Chemical Engineering 3 -

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2) Mechanisms: - “Dry” agglomeration (compaction) - “Wet” agglomeration
3) Equipment
Elastic deformation
Plastic deformation
Brittle failure
Strain (Δx/x0)
Stress (Force/Area)
D… relative density ρ/ρ0 P… applied pressure A… particle rearrangement Py… yield pressure (material property)
Low Py … soft/plastic materials (5-50 MPa) High Py … hard/brittle materials (100-1000 MPa)
Roll compaction
- Eject
Need to use lubricants (e.g. magnesium stearate) to avoid sticking to punch or die walls and reduce wear.
Problems: capping, de-lamination
Wet Granulation
Principle: contact powder with a liquid binder, wet powder particles become cohesive, agglomeration occurs during particle collisions, binder sets to form mechanically stable granules.
Binder types: - melt binders ~ melts, solidify upon cooling (e.g. PEG) - aqueous binders ~ solutions, solidify upon drying (e.g. PVP) - water ~ partial dissolution and recrystallisation of ingredient(s)
Binder application: - spray (liquid atomisation) for low-shear processes - mechanical dispersion in high-shear processes
Granulation processes: - fluid bed granulation - high-shear mixer granulation
Fluid bed granulation - batch
Fluid bed granulation - continuous
Fluid bed granulation - continuous
Pan granulator

Image © Ullmann’s Encyclopedia of Industrial Chemistry
A) pendular
B) funicular
C) capillary
Principle of operation: -Prepare a paste from API, excipients, binder, water -Extrude paste through screen to form “noodles” -Contact extrudates with a high-speed rotating disk -Dry resulting spherical pellets
…but it is also possible to carry out spheronisation after wet granulation
Population balance of agglomeration


phys β0 ... collision frequency
Conditions for agglomeration of wet patricles
Criteria for coating vs. agglomeration:

: viscous Stokes number : reduced particle mass : reduced particle diameter : velocity of collision
: binder viscosity : thickness of binder layer : particle surface roughness
vSt m~