Study of the feeding performance of mesoporous silica in a loss-in-weight feeder

Accurate and reliable continuous feeding is essential for the continuous manufacturing of solid-dose pharmaceuticals to ensure the reproducible composition of the final product. Consistent feeding of cohesive powders is challenging and requires an understanding of the interplay between material properties and feeder configuration. This study presents the volumetric and gravimetric feeding behaviour of a cohesive pharmaceutical, excipient mesoporous silica, at low feed rates (< 0.6 kg/h) using a twin-screw loss-in-weight feeder. The study investigates how the screw pitch, screen type and gravimetric setpoint impact the feed factor and feed rate variability. Additionally, the flow function and bulk density of the fed and unfed silica samples were determined and related to the feeding process parameters. Volumetric experiments highlight inconsistent feed due to the poor screw flight filling at high screw speeds and for configurations with the larger pitch, coarse concave screw. Poor screw flight filling also resulted in an inverse relationship between screw speed and feed factor in volumetric mode. In gravimetric mode, feed variability, expressed as %RSD, was greatest at the lower gravimetric setpoints with minimal impact due to tooling configuration. Discharge screen set-up was identified as the parameter which had a significant effect on the bulk density and flowability of the powder post-feeding.