Total-recycling partial-discard strategy for improved performance of simulated moving-bed chromatography

Simulated moving-bed (SMB) chromatography has become one of the most useful techniques for difficult separations, such as enantiomer separations. We propose a novel “total-recycling partial-discard” (TR-PD) SMB operation strategy in which a portion of the product is temporarily stored or treated and then totally recycled as an additional feed. This new strategy can attain high purities with minimal recovery losses by varying the discard amount and discard length through changes in the effluent flow rates within a switching period. Remarkably, this method can achieve considerably higher extract purity and raffinate recovery. By using varied effluent flow rates during a switching period and intermittent evaporation steps for concentrating discarded portions, the TR-PD operation can overcome the limitations of the previously suggested fractionation and feedback SMB and recycling partial-discard operations, which have difficulties in recycling all of the discarded portions.