DE1018047B - Process for the production of terephthalic acid, its salts or other derivatives from potassium benzoate - Google Patents

Description

GERMAN

The subject of the main patent 958 920 is a process for the production of terephthalic acid by heating potassium benzoate to a temperature above 340 ° in the presence of carbon dioxide, optionally the potassium terephthalate initially obtained is converted into the free acid by known methods. According to the procedure of Additional patent 965 399 one obtains particularly good yields in this process if one does the heating in the presence of catalytically active metals, especially in the presence of cadmium, furthermore also of zinc, lead and mercury or of compounds of these metals. Except for carbon dioxide can also use other inert gases, e.g. B. nitrogen, serve as a protective gas.

It has now been found that it is possible to further improve the yields in this process and to obtain very good yields even without the use of pressure, ie even at normal pressure or even in vacuo, if one takes place in the presence of certain catalysts and in the presence of Alkali carbonates works and hereby adheres to certain proportions of the reactants. According to the invention, reaction mixtures are processed which contain at least 0.25 mole of cadmium fluoride per mole of benzoate, preferably potassium benzoate, and 1 mole of alkali metal carbonate, preferably potassium carbonate, per mole of cadmium fluoride, the latter being partially replaced by the equivalent amounts of alkali metal halide, in particular alkali metal chloride or alkali metal fluoride can (1 AIk ₂ CO ₃ = IAIk ₂ F ₂ = 2AIkCl; Alk = alkali metal cation). In general, larger amounts of catalyst are used, which are at least 0.35 mol, preferably 0.5 to 1 mol of cadmium fluoride per mol of benzoate. In special cases it is also possible to work with even larger amounts of catalyst. The cadmium can be completely or partially replaced by equivalent amounts of zinc.

The reaction mixture can also contain diluents, especially alkali halides, especially alkali chlorides and fluorides and alkali carbonates. The amount of diluent will be but generally do not exceed 50 percent by weight of the reaction mixture. In this crowd are the amounts of alkali halides and resp. or carbonates not included.

The reaction mixture accordingly contains at least the three components as necessary constituents. th: an alkali benzoate, a fluoride of the catalyst metal and alkali carbonate, partially by a Alkali halide can be replaced. Now these necessary ingredients don't necessarily need to be in shape

for the production of terephthalic acid,

their salts or other derivatives

from potassium benzoate

Addition to additional patent 965 390

Applicant:

Henkel & Cie. GmbH,
Düsseldorf-Holthausen, Henkelstr. 67

Dr. Hartwig Schutt, Hagen (Westphalia),

and Dr. Werner Stein, Düsseldorf-Holthausen,

have been named as inventors

the above-mentioned compounds to be introduced into the reaction mixture; those in the mentioned Cations and anions in compounds can represent each other, and you come to similar results if, for example, instead of the mixture:

2 AIkB + MeF ₂ + AIk ₂ CO ₃
the following mixtures are used:

2AIkB + MeCO ₃ + AIk ₂ F ₂

MeB ₀

AIk ₂ F ₂

AIk ₂ CO ₃

(Alk = alkali metal cation, preferably potassium ion, Me = zinc or cadmium, B = benzoic acid anion). Although the last two mixtures are composed of different compounds than the first mentioned Mixture, all mixtures have the same percentage composition. Instead of the alkaline infinite you can also use fluorides of other, non-catalytically active metals, z. B. the des Magnesium, calcium or other alkaline earths.

In general terms, the technical teaching according to the invention consists in the thermal To process the rearrangement of salt mixtures that contain the cations of alkali metals, especially potassium ions, and the cations of the catalytically active zinc or cadmium and the anions of benzoic acid, of fluorine and optionally other halogen anions and carbonate anions, wherein firstly, per mole of benzoate, at least 0.25 mole of cadmium and / or zinc ions and, secondly, per mole

709 757/327

of the catalytically active metal ion at least 2 equivalents of fluorine ions and at least 2 equivalents Carbonate ions are present, the carbonate ions partially, e.g. B. up to two thirds, preferably up to half, by the equivalent amount of halogen ions can be replaced. the Alkali ions can be partially replaced by ions of other, non-catalytically active metals, the amount of which is generally not substantially greater than 2 equivalents per mole of the catalytic effective metal. If the reaction mixture contains alkali halides or carbonates as diluents, then the amount of ions of catalytically inactive metals can be greater; but it is in the generally hardly exceed 1 equivalent of metal ion per equivalent of alkali ion.

The benzoate to be rearranged does not need to be used as such, it can also be used in the form its educational components are applied, e.g. B. in the form of mixtures of the free acid, its chloride or especially their anhydride with alkali carbonate.

It has been shown that particularly beneficial effects are achieved if the components of the Reaction mixture mixed together as evenly as possible. For this purpose one can use the ingredients of the reaction mixture individually in ball mills, vibrating mills, rotary mills or grind other devices finely, e.g. B. up to flour or dust fineness, and then carefully together Mix; but you can also first mix the constituents of the reaction mixture with one another and then grind the mixture. In many cases it is convenient to use the mixture of starting materials to react in as compact a state as possible. For this purpose one can through the mixture Compress pressure, sintering or other measures.

The constituents of the reaction mixture can also be in the form of aqueous solutions or slurries put them together and put them into one without taking account of any excretions that may occur Transfer dry product, which is done in conventional equipment, e.g. B. drum dryers, atomizers, etc., happen can, whereby it is advantageous to work towards a compact, coarse powder with a high bulk density. This powder can be ground and / or compacted before the reaction.

Otherwise the reaction is carried out as described in the earlier patents is. The reaction mixture is heated to a temperature between 300 ° and the decomposition temperature of the carboxylic acids present in the mixture Salts is, preferably at a temperature of 350 to 550 °. To prevent overheating of the reaction mixture on the wall of the reaction vessel avoid, thorough and thorough mixing is recommended. As with those described in the earlier patents A ^ experience, then here too the presence of inert gases, preferably carbon dioxide, furthermore hydrogen, nitrogen, methane, ethane, propane, butane, etc. are expedient. It also recommends to process the reaction batch in as anhydrous state as possible. The approach or its components are expediently processed in a well-dried state, which is the case with water of crystallization containing or hygroscopic starting materials is very important.

As far as the reactions described in the following examples were carried out under normal pressure were, the materials dried at about 100 to 120 ° ge 7 ° yield were in open vessels made of glass or metal that has been purged with inert gas from the start of heating to cooling. The mixture was heated to the stated temperature and during the stated time at this temperature left. After cooling, the reaction product was ground and the soluble fractions by treatment dissolved with hot water and the undissolved components filtered off. The filtrate became terephthalic acid precipitated by a mineral acid (hydrochloric acid or sulfuric acid) by washing with hot Water purified and dried. In the reaction product or in the aqueous solutions, if appropriate existing by-products (e.g. benzene, starting material or other newly formed carboxylic acids) were not isolated.

In the technical implementation of the process, it is not expedient to remove the terephthalic acid from the to deposit aqueous solutions of their alkali salts by mineral acids, as this removes the alkali ions, especially the valuable potassium ions, in one that cannot be reused for the process Shape. It is therefore advisable, as already suggested, to remove the terephthalic acid from the aqueous Solutions of their alkali salts, for example by means of carbon dioxide, preferably under pressure, in the form the sparingly soluble acidic alkali salts, in particular the monopotassium salt, to be deposited. The latter can one z. B. by heating in aqueous suspension into the sparingly soluble free acid and the soluble Transfer dialkali salt. It is also useful, the monoalkali salt by treatment with benzoic acid in to convert aqueous suspension in the heat into terephthalic acid and alkali metal benzoate. The latter can be dried and can be used as starting material for the process according to the invention. In the end you can also do without the carbon dioxide precipitation and the alkali terephthalate with the help of Convert benzoic acid into terephthalic acid, the reaction advantageously being carried out in several stages performs.

When carrying out those described in the examples. Experiments became the starting materials finely ground and mixed well together.

example 1

100 g potassium benzoate

43 g of potassium carbonate

47 g cadmium fluoride
Density of the mixture: 700 g / l for 2 hours at 420 ° at normal pressure

under carbon dioxide
34 g terephthalic acid (AN = 675)

Example 2

10.0 grams of potassium benzoate

4.3 g potassium carbonate

4.7 grams of cadmium fluoride
Density of the mixture 1100 g / l 6 hours at 410 ° under normal pressure and carbon dioxide
4.2 g terephthalic acid (AN = 676)

Example 3 *

100 g cadmium benzoate
39 g potassium carbonate
33 g potassium fluoride

4 hours at 420 ° under normal pressure and carbon dioxide

37 g of terephthalic acid

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Example 4

100 g of potassium benzoate

54 g cadmium carbonate

36 g potassium fluoride for 2 hours at 420 ° under normal

pressure and carbon dioxide 29 g terephthalic acid

Example 5

10 g zinc benzoate

4.5 g potassium carbonate

3.8 g of potassium fluoride in the reaction vessel by pulverizing

compacted for 1 hour at 420 ° under normal 15 reaction

pressure and carbon dioxide 1.8 g yield of terephthalic acid

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example

100 g potassium benzoate

47 g cadmium fluoride

40 g of sodium carbonate for 1 hour at 420 ° under normal pressure and carbon dioxide 36 g terephthalic acid (AN = 675)

example

100 g cadmium benzoate

22 g caleium fluoride

39 g potassium carbonate

1 hour at 420 ° 17 g of terephthalic acid

example

100 g cadmium benzoate

24 g sodium fluoride

39 g of potassium carbonate for 1 hour at 420 ° under normal pressure and carbon dioxide 22 g of terephthalic acid

Example 9

20 g cadmium benzoate

70 g zinc benzoate

66 g potassium fluoride

39 g potassium carbonate
1 hour at 420 ° under normal pressure

and in an open roller autoclave

Carbon Dio'Xyd
24 g of terephthalic acid

Example 10

100 g potassium benzoate

38 g potassium fluoride

41 g zinc carbonate
6 hours bed 410 ° under carbon

dioixyd at normal pressure
34 g of terephthalic acid

Claims (2)

Patent claims: 1. Further development of the process for the production of terephthalic acid, its salts or others Derivatives of potassium benzoate by heating to a temperature above 340 ° in the presence of alkali carbonates and / or of alkali halides, inert gases and catalytically active salts of cadmium or zinc according to patent 965 399, characterized in that mixtures are processed at normal pressure which a) per mole Benzoate at least 0.25 moles of cadmium or zinc ions and b) contain so much carbonate ions, that per mole of catalyst metal at least 2 equivalents of fluorine ions and at least 2 equivalents Carbonate ions are present, the carbonate ions partly by equivalent amounts of Halide ions can be replaced. 2. The method according to claim 1, characterized in that per mole of benzoate at least 0.35, preferably 0.5 to 1 mol of cadmium or zinc ions added. © 709 757/327 10.