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NITRO DERIVATIVES OF NAPHTHALENE 439

is charged with 2500 1. of a mixture of spent acid and nitronaphthalene from the prev-
ious batch, warmed to 50-55°C. 1100 kg of naphthalene is added during about 15 min,
while the nitrator contents are stirred. During this operation the temperature falls
to 40-43°C. Then 800 1. of a nitrating mixture of the composition:
HNO 3 33%
H 2 SO 4 47.5%
H 2 O 19.5%
(sp. gr. 1.625-1.635 at 20°C) is added during 3 hr, the temperature rising by the

end of the procedure up to 45°C. Then the rest of the naphthalene and acid are

added during about 8 hr, in five lots: four of 200 kg each, alternating with 200 1.

batches of the nitrating mixture, then the last of 300 kg of naphthalene, followed

by 450 1. of the acid. In all, 2200 kg of naphthalene and 2050 1. (3300 kg) of the

nitrating mixture is charged into the nitrator.

The temperature may rise during this period to 55°C. After all the acid has been

added, the nitrator contents are stirred for another half an hour at 55°C and a sample

is taken.

The nitronaphthalene precipitated by cooling, after washing with water should

not melt below 51°C and should not smell of naphthalene. If the test is satisfactory,

a part of the mixture in the nitrator is conveyed to a separator and the remaining

2500 1. is left for the next batch. The latter quantity is controlled by the depth of

immersion of the pipe that conveys the mixture to the separator. The whole nitration

process takes 12 hr.

Separation. Separation of nitronaphthalene from spent acid is effected in a cast

iron separator, heated by a steam jacket, which permits the temperature to be

maintained at 50-55°C. The separation of the mixture into two layers requires

3 hr. Then the lower layer of the spent acid is drawn off to an intermediate tank

of 10 m^3 capacity and is allowed to cool. As a result, unreacted naphthalene col-

lects at the surface as a crystalline mass. It is skimmed off mechanically.

Spent acid of the composition:

H 2 SO 4 63%

HNO 3

NO 2

trace

is sent to be concentrated.

H 2 O about 37%

Granulation and washing. The molten nitronaphthalene in the separator is

drained off to a granulator, previously charged with 6000 1. of cold water. During

the introduction of nitronaphthalene compressed air is passed through the grant-

lator to agitate the water. This causes the nitronaphthalene to solidify in the form

of granules. The granulation process requires one hour, then the flow of air is stopped

and the water is drawn off through a siphon. The siphon pipe inlet is provided with

a wire gauze to prevent the nitronaphthalene from being carried away. When the

first portion of water has been drained off the nitronaphthalene left is agitated with -

new portions of water (6000 1. each) until neutrality (Congo red test). Usually 2-3

washings are sufficient. The washing process requires about 6 hr.