US2462948A - Flotation process of clarifying regenerating baths - Google Patents

Description

Patented Mar. 1, 1949 UNITED STATES PATENT oFri'ce rtorarron rnocass or ctnmryme anennnm'rme BATHS Joseph. L. Costa, Woonsocket, and William Harlow Kaliler, Saylesville, It. I..- asslgnors, 'liy mesne assignments. to Woonsocket Rayon, Inc., a corporation of Delaware No Drawing. Application May 19, 1943,

Serial No. 487,840

6 Claims. 1

The present invention relates to improvements in the flotation process of clarifying regenerating baths used in the preparation of cellulosic articles of artificial origin. More specifically it has to do with carrying out of the process in the presence of a betaine in the regenerating bath.

The primary object of this invention is to provide a composition of regenerating medium which will allow an economical and eflicient application of the flotation process and which will be entirely free from deleterious eifects upon the extrusion step. The application of this invention to the viscose process will be described in detail in the following specification, but it will be'understood that the scope of the invention is intended to embrace any process of regener'atlngcellulosic solutions in which the regenerating medium, in general a liquid bath, becomes fouled with impurities or by-products inherent to the extrusion step, such as, for example, the cuprammonium process.

In accordance with the applicants invention the process of purifying the regenerating bath by flotation, which has been the subject of several United States Letters Patents, including Nos. 2,105,684 and 2,153,449, is carried out in the presence of an acid stable frothing agent, which compound is characterized by the following general formula:

resulting the loss of the ionizable H from concentrations particularly those containing acid.

The importance of this property will be shown resulting from the loss of the ionizable H'- from the sulfonic acid group in consequence of the neutralization of the latter upon the nitrogen a om.

Applicants have found that the presence of minute quantities of compounds of the above structure makes possible the production of a copious froth by the use of flotation machinery of conventional designeven when dealing with regenerating baths of the usual high electrolyte This result is not obtainable by the use of the usual flotation reagents in the presence of high electrolyte and acid concentrations. Moreover it has been found that such substances are excellent collectors of the sulfur and other impurities usually found in precipitating baths so that the flotation process is very emcient without the further addition of substances which might be deleterious to the extrusion step.

A further advantage exhibited by the compounds of the structure set forth above is their freedom from forming precipitates with the heavy metals which are usually present in regenerating baths,

for example, zinc and lead. An important source of loss of compounds used in minute quantities is thus prevented.

A still further advantage of such compounds is their lack of pronounced ionogenic tendencies.

below: The efflciency of the flotation method as a whole for the clarification of rayon regenerating baths depends in no small part upon the prevention of accumulation of solid impurities at 86 their point of inception, i. e., at, and even in the the carboxyl group in consequence of the neutralization ofthe latter upon the nitrogen atom. Likewise, by residue of a sulfonic acid group is meant the configuration V spinneret orifices themselves.' Since the formation of solid impurities undoubtedly takes place at or .near the boundary between the strongly alkaline spinning solution and the highly acid regenerating bath, it is obvious that a surface active agent substantially neutral in character will have the best likelihood of being present in the critical zone of precipitation of such impurities. As a result of the presence of compounds of the structure disclosed above the precipitated solidv Particles of impurities are prevented from agglomerating or adhering to the spinneret surfaces and are rendered hydrophobic in character, so as to be readily removed by the flotation process.- In other words the special virtue'oi these compounds is that they are strongly polar. but with little-or no tendency to ionize.

- In this connection it should be pointed out that many of the surface active agents heretofore r. 55 employed for attaining the above mentioned ends,

. aceaaea asexemplified by the cation active compounds.

have a marked afllnity for cellulose, which property results in a high rate of exhaustion by the continuous production of a fresh cellulose sur- '1. In the froth flotation process of clarifying We'claim:

face as the extrusion process is carried out over 5 which baths are fouled by impurities incident to I. (a) In a commercial operation a regeneratby cit- 2 P. P. M. in a single pass.

ing bath containing approximately sulfuric acid and sodiumsulfate by weight was treated continuously with an amount of C-cetyl trimethyl betaine that would give approximately 0.00003% of the bath being circulated from the storage and heating tanks over the spinning frames and through a flotation machine of conventional design before returning to the, storage tanks. It is estimated that under such conditions a concentration of the C-cetyl trimethyl betaine was maintained at a level of approximately above the ratio at which it was addedowing m/the regeneration step, the step of floating said impurities out of the bath in a froth formed in the presence 'of a betaine of the following general formula:

I Rr-N-Jh il 2. In the froth flotation process of clarifying acid regenerating baths for repeated use in the preparation of cellulosic articles from viscose, which baths are fouled by impurities incident to to the incomplete removal of the frothing agent in the flotation step. Under such con-- ditions the amount of suspended impurities in the spinning bath was reduced from 18 P. P. M. to 5 P. P. M. by a singlepass through the flotation'machine, the concentration of suspended impurities being determined- 'by turbidimetric records which previously ha been calibrated gravimetrically.

(b) In a continuation of the operation described above the addition of the C-cetyl trimethyl betaine was doubledwith the fol-' lowing results: The average suspended matter was reduced from 14 P. P. M. to 2 P. P. M. during a single pass through the flotatioh machine.

(c) In a further continuation of the operations the addition of the' C-cetyl trimethyl betaine was trebled over that used in I (a), i. e. brought to approximately 0.0001%, with the following results: The suspended impurities were reduced from 13 P. P. M. to However, the amount of froth was excessive under these conditions resulting in diiflcult manipulation of the flotation machine and the loss of considerable quantity of the spinning bath. It is concluded from the above tests that the optimum amount of this frothing agent in a bathof approximately the composition cited would be near to that mentioned in Example I (b).

II. In a similar manner the compound C-myristyl trimethyl betaine was tested at varying rates from 0.00003% to 0.00008%. The results in this case were substantially the same except that the optimum concentration was found to lie slightly higher than that of the C- cetyl betaine above. I

the scope of the the regeneration step, the step of floating said 26' impurities out of the bath in a froth formed in the presence of a betaine of the era] formula: a

following gen- Rr/-N B| I i--X wherein Nis a nitrogen atom, R1 is an alkyl group of from 3 to 20 carbon atoms, Ra, R: and R4 are 36 alkyl groups at least one of which must contain from 8 to 20 carbon atoms in the event that R1 contains less than 5 carbon atoms, and X represents the residue of a carboxyl group.

3. The process as described in claim 2 in which I The following references are of record inthe JOSEPH L. COSTA. WILLIAM HARLOW KAHLER.

REFERENCES CITED 5 die of this patent:

UNITED STATES PATENTS Number Lontz.. Dec. 21 1943