US1376671A - Process of recovering salts formed in the manufacture of artificial silk - Google Patents

Description

UNITED STATES PATENT OFFICE.

EMILE BRONNER'I, OF MIILHAUSEN, ALSAGE-L ORRAINE, FRANCE.

PROCESS OF BECOVERING SALTS FORMED IN THE MANUFACTURE OF ARTIFICIAL Patented May 3, 1921.

' SILK.

1 37 71 Specification of Letters Patent.

No Drawing.

T 0 all whom it may concern:

Be it known that I, EMILE BRONNERT, a citizen of the Republic of France, residing at l Quai du Barrage, in Miilhausen, Alsace- Lorraine', France, have invented certain new and useful Improvements in Processes of Recovering Salts Formed in the Manufacture of Artificial Silk, of which the following is a specification.

This invention relates to the production of artificial silk and its object is to provide a process for the suitable recovery of a spinning bath from the salts formed by the spinning of viscose in sulfuric acid mixed with soluble sulfates.

It has already been proposed to recover the Glauber salt or sulfate of soda from the sulfuric acid baths used with admixture of salt for spinning, viscose. Practically this recovery has not yet been carried out in any artificial silk factory of the world, at least not to any considerable or useful extent; on the contrary the washing water containing the Glauber salt has all been allowed to run to waste and so far not utilized.

Recently, however, on again taking up the wholesale production of the special line of artificial silk known as staple fiber, the idea was again entertained of the utilization of the salts contained in the spinning baths, and a practical solution of the problem was sought.

Now it has been found that from the spinning baths properly so-called the sodium sulfate formed is recoverable with difficulty. For example, in spinning baths of strong salt content and the usual content of sulfuric acid exceeding the bisulfate proportion, almost e v'bole qu ntity of sodium sulfate forms-{l remains adherent to the threads arising from the ath with the usual speed of about 45 m. per minute.

A portion of the salt may undoubtedly be recovered by allowing its solution to drip off the spools or reels or by shaking it off the threads. The major portion, however, can only be recovered by subsequent lixiviation of the threads and the diluted wash water must then be steamed with the expenditure of coal and then caused to crystallize, sometimes by additional cooling. The salt thus crystallized outmust then be removed and be separated from the acid mother lye by lixiviation.

The free acid still present in the wash Application filed September 7, 1920. Serial No. 408,690.

water can be neutralized by the addition of caustic soda or soda, so as to permit ordina riy pans of iron or silicon iron to be used.

hen attempts were made to reduce the quantity of wash water by lixiviation of the raw, slightly acid thread masses with limited quantities of water and by repeated wash-.

ing with the same water. On using baths of strong salt content it was found that, upon the addition of 3 liters of water per hour, or the first wash water upon the masses of thread (about 3 kg. dry weight) a further enrichment is no longer possible after the wash water has been once used owing to the occurrence of a compensatory condition of about 18 to 20% sodium sulfate and 34% acid in the wash water and upon the thread. In cold weather the tendency for crystallization of the Glauber salt is also manifest in an unpleasant manner, namely by stopping up of the pipes. Finally care must be taken not to begin too soon with the use of the fresh threads as otherwise prior to the complete coagulation and neutralization of the soda the threads only stick or adhere together.

Now it has been found that there can be recovered from the thread masses a far greater quantity of salt if, at the beginning, not pure water but diluted sulfuric acid is used for the lixiviation, the content of the solution in acid being sufficient to change the sulfate contained-in the-threads into the much more easily soluble bisulfate. This does not choke the pipes. A 10 to 12% acid is preferable, but I am not bound to this concentration. The concentration must be adapted to the bath concentrations used at the time.

The greatest advantage, however, consists in the fact that the working up of these concentrated solutions is extremely simple and advantageous.

Consideration of the matter will show that it would be quite contrary to the purpose in view to attempt to produce Glauber salt,- either for sale or for reuse in the spinning bath by dissolving the Glauber salt in sulfuric acid. To render the Glauber salt in condition for sale a further purification would be necessary either by crystallizing or by filtration of the solutions for the removal of adherent quantities of sulfur from the spinning bath.

A quantity of fresh. sulfuric acid must always be suppliedto the existing bath, in

the same proportion .as this is weakened by the caustic soda from the viscose and furthermore sulfate as a substitute for that carried away must be added; thus the production of bisulfate or of a concentrated bisulfate solution, even also containing excess acid under certain circumstances, is the most suitable method of recuperation of the sodium sulfate formed upon the threads.

The corresponding sulfuric acid washing waters are concentrated in suitable manner, as, for example, in steam heated lead pans, in sulfuric acid concentrating towers, wherein hot gases of combustion meet the trickling bisulfate solution, or by means of other devices, in a state to be directly run back to the spinning bath, and used therein without other alteration of its concentration, as the concentrating in. the concentration apparatus may be carried out so as to reduce the a strength to the normal or standard used in the baths, or within permissible approximations of such standards.

The lixiviation of the thread masses and liberation as far as ossible from the washing liquid can be e ected according to the most varied processes, either in vats with circulating liquors and subsequent pressing v erable importance,

' salts formed.

formed in the spinning bath I otash arising possesses still more than lauber salt the unpleasant property of crystallizing. Hence when working with potash combinations the use of the processdescribed is ,preminently useful as potassium bisulfate is just as easily soluble. Because of the high commercial value of potash, the reduction in thepotashlosses is of consid- Magnesium and zinc salts, which often serve as an addition to spinning baths, do not effect my process for the recovery of the What I' claimis l 1. The process of recovering the salts formed in the manufacture of artificial silk consisting in lixiviating the threads with dilute sulfuric acid to convertthe salts into salts of a more soluble character.- V y 2. The process of recovering salts formed in sulfuric acid recipitation baths containing dissolvedsu fates used in the manufactureof artificial silk from viscose solutions, comprising lixiviating the threads in sulfuric acid solutionto convertthe sulfates formed in the precipitating bath into the -bisulfate.

In witness whereof I have hereunto si ned my name in the presence of two subscri. ing

wltnesses.

" 'ELHLEIBBONFNERT. 7 I