Multipurpose stirring and blending vessels equipped with various impeller systems are indispensable in the pharmaceutical industry because of the high flexibility necessary during multiproduct manufacturing. On the other hand, process scale-up and scale-down during process development and transfer from bench or pilot to manufacturing scale, or the design of so-called scale-down models (SDMs), is a difficult task due to the geometrical differences of used vessels. The present work comprises a hybrid approach to predict mixing times from pilot to manufacturing scale for geometrical nonsimilar vessels equipped with single top, bottom or multiple eccentrically located impellers. The developed hybrid approach is based on the experimental characterization of mixing time in the dedicated equipment and evaluation of the vessel-averaged energy dissipation rate employing computational fluid dynamics (CFD) using single-phase steady-state simulations. Obtained data are consequently used to develop a correlation of mixing time as a function of vessel filling volume and vessel-averaged energy dissipation rate, which enables the prediction of mixing times in specific vessels based on the process parameters. Predicted mixing times are in good agreement with those simulated using time-dependent CFD simulations for tested operating conditions.

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In a continuous pharmaceutical manufacturing line the rotary tablet press was viewed as the master of control concept and defined the mass flow through the entire process. According to a conventional control concept, missing mass flow from an upstream unit operation leads to a shutdown of the tablet press. Various operating scenarios were simulated and the influence of turret speed on the tablet properties was experimentally investigated. Changes in the turret speed alter the critical process parameters dwell time and die filling time. Their influence was evaluated using two model formulations with different compaction behavior.

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