Chemistry Reference
In-Depth Information
droplet drying on the physical stability of the SDD formulation. Slower drying rates can
lead to SDDs with higher densities, which can be desirable from a powder handling
perspective. For these reasons, it can be advantageous to conduct early development
work on small-scale closed-cycle spray dryers rather than the more commonly available
small-scale open-cycle spray dryers.
9.5.3 Scale-Up Methodology
The goal of scale-up is often to ensure that the SDD particle attributes (e.g., particle size,
density, physical state, and morphology) remain consistent while achieving the necessary
throughput to meet clinical and/or commercial demands. This can be achieved by
matching droplet size and drying rate during scale-up. A methodology similar to the one
described in Section 9.4 can be employed.
Correlations can be developed to predict droplet size based on spray solution
attributes (e.g., viscosity), nozzle geometry, and atomization parameters (e.g.,
P
nozzle
)at
the larger scale spray solution throughputs. As described above, the PDPA can be used to
characterize the droplet size distributions produced by the larger scale atomizers. By
using atomization correlations and/or measuring the droplet size distribution, an atomizer
can be selected that produces the same droplet size distribution as that produced by the
smaller scale nozzles.
A thermodynamic mass and energy balance model can be developed, taking into
account
T
cond
and the recycled solvent vapor. The thermodynamic plot can be extended
from two dimensions to three and can be used to show all six key process parameters
described in Table 9.2. Example three-dimensional thermodynamic plots are shown in
Figure 9.16. The thermodynamic operating space can be de
ned using the same
methodology described in Section 9.4. In addition to the
T
in
, process ef
ciency, RS
out
,
and formulation constraints described in the previous section, there may be equipment
Figure 9.16.
Three-dimensional thermodynamic plots showing the six key parameters
including
T
cond
, which is important for larger scale dryers. (a) Contours of constant
T
out
and
(b) contours of constant RS
out
.
