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248 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

is washed with water, and then transferred in a molten state to a purification unit.

where it is dried at 120°C and 15 mm Hg. The product is crude dinitrobenzene.

The amount of H 2 SO 4 in the waste acid from dinitration is about 80%. After

mixing with nitric acid it can be used for mononitration.

Purification. 4500 kg of molten dinitrobenzene (i.e. one charge of the ni-

trator) are run into a washing tank (C). The tank of 12 m^3 capacity must be made

of stainless steel, lined with tiles, and fitted with a lead coated lid and a lead

coated stirrer. 3000 1. water at ca. 80°C are run into it over the dinitrobenzene, with

constant stirring. The whole is allowed to cool until granulation begins at ca. 70°C,

the exact temperature depending on the stirrer and on the quality of the dinitro-

benzene. Immediately granulation begins, 650 kg of sodium sulphite are introduced

at a rate of 100 kg per 15 min. The temperature rises to 78°C and stirring must

be continued for another 3 hr.

Samples should be taken, filtered, washed and dried. The setting point should

not be lower than 88.5°C. If it is too low, 25-30 kg more of sodium sulphite are

added.

The contents of the washing tank are cooled by circulating water within the

jacket to 20-25°C. The mother liquor is pumped off through a wire gauze and

the product is washed with cold water. Washing is continued until the colour chan-

ges from dark red to light yellow. The dark wash-liquors are discarded, the light

ones being kept for the next batch.

The washed product is heated to 95°C and when in a molten state it is dried

under reduced pressure. The drier consists of a jacketed cylindrical vessel of 12 m^3

capacity. Finally, the pure dried product is turned into flakes.

The product has the setting point 88.5-89°C.

The yield is 100 kg of crude dinitrobenzene from 48 kg of benzene (96.7%

theoretical). 100 kg of pure dinitrobenzene are obtained from 118 kg of crude

product. This makes an overall yield of 81.9% calculated on benzene.

The crude product, according to Griesheim’s experience, contains: 85% of

meta-, 13% of ortho- and 2% of para- isomers.

TRINITROBENZENES

Three isomers of trinitrobenzene are known: 1,3,5-trinitrobenzene (sym-tri-

nitrobenzene), 1,2,4-trinitrobenzene and 1,2,3-trinitrobenzene:

Their melting points are: 122°C, 62°C and 127.5°C respectively.