urbaf2

TNT MANUFACTURE 367

In this plant each of the nitrators is connected with a separator, into which
the liquid from the nitrator overflows and where the nitro compound is separated

from the acid. The upper, nitro compound layer then flows to the next nitrator,

containing a more concentrated acid, while the lower acid layer passes through

a siphon to another nitrator, where less vigorous nitration takes place. Both liquid

phases-that of the acid and that of the material being nitrated-flow in counter-

current to each other. Figure 85 represents a schematic diagram of a unit for contin-
uous nitration (after MacNab [18]).

FIG. 85. Diagram of the British continuous nitration of toluene to

TNT (according to McNab ([18]).

The unit comprises 14 nitrators and 14 separators. The first nitrator is fedwith

nitrotoluene, prepared in another unit by the batch process. Nitrators from (2) to

(14) are fed with acids of an increasing concentration. The acid in the “middle”

nitrators, from (5) to (22), is of the following composition:

HNO 3 8-10%

NO 2 1%

H 2 SO 4 80-82%

H 2 O 11%

Into nitrator (24) a nitrating mixture prepared from 96% sulphuric acid and
anhydrous nitric acid is introduced. The spent acid flowing from nitrator (2) to nitrator

(I) is detoluated here by agitating with nitrotoluene whence it flows away as waste

acid of the composition:

HNO 3 1%

NO 2 4%

H 2 SO 4 78-80%

H 2 O 14-16%

organic matter 1-1.5%

In the nitrators the following temperatures are maintained:

Nitrators l-2 40°C

3 70°C

4-13 100°C

14 90°C