Inline acoustic monitoring to determine fluidized bed performance during pharmaceutical coating

Fluidized beds are used by pharmaceutical manufacturers for multi-particulate drug coating. They provide effective mass and heat transfer; however, unit optimization can be difficult due to the multivariate nature of a fluidized bed system. This research explores the use of passive acoustic emissions monitoring as a method to improve temperature management during pellet coating. A piezoelectric microphone was placed inside the exhaust of a conical top spray fluidized bed. Spherical 1000 μm pellets were coated while recording acoustic emissions. Fluidization air temperature was adjusted between trials as a controlled variable to determine if pellet drying rate could be extracted from the data. During each trial, pellets became damp as the coating solution was applied. Drying stages were used to remove moisture whereby pellet fluidization continued without spraying. The moving standard deviation of the acoustic emissions increased by approximately 40 mV during each 2-min coating stage. The emissions then decreased during drying. This decrease was at a rate proportional to pellet drying independently measured at each controlled temperature. The overall coating-drying emissions profile was similar for trials using either sugar or Acryl-EZE® coating solutions. Passive acoustic emissions monitoring is non-invasive and provides reliable coating and drying information during fluidized bed operation.