(320aq) Study on Packing Structures in Liquid Chromatography (Lc) Columns Based on X-Ray Ct

It is well known that the efficiency of LC-columns strongly depends on the homogeneity of the packed bed. Measurement of local system parameters related to the column cannot be achieved easily without the deterioration of the flow field, as the separation takes place inside closed columns. CT provides the opportunity to measure local packing properties in a non-destructive way. Axial compression columns packed with different Silica-Gels were invastigated with a CT-Scanner at several axial positions. Potassium iodide (KI) solutions in Methanol were conveyed through the column. The high X-Ray attenuation of KI rendered the determination of intra-column breakthrough curves possible. By fitting the Equilibrium-Dispersive-Model (EDModel) to the experimental, local breakthrough curves, information about the spatial variation of the column efficiency and the velocity distribution was obtained. The Kozeny-Kármán-equation allowed to estimate local interstitial void fractions. It was found that the packing can be divided into a homogeneous core region, where porosity and efficiency vary only slightly and into a wall region with decreasing porosity and efficiency, respectively. The results in terms of local porosities and dispersion coefficients were then used to develop CFD-Models of the investigated columns. The simulations were performed assuming a rotational symmetry (2D-Model) of the flow field in order to keep the computational effort reasonable. The breakthrough curves calculated with the CFD-Models match the experimental results better than the commonly used EDModel. Work in progress covers the impact of different packing materials, e.g. spherical and irregular materials and different packing modes upon the packing properties. The CFD-Model is under further development, taking the extension to a 3D-Model into account. The final aim is to get a better understanding of the packing structure and its dependency on different packing parameters.