Hydrodynamic and dispersion behavior in a non-porous silica monolith through fluid dynamic study of a computational mimic reconstructed from sub-micro-tomographic scans

Abstract

An analysis of the transport properties of the bulk homogeneous core of a commercially available silica monolith (Chromolith®) is presented via direct numerical simulations in a topological model reconstructed from 3D nanotomographic scans at isotropic resolutions of 390nm, 290nm and 190nm. The pore and skeleton size distributions were calculated from image analysis and a representative unit cell from each resolution was reconstructed to simulate the hydrodynamic transport properties using Computational Fluid Dynamics (CFD). A 30μm×30μm×30μm unit cell extracted at 190nm resolution was found to be representative of hydrodynamic permeability. Numerical peak parking simulations yielded an axial external obstruction factor (γe) of 0.8. Mass transfer characteristics of a large non-penetrating molecule (BSA) were evaluated under non-retained conditions so as to elucidate the eddy dispersion contribution to total HETP. Transverse and axial dispersion length scales in the reconstructed model were resolved and related to the structural heterogeneities in the silica monolith. Deviations of simulated HETP from experimental measurements were attributed to a transcolumn dispersion contribution, which amounted to about 90% of the total HETP. The presented approach provides great scope to analyze the contributions of pore network topology to separation performance of silica monoliths (and other porous media) in HPLC applications. A significant reduction in simulation time and memory resources has been observed due to the lower scanning resolution, without significant loss in prediction accuracy.