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During the last years, the performance potential of the conventional simulated moving bed (SMB) process [1], typically based on four distinct zones, has been enhanced by dynamically varying otherwise constant operating conditions during the separation, leading to a number of derived processes like VariCol [2] or ModiCon [3]. Recently, a novel operating mode was presented that utilizes a combination of fractionation and internal feed-back to increase process performance [4]. This fractionation and Feed-back SMB mode is based on sub-dividing each switching time into distinct phases for one outlet and the feed inlet. Within the production phase, purity requirements are met in both outlet streams and they are collected as product fractions. For the remainder of the switching time, the recycle phase, product collection is stopped for one of the two streams, as a given purity threshold is crossed, and this fraction is collected in a buffer vessel. The second outlet stream, yielding the desired product quality over the complete cycle, is collected permanently. This approach allows for more productive operating conditions, as the purity requirements only have to be met within the production phase, while still meeting purity requirements. Similarly, two phases can be defined at the feed inlet: during the feed-back phase, the content of the buffer vessel fed into the SMB system, while for the remainder of the cycle time, the initial feed mixture is used. This set-up effectively minimizes the loss of product that would occur if only a fractionation was implemented. In this poster, two alternative implementation forms of this process, extract or raffinate fractionation and recycle, will be compared regarding their potential to solve a given separation problem. For evaluation of performance, an adapted form of the well-known mII-mIII-diagram as well as a Pareto analysis will be used. The latter is based on two goal functions, which reflect the need for separation processes that are productive and at the same time avoid losing valuable products, while yielding a given purity. This comparison will be conducted by means of an extensive simulation study for both linear and non-linear isotherms.
[1] D. B. Broughton, C.G. Gerhold, Continuous Sorption Process Employing Fixed Bed of Sorbent and Moving Inlets and Outlets, US Patent 2 985 589 (1961)
[2] O. Ludemann-Hombourger, R. M. Nicoud, M. Bailly, The "VariCol" process: a new multicolumn continuous chromatographic process, Sep. Sci. Technol. 2000, 35, 1829
[3] H. Schramm, M. Kaspereit, A. Kienle, A. Seidel-Morgenstern, Simulated moving bed process with cyclic modulation of the feed concentration, J. Chromatogr. A 2003, 1006, 77
[4] L. C. Keßler, A. Seidel-Morgenstern, in PREP 2007 - 20th International Symposium, Exhibit & Workshops on Preparative / Process Chromatography, Ion Exchange, Adsorption / Desorption Processes & Related Separation Techniques, Baltimore, MD, USA, 2007
