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In the course of the last decade the concept of simulated moving bed (SMB) chromatography has been successfully applied in a variety of fields, from the separation of enantiomers to the purification of pharmaceutical proteins. In most cases these separations are realized with a classical implementation of the process, using four distinct zones and constant operating conditions for internal factors (e.g. switching time, liquid velocities) as well as for external factors (e.g. solvent strength). In order to further increase the potential of SMB chromatography several more sophisticated modes of operation have been presented, dynamically varying certain parameters during the separation. Prominent examples are VariCol [1] , PowerFeed [2] and ModiCon [3]. Using a different angle to enhance the performance a concept using an internal concentration step between zones I and II has been described recently [4,5].
Besides optimizing the process for binary separations research has also focused on the need for a continuous multicomponent separation, mostly in the form of ternary separations. To achieve this a number of different approaches have suggested the extension of zone numbers, ranging from 5-Zone open loop up to 14-Zone closed loop setups [6].
Recently a 8-Zone closed loop separation unit utilizing an external concentration step was presented [7]. In one example of this technique the feed mixture containing three components enters the unit between zones VI and VII. Either the two most or least retained components are directed to either the extract or raffinate outlet. The stream withdrawn at this port is then concentrated and fed back into the unit between zones II and III, utilizing the performance enhancing effects of an extra-column enrichment. With this modification it is possible to tackle limitations due to the unavoidable fixation of solid flow rate in all zones.
In this presentation the possible impact of using different kinds of concentration steps in continuous chromatography will be discussed. The previously described 8-zone process for ternary separations will be used to illustrate some of the possible beneficial effects.
[1] M. Bailly, P. Adam, O. Ludemann-Hombourger, R.M. Nicoud, WO 2000025885 (2005)
[2] Z. Zhang, M. Mazzotti, M. Morbidelli, Journal of Chromatography A 1006 (2003) 87.
[3] H. Schramm, A. Kienle, M. Kaspereit, A. Seidel-Morgenstern, WO2004014511 (2004)
[4] M. Bailly, R.M. Nicoud, P. Adam, O. Ludemann-Hombourger, US 2006124549 (2006)
[5] G. Paredes, H.K. Rhee, M. Mazzotti, Industrial & Engineering Chemistry Research 45 (2006) 6289.
[6] P.C. Wankat, Ind. Eng. Chem. Res. 40 (2001) 6185.
[7] L.C. Keßler, A. Seidel-Morgenstern, Journal of Chromatography A 1126 (2006) 323.
