US2446541A - Extraction of nitrocellulose from nitrating solution - Google Patents

Description

Aug, W, 4. E. E. LITKENHOUS EXTRACTION OF NITROCELLULOSE FROM NITRATING SOLUTION Filed Nov. 13, 1942 2 Sheets-Sheet 1 MIXED 196/08 so; VENT /l3 Aug. 1, nm. E. E. LHTKENHOUS EXTRACTION OF NITROCELLULOSE FROM NITRATING SOLUTION Filed Nov. 13, 1942 2 Sheets-Sheet 2 a2 a6; a?

i U! L will Emm m m V nac'rron F nrrnoonnwnosn FROM mrna'rmo SOLUTION Edward E. Litkenhous, Nvllle, Tenn, asslgnor to Tennessee Products @orporation, Nashville, Tenn, a corporation of Tennessee Application November 13, 1942, Sl No. 465,501

This invention relates to an improved process for the manufacture of smokeless powder.

Theprincipal feature of the invention resides in subjecting a mixture of cellulose nitrate and its original nitrating acids to solvent extraction with a solvent for cellulose nitrate which is nonreactive to the same and to the mixed acids and immiscible with water and acids. The process is distinguished from the usual procedures, in that the cellulose nitrate is extracted from the mixed acids which are present in appreciable amount and highly concentrated.

Heretofore, it has been customary to subject the cellulose nitrate after nitration and befofe colloidizing to time-consuming, hazardous, and expensive operations for removing all or most of the nitrating acids. In the present process, preferably no substantial part of the original acids are removed, such as would be the case where the cellulose nitrate is treated by the usual steps of wringing, drowning, poaching, boiling, and washing. There may be some removal of the nitrating acids, as, for instance, by draining, but the customary steps mentioned above are unnecessary.

The colloidizing treatment following acid removal has generally involved treating the cellulose nitrate, denuded of its acid, to alcoholether, acetone, or ethyl acetate, and similar compounds which are solvents for the cellulose nitrate. These solvents are often reactive with the cellulose nitrate, the mixed acids, and water to such an extent as to impair the quality of the 6 Cla. (Cl. 260-223) final product, and hence it has been regarded as necessaryto employ some drastic preliminary acid removalv treatment as mentioned, to eliminate all or most of the nitrating acids before the cellulose nitrate could be satisfactorily colloidized for making smokeless powder. I have now successfully extracted the cellulose nitrate from its highly concentrated mixed acids with a sol- .vent of the character described above, and the cellulose nitrate-nitrating acids mixture has contained the nitrating acids in amount varying from a condition where the cellulose nitrate is substantially wetted by the acids to a condition in which it is entirely immersed in the acids.

The removal of acids, prior to colloidizing, requires that the treatment stabilize the cellulose nitrate against reversal of the reaction which might producedenitration, and particularly must be conducted with every precaution to preclude firing. For example, where wringing of the cellulose nitrate is employed, great care must be exercised to immediately drown the cellulose nitrateto prevent firing, and it is recognized that the customary procedures are, at best, ex- I tremely hazardous. In the present process, the cellulose nitrate is always wetted or covered by the acids and solvent so that firing is reduced to a minimum. In a preferred procedure, the entire Further, by way of explanation, the cellulose nitrate, as ordinarily made, has a characteristic tubular form, and, therefore, removal of the acid necessarily involves washing out the acid from both the external and internal structure of the cellulose nitrate. By my process, in which the cellulose nitrate is solvent extracted from the nitrating acids-cellulose nitrate mixture, there is no-interstitial structure remaining to retain the acids, and hence a continuous process is made available which is rapid and safe,

During the gelatinizing treatment, in accordance with this invention, and at the completion of the same, the extracted cellulose nitrate with its solvent forms as a separate layer from the acids and water. This layer of cellulose nitrate solution which has been denuded of its acids by the extraction step may, if necessary, be subsequently purified by any customary practice to remove last traces of. acids which would constitute impurities, such as spots in the final product.

Another feature of this invention consists in eliminatingthe use of conventional blending with its well-known hazards, since it is possible by my process to thoroughly blend large quantities of the cellulose nitrate solution in appropriate-sized solution tanksand obtain uniform production.

through spinnerettes, either under or out of water, to form a novel thread. This thread may be suitably bonded into bundlesto give an irregular-shaped powder after the manner of the wellknown rosette. The cellulose nitrate is also highly suitable for the manufacture of wellknown ball powder, extruded powder, and strip days under existing processes and afl'ords optimum safety because in a manufacturing area, there will only be a small amount of powder of the order of about 50,000 pounds, as compared with 2,800,000 pounds under existing processes for daily production of 100,000 pounds of powder.

In the accompanying drawings, I have illustrated a flow sheet of the general operation and a number of modifications. It will be appreciated that the invention may be further modified in accordance with the broad. idea involved and,

therefore, both the drawing and the following description are to be considered as illustrative of, rather than limiting, the invention.

Referring to the drawings:

Figure 1 is a flow sheet, showing the manner in which the invention process is broadly conducted;

Figure 2 is a p erspective view of a rosette built up of spun threads of smokeless powder;

Figures 3 tot are preferred modifications of the invention and the showings are diagrammatic, and

Figure '7 is a diagrammatic view of a further modification,

lose in moist or dry condition from cotton, wood fibers, straw, newsprint, or other source, suitably prepared for nitration as required, is continuously introduced from the hopper ill to the nitrating apparatus I l; Nitration can be carried on in any suitable manner and to any desired degree, and it will be understood, of course, that pyrocotton, gun cotton, as well as other nitric acid esters of cellulose, may be produced:

From the nitrating apparatus, the cellulose nitrate-acids mixture is carried to and treated in an extraction tank l2 with a solvent for cellulose nitrate which is non-reactive thereto and to the highly concentrated mixed acids as well as immiscible with the acids and water. Such a solvent is preferably one or a mixture of the two mono nitro-propanes or other aliphatic nitro compounds which are carbon to nitrogen bridged In the same manner, the solvent is essentially non-reactive with respect to the acids, i. e., it does not react with the same or otherwise deleteriously affect the acids or the solution. The solvent, moreover, as explained, is immiscible with the acids and with the water. In other words, the solvent extraction agent does not cause any objectionable 'side reactions. The solvent extraction time may be readily controlled, and in some cases may consume up to several hours.

In traveling from the nitration chamber to the gelatinizing or solvent extraction chamber, some of the acidmay be drained or filtered off or removed by light pressing, as where the bulk of the acid is excessive or the size and nature of the e:'.- traction chamber requires some slight reduction in the volume of the mixture. In any event. however, the cellulose nitrate-acids mixture is introduced into the 'gelatinizing chamber in a condition containing an appreciable amount of its concentrated nitrating acids by which it is wetted and from which acids it is to be solvent extracted. In some cases, the cellulose nitrate is saturated with the acid or covered with the same, or actually in a condition where it is immersed in the nitrating acids.

This gelatinizingoperation in the tank 12 takes place in the presence of agitation and during and following solvent extraction, the solution separates or stratifies out as a layer above the acid and water. The cellulose nitrate solution so produced is substantially denuded of its acid and may be either blended in the tank I3 with another solution of cellulose nitrate. if necessary, or directly drawn from the extraction tank l2 and after suitable solvent adjustment in the tank 14, if necessary, compounded in the chamber l5, fabricated in the apparatus 16, and dried in a suitable manner at II. The blended solution mixture may be treated in the same manner.

Referring to the term "solution of the cellulose nitrate, I mean that the cellulose nitrate is in colloidal suspension in the solvent, or is present as a true solution therein, or is a characteristically gelatinized mass, or a combination of the several conditions.

The nature of the extraction treatment is such that the acids are displaced by the solvent as just described, and while the solution may contain in some cases, traces of acid which might ultimately become impurities, as for instance spots, this can be taken care of by washing or washing with some mild neutralizing agent, or both, as desired.

The system for operating the process is preferably closed, i. e., out of access to air and other influences which might cause firing, and this, in addition to having the cellulose nitrate always wetted with an amount of acid or solvent as will preclude firing, considerably reduces the hazards of operation.

The nitration and gelatinization preferably constitute a continuous process and, in fact, the whole system may be continuous, including the step of fabricating, whereby high speed safe production is assured. This is particularly important in connection with the novel step of spinning the cellulose nitrate to make threads l8 as illustrated in Figure 2. These threads may be prepared by passing the cellulose nitrate through a suitable spinnerette machine, either under or out of water, whereby the thread is continuously spun from a supply of cellulose nitrate continuously fed to the spinnerette from the preceding apparatus. After the thread is formed, it may be out before or after drying.

A plurality of threads l8 may be bound together in any suitable manner to form a rosette, as shown in Figure 2. The bonding means may be any suitable adhesive, for example, one having retarder characteristics, or one of the threads or some other flexible material may be employed to hold the threads together. In some 09,568,121! bond may be obtained from the adhesive nature of the wet thread, in which case the threads are compressed together while in moistened state and the rosette is suitably dried. The spinnerette openings may have various contours, and in preparing the rosette, it is preferable that all of the threads have the same contour. The rosette,

of course, will have the desirable irregular overall contour shown. 7

While it is preferred to use the customary mixed acids for nitrating, other nitrating agents may be used, such as nitric acid, other mixed acids, and organic nitrates.

The foregoing general description is common to each of the several processes to be now set forth and which will exemplify the invention in the manufacture of pyrocotton and also my novel process of continuous countercurrent nitration and solvent extraction.

countercurrent Nitration I Referring to Figures 3 and 4, the cellulose is introduced to an apparatus which allows countercurrent nitration to be continuously conducted- This apparatus may consist of a plurality of communicating tubular members 30 arranged in an inclined plane at different elevations, as shown in Figure 3, or at the same elevation, as shown in Figure 4. Each of the tubular members contains a suitable conveyor mechanism 3|, such as a screw conveyor, by which the cellulose is moved in one direction, as indithe closed system, air and other influences which might cause firing are negligible. Progressive nitration is carried out by increasing the concentration of nitric acid in the direction of movement of the cellulose and cellulose nitrate through the tubes, and to this end, the concentrated mixed acids are introduced to the tube 33 which constitutes the final stage of nitration. From this tube 33, the nitric acid progressively decreases in strength to the tube 32 which is the point of introduction of the cellulose and the point of removal of the spent acids. At the final or last stage of nitration 33, the concentration of mixed acids is substantially 21% nitric acid, water, and 64% sulphuric acid, and the tube 33 is sufficiently long or the partially nitrated cellulose is allowed to travel therethrough for such a time as to produce pyrocotton. The concentration of acid can be any (D. V. S.') dehydrating value of sulphuric acid, which will give a final nitration of 12.6:.1%. The temperature is maintained at about 30 'to 35 C., and while the cotton may be conveyed through the several tubes or stages of progressive nitration at any desired speed, it is preferred to complete the operation in about to 50 minutes.

As will be appreciated, .nitric acid is used up, and this is continuously replenished by introducing at the final stage 33 the fortified acid or fresh acid having the concentration above noted, so that substantially constant conditions are maintained throughout the stages of nitration, i. e., the strongest concentration of acids is in the tube 33 where nitration iscompleted, and this concentration progressively decreases in the tubes, being least in the tube 32 where the cellulose is added and spent acids are removed and recovered. The fortifying or fresh acids are continuously introduced to the tube 33 through the inlet 34, and the spent acids are continually removed from the tube 32. Likewise, cellulose is continually introduced'to tube 32 and discharged from tube 33 as will be more fully explained.

The process employed in Figure 4 is identical with that of Figure 3, it being observed that the tubes are arranged in the same plane. It is preferred to employ conveyors 31 in each of the tubes 30 and to utilize a pump 35 for pumping the acid into the tube 33 and through the closed system toward the tube 32.

The procedure just described embodies progressive, continual, infinitesimal change in the nitration from the tube32 to the tube 33.

Feferring to Figure 5, I sometimes use a plura ityof tanks 36 in which the nitration is progressively and continuously conducted and a change in nitration is by finite difierences. That is to say, and referring to Figure 5, the cellulose is introduced to the tank 36 in which a predetermined amount of nitration is accomplished, whereupon the partially nitrated cellulose is allowed to flow to the next or lower tank 36 where a definite increase in nitration is likewise conducted. This procedure is continued in the suc-. ceeding tanks at the several lower levels in which a predetermined increase in nitration is achieved in each succeeding tank until the desired degree of final nitration is reached. i The partially nitrated cellulose in the tank 3 may be allowed to overflow to the next lower tank 36 through a duct 3.1 or be drawn off into the lower tank through a duct 38, as shown in Figure 5. The acid from one tank may be conducted to succeeding tanks through ducts 39 in the opposite direction from the travel of the cellulose and cellulos nitrate, as by pumping.

Referring to Figure 6, there is illustrated a I similar process in which the tanks 36 are all dis- Figures 3 and 4.

In Figure 7, I have illustrated a single tank in which nitration by infinitesimal differences or by finite differences may be utilized, and this may be carried out by simply adding the nitrating acids to the tank to effect final nitration or by running the nitrating acids through the tank for this pur pose. Of course, the cellulose and cellulose nitrate may similarly be passed through a tank contain; ing the nitrating acids to accomplish the same result.

It will be noted that with either of the processes of nitration, the cellulose is always maintained in a condition where it is sufilciently wetted or covered by the nitrating acids to insure against Continuous progressive nitration is preferred, but intermittent nitration may be used, particularly with the process described in Figure 7; in fact, as stated above, nitration may be carried out in any of the usual conventional ways, if desired.

In connection with the preferred form of nitration, namely, the countercurrent system, .using inclined tubular chambers, this is particularly desirable for commercial installations, in that it can be located in the ground on a hillside where, with suitable camouflage, there is little danger of the nitrating plant being detected from the air.

Solvent ectraction' Upon completing nitration, it is preferred to continue immediately the treatment of the nitrated cellulose in the presence of an appreclable amount of its nitrating acids, and to this end, the mixture of acids and. cellulose nitrate is .traveled by a conveyor or pumped as shown in of nitration, so that the operations of nitration and gelatinization are continuous. In traveling from the final nitration stage to the gelatinizing or solvent extracting stage, some of the acid may drain oil of the cotton, or. there may be some intermediate flltering or squeezing to remove a part of the acid. In any event, however, the cellulose nitrate is introduced into the gelatinizing chamber in a condition containing an appreciable amount of its concentrated nitrating acids by which it is wetted and from which acids it is to be-solvent extracted. .In some cases, the nitrocellulose is saturated with the acid or covered with the same.

It will be noted that in all of the processes, the cellulose nitrate is so substantially wetted or covered by acids or solvent that the likelihood of firing in air or from other causes is considerably reduced. Moreover, the use of a closed system serves to further eliminate the hazard of firing.

Acid is preferably continuously removed during gelatinizing and transferredto one of the stages of nitration or recovered. Likewise, solvent is preferably continually introduced to insure complete dissolution of the cellulose nitrate. It is, of course, understood that the cellulose nitrate in solution is preferably continually removed from the gelatinizing chamber.

In the solvent extraction step, the cellulose nitrate is extracted from the acids which are replaced by the solvent, with agitation and intimate mixing by any suitable means with the result that the cellulose nitrate is more rapidly taken intosolution and stratifies as the upper layer in the gelatinizing chamber.

Referring to Figure 7, in the vat system using thesingle tank as above described, after nitration-has proceeded to the desired extent, some of the acid may be removedbefore the solvent is' introduced, but this is unnecessary. Gelatinization is conducted as just described to dissolve all of the cellulose nitrate and it is accompanied by agitation to promote intermixing and rapid solution. Stratification takes place in that a top layer of cellulose nitrate solution is formed which separates out from a lower layer of the acids and water from which the cellulose nitrate has been extracted. Acid may be removed and solvent added as gelatinization proceeds.

, The cellulose nitrate-acids mixture in the tank shown in Figure 7 may contain the original nitrating acids in any substantial amount, as above described, for treatmentwith the gelatinizing solvent.

The tank shown in Figure 7 may be an open tank, but is preferably closed. Since the cellulose nitrate in the tank is at all times wetted with acids and solvent, at least to the extent as to prevent firing, the operation can be conducted in the presence of air, but it is preferred, as explained, to carry out the process in the absence of air and other influences which might cause firing.

The important feature in all of the processes described above is that the solvent extraction takes place upon a mixture of the nitrating acids and the unwashed cellulose nitrate, i. e., in the presence of an appreciable amount of the original nitrating acids from which the cellulose nitrate is extracted. In carrying out the gelatinization or solvent extraction as will be appreciated, the solvent replaces the acid in the cellulose nitrate, and the cellulose nitrate is at all times wetted or covered with the acid or the solvent.

Also, in each of the processes, the spent acid is returned to the system and the cellulose nitrate solution may be continuously removed from the system for further treatment.

The gelatlnizing treatment in each of the processes takes place at a temperature of about to C.

The cellulose nitrate solution orgelatinized cellulose nitrate is substantially pure nitrocellulose, i. e., is substantially free of its original mixed acids. In some cases, however, traces of the mixed acids remain in the cellulose nitrate, and such impurities are removed therefrom in any suitable manner, usually by conventional washing and/or washing with mild alkaline solution to neutralize the same.-

Blending It has heretofore been common place to blend the smokeless powder by mixing appropriate quantities of separately prepared powder having difierent properties which contribute to the production of a final product of the desired quality. In the present instance, it is unnecessary to blend in the dry state, but on the contrary, the blending is accomplished with the cellulose nitrate in I solution, i. e., in its wet phase. I have discovered that it is possible vto obtain an even, consistent, uniform mixture by blending cellulose nitrate solutions produced as heretofore described. I

This blending may take place as a continuous operation in the in the cellulose nitrate solution from another line or operation, or the blending may take place as a batch operation in a large size tank suitable for the purpose. Where blending is carried out, the solutions to be blended may have been previously purified'to relieve them of impurities, or the purifying, i. e., the. washing or neutralization, or both, may take place upon the blended wet mass while the same is being blended, or this purifying may occur after the blending constituents have been thoroughly intermixed to a final blended product.

Smokeless powder It is an important feature of this invention that drying of the cellulose nitrate and the products gelatinizing chamber by runnin obtained therefrom maybe accomplished without preliminary water drying, as is required in the uum, and in some cases, solvent, or a combination of these various methods.

I claim: 6

1. In the process for the manufacture of cellulose nitrate the step which comprises treating cellulose nitrate containing an appreciable amount of its nitrating agents with a normally liquid nitro paraflin and dissolving the cellulose nitrate.

2. The process in accordance with claim 1 wherein the compound is a mono-nitro-propane.

3. A process in accordance with claim 1 wherein the compound is nitro-methane.

4. The process in accordance with claim 1 wherein the compound is nitro-ethane.

5. In the process for the manufacture of cellulose nitrate the steps which comprise treating cellulose with nitrating acids in progressively increasing concentration of nitrating acid while moving the cellulose nitrate in one direction and the nitrating acids in the opposite direction, and treating the cellulose nitrate in the presence 01' its nitrating acids with a. normally liquid nitro paraiiln in amount to dissolve the cellulose nitrate and substantially replace the acids therein, and dissolving the cellulose nitrate from said acids.

6. The process .in accordance with claim 1 wherein a mixture 01' normally liquid nitro para!- flns is employed.

- EDWARD E. LITKENHOUS.

REFERENCES crmp The following references are of record in the iile of this patent:

10 UNITED STATES PATENTS OTHER REFERENCES Little, Chemical Abstracts (1939), vol. 33, col. 30 9480.

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