A methodology for the optimization of wet granulation in a model planetary mixer

This paper investigates a methodology for the optimization of wet granulation processes in planetary mixers. A model formulation was granulated in a planetary mixer (two different bowl sizes). The wet masses were characterized by their bulk density and consistency (as measured by mixer torque rheometry), and the feasibility of scale-up from one mixer bowl to the other was studied using a dimensionless numbers approach for the estimation of the power consumption at the granulation end point. Both bowls gave the same dimensionless power relationships (a relationship between the power number, Reynolds number, Froude number, and bowl fill ratio), which could therefore be used for calculating the power consumption level when the wet mass achieves its target values of density and consistency, i.e., the point at which granulation should be stopped. It was also shown that batches granulated in different conditions (batch size, blade speed) in two planetary mixers, but presenting similar wet mass characteristics (bulk density and consistency) led to dry granules of similar properties: granule size distribution, density, friability, and flow. This work suggests that it is possible to characterize the wet mass by only two parameters which describe the quality of the downstream granules. The scale-up procedure based on the use of dimensionless numbers was found to be applicable to planetary mixers, provided they give one common dimensionless power relationship.