US2347660A - Manufacture of explosives - Google Patents

Description

Patented May 2, 194.4

, 2,347,660 MANUFACTURE or ExPaosrvns Jerome G. Burtle, Godfrey Township, Madison County, 111., assignor to Western, Cartridge Company, East Alton, 111., a corporation of Dela- No Drawing. Application July 16, 1941, Serial No. 402.720

11 Claims.

This invention relates to a method for pro ducing purified granular nitro-aromatic exploslves, particularly nitro-aromatic nitramines such as trinitrophenylmethylnitramine (tetryl).

The various nitro-aromatic compounds which have been used as base charges in detonators, and as booster or bursting charges in explosive shells, bombs, and demolition cartridges must meet rigid requirements not only With respect to chemical purity and stability, but also with respect to handling properties. Thus, before being acceptable for use, each individual nitroaromatic explosive must generally pass tests with respect to stability, melting point, and absence of foreign material or matter which is insoluble in a liquid known to be a good solvent for the particular explosive. In addition, where the explosive is to be handled as a solid, i. e. pressed. into pellets or loaded volumetrically into shells, specifications generally call for free-flowing qualities of the solid explosive as well as definite ranges of particle size. It is accordingly essential that the explosive product should possess both high chemical purity and proper physical form,

The nitro-aromatic compounds which may be used as high explosives are generally obtainable by a process of nitrating a suitable interme diate with the use of mixed acid. The crude material obtained after separation from the nitration mixture and thorough washing is characterized by the presence of of impurities which impair the stability and/or adversely aiiect other properties such as color, solubility, and melting point. Accordingly, one or more purification treatments are generally required for the obtainment of a product of acceptable purity. Furthermore, if the form and size of the particles is not correct at this stage, an additional crystallization or granulation step must be provided in order to produce a product which will meet the specified requirements not only with respect to purity but also as to physical form.

It has accordingly been extremely difiicult to obtain an entirely satisfactory product, and, in

the case of tetryl for example, no simple method has heretofore been described whereby the desired granulation and purification can be effected simultaneously. Thus, when the process employed is that of crystallization from a volatile hydrocarbon or chlorinated hydrocarbon solvent, the solution having previously been washed by agitation with warm water, the resulting product is characterized by suitable purity but unsatisfactory handling properties due to improper physical form. Likewise, when the product is prepared by dissolving the crude in a solvent such as acetone and then mixing the solution with Water, the process may be carried out so as to result in material having satisfactory granulation, but the stability of the product is not consistently satisfactory.

An object of this invention is to provide an improved simplified process for the production of stabilized free-flowing tetryl, Intro-aromatic nitramines, or other nitro-aromatic explosives.

Another object of this invention is to provide an improved method for the granulation of tetryl, nitro-aromatic nitramines, or other nitroaromatic explosives whereby granulation and stabilization are effected simultaneously.

A further object of this invention is to .provide a method for the preparation of solid nitroaromatic explosives from solution in an oxygencontaining organic solvent, whereby any deleterious action of the solvent on the explosive is avoided.

A further object of the invention is the provision of a simple and convenient method for converting a crude nitro-aromatic explosive into a stable free-flowing granular product.

Other objects will be apparent from the following detailed description.

In accordance with this invention, generally stated, a crude Intro-aromatic explosive is converted into a free-flowing granular product having considerably enhanced stability and purity by dissolving the same in a volatile oxygen-containing organic solvent, in the presence of sufficient acid to prevent any deleterious reaction between the explosive and the solvent, and then separating the product from the solution under conditions controlled to produce the desired granulation.

The method of this invention is adapted for the treatment of the Intro-aromatic explosives such as trinitrotoluene, the polynitronaphthalenes, tetranitroaniline, and particularly of nitroaromatic nitrarnines, such as tetryl, and tetryl analogs such as trinitrophenyl-ethyland -butyl-nitramine and hexanitrodiphenyl-ethylenedinitramine (di-tetryl). The material for treatment may consist, of the crude obtained from the nitration step, or in general of explosive having inadequate stability, purity, or physical form, such as may result from partial deterioration after extended storage.

'In applying this process to the manufacture of tetryl, the crude may be obtained by the nitration of dimethylaniline, but is preferably prepared by the nitration of dinitromethylaniline, obtained for example by the interaction of 1,2,4-chlorcdinitrobenzene with 1 methylamine, in view of the advantages with respect to yield, purity, and ease of nitration in accordance with the latter method.

The solvent to be employed in accordance with the present procedure consists largely or entirely of a volatile oxygen-containing organic solvent, having good solvent propertiesior the explosive under treatment and which is proferably characterized by complete or substantial miscibility with water. Ketones, esters, and others, as exemplified by'acetone, methylacetate, and dioxan, have been found particularly suitable, and the solvent for the explosive whether a single or composite liquid, should preferably have a boiling point within the range of 40 to 110 (3., although liquids of higher boiling point many at times be useful.

Oxygen-containing organic liquid solvents are advantageous since solutions containing 10%- 50% or more by weight of the explosive can readily be prepared at convenient operating temperatures by the use either of an individual solvent chosen from this group or of a suitable solvent mixture composed largely of one or more members of this group, and a free-flowing granular product is readily obtainable therefrom, as for example by precipitation of the explosive on mixing the solution with a sufi'icient amount of water. However, explosive material prepared in this manner not only fails to meet the requirements of stability tests, but frequently displays poorer results than the starting material.

A particularly severe test which is app to nitroaromatic explosives is the 120 C. vacuum stability test (as described by Farmer in the Journal of the Chemical Society, vol. 117, pages 1432-1445, (1920), in which 5 grams of the dry explosive are heated under vacuum for 40 hours, the volume of gas liberated by the sample during this heating period being determined by measuring the increase in pressure produced within the system. A sample which liberates less than 4.0 cc. of gas under the conditions of the test is considered to have a high order of purity and stability, While the evolution of more than 6.0 cc. of gas is considered to indicate the presence of excessive amounts of deleterious material. extreme sensitivity of this test is indicated by the fact that excessive volumes of gas may be obtained from samples which would otherwise ap- The I of gas under the conditions of the test.

matter, and by other tests of stability, for example, the Abel test, in which a 1.5 gram sample must produce no discoloration of standard potassium iodide-starch test paper in less than 20 minutes at 99 C.

It has been found that the use of volatile oxygen-containing organic solvents in the treatment of tetryl leads to a product of suitable physical form but not having consistently adequate purity as revealed by the 120 C. vacuum stability test. It has furthermore been found that repetition of the treatment produces no improvement in the product in this respect. Also, attempts to produce an entirely satisfactory explosive product by subjecting material of excellent purity but poor physical form, obtained by crystallization from benzene or toluene, to treatment with an oxygen-containing organic solvent likewise result in failure to obtain a consistently good product.

Further investigation has revealed that the probable cause of the instability of products resulting from such treatments resides in an interaction between the explosive nitroaromatic compound and the oxygen-containing solvent, giving rise to, compounds causing the evolution The occurrence of chemical action between the explo sive and the solvent in such solutions is confirmed by the observation of a marked deepening in color from yellowish-brown to orange or even dark red on standing, which change in color is considerably accelerated by a rise in tempera ture and/or in the presence of moisture.

As a result of extensive research, I have discovered that the color change can be prevented and a product consistently obtained which satisfactorily meets all test requirements, by the precaution ofincorporating a sufficient amount of acid with the solvent. A variety of acids have been found elTective for the purpose, including organic acids such asformic, acetic, tartaric, and salicylic, and inorganic acids such as hydrochloric, sulfuric, phosphoric, and nitric. For each individual acid, a minimum ratio to the explosive may readily be established by small scale experiments below which effective action is not consistently obtained, as Well as a maximum ra tio above which no further improvement is secured or, in some cases, deleterious action may occur. For reasons of economy and because it is essential to remove the acid completely from the finished product, it is preferable to employ the smallest amount of acid which is consistently efiective.

The advantage in using an acidified oxygencontaining solvent, in accordance with this invention, is apparent from the following table which lists the stability test results obtained on samples of tetryl treated with acidified solvents as contrasted with acid-free solvents. A solution of tetryl in the indicated solvent was prepared at 40-50 0.; water at -90 C. in the ratio v of 4 parts of. water per part of tetryl was then pear to be of high chemical purity as judged from melting point, color, absence of insolub e added to the solution during vigorous agitation; and the precipitated tetryl was then filtered, subjected to a washing treatment with water at C., filtered, and dried. In each case, the table indicates the parts by weight of solvent and of acid used per part by weight of tetryl. The experimental conditions were identical in each comparison, so that the results indicate directly the beneficial effect of the presence of acid in the solution of explosive.

Table Gas volume evolved Solvent Acid in 40 hours at None 15 cc. or more. 0.24 formic. 8.5. 0.20 salicyl 6.9. 0.006pho sphoric. 5.7. 0.00 hydrochlo- 4.7.

no. 0. 34sulfuric 4.5. 0.21 nitric 3-6. }None 12 or more.

:1 .1358benzene (or toluene). mmc

.1 acetone .1408methanol g m .1 acetone... r A0 methanol }0.21 nitnc 7.%lr2).8 cc. 1n 20 1.58 acetone... g ethyl he }None (1.1 111-20 hrs). 1. acetone... I g'thiyl ether }0.21 11ltrlc 20 (6.5 111 20 hrs.). 1'. ace one--. J52 acetic mi }None. 12 (4.2 in 20 hrs).

9 (3.1 in 20 hrs).

e }Nonc 1. 6.3.

1 1s acetone-.. blggethyl methyl ketone-- mmc ac one 1% mhylem, glycol }No e so 1 1 0.acone L12 methylene glycol }0.2l nitric 18 (0.9 111 1b hrs). 1.18 acetone .651)- ethylene dichloride one 1. Sacetone .63' ethylene dichloride. 1.18 acetone.. .458ethytl acetate -"f 1.1 ace 0ne ethyl acetate }0.2l nitric 5.0. 1 87 methylacetate None. 4.9. l 87 methyl acetate 0.21 nitric 3.0. 2.17 dioxane None 5.1. 2.17 dioxane 0.21 nitric V 2.7 1.65 methyl acetone (20- None 9.3.

25% methanol, 27.531%

mehyl)acetate, 47.5-51% ace one 1.65.1nethyl acetone 0.21 nitric 3.5.

As a further illustration of the striking contrast between the efiect of an acid-free and an acidified oxygen-containing organic solvent, stable tetryl which evolves less than 4 cc. of gas in the 120 C. vacuum stability test, becomes unsuitable after treatment with the acid-free solvent such as acetone, liberating a volume of 6 or more cc. of gas under the 120 test, while a sample of the same material, after being subjected to treatment with. the acidified solvent under otherwise identical conditions, will still be found to liberate less than 4 cc. of gas under the test/conditions. 7 V

While, as indicated above, a variety of acids have been shown to be efiective for the purpose,

"""the inorganic acids display greater activity and may be used in smaller proportions than the organic acids. Precautions are required in the use of hydrochloric, sulfuric, and phosphoric acids in that proportions in excess of those listed in the above table should not be exceeded, and, in the case of sulfuric and phosphoric acids, the temperature of the solution of the explosive should be maintained not higher than about 40 C. Nitric acid is the preferred acid for use in the process, in view of the wide range of effective proportions, from about 0.05 to 0.40 part of acid per part by weight of tetryl, and the fact that no special precautions are required in its use.

The crude material for treatment in accord ance with the present process may be in the dry state or it may contain a residual moisture content, for example 8-l5%, which is retained following the final step of separating the explosive material from the wash water, as by centrifuging subsequent to the step of nitration. It is generally preferable to have the crude as free from residual nitrating acid as can be accomplished by thorough washing, particularly when the operations are so carried out that the crude is stored for a period of time before being subjected to the purification and granulation step.

The process of this invention is accordingly applicable for the ready conversion into a product which is satisfactory in all respects from a starting material which is inadequate with respect either to purity or physical form or both. The material is dissolved to form a 10% to solution by weight in a solvent which is composed entirely or predominantly of a volatile oxygen-containing organic solvent at a temperature which is somewhat below the normal boiling point of the. solvent and which is, in any case, not higher I than about 90 C. Typical preferred solution temperatures are 40 to 50 C. for acetone or methyl acetate; 40 to C. for methyl acetone, and for mixtures predominantly of acetone with benzene, toluene, ethylene dichloride, or ethyl acetate; and 40 to 90 C. for dioxane or other high-boiling solvents or solvent mixtures.

Care is taken to provide sufiicient acid in the solution to prevent any deleterious action between the explosive and the solvent, for example at least about 0.05 part by weight of nitric acid per part by weight of explosive.

After filtration to insure the removal of any insoluble matter, the solution is treated to cause separation of the explosive in a highly purified state and having satisfactory granular form. Preferably the separation is accomplished by mixing the solution with warm water during vigorous agitation, under conditions controlled to prevent any substantial loss of solvent by volatilization. The explosive is then separated from the warm mother liquor by decantation or filtration, is thoroughly washed with warm water to remove the residual acid, solvent, and any other water-soluble constituent, and is then dried to the desired low moisture content. Another mode of separation of the explosive consists in cooling the solution to cause crystalliaa% tive" embodiment of the method in accordance with this invention, crude tetryl having a deep yellow color and a melting point between 126 and 128 C. obtained by the nitration of dinitromethylam'line with mixed acid, is converted to a very pure and stable product of satisfactory granularity, pale yellow in color and having a melting point between 128.8 and 129.1 C., by the following procedure:

Crude tetryl is dissolved in acidified acetone at a temperature of 40 to 50 C. to form a solution containing 1 part by weight of tetryl, 1.3 to 1.7 parts by weight of acetone, and 0.05 to 0.25 part of nitric acid, the required amount of acid having been added to the acetone in the form of a concentrated aqueous solution, for example as a to 73% solution in water.

After filtration of the solution to remove insoluble matter, warm water is rapidly added thereto during vigorous agitation of the emulsifying type. The water, preferably distilled or otherwise treated to have a low content of dissolved solids, is added at a temperature of 55 to C. and in the ratio of about 4 parts by weight of water to 1 part by weight of the explosive.

Following a further brief period ofagitation, the tetryl becomes solidified to pale yellow roughly spherical individual particles or agglomerates. These may be separated from the Warm mother liquor by filtration at about 65 C. on suitable filter beds, and the mother liquor may be treated for recovery of the dissolved-explosive and solvent content.

The tetryl retained on the filter bed is then subjected to a thorough washing with warm water at about 70 to 80 C, in order to remove residual acid, solvent, and other water-soluble constituents. After drying and sieving, the product may be stored ready for use.

Products prepared in accordance with the above procedure invariably display the liberation of less han 6 cc. of gas under the conditions of the 120 C. vacuum stability test, and about 4 cc. or less of gas in most cases. Likewise, the physical form is highly satisfactory, since the material is free-flowing and non-dusting, and the size of the individual particles or agglomerates is largely within the desirable range of 0.006 to 0.0336 inch for the largest dimension. The product likewise meets all other requirements with respect to chemical purity and stability.

In accordance with another embodiment, an acidified solution of crude tetryl in acetone, containing 1 part by weight of tetryl, 1.6 parts acetone, and 0.21 part nitric acid, is heated to 50 C., and added rapidly during vigorous agitation to 4 parts by weight of Water at 85 C. contained in a closed vessel. Following a brief period of vigorous agitation, the crystallized tetryl is separated from the mother liquor as by filtration, thoroughly washed with warm water, and dried. The mother liquor may be treated for recovery of its content of explosive and solvent. The tetryl product consists of individual short thick crystals characterized by very favorable free-flowing and non-dusting qualities and by exceptional purity and stability in accordance with the known tests, evolving from 1.1 to 2.5 cc. of gas, averaging about 1.75 cc., during the 120 C. test.

The washing, treatment following filtration may conveniently be carried out by suspending the tetryl in warm water, heated to a temperature of '70? to 80 (7., for 3 to 4 hours with one intermediate change of water after 1 to 2 hours. This treatment when applied following'the treatment with acidified oxygen-containing solvent has been found to reduce the volume of gas liberated during the 40 hour 120 C. test by 1 to 2 cc. Below 70 C., the purification action is too slow while above 80 C., hydrolysis of the tetryl sets in, impairing the quality of the product. This extent of improvement in the final product .by means of this type of final hot water washing treatment is not obtainable when the prior processing treatment has been effected by means of an oxygen-containing solvent free of acid.

A particularly favorable tetryl product may be obtained by the use of acid in a -50% Solution of tetryl at a temperature above 40 C. and mixing with water at a temperature above 50 0., all at atmospheric pressure, in accordance with the procedure disclosed and claimed in the co-pend- ,ing application of Delbert R. Jones, Serial Number 402,718, filed July 16, 1941, whereby the explosive is initially separated as a liquid phase which persists for some time and subsequently becomes solidified into solid granules or agglomerates. The solid explosive is then advantageously given a thorough washing with water, as described above, and dried.

It is to be understood that this invention is not limited to the details of procedure hereinbefore specifically described for the purpose of illustration but that variations and modifications may be made without departing from the spirit thereof, and that such variations and modifications are, although not specifically described herein, contemplated by and within the scope of the appended claims. The term oxygen-containing organic solvent, as used herein, refers to a sol vent consisting entirely or predominantly of one or more organic liquids in which at least one oxygen atom forms an integral part of the molecule.

Having now described the invention, what is claimed as new and is desired to be secured by Letters Patent is: Y

1.'In themanufacture of explosives, the process comprising preparing a-10-% to 50% solution of a nitro-aromatic explosive in a volatile oxygencontaining lorga'nic solvent normally reactive therewith to impair'its thermal stability, said solution containing 0.05 to 0.25 part of nitric acid per part of the said nitro-aromatic explosive to inhibit such deteriorating effect, and mixing said solution with'water to separate the said explo- SlVe; Y

2. In the manufacture of explosives, the proc ess comprising preparing a 10% to 50% solution of a nitro-aromatic nitramine in a volatile oxygen-containing. organic solvent chosen from the group consisting of ketones, sters, and ethers, said solution containing 0.05 to 0.25 part of nitric acid per part of the said nitro-aromatic nitra-f mine to inhibit such deteriorating effect, and mixing said solution with water to separate the said nitramine.

3. In the manufacture of explosives, the process comprising preparing a 10% to 50% solution of tetryl in a volatile oxygen-containing organic solvent chosen from the group consisting of ketones, esters, and ethers, said solution contain; ing 0.05 to 0.25 part of nitric acid per part of the said tetryl to inhibit such deteriorating effect, and mixing said solution with water to separate the tetryl. v

4. In the manufacture of explosives, the process comprising preparing a 10% to 50% solution of tetryl in a volatile oxygen-containing organic solvent chosen from the group consisting of ketones, esters, and ethers, said solution containing 0.05 to 0.25 part of nitric acid per part of the said tetryl to inhibit siich deteriorating effect, mixing said solution with water to separate the tetryl, and washing the separated tetryl with water ata temperature of 70 to C.

5. In the manufacture of explosives, the process comprising preparing a solution of a intro-aromatic explosive in acetone, said solution containing 0.05 to 0.25 part of nitric acid per part of explosive, and mixing said solution with water to separate the said explosive.

6. In the manufacture of explosives, the process comprising preparing a solution of a nitro-aromatic nitramine in acetone, said solution containing 0.05 to 0.25 part of nitric acid per part of explosive, and mixing said solution with water to separate the said nitramine.

7. In the manufacture of explosives, the process comprising preparing a solution of tetryl in acetone, said solution containing 0.05 to' 0.25 part of nitric acid per part of tetryl, and mixing said solution with water to separate the tetryl.

8. In the manufacture of explosives, the process comprising preparing a solution of tetryl in acetone, said solution containing 0.05 to 0.25 part of nitric acid per part of tetryl, mixing said solution with water to separate the tetryl, and washing the separated tetryl with water at a temperaof the said explosive and a minor proportion of an added acid in a volatile oxygen-containing organic solvent chosen from the group consisting of ketones, esters, and ethers, and mixing said solution with water to separate the explosive.

11. In the manufacture of explosives, the process comprising thoroughly washing a nitro-aromatic explosive with water, preparing a solution of the said explosive and a minor proportion of an added acid in a volatile oxygen-containing organic solvent chosen from the group consisting of ketones, esters, and ethers, solidifying the explosive from the said solution, and thoroughly washing the solidified explosive with water.

JEROME G. BURTLE.

CERTIFICATE OF CORRECTION. Patent No. 25 L660. May 2, 191m.

JEROME G. BURTLE.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, first column, line 52, for the words "presence of of" read presence of--; page 2, first column, line 59, for "many" read may-; page L;., first column, line 17, for "han" read -than; and second column, lines 21 and 22, claim 1, for "normally reactive therewith to impair its thermal stability" read -Chosen .from the group consisting of ketones, esters, and ethers-; lines m" I 'H 2b. and 25, same claim, line 55, claim 2, line 1414., claim5, and lines 55 and 51+, Claim l strike out "to inhibit such deteriorating effect"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this Lyon day of July, A. D. 19th.

Leslie Frazer (Seal) Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION. Patent No. 2,5h7,660. 4 May 2, 191m.

JEROME G. BURTLE.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, first column, line 52, for the words "presence of of" read -presence of-; page 2, first column, line 59, for "many" read -may; page L, first column, line 17, for "han" read than-; and second column, lines 21 and 22, claim 1, for "normally reactive therewith to impair its thermal stability" read chosenfrom the group consisting of ketones, esters, and ethers; lines 21; and 25, same claim, line 55, claim 2, line M claim 5, and lines 55 and 5b., claim 14., strike out "to inhibit such deteriorating effect"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this hth day of July, A. D. 19%.

Leslie Frazer (Seal) Acting Commissioner .of Patents.