US3341515A - Manufacture of hydrocarbon-wet, densified nitrocellulose - Google Patents

Description

3 341 515 MANUFACTURE (SF I-iYDROCARBflN-WET, DENSIFIED NlITROCELLULOSE Frank J. Connelly, Wilmington, Del., assignor to Hercules Incorporated, a corporation of Delaware No Drawing. Filed July 28, 1964, Ser. No. 385,750

, 11 Claims. (Cl. 260223) This invention relates to nitrocellulose manufacture, and more particularly to a new and improved process for producing hydrocarbon-wet densified nitrocellulose particles which are free-flowing and have a high bulk density.

As is well known, nitrocellulose in the dry state is extremely hazardous and dangerous. Consequently, all commercial nitrocellulose is supplied to the trade wet with a nonsolvent liquid in order to minimize fire hazards during storage, shipping and handling of the nitrocellulose. For most purposes, the wetting liquid employed is an alcohol such as ethanol, isopropanol or butanol. However, for certain specialty uses the nitrocellulose may be supplied wet'with water, instead of with an alcohol. There are, however, important uses for nitrocellulose where it would be highly desirable to employ nitrocellulose wet with a volatile hydrocarbon liquid such as toluene rather than with an alcohol or water. Heretofore, however, methods which have been proposed for producing nitrocellulose wet with a volatile hydrocarbon liquid have been deficient in various respects.

For example, it has been proposed to produce a hydrocarbon-wet nitrocellulose by placing fibrous nitrocellulose wet with water in a still containing an excess of a volatile hydrocarbon liquid, and then subjecting the contents of the still to distillation either at atmospheric or reduced pressure until substantially all of the water has been removed from the nitrocellulose.

However, the resulting fibrous nitrocellulose wet with hydrocarbon liquid retains far too much hydrocarbon liquid, and must then be subjected to pressure in a conventional hydraulic press to squeeze out excess hydrocarbon liquid, after which the compressed blocks must be broken up for packing into barrels. The above pressing and block breaking steps are inherently quite expensive and hazardous. Moreover, since the bulk density of fibrous nitrocellulose is quite low, the nitrocellulose must be packed into the barrels by compressing it with a hydraulic ram to increase barrel loadings, in order to reduce shipping costs. As a result of compression in packing, nitrocellulose users find the fibrous material quite difficult to unload from the barrels.

It is also known that fibrous nitrocellulose, conventionally dehydrated with an alcohol such as denatured ethyl alcohol, isopropanol or butanol can be further processed to produce a substantially hydrocarbon-wet nitrocellulose by displacing the alcohol with a hydrocarbon liquid in an additional series of steps comparable to the alcohol dehydration steps. The double displacement processing required is obviously much too expensive, and is hazardous as noted above, and the resulting product is also subject to the additional disadvantage of being difficult to unload from barrels.

It is an object of this invention, therefore, to provide an improved process for producing a hydrocarbon-wet nitrocellulose, which has economic and procedural advantages over prior art methods, and which substantially overcomes the limitations and deficiencies of prior art methods.

Another object of this invention is to provide a hydro carbon-wet nitrocellulose product of improved form which can be transported more economically and unloaded from barrels more easily than conventional fibrous nitrocellulose.

A still further object of this invention is to provide an 334L515 ?atented Sept. 12, 1967 improved process for producing a densified nitrocellulose product wet with a hydrocarbon liquid instead of with an alcohol or water.

These objects and others are accomplished in accordance with the present invention which, generally described, comprises agitating a slurry of water-moist fibrous nitrocellulose in a volatile organic liquid mixture of hydrocarbon diluent and nitrocellulose solvent, said organic liquid mixture being only a softening and swelling agent for said nitrocellulose incapable of dissolving said nitrocellulose, said solvent being soluble in water to the extent of at least about 2.5% by weight and being distillable from said slurry at a temperature below the boiling point of said hydrocarbon diluent, whereby the nitrocellulose fibers become softened and swollen and the fibrous structure of the nitrocellulose is destroyed without dissolution of the nitrocellulose, said agitation being sufiicient to maintain uniform distribution of said nitrocellulose in the slurry, but insuificient to have any substantial shearing and comminution action on the softened and swollen nitrocellulose, thereafter removing substantially all of the nitrocellulose solvent and water by distillation 'while continuing agitation whereby the softened and swollen nitrocellulose particles are transformed into smooth, hardened, densified, irregular particles of nitrocellulose slurried in hydrocarbon diluent, and recovering the resulting densified nitrocellulose particles wetted with sorbed hydrocarbon diluent by draining excess hydrocarbon diluent therefrom.

The terms sor and sorbed are used herein in the description and claims in their usual sense to mean the ability of the nitrocellulose to take up and hold a liquid, either by adsorption or absorption, or by a combination of adsorption and absorption, substantially independent of the force of gravity.

In a preferred practice of this invention, water-wet fibrous nitrocellulose, after conventional treatments for stabilization and viscosity adjustment, is drained substantially free of excess water by any convenient means, such as by gravity drainage, with or without centrifugation or suction drainage, to produce water-moist nitrocellulose fibers containing between about 30% and about 60% by weight of sorbed water, based on total weight of watermoist nitrocellulose fibers. The resulting water-moist fibrous nitrocellulose is then introduced and dispersed in a volatile hydrocarbon diluent in a jacketed vessel by means of a turbine type agitator, or similar mixing device, to form a slurry. While agitating the slurry, a nitrocellulose solvent, in an amount sufiicient to form with the hydrocarbon diluent an organic liquid mixture which is only a softening and swelling agent for the nitrocellulose incapable of dissolving the nitrocellulose, is introduced into the slurry, and agitation is continued until substantially all of the nitrocellulose fibers have become softened and swollen and the fibrous structure of the nitrocellulose has been substantially destroyed, a matter of about 15 minutes to about /2 hour. If desired, the slurry of nitrocellulose in hydrocarbon diluent may be initially heated to an elevated temperature on the order of about 50 C. to about C. prior to introduction of the nitrocellulose solvent into the slurry, in which case it is desirable to introduce the nitrocellulose solvent beneath the surface of the slurry to avoid premature rapid evaporation of the solvent. This initial preheating of the hydrocarbon-nitrocellulose slurry is advantageous in that the softening and swelling action brought about by introduction of the nitrocellulose solvent to the slurry is greatly accelerated thereby, and it is neither necessary nor desirable to apply any additional heating during the course of the softening and swelling of the nitrocellulose fibers.

When observation indicates that substantially all of the nitrocellulose fibers have become softened and swollen and the fibrous structure of the nitrocellulose has been substantially destroyed, jacket heat is applied to the slurry and substantially all of the nitrocellulose solvent and water are removed from the slurry by distillation while continuing agitation to transform the softened and swollen particles of nitrocellulose into smooth, hardened, densified irregular particles of nitrocellulose slurried in hydrocarbon diluent. Since a portion of the hydrocarbon diluent also distills off with the nitrocellulose solvent and water, it may be found to be desirable to add additional hydrocarbon diluent to the slurry either prior to or during distillation to insure a large excess of hydrocarbon diluent at all stages of the distillation. Agitation is maintained until hardening and densification of the nitrocellulose particles is complete in order to minimize agglomeration during hardening, and distillation is stopped when the boiling point approaches the boiling point of the hydrocarbon diluent. The resulting hardened and densified particles of nitrocellulose are readily recovered in a hydrocarbon-wet state by draining off excess hydrocarbon liquid by any convenient means, such as by gravity drainage, suction drainage, centrifugation, or by a combination of such means.

If desired, various additives such as nitrocellulose stabilizers, carbon black, and other desirable additives which are soluble or dispersible in the organic liquid mixture can be introduced into the slurry at any convenient point in the process and become very uniformly distributed into the nitrocellulose product.

The hydrocarbon-wet product of this invention is composed of small, hard, densified irregular particles of nitrocellulose having a diversity of particle sizes, a majority of which are within the range from about inch to about A inch in their greatest dimension, and which when magnified appear to have smooth, glazed surfaces. These particles have a degree of densification corresponding to a bulk density of at least about 20 pounds per cubic foot, dry basis, and have a free gravity-draining physical structure capable of holding no more than about 50% by weight of sorbed hydrocarbon liquid, based on weight of the hydrocarbon-wet nitrocellulose. The level of sorbed hydrocarbon in the particles can be readily lowered to a value within the range from about 20% to about 30% by weight by suction drainage or by centrifugation. Fibrous nitrocellulose in loose bulk form which has not had its physical form and structure altered by the process of this invention has a bulk density of about 11 to 13 pounds per cubic foot, dry basis, and a free-gravity draining physical structure capable of holding between about 55% and 60% by weight of sorbed hydrocarbon liquid, based on weight of the hydrocarbon-wet nitrocellulose, and must be subjected to hydraulic pressing to reduce the volatile content to an acceptable level.

The hydrocarbon-wetted product of this invention is further characterized by being free flowing and relatively incompressible. The chemical characteristics of the product of this invention are apparently the same as conventional nitrocellulose, since no chemical action is involved in the process of producing this product.

The general nature of the invention has been set forth and the following examples are presented as specific illustrations thereof. All parts and percentages are by weight unless otherwise stated.

EXAMPLE 1 Water-wet fibrous nitrocellulose, 11.5% nitrogen by weight, 5-6 seconds ASTM 7 inch falling ball viscosity, and having a bulk density, dry basis, of 13.3 pounds per cubic foot, after conventional treatments for stabilization and viscosity adjustment, was dewatered by centrifugal drainage to a water-moist nitrocellulose containing 68.86% by weight of nitrocellulose and 31.14% by weight of sorbed water.

One hundred eight and y (108.9) parts of this watermoist nitrocellulose containing 75 parts nitrocellulose, dry

weight, and 33.9 parts water were then introduced and dispersed at room temperature with agitation in 543.2 parts of toluene in a jacketed vessel equipped with a turbo blade agitator to form a slurry. This slurry was then initially heated to approximtaely C., and while continuing agitation, 121 parts of methyl ethyl ketone were introduced into the slurry beneath the surface of the slurry. Composition of the slurry after addition of the methyl ethyl ketone was:

Nitrocellulose, dry weight percent 9.70 Water-added with the nitrocellulose do 4.40 Methyl ethyl ketone do 1565 Toluene do 70.25 Ratio-methyl ethyl ketone/ nitrocellulose parts 1.61 Ratiotoluene/methyl ethyl ketone do 4.5

Agitation was continued for 30 minutes without any further application of heat, whereupon jacket heat was applied to the slurry and substantially all of the water and methyl ethyl ketone were removed from the slurry by distillation while continuing agitation. A total of 216 parts of additional toluene were introduced into the slurry during the distillation. Temperature at the start of the distillation was 77 C., and distillation was discontinued when the temperature in the slurry reached 108 C.

The above treatment transformed the initial water-moist fibrous nitrocellulose into smooth, hardened, irregular particles of densified nitrocellulose wetted with toluene, and the resulting slurry of densified nitrocellulose particles in toluene was then deliquified by gravity drainage. The toluene-wet densified nitrocellulose product obtained thereby contained 57.5% nitrocellulose, 42% sorbed toluene and 0.5% water by weight, and had a bulk density, dry basis, of 24 pounds per cubic foot. The densified particles flowed easily over each other and were readily poured into and out of containers like dry sand or fine gravel.

The fibrous nitrocellulose employed in this example was in the form of relatively uniformly sized fiber aggregate particles obtained by nitrating cellulose fiber aggregate particles prepared by cutting sheets of pulpboard into particles approximately A; inch x inch x inch in dimension. These fiber aggregate particles were not materially changed in physical form or dimension during nitration thereof.

The ASTM inch falling ball viscosity characteristic of the nitrocellulose was measured on a 12.2% by weight solution of the nitrocellulose in a solvent composed of 55 toluene, 25% denatured ethyl alcohol, and 20% ethyl acetate by weight at 25 C., noting the time in seconds for a inch steel ball to fall freely ten inches through the solution.

A portion of the same initial water-moist fiber aggregate nitrocellulose particles slurried in toluene, as described above, but without the addition of methyl ethyl ketone to the toluene slurry, was subjected to distillation with agitation to remove substantially all water from the nitrocellulose. This treatment did not alter or transform the fibrous nature of the nitrocellulose, and the resulting slurry of fibrous nitrocellulose particles in toluene was then deliquefied by gravity drainage. The fibrous toluenewet nitrocellulose product obtained thereby contained 50.9% nitrocellulose, 48.7% sorbed toluene and 0.4% water by weight, and had a bulk density, dry basis, of 14 pounds per cubic foot. The fibrous particles clung to each other and could not be poured into and out of containers.

EXAMPLES 215 A series of toluene-wet, smooth, hardened, densified nitrocellulose granular products was prepared following substantially the same procedure described in Example 1. The same nitrocellulose prepared in the same manner described in Example 1 was employed in this series. In Examples 28, inclusive, the ratio of toluene to methyl ethyl ketone was varied while maintaining the concentration of nitrocellulose in the slurry constant at 10% by falling ball viscosity characteristic of 5-6 seconds and a nitrogen content of 12% by weight and in the form of loose bulk fibers obtained by nitrating shredded wood pulp was employed in place of the nitrocellulose fiber aggregate particles employed in Example 1. In Example 22, fibrous nitrocellulose having a 5-6 second -inch falling ball viscosity measured in accordance with Military Spec. JAN-N-244 and a nitrogen content of 12.6% by weight, and in the form of loose bulk fibers obtained by nitrating picked cotton lin-ters was employed in TABLE 1 Slurry Composition Operational details Example No. Total Methyl ethyl Ratio methyl Ratio toluene Agitation prior nltrocellulose, Nitrocellulose, Water, ketone, Toluene, ethyl ketone to to methyl to distillaparts percent percent percent percent nitrocellulose, ethyl ketone, tion, minutes (dry weight) parts parts Operational Details Toluene-Wet Nitrocellulose Product Example Temperature Temperature Additional N itrocellu- N o. in slurry at in slurry at toluene added Bulk lose Sorbed Residual start of en of to slurry Remarks density, content, toluene, water, distillation, distillation, during lbs./cu. ft. percent by percent by percent by 0. C. distillation, (dry basis) weight ht parts weight weig Nitrocellulose dissolved and thick emulsion formed.

77 109 173 Some agglomeration during densification process, causing some lumpincss in product. 24. 0 51. 3 48. 03 0.67 77 109 260 24. 0 55.0 44. 4 0.60 77 25. 0 56. 5 42. 93 0. 57 77 25.0 61. 2 38. 27 0.53 78 23. 7 55. 1 44. 53 0.37 78 18. 4 57. 0 42.60 0.40 76 24.0 55.0 44. 71 0.29 76 24. 0 59. 4 40. 14 0. 46 74. 5 24.0 60. 3 39. 34 0.36 74 25. 0 56. 3 43. 42 0.28 78 25. 0 56. 5 43. 08 0. 42 76 23. 8 57. 4 42. 03 0. 57 78 22. 5 49. 2 50. 15 0. 65

EXAMPLES 1623 A series of hydrocarbon-wet, smooth, hardened, densified nitrocellulose granular products was prepared following substantially the same procedure described in Example 1, with the following exceptions. In Example 16, the water-wet nitrocellulose fiber aggregate particles were merely gravity-drained of excess water before slurrying in toluene instead of being centrifuged, as described in Example 1. In Example 17, heptane was employed as the volatile hydrocarbon liquid in place of the toluene employed in Example 1. In Example 18, actone was employed as the nitrocellulose solvent in place of the methyl ethyl ketone employed in Example 1. In Example 19, methyl acetate was employed as the nitrocellulose solvent in place of the methyl ethyl ketone employed in Example 1. In Example 20, fibrous nitrocellulose having an ASTM A -inch falling ball viscosity characteristic of 5-6 seconds and a nitrogen content of 11% by weight and in the form of loose bulk fibers obtained by nitrating picked cotton linters was employed in place of the nitrocellulose fiber aggregate particles employed in Example 1. In Example 21, fibrous nitrocellulose having an ASTM -inch ployed in Example 1. In both of Examples 22 and 23,

the hydrocarbon diluent and nitrocellulose solvent were mixed together initially and the water-moist fibrous nitrocellulose was slurried in this mixture of diluent and nitrocellulose solvent in place of slurrying the watermoist nitrocellulose in hydrocarbon diluent and then adding the solvent, as described in Example 1.

The JAN-N-244 viscosity characteristic of the nitrocellulose employed in Example 22 was measured on a 10% by weight solution of the nitrocellulose in a' solvent composed of 11.1% denatured ethyl alcohol and 88.9% acetone by weight at 25 (3., noting the time in seconds for a A6-11'1Ch steel ball to fall freely ten inches through the solution. 7

Table 2 following presents data relative to the composition of the slurry, operational details in the transformation of the initial fibrous nitrocellulose into smooth, hardened, irregular particles of densified nitrocellulose, and the bulk density and composition of the densified hydrocarbon-wet nitrocellulose product.

TABLE 2 Slurry Composition Operational details Example No. Ratio nitrocel- Ratio hydro- Total nitrocel- Nitrocellulose Hydrocarbon lulose solvent carbon diluent Agitationprior lulose, parts Nitrocellulose, Water, percent solvent, perdiluent, pen to nitroeelluto nitrocelludist llation,

(dry weight) percent cent cent lose, parts lose solzrent, minutes par s Operational Details Hydrocarbon-Wet Nitrocellulose Product Example Additional No. Temperature Temperature hydrocarbon Bulk den- Nitrocellu- Sorbcd hy- Residual in slurry at in slurry at diluent added Remarks sity, lbs/Cu. lose content, drocarbon, water, perstart of distilend of distilto slurry it. (dry percent by percent by cent by lation, C. lation, C. during distilbasis) weight weight weight lation, parts 77 109 5 606 25 49 9 49. 51 0.59 67 93 32.4 84 2 14.85 0.95 65 106 20.8 64 5 35.01 0.49 63 105 23. 2 62 8 37.01 0.19 75 106 23. 0 54 7 44. 72 0.58 75 106 22.7 49 0 50.71 0.29 66 93 Diluent-solvent mixture ini- 28. 2 69 3 29. 94 0.76

tially, heated to 60 C. 77 106 Dilucnt-solvent mixture ini- 20.8 59 5 40.07 0.43

tially heated to 75 C.

1 11.5% nitrogen by weight, 5-6 second ASTM t -inch falling ball viscosity, fiber aggregate particles x Mt K152 inch. 1 11% nitrogen by weight, 5-6 second AS'IM A -inch falling ball viscosity, 3 12% nitrogen by weight, 5-6 second ASTM et -inch falling ball viscosity, 4 12.6% nitrogen by weight, 5-6 second JAN-N-244 MG-inch ialling ball viscosity, loose bulk fibers obtained by nitrating picked cotton linters.

' Methyl ethyl ketone.

Acetone.

1 Methyl acetate.

8 Toluene.

Heptane.

Each of the water-rnoist nitrocelluloses in the form of loose bulk fibers employed in Examples 20, 2.1, and 22, slurried in hydrocarbon diluent, but without the addition of nitrocellulose solvent to the slurry, Was subjected to distillation with agitation to remove substantially all water from the nitrocellulose. This treatment did not alter or transform the fibrous nature of any of the nitrocelluloses subjected thereto, and the resulting slurry of fibrous nitrocellulose in hydrocarbon liquid in each case was then deliquefied by gravity drainage. The bulk density and composition of each of the fibrous hydrocarbon-wet nitrocellulose products is set forth in Table 3 following.

The smooth, hardened, densified nitrocellulose granules of this invention can be produced from any fibrous nitrocellulose, obtained by nitrating natural or artificial fibers of cellulose, such as cotton, purified cotton linters, purified wood pulp, regenerated cellulose fibers, and the like, in such forms as picked linters, shredded wood pulp, fluffed bulk fibers, finely ground or cut fibers, fiber aggregate particles, and the like. A particularly preferred form of fibrous cellulose for the purposes of this invention is prepared by cutting pulpboard or linterboard sheets into relatively uniformly sized fiber aggregate partiloose bulk fibers obtained by nitrating picked cotton linters. loose bulk fibers obtained by nitrating shredded wood pulp.

cles which are not materially changed in physical form or size during nitration thereof.

Substantially all commercial types and grades of fibrous nitrocellulose are suitable for the purposes of this invention, having nitrogen contents from about 10.9% to about 13.5% nitrogen by weight, and of any viscosity characteristic from the very low viscosity 10 centipoise type to exceedingly high viscosity types as exemplified by dynamite grade nitrocellulose.

It is apparent from the foregoing description and examples that this invention provides a simple and economical route for transforming fibrous nitrocellulose wet with water directly into hardened, densified nitrocellulose granules wet with a hydrocarbon liquid. This is advantageous, since nitrocellulose after stabilization and viscosity adjustment is always thoroughly washed with water, and is therefore wet with water.

In practicing this invention it is advantageous, although not necessary, to drain off excess water by any convenient means such as gravity drainage, suction drainage, centrifugation, or the like, to produce a water-moist fibrous nitrocellulose, wetted with sorbed water, and these water-moist fibers are used directly in the process of this invention. These water-moist nitrocellulose fibers feel damp, and generally retain an amount of sorbed water within the range from about 30% to about 60% by weight of water, the lower amounts between about 30% and about 45% by weight being obtainable generally by suction drainage or centrifugal drainage. Since water is substantially all removed in the process of this invention, it is preferable and economically desirable to employ watermoist fibrous nitrocellulose which has been dewatered by suction or centrifugal drainage.

In practicing this invention the water-moist fibrous nitrocellulose may be either initially dispersed and slurried in the selected hydrocarbon diluent with subsequent addition of the selected nitrocellulose solvent to the nitrocellulose-hydrocarbon slurry, or alternatively, the selected hydrocarbon diluent and nitrocellulose solvent may be initially mixed together, and the water-moist fibrous nitrocellulose then dispersed and slurried in the resulting organic liquid mixture of hydrocarbon diluent and nitrocellulose solvent. In either alternative the upper practical limit for the amount of nitrocellulose fibers in the slurry is governed by the ability to agitate the slurry effectively, and for some physical forms of fibrous nitrocellulose this upper practical limit can be in the neighborhood of 20% by weight or evenhigher. For example, the fibrous nitrocellulose to be densified may be jordaned, or ground in a ball mill, or otherwise comminuted, if desired, and such comminution makes it possible to increase the quantity of nitrocellulose which can be effectively agitated in the slurry. Generally, somewhat smaller densified particles are produced when jordaned or otherwise comminuted fibrous nitrocellulose is employed. It will be understood, however, that jordaning, or otherwise comminuting fibrous nitrocellulose is not necessary for the practice of this invention. Generally, slurries containing from about 6.5% to about 18% by weight of fibrous nitrocellulose, dry weight, have been employed, and preferably between about and about by weight of nitrocellulose.

The organic liquid mixture which is employed as the medium for the densification of the nitrocellulose is a mixture of hydrocarbon diluent and nitrocellulose solvent which is completely miscible with said diluent. It is important and necessary for the hydrocarbon diluent and nitrocellulose solvent to be proportioned in the mixture so that the mixture is only a swelling and softening agent for nitrocellulose fibers, incapable of dissolving said fibers. Suitable proportions .of hydrocarbon diluent and nitrocellulose solvent to obtain this objective vary depending principally on the particular hydrocarbon diluent and nitrocellulose solvent selected, and to a somewhat lesser extent on the nitrogen content and viscosity characteristic of the nitrocellulose to be densified. However, with any particular selection of hydrocarbon diluent and nitrocellulose solvent, it is a simple expedient to carry out a preliminary trial by slurrying the desired water-moist fibrous nitrocellulose in the selected hydrocarbon diluent and then progressively adding the selected nitrocellulose solvent with agitation until the point is reached where the mixture begins to swell the fibers. It is then a simple matter in practicing this invention to make minor increases or decreases in the ratio of hydrocarbon diluent to nitrocellulose solvent to obtain the desired bulk density and free-draining characteristics in the finally densified nitrocellulose product.

As a further guide in practicing this invention, it has been found that when employing mixtures of an aromatic hydrocarbon diluent such as toluene and a ketone solvent such as methyl ethyl ketone, the ratio of hydrocarbon diluent to nitrocellulose solvent in the organic liquid mixture can vary between about 3.5 and about 6.5 parts by weight. When employing mixtures of an aliphatic hydrocarbon diluent such as heptane and a ketone solvent such as methyl ethyl ketone, the ratio of hydrocarbon diluent to nitrocellulose solvent in the organic liquid mixture can vary from about 2.5 to 3.5 for densification of a nitrocellulose having 11.5% nitrogen, and from 2 to 3 for densification of a nitrocellulose having 12.6% nitrogen. Reference to the examples will reveal other typical mixtures of hydrocarbon diluent and nitrocellulose solvent suitable as guides for practice of this invention.

Nitrocellulose solvents suitable for the purposes of this invention are the lower molecular Weight ketones, esters, glycol ether-alcohols and glycol ether-esters which are soluble in water to the extent of at least about 2.5% by weight. Some typical nitrocellulose solvents which are suitable for practice of this invention include, for example, methyl formate, ethyl formate, methyl acetate, ethyl acetate, isopropyl acetate, methyl propionate, acetone, methyl ethyl ketone, diethyl ketone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, methoxyethyl acetate, and the like. Preferably, the nitrocellulose solvent should have a boiling point below the boiling point of the hydrocarbon diluent employed, or should form a minimum boiling azeotropic mixture with the hydrocarbon diluent and/or with water. Methyl ethyl ketone is especially preferred for the purposes of this invention since, in addition to having suitable solubility in water and forming a minimum boiling mixture with water, it is also free of any tendency to'hydrolyze. In general, a ratio of introcellulose solvent to nitrocellulose within the range from about 0.7 part to about 3 parts of said solvent per part of nitrocellulose by weight has been found to be suitable for the purposes of this invention.

Any volatile hydrocarbon which is liquid at ordinary temperatures and atmospheric pressure may be employed for the purposes of this invention including aliphatic, cycloaliphatic, aromatic, arylaliphatic and aliphatic aryl hydrocarbons, and mixtures of any of these. Some typical hydrocarbons include, by way of example, hexane, heptane, octane, isooctane, nonane, and'the like, various proprietary petroleum distillate cuts such as textile spirits, mineral spirits, lactol spirits, V.M. & P. naphtha, gasoline, kerosene, and the like, cyclopentane, cyclohexane, methyl cyclohexane, benzene, toluene, xylene, ethyl benzene, styrene, u-methyl styrene, various proprietary aromatic hydrocarbon distillate cuts, mixtures of aliphatic and aromatic hydrocarbons, and the like. Preferred hydrocarbons for the purposes of this invention are toluene, and aliphatic hydrocarbons which boil in the range of heptane and lactol spirits petroleum cuts.

Softening and swelling of the nitrocellulose fibers occurs quite rapidly in the organic liquid mixtures employed in this invention. It is important, therefore, to continuously maintain agitation of the slurry throughout the process and until the softened and swollen nitrocellulose particles have been hardened by removal of substantially all of the nitrocellulose solvent by distillation. Agitation prevents substantial agglomeration of the softened and swollen nitrocellulose particles into lumps, and should be suflicient at all times to keep the nitrocellulose uniformly distributed throughout the slurry without causing any substantial shearing and comminution action on the softened and swollen nitrocellulose. For this purpose, any conventional paddle blade, propeller blade, or turbine blade agitator is suitable.

As indicated by the examples, the hydrocarbon-wet densified nitrocellulose particles of this invention may, and usually does, contain a small residuum of sorbed water, usually substantially less than 1% by weight of the final product. Such residuum of sorbed water, however, is without significant interference with use of the hydrocarbon-wet densified nitrocellulose in lacquers, protective coatings, adhesives, inks, and the like.

What I claim and desire to protect by Letters Patent is:

1. A process for producing hydrocarbon-wet, densified nitrocellulose particles which comprises:

(a) subjecting to non-shearing agitation a slurry of water-wet fibrous nitrocellulose in a volatile mixture of a hydrocarbon and a nitrocellulose solvent which is completely miscible therewith and which is soluble in H O to the extent of at least about 2.5% by weight, said mixture being capable of softening the fibrous nitrocellulose without dissolving the same;

(b) hardening the nitrocellulose particles by distilling oft" water and nitrocellulose solvent from the slurry, while continuing agitation; and

(c) recovering densified nitrocellulose particles wet with sorbed hydrocarbon diluent.

2. A process for producing hydrocarbon-wet densified nitrocellulose particles which comprises the following steps:

(a) subjecting a slurry of water moist fibrous nitrocellulose in a hydrocarbon to non-shearing agitation;

(b) while continuing agitation, adding thereto a nitrocellulose solvent which is completely miscible with the hydrocarbon and soluble in water to the extent of at least about 2.5% by weight, in an amount suificient to soften the nitrocellulose fibers without dissolving the same;

() continuing agitation until substantially all of the nitrocellulose fibers are softened and swollen;

(d) hardening the nitrocellulose particles by distilling off nitrocellulose solvent and water, while continuing agitation; and

(e) recovering densified nitrocellulose particles wetted with sorbed hydrocarbon diluent.

3. A process for producing hydrocarbon-wet densified nitrocellulose particles which comprises:

(a) subjecting to non-shearing agitation a slurry of water-wet fibrous nitrocellulose in a volatile mixture of a hydrocarbon and a nitrocellulose solvent which is completely miscible therewith and which is soluble in H O to the extent of at least about 2.5% by weight, said mixture being capable of softening the fibrous nitrocellulose without dissolving the same;

(b) continuing agitation until substantially all of the nitrocellulose fibers are softened and swollen;

(c) hardening the nitrocellulose particles by distilling off water and nitrocellulose solvent from the slurry, while continuing agitation; and

(d) recovering densified nitrocellulose particles wet with sorbed hydrocarbon diluent.

4. A process in accordance with claim 1 in which the hydrocarbon diluent is toluene and the nitrocellulose solvent is methyl ethyl ketone.

5. A process in accordance with claim 1 in which substantially all of the nitrocellulose solvent and water are removed from the slurry by distillation with addition of hydrocarbon diluent to the slurry.

v 6. A process in accordance with claim 2 in which the nitrocellulose solvent is added to the slurry of watermoist fibrous nitrocellulose in hydrocarbon diluent beneath the surface of the slurry.

7. A process in accordance with claim 2 in which the hydrocarbon diluent is toluene and the nitrocellulose solvent is methyl ethyl ketone.

8. A process in accordance with claim 6 in which the ratio of toluene to methyl ethyl ketone is between about 3.5 parts and about 6.5 parts of toluene per part of methyl ethyl ketone by weight. 7

9. A process in accordance with claim 2 in which the hydrocarbon diluent is heptane and the nitrocellulose solvent is methyl ethyl ketone.

10. A process in accordance with claim 2 in which the hydrocarbon diluent is toluene and the nitrocellulose solvent is acetone.

11. A process in accordance with claim 2 in which the hydrocarbon diluent is toluene and the nitrocellulose solvent is methyl acetate.

References Cited UNITED STATES PATENTS 2,715,574- 8/1955 Cox et al 1492 2,885,736 5/1959 ONeill 149-2 XR 3,057,012 10/1962 Lufkin 260223 XR 3,198,645 8/1965 Plunguian 260-223 XR 3,236,702 2/1966 Sapiego 260-223 XR 3,251,823 5/1966 Murphy et al. 260-223 DONALD E. CZAJA, Primary Examiner.

LEON J. BERCOVITZ, Examiner. R. W. MULCAHY, Assistant Examiner

Claims (1)

1. A PROCESS FOR PRODUCING HYDROCARBON-WET, DENSIFIED NITROCELLULOSE PARTICLES WHICH COMPRISES: (A) SUBJECTING TO NON-SHEARING AGITATION A SLURRY OF WATER-WET FIBROUS NITROCELLULOSE IN A VOLATILE MIXTURE OF A HYDROCARBON AND A NITROCELLULOSE SOLVENT WHICH IS COMPLETELY MISCIBLE THEREWITH AND WHICH IS SOLUBLE IN H2O TO THE EXTENT OF AT LEAST ABOUT 2.5% BY WEIGHT, SAID MIXTURE BEING CAPABLE OF SOFTENING THE FIBROUS NITROCELLULOSE WITHOUT DISSOLVING THE SAME; (B) HARDENING THE NITROCELLULOSE PARTICLES BY DISTILLING OFF WATER AND NITROCELLULOSE SOLVENT FROM THE SLURRY, WHILE CONTINUING AGITATION; AND (C) RECOVERING DENSIFIED NITROCELLULOSE PARTICLES WET WITH SORBED HYDROCARBON DILUENT.