Shock layer thickness and optimum linear velocity in displacement chromatography

Abstract

The width of the mixed zones between two successive bands in the isotachic train represents the loss in recovery yield achieved in displacement chromatography. Intuitively, this width depends on the mobile phase flow velocity, but no systematic study of this effect has yet been performed. On the other hand, constant pattern behavior and the theory of shock layer are well known in chemical engineering. Using this approach, and assuming competitive Langmuir isotherm behavior, an analytical equation is derived which relates the shock layer thickness (SLT) in displacement chromatography and the column design and operating parameters. Using this equation, it is possible to investigate the dependence of the SLT between two consecutive bands in the isotachic train on the mobile phase velocity, the concentration and the retention factor of the displacer and the separation factor of the two components. In displacement chromatography, the optimum mobile phase linear velocity ( u opt s) for minimum shock layer thickness, or maximum recovery yield depends not only on the coefficients of axial dispersion and mass transfer resistance of the two components, as does the optimum mobile phase velocity ( u opt L) in linear chromatography, but also on the retention factor and the concentration of the displacer. The results of the study of this analytical equation are in excellent agreement with those of numerical calculations.