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A computational study of the porosity effects in silica monolithic columns
Author(s) -
Gzil Piotr,
Vervoort Nico,
Baron Gino V.,
Desmet Gert
Publication year - 2004
Publication title -
journal of separation science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.72
H-Index - 102
eISSN - 1615-9314
pISSN - 1615-9306
DOI - 10.1002/jssc.200401788
Subject(s) - porosity , van deemter equation , tortuosity , thermal diffusivity , materials science , monolith , chemistry , computational fluid dynamics , composite material , mechanics , analytical chemistry (journal) , geometry , volumetric flow rate , chromatography , thermodynamics , mathematics , physics , biochemistry , catalysis
We report on a theoretical study of the influence of the through‐pore porosity on the main chromatographic performance parameters (reduced theoretical plate height, flow resistance, and separation impedance) of silica monoliths. To investigate this problem devoid of any structural uncertainties, computer‐generated structural mimics of the pore geometry of silica monolithic columns have been studied. The band broadening in these synthetic monoliths was determined using a commercial Computational Fluid Dynamics (CFD) software package. Three widely differing external porosities (ε = 0.38, ε = 0.60, and ε = 0.86) are considered and are compared on the basis of an identical intra‐skeleton diffusivity ( D s = 5×10 –10 m 2 /s), internal porosity (ε int = 0.5), and for the same phase retention factor ( k ´ = 1.25). Since the data are obtained for perfectly ordered structures, the calculated plate heights and separation impedances constitute the ultimate performance ever to be expected from a monolithic column. It is found that, if silica monoliths could be made perfectly homogeneous, domain size‐based reduced plate heights as small as h min ≈ 0.8 (roughly independent of the porosity) and separation impedances as small as E min ≈ 130 (ε = 0.60) and E min ≈ 40 (ε = 0.86) should be achievable with pure water as the working fluid. The data also show that, although the domain size is a much better reduction basis than the skeleton size, the former is still not capable of bringing the van Deemter curves of different porosity columns into perfect agreement in the C term dominated velocity range. It is found that, in this range, large porosity monoliths can be expected to yield smaller domain size‐based reduced plate heights than small porosity monoliths.