US2415423A - Process of nitration - Google Patents

Description

1947. A. o. FRANZ ETAL PROCESS OF NITRATION Filed March 31, 1943 INVENTOR AEVEL OFQA/VZ3GQ/N CKEPL/NGEQ ATTORNEY Patented Feb. 11, 1947 Nl'iE STS 2,415,423 rnocnss or NrrnA'rioN Arvel 0. Franz and Orin (l. Keplinger, Alton, Ill., assignors to 01in Industries, Inc., a corporation of Delaware Application March 31, 1943, Serial No. 481,368

4 Claims.

This invention relates to the manufacture of explosives and more particularly to a continuous nitration process in the manufacture of tetryl.

Tetryl has been commercially prepared heretofore by both continuous and intermittent type processes involving the nitration of dimethylaniline. Such processes have been attended by the disadvantage that high-priced raw materials were required and a low yield of product Was obtained.

The preparation of tetryl by an intermittent type process involving the nitration of dinitromethylaniline has been previously described, for instance by Gerard Desseigne on pages 156-170 of volume 28 of Memorial des Poudres (1938), and with this reaction an increased yield is obtained with an economy of nitric acid and aromatic hydrocarbon. Such intermittent processes however are attended by the disadvantage that relatively large expensive apparatus is required with many separate processing steps and with a large amount of explosive in process.

It is an object of this invention, therefore, to provide a continuous process for the nitration of dinitromethylaniline to form tetryl.

Another object of this invention is to provide a continuous process for manufacturing tetryl free of the disadvantages attending such prior processes.

Another object of the invention is to provide a continuous process for effecting an efficient nitration of an aromatic compound in the production of tetryl.

Other objects and advantages will become apparent from the following description and drawing in which,

Figure 1 shows a plan View of a nitrating apparatus suitable for carrying out the process of this invention, and

Figure 2 shows a vertical section, taken at XX, of the nitrator of Figure 1, and

Figures 3, 4, and 5 are diagrammatic views illustrating various forms of opposing circulation of the reaction mixture which may be employed in carrying out this invention.

These objects and advantages are obtained in accordance with the present invention by the provision of a novel process in which th nitrating 2 trated material being continuously discharged at the end of said path.

It has now been found that the heat of reaction can be adequately dissipated and the period necessary for reaction is readily obtained when the nitrating mixture is passed along a vertical U-shaped path with agitators in the mixture providing zones of opposing circulation in accordance with this invention. The apparatus set forth herein for carrying out the process of this invention is described and claimed in our copending application, Serial No. 481,369, filed March 31, 1943.

Referring to the drawing, which represents a preferred embodiment of an apparatus for carrying out the nitration process, an upright U- shaped nitrati ng vessel i is shown provided With external cooling or heating jackets 2, 3, 4, 5, 6, 'i, and 3 having inlets and outlets 2'5, charging inlets t and H3 in the arm II for introducing the nitrating acid and aromatic compound to be nitrated into the vessel i, and outlet l2 on the discharge arm l3 for discharging the spent acid and product.

The reagents are introduced through inlets 9 and iii, preferably at some distance above the surface of the reacting mixture in the nitrator. By thus maintaining the inlets out of contact with the reaction mixture, all possibility for either the reaction mixture of any of its constituents to return through either inlet 9 or ID is avoided. Vents 23 and 24 may be employed for removing any fumes from the nitrator l and for maintaining the contents at atmospheric pressure. Thermometer Wells 26 may be employed for determining the temperature of the contents of the vessel I.

Agitators, la, l5, it, 2B, 2!, and 22 maintain the mixture uniform and maintain any precipitated tetryl uniformly suspended in the solution. The agitators, i4, i5, l8, 2!], 2!, and 22 may be so adjusted that no appreciable head of liquid ocours in either arm l! or E3 and are so shaped and arranged that they form the mixture into at least two zones of opposing circulation so that practically no part of the mixture in arm l3 returns to arm H. Outlet It at the bottom of the vessel l is included to provide a means for completely draining the vessel 1 in case of emergency or for cleaningpurposes and the like.

Incarrying out .the process the aromatic intermediate, preferably dissolved in a suitable liquid, and the nitrating acid are fed in proper proportion respectively through inlets 9 and I0 into the arm II to form an initial reaction zone with thorough mixing by the agitator M, and during the initial reaction the mixture is cooled to the desired temperature by heat exchange with a cooling medium circulated through the jacket 2. The mixture gradually passes through the succeeding zones of localized agitation, the temperature being controlled by means of jackets 3, l, 5, 6, I, and 8 and the product and spent acid are discharged by overflowing from the outlet I2 at a rate corresponding to the feed of raw materials.

After leaving the initial reaction zone,'in one embodiment of the invention, the mixture may be directed by at least one agitator toward the outlet l2 and subsequently by at least one agitator away from the outlet i2, so that adjacent opposing zones of circulation are set up in which the mixture in one zone is circulated in a direction opposite to that in the other zone, for instance as illustrated at 21 and 28, Figure 3. With the mixture thus circulating in opposite directions in these zones, travel of the mixture from one zone to the other is suificiently retarded for practical operation, and such travel results for the most part only toward the outlet at a rate corresponding to the feed of reagents through inlets and I 0.

In other embodiments of the invention the opposing zones of circulation may be formed by providing zones or" substantially localized agitation with or without a head of the mixture in one arm of the vessel, or by providing substantially horizontal agitation in which the mixture in both arm of the container is propelled either in clock-wise or a counter-clock-wise direction, or in any other suitable manner. Propeller type, paddle type, or any other suitable type of agitators may be employed, provided that they are so adjusted as to create the desired successive zones of opposingly directed circulation. For instance, when the agitator shafts I? and lil are rotated in a clock-wise direction, the mixture in both the charging and discharging arms II and 13 respectively, tends to rotate likewise in a clock-wise direction but at the bottom of the U, where the two columns of the mixture join, the direction of circulation on the charge side opposes that on the discharge side, for example as illustrated at 3! and 32, Figure 5, so that zones of opposing circulation are set up.

By feeding the raw materials into one arm of the U-shaped vessel and controlling the agitation to form such opposing zones of forced circulation, the raw materials are prevented from short-circuiting from the inlets 9 and ill to the outlet l2 before the reaction has been completed and likewise, the completely reacted material is prevented from returning to the inlet arm, so that during the gradual travel of the constituents from the inlets 9 and I0 through the vessel to the discharge outlet i2, each portion of the material to be nitrated is kept uniformly mixed with its proper portion of the nitrating acid.

By way of illustration, following is a typical embodiment of the invention in which dinitromethylaniline is nitrated with a nitrating acid consisting of a mixture of nitric acid, sulfuric acid and water.

The dinitromethylaniline is put into liquid form or solution by dissolving one part in 2.43 parts by weight of sulfuric acid (66 B.). The nitrating acid employed contains 68% nitric acid, 16% sulfuric acid and 16% water. The diameter of the tube forming the U-shaped vessel l employed is about 16 inches and the apparatus is about 4 /2 4 feet high. The liquid travels about 11 feet in going from the inlets 9 and H] to the outlet l2.

In first starting the nitration, the above described mixed acid is run into the nitrator through inlet ill at the rate of 18.8 gallons per hour until the nitrator is about /4 full. The feed of acid is then stopped and the above described dinitromethylaniline solution is run into the nitrator at the rate of 50 gallons per hour for an equal length of time. When this is accomplished the nitrator is sufficiently filled for the continuous nitration operation to be started.

The dinitromethylaniline solution is then fed in through inlet 9 at a rate of about 50 gallons per hour and the mixed acid is simultaneously fed in through inlet 10 at the rate of about 18.8 gallons per hour, thus providing about 0.765 part by weight of nitric acid per each part by weight of dinitromethylaniline, or only about 20% over the theoretical acid requirement. At this rate of speed, i. e., a nitration cycle of minutes, a yield of about 300 pounds of tetryl per hour was obtained,

By increasing the rate of feed of the reagent, this nitration cycle can be reduced to as short a time as 20 minutes or even shorter with satisfactory results and such increased feed of reagents provides a proportionately increased production rate. This flexibility of production rate is a decided advantage over prior processes.

The agitator l4 provides for immediate and uniform mixing of the nitrating acid and dinitromethylaniline solution. Agitator shafts l7 and is are rotated in a clock-wise direction, thus providing opposing circulation at the bottom of the vessel 1 as illustrated at (it and 32, Figure 5, the agitators being of the type tending to circulate the mixture in a horizontal direction. Agitators E4, 56, and 22 have their blades so adjusted as to direct the mixture away from the sidewalls of the container, for instance as illustrated at 30, Figure 4, and agitators I5, 28, and 2! have their blades so adjusted as to direct the mixture toward the sidewalls, for instance as illustrated at 29, Figure 4, thus providing several zones of opposing circulation. The mixture is kept at a reaction temperature of 55 C. by flowing water or other coolant, as required through the temperature controlling jackets 2, 3, 4, 5, 6, l, and 8.

The mixture in the initial reaction zone has a purplish color which disappears usually before reaching the bottom of the U-shaped vessel 1 and changes to a yellow color which persists up to the outlet [2. By virtue of the vigorous agitation maintained throughout the vessel, any tendency of the precipitated tetryl to segregate is prevented. A tetryl product is obtained at a yield in the range of about to 99% of the theoretical, having a pale yellow color and after moderate washing, a melting point in the range of about 127 to 129" C. and an acidity, calculated as sulfuric acid, equal to about 0.1% to 0.3%, or less.

Accordingly, the nitration temperature is maintained from the time of mixing of the raw materials until the reaction is completed, the necessity for starting the reaction at relatively low temperatures as in prior processes and equipment is avoided, and a shorter nitration cycle is thus provided. By adding the proper proportion of nitrating acid which is preferably at least 10% above the theoretical requirement to each part of dinitromethylaniline and maintaining a uniform mixture of the materials in each zone of circulation while controlling the temperature of the mixture to about 50 to 60 C. throughout its gradual travel through the vessel, practical all overnitration and oxidation of the dinitromethylaniline is prevented. The precipitation of the tetryl during the nitration tends to thicken the mixture and thus materially aids in the bafiling effect, resulting from the zones of opposing circulation, which prevents any undesirable intermixing of the various strata of the mixture in the nitrator.

For the most efficient production of tetryl, the temperature of the mixture from the time of mixing raw materials until the reaction is complete is held below 80 C. and preferably between 50 to 60 0., or at about 55 C. If desired, a lower temperature may be maintained in the initial reaction zone and in the subsequent zones of circulation, although a product of poor stability may result therefrom. To obtain tetryl of exceptionally good stability, a to excess of nitric acid over the theoretical requirement is preferred, since greater amounts tend to cause some oxidation, whereas lesser amounts tend to result in incomplete nitration.

Although the nitration of dinitromethylaniline is described in the above specific embodiment, tetryl may be prepared in accordance with this invention by the nitration of any other suitable aromatic intermediate, and likewise, although sulphuric acid is described as the solvent for the dinitromethylaniline and as the dehydrating component of the nitrating acid, any other suitable solvent and dehydrating agent may be employed, for instance phosphoric acid.

In accordance with this invention, the aromatic compound to be nitrated and the nitrating acid, after being thoroughly mixedin the initial reaction zone, tend to travel toward the discharge outlet with practically no intermixing with subsequently added raw materials, or with the more completely reacted material, while at the same time a thorough localized circulation of the mixture is provided, until the reaction is complete and the product is discharged from the nitrator.

Following is another embodiment of the invention describing the use of the apparatus in the manufacture of nitroglycerine.

The nitrating acid employed is composed of about 50% nitric acid and 50% sulfuric acid. The nitrator has about the same dimensions as those described in the above embodiment for the nitrator used in the manufacture of tetryl. In first starting the operation, the nitrator is filled with a spent acid containing about 20% nitric acid, 64% sulfuric acid, and 16% water. Anhydrous glycerine is then fed in through inlet 9 at a rate of about 18.1 gallons per hour and the nitrating acid is simultaneously fed in through inlet H0 at the rate of about 72.5 gallons per hour, thus providing about 5 parts by weight of nitrating acid per each part by weight of glycerine, with only about 28% excess over the theoretical nitric acid requirement. t this rate of feed, a yield of about 441 pounds of nitroglycerine per hour was obtained.

Only agitators such as at it, it, 20, and 22 were employed for the nitroglycerine manufacture, agitators l5, 2!], and 22 having their blades so shaped and adjusted as to direct the mixture in a downward direction and agitator hi having its blades so shaped and adjusted, in any of the well-known ways, as to produce an emulsifying action with very turbulent agitation. A plurality of zones of opposingly directed circulation are thus provided, for instance, as illustrated in Figure 3. The mixture in the nitrator is kept at a reaction temperature of about 16 C. to 20 C. by flowing any suitable refrigerant through the jackets 2', 3, 4, 5, 0, Land 8. Any fumes that develop during the reaction are readily disposed of through vents 23 and 2d. The large amount of heat involved in such reactions is readily dis sipated in accordance with this invention by means of the large cooling surface provided per unit volume of reaction mixture and the turbulence of agitation.

By thus providing a tubular reaction vessel in which the reaction mass is agitated rapidly in more or less discreet zones at least three desirable objectives are attained. Firstly, vigorous agitation and thorough mixing of reagents is accomplished without permitting any portion of the reaction mass to proceed directly from inlet to outlet without reacting, or any portion of reacted product to remix with the entering reagent. Secondly, a desirably large cooling surface is provided without the introduction of complicated or cumbersome internal coils. Thirdly, a greatly improved overall heat transfer ooefdcient can be obtained, since vigorous agitation reduces the thickness of the stagnant film on the inside of the reaction vessel. In this case the thickness of this film substantially controls the overall heat transfer coemcient which can be obtained.

While certain specific details are set forth herein, it should be understood that considerable modification and change can be made without departing from the spirit and scope of the invention, and that the invention is to be limited only insofar as set forth in the appended claims.

What we claim is:

1. In the manufacture of tetryl, the step of nitration which comprises uninterruptedly bringing the aromatic compound to be nitrated and the nitrating acid together, continuously flowing the resulting mixture through a confined extended successively descending and ascending path, concomitantly creating intra-stream circulations at a plurality of zones along said path,

a some of said intra-stream circulations being opposingly directed, and continuously discharging the spent acid and the tetryl at the end of said path.

2. In the manufacture of tetryl, the process which comprises continuously bringing together a nitrating acid and the compound to be nitrated while violently agitating and cooling the resulting mixture, flowing the mixture through a confined extendedsuccessively descending and ascending path, concomitantly creating intrastream circulations at a plurality of zones along said path with the direction of intra-stream circulation in at least one of said zones being substantially opposite to that of a contiguous zone, and continuously removing the tetryl and spent acid at the end of said path.

3. The process of nitration comprising flowing a mixture of the nitrating acid and the compound to be nitrated in a continuous stream through a confined extended successively descending and ascending path, concomitantly creating intra-stream circulations at a plurality of zones along said path, some of said intra-stream circulations being substantially oppositely directed, all while maintaining the mixture at reaction temperature, and discharging the reaction products at the end of said path.

4. The process of nitration comprising flowing a mixture of the nitrating acid and glycerine in a continuous stream through a confined ex- '2' 8 tended successively descending and ascending path, concomitantly creating intra-stream cir- UNITED STATES PATENTS culations ata plurality of zones along said path, Number Name Date some of said intra-stream circulations being sub- 1,943,031 Meissner Jan. 9, 1934 stantially oppositely directed, all while main- 5 2,256,999 Castner Sept. 23, 1941 taining the mixture at reaction temperature, and

discharging the reaction products at the end of FOREIGN PATENTS said path. Number Country Date ARVEL o. FRANZ- 217,614 B1 itish June 20, 1924 ORIN o. KEPLINGER. OTHER REFERENCES Chem. Abstracts, Vol. 33, p. 9646 (1939). (Copy REFERENCES CITED m Pat Om Lib) The following references are of record in the Chem. Abstracts, V p- 463 (1923)- DY file of this patent: 15 in Pat. Off. Lib.)

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