MODELING OF DISPLACEMENT CHROMATOGRAPHY USING NONIDEAL ISOTHERMS

The chromatographic transport problem in the displacement separation of multi-component mixtures leads to a set of coupled, non-linear partial differential equations. Neglecting axial dispersion, the set of equations can be solved using a transformation of variables (h or omega transformation) for the case that the multi-component distribution function is considered to be ideal (Langmuirean). If intermolecular interactions (non-idealities) are taken into account in the description of the multi-component distribution equilibrium, such a transformation of variables is no longer possible. The displacement separation of binary mixtures was analysed by applying shock-wave theory to the problem of non-ideal distribution isotherms. A description of the separation as a function of time and distance was obtained (development graph). Experimental results pertaining to the separation of Na-K mixtures using Li as the carrier and Rb as the displacer are presented. Quantitative agreement with predicted development graphs was obtained if non-idealities were taken into account, whereas the use of multi-component Langmuir isotherms yielded agreement with experimental results over only a limited composition range.