Influence of Operating Conditions on Sublimation Kinetics

Moreover, the use of drying curves enables detection of the main governing mechanisms that control the heat and mass transfer phenomena and, in this way, enables one to determine the main input physical variables for setting up and validating software for the control and monitoring of the freeze-dryer (shelf temperature or total gas pressure). 

The influence of shelf temperature and of sublimation chamber total gas pressure on the drying curve (X(t)) and on the drying rate curve (— ) is discussed below. As observed by many authors during the drying of different types of materials, for example during the convective or infrared reactive drying of thin coating films, the 

A coherent set of drying kinetics data concerning the freeze-drying of model pharmaceutical formulations in vials under standard operating conditions, namely at very low total gas pressure (10-26 Pa) and at low sublimation temperature (—5 to —25 °C) was published recently by Hottot et al. (2007). A typical set of sublimation rate data gained by these authors is presented in Fig. 3.21 concerning the influence of 

The previously discussed experimental data have recently been extended to pharmaceutical formulations with organic co-solvent - active principle ingredient (API) + water + fert-butyl alcohol (TEA) - by Daoussi et al. (2009) who used an automatic microbalance placed inside the product chamber to determine the sublimation kinetics. The same shapes of sublimation kinetics curves were observed. 

Fig- 3.23 Drying kinetics as a function of total solvent (water - - TBA) content at different shelf temperatures formulation at 20% water + 80% TBA (by mass). Influence of shelf temperature. According to Daoussi et al., 2009. 

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