The Manufacture of TNT

The complete manufacture of trinitrotoluene involves the several processes of nitration, separation, washing, crystallization and possibly purification. The experimental stage has been passed in every one of these various divisions in the manufacture of this product, until the modern plant runs as smoothly as a well-oiled machine. The apparatus necessary to carry on any one or all of the steps in the manufacture of TNT is now well standardized, and many excellent machines are on the market for accomplishing the end toward which every manufacturer works—a pure product. A detailed description of the necessary apparatus will not be gone into, but a brief outline of the requirements to be fulfilled by the various machines will be given in their respective places. 

The first step in the manufacture of TNT is the the nitration. This reaction is carried out in a large vessel called the nitrator. This nitrator is generally a cylindrical kettle or tank, built of either an acid-proof cast metal or of boiler plate. The material of which the nitrator is built should be thoroughly tested with the acids of various concentrations met with in the manufacture of the product. The nitrator must be well equipped with cooling coils and heating coils so placed that the temperature of the reacting mixture 

I have noticed a tendency in quite a number of TNT plants to perform the nitration in a rather slip-shod manner, and on remarking concerning it this reply was made Well, its cheaper to use a little less acid in the nitration and pmify the product afterwards. This policy is very bad, it is both expensive and non-efficient. It must be remembered that while TNT is 

In addition, the toluene must be practically free from olefines or members of the di-olefine series. This demands that the toluene be washed several times with concentrated sulphmic acid to remove these compounds. The laboratory test for olefines consists in agitating some of the toluene with a certain percentage of concentrated sulphuric acid. If olefines are present, the acid layer will acquire a yellow to red color. This color must not be deeper than whatever shade the certain plant has adopted as its standard. The comparison standard colors consist of definite concentrations of solutions of potassium dichromate, chromic acid, etc. 

The presence of olefines is dangerous because these substances form nitro-compounds in the nitration process, and these compoimds are rather unstable. A fire or even an explosion may possibly result if the toluene is not freed from them. The presence of members of the aliphatic or paraffin series is not nearly so detrimental as the presence of the olefines. These compounds do not react on nitration, and with the three-stage process they may be removed after the nitration to mononitrotoluene. 

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T he petroleum industry entered the field of aromatics production largely because the unprecedented demand for toluene for the manufacture of TNT at the outbreak of World War II in 1939 could not be met by other sources. As a result of its efforts, the industry supplied 75 to 85% of all the toluene which was nitrated for TNT production during the latter years of World War II. Since that time the petroleum refiners have remained in the field and at present they are major suppliers of toluene and xylenes. In Table I it is shown that in 1949 about 59% of the toluene and 84% of the xylenes produced in the United States were derived from petroleum sources. The petroleum industry has diversified its operations in the field of aromatics production until at present a variety of materials is offered. Table II presents a partial list of the commercially available aromatics, together with some of their uses. A number of other aromatics, such as methylethyl-benzene and trimethylbenzene, have been separated in small scale lots both as mixtures and as pure compounds. 

Around 1902 the Germans and British had experimented with trinitrotoluene [(TNT) (C7H5N306)], first prepared by Wilbrand in 1863. The first detailed study of the preparation of 2,4,6-trinitrotoluene was by Beilstein and Kuhlberh in 1870, when they discovered the isomer 2,4,5-trinitrotoluene. Pure 2,4,6-trinitrotoluene was prepared in 1880 by Hepp and its structure established in 1883 by Claus and Becker. The manufacture of TNT began in Germany in 1891 and in 1899 aluminium was mixed with TNT to produce an explosive composition. In 1902, TNT was adopted for use by the German Army replacing picric acid, and in 1912 the US Army also started to use TNT. By 1914, TNT (1.4) became the standard explosive for all armies during World War I. 

In explosive industries, as for instance in the manufacture of TNT, pollution may be caused by TNT dust, the strongly acid fumes of oxides of nitrogen and sulfur and the vapors of tetranitromethane. AH of these are harmful to both man and vegetation Refs 1)C.M.Christian, "Air Pollution Lit-... 

Since nitro compounds have certain specific properties, which influence the choice of methods for heating wastes, some special methods are described later in the technological section dealing with methods of the manufacture of individual nitro compounds. Diminishing water pollution by washes from the manufacture of TNT is a most complex problem. This will be discussed in detail on p. 390. 

Recently, as the disposal of large volumes of toxic waste waters from the purification of TNT by sulphitation has. become a problem (p. 390), new ways are being sought for the manufacture of TNT free from the unsymmetrical isomers. Apart from the possibility, mentioned above, of the utilization of nitrotoluene obtained by nitrating toluene with a mixture of acetic anhydride and nitric acid, factories TNT are now tending to separate nitrotoluene isomers by methods similar to those applied in the manufacture of dyestuffs intermediates. 

Tolulene is the principal raw material for the manufacture of TNT. It is produced from light oil and from the gases obtained by the dry distillation of coal. 

This method known from the description of the process at the Kriimmel. factory was used by the German explosives industry during World War II. Figure 82 represents a flow diagram of the manufacture of TNT by this method. 

The problem of the neutralization of waste water from the manufacture of TNT, and the possibility of utilizing the dinitrotoluenesulphonic acids present in them acquired a considerable importance during World War II, owing to the enormous output of TNT. In Germany alone the production of TNT was over 20,000 tons a month, whereas during the World War I it averaged merely 3000 tons a month. 

The manufacture of TNT is one of die safest operations in the explosive industry. Nevertheless, any negligence about safety regulations may have disastrous consequences. Because the manufacturing process is regarded as safe, the feet must not be overlooked that less experienced personnel may disregard the regulations. 

Many nitro derivatives of benzene and naphthalene were of importance in the past, since toluene - the starting compound in the manufacture of TNT - could only be prepared by distillation of coal. Owing to the advances in petrochemistry, toluene is now available in practically unlimited amounts the bulk of the toluene now produced is employed as the starting material for the preparation of toluene diisocyanate (TDI) used in the production of plastics. 

Nitrotoluene is of importance as an intermediate or precursor for in the manufacture of TNT. There are three isomers, of which only the ortho-and para-isomers can yield pure 2,4,6-trinitrotoluene. Mononitration of toluene yields mostly the orthocompound, as well as 4% of the meta-, and about 33% of the para-compound. 

Many engineers have investigated to the extreme the conditions necessary for the best yields and the best product possible in the manufacture of TNT. Much credit is due one of these investigators, M. Coparisow, because of the light his research has thrown upon the nitration of toluene, and the cure for the troubles encoimtered in this reaction. A summary of Copari-sow s work is given here, it being taken from a recent article. (3)... 

In the process of the manufacture of TNT, Copari-sow points out the following as being matters requiring particular care and watchfulness ... 

A peculiar use is made of the spent acid in some parts of Eussia. (8) The waste acid from the manufacture of TNT contains 62 to 72 per cent sulphuric and 2 to 3 per cent nitric acid. This is used to prepare super-... 

A modification of the sulphuric acid process has been patented (1) when applied to a mixture of mono-nitrotoluenes and paraffin hydrocarbons. The nitration of the toluene is carried on carefuUy so as to take it only as far as the mononitrotoluene. The mono-nitrotoluene is dissolved in sulphuric acid, but any paraflShs that may be present will not dissolve, and will form a separate layer. A separation of these two layers and the subsequent nitration of the sulphuric acid solution of mononitrotoluene yields a very high grade TNT. Thus a toluene containing a comparatively large percentage of paraffins may be utilized in the manufacture of TNT. 

Previous to 1914, there were in all less than a half-dozen accidents reported in TNT plants. Within the last year there have been not less than twenty explosions and accidents in the United States alone. It is true that not all of these have been due to the detonation of TNT, but probably every one has been due to carelessness on some employee s part. With conditions as existed previous to the war, the manufacture of TNT could be carried out with as great care as was thought necessary, but with the total rearrangement of conditions as they exist to-day, there is no doubt but that in many cases certain details which, although minor in nature, are really important, are not given the attention they require. 

There is surely no step in the manufacture of TNT which is entirely free from danger. Every step in the process should receive the utmost attention, and minor details should be worked out with the same care as the greater problems, rather than to take a chance that no accident will result. 

Continuous methods are now prevalent in the industrial methods of the manufacture of TNT. A general tendency is to use ... 

Important for industry is the reaction of the substitution of a nilro group by a sulphonic group as was described in Vol. I (pp. 201, 207). The mechanism of the reaction is now given in the chapter dedicated to the manufacture of TNT and other higher nitrated aromatics. 

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