urbaf2

TNT MANUFACTURE 363

TWO-STAGE MANUFACTURE OF TNT

(OLD ITALIAN METHOD)

In Italy a two-stage process of nitration has been used:

Toluene -> Dinitrotoluene -> Trinitrotoluene

For the nitration of toluene to dinitrotoluene a nitrating mixture of the composition :

HNO 3 28%

H 2 SO 4 60%

H 2 O 12%

is used.
Crude DNT, after it had been separated from acid and washed with water, was
sometimes purified by sulphitation. This material partly freed from isomers and

derivatives of m-nitrotoluene, was further nitrated.
The trinitration did not differ much from that described above. The mode of
separating crystalline TNT from acid is worth mentioning. In this method the nitra-

tor played the role of a crystallizer after nitration had been completed. The reaction

mixture was cooled with continuous stirring until crystallization of the TNT began.

To initiate the crystallization some water was added to the nitrator. Some of the

crystalline TNT obtained in a previous batch might also be added if necessary.

TNT formed crystals which, while still in a hot state, were separated from the

spent acid in a vacuum filter or in a centrifuge. The degree of TNT purity could

be regulated by temperature during crystallization. A very pure product could be

obtained, by using a relatively high temperature (e. g. 75°C).

From the spent acid TNT of lower quality was obtained on cooling. By using

a lower temperature of crystallization in the nitrator, crystals of grade II TNT were

obtained which in turn could be purified by sulphitation.

Belenkii [8] describes the U.S.S.R. process of crystallization of TNT in the

nitrator as follows. TNT crystallization begins at 76°C. This temperature rises

by 0.5°C owing to heat of crystallization. By this time the quantity of TNT dissolved

in the spent acid amounts to about three quarters of the total. At the initial stage

of crystallization, at a temperature of 76°C to 75°C cooling should be very slight.

Usually the flow of cooling water to the coil is stopped.

As soon as the temperature falls to 75°C the nitrator contents should be cooled

vigorously and simultaneously the speed of rotation of the stirrer should be reduced

to avoid pulverizing the crystals. When the temperature has fallen to 30-35°C

cooling is discontinued, and almost pure α− trinitrotoluene is filtered off. If the

Process of crystallization is properly carried out most of the impurities will remain
in the acid.

The TNT is filtered off in a vacuum tank and washed, first with 70% and

then with 45% sulphuric acid, each used in the proportion of 800 kg for 1000

kg of TNT, and finally several times with water. By using acid of a gradually

reduced concentration for washing a very effective removal of oily impurities of
DNT and of isomers of trinitrotoluene can be achieved.