The study presents a method to estimate the mass transfer rate during primary drying based on μ-computed tomographic measurements of a freeze-dried cake. The study was carried out in a defined setup in a lyomicroscope and confined geometry in which freezing occurred under homogeneous nucleation, and drying under mass-transfer-limited conditions. Pore size distribution, effective diffusivity, and primary drying rates of maltodextrin solutions at different weight concentrations (5%, 10%, and 20% (w/w))and different cooling rates were determined. Furthermore, the effect of annealing treatment on primary drying rate was studied. Two different annealing treatments were tested, one for 90 min at −10 °C and another for 180 min at −5 °C. It was shown that solid concentration and annealing above Tg’ have the strongest impact on pore size and, subsequently, on primary drying rate. Therefore annealing represents a powerful tool to accelerate primary drying which is the most time-consuming step during lyophilisation.
- Drying kinetic
- Freeze drying
- X ray micro-computed tomography
- Pore size
- Knudsen diffusion
Foerst, P., Melo de Carvalho, T., Lechner, M., Kovacevic, T., Kim, S., Kirse, C., & Briesen, H. (2019). Estimation of mass transfer rate and primary drying times during freeze-drying of frozen maltodextrin solutions based on x-ray μ-computed tomography measurements of pore size distributions. Journal of Food Engineering, 260, 50-57. https://doi.org/10.1016/j.jfoodeng.2019.05.002