DE2124329C3 - Process for the preparation of alkali salts of ambiopolycarboxylic acids - Google Patents

Description

The invention relates to an improved process for the preparation of low-by-product alkali salts of aminopolycarboxylic acids, which is based on the reaction of alkali cyanides, formaldehyde and ammonia or amines.

The aminopolycarboxylic acids which can be prepared by alkaline condensation of the starting substances mentioned are important as complexing agents. In the alkaline mode of representation, 1 mole of free ammonia is produced from the cyanide per mole. In the preparation of the simplest representative, nitrilotriacetic acid or its alkali salt, in which ammonia is initially introduced as the reactant, ² mol of ammonia are released per mole of cyanide.

The problem has always arisen that, due to the excess of ammonia, more nitrogenous substances have arisen By-products were formed. In the production of nitrilotriacetic acid z. B. Glycine and iminodiacetic acid in varying amounts. Originated from the higher aminopolycarboxylic acids corresponding by-products.

This disadvantage has generally been attempted, as described in numerous patents, thereby to remedy that the ammonia formed in the reaction at the moment of formation from the Reaction mixture removed.

In the production of tetraalkali metal salts of ethylenediaminetetraacetic acid z. B. after the Method of German patent 10 83 829 such proceeded that one adds formaldehyde as the last of the reaction components and at the same time the any ammonia produced is continuously removed.

The ammonia was generally removed in such a way that the Reaction system blown air through it, or else that one worked first under positive pressure and then lowered the pressure with further addition of the starting components.

Another disadvantage arises from the fact that other by-products often occur during the condensation reaction emerged, which made themselves noticeable in a more or less strong discoloration of the reaction product.

In more recent methods one tried to counteract this problem by the fact that the ammonia through Blowing distant air, while at the same time,

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65 due to the oxygen contained in the air, the colored by-products were oxidized and thereby lightened. When air is blown through, however, the reaction system is still under such a high ammonia pressure, ie the concentration of ammonia is so high that the formation of the nitrogen-rich by-products mentioned above cannot be suppressed to a sufficient extent. This applies both to the production of nitrilotriacetic acid and to the production of the higher aminopolycarboxylic acids, the production of which is based on the reaction of alkali metal cyanide and formaldehyde

The task was to develop a production method that would allow the purest possible alkali salts to obtain such aminopolycarboxylic acids, which should firstly be obtained in as colorless a form as possible and Second, the content of pure aminopolycarboxylic acid alkali salts should be as high as possible, without too high a proportion of the nitrogen-rich by-products mentioned.

The solution to this problem is achieved with a process for the production of alkali salts Aminopolycarboxylic acids from alkali metal cyanide, formaldehyde and ammonia or the corresponding amines, wherein the ammonia formed during the reaction is continuously removed from the reaction mixture and the reaction system is under the action of oxygen-containing gases, and that as a result is marked. that during the process air under the reduced pressure of approx. 200 to 500 mm Hg sucked through.

This combination of two measures known per se produces the unexpected technical effect achieved that with ongoing removal of the ammonia formed from the system, namely by reduced pressure with sufficient oxygen supply at the same time, the content of by-products is very high kept low and the colored impurities can be removed by oxidation. Associated with it an improvement in the yield of ethylenediaminetetraacetic acid tetrasodium salt by up to 17% and a strong reduction in hygroscopicity.

From German patent 8 37 999 it is known that ammonia produced in the reaction is in a process for the preparation of alkali salts of nitrilotriacetic acid also under reduced pressure remove. But as this patent teaches, the removal of the ammonia takes place at a reduced rate Pressure by distillation. No air is sucked through here, just care supported that the gases present in the reaction system are removed more quickly. But this causes the our task underlying effect of decolorizing the colored ones present in small quantities By-products due to the depletion of the system in oxygen do not appear, but this discoloration must be removed afterwards.

The alkali metal salts of aminopolycarboxylic acids accessible by the process according to the invention are, for. B. those of nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid and N-hydroxyethylethylenediamine triacetic acid.

In the case of the alkaline condensation for the production of aminopolycarboxylic acids, alkali salts are followed the prior art generally so that aqueous ammonia or aqueous dissolved polyamines and the calculated amounts of alkali metal cyanide (preferably

Sodium cyanide) in the form of, for example, 20 to 40 percent solutions and formaldehyde solution (e.g. in the commercial form as a 40 percent solution) at approx. 60 to 100, preferably 80 to 90 ° C, inflicts. During the first batch, this may be done under pressure and then the ammonia is removed after releasing the pressure by blowing air through it

This principle of operation, which is known in principle, is now modified according to the invention in such a way that air is sucked through while using an apparatus that allows the setting of a negative pressure of 200 to 500 Torr allowed

In the case of the production of e.g. B. Ethylenediaminetetraacetic acid tetrasodium salt you put ethylenediamine and water in the reaction vessel and are at the same time Alkali metal cyanide solution and formaldehyde solution of the above concentration at those given above Temperatures too. Here, air is sucked through the solution during the entire process, with the pressures according to the invention must prevail in the system.

The process products obtained with the procedure according to the invention are distinguished from the obtained so far by a very low content of by-products and are also almost colorless.

The following examples illustrate the invention without to limit them to the production of the listed compounds.

Table 1

Composition of dry sodium nitrilotriacetate, obtained after the previous and after manufacturing method according to the invention.

Components

Example IA (previous driving style)
Manufacture of sodium nitrilotriacetate

720 liters of 25 percent ammonia solution and 430 liters of water are placed in a stirred kettle. At 80 to 85 ° C, 2360 kg of 30 percent sodium cyanide solution are pumped in 6 times and then 1258 kg of 40 percent formaldehyde solution are metered in 6 times over the course of 2 hours, a pressure of 0.5 to 2 atmospheres being established. Then the boiler is depressurized. Now 3 batches of sodium cyanide and formaldehyde are fed in without pressure, with about 300 m ^{3 of} air being blown per hour at the same time. 26,000 kg of cyanide-free solution with a color number of approx. 250 APHA are obtained.

Previous invention

Working method according to

Way of working

ίο sodium nitrilotriacetate approx. 80% approx. 85%

Sodium glycinate 1.4% 0.2%

Sodium iminodiacetate approx. 3% approx. 0.3%

Water (according to Karl 5.5% 5.5%

Fisherman)

Sodium glycolate
Sodium formate
Sodium oxalate approx. 9% remainder approx. 9%

sodium
Hexamethylenetetramine

Example 2 A (previous mode of operation)

Production of ethylenediaminetetraacetic acid tetrasodium salt

1200 kg of alylenediamine and 760 kg of water are placed in a stirred kettle at 85 ° C., while 100 m ^{3 of} air are passed through, 12,700 kg of 30 percent sodium cyanide solution and 5800 kg of 40 percent formaldehyde solution are added in 5 batches, one after the other. It takes about 35 hours in total. This gives 15,600 kg of cyanide-free solution with a color number of 100 APHA. Using potentiometric titrations, the following total analysis of the solution is calculated:

Example IB ^- (procedure according to the invention)

720 liters of 25 percent ammonia solution and 430 liters of water are placed in a stirred kettle. At a temperature of 80 to 85 ° C., 10 100 kg of 30 percent sodium cyanide solution and 4700 kg of 40 percent formaldehyde solution are now metered in simultaneously over a period of 16 hours; the pressure rises to 1.7 to 1.8 atmospheres. The pressure is then released and the ^{air is blown with about 300 m 3 of} air per hour for 2 hours. The boiler is then evacuated to 350 Torr. Now, at this vacuum and 80 to 85 ° C., a further 2700 kg of 30 percent sodium cyanide solution and 1250 kg of 40 percent formaldehyde solution are metered in over the course of 7 hours. 15,350 kg of cyanide-free solution with a color number of 150 APHA are obtained.

The solutions obtained by both procedures were evaporated to dryness and the obtained powder analyzed The analysis values are compiled in the following table:

Ethylenediaminetetraacetic acid tetra- 36.5% sodium salt Ethylenediamine triacetic acid trisodium 1.9% salt Mitrilotriacetic acid trisodium salt 3.5% Residual complexing agent 3.4% water approx. 48% Hexamethylenetetramine Sodium oxalate Sodium glycolate 6.7% Sodium formate sodium

Example 2 B (procedure according to the invention)

1600 kg of ethylenediamine and 4000 kg of water are placed in a stirred kettle. With a pressure reduced to 350 Torr and simultaneous suction of approx. 20 m ^{3 of} air per hour at 85 ° C, 17,700 kg of 30 percent sodium cyanide solution and 8150 kg of 40 percent formaldehyde solution are metered in within 24 hours. 21,200 kg of cyanide-free solution with the color number less than 100 APHA are obtained. The following analysis values are found:

Ethylenediaminetetraacetic acid tetra- 44.4%
sodium salt

Ethylenediamine triacetic acid trinalrium salt 0.5%

Nitrilotriacetic acid trisodium salt 1.1%

Residual complexing agent 0.8%

Water 51.5%

Hexamethylenetetramine

Sodium glycolate

Sodium formate J. 1.7%

Sodium oxalate

sodium

The ethylenediaminetetraacetic acid tetrasodium salt solutions are vaporized from Example 2 A and 2 B to dryness, a powder is obtained with the following analyzes:

Table 2

a pressure reduced to about 350 torr 16,700 kg of 30 percent sodium cyanide solution and 7650 kg of 40 percent formaldehyde solution are metered in at the same time within 24 hours; about 20 m ^{3 of} air per hour are sucked through. 20,700 kg of cyanide-free solution with a color number of 70 to 80 APHA is obtained.

The following analysis data are found:

Components Previous Inventive Way of working appropriate Way of working Overall complex 87-88% 91-92% artist *) Ethylene diamine tetra 73-74% 90% acetic acid tetra sodium salt Ethylenediamine tri- 3-4% approx. 1% acetic acid- Trisodium salt Residual complexing agent 4-5% approx. 1.5% water 3-4% 3-4% Hexamethylenetetramine Sodium formate sodium 4.3% Sodium glycolate Sodium oxalate H2O absorption after 94% 53% 48 hours Increase in yield + 16.5% EDTA-Na "

*) Potentiometric with Fe ³⁺ on. the basis of the molecular weight of the tetrasodium salt (380).

Example 3 (procedure according to the invention)

Production of diethylenetriaminepentaacetic acid pentanalrium salt

Invention Previous appropriate Way of working Way of working Potentiometric 45.0% 41.3% Titration with FeCb Water (after Karl 53.0% 53.0% Fisherman) Content of water 95.6% 87.9% free powder

Example 4 (procedure according to the invention)

Manufacture of N-hydroxyethylethylenediamine
triacetic acid trinatrium salt

2920 kg of N-hydroxyethylethylenediamine and 2500 kg of water are placed in a stirred kettle. With a pressure reduced to 350 Torr and simultaneous suction of about 20 m ^{3 of} air per hour at 80 to 85 ° C within 24 hours, 14,860 kg of 30 percent sodium cyanide solution and 6850 kg of 40 percent formaldehyde solution are metered in at the same time. 21,800 kg of cyanide-free solution with a color number of approx. 150 APHA are obtained and the following analytical data are found:

Invention Previous
proper way of working

Way of working

1950 kg of diethylenetriamine and 2000 kg of water are placed in a stirred kettle. At 80 to 85 ⁰ C and

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Potentiometric 43.3% 40.2% Titration with FeCb Water (after Karl 52.8% 52.8% F i s c h e r) Content of the anhydrous 91.8% 85.0% Powder

Claims (1)

Claim: Process for the preparation of alkali salts of aminopolycarboxylic acids from alkali cyanide and formaldehyde and ammonia or the corresponding amines, the resulting in the reaction Ammonia is continuously removed from the reaction mixture and the reaction system under the Exposure to oxygen-containing gases, characterized in that one during of the process sucks air through under the reduced pressure of approx. 200 to 500 mm Hg