US2319428A - Rayon manufacture - Google Patents

Description

Patented May 18, 1943 ESPATENT OFFICE,

' RAYON MANUFACTURE Arthur r. F. Mothwuri', Philadelphia, Pa., asslgnor, by mesne assignments, to Imperial Bay'- on Corporation, Gloucester, N. 1., a corporation of Delaware No Drawing. Application October 5, 1940,

serial No. 359,901

7 Claims.

This invention relates to the manufacture of artificial fibres or other regenerated cellulose products by the cuprammonium process and has as, its particular object a novel method oi. regenerating cellulose from its cuprammonium solutions.

A further object of this invention is to effect this regeneration by fewer operations than were,

which it is readily removed from the thread by subsequent washing, to which components neutral salts for physically influencing coagulation may be added.

As substances or the first description we select metallic salts which attract ammonia to enter therewithinto compounds 01 higher stability than the copper-ammonia-cellulose complex. Such salts for instance are:

heretofore, considered necessary.

Another important object of this invention is to lower the cost of the cuprammonium process.

Still other objects and advantages, inherent to the features and practice 01' .our invention, will more fully appear in the following explanation:

When regenerating cellulose from cuprammonium cellulose solutions, for example in the production of artificial fibres, the treatment or treatments'to be employedprior to flnal washing have to serve the two purposes liberating their ammonia contentand of converting copper content into a readily removable solution. i It is obvious that application 01 acids, by neu-' tralizing ammonia and by dissolving copper, can take care of .both purposes. However, experience has shown that the action of acids is-too rapid and that the ensuing thread is stiff and brittle and invariably uneven in structure and afllnity for dyes.

Practice has, therefore, turned to other means of precipitation with ,a resulting preference ior caustic soda in more or less diluted form.

Caustic, in contact with the spinning. solution, expels ammonia from the soluble copper ammonia cellulose complex, and deposits most of the copper content of the latter as insoluble copper hy- 35 droxide within the coagulating thread which leaves the precipitating bath in a highly hydrated,

Copper salts, zinc salts, calcium chloride, sulphate of alumina, etc. I

Components of the second escription must be able to function'as solvents forcopper hydroxide in an alkaline solution. Ammonia salts, salts of oxycarbonic acids, like glycolates,tartrates, ci-

' trates, etc., or glycerine and its homologues,

sugars and others can serve this purpose.

It is the substance or this invention, that no satisfactory results are, obtained by combining representatives of the two groups indiscriminately, but that the respective components have to be selected and proportioned with careful consideration of possible interreactions.

The following instance is meant to convey a clearer conception oi this important point:

In practice, I preier, for the sake of economy, to apply a combination of copper sulphate and ammonium sulphate.

Copper sulphate, acting as component or the first description, absorbs ammonia, whereby the reaction goes successively through the following two. stages:

which stages account for the-tact. that in the presence otsufllci'ent ammonia salt,- copper sulsemi-plastic state so that en acid treatment hasa e wilf' ra am ni f m h into'iollow in order to tree it from copper and to termedla e precip t pp r mm r 80 complete its deflation and setting. i ble coppertetramine sulphate.

Comparedwith the course oi. an acid precipit'a- T w q C P Q by he s ond formula tion, such proceeding adds at least one more opqualifies ammonium Sulphate h cm eration and additional expenses for caustic and solvent r m ydr xide. v sulphuric acid which a one-stage coagulation While it further implies that ammonium sulwould avoid. phate alone may act, in a chemical sense, a The present inventionprovidesa non-acid 'preone stage precipi n r cum-ammonium cellu cipltating bath whichbiiers all the benefits oi lose solutions. such action is, in-pm ce. predia single treatment and eliminates atthe same .cated on the ratio or ammonia to copper hydroxtime the defects andinbonveniencea'which the i n nts t e spinnin solution being p- I application ,oiireesacid and subsequent neutrali- 801 0 38 t M9 B8 stipulated bra ove ditssation would involve. I W" tion or0.85,to 1. i i J In principle, the composition of the new p'r'e- Bucha oonditionis not applicable to our-case: eipitatingbh comprises two active components with all cuprammonlum cellulosesolutions that or which the'flrstisabietoabsorb ammonia, while the second has to, dissolve copper toja, form in duces a large excess or against hi h ratio is much higher '(1.5'-1.8 to. 1 It introcoagulating action of ammonium sulphate alone cannot materially develop beyond the purely physical effect of a salt solution.

To direct it'deilnitely along the desired chemical line the presence of copper sulphate has been found expedient and effective. It engages the excess of ammonia and, thereby, leaves ammonium sulphate free to exercise its function as a solvent for copper hydroxide.

It can be seen that the amount of copper sulphate must be just suflicient to convert the prevailing surplus ofammonia into copper tetramine sulphate, in other words-and this is one and to. prevent its precipitation byadding a corresponding amount of glycerine or corn syrup which addition has the further advantage of assisting in the removal of copper from the thread in the subsequent washing.

It will be further seen, that there is a minimum amount of sulphate of ammonia required as solvent, but that there is no limitation to any reasonable increase above that minimum amount; in fact, the margin left for the percentage of this component or for any neutral salt in its stead represents one of the various means of modifying coagulation. As the rate of diffusion rises with increasing temperature, another means of modification consists in the temperature at which the precipitating liquor is applied. Also other suitable additions such e. g. as favor or prevent deflation may be made.

The problem of reconditioning the withdrawn precipitating liquor for repeated use, which is of great consequence from an economical point of view, offers no difficulty; during the course of the reaction the entire ammonia and copper content of the spinning solution has been converted a into copper tetramine sulphate.

The latter is subject to the following reactions: I

soimnmcu-i-msoi omen), 2S04(NH4 )2 ment a portion of the liquor, equivalent to said increase, is definitely withdrawn and treated for recovery of ammonia. For the balance enough copper hydroxide or basic copper sulphate is dis lowered by forcing the acid. a

Economies effected by this method as compared with the favorite two stage caustic precipitation are substantial. Of the chemicals used in the two stage process there are saved the total of caustic, that part of the sulphuric which is required for its neutralization and the use of any additional chemicals for copper recovery. In addition, the one stage method creates conditions very favorable for reclaiming ammonlai Though a combination of copper sulphate and ammonia sulphate for precipitation involves a maximum of economy, and is therefore the most interesting phase of this invention, its principle can be extended to other combinations. 1

In giving instances of the manner in which this invention is carried out in practice, I relate them all to a spinning solution containing:

evaporation before adding I Percent Cellulose (100%) 4 Ammonia (100%) 3.6 Copper hydroxide 2.4

to a spinning speed of 64 meters (71 yards) per minute and to 150 denier yarn.

Example #1 The precipitating bath is made up as follows:

It circulates at ordinary temperature at a rate of 500 cc. per jet and per minute.

Of the 3.6% ammonia contained in the spin ning solution, 2.76% represents what I have previously termed as excess ammonia.

The amount of copper sulphate is originally calculated to absorb this excess as copper tetramine sulphate. In the further course of precipitation the current requirements are established by tests and held at the point where additional copper sulphate creates cloudiness by precipitating copper hydroxide. Glycerine is added to provide for possible fluctuations of the copper sulphate content of the precipitating liquor.

- Duringcoagulation all available ammonia and copper hydroxide (except that held in solution by the glycerine) is converted into copper tetramine sulphate.

Under proper consideration of the losses of liquid, through adhesion to the thread and of the changes in volume, various methods may be employed for conditioning the withdrawing precipi tating liquor for repeated use.

I prefer to proceed in the following manner: about one-eighth of the withdrawn precipitating liquor is by-passed. To thebalance, which solved in sulphuric and enough'water is-added to restore original concentration of copper sulphate) as well as the original volume.

; Theoretically, the total amount of sulphuric this amount is less due to loss of ammonia through adhesion to the thread, through evapoacidhee'ded'should correspond to the ammonia content of the spinning solution-in practice,

. ration and other causes-and may be further 75 is recirculated, enough sulphuric acid is contin-v B. .per minute and litre.

After the copper precipitate is removed by filtration or otherwise, enough copper sulphate solution and water is added to restore the precipitating bath to its original volume and content of copper sulphate per litre.

-to be around 1.30 grams of sulphuric acid, 60

zation of fresh copper sulphate solution of known.

percentage in its restoration. This gives more accurate results than could be obtainedby add-' ing first an amount of sulphuric acidsuflicient to precipitate all of the copper and then adding H T 5 that part of the available ammonia originating,

more acid to dissolve that portion of the precipitated copper needed for recirculation. I The by-passed portion is freed oi the copper by acid, is neutralized with'lime and is subjected to distillation for the recovery of ammonia.

The wash waters are treated for copper recovery only.

It circulates at a temperature of 40-45 C. (IMF-113 F.) and at a rate or 500 cc. per min ute perjet.

The reactions which take place are similar to those of the preceding-example; copper is dissolved to copper tetramine salt while-ammonia combines with calcium chloride, so that reconditioning of the withdrawn liquor can be efiected by muriatic acid.

It is, however, more advantageous in the case of recovery to precipitate the copper as copper sulphide, preferably with calcium sulphydrate,

and to force evaporation of ammonia so that the acid is not the only way of reconditioning the withdrawn precipitating liquor. There are other possibilities as, for instance, removal of the excess or total copper content as copper sulphide,

' basic copper carbonate, etc. or evaporation or ammonia may be forced to efiect precipitation of copper and to lower consumption of sulphuric .acid or any one or these various methods may be used in conjunction with others.

the spinning maintained at a constant chemical ratio to the ammonia concentration or the spinning solution, said ratio being such that substantially the whole of the ammonia contentnot otherwise consumed or lost during the reaction will be; absorbed by said copper sulphate.-

3. Process according to claim 1, in which-the copper sulphate is introduced slightly in excess of that quantity substantially sufficient to bind from the spinning solution that is not otherwise consumed during'the reaction, saidexcess resulting in a precipitate-said ammonium sulphate being introduced to keep in solution said precipitate produced by the excess onsaid first component.

r 4. Process according to claim 1 in which the 7 Example #2 The precipitating bath is made up as follows:

Grams Chloride 0f flmmflflil 150 Chloride of calcium -e 2.4 Glycerine; per 1,000 cc .25

temperature of the precipitating bath is kept be-' tween and 60. C.

5. Process of regenerating cellulose from a cuprammonium solution in a single stage which consists in spinning a cuprammonium solution in a precipitating bath comprising, besides water as a solvent, two chemically active components of which the first component is copper sulphate 4 and the second component is ammonium 'sulphate, and the copper sulphate is not consequentially more than the amount necessary to There are and will be'yet other modiflcations of my process at my hands and atthe' hands of others. Each and all of the modifications which conform to its generic spirit are intended to be protected to me through this patent application at large, irrespective of the circumstantial terminology of the claims appended.

What is claimed is:

l. The process of regenerating cellulose from its cuprammonium solutions in a single stagewhich consists in spinning the cuprammonium solution in an alkaline precipitating bath, which bath comprises, besides water as a solvent, two chemically active components, or which one is a copper sulphate for attracting. and. absorbing absorb as copper tetramine sulphate that part of the ammonia content of the spinning solution which is not consumed in dissolution of the copper hydroxide oi the spining solution by the ammonium sulphate lost.

6,.Process of regenerating cellulose from its cuprammonium solution which comprises the step of precipitating and decoppering in singlev stage by the use of a spining bath substantially the entire body of which is during the spinning l continuously in a non-acid condition, which process comprises the further step of withdrawing at least part of the precipitating liquor containing copper sulphate and water and the withdrawn used precipitating liquor is reconditioned for re-circulation, said process comprising the addition oi. suflicientsulphuric acid to precipitate all its copper content, the process'comprising the further step of withdrawing for ammonia recov cry a portion or the liquor that contains the total gain in ammonium salt due to the use of the bath, and the" process comprising the step of restoring the remainder of the liquor to the composition and volume which the original precipitatin'g bath possessed before its use, by the addition of copper sulphate and water.

. 'I. Process of regenerating cellulose from its cuprammonium solution in which precipitation and decopperin'g are carried out iniasingle stage by means of one spinning bath, which bath con- .tains copper sulphate and water, the process comprising the step of withdrawing precipitating liquor and reconditioning it for re-use by forcing precipitation of copper'hydroxide and evaporationot ammonia to the extent of the gain in ammonia and the other 01 which isammonium copper and ammonia from the immediately preceding use, removing the precipitated copper hydroxide-and restoring the liquor to its orig'-. inal composition and volume by the addition of.

copper sulphate and water as necessary.

ARTHUR l'. P. MO'I'HWURF.

concentration or the coppersulphate is during v