Chemistry Reference
In-Depth Information
Figure 9.13.
(a) Physical situation of SDD particle drying and limiting factors depending on
mode (
l
(l≈particle radius;
D
=
diffusivity of solvent vapor through amorphous SDD matrix).
(b) Example SDD secondary drying curves with and without bed agitation (1000 l scale).
9.5 SPRAY DRYING SCALE-UP
The spray drying process is a continuous unit operation that allows
flexibility during
manufacturing to accommodate the desired throughput or batch size. It is readily scalable,
accommodating formulation screening at milligram quantities to commercial-scale manu-
facture at metric ton quantities. Equivalent particle attributes are achievable across a wide
range of spray dryer scales. Spray drying processes have been successfully scaled up in the
food, pharmaceutical, and other industries with the precision to meet speci
c powder
property targets. Masters cites an example spray dryer that produces nearly 10 tons of milk
powder an hour with stringent requirements on the spray-dried powder [16].
Figure 9.14 shows typical SDD spray drying scales and qualitatively describes the
overlap of the achievable product properties. It is important to keep scale-based
differences in mind during process development at the laboratory scale in preparation
for future scale-up or commercialization. However, by using a methodical approach to
process de
nition and understanding the key changes that occur between scales, process
parameters can be ef
ciently selected during scale-up while maintaining the CQAs of the
SDD formulation across scales.
It is important tomaintain consistency in equipment during scale-up for items such as the
gas disperser, atomization technique (e.g., pressure-swirl nozzle, two-
uid nozzle), chamber
aspect ratio, and cyclone ef
ciency. If the equipment
is selected carefully and well
understood, the SDD spray drying process can be ef
cientlyscaledupbyfocusingon
the differences across scales that impact the key physical situations of (1) droplet formation
and (2) drying rate.
