Development of a non-triangular separation region for improving the performance of a three-zone simulated moving bed...

For a three-zone simulated moving bed (SMB) chromatography with linear isotherms, the feasible set of operating parameters for complete separation is known to exist within a triangular region of the triangle theory that is formed in the operating parameter plane spanned by the flow-rate-ratios in the separation zones (II and III), which are commonly denoted as m(2) and m(3). Such an operating region for complete separation region, however, has been established only in the first quadrant (m(2), m(3)) plane, where m(2)>0 and m(3)>0, until now. In this study, a new complete-separation region was developed in the third quadrant (m(2), m(3)) plane, where m(2)<0 and m(3)<0, regarding a three-zone SMB process for the first time. The results showed that the new separation region created in the third quadrant (m(2), m(3)) plane took a non-triangular shape. The operating parameters within such a non-triangular separation region were capable of guaranteeing complete separation for an ideal system with no mass-transfer effects. For a non-ideal system with considerable mass-transfer effects, the operating parameters that were selected with a sufficient margin from the boundaries of the non-triangular separation region led to high purities. One of the noteworthy features in the pattern of solute migration for such case was that both low-affinity and high-affinity solutes reached their corresponding product ports after taking a turn around the SMB bed once. Finally, it was confirmed from the results of SMB optimization based on genetic algorithm and detailed model that the operating parameters in the third quadrant (m(2), m(3)) plane, if chosen properly, could ensure higher purities or higher throughput than the optimal operating parameters in the first quadrant (m(2), m(3)) plane.