Gzil Piotr, Vervoort Nico, Baron Gino V, Desmet Gert
Vrije Universiteit Brussel, Department of Chemical Engineering (CHIS-TW), Pleinlaan 2, B-1050 Brussels, Belgium.
J Sep Sci. 2004 Jul;27(10-11):887-96. doi: 10.1002/jssc.200401788.
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 (epsilon = 0.38, epsilon = 0.60, and epsilon = 0.86) are considered and are compared on the basis of an identical intra-skeleton diffusivity (Ds = 5 x 10(-10)m2/s), internal porosity (epsilon(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) approximately 0.8 (roughly independent of the porosity) and separation impedances as small as Emin approximately 130 (epsilon = 0.60) and Emin approximately 40 (epsilon = 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.
我们报告了一项关于通孔孔隙率对硅胶整体柱主要色谱性能参数（折合理论塔板高度、流动阻力和分离阻抗）影响的理论研究。为了在不存在任何结构不确定性的情况下研究这个问题，我们对硅胶整体柱孔几何结构的计算机生成结构模拟进行了研究。使用商业计算流体动力学（CFD）软件包确定了这些合成整体柱中的谱带展宽。考虑了三种差异很大的外部孔隙率（ε = 0.38、ε = 0.60和ε = 0.86），并在相同的骨架内扩散率（Ds = 5×10⁻¹⁰ m²/s）、内部孔隙率（ε(int) = 0.5）以及相同的相保留因子（k' = 1.25）的基础上进行了比较。由于数据是针对完全有序的结构获得的，因此计算得到的塔板高度和分离阻抗构成了整体柱有望达到的极限性能。研究发现，如果能够使硅胶整体柱完全均匀，以纯水作为工作流体时，基于域尺寸的折合塔板高度可小至h(min)约为0.8（大致与孔隙率无关），分离阻抗可小至Emin约为130（ε = 0.60）和Emin约为40（ε = 0.86）。数据还表明，尽管域尺寸比骨架尺寸是更好的折合基础，但在C项主导的速度范围内，前者仍无法使不同孔隙率柱的范德姆特曲线完全一致。研究发现，在这个范围内，大孔隙率整体柱有望比小孔隙率整体柱产生更小的基于域尺寸的折合塔板高度。
