DD300426A5 - PROCESS FOR RECOVERING N, N-DIMETHYLACETAMIDE - Google Patents

Abstract

The process is used in the plastics industry for the recovery of N, N-dimethylacetamide from aqueous solutions by extraction. The object of the invention is the cost and energiegüstigen recovery of anhydrous N, N-dimethylacetamide from aqueous solutions. The object of the invention is to provide a process for the recovery of N, N-dimethylacetamide from aqueous solutions by extraction, which makes it possible to recover the N, N-dimethylacetamide with a high yield and purity by using specific organic compounds and dichloromethane as the extraction agent. The present invention provides a process for the recovery of N, N-dimethylacetamide from aqueous solutions by extraction in which dichloromethane as extractant in the presence of a substituted nitrogen compound, such as amine derivatives, amides or nitrogen-containing ring compounds of at least 10% based on the N, N Dimethylacetamide is used. Hexamethylphosphorsaeuretriamid is preferably used as a substituted nitrogen compound.

Description

Field of application of the invention

The invention relates to a process for the recovery of Ν, Ν-dimethylacetamide from aqueous solutions by extraction, which is used in the chemical industry, especially in the plastics industry.

Characteristic of the known state of the art

Anhydrous Ν, Ν-dimethylacetamide is known as a solvent for a number of substances, especially polymers, so it is also used in the production and processing of aromatic polyamides to films and fibers as a solvent, wherein Ν, Ν-dimethylacetamide-containing aqueous waste liquors arise The recovery and re-use of N, N-dimethylacetamide from these aqueous solutions over several separation and purification stages is of great economic and ecological importance, since Ν, Ν-dimethylacetamide is expensive on the one hand and harmful to health on the other hand. Limit concentrations of 0, 4 mg Ν, Ν-dimethylacetamide per 1 liter of wastewater.

It is known from / 1 / that Ν, Ν-dimethylacetamide can be extracted from a NN-dimethylacetamide / LiCl / water mixture with the aid of isobutanol. The distribution coefficient was found to be 0.9. A disadvantage of this method, however, is that isobutanol has a high boiling point (108 ⁰ C), whereby the distillative separation of the extraction of M, Ν-dimethylacetamide is difficult

In order to eliminate the disadvantages of the separation by distillation, an extraction of Ν, Ν-dimethylacetamide from aqueous solution has been proposed by / 2 / and in PS SU 811144, wherein as extractant of 121 chloroform and in PS SU 811144 a mixture of chloroform and Ether (1 5 to 1.7) are used in the presence of Na ₂ SO ₄ .

In the above proposals, the salting-out effect is used by using inorganic salts to improve the distribution coefficient

For example, according to / 2 / and PS SU 811144 Na ₂ SO _{4 are used} in a concentration of 178 g Na ₂ SO ₄ per 1 liter of aqueous solution. The extraction efficiency increases from 8% to 30% due to this salting-out effect.

It has been found that removal of the not inconsiderable amount of sodium sulfate is difficult in this process. It has been found that extraction with chloroform as extractant without the addition of inorganic salts brings about a non-economic distribution coefficient

When working with chloroform, special precautions must be taken

Object of the invention

The object of the invention is the cost and energy-favorable recovery of anhydrous Ν, Ν-dimethylacetamide from aqueous solutions, which is suitable as a solvent for the preparation of aromatic polyamides.

Explanation of the essence of the invention

The invention has for its object to provide a process for the recovery of Ν, Ν-dimethylacetamide from aqueous solutions by extraction, which allows by the use of special organic compounds and dichloromethyl as the extraction agent, the Ν, Ν-dimethylacetamide with a high yield and purity According to the invention, the object was achieved by a process for the recovery of Ν, Ν-dimethylacetamide from aqueous solutions by extraction in which aliphatic chlorinated hydrocarbons are used as extraction agent, characterized in that dichloromethane as the extraction agent in the presence of a substituted nitrogen compound of at least 10% with respect to N, N-dimethylacetamide As a substituted nitrogen compound, amine derivatives, amides or nitrogen-containing ring compounds are used. Preferably, hexamethylenephosphoric triamide is used as the substituted nitrogen compound.

Surprisingly, it was found that in the extraction of Ν, Ν-dimethylacetamide from aqueous solutions using dichloromethane as the extraction agent by adding a substituted nitrogen compound to Ν, Ν-dimethylacetamide / water mixture, the distribution ratio of Ν, Ν-dimethylacetamide in favor of organic Phase improves this

Effect is greater, the more voluminous the substituents are. The adjacent C = O group in amides has no influence. It is also possible to use nitrogen-containing ring compounds.

The use of partially substituted nitrogen compounds is also possible; However, these do not show the great effect as the fully substituted nitrogen compounds.

The chlorinated hydrocarbon as extractant can be very easily separated by distillation due to the high vapor pressure. The resulting in this extraction process solvent mixture Ν, Ν-dimethylacetamide / substituted nitrogen compound can be separated by simple vacuum distillation.

The recovered N, N-dimethylacetamide is pure by gas chromatography. The solution according to the invention prevents impurities from being carried into the N, N-dimethylacetamide by a salt addition which is otherwise customary due to the salting-out effect.

The substituted nitrogen compound is also recovered purely by gas chromatography and can be used again.

Reuse of the reclaimed solvents did not detect any disturbances in the reaction kinetics.

The proportion of Ν, Ν-dimethylacetamide in the residual water after a continuous extraction is 0.17%.

Hexamethylphosphoric triamide was no longer detectable by gas chromatography in the residual water.

Exemplary of the substituted nitrogen compounds according to the invention are the following representatives:

for aminic compounds triethylamine,

for amides, hexamethylphosphoric triamide and

for heterocyclic nitrogen compounds, N-methylpyrrolidone and N-acetylcaprolactam. Compared with the known technical solutions, the solution according to the invention has the following advantages:

The solution according to the invention is simple and energy-efficient feasible. The Ν, Ν-dimethylacetamide can be recovered from the aqueous solution with a large yield. It can be easily separated from the substituted nitrogen compound and recovered in such purity that it can be reused for polymer production. The water content can be lowered below 0.05% by the process of the present invention, and the substituted nitrogen compound can also be almost completely recovered and reused.

embodiment

The invention will be explained in more detail below in the following embodiments.

example 1

10 g of Ν, Ν-dimethylacetamide were mixed with 50 g of water and shaken out with 50 g of dichloromethane for 3 minutes in a 500 ml separating funnel. The amount of Ν, Ν-dimethylacetamide in the organic and in the aqueous phase was determined gravimetrically.

For a simple extraction of Ν, Ν-dimethylacetamide from aqueous solution without the addition of a substituted nitrogen compound, a distribution coefficient of K = 0.085 was determined.

For the distribution coefficient K: K = Co / Cw,

where: Co - weight concentration of the substance X to be extracted in dichloromethane fgX / g dichloromethane]

C _w - equilibrium concentration of the substance X to be extracted in water [g X / g H ₂ O].

Example 2

A mixture of a total of 10 g of Ν, Ν-dimethylacetamide (A) and hexamethylphosphoric triamide (B) in 50 g of water was prepared and shaken with 50 g of dichloromethane for 3 minutes in a 500 ml separating funnel.

The ratio of A to B was changed as follows:

9.5: 0.5; 9: 1; 8.8: 1.2; 8.5: 1.5; 8: 2; 7.5: 2.5; 6: 4; 5: 5; 2: 8 and 1: 9.

The determined distribution coefficients for the mixture of A and B in total and for Ν, Ν-dimethylacetamide (A) are given in Table I.

The distribution coefficient for hexamethylphosphoric triamide is 0.90.

Table I: K A + B ka FROM 0.23 0.22 9.5: 0.5 0.36 0.32 9: 1 0.37 0.33 8.8: 1.2 0.42 0.36 8.5: 1.5 0.43 0.35 8: 2 0.44 0.32 7.5: 2.5 0.57 0.38 6: 4 0.67 0.54 5: 5 1.07 2.52 2: 8 1.08 10.69 1: 9

Example 3

A mixture of a total of 10 g of Ν, Ν-dimethylacetamide (A) and triethylamine (C) in 50 g of water was prepared and shaken with 50g of dichloromethane in a 500 ml separating funnel for 3 minutes. The ratio of A to C was changed as follows

7,5 2,5,5 5 and 2,5,7,5

The distribution coefficients determined for the mixture of A and C in total and for A are given in Tables. The distribution coefficient for methylamine is 33.0

Table II Кд + с ka A C 0.86 0.39 7.5 2.5 1.63 0.41 5 5 4.37 0.65 2.5 7.5

Example 4:

The procedure was as in Example 3, except that instead of triethylamine N-Methylpyrrohdon (-2) or N-acetylcaprolactam were used The determined distribution coefficients are given in Table III.

Table III AY Ka + y ka Κγ Y = N-methylpyrrohdone (-2) 7.5 2.5 5 5 2.5 7.6 0.33 0.44 0.46 0.29 0.41 0.42 0.45 0.45 0.45 Y = N-acetyl caprolactam 7.5 2.5 5 5 2.5 7.5 0.56 1.12 2.70 0.30 0.32 0.48 35.2 35.2 35.2

Example 5

16 g of Ν, Ν-dimethylacetamine were mixed with 60 g of hexamethylphosphoric triamide and 400 g of water and placed in a continuous perforator for specific heavier extractants and extracted with dichloromethane. After 3,4,5,6 and 7 hours, a sample was taken from the aqueous phase and the content of N, N-dimethylacetamide and hexamethylphosphoric triamide is determined by gas chromatography (see Table IV)

Table IV N, N-dimethylacetamide hexamethylphosphoric Time sauretriamid m [g] m [g] [H] 16 60 0 5.90 7.15 3 4.10 2.90 4 2.40 0.95 5 1.35 not detectable 6 0.90 not detectable 7

Claims (3)

1. A process for the recovery of Ν, Ν-dimethylacetamide from aqueous solutions by extraction, in which aliphatic chlorinated hydrocarbons are used as the extraction agent, characterized in that dichloromethane as extractant in the presence of a substituted nitrogen compound of at least 10%, based on Ν, Ν- Dimethylacetamide, is used. 2. The method according to item 1, characterized in that are used as a substituted compound amine derivatives, amides or nitrogen-containing ring compounds. 3. The method according to item 1 and 2, characterized in that is used as the substituted nitrogen compound Hexamethylphosphorsauretriamid.