The Checkerboard Model: New Insights in the Eddy-dispersion of Packed Bed Columns for Liquid Chromatography

Desmet, G. (Invited speaker), Sander Deridder (Contributor)

Activity: Talk or presentationTalk or presentation at a conference

Description

Using the general plate height model of chromatography, researchers have reached a clear consensus that about half of the band broadening observed in a packed bed originates from the heterogeneity of the flow paths, usually referred to as eddy-dispersion. After many decades of intense research on the modelling of the eddy-dispersion effects in packed bed liquid chromatography, the prevailing theory is still Giddings’ coupling theory. Although this theory has proven to provide a good qualitative description of the experimentally observed relationship between the observed eddy-dispersion and the flow rate, the theory also has a number of clear shortcomings. It does not predict a retention factor dependency, whereas there is now abundant proof it clearly exists in practice. Nor does it predict the presence of a strong C-term like contribution, which is often observed experimentally as well. Other remaining issues with the coupling theory is that it fails to represent the dispersion in ordered media and moreover seems to be in contradiction with the laminar nature of the flow: whereas Giddings’ coupling theory depicts the flow as a series connection of independent velocity biases, it is well known that in laminar flow systems the dispersion in a given zone also depends on the dispersion history it carries from the preceding zone(s).

To investigate the above potential shortcomings, we will report on the insights obtained by simulating the band broadening via computational fluid dynamics in a number of artificial flow-through media consisting of a binary distribution of discrete zones with an alternating packing density and corresponding flow permeability. As such, the studied geometry can be seen as one of the most simple representations of the structure of a packed bed column at the multi-particle level. Referring to this model as the "checkerboard model ", the alternation of zones fits the generally accepted description of a packed bed medium, typically viewed as a conglomerate of multi-particle zones with different packing densities. Similar to Giddings' random walk-model, the checkerboard distribution model can be applied at different levels, i.e., with velocity bias zones persisting over different length scales. First, checkerboard models are considered where the different porosity zones are distributed following regular and repeated patterns. In a second step, the model was extended to a disordered checkerboard-distributions wherein the local packing density of the zones no longer changes in a binary mode but follows a random distribution. Finally, the model is also applied to understand the nature of the eddy-dispersion observed in perfectly ordered packed bed systems.
Period17 Jun 2019
Event titleHPLC 2019: the 48th International Symposium on High-Performance Liquid Phase Separations and Related Techniques, 16-20th June 2019, Milan, Italy.
Event typeConference
LocationMilan, Italy
Degree of RecognitionInternational