94
C. Neugebauer et al.
These trends are in line with the results from the SEM analysis and the roughness
measurements. Because of the smoother and more compact surfaces of the particles
with increasing drying potential, the particles are layered more compactly, resulting
in higher of solids content (see Fig. 17a) due to high nucleation rates and reduced crystal growth. In consequence, the void fraction inside the granule structure decreases,
resulting in a reduction of the granule porosity (see Fig. 17b). Furthermore, the reduction of voids and defects inside the granule leads to higher compression strengths
(see Fig. 17c).
5 Population Balance Model Extension: Influence
of Thermal Operating Conditions
Product design is one of the key disciplines in particle formulation processes, usually
driven by quality-by-design principles in combination with a fundamental process
understanding, focusing on key features of solids handling properties, like flowability, the dissolution behavior, the release rates or the storage stability. Furthermore
granule characteristics, like the solids density, moisture content, granule surface morphology, surface roughness, compression strength and the wetting behavior play a
major role for the development of tailor-made granule properties for specific uses in
pharmaceutical, food and other industrial applications. The particle properties can be
influenced by several process parameters, like drying temperature, liquid feed rate as
well as droplet size of the atomized liquid feed. Additionally the peripheral process
units and downstream processing play a distinctive role.
Figure 14 clearly shows that the morphology of the particles is changing significantly with the thermal operating conditions. In particular, the shell porosity is
increasing with increasing rate of the injected liquid from the left to the right in
Fig. 14. Further it is increasing with decreasing temperature of the fluidization air
from the top to the bottom in Fig. 14.
Following the ideas in Refs. [1, 16], the behavior shown in Fig. 14 was modeled
by correlating the shell porosity with the drying potential η.
It turns out that for the present test system the relation between shell porosity and
drying potential can be described in good approximation by a linear correlation.
shell (η) = shell,0 − shell η.
(16)
Other particle properties like surface roughness and compression strength can
also be correlated with the drying potential as shown in the previous section. Alternatively, they can be obtained as a function of porosity and particle size distribution
as suggested in Litster and Ennis [51].
Using the correlation between shell porosity and the drying potential according
to Eq. (16), the population balance model presented in Sect. 2 can be extended to
account for the influence of the thermal conditions on particle porosity [52]. For this,
C. Neugebauer et al.
These trends are in line with the results from the SEM analysis and the roughness
measurements. Because of the smoother and more compact surfaces of the particles
with increasing drying potential, the particles are layered more compactly, resulting
in higher of solids content (see Fig. 17a) due to high nucleation rates and reduced crystal growth. In consequence, the void fraction inside the granule structure decreases,
resulting in a reduction of the granule porosity (see Fig. 17b). Furthermore, the reduction of voids and defects inside the granule leads to higher compression strengths
(see Fig. 17c).
5 Population Balance Model Extension: Influence
of Thermal Operating Conditions
Product design is one of the key disciplines in particle formulation processes, usually
driven by quality-by-design principles in combination with a fundamental process
understanding, focusing on key features of solids handling properties, like flowability, the dissolution behavior, the release rates or the storage stability. Furthermore
granule characteristics, like the solids density, moisture content, granule surface morphology, surface roughness, compression strength and the wetting behavior play a
major role for the development of tailor-made granule properties for specific uses in
pharmaceutical, food and other industrial applications. The particle properties can be
influenced by several process parameters, like drying temperature, liquid feed rate as
well as droplet size of the atomized liquid feed. Additionally the peripheral process
units and downstream processing play a distinctive role.
Figure 14 clearly shows that the morphology of the particles is changing significantly with the thermal operating conditions. In particular, the shell porosity is
increasing with increasing rate of the injected liquid from the left to the right in
Fig. 14. Further it is increasing with decreasing temperature of the fluidization air
from the top to the bottom in Fig. 14.
Following the ideas in Refs. [1, 16], the behavior shown in Fig. 14 was modeled
by correlating the shell porosity with the drying potential η.
It turns out that for the present test system the relation between shell porosity and
drying potential can be described in good approximation by a linear correlation.
shell (η) = shell,0 − shell η.
(16)
Other particle properties like surface roughness and compression strength can
also be correlated with the drying potential as shown in the previous section. Alternatively, they can be obtained as a function of porosity and particle size distribution
as suggested in Litster and Ennis [51].
Using the correlation between shell porosity and the drying potential according
to Eq. (16), the population balance model presented in Sect. 2 can be extended to
account for the influence of the thermal conditions on particle porosity [52]. For this,