Passive acoustic emissions monitoring of the coating of pellets in a fluidized bed—A feasibility analysis

Abstract

Pharmaceutical pellets are small spherical particles that contain the active ingredient or drug. They are often film coated and packed into capsules as a multiple unit dosage form to provide modified drug release. Conventional methods used to evaluate pharmaceutical film coatings require invasive sampling and off-line testing, which are time consuming, disruptive to the process and often non-representative of the pellet bed indicating the need for developing more reliable monitoring methods. Passive acoustic emissions measurements have shown potential as a monitoring tool due to the non-invasive nature and real-time means of collecting process information. The goal of this study was to assess passive acoustic emission monitoring of the coating of pellets in a fluidized bed. Microphones were attached to the exterior of a top spray fluidized bed reflecting local fluidization conditions and information on nozzle performance. Decreased fluidization conditions were identified from acoustic emissions acquired at the interface of the liquid spray and fluidized pellet bed, influencing the distribution of the coating spray throughout the bed and drying of the film coat around the pellet core. Acoustic emissions acquired from the exhaust of an air outlet at the top of the column showed potential application for the detection of nozzle clogging. Continued research regarding the development of passive acoustic emissions monitoring would provide important information about fluidized bed coating of pellets and potentially improve process control for the determination of an optimum coating end-point.