Page 241 - Chiral Separation Techniques
P. 241

Chiral Separation Techniques: A Practical Approach, Second, completely revised and updated edition
                                                                   Edited by G. Subramanian
                                                       Copyright © 2001 Wiley-VCH Verlag GmbH
                                           ISBNs: 3-527-29875-4 (Hardcover); 3-527-60036-1 (Electronic)
             9 Modeling and Simulation in SMB

                  for Chiral Purification



                  Alírio E. Rodrigues and Luís S. Pais









             9.1 Introduction


             Simulated moving bed (SMB) is a powerful technique for preparative-scale chro-
             matography which allows the continuous injection and separation of binary mix-
             tures.  The concept has been known since 1961 [1], the technology having been
             developed by UOP in the areas of petroleum refining and petrochemicals, and known
             as the “Sorbex” process [2, 3]. Other successful SMB processes in the carbohydrate
             industry are the production of high-fructose corn syrup (“Sarex” process) and the
             recovery of sucrose from molasses. Other companies developed alternative pro-
             cesses for the fructose-glucose separation [4]. Reviews on adsorptive processes are
             given in Rodrigues and Tondeur [5] and Rodrigues et al. [6].
               The SMB concept was developed in order to overcome the limitations of conven-
             tional batch chromatography, mainly the discontinuous character of the process and
             its high cost due to the large eluent and adsorbent requirements. The interest for
             SMB operation increases for low-selectivity separations. At high selectivity, the col-
             umn can be highly loaded and there is little difference between the performances of
             SMB and other discontinuous techniques. Generally, batch processes are more eco-
             nomic at very small scale if we take into account the lower cost of equipment. At
             larger scales, however, the savings in both solvent and chiral stationary phases make
             SMB technology the correct choice. In view of these properties, SMB technology is
             particularly appropriate for chiral separations. The resolution of enantiomers is usu-
             ally a binary separation problem characterised by low selectivities and high costs of
             eluent and chiral stationary phases.
               The SMB technology has found new applications in the areas of biotechnology,
             pharmaceuticals and fine chemistry [7–9]. SMB systems are available for a full
             range of production rates, from 10 to 1000 g per day, up to industrial scale of 5 to
             50 tons per year. SMB chromatography is a useful tool for the pharmaceutical indus-
             try where, for preliminary biological tests, only a few grams of the chiral drug are
             needed. Furthermore, SMB can provide the two pure enantiomers, which are
             required for comparative biological testing [10]. On the other hand, pharmaceutical
             companies work with short drug development times. SMB technology, combined
             with proper chromatographic chiral stationary phases, can be a rapid system, easy to
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