Influence of the Particle Size Distribution on Hydraulic Permeability and Eddy Dispersion in Bulk Packings

Abstract

The narrow particle size distribution (PSD) of certain packing materials has been linked to a reduced eddy dispersion contribution to band broadening in chromatographic columns. It is unclear if the influence of the PSD acts mostly on the stage of the packing process or if a narrow PSD provides an additional, intrinsic advantage to the column performance. To investigate the latter proposition, we created narrow-PSD and wide-PSD random packings based on the experimental PSDs of sub-3 μm core-shell and sub-2 μm fully porous particles, respectively, as determined by scanning electron microscopy. Unconfined packings were computer-generated with a fixed packing protocol at bed porosities from random-close to random-loose packing to simulate fluid flow and advective-diffusive mass transport in the packings' interparticle void space. The comparison of wide-PSD, narrow-PSD, and monodisperse packings revealed no systematic differences in hydraulic permeability and only small differences in hydrodynamic dispersion, which originate from a slightly increased short-range interchannel contribution to eddy dispersion in wide-PSD packings. The demonstrated intrinsic influence of the PSD on dispersion in bulk packings is negligible compared with the influence of the bed porosity. Thus, the reduced eddy dispersion observed for experimental core-shell packings cannot be attributed to a narrow PSD per se.

Computational investigation of longitudinal diffusion, eddy dispersion, and trans-particle mass transfer in bulk, random packings of core–shell particles with varied shell thickness and shell diffusion coefficient

“…We employed a threedimensional cubic lattice with 19 links at each lattice node, the so-called D 3 Q 19 lattice [47]. The lattice spacing l was adjusted to l = d p /60, i.e., 60 nodes per particle diameter [25,43]. After discretization of the generated bed structures the LBM lattice had dimensions of 600 × 600 × 8400 nodes.…”

“…Periodic boundary conditions were imposed at the external faces of the computational domain. Further parameters and implementation details used for the LBM in this work can be found in [25,33,43,45].…”

“…(2)) compared to those in columns packed with conventional fully porous particles [4,24]. Later, numerical simulations of hydrodynamic dispersion in bulk random packings of polydisperse particles [25] and the morphological analysis of physically reconstructed packed beds [26] revealed that the smaller eddy dispersion contribution to band broadening in columns packed with core-shell particles should be attributed to a higher transcolumn homogeneity rather than an improved bed morphology on smaller length scales. The origin for the decrease of B and H long terms can be explained by a reduction of the total packed-bed volume accessible for diffusion due to the presence of the particles' solid cores.…”

“…Finally, the transport of point-like tracers in the interparticle void space and porous shells of the packing particles was modeled by a random-walk particle-tracking (RWPT) technique. A similar simulation approach was previously applied to study the effect of packing porosity, morphology, and particle size distribution on effective diffusivity and eddy dispersion in packed beds [25,[27][28][29][30][31]; to analyze the impact of the packing confinement on eddy dispersion [32,33]; to study hydrodynamic dispersion in silica and polymeric chromatographic monoliths [34][35][36][37][38]; and to investigate the influence of analyte retention and adsorption kinetics on mass transport in open channels and packed beds [39][40][41]. In this study, we mainly focus on the analysis of the influence of two core-shell particle characteristics -the shell thickness and the value of the effective diffusion coefficient in the shell -on the plate height.…”

How changing the particle structure can speed up protein mass transfer kinetics in liquid chromatography

“…They seem most likely to be related to larger particle-to-particle and particle-to-column wall shear friction forces and to the subsequent reduction of the trans-column structure heterogeneity of beds packed with them. The tightness of the particle size distribution (PSD) of shell particles has virtually no impact on the band spreading in the interstitial mobile phase [28]. The low B term is unambiguously explained by the presence of the solid core, which prevents analytes from diffusing in a significant fraction of the column volume ( 25%) and enhances solute obstruction.…”