Chemistry Reference
In-Depth Information
amorphous SDD with the desired particle size. A wide variety of atomizers are avai-
lable, allowing the
flexibility to address formulation or solution property constraints.
Droplet sizes and distributions can be modi
ed based on input energy or atomization
technique (e.g., hydraulic, pneumatic, or electric), nozzle geometry, or solution property.
By controlling atomization parameters, a range of particle sizes can be precisely
engineered.
Table 9.1 shows the atomizers that are commonly used to spray dry SDDs,
highlighting the advantages and drawbacks for speci
c nozzles [7]. The most commonly
used atomizer types are two-
uid and pressure-swirl atomizers. They are well charac-
terized and widely available from commercial vendors in a variety of geometries, so they
can be selected to meet the needs for specific formulations or equipment scales. These
nozzles also allow for the most straightforward scale-up of the atomization process and
are robust across the range of SDD formulations.
Pressure-swirl nozzles are typically the preferred option for SDD manufacture
because they (1) reliably and reproducibly produce a wide range of droplet sizes
with narrow particle size distributions and (2) offer maintenance-free operation, including
TABLE 9 . 1 . Atomizer Options for SDD Manufacture
Atomizer
Advantages
Drawbacks
Two-fluid
Large liquid orice prevents
clogging
Capable of atomizing high-
viscosity solutions
Broadly applicable
May be preferred if targeting
small particle sizes
Broad particle size span (e.g.,
>
2)
Requires gas compressor or
high usage of high-pressure
nitrogen
Can be prone to bearding/
product buildup
Not preferred for larger
particle sizes
Pressure-
swirl
Narrow particle size span
(e.g., 1.5-2)
Robust and scalable (self-cleaning
designs available for spray drying)
Tunable over a range of particle
size targets
No atomizing gas is required
Requires high pressure
(up to 250 bar at large scale)
Limited ability to make small
particles at large scale
Rotary disk
Narrow particle size span
(e.g., 1.5-2)
Requires spray dryer with
short/wide aspect ratio
Not amenable to viscous
film-forming feedstocks
(makes floss and filaments)
Independent control of liquid
feed rate and atomization energy
Ultrasonic or
electrostatic
Capable of narrow span
Low shear/velocity of droplet
ejection
Limited ow range (not scalable)
Challenging with viscous
feedstock
Particle charge must be
dissipated (for electrostatic)
