Elucidation of Drying Mechanisms of De-Solvation and the Establishment of a Drying Model

To predict the drying performance of an API de-solvation process, a fundamental understanding of the drying mechanisms is required to establish a drying model that can predict the API drying time.  A case study is presented in which the selected form of the API is a desolvated, crystalline form.  This form was generated upon drying the wet cake of the solvated form in a commercial-scale dryer.  The dynamic behavior of this drying process was monitored in the lab using in-situ Raman, mass spectrometry, and an automatic weighing device.   SEM images of the dried product were used to define the geometry of diffusion and the diffusion length.  The diffusion model established was scale independent and was used to predict the drying time in the pilot scale dryer.  The drying time predicted from the model was in excellent agreement with the data obtained experimentally, and the desired API crystal form was generated.