Page 112 - Chemical and process design handbook

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AMMONIUM NITRATE

Ammonium nitrate (NH NO ), a colorless crystalline solid, occurs in two
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forms: (1) α-ammonium nitrate (tetragonal crystals, stable between –16°C
and 32°C; melting point: 169.9°C; density: 1.66) and (2) β-ammonium
nitrate (rhombic or monoclinic crystals, stable between 32°C and 84°C
with decomposition occurring above 210°C; density: 1.725).
When heated, ammonium nitrate yields nitrous oxide (N O) gas and can
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be used as an industrial source of that gas. Ammonium nitrate is soluble in
water, slightly soluble in ethyl alcohol, moderately soluble in methyl alco-
hol, and soluble in acetic acid solutions containing ammonia.
Ammonium nitrate is manufactured from ammonia and nitric acid.
NH + HNO → NH NO
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In the process (Figs. 1 and 2), the gases are fed to the reactor in which
the heat of neutralization boils the mixture, concentrating it to 85% nitrate.
Vacuum evaporation at 125 to 140°C further concentrates the solution to
95%. The last water of this hygroscopic material is very difficult to
remove. The hot solution is pumped to the top of a spray tower 60 to 70 m
high, where it is discharged through a spray head and solidifies as it falls
in the air to form small spherical pellets, prills, of 2 mm diameter that are
screened, further dried, and dusted with clay to minimize sticking.
If properly proportioned and preheated, the reaction can be run contin-
uously to produce molten ammonium nitrate containing very little water
(1 to 5%), which can be formed into small spheres (prills) by dropping the
reaction product through a shot tower or into flakes by cooling it on belts
or drums. By fluidized bed treatment, it is possible to obtain a dry granu-
lar material as product; batch processes have also been used.
Ammonium nitrate finds major applications in explosives and fertilizers,
and additional uses in pyrotechnics, freezing mixtures (for obtaining low
temperatures), as a slow-burning propellant for missiles (when formulated
with other materials, including burning-rate catalysts), as an ingredient in
rust inhibitors (especially for vapor-phase corrosion), and as a component
of insecticides.

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