urbaf2

NITRATION WITH NITRATING MIXTURES 161

high temperature and cannot be kept molten it is necessary to create the necessary

conditions to ensure the formation of a fine-crystalline or granular product. It
is only then that bottom discharge will be feasible. The nitrator contents are then

transported immediately to a centrifuge, or in the case of explosives sensitive to

impact (sensitivity of the order of that of tetryl or higher), the solid product is

filtered off under reduced pressure.

The separated solid or liquid product is then washed with water in order to

remove acids, and subsequently purified according to its properties and the nature

of the impurities present. Finally the pure product is obtained in the required phys-

ical form.

FIG. 35. Flow diagram, nitration discharge of the nitrator by means

of the compressed air: 1 - nitrator; 2 - separator; 3 - pressure-egg.

WASTE WATER

The technology of nitration processes is unavoidably associated with the problem

of waste water disposal. The water, which comes from washing the nitration prod-

uct, contains acid components from the nitrating mixture, and nitro compounds.

Both the acids and the nitro compounds in solution, or suspended, or in both

states are highly noxious for the flora and fauna of rivers and lakes.

Thus, nitro compounds in a concentration as low as a few milligrams per litre

are lethal to fish. Wastes from the manufacture of hexyl (hexanitrodiphenylamine)

are particularly toxic, killing fish at a concentration as low as 0.1 mg of hexyl per

litre. For this reason, the removal of these compounds from the waste water prior

to its discharge is of primary importance.

As a rule acids are removed from waste water by discharging it into pits filled

with limestone, where they are neutralized.