Successfully transferring the manufacturing process across lyophilizers, especially for scale-up, requires a knowledge of the drying kinetics of the product. Experimental approaches to determine the drying kinetics and optimal drying cycle can be time consuming and utilize expensive active drug substance. Additionally, the drying kinetics at the small scale may not translate to a large scale lyophilizer due to differences in equipment design, internal hydrodynamic and heat transfer conditions. In this work, we present a numerical model for the overall transport of moisture and heat transfer during lyophilization, that includes the drying kinetics in each vial as well as heat and mass flow dynamics inside the equipment. For this purpose, we use a one-dimensional product model coupled with a time-dependent three-dimensional computational fluid dynamics solution of the flow field in the drying chamber to evaluate the local hydrodynamic conditions in the lyophilizer. The time-dependent drying process in each vial is modeled using different geometric approximations for vials. For larger equipment, such as pilot-scale and production-scale lyophilizers, the vials are divided into groups that have similar boundary conditions. In this way, the coupled problem can be solved for the entire batch to provide information about the critical process parameters and to estimate product drying times. This coupled lyophilization model is proposed to be used for laboratory, pilot, and production scale lyophilization systems. The results of the 1D model coupled with the 3D CFD model show that the model can resolve spatial variations of the chamber pressure and the drying kinetics at different scales. The simulations show that chamber pressure is highest in the center of the shelf and decreases toward the sides. Presented by Dr. Fay Metsi-Guckel, Ph.D. Associate Principal Scientist, Merck & Co
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