Designs of simulated-moving-bed cascades for quaternary separations

Although basic architecture is important for all simulated-moving-bed (SMB) systems, it is particularly important for the separation of multicomponent mixtures because there are not yet standard schemes. New designs are proposed for SMB cascades separating quaternary mixtures. The local equilibrium model is used to determine the minimum desorbent-to-feed ratios (D/F) and productivities for 21 different SMB systems with linear isotherms. An easy-split SMB cascade can theoretically achieve the thermodynamic minimum D/F = 3.0. On the basis of the results, tentative selection rules for SMB systems are proposed for quaternary separations with linear isotherms. Detailed simulations agreed qualitatively with the equilibrium model predictions.