US2402180A - Trinitrotoluene manufacture - Google Patents

Description

June l, 1946.

l C. F. PPAZON TRINITROTOLUENE MANUACTURE Filed July 4, 1942 HL TERN/TEL Y FR MNT lzdrls BY IN V EN TOR, v Ffa/45120111 WMMW.

Patented June 18, 1946 UNITED STATES PATENT OFFICE TRINITROTOLUENE MANUFACTURE Charles F. Papazoni, Allentown, Pa., assignor to Trojan Powder Company, a corporation of New York Application July 4, 1942, Serial No. 449,772

(c1. 26o-s45) v 2 Claims.

tion progressively from the mono to the tri-v stage, or conversely, decrease in concentration from the tri-stage to the mono-stage. Fresh acids (oleum and mixed acid) are used onlyvin the tri-stage nitration. 'Ihe tri and di-stage spent acids are fortified (butted up) with nitric acid to furnish the mixed acids used for the dinitration and mononitration, respectively. Thus, it is customary to use the spent acid from the trinitration, after fortification with fresh nitric acid, as the mixed acid for the dinitration, and likewise, to fortify the di-spent acid with nitric acid in making the mono-mixed acid. The spent acid from the mononitration is sent to the denitrator, for the recovery of the nitric acid, and later to the sulfuric acid concentrator to provide concentrated sulfuric acid. The mono.- spent, therefore, is the only spent acid that leaves the nitrating system.

The spent acids from the di and trinitration are ordinarily withdrawn from the nitrators to mixing tanks in another building, there fortiiied with the required amount of nitric acid, and then dropped into a blow case, a closed vessel adapted to withstand pressure. Compressed air is introduced over the acid in this vessel and the acid forced by displacement under the pressure of the air from the blow case to a receiving (scale) tank in the proper nitrating building.

In the handling of this spent acid in the con- Ventional system, there is some unavoidable corrosion of equipment and loss of nitric acid, not only from the spent acid but also from the fortifying nitric acid introduced into the mixing or fortifying tank and subsequently passed t the blow case, scale tank, and back to the nitrator. Furthermore, there are caused many delays in the operating system due to blowing of safety discs. plugging of standpipes, freezing of delivery lines, and occasional explosions, for all of which the use of the blow case is largely responsible. These difficulties are especially pronounced with the tri-spent acid after fortification. This trispent acid contains usually betweenv l5 and 18% of organic material, chiey TNT, and is frequently responsible for blow case explosions in spent acid fortification and handling.

When the spent acidis thus fortified in the mixing'tank and held for a short time at least in the blow case, the nitric acid added frequently causes further nitration to-a hazardous extent` of i'certain nitratable organic material presentinthe spent acid. As the acid stands rfin the blow case, this reaction progressesV in the presence of the' compressed air and altogether too frequently there are explosions with destruction of buildings and equipment, resulting in delays in production aswell as possible injury to workmen and surrounding property. 1

In the attempt to reduce blow case explosion hazards, the blow cases are ordinarily provided with a safety sealvof sheet lead discs or the like which will rupture at certain set pressures, say 40 to 45 pounds to the square inch. These discs corrode, soften and weaken with age and use,

and frequently give wayunnecessarily. In replacing these discs some time is required, during which delay there is often freezing or solidication of organic matter in the standpipe (exit line) of the blow case or in the delivery lines to the nitrating buildings so that these lines must also be opened up and freed of plugging material before acid can be delivered from the blow case and dperations resumed. During Y cold weather, the delivery linev from the blow case to the nitrator buildings voften freeze when there has been no trouble in the blow case. Therefore the elimination of the fortier building and the separate handling of the spent acids thru pipe lines, as in my invention, results in considerable saving of time previously lost thru these difficulties.

The present invention vprovides a method of overcoming these di'iculties.

Briey stated, the present invention comprises leaving the spent acid from the trinitration stage in the nitrator, fortifying this spent acid in the nitrator itself, and to the resulting di-mixed acid adding mononitrotoluol (the reverse of the present practice). The invention comprises also settling and separation of the di-spent acid and transferring it without the application of any .pressure upon it, to the mono-nitrator where it is fortified to mono-mixed acid and used for the mononitration. According to the invention,

pressure of approximately atmospheric is main- -tained upon the spent acids to bereusedrafter fortification, the said pressure being maintainedk at all times both before and after the fortifica- 'Y tion. For best results in reducing the manu- 3 facturing hazards, the trl-spent acid is maintained at all times under observation and control and the temperature not allowed to rise substantially above 230 F.

According to this method, there is complete elimination of (l) the blow case and the entire fortification building including its mixer tank and the exposed acid lines from the blow case to the nitrator buildings, (2) application of either pump or air pressure to the di and tri-spent acids, and (3) transfer of any tri-spent in any manner.

Using this method, it is possible to increase the production of a standard TNT line by approximately iifty percent, due to shortening of the time required for butting up of spent acid, elimination of transferring of same, shortening of the overall nitration time, and avoidance of the difficulties and delays involved in the use of the blow case.

It will be understood that the nitrators, the compositions of all acid mixtures used in the several nitration stages, the spent acid compositions, temperatures of nitrations, and all details not otherwise stated are those that are conventional in making DNT and TNT.

According to my method, the fortification of the spent acids for the mono and dinitration is conducted under the same type of control as used conventionally in making nitrations. In other words, at the time the fortifying nitric acid is added to the tri-spent or the di-spent acids, variations in temperature are recorded, the mixture is thoroughly and continuously agitated, the operations are observed through windows properly lighted, and the mixture cooled by cooling coils that are conventional in TNT nitrators to avoid any overheating. Thus, there is the same careful control of conditions in butting up as previously used heretofore only in the nitration step and is not possible in the blow cases. Since there is no pressure upon any of the spent and mixed acids at any time in the operation, there is no possibility of confinement such as exists in blow cases which not only increases the possibility of explosion but also the extent of the resulting damage.

Attaining the advantages of this invention is facilitated by placing the di and trinitrators at an elevation above the mononitrator, so that the spent acid from the dinitration step iiows downwardly through a connecting line to the mononitrators. After a dinitration has been effected in a given nitration vessel, agitation is discontinued and the resulting di-spent acid is settled, withdrawn from the bottom of the nitrator, and dropped to the mononitrator where it is fortified to mono mixed acid. To the dinitrotoluene left in the nitrator, oleum is added and then tri-mixed acid in the usual way.

After the trinitration is thus effected, agitation is discontinued, and the charge allowed to separate, then the TNT (top layer in the nitrator) is withdrawn, .by decantation thru outlets in the side of the nitrator and the spent acid is allowed to remain in the nitrator. This spent is fortified with nitric acid in situ for a dinitration. In other words, the di and trinitrators are used alternately for the di and trinitration steps. Ordinarily two of the di and tri-nitrators are required for one mononitrator for a plant of balanced capacity.

With my improved method as much as 30 to 60 minutes is saved on each cycle of toluene nitrated to TNT with the consequent larger increase of capacity in standard TNT line.

'I'he method is illustrated diagrammatically iny the attached now sheet which forms a part of this speciiication and will be described for the purpose of illustration in greater detail in connection with the drawing.

Nitric acid is added in the mononitrator to butt up the there present di-spent acid separated from a previous nitration of the toluene to the di-stage. During the addition of nitric acid, the di-spent acid is stirred continuously and the charge is cooled (as much as necessary) by @001mg coils that are usual in toluene nitrators to avoid overheating due to nitration of nitratable material in the spent acid. After the fortification is complete, toluene is added to the mono-mixed acid and stirring continued at the usual temperature for making mononitrotoluene.

After the nitration to mononitroluene is commercially complete, the stirring is discontinued, the charge settled and separated, and spent acid and mononitrotoluol drawn off and sent to respective houses for further treatment; mono spent acid to the recovery and mononitrotoluol to ditri houses for further nitration.

The mononitrotoluene so made is pumped to the di-nitrator. Here the mononitrotoluene is stirred into a mixture of tri-spent acid which has been fortified in situ with the required proportion of nitric acid to make a di-inixed acid. After the nitration to the di-stage is complete, the di-spent is passed downwardly, under only atmospheric pressure upon its upper surface, into the mononitrator for fortification there and reuse in the mononitration stage as described.

After the cli-spent has been withdrawn from the dinitrator, there is added to the dinitrotoluene there contained a fresh mixture of oleum and trimixed acid in such proportion as to give the concentration of sulfuric and nitric acids required for making TNT.

After this trinitration has been conducted under the usual conditions as to stirring, cooling, period of time, and temperature, then the agitation is discontinued, the charge settled, and the TNT withdrawn, from above the settled tri-- spent acid thru side openings in the nitrator to washing and subsequent purification and finishing operations which are conventional in TNT manufacture. The tri-spent is left in the nitrator and is there fortified by the addition of the calculated quantity of nitric acid to make it suitable for (ii-mixed acid for which purpose the fortied material is then used with mononitrotoluene (MNT) to make dinitrotoluene (DNT).

The di and trinitrators are interchangeable and are usually two in number for each monontrator. One nitrator is used first in making dinitrotoluene. Then the same nitrator is used in making a batch of the trinitrotoluene, its next use being in making the dinitrotoluene. In this way, there is avoided any transference of the hazardous tri-spent acid and particularly transfer of this spent after fortification back to the di-tri nitrator.

From the time the fortification of thedi and tri-spent acids is initiated, the acids are stirred and under careful control, including cooling, when necessary to maintain the temperature at a safe level, which for the more hazardous trispent acid is never substantially above 230 F., until the fortification is complete, the resulting mixed acids having been used in nitration, and the acids having been again become spent.

The di and trinitrators are located at an elevation above that of the mononitrators, so that the di-spent acid flows by gravity through a suitable pipe line to the mononitrator.

It wil1 be understood also that it is intended to cover all changes and modications of the example of the invention herein chosen for the purpose of illustration which do not constitute departures from the spirit and scope of the invention.

What I claim is:

1. In making trinitrotoluene, the method which comprises running the spent acid, Without the application of pressure thereto, from the dinitration stage into the mono-nitrator, adding to the said spent acid the required amount of nitric acid for fortification to mono-nitration acid, adding toluene with stirring and nitratng the toluene to mononitrotoluene, discontinuing the stirring and removing the resulting mononitrotoluene from the mono-nitrator, fortifying tri-spent acid from a previous nitration in the vessel in which it was formed originally with the required proportion of nitric acid to make di-nitration acid, introducing the mononitrotoluene gradually and with stirring into the resulting di-mixed acid to make dinitrotoluene, then discontinuing the stirring and transferring the di-spent acid, without the application of pressure thereto, to the mono-nitrator for fortication there and for reuse in the mono-nitration stage as already described, agitating the dinitrotoluene in the nitrator where made with trinitrating acid to convert the dinitrotoluene into trinitrotoluene, then discontinuing the agitation and withdrawing the trinitrotoluene from above the settled tri-spent acid, fortifying the tri-spent acid left in the nitrator by the addition of the calculated quantity of nitric acid to make it suitable for di-nitration acid, adding mononitrotoluene With stirring to th resulting di-nitration acid to make dinitrotoluene,-and continuing the cycle of steps described.

2. In making trinitrotoluene by the method comprising nitration of toluene in a plurality of stages with the formation of mono, di and trispent acids and the use of fortified di and trispent acids in subsequent stages, the improvement which comprises carrying out the following operations in the same nitrating vessel: nitration of dinitrotoluene to trinitrotoluene by the addition of the tri-nitrating acid, separation of the resulting trinitrotoluene and tri-spent acid by removing the trinitrotoluene layer leaving the tri-spent acid in the nitrator where formed, fortification of the tri-spent acid in situ to form di-nitrating acid; and addition of mononitrotoluene with stirring to the di-ntrating acid to form dinitrotoluene, discontinuing the stirring and separation of the dinitrotoluene from kthe di-spent acid by removing the di-spent acid from the nitrator, and allowing the dinitrotoluene to remain in the nitrator ready for the tri-stage nitration as described above.

CHARLES F. PAPAZONI.A

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