Simulated moving bed starting conditions using an empirical model for S-shaped adsorption isotherms

Simulated moving bed (SMB) chromatography is a complicated process that generally requires modeling to determine starting conditions. Typically one uses the triangle theory to arrive at these starting conditions. The most common adsorption isotherm model used to construct the triangle is the Langmuir isotherm or an isotherm derived from the Langmuir isotherm. Often, modeling software supplied by the SMB manufacturer is used to determine the Langmuirian isotherm parameters. This proprietary approach, while successful in most cases, gives inaccurate results when the adsorption of one of the components is dominated by an S-shaped isotherm. Such failures require lengthy and expensive trial-and-error procedures to optimize the separation. In this paper, we apply an empirical model for S-shaped isotherms to the problem. With this isotherm model a triangle was constructed using the equilibrium dispersive model to simulate the SMB process. The starting conditions predicted by this approach were far more accurate than those determined by the proprietary approach.

► The commonly used, off-the-shelf modeling program Lico-HELP uses the modified Langmuir isotherm to model adsorption. This approach does not give accurate SMB starting conditions when the adsorption of one or more components is governed by an S-shaped isotherm.
► We develop an empirical isotherm to model such Type V adsorption.
► Using our empirical S-shaped isotherm and simulations of the SMB process, we construct numerically a triangle plot.
► The SMB starting conditions predicted by our approach were far more accurate than those produced by the Lico-HELP procedure.