1.5 to 40 bar and at a temperature of trimellitic acid and together with the products of 180 to 240 ^c C in the presence of an inert gas in the incomplete oxidation, such as. B. dehydrated with aldehydes in a known manner and dehydrated from the and aldehydic acids, after adding pseudocumene in undissolved dicarboxylic acids at a dehydration stage, whereupon first the temperature of 60 to 170 ⁰ C is filtered off that acetic acid and then after adding a dehydration, if necessary, the so separated dicarboxylic acids approximately catalyst, z. B. a mineral acid, also the pseudocumene in the presence of the initiating 30 obtained above and the water formed during the dehydration by means of or not as an initiating agent distilled off However, the filtrate of the dehydration reaction remaining in the hyde and aldehyde acids polymerize and contaminate the trimellitic anhydride. Trimellitic anhydride in a manner known per se 35 The object of the invention is therefore to provide a process for the preparation of trimellitic anhydride, which is purified by fractional distillation 2. The method according to claim 1, characterized by creating of pseudocumene, the one the technical draws attention to the fact that the purest possible adherence is obtained from that which corresponds to the requirements of the oxidation To deliver the crude mixture before the addition of the drid with a high yield allows pseudocumene about 50 percent of the used. Acetic acid is used as initiation and water of reaction is distilled off by means or promoters of the oxidation reaction Products of the incomplete oxidation of pseudocumene, as far as this is mainly aldehydes and aldehydic acids are returned to the oxidation stage, which among other things increases the degree of conversion of the Pseudocumols result. The invention relates to the process described in the claims at the same time as obtaining the promoters defined subject. used Voroxidate will also solve the problem of The oxidation of methylbenzenes with air is solved by separating the crude trimellitic acid. B. 50 one from the crude oxidation solution first the oxidation at 100 to 320 ° C in acetic acid in water and part of the reaction medium serving z. B. of cobalt acetate as a catalyst and acetic acid and then by adding in the presence of an initiating agent or promoter, pseudocumene to the residue at below 100 ⁰ C the t. B. of benzoyl peroxide, acetaldehyde or methyl trimellitic acid together with other Polycarbonsäuithylketon, carried out When the oxidation of 55 ren, especially dicarboxylic acids, fails. The lead-pseudocumene which results under these reaction conditions contains the or represents the initiation, however, one mainly represents mixtures of the isomeric agents for the oxidation. Dimethylbenzoic acids. The separation into trimellitic acid and dicarboxylic acid According to US Pat. No. 2,833,816, Trimel is on the one hand and in aldehydes, aldehydic acids as well lithic acid by oxidation of pseudocumene with air in 60 monocarboxylic acids, on the other hand, can be obtained by a Acetic acid at 50 to 275 ° C using a careful washout of the crystals of the polycarbonate catalyst system, which heavy metal and bromine acids with pseudocumene taken particularly far as an initiator (promoter) are produced. The use of pseudocumene for Unlike the process of US patent leaching, there was an improvement in yield 45 528 this results in a thorough oxidation of the 65 of trimellitic acid. Reaching methyl groups; Disadvantages of this method are due to the separation of aldehyde products with but only a low yield of trimellitic acid in the mother liquors before the introduction of the polycarboxylic acids the fact that the reaction medium because of ren in the dehydration is simultaneously the formation