Theoretical study of multicomponent continuous countercurrent chromatography based on connected 4-zone units

Continuous countercurrent or simulated moving bed (SMB) chromatography is a well-established separation technology. Conventional processes are based on four zones which fulfil distinct functions in order to split a feed into two fractions. Frequently there is an interest in isolating a target component out of a feed mixture containing more than two components. Modifications of the classical SMB process are required to solve this task. In the last years several concepts exploiting more than four zones have been suggested. To analyse these concepts the equilibrium theory has been frequently applied, neglecting all kinetic effects. It is the purpose of this paper to apply an equilibrium stage model in order to describe the performance of a combination of two or three 4-zone true moving bed units which are connected in series or integrated into 8- or 12-zone true moving bed units. The performance of such units is evaluated with respect to their potential to continuously separate ternary or quaternary mixtures. The analysis is based on the assumption of linear adsorption isotherms. An important aspect is the introduction of additional purge streams required for a successful operation of integrated 8- and 12-zone units.