On the use of temperature measurement to monitor a freeze-drying process for pharmaceuticals

In a freeze-drying process for pharmaceuticals it is necessary to monitor product temperature and to identify the ending point of the ice sublimation stage. Besides, it can be worthwhile estimating the heat and mass transfer coefficients, in such a way that a mathematical model can be used to optimize in-line (or off-line, in a successive run) the process. Both results can be achieved using the temperature measurement. In this paper three different approaches are presented, namely (i) the simple use of the temperature measure, (ii) the combination of the temperature measure with a model of the process, and (iii) a soft-sensor. The strengths and drawbacks of the different approaches are discussed, with particular emphasis on the real-time monitoring of the process.