Development of a Population Balance Model of a pharmaceutical drying process and testing of solution methods

Drying is frequently used in the production of pharmaceutical tablets. Simulation-based control strategy development for such a drying process requires a detailed model. First, the drying of wet granules is modelled using a Population Balance Model. A growth term based on a reduced model was used, which describes the decrease of the moisture content, to follow the moisture content distribution for a batch of granules. Secondly, different solution methods for solving the PBM are compared. The effect of grid size (discretization methods) is analyzed in terms of accuracy and calculation time. All tested methods are compared based on their ability to predict moment dynamics and the distribution, and their computational burden. The Method of Characteristics, a fast method, is able to calculate the distribution accurately with a coarse grid. The Quadrature Method of Moments requires even less calculation time, but results in a set of moments.

► A reduced complexity drying model was incorporated in a PBM as growth term.
► The behaviour of a batch of drying particles was simulated for the first time.
► Discretization and moment-based solution methods were compared.
► The Method of Characteristics with reasonable grid size performed best.