Displacement Chromatography with a Nonideal Column

We discuss in this first part the formation of the isotachic train using the equilibrium-dispersive model and the influence of the various parameters that control the characteristics of this train the displacer concentration, the sample size, the column length, the concentration of the feed, and the column efficiency. The results differ from those reported in Chapter 9, which were obtained with the ideal model in which there is no dispersion. Because the differences observed consist essentially in the formation of mixed zones between the bands in the isotachic train, many results remain similar. We also discuss the behavior of trace components, either those contained in the sample or those contained in the displacer. 

Frontal Analysis, Displacement and the EquiMbrium-Dispersive Model 

010 cm, and sample size, (a) Sample size 50, 50, and 100 mg of the first, second, and third components, respectively, (b) Sample size 100, 100, and 200 mg of the first, second, and third components, respectively. 

Although the general phenomena and the qualitative results described in this section remain valid for any isotherm model, provided they are convex upward and do not intersect, the quantitative results of the shock layer theory presented in Chaptersl4 and 16 are valid only when the adsorption behavior of the mixture components is properly described by the competitive Langmuir isotherm model. The theory shows conclusively that, when the separation factor decreases, the shock layer thickness, hence the width of the mixed zone in the isotachic train, increases in proportion to oc + l)/ a — 1) (Eqs. 16.27a and 16.27b). At the same time, the column length required to reach isotachic conditions increases also indefinitely, as predicted by the ideal model. 

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