title: Linear two-step gradient counter-current chromatography analysis based on a recursive solution of an equilibrium stage model.
abstract: The implementation of gradients in continuously operated chromatographic counter-current processes has recently attracted considerable interest as a method to improve the performance of this effective separation method. If liquid mobile phases are applied it is advantageous to set the solvent strength in the desorbent stream higher than that in the feed stream. As a consequence. the components to be separated are more retained in the adsorption zones and more easily eluted in the desorption zones. Due to the additional degrees of freedom the design and the optimization of such a two-step gradient counter-current process is difficult. In this paper a steady state equilibrium stage model is used to simulate the process under linear conditions. A simple solution of the underlying model equations is presented capable to describe efficiently the unit for large stage numbers typically encountered in chromatographic columns. Due to the rapidity of the algorithm developed a broad range of operating conditions can be evaluated systematically for different types of gradients. The impact of (a) the functional dependence of the adsorption equilibrium constants on the solvent composition, (b) the number of equilibrium stages and (c) the specification of purity requirements is illustrated and discussed based on results of parametric calculations. The results achieved emphasize the potential of two-step gradient counter-current chromatography.
authors.affiliation: Otto-von-Guericke-Universität Magdeburg, Institut für Verfahrenstechnik, P.O. Box 4120, D-39106 Magdeburg, Germany.
authors.forename: Daria
authors.initials: D
authors.lastname: Beltscheva
authors.forename: Peter
authors.initials: P
authors.lastname: Hugo
authors.forename: Andreas
authors.initials: A
authors.lastname: Seidel-Morgenstern
mesh_terms: D003377:Countercurrent Distribution / Q000379:methods*; D008962:Models, Theoretical