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TNT MANUFACTURE^385

After half an hour the stirrer is stopped, the solution is separated by decantation

and the TNT left behind is washed with water again at 85-90°C. If TNT of very
high purity is required (m. p. 80.6%) it is sulphitated once more with a 0.5%

solution of sodium sulphite.
The washed TNT is then air dried in a water heated tank of capacity 15 m^3 ,
at 85-90°C. At this stage of manufacture samples are taken for determining the
freezing point of the product. Finally the dry TNT is flaked on a steel drum with
a bronze knife.

Continuous methods

Continuous washing with sodium sulphite was also applied at Schlebusch

(Fig. 98).

FIG. 98. Continuous washing with sodium sulphite of TNT in Schlebusch (CIOS XXIV - 4).

The purifying unit consisted of four washing tanks (I) and four separators (2).

As in the nitration plant the vessels were arranged in cascade. The first washing

tank was for washing the TNT with water, the next one for washing with sodium

sulphite and the last two again for washing with water. Each was 0.5 m high and

0.8 m in diameter.

61 62 63

FIG. 99. Meissner’s continuous process of washing nitrotoluenes including TNT

(co-currentsounter-current method [20]).

Meissner’s continuous process for washing nitrotoluenes, applied also for TNT

(Fig. 99), belongs to the co-current-counter-current type. The quantity of water

used should be as small as possible, thus reducing the losses of nitrotoluenes to