ABSTRACT
Pharmaceuticals are usually obtained by crystallization.
Under most conditions their particle size seldom grows
larger than 1 mm. Generally, owing to their low solu-
bility, the crystals are small or very small. The particle
size distribution of a typical pharmaceutical as meas-
ured by sieve analysis is shown in Figure 29.1. From the
point of view of drying technology, for monodisperse
materials, such as ASA and sodium p-aminosalicylate,
the aerodynamic conditions in dryers are much easier
to select. If particle size distribution is unimodal but
widespread (e.g., Urotropin or phenyl salicylate) or
bimodal (e.g., codeine, streptomycin, or sulfanilamide),
the material is more difficult to dry in suspended state
as particle segregation may occur.
