Microscopic and macroscopic investigations of the transient hydrodynamic memory behavior of chromatographic columns

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During the industrial application of preparative chromatography columns, unwanted phenomena are frequently encountered like medium wall detachment, partial bed subsidence, formation of flow channels, and irreversible compaction of the particle bed. It was shown in own previous work that these phenomena are a result of inhomogeneities of the particle bed which are caused by the packing process. During the first 3 year long funding period, a novel micro-chromatography column was developed which enabled a detailed experimental examination of the hydrodynamic behavior. A novel deterministic, three-dimensional, hybrid simulation model was developed by coupling computational fluid dynamics (CFD) and the discrete element method (DEM). This model enabled to simulate the interactions between single chromatography particles as well as between particles and fluid. A good agreement of simulation results and experimental data was obtained. The complex compression/relaxation behavior of the chromatography packing during flow compression and mechanical compression was studied. The resulting axial flow profiles turned out to be different for flow compression and mechanical compression. During flow compression, a linearly increasing pressure profile along the column height was observed with the highest compression taking place near the column outlet. During mechanical compression, however, the pressure profile along the column height was exponential with the highest compression occurring near the column inlet below the adaptor. Therefore, during the second 12-month long funding period, proper modelling-based combinations of flow compression and mechanical compression packing strategies are to be investigated in order to obtain a more homogeneous packing structure. In this context, empirically established and industrially applied packing procedures will be improved in terms of the achievable packing homogeneity. The additionally introduced model parameters of the extended simulation model will be identified by individual parameter studies. The newly developed model will enable to investigate the packing compaction behavior due to particle rearrangement and particle migration for the first time. The required computational time of the simulation model will be reduced significantly by applying the coarse grain concept. This will enable the prediction of the hydrodynamic behavior of preparative chromatography columns with high accuracy in order to avoid irreversible deterioration of the packing and to improve the packing procedures on the basis of the simulation model.