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NITRATION WITH NITRATING MIXTURES 155

Figure 27 shows the influence of the concentration of a nitrating mixture on the

nitration of nitrobenzene and the phase conditions at the completion of the nitration

of nitrobenzene to dinitrobenzene, after cooling the mixture down to 35°C. The

relationship between the rate of nitration of benzene to dinitrobenzene and the

FIG. 28. Rate of nitration of benzene to dinitrobenzene as a function of the molar

concentration of sulphuric acid. (Various curves correspond to various molar

concentrations of H 2 SO 4 , when [HNO 3 ] = 1.) (Hetherington and Masson [9]).

molar concentration of sulphuric acid arc shown in Fig. 28 (Hetherington and

Masson’s data [9]).

The influence of sulphuric acid in O-nitration processes, as for example in the

esterification of cellulose with a mixture of sulphuric and nitric acids, appears to

be somewhat different. This will be dealt with in the chapter on esters (Vol. II).

DESIGN OF NITRATORS

The nitrators used in the manufacture of aromatic nitro compounds consist

of iron vessels (Fig. 29), equipped with a stirrer (I) and a jacket (2) for cooling or

heating the contents, as well as with a lid (3), connected with a ventilation pipe (4).

Gaseous products from the nitration process (NO, NO 2 , HNO 3 , SO 3 , SO 2 , CO,

CO 2 ) are conducted away through it. The ventilation duct is equipped with a

sight glass (5), which permits the observation of waste gases - mainly their colour.

In addition to the ventilation duct the lid is equipped with two feed pipes, one

for acids, (6), and one for the substance to be nitrated, (7), a thermometer sleeve (8),

a delivery pipe for compressed air (9) and a pipe (10), reaching down to the bottom,

for discharging the nitrator contents by means of compressed air. It is essential

to furnish the lid with a manhole (II). During nitration, the manhole opening is

closed by a thin sheet of aluminium, which at the same time plays the role of a
safety valve in case the pressure should rise inside the vessel.

The nitrator capacity may vary and may be as large as 15 m^3. Its dimensions

depend on the compound to be nitrated and on the method of nitration; for example,