Characterization of Lyophilization of Frozen Bulky Solids

Foerst, Petra; Gruber, Sebastian; Schulz, Michael; Vorhauer, Nicole; Tsotsas, Evangelos

doi:10.1002/ceat.201900500

Cited by 5 publications

(3 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Similar conclusions as in this paper were drawn from neutron imaging of frozen particle beds, where several open questions were addressed in References [41,42]. On the basis of these studies, we will investigate more deeply the drying of frozen blocks and particle packings with different experimental technologies and pore network modeling [43].…”

Section: Discussionsupporting

confidence: 67%

Freeze-Drying with Structured Sublimation Fronts—Visualization with Neutron Imaging

et al. 2020

Self Cite

View full text Add to dashboard Cite

The particular structure of the sublimation front in vacuum freeze-drying of porous media is, in most situations, not accessible at the pore scale. The classical measurement techniques access the process only globally. Knowledge about the structure of the front, however, is necessary for prescriptive analysis of freeze-drying, as it dictates not only drying velocity, drying time, and overall energy consumption, but also the material properties after drying. This is especially relevant in situations in which the freeze-drying process is carried out close to the collapse temperature of the product. We, therefore, study the sublimation of ice with neutron tomography and analyze the spatial formation of the dry space using the example of frozen cylindrical maltodextrin with drying parameters at the limit of material collapse. We show that the sublimation front forms unique fractal structures that differ strongly from the usual form of a flat front. Distinct dry fingers covering the sample, in addition to a fractal peripheral sublimation front, were observed. The findings are important for the understanding of freeze-drying processes and will serve as a basis for the development of microscale models of freeze-drying.

show abstract

Section: Discussionsupporting

confidence: 67%

Freeze-Drying with Structured Sublimation Fronts—Visualization with Neutron Imaging

et al. 2020

Self Cite

View full text Add to dashboard Cite

show abstract

“…This elucidates the geometric interactions needed to improve throughput in a filter cake. Furthermore, a homogeneous porosity distribution was observed in the annular spaces of this system, showing potential for applications demanding porosity control, such as the freeze-drying of bulky solids [43] and heat transfer in a fixed-bed reactor [44]. Additionally, variations of the coefficient of friction and insert thickness were considered but did not show significant effects.…”

Section: Discussionmentioning

confidence: 96%

Assessing the wall effects of packed concentric cylinders and angular walls on granular bed porosity

2022

View full text Add to dashboard Cite

The effect of added wall support on granular bed porosity is systematically studied to elucidate performance enhancements in filtration processes achieved by using inserts, as demonstrated experimentally (Bandelt Riess et al. in Chem Eng Technol 2018, 2021). Packed beds of spheres are simulated through discrete element method in cylinders with different internal wall configurations. Three containing systems are generated: concentric cylinders, angular walls, and a combination of both. Variations of particle size and wall friction and thickness are also considered, and the resulting granular bed porosities are analyzed. The porosity increase is proportional to the incorporated wall support; the combination of cylindrical and angular inserts displays the greatest effect (up to 26% increase). The sinusoidal porosity values near the walls are exhibited to clarify the effects. The presented method can change and evaluate granular bed porosity increments, which could lead to filtration process improvements, and the obtained behaviors and profiles can be used to explore additional effects and further systems. Graphical abstract

show abstract

“…The dynamic temporal evolution of the sublimation front can be assessed using in operando imaging techniques with high contrast between the propagating dry pores, solids and ice [ 12 , 13 , 15 , 16 , 20 , 21 ]. At the same time, pore scale models can assess heat and mass transfer kinetics at the front.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study of the Impact of Pore Structure on Drying Kinetics and Sublimation Front Patterns

et al. 2022

Self Cite

View full text Add to dashboard Cite

Freeze-drying frozen maltodextrin solutions with solid contents of 5% and 30% (w/w) was experimentally investigated using neutron imaging at PSI Villigen/Switzerland. Different solid contents, as well as annealing at −5 °C for 11 h, were used to modify the porous structure of the samples, which was quantified using X-ray computed tomography. Annealing of the 5% (w/w) sample, with a pore size distribution (PSD) of 23.7 ± 11.1 µm, yielded a very open pore space with high porosity (ε = 0.96) and a PSD of 33.0 ± 27.0 µm. In contrast, the higher solid content resulted in small, lamellar, narrow pores with high anisotropy and a porosity of ε = 0.65, as well as a PSD of 13.5 ± 4 µm. In operando neutron imaging was used to show the impact of the structure of frozen maltodextrin on the overall drying kinetics and shape of the sublimation front during freeze-drying. For this purpose, a freeze-drying stage was employed, which allowed a novel approach to time- and space-resolved monitoring of the ice phase. The sublimation front propagation was quantitatively analyzed based on ice saturation profiles and sublimation rates. The dependence of drying velocity on structure is nicely demonstrated by the data. In addition, it is shown that the sublimation front widened during freeze-drying, resulting in either rather concave or convex shape depending on morphological parameters.

show abstract

Characterization of Lyophilization of Frozen Bulky Solids

Cited by 5 publications

References 17 publications

Freeze-Drying with Structured Sublimation Fronts—Visualization with Neutron Imaging

Freeze-Drying with Structured Sublimation Fronts—Visualization with Neutron Imaging

Assessing the wall effects of packed concentric cylinders and angular walls on granular bed porosity

Experimental Study of the Impact of Pore Structure on Drying Kinetics and Sublimation Front Patterns

Contact Info

Product

Resources

About