TNT MANUFACTURE 361The acid liquid DNT is metered and fed into a cast iron nitrator of 12 m
3
cap-
acity by means of compressed air. Then acid T 3 of the composition:HNO 3 24%
H 2 SO 4 70%
SO 3 6%is added. This T 3 mixture is prepared from concentrated nitric acid and 27% oleum.
Alternatively, the nitrator may be fed first with acid and then with DNT.
The DNT to acid ratio is 1:2.5-2.6 4000 kg of TNT are obtained per batch,
The reaction is completed in 35 hr, and the post-reaction period is 24 hr.
If acid is added to the DNT in the nitrator, the temperature within is kept at
83-85°C, and then raised to 96°C while if DNT is added to the acid, a tempera-
ture of 74-78°C should be maintained. When the two substances have been mixed,
the temperature is gradually raised to reach 96°C in one hour.
The whole process lasts for 6 hr. Then the reaction mixture is allowed to remain
at rest for half an hour, to separate the product from the acid. After separation,
the molten TNT is conveyed by means of compressed air to a cast iron washing
tank of 8 m^3 capacity and the spent acid to a wrought iron diluter of 15 m^3 capa-
city.
The TNT in the washing tank is stirred, while hot, with nearly 70% sul-
phuric acid, to wash out nitrogen oxides and the rest of the HNO 3 or nitrosyl-
sulphuric acid. Then it is separated from the acid and transferred to a separate,
building for final washing. TNT, after it has been washed with sulphuric acid,
contains l-2% of HNO 3 and l-2% of H 2 SO 4.
The spent acid, to which the acid from TNT washing has been added, is diluted
with sufficient water to obtain the composition given above. The dilution results
in further separation of TNT, which is added to the main portion. The diluted spent
acid is conveyed to dinitration.
Nitration plant. The nitrators for mononitration (both the pre-nitrators of
0.5 m^3 capacity and the main nitrators of 15 m^3 capacity) are made of cast iron.
The same material is used for all other parts of the plant in which not too con-
centrated acids are processed, e.g. dilutors, washing tank, tanks for nitro com-pounds, etc.
Those parts of the plant which are used for operations with concentrated acids
(e.g. nitrators of 15 m^3 capacity for di- and tri-nitration) arc made of wrought
iron.
Washing tanks for the final washing of nitro compounds with water (the water
from the operation is slightly acid) are made either from stainless steel or from
wrought iron lead lined or they may be constructed of bricks bonded by an acid
resistant cement and lined with sheet lead and with acid resistant tiles (Fig. 83).
All pipes for conveying molten TNT from one part of the plant to another are
heated either by hot water or steam jackets.