Pharmaceutical tablets are still largely produced using batch processes, at which the production line is divided into successive sub-processes. In order to reduce product waste and production time and to increase the flexibility of tablet production, the Food and Drug Administration (FDA), among others, promotes research and innovations in the field of continuous production for the manufacturing of pharmaceuticals. The QbCon1 unit developed by L.B. Bohle Maschinen +Verfahren GmbH is one of the research field innovations. The plant combines all three necessary process steps of continuous raw material dosing (premix of excipients and active ingredients), twin-screw wet granulation and fluid bed drying to enable continuous wet granulation and drying of the tableting mixture. In this article, the continuous fluid bed dryer is firstly presented. Subsequently, a continuum based model is developed for the drying process. The aim is to develop a model that can be used for model-based product quality control. From a control engineering point of view, this is a multi-variable problem, since different process variables (e.g. drying air temperature, air mass flow, conveying speed of the granules) have an influence on the drying process. The control of the Process Variables (PVs) is carried out with the aid of standard industrial PID controllers. The tuning and validation of PVs controllers is based on empirical investigations or using developed actuation models. Finally, a concept for the control of one of the process main critical quality attributes (CQAs), namely the tablet mixture moisture content, is presented with the aid of a model based controller approach. The model constructed for the drying process has shown a good match to the real process with a maximum of 1.18% prediction standard deviation from the experimentally measured mean moisture content. Moreover, the model based controller approach feasibility is demonstrated using a closed loop simulation of an implemented Nonlinear Model Predictive Controller (NMPC).
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