Perspectives: Making it Work

Vacuum Shelf Dryer Provides More-Uniform Cakes

Different approach to endpoint determination leads to greater consistency

By Steve Webb, Eli Lilly and Company
Apr 13, 2016

Shelf drying is a common unit operation for reducing the liquid solvent content of solid cakes prior to material storage or downstream processing. Where the use of high temperatures could result in product stability issues, shelf dryers may employ vacuum to evaporate volatiles at low temperatures. Pharmaceutical manufacturing, for one, often requires efficient drying at less than ambient temperatures. The combination of shelf drying and sub-atmospheric pressure allows for efficient volatile material evaporation while maintaining the solid cake at relatively low temperatures. Determining the drying endpoint using in-process conditions that accurately predict the solid-cake moisture content minimizes the potential for a need to stop and restart the operation. We have found in a case study that the absolute pressure during a vacuum shelf drying operation correlates closely with the volatiles’ content of solid cake and, thus, can serve to regulate drying time.

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