Modelling of hierarchical structure formation during spray drying via CFD-DEM coupling and continuous species transport

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Particle and aggregate structures in the micro- and nanometer range are the basis of countless products in analytical technology as well as in the chemical, biotechnological and pharmaceutical industries. Defined porous systems composed of particles are used, for example, in chromatographic purification, in catalytic applications (e.g. for energy storage or catalytically activated reactions) and as carrier systems for the defined release of active pharmaceutical ingredients. The product properties of porous systems for the respective application depend not only on the substance properties themselves, but also to a large extent on the underlying particle or aggregate structure. In addition to the material and surface properties of the nano- and microparticle building blocks, the subsequent process steps such as formulation, processing and drying have a decisive influence on the structure formation and the associated technical application properties. The question arises as to how such aggregate systems can and must be structured for the various applications in order, for example, to ensure optimum mass transport and at the same time exhibit defined mechanical stability. In previous projects, various aggregate systems have been produced and investigated by spray drying from nanoparticulate suspensions. In this project, CFD-DEM simulations will be established to reveal the structure forming mechanisms at the particle scale and to fully describe the resulting aggregate microstructure, in particular the formation of hierarchical structures in the first drying stage by WG Schilde. In parallel, a modelling approach based on a continuous species transport model will be further developed by WG Levy. For that, the consideration of multiple particle sizes and particle interactions in both the first and second drying stages is planned. Knowledge from the CFD-DEM simulations will support the model development to benefit both from their information on particle scale while keeping the computational cost low. This will allow the influence of different process and formulation conditions on the product to be investigated efficiently. Ultimately, the models should enable process optimization and prediction of structure formation during spray drying.