Fluidized bed drying has been widely employed in pharmaceutical manufacturing processes. Due to the considerable cohesiveness of wet pharmaceutical granules, channelling phenomena pose significant challenges to fluidization and drying. In this work, the drying performance of pharmaceutical granules in a pulsation-assisted fluidized bed dryer was experimentally investigated. The drying rate and energy efficiency were investigated with representative pharmaceutical powders, including active pharmaceutical ingredients (APIs). It is found that the pulsed airflow is effective in enhancing the drying rate at higher superficial gas velocity. A lower pulsation frequency is more favourable to improve the drying rate. During the constant rate period, energy efficiency is between 60% and 45% for the drying process, while the energy efficiency decreases to 10% during the falling rate period. A pulsed fluidized bed dryer has shown a higher energy efficiency than a conventional one with a constant air flow. Among nine thin-layer drying models examined in this work, the Midilli and Kucuk model has shown the best agreement between the experimental data and the predicted results.
Monitoring the microstructure of the granule in the wet granulation process could play a decisive role in obtaining high-quality granules. Due to the complex, fast and opaque nature of wet granulation, it cannot be captured by conventional methods. In this study, synchrotron x-ray imaging was employed for the first time to investigate the internal real-time pore evolution during the granule formation process, based on the single droplet impact method. It was found that granules from coarser and more homogenous powders experienced a higher rate of pore evolution during nucleation with a more uniform pore distribution. Dynamic wetting studies showed the granule formation mechanisms, the crater mechanism was found for most binary mixtures with 50 wt. % excipients. According to the physical tests, the granules with lower porosity and finer pores exhibited higher hardness and a slower dissolution rate.
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