In-Line Optimization and Control of an Industrial Freeze-Drying Process for Pharmaceuticals

This paper deals with the in-line optimization and control of the freeze-drying process of pharmaceuticals in vials. The proposed control system, named LyoDriver, uses a mathematical model of the process to calculate the values of the temperature of the heating fluid: the goal is to minimize the time required to get the desired amount of residual water in the dried product, and to maintain product temperature below the maximum allowed value, thus preserving product quality. The values of product temperature and residual ice content, as well as other parameters, are required to perform the calculations: these variables are estimated in-line by means of the Dynamic Parameters Estimation algorithm, an advanced tool based on the pressure rise test, but also other monitoring systems can be used. Two different control algorithms are presented and investigated by means of mathematical simulation and experiments carried out in a small industrial-type apparatus (LyoBeta 25 by Telstar). Results show the effectiveness of LyoDriver in a wide range of operating conditions, even when the process becomes mass-transfer controlled, or when the operating pressure is changed.