The influence of moisture on the fluidization behaviour of porous pharmaceutical granule

The influence of moisture content on the fluidization behaviour of placebo pharmaceutical granule has been studied in a 14 cm diameter cylindrical fluidized bed column. The dry granule has a mean diameter of 207±9μm and exhibits a bimodal size distribution with modes of 169 and 1600μm. Bed pressure drop profiles and tapped density measurements were generated for granule moisture contents between 5 and 30 wt%, which corresponds to typical final and initial moisture contents experienced during drying. At high moisture contents, the wet granule exhibits Geldart C type powder behaviour as channelling and defluidization exist. As the moisture content is reduced, the granule fluidity improves and demonstrates behaviour characteristic of Geldart B powders. The changing fluidization behaviour was quantified using parameters such as the full support velocity, full support bed voidage and Hausner ratio. These parameters were found to increase significantly above granule moisture contents of 10 wt%. The increase in the Hausner ratio suggests that the interparticle force load in the bed increases. This change in interparticle force load is responsible for the increase in the full support velocity and bed voidage.