Design of Simulated Moving Bed Separations: Generalized Langmuir Isotherm

In this paper, exact criteria for the complete separation of binary mixtures in simulated moving bed (SMB) units are developed. They apply to systems subject to the generalized Langmuir isotherm, whose definition yields four different types of isotherms corresponding to different combinations of Langmuir and anti-Langmuir behavior of the components to be separated. These criteria are derived in a similar way in the different cases using the equilibrium theory of chromatography applied to the equivalent true moving bed (TMB) unit. Separation performance is controlled by the dimensionless flow rate ratios. The complete separation region in the operating parameters space has boundaries that are constituted of straight lines and curves, defined through simple and easy-to-use equations. These in turn depend on the adsorption isotherm parameters and on the composition of the feed mixture. The analogies and differences observed among the four isotherms in terms of complete separation region are analyzed and discussed.