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152 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

MIXING OF REAGENTS DURING NITRATION

There are three methods of mixing organic substances to be nitrated with nitra-

ting mixtures:

(1) adding the substance to the acid,

(2) adding the acid to the substance,

(3) simultaneous introduction of both acid and organic substance into

the nitrator.

The first method is the one most frequently applied. It has, however, certain

drawbacks. The first portions of the nitrated substance are introduced into an

excess of nitrating mixture and may be converted to a higher degree of nitration

than required and may also undergo oxidation processes; hence the uniformity

of the product may not be satisfactory. Also some substances sensitive to con-

centrated acid may be decomposed by contact with an excess of acid necessitating

application of the second method. In the second method the substance to be ni-

trated is contacted with an inadequate quantity of nitrating acid. This might be

advantageous for the reason mentioned above. However, when aromatic hydro-

carbons with alkyl side groups (e.g. toluene) are nitrated, reaction of the hydro-

carbon with an inadequate amount of nitrating mixture may lead to the formation

of dark coloured complex compounds and even tarry matter (see p. 77). In this

instance the first method is more advantageous. The best method, which con-

sists in simultaneous introduction of both reactants into the nitrator, has the ad-

vantage that it is applicable in continuous nitration processes.

As already mentioned earlier, nitration proceeds mainly in the acid phase.

Strictly speaking the acid phase consists of an acid saturated with an organic

substance. On the other hand, the organic phase is in turn saturated with an acid.

The reaction rate in an acid phase is much higher than that in an organic phase

(see p. 40). By vigorous stirring the contents of the nitrator are kept emulsified

and the phases are kept mutually saturated due to diffusion over a very large

interfacial area.

Insufficient mixing may easily result in a low nitration rate owing to the small

interfacial area. It can also lead to a non-uniform nitration process. Owing to

inadequate construction of the stirrer, too low a speed of rotation, or an inter-

ruption in stirring, so-called dead spaces may easily be formed in which non nitra-

ted or not fully nitrated substances accumulate. If a rather large quantity of the

mixture is stirred suddenly, rapid extension of the interfacial area takes place,

followed by the generation of large amounts of heat and a rise in temperature.

This may cause a spontaneous decomposition of the reaction mass in the nitrator,

and then an explosion.
Such an accident, well known in the history of the chemical industry, happened

at the Rummelsburg factory in 1914 during the nitration of benzene. The trans-
mission belt slipped off and caused the stirrer to stop. In spite of this benzene

continued to flow into the nitrator. When the fault was noticed, the stirrer