DE1062387B - Process for the preparation of used rain and wash baths - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

INTERNAT. KL. D Ol f

PATENT OFFICE

C 0 8 L 33/20

EXPLAINING EDITORIAL 1062 387 ANMEtDETAG:

C7095IVc / 29b

FEBRUARY 4, 1953

NOTICE THE REGISTRATION AND ISSUE OF THE EDITORIAL: JULY 30, 1959

The invention relates to a method for processing used precipitation and washing baths, such as when shaping solutions of acrylonitrile polymer in dimethylacetamide and acetic acid incurred in precipitation baths made of water and dimethylacetamide. This procedure is characterized by that the excess of the precipitation medium is fed to a recovery stage in which the Water removed by distillation and the λίκ ^ ΐιυΐ ^ separated from dimethylacetamide and the acetic acid formed therefrom by hydrolysis and so much Acetic acid is removed from the mixture that when the mixture is used to make fresher Polymerisatlösung the concentration of acetic acid in the solvent mixture within a range is constant from 1 to 4%.

In the manufacture of molded articles from polymeric materials containing acrylonitrile, it is customary that acrylonitrile polymer in a solvent such as N.N-dimethylacetamide. to solve. The structures are created by the fact that the solution of the polymer in an evaporating Atmosphere, such as nitrogen or the like, or in a precipitation bath is squeezed out, which is from water, or from water, which a certain amount of solvent contains, ordered. The precipitated bodies thus obtained are then washed to remove the residual solvent to remove.

In every technical process, such as in the production of threads from in N, N-dimethylacetamide dissolved acrylonitrile polymer, it is expedient to remove the N, N-dimethylacetamide from the aqueous Solutions as they are obtained in the precipitation and / or washing process to recover and to use it again for the production of additional spinning solutions of the polymer.

It has now been found that aqueous solutions of Ν, Ν-dimethvlacetamide during this process hydrolyze to some extent by distillation, thereby adding acetic acid and dimethylamine form which, according to the teachings of the prior art, must be removed. That distance required heretofore added expensive equipment and generally increases the cost of solvent recovery.

Acrylonitrile polymer can be dissolved in N, I \ ^T -dimethylacetamide and acetic acid, the latter must be in such a proportion as it is to be maintained in the system during the process, namely from 1 to 4 percent by weight and preferably from 2 to 4% in the solvent. The solution produced in this way is pressed out through a spinneret and processed by evaporation or in a precipitation bath, the water and N, N-Di process
used felling and washing baths

IO

Applicant:

The Chemstrand Corporation,
Decatur, Ala. (V. St. A.)

Representative: Dr. E. Wiegand, Munich 15,
and Dipl.-Ing. W. Niemann, Hamburg 1, Ballindamm 26, patent attorneys

Claimed priority:
V. St. v. America 6 February 1952

Roy William Sudhoff, Decatur, Ala. (V. St. A.),
has been named as the inventor

contains metliylacetamide, like. The threads will

then washed with water to remove the residual solvent. The overflow from the Precipitation bath or the aqueous solution obtained by washing the structures or the gases from the dry spitin process is obtained is through a return

extraction system passed through. In some cases of dry spinning processes, there is a washing of the structures not necessary, and in this case the scrubbing liquid becomes the excess precipitating gases alone passed through the recovery system. The felling

and wash baths, which consist of solvent and water, are in the recovery system then subjected to distillation, the water being distilled off and the distillate, which is N, N-dimethylacetamide and acetic acid, in the process

is recycled to produce additional dope. The acetic acid is used during the Distillation formed by hydrolysis of the N, N-dimethylacetamide, with the exception of the small amount, which was added at the start of the process.

The water that was separated during the distillation in the recovery process is reversing back to the washing system or precipitation bath. A small amount of dimethylamine, which during the Distillation is formed before or with the

Water is distilled off, but most of the Dimethylamine is due to volatilization during the Wash level lost.

In order to keep the predetermined amount of acetic acid constant in the system, a portion of the solvent coming out of the recovery system is taken out and the acetic acid is removed therefrom. The acetic acid-free N, N-dimethlylacetamide thus obtained is reintroduced into the system and the correct acetic acid balance is thereby maintained. In this way only a small part of the N, \ ^T -dimethylacetamide needs to be treated in such a way that all acetic acid is removed from it. Heretofore, it has been considered necessary to treat all of the solvent to remove the acetic acid therefrom, as it was previously believed in the art that the presence of acetic acid was unfavorable for the production of satisfactory filaments and the like. Alternatively, if desired, only a portion or a portion of the acetic acid can be removed from all of the solvent in order to maintain the predetermined acetic acid balance.

Since the hydrolysis of the N, N-dimethylacetamide in normal processes for making molded articles from acrylonitrile polymers cannot be prevented, is therefore the present of acetic acid in such spinning solutions is unavoidable. For creating useful structures from solutions of acrylonitrile polymers in N.N-dimethylacetamide the dimethylacetamide must contain controlled amounts of acetic acid. The acetic acid concentration in the solvent mixture is in a range of 1 to 4 weight percent and preferably Keep 2 to 4 percent by weight.

The method according to the invention for reprocessing used precipitation and washing baths is described below described with reference to the drawing, which schematically shows the path of the precipitation and washing baths.

In this drawing, the tank in which the polymer is dissolved is denoted by 10.

The polymer is added to the tank 10 by suitable means 41, e.g. B. a feed screw added. Additional acetic acid-free solvent is in the tank 10 through the line 42 from the Storage tank 43 added to compensate for the loss due to leaky pumps or evaporation. Any suitable automatic liquid meters may be attached to line 42 adjusted so that the correct amount of acetic acid-free solvent is added to the system will.

A pipe or line 11 is provided to transfer the spinning solution into the storage tank 12, from which it is removed by a pump 14 to the spinneret 16 through the pipeline 15. the The spinneret is immersed in a precipitation bath 17, which consists of 50% water and 50% N.N-dimethylacetamide consists. The water and N.N-dimethylacetamide can e.g. B. each vary from 20 to 80%.

The precipitated threads 3 then go under the guide roller 18, which is immersed in the felling bath 17 via the guide roller 19 to the washing chamber 21, in which the threads with a stream of warm water, which preferably flows in countercurrent, are brought into contact. It is recommended to wash water to be used at temperatures of approximately 50 ° C to boiling point. The water becomes the Washing chamber supplied by means of a pipe or a pipe 22. The threads then go over one

Guide roller 24 to a drying drum 25 and they ννίξτ- "' j. The finished in the usual way. * 4k **'' ^s

The washing water containing Ν, Ν-dimethylacetamide washed off the threads 3 leaves the washing chamber 21 through the line 26 and goes to the still 27 where it is concentrated to a content of 30 to 50% solvent. The enriched solvent leaves the still 27 through the line 28. The water separated off in the still is returned to the washing chamber 21 from the top of the column through the pipe 22b, which is connected to the water supply pipe 22. A part of the washing water removed from the washing chamber 21 goes through the pipe 22a to the spinning bath 17 to dilute the same since the Ν, Ν-dimethylacetamide is continuously introduced into the bath through the spinneret.

The overflow from the precipitation bath 17, which contains approximately 60% solvent, flows through the line 30 to the still 31. The pre-distilled water-solvent mixture, which comes from the washing water and which flows through the pipe 28, is added to the excess spinning bath 32 combined, the mixed solution then goes into the still 31. This is operated at such a pressure and such a temperature that the liquid at the bottom of the still, which leaves this through line 33, is essentially anhydrous. On the bottom of the still 31 Ν, Ν-dimethylacetamide and acetic acid, which were formed by hydrolysis in the stills 27 and 31, collect. The water is taken off at the top of the still 31 and goes through the lines 22b and 22 to the washing chamber 21.

As stated earlier, it is necessary to remove the acetic acid from part of the liquid at the bottom the still 31 to remove. This liquid in the lower part of the bladder 31 consists of recovered Solvent and acetic acid, which in the stills by hydrolysis of the N, N-dimethylacetamide was formed. This is done by drawing the liquid from the bottom of the still through line 33 to a treatment tank 34 leads and from there through the line 34a to the still35. From the still 35 goes the acetic acid-free Ν, Ν-dimethylacetamide through the pipe 40 to the tank 10, in which the spinning solution is mixed. A pipeline 330 connects the lines 33 and 40 and has a valve 38. In addition, there should be a valve 36 in line 33 and a valve 37 in line 40. With the appropriate Adjustment of the valves 36, 37 and 38 is only a small predetermined proportion of the liquid from Bottom of the still through tank 34 and still 35.

In the tank 34 the liquid from the bottom of the still is treated with sodium hydroxide, to neutralize them and then the neutralized mixture in the pot 35 is distilled. The amount the solvent mixture which periodically passes through tank 34 and still 35 and acetic acid must be removed to the predetermined desired concentration of acetic acid Maintaining in Ν, Ν-dimethylacetamide is compared to the total amount of solvent, which per unit of time through the recovery system goes through, relatively small. The ratio of hydrolysis is in a system which, Applying two stills as shown, approximately

Claims (2)

0.05% per pass. Based on the production of about 1588 kg of threads per hour and while maintaining an acetic acid concentration of 2%, as in the present example, and based on a hydrolysis ratio of approximately 0.05%, about 9400 kg of solvent mixture per hour pass through the recovery system. About 160 kg or approximately 1.7% of this is chemically treated in the tank 34 and distilled in the bladder 35. In order to keep the acetic acid concentration in the system in a range of 1 to 4 percent by weight, it is only necessary when working according to the invention to treat approximately 0.5 to 50A) of the total recovered solvent in the vessels 34 and 35 in order to remove the acetic acid therefrom remove. It has further been found that the ratio of hydrolysis varies from 0.03 to 0.06% depending on the number of stills used. It is wildly noted that optionally only one or more than two stills can be used for solvent recovery, if so desired. As another embodiment, the neutralization step can be omitted and the mixture of N, N-dimethylacetamide and acetic acid can be distilled. The boiling point of N, N-dimethylacetamide is approximately 4 ° C different from the boiling point of the azeotropic mixture of acetic acid and N, \ T-dimethyl acetamide. It is, however, because of the small volume of the mixtures which must be distilled in the process of the invention; a distillation practically. PvT 1 ·. N TAXSl1R I 'CHE: 1. Process for reprocessing used: Precipitation and washing baths, such as those used in deforming | of solutions of acrylonitrile polymer in dimethylacetamide and acetic acid in precipitation baths obtained from water and dimethylacetamide, characterized in that the excess des Precipitation medium is fed to a recovery stage in which the water is distilled removed and the mixture of dimethylacetamide and the acetic acid formed therefrom by hydrolysis separated and so much acetic acid is removed from the mixture that the concentration the acetic acid in the solvent mixture is constant within a range of 1 to 4%. 2. The method according to claim 1, characterized in that the acetic acid by neutralization the mixture is removed with an alkali and that the neutralized mixture is then distilled will. Older patents considered: German Patent No. 1 034 812. 1 sheet of drawings © 909 579/420 7.