DE1618570C3 - Process for purifying adipic dinitrile - Google Patents

Description

The invention relates to a method for purifying crude adipic dinitrile.

Adiponitrile is produced in large quantities as an intermediate for the production of polyamide 66 (polyhexamethylene adipamide). It takes adipic dinitrile in a highly pure state to reduce it to pure hexamethylenediamine, which is one of the intermediates from which the polymer is directly made. Even very small amounts of impurities in the hexamethylenediamine have a profound effect on the properties of the polyamide made from it. Whether it is produced by dehydrating ammonium adipate (adipic acid and ammonia) or by reacting 1,4-dichlorobutene and sodium cyanide or by reductive dimerization of acrylonitrile or in some other way, crude adiponitrile can only be purified sufficiently with difficulty to be used as an intermediate for the production of Nylon to serve.

Crude adipic dinitrile produced by dehydrating ammonium adipate contains as Impurities

a) Products of incomplete implementation, such as B. cyan valeramide and cyan valeric acid and

b) decomposition products, such as. B. 2-Cyancyclopentylidenimine and pyrimidine derivatives.

The boiling points of some such impurities are so close to the boiling point of adipic acid dinitrile, that to achieve a good purification by fractional distillation either a multi-stage Must perform distillation or distillation columns with a large number of trays and high reflux ratios must apply.

It is known to use crude adipic dinitrile rather than through a fractional distillation through a fractional distillation Crystallization or cleaning with exchange resins.

It is also known that the imine present in the crude adiponitrile as an impurity before the Distillation to hydrolyze to a ketone. Another known method is the raw Adipic acid dinitrile with aqueous formaldehyde at high temperatures, e.g. B. at 100 ° C, treated to to convert certain impurities into water-soluble methylol compounds.

The invention now relates to a method for purifying adiponitrile by dewatering obtained from ammonium adipate by treatment with an aldehyde and water at a temperature within a range of ambient temperature to 50 ° C, characterized by is: that formaldehyde or acetaldehyde is used as aldehyde and the treatment in a pH of 1 to 6 in the presence of sulfate, nitrate, chloride, phosphate or p-toluenesulfonate anions and carried out by hydrogen ions.

Formaldehyde is preferably used as the aldehyde. The aldehyde is said to be used in such an amount be that it can react with the whole amount of the impurity to be separated. at Use of formaldehyde are mostly amounts of about 1 to 2 percent by weight of the impure Adipic acid dinitrile sufficient.

The amines from which the ammonium ions are derived are in particular primary or secondary Alkylamines, especially methylamine or dimethylamines, are suitable.

Of the anions of strong acids that should be present according to the invention, the sulfate and Nitrate ions to be preferred because they are cheap and not very corrosive than e.g. B. chloride ions.

The treatment with the aldehyde can expediently be carried out so that the impure Adipic dinitrile in a substantially water-insoluble solvent of low polarity, e.g. Am an aromatic hydrocarbon, such as toluene or benzene, is dissolved and that the solution with an aqueous solution is washed containing the aldehyde and anions and optionally cations of the type described above.

The treatment of the crude adiponitrile with the aldehyde according to the invention is as follows Effects:

1. Neutral heterocyclic impurities (e.g. pyrroles) react with the aldehyde and result in it Products obtained by washing with water, by filtration or as high-boiling stills can be separated. In the presence of ammonium cations, the products are mostly water-soluble; in the presence of hydrogen ions alone, the products are mostly solids or High molecular weight tars.

2. 2-Cyancyclopentylidenimine becomes 2-Cyancyclopentanone hydrolyzed, which can be more easily separated from adiponitrile by distillation can or preferably by subsequent alkaline leaching and subsequent washing removed with water.

3. Heterocyclic and other bases are dissolved in the aqueous liquid from adipic acid dinitrile severed.

According to a preferred embodiment, the adiponitrile is purified by having a Solution of the crude adipic dinitrile in a water-insoluble solvent of low polarity with the aldehyde and water at pH 1 to 3 in the presence of those described above Treated ions, after which one the non-aqueous

3 4

Phase separated, with an aqueous alkali solution. The distillate consists essentially of pure extracted and, if desired, washed with water adipic acid dinitrile, which does not contain any heterocyclic and then the solvent and finally the pure impurities and no 2-Cyanocyclopentylideniinin

Contains adipic acid dinitrile from high-boiling residues. ·

distilled off. 5 The products will be incomplete implementation

In this process, the aldehyde treatment can be carried out from the ammonia extract by evaporating the Development appropriate at ambient temperature, z. B. won water. If desired, this can be done in the 20 ° C, without external heating or cooling, adipic acid dinitrile dissolved in aqueous solution before the be guided. Contact times of 10 to 15 minutes, evaporation with fresh solvent to a large extent are sufficient at ambient temperature, which the ver io can be removed. The secondary drives separated in this way especially suitable for continuous work- products can be used together with fresh adipic acid th power. and ammonia to the adipic acid dinitrile reaction

As an aqueous alkali solution, a solution can be returned from the vessel and converted into adipic acid dinitrile.

Sodium hydroxide or ammonium hydroxide are seduced.

be turned. Subsequent washing with washing 15 According to this example, instead of 10 parts, one

water is favorable to the presence of alkali in 10 percent aqueous sulfuric acid solution too

to avoid distillation, but not necessarily 10 parts of an aqueous 10 percent solution of

necessary. The distillation at the end of the process nitric acid, hydrochloric acid, phosphoric acid or p-toluene

can be a fractional distillation to use small olsulfonic acid.

Quantities of low-boiling substances are removed ao,

be able; however, the use of costly e 1 s ρ 1 e i

Rectifiers not necessary. It will be 100 parts by dewatering

In any embodiment, the process can be carried out on adipic acid dinitrile produced on ammonium adipate,

the crude Adipinsäuredinitril, which by dehydration 10 parts of acetaldehyde and 10 parts of a 1 Oprozentigen

from ammonium adipate, aqueous sulfuric acid solution is applied together for 1 hour

den, however, it is advantageous if the crude product is stirred at room temperature. The aqueous layer

first with a weak aqueous solution of (pH value 1 to 1.5) is separated, and the organic

Ammonia in a concentration of e.g. B. about 1% niche layer is with 100 parts of a 1 percent

or an amine is extracted. In the crude gene aqueous sodium hydroxide solution and then with

Adipic acid dinitrile is often washed with sufficient 30 100 parts of water.

Amount of ammonia present that with simple The solvent is evaporated, whereupon the

Extract with water such an aqueous solution product is roughly distilled and which is at about 155 ° C /

arises. Through this treatment products are collected 10 torr boiling fraction,

incomplete reaction, e.g. B. cyanvaleramide and the distillate consists of adipic acid dinitrile, the

Cyanovaleric acid, removed; they can be recycled 35 no heterocyclic impurities and no

contain the total yield of adipic acid 2-cyanocyclopentylidenimine,

increase dinitrile. .

A preferred embodiment of the method Example 3

of the invention for the purification of impure adipin removal from heterocyclic compounds

Acid dinitrile therefore consists in the fact that one lo- 40 (which in by dehydrating ammonium adipate

solution thereof in a water-insoluble non-polar manufactured adipic acid dinitrile occurring type)

Solvent continuously with a weak than high-boiling derivative.

aqueous solution of ammonia extracted and the There are 100 parts of adiponitrile, which is about Products of incomplete reaction from the aqueous 500 parts per million of heterocyclic compounds Phase wins and the non-aqueous phase continuously contains 45 parts, with 1.5 parts of 85 percent phosphorus further acid and 1 part of a 37 percent aqueous form processed in the manner described above, aldehyde solution processed for 10 minutes at room temperature

The invention is described below on the basis of embodiment. The aqueous layer (pH about 2) is removed

management examples explained in more detail, the quantities separated, and the oily residue is 50 parts

information is based on weight. 50 water washed. The wet oil becomes anhydrous

_B. -Ii calcium chloride dried, and a sample (50 parts)

Example 1 is distilled under reduced pressure. The main

Adipinitrile (100 parts; by dehydration fraction (45 parts), boiling point 155 ° C / 10 Torr, is made from ammonium adipate) and toluene colorless and essentially free of heterocyclic (100 parts) are used to remove products 55 impurities and do not react with incomplete reaction with a dilute aqueous manganate in acid (extracted with a reaction time of 1 Mirigen ammonia solution. The organic ute at room temperature). The still residue layer is then 10 minutes at room temperature is dark brown,
with a mixture of 5 parts of a 35 percent example 4
aqueous formaldehyde solution and 10 parts of a 60

10 percent aqueous sulfuric acid solution is 100 parts by dehydrating

stirs. The aqueous layer (adipic acid dinitrile made with a pH of ammonium adipate

1 to 1.5) is separated and the organic layer and 100 parts of toluene to remove products

with 100 parts of a 5 percent aqueous sodium incomplete reaction with a dilute

hydroxide solution and then extracted with 100 parts of water 65 aqueous ammonia solution. The organic

to wash. The toluene is distilled off, and the oily layer is then mixed with a mixture of 5 parts

The residue is distilled, the fraction being that of a 35 percent aqueous formaldehyde solution

boiling at about 155 ° C / 10 torr, is collected. and 5 parts of a 10 percent aqueous am-

Stirred monium sulfate solution at 20 to 30 ° C for 20 minutes. The aqueous layer (pH 2) is separated and the organic layer with 100 parts of one 5 percent sodium hydroxide solution and then washed with 100 parts of water. The toluene is distilled off, and the oily residue is distilled, the fraction boiling at about 155 ° CV10 Torr is collected.

The distillate consists essentially of pure adiponitrile, which has no heterocyclic impurities and does not contain 2-cyanocyclopentylidenimine.

Example 5

Adipic acid dinitrile is treated as in Example 4, but continuously. The adipic acid dinitrile / Toluene mixture is extracted in countercurrent in a 3-stage rotary disk extraction column. the extracted toluene solution is then stirred with the aqueous formaldehyde solution and ammonium ao sulfate treated.

After the aqueous layer has been separated off, the Toluene solution in countercurrent initially with the aqueous Sodium hydroxide solution and then extracted with water in two further extraction columns. The »5 Main part of the toluene is continuously in a still under atmospheric pressure and the Remainder distilled off in another still under reduced pressure.

"The product is subjected to a short-path distillation, the residues being 3%. This gives adipic dinitrile, which is not heterocyclic Contains impurities and does not contain cyanimine.

Example 6

There are 100 parts of crude adipic acid dinitrile and 100 parts of toluene to remove incomplete reaction products with 100 parts of a 2 percent extracted aqueous ammonia solution and 100 parts of water.

Then a mixture of 5 parts of an aqueous 37prozentigen Fonnaldehydlösung and 10 parts is added one lOprozentigen Diäthylaminhydrochloridlösung, and the resulting mixture is stirred for 20 minutes at 20 to 30 ⁰ C.

The aqueous layer (pH 3) is separated off and the organic layer is extracted with 100 parts of a 2 percent aqueous sodium hydroxide solution and 100 parts of water. The toluene is distilled off 10 Torr whereupon the adiponitrile at 155 ⁰ C / is evaporated. The product is free from cyanimine and heterocyclic impurities.

Claims (3)

Patent claims: 1. Method of purifying adipic dinitrile obtained by dehydrating ammonium adipate obtained by treatment with an aldehyde and water at a temperature within a range from ambient temperature to 50 ° C, characterized in that that formaldehyde or acetaldehyde is used as aldehyde and the treatment in a pH of 1 to 6 in the presence of sulfate, nitrate, chloride, phosphate or p-toluenesulfonate anions and hydrogen ions is carried out. 2. The method according to claim 1, characterized in that when carrying out the method ammonium ions are also present. 3. The method according to claim 1, characterized in that the treatment at a pH value of 1 to 3 carries out.