Патент USA US2403493код для вставки
Patented July 9, 1946 2,403,493 UNITED sTATEs PATENT oFElcE 2,403,493 MANUFACTU ING NITROCELLULOSE Frederick J. Bouchard, Radford, Va., Robert C. Gunness, Chicago, Ill., and Raphael L. Stern, South River, N. J., assignors to Hercules Pow der Company, Wilmington, Del., a corporation v of Delaware Application May 19, 1943, Serial No. 487,558 12 Claims. (Cl. 260--220) 1 2 This invention relates to the manufacture of nitrocellulose and more particularly it relates to the recovery of spent nitrating acid adhering to nitrocellulose after separation of the nitrocellu lose from the major portion of the spent acid supernatant-spent acid. In accordance with this formed in the nitration step. ~ invention, nitrocellulose wet with such adhering spent acid is drowned by admixture with a quenching or drowning volume of an aqueous Y mixed acid (nitric and sulphuric acids), having a concentration between about 10% and about Nitrocellulose is prepared by nitrating cellu 25%, the volume thereof being sufficient to lose in a large excess such as 30-65 times by reduce the concentrationof the resulting acid in and on the nitrocellulose from above about 75% weight of the cellulose of “mixed acid.” “Mixed acid” is a mixture of nitricfacid, sulphuric acid and a relatively small proportionof water. The spent acid from the nitration is slightly weak-v ened in nitric acid and slightly increased in water content. It is absolutely essential that it be recovered for fortification and re-use. The major part of the spent `acid is relatively easily separated from `the nitrocellulose. However, it is quite diñ'ìcult to recover the-remaining portion wetting the nitrocellulose without damaging the quality of the nitrocellulose. It has been proposed to wash nitrocellulose containing strong spent acid with progressively more dilute spent acid so as to lose a minimum> _ to between about 10% and about 25% substan tially instantaneously. The nitrocellulose is then removed from the drowning acid and spent acid` remainingtherein may be displaced, or other wise removed by water or other washing liquid essentially water, or both. The dilute acid formed by such washing may be added to the drowning acid to permit and to aid in maintaining the concentrationY in the 10 to about 25% range. Nitric acid is evaporated from a portion ofy the drowning acid to recover a nitric acid fraction. A sulphuric acid fraction may be recovered from the evaporation residuum. It has been found that the drowning acid of 10-25% concentration unexpectedly has substan 25 tially no denitrating effect, i. e., denitration is of nitric acid. This method has the serious ob jection that the nitrocellulose is subjected to de nitrating conditions and becomes nonuniform and negligible in the period of a few minutes or few variable in ultimate degree of nitration. It has hours between drowning and complete separation also been proposed to use wash water repeatedly _of the drowning acid. At the same time it has until its acid concentration permitted treatment been found practical to recover the nitric acid with ferrous sulphate or like reducing agent to 30 and sulphuric acid from the drowning acid by recover nitric oxide. This method has the objec evaporative fractionation. ~` 'tion of nonuniform treatment of succeeding > The process in accordance with this invention batches of nitrocellulose, is inefficient in nitric may be more completely described in connection acid recovery, and loses sulphuric acid present. with the accompanying drawing which illustrates the process diagrammatically. These and other methods for recovery of lspent acid -have either subjected the nitrocellulose to Referring to the drawing the flow of pertinent varying periods of treatment with acid Vor to vary material is shown as originating in a nitrator I ing concentrations causing serious nonuni from which the nitration mixture passes to'a formity. separator 2, which may be a centrifuge, squeeze Thus, in practical operation, nitrated cellulose 40 roll equipment or the like, and which removes the has been removed from supernatant acid by cen greater part of the spent acid from the nitrated trifuging, squeezing or the like, to obtain nitro cellulose. The free spent acid so obtained is ledcellulose wet with one to three times its weight to storage for fortification and re--use. The nitro cellulose with adhering spent acid passes to the of adhering spent acid. Thismaterial has then been drowned in a large volume of water to 45 drowning equipment 3 Where it is rapidly mixed decrease the concentration of the'acid in contact with a large volume of drowning liquor, which with the nitrocellulose to below~2 or 3% very rap reduces the concentration of the acid wetting idly to prevent denitration by intermediate strength acid. The retained or adhering spent acid has been lost and has caused disposal dif ñcu-lties since it has been diluted too greatly for recovery. - I ' The process according to this invention is con cerned with the recovery ofthe spent acid ad the nitrocellulose substantially instantaneously to below denitrating'levels. The nitrocellulose and " drowning acids pass to a rotary filter 4 which sep arates‘the‘nitrocellulose from the drowning acid. Portions of drowning acid remaining in the nitro cellulose after-the initial separation are washed with water, or with vapor condensate, which is hering-to nitrocellulose after its separation from' 55; essentiallyfwater, or preferably, first with the 2,403,493 l 3 4 vapor condensate and then further with water, the vapor condensate being obtained as herein after described. The vapor condensate and/or The nitrocellulose is removed from the drown ing acid by a rotary filter, washed on the iilter by displacement first with a water vapor con densate containing about 1% nitric acid and water form a dilute acid in the washing oper ation, which dilute acid is admixed with sep fil then by a small amount of pure Water. arated drowning acid. The drowning acid flows from the filter back to the drowning equipment either directly7 or, preferably, through sedimenta It is then treated, in thefusual manner for stabilization, viscosity adjustment and dehydration. The drowning acid is recycled through a sedimenta tion tank removing most of any associated nitro tion equipment or a filter to remove nitrocellu lose iines. The washed nitrocellulose passes from 10 cellulose fibers. A portion of the drowning acid, substantially equivalent to the quantity added by the filter into a slurry tank 5 in which Vit is sus the strong acid wetting the nitrocellulose and the Wash water, is withdrawn and initially con centrated tovabout 45% total acid concentra tion equipment 6. A portion of the drowning acid separated from 15 tion. It is .then evaporated to strip it of nearly all of its nitric acid to form a nitric acid water the nitrocellulose, preferably a quantity about vapor fraction equivalent to about 30% nitric equivalent to that added in the nitrocellulose and acid and a liquid residual fraction of about 65% Wash liquid, is bled off and passed to a concen sulphuric acid. The sulphuric acid is denitrated trator which consists of a concentration column 8 and an operatively associated evaporator 9 20 to free it of residual nitric acid by steam to yield a oki-68% sulphuric acid. The nitric acid vapors equipped with a suitable heating coil. The con pended in water for subsequent purification usually in a series of tubs represented as purifica centralìor separates the drowning acid portion are concentrated to form a concentrated nitric acid of (S5-67% `nitric acid content and a vapor into the vapor fraction, essentially Water vapor essentially water but containing about 1% of with a> small content of nitric acid, and a liquid fraction _of mixed acid of increased concentration. 25 nitric acid. Thevapors from the concentrators This mixed acid passes` to an evaporator l0 equipped with a suitable heating coil. The ma jor portion of the nitric acid in the mixedacid is evaporated from the drowning acid portion in this evaporator to form a vapor fraction contain 30 ing nitric acid and water. The liquid residuum leaving the evaporator is apartiallyV concentrated sulphuric _acid fraction containing a small amount of nitric acid. This liquid passesto a sulphuric are condensed, cooled and used as nitrocellulose wash Water to recover the nitric acid content of the drowned filtered nitrocellulose and to aid in maintaining the concentration of the drowning acid in the range desired. It will be appreciated that it is not essential to use vapor condensate for Washing thev nitro cellulose. However, such operation permits sub stantial recovery of the small nitric acid con acid denitrator i3 where, bythe action of steam, 35 tent of the vapor condensate and it further pro vides a means of maintaining the drowning acid remaining vnitric acid is evaporated to form'> an in the' lll-25% rangein which it is effective in aqueousnitric acid vapor. The sulphuric acid drowning the nitrocellulose and at the same time liquid 4fraction leaves in a denitrated form. The recoverable. The vapor condensate in general aqueous nitric acid vapor leaving the evaporator I0 and the nitric acid vapor leaving the denitra 40 will include nitric acid in any quantity up to about 3%. It will be appreciated that the vapor tor i3 pass with partial or no condensation to a condensate may be returned directly to the drown nitric acid concentrator which consists of the ing acid without use for washing. concentrator column H and an operatively asso Under most conditions of operation, it is nec ciated evaporator l2 provided with a suitable . essary to add small quantities of water to the heating coil, The nitric acid concentrator re system to prevent the drowning acid from build solves the nitric acid fractions fed thereto into ing up in concentration to a level at which deni a liquid concentrated nitric acid fraction and a tration of nitrocellulose aft-er drowning ceases to vapor Vfraction consisting essentially- of water 4 be negligible. Such make-up water is conven vapor but in most cases containing a `small amount of nitric acid. The vapors from one or 50 iently added by using pure water as a final wash for thenitrocellulose on the filter and merging both of the concentrators 8 and ll may be led to a condenser I4 where theyform a vapor con the resultant Wash water with the drowning acid. ' By this expedient, substantially all of the drown ing acid is removed and recovered from the nitro be used in Washing nitrocellulose on the rotary 55 cellulose. The nitric acid may be recovered by distilla filter 4, thereby permitting complete recovery of tion from the 10-25% mixed drowning acid and the drowning acid from the nitrocellulose and subsequently further concentrated. However, it recovery of the small amount, of nitric acid in has been found that preconcentration to form a the vapor condensate. The columns 8 and Il may be of packed or bubble-cap construction. 60 mixed acid of about 35% to about 60% concentra tion greatly Aimproves the eñ‘iciency of the steps In a typical operation serving as an example of evaporating or distilling the nitric acid and of the process, cellulose is nitrated with 45 times subsequently concentrating it. Such preconcen its weight of mixed acid to form a spent mixed tration Yalso makes practicable subsequent deni acid containing about 25% nitric acid, about 55% sulphuric acid and about 20% water. The nitra 65 tration of the residual sulphuric acid. The con centration is accomplished by evaporation of tion mixture is centrifuged, eliminating the ma essentially water from> the acid. jor portion of the spent acid, but leaving a quan Usually the aqueous nitric acid fraction ob tity in the nitrocellulose of about 1.1 times the tained is concentrated to (iO-68%. The fraction weight ofthe nitrocellulose. The wetnitrocel lulose is then drowned with mixed 4acid dilutedl 70 may first be condensed but Ypreferably the vapor ous fraction with partial or no condensation is to 20% total acid concentration in a quantity introduced directly into a concentrating column. of approximately 50 times the weight ofthe Thev sulphuric acid> fraction is conveniently nitrocellulose (dry basis). The increase in con brought to 50-'75%` as denitrated and may then centration in the drowning acid produced by the strong. acid wetting. nitrocellulose> is- about 2%. 75 be further concentrated in other equipment when densate containing a small amountof >nitric acid. This condensate, preferably cooled, may then 2,403,493 .v6 stronger'. acid is desired. The denitration' step separates the small residual quantity of nitricacid, which is less than 5% of the residual frac tion, from the sulphuric acid to permit. ready loseiis separated from supernatant spent mixed acid-of~above about '75% total acid concentra tion by weight, drowned to reduce- the concen tration of acid wetting thenitrocellulose rapidly to below. concentrations causing substantial de nitration, and then .puriñed a process which _com It is essential that the concentration of th prises'carrying out the drowning of the said sep drowning acid be held within therange herein arated nitrocellulose wet with spent acid by mix above specified. The concentration must be no ing it with a quenching volume of aqueous mixed greater than about 25% since otherwise denitra tion of the nitrocellulose 'occurs during and after 10 nitric and sulphuric acid having a concentration of about 10 to about 25% by'weight of total acid, drowning in a variable and unpredictable man said'volume'being sufficient to reduce .the con ner. `At below concentrations of 25% and with centration of the spent acid on and .in the nitro use of vthe drowning acid in a volume to insure concentration of the sulphuric acid. ~ that the mixture resulting is below about 25%, cellulose to between about 10% and about"25% substantially'no denitration occursand further 15 substantially instantaneously,> removing the drowned nitrocellulose from the drowning acid, more, the nitrocelluloseobtained is highly uni and evaporating nitric acid from a portion of formxfrom'batch to batch. Concentrations of the drowning acid. ' drowning acid below about 10% do- not permit 2.' In a procedure for manufacturing nitro obtaining the economies of the present invention since 'recovery ofthe component nitric and sul 20 cellulose in which cellulose is nitrated in an excess of mixed acid and the resulting nitrocellu phuric acids fromthe acid is impractical. A con lose is separated from supernatant spent mixed centration between 15% and 20% is preferred. , The mixed acid wetting the nitrocellulose -after its removal from the major portion of the spent acid will have a total acid concentration in ex cessrof about 75%. The ratio of sulphuric acid to nitric acid will be between about 4: 1 and about acid of above about 75% total acid concentration by weight, drowned to reduce the concentration 25 of‘acid wetting the nitrocellulose rapidly to be low concentrations causing substantial denitra tion, and then purified, a process which com 0.5:1, usually between 3:1 and 1:1', by weight. prises carrying out the drowning of the said sep 'I‘he same relationship between sulphuric acid and arated nitrocellulose wet with' spent acid by mix nitric acid will apply in the drowning acid. 30 ing it with a quenching volume of aqueous mixed nitric and sulphuric acid having'a concentration The elîectiveness of `the present process in economic recovery of spent acid is in no »small part dependent upon recovery of the drowning acid wetting the drowned nitrocellulose by means ofthe rotary lilter which provides a filter sur face through which the drowning acid may be drained, and which further provides for eñicient displacement of residual acidthroughthe ñlter of about 10 to about 25% by weight of total acid', said volume being suñîcient to reduce the concen tration of the spent acid on and 'in the nitro 35 cellulose to between about 10% and about 25% substantially instantaneously, removing ' the drowned nitrocellulose from the drowning acid, washing the nitrocellulose with essentially water thereby obtaining a dilute acid, adding said dilute surface with the essentially pure water of the con densedvapor obtained from the 'acid concen 40 acid to the drowning mixed acid in a quantity no more than that maintaining the drowning acid trators and with the iinal wash of pure water. The Viilter further provides a very convenient ’ between about 10% and about 25% in total acid manner for introducing an amount of water to the concentration, and evaporating nitric acid from a drowning acid suiiîcient or nearly suñicient to portion of the drowning acid. ' ' maintain the concentration of the drowning acid 3. In a procedure for manufacturing nitrocel in the critical range by compensating for the lulose in which cellulose is nitrated in an excess effect of the addition of strong acid in the nitro of mixed acid and the resulting nitrocellulose is cellulose. However, it will be appreciated that separated from supernatant spent mixed acid of water added as such or in the form‘oi dilute above about 75% total acid concentration by acid will be in a quantity- no more than that 50 weight, drowned to reduce the concentration of quantity which is required to maintain the con centration at the desired level in the critical range. ' By maintenance of the drowning acid substan tially constant in concentration, a highly uni form nitrocellulose product is obtained. It has been found that the method of this invention pro duces a uniform nitrocellulose of a quality fully acid wetting the nitrocellulose rapidly to below concentrations causing substantial denitration, and then puriñed, a process which comprises car-` rymg- out the drowning of the said separated ni-trocellulose wet with spent acid by mixing it with a quenching volume of aqueous mixed nitric and sulphuric acid having a concentration of about 10 to about 25% by weight of'total acid, said volume being sufficient to reduce the concentra equivalent to material obtained by drowning as heretofore with water involving complete loss of 60 tion of the spent acid on and in the nitrocellu retained acid. ' lose to between about 10% and about 25% sub The present process is'of particular usefulness stantially instantaneously, removing the drowned in permitting direct and simple recovery of- the nitrocellulose from the drowning acid, washing nitric acid contained in the retained spent acid, the >nitrocellulose. with a condensed vapor essen and furthermore it leads to recovery of both the 65 tially water thereby obtaining a dilute acid, add- nitric acid and the sulphuric acid therein. AIn ing said dilute acid to the drowning mixed acid, addition, the problem of Vdisposal of waste dilute evaporating a portion of the drowning acid to acid is avoided. Y form an evaporated nitric acid fraction and a All acid concentrations herein and in the claims fraction of essentially water vapor, and condens are in percent by weight. > u . 70 ing the water vapor fraction to form the afore What we claim and desire to protect by Letters said condensed vapor. Patent is: . .v 4. In a procedure for >manufacturing nitro 1. In a procedure forl manufacturing nitro cellulose in which cellulose is nitrated in Yan ex cess >of mixed acid and the resulting nitrocellu cess'of _mixed acid `.and the -resulting nitrocellu lose'v is separated: ‘from supernatant- spent vmixed cellulose in which cellulose isvnitrated in an ex 2514035493 7 8 acid of above about '75% total 'acidconcentra tion by weight, drowned to reduce the concen~ tration vof .acid wetting the'nitroce'llulose rapidly ofïmixed .acid and .fthe resulting .nitrocellulose is separated fromisupernatant spent mixedacidiof above about 75% total .acid concentration by Weight, drowned to .reduce .thefconcentration of to below concentrations causing.‘substantialv ‘de-V nitra'tion, and then purified, alprocessiwhi‘ch >com Ul prises icarrying .out the drowning :of the .saidrsepe aratedxnitrocellul'ose `wet with spent .acid by mix ing it with a quenching volume .of .aqueous mixed nitric -and sulphuric acid having aconcentration of about 10 to about 25% by Weight of total acid, said volume being suiiicient to reduce the con~ centration of the spent acid'on and in the >»nitro cellulose to betweenabout 10% and about25% sub acid wetting the nitrocellulose rapidlyto. below concentrations causing substantial . denitration, and. then puriñed,` aprocess .which comprises car rying 'out fthe. drowning yof the .said separated vni trocellulosev wet with .spent acid .by mixing 'it .with O aquenching 'volume of .aqueous .mixed .nitric and sulphuric acid having a. concentration vof :about 10.-to about-25% byzweight of .total acid, said volume .being >:suñicien't .toreduce .the concentra tion of thespent .acid `on and. in -the .nitrocellu stantially instantaneously, :removing the drowned nitrocellulose from the drowning acid, evaporat . lose to between„about.l0%.and about .25% sub ing a _portion of the drowning acidltoj form-»a fraction o_f essentially water vapor, 'condensing the Vapor fraction, and returning condensed Vapor to the drowningv acid in an `amount permitting the concentration of the drowningv'acid to be `main 20 tained between about 10% and about 25% Vby Weight. stantially instantaneously, .removing :the drowned nitrocellulose Vfrom thedrowningacid, .evaporate ing nitric acid from a .portion of the drowning acid, :and recovering a ysulphuric acidiractionof increased concentration frornthesaid portion; 8; In aprocedurefor manufacturingnitrocellu lose .in which cellulose is nitrated .inv an excess 4:of mixed acid and the .resultingnitrocellulose is separated from supernatant spent mixed acid of v5. In a proceduce .for manufacturingnitrocel lulose in which cellulose is nitrated in an excess of.mixed acid and the resulting nitrocellulose 25. above about 75% total acid concentration by weight, drowned to'reduce the concentration `.of acid wetting the nitrocellulose rapidly `to .below of above about 75% total acid concentration by weight, drowned to reduce the concentration of concentrations causing substantial denitration, acid wetting the nitrocellulose rapidly to below and then purified, a process which comprises car rying out the drowningof thesaidseparated .ni concentrations causing> substantial denitration, and then pur'iiied, a process which comprises .car trocellulose wet with spent acidby mixing it .with is .separated from supernatant spentmixed acid rying out the drowning ofthe said separated ni trocellulose wet with spent acid by mixing it with a quenching volume of aqueous lmixed Anitric and a quenching `volume of aqueous mixed nitric 'and sulphuric acid having a concentration of about 10 to about 25% by weight of total acid, said volume being suiiicient to reduce the concentra 35 sulphuric acid havingfa concentrationof .about l0 to about 25% by weight of totalacid, said volume being sufficient to reduce the/concentra tion of the spent acid on and Vin the` nitrocel1u~ lose to between about 10%` and about 25% sub tion ofthe spent acid on and in the nitrocellu stantially instantaneously, removing ,thedrowned lose to between about 10% and about 25% sub stantially instantaneously', removing the drowned nitrocellulose. from the drowning acid, «concen trating a portion of the drowning acid, andevap orating .nitric acid from the concentratedpor nitrocellulose from thewdrowning acid, evaporat ing a portion of the drowning acid -to form a .ni tionto recover a nitric acid fraction and a sul tric acid fraction, concentrating .the .nitric acid phuric .acid Aresidual fraction. . fraction to form a concentrated acid-fraction and 9. In a `procedure for manufacturing .nitrocel lulose .in which cellulose is nitrated in .an excess :of a .fraction essentially Water vapor, condensing the said water vapor fraction, Vand returningthere sulting. .condensate .to thedrowning acidrin an amount permitting the concentration of the drowning acid to be maintained between about 10%. and about .25% by Weight. mixed acid >and the: resulting nitrocellulose .is separated from supernatant spent .mixed acid of abovev about 75% total- acid concentration .by Weight, drowned to reduce the concentration .of acid wetting'the nitrocellulose. rapidly to below 6.> In a procedure .for manufacturing nitrocel lulose in which cellulose is .nitrated' in van excess concentrations causing; substantial 'denitration., of mixed acid and the .resulting-.nitrocellulose is separated -from supernatant spent mixed acid :of above about '75% total acid» concentration by 5 weight, drowned to reduce the. concentration Yof nitrocellulose wet withV spent acid .by mixing it with a quenching volume oî‘aqueous .mixed nitric and then purified, a process which comprises carrying out the drowning of the said separated and sulphuric acidv having a concentration of acid wetting the nitrocelluloserapidly to vbelow about 10 to about V25% .by weight'of totalaci'd, vsaid concentrations causing substantial denitration, volume .being `suiîicient to reduce the concentra' and then’puriiied, a process which .comprisescar‘ rying out the drowning of 'the said separated .ni trocellulose wet with spent acid bymixing it with tion‘of thefspent acid. yon andin'the nitrocellulose to between about 10% and. about 25% substan a quenching volume of aqueous mixed :nitricand sulphuric acid having a concentration of about trocellulose from. the drowningacid, concentrat 10 to about >25% by weight of total. acid, saidfvol urne being sufficient to reduce. the concentration of the spent acid on andl inthe nitrocelluloseto between about 10%. and` about 25%.»substantially ing nitric acid .from the concentrated portion to instantaneously, removing-«the drowningacid from: the nitrocellulose fibers -bydrainage- through aA filter surface and by displacement .of;residual«acid„ from the nitrocellulose through fthe :iilter :surface with essentially water, >and .evaporating nitric acid from .a portion of-.the drowning acid.; 7. y In Va procedure . for 'manufacturing :nitrocel-.y tially instantaneously, removing the .drowned .ni- _ ing-a portion >ofthe drowning acid, and evaporat , recover-.a nitricv acid >fraction and a sulphuric acid residual fraction and concentrating the nitric acid fraction to 60-69%.. 10. In a procedure for manufacturing nitro cel-lulose'in‘which‘ `cellulose iS.»n-itrated in an vex cess of mixed acid and the resulting- nitrocellulose isseparated from supernatant spent mixed acid'of above about '75% total acid concentration by weight, drowned tol reduce theiconcentrationof acid ¿wetting the vnitrocellulose rapidly to below lulose .in which celluloseV is nitrated 'in :an excessv 75 concentrations. causing> substantialVV denitration, 2,403,493 10 and then puriñed, a process which comprises car treated, concentrating the nitric acid fraction to rying out the drowning of the said separated ni trocellulose wet with spent acid by mixing it with a quenching volume of aqueous mixed nitric and sulphuric acid having a concentration of about 10 to about 25% by weight of total acid, sai-cl vol form a concentrated nitric acid fraction and a second vapor fraction essentially water vapor with a small content of nitric acid, condensing the two essentially Water vapor fractions, and returning the condensate to the drowning mixed acid in an amount permitting the total acid concentration of the drowning acid to be maintained between ume being sufficient to reduce the concentration of the spent acid on and in the nitrocellulose to between about 10% and about 25% substantially about 10% and about 25%. instantaneously, removing the drowned nitrocel 10 l2. In a procedure for manufacturing nitrocel lulose from the drowning acid, concentrating a lulose in which cellulose is nitrated in an excess of portion of the drowning acid, subjecting the re mixed acid and the resulting nitrocellulose is sep sulting acid to evaporation to form a vapor frac arated from supernatant spent mixed acid of tion of water and a major portion of the nitric above about 75% total acid concentration by acid in the drowning acid concentrate and a liquid 15 weight, drowned to reduce the concentration of fraction of aqueous sulphuric acid containing the acid wetting the nitrocellulose rapidly to below remaining nitric acid, denitrating the sulphuric concentrations causing substantial .denitration, acid fraction to form an aqueous nitric acid vapor, and then puriñed, a process which comprises car and subjecting the tWo said nitric vapors to con rying out the drowning of the said separated rli centration to form and recover a concentrated 20 trocellulose wet with spent acid by mixing it with nitric acid fraction. a quenching volume of aqueous mixed nitric and 11. In a procedure for manufacturing nitrocel sulphuric acid having a concentration of about lulose in which cellulose is nitrated in an excess of 10 to about 25% by weight of total acid, said vol mixed acid and the resulting nitrocellulose is separated from supernatant spent mixed acid of , above about '75% total acid con-centration by weight, drowned to reduce the concentration of acid wetting the nitrocellulose rapidly to below concentrations causing substantial de ume being suilicient to reduce the concentration of the spent acid on and in the nitrocellulose to between about 10% and about 25% substantially instantaneously, removing the drowned nitrocel lulose from the drowning acid, concentrating a nitration, and then purified, a process which , comprises carrying out the drowning of the said separated nitrocellulose wet with spent acid by mixing it with a quenching volume of aqueous mixed nitric and sulphuric acid having a concentration of about 10 to about 25% by weight of total acid, said volume being suñicient to re duce the concentration of the spent acid on and portion of the drowning acid to form an acid con centrate fraction and a vapor fraction essentially water vapor with a small content of nitric acid, subjecting the acid concentrate to evaporation to form an aqueous nitric acid vapor fraction and a residual fraction containing the sulphuric acid of the drowning acid portion treated, concentrat in the nitrocellulose to lbetween about 10% and ` ing the nitric acid fraction to form a concentrated nitric acid fraction and a second vapor fraction essentially water vapor with a small content of about 25% substantially instantaneously, remov nitric acid, condensing the two essentially water ing the drowned nitrocellulose from the drowning~ 40 vapor fractions, washing nitrocellulose Wet with acid, concentrating a portion of the drowning acid residual drowning acid to remove said residual to form an acid concentrate fraction and a vapor fraction essentially water vapor with a small con acid and to form therewith a diluted acid, and adding said diluted acid to the drowning acid. tent of nitric acid, subjecting the acid concentrate to evaporation to form an aqueous nitric acid va por fraction and a residual fraction containing the 'sulphuric acid of the drowning acid portion 45 FREDERICK J. BOUCHARD. ROBERT C. GUNNESS. RAPHAEL L. STERN.