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‘Cycle to Cycle’ Optimizing Control of Simulated Moving Beds for a Nonlinear Chiral Separation–Theory and Experiments


C. Langel, C. Grossmann, M. Mazzotti, M. Morbidelli, M. Morari

International Symposium, Exhibit & Workshops on Preparative / Process Chromatography, (PREP 21). Philadelphia, PA, USA.

Recently, our group has implemented an automated on-line HPLC monitoring system for ‘cycle to cycle’ optimizing control of simulated moving beds (SMB) for the separation of chiral components. The monitoring system was developed to obtain precise and accurate data about the concentrations in the two product streams averaged over one cycle, required as feedback information for the controller. The online HPLC monitoring system can handle multicomponent systems, it is not affected by impurities and the measurements are straightforward and very precise. This is a substantial improvement compared to a system based on optical detection devices, since the efficiency of the controller is greatly affected by the quality of the feedback information from the plant. However, the analysis time of the HPLC may be in the range of the cycle time or even longer, which introduces a time delay in the measurements. In summary, the action of the controller is based on accurate feedback information from the plant that is available only once per cycle or even less frequent, if the analysis time exceeds the cycle time. This work presents experimental results for the nonlinear chiral separation of guaifenesin enantiomers in Ethanol using Chiralcel OD as stationary phase. In order to challenge the controller under realistic operation conditions various case studies have been carried out, i.e. introducing pump disturbances, changing the feed concentration during operation or varying the purity specifications in the course of operation. Furthermore, it reports the theoretical modifications and extensions that had to be done to the control scheme to cope with the possibility of having an HPLC analysis time that exceeds the cycle time of the SMB operation. This would increase the flexibility of the monitoring system. The performance of such a scheme is assessed as well. The results illustrate the effectiveness of the SMB controller in combination with the new monitoring system for the nonlinear separation of chiral compounds.


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M. Morari

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