Mechanistic models with experimental comparison for microwave-assisted lyophilization in a vial.

Abstract

Microwave heating has been shown to accelerate pharmaceutical lyophilization but robust process models, crucial to ensuring that the process is efficient without damaging products, are still scarce. Building on both high-frequency microwave lyophilization experiments and recent modeling efforts, we develop a 2D level set simulation which refines the assumptions made in lumped capacitance (LC) models. The 2D level set model is also capable of integrating information about measured porous structures and accounting for experimental observations where thermocouples are placed imperfectly. Of the 4 empirical parameters in the LC model, we remove one based on level set results and estimate two more by electromagnetic simulation, recommending a new variant of the 0D lumped capacitance model. This LC model is compared to experiments in both microwave-assisted lyophilization and microwave vacuum drying of products in vials, emphasizing that microwave heating of the vial wall and heat conduction from the vial wall to frozen product cannot be neglected. The implementations of the new models, alongside the analysis, are published as open source Julia code.

Graphical abstract: