Continuous pellet coating in a Wurster fluidized bed process

Coating of particles in fluidized beds is a widely spread technique to generate well defined properties of the dispersed solids or to protect active ingredients. The majority of coating processes is conducted batch-wise, losing the possible advantages of the continuous mode of operation, such as reduced cost or improved process control. Especially in case of multi-layer coating, significant benefits could arise from continuous operation. The present work contributes to the development of continuous fluidized bed coating for pharmaceutical and chemical applications. The feasibility of the operation is demonstrated on a single-stage, continuously operating Wurster coater. Experiments are conducted with MCC (micro-crystalline-cellulose) as nuclei and sodium benzoate as the coating agent. The continuous withdrawal of the coated product is realized by means of a sluice and an external separation tube. Apart from the experimental results, the contribution presents an approach to model the continuous coating process based on population balances and compares experimental and simulation results.

► Continuous coating in a Wurster type fluidized bed.
► Proposal of plant modifications and process control.
► Experimental investigations of process dynamics (parameter variations).
► Derivation of mathematical process model based on population balances.
► Comparison of mathematical model and experiment.