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Experimental implementation of an automated online HPLC monitoring system for ‘cycle to cycle’ optimizing control of SMB processes


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

International Symposium on Preparative and Industrial Chromatography and Allied Techniques (SPICA), Zurich, Switzerland

In continuous chromatography, Simulated Moving Bed (SMB) is a firmly established powerful technique for the separation of fine chemicals and enantiomers. Nowadays, Simulated Moving Bed (SMB) units are most often operated sub optimally to guarantee robustness of the operation and to account for system and operation uncertainties. The use of a controller can optimize the operation conditions and increase the productivity of an SMB unit. In our group, a ‘cycle to cycle’ optimizing control concept for simulated moving bed (SMB) units was validated experimentally for the separation of achiral and chiral components. The feedback information for the controller was determined with online optical detectors, i.e. UV-detector and polarimeter, positioned at the extract and raffinate ports. To overcome the limitations of these detecting devices an automated online HPLC monitoring system was developed and installed to monitor the product streams at the outlet streams. This measurement technique leads to more accurate results, can handle multicomponent systems, and is less affected by possible impurities in the product streams compared to the optical detectors. However, the HPLC measurements can be carried out less frequently, i.e. once per cycle and the analysis time can be in the order of the cycle time, which introduces a significant time delay in the measurements. As a consequence, the controller actions are based on more accurate and straightforward but less frequent and time delayed feedback information of the plant. This work presents the design and the implementation of an automated online HPLC monitoring system that determines the average concentrations of the raffinate and extract stream over one cycle, required as feedback information for the controller. To cope with the above mentioned inherent time delay in the feedback information the original control scheme had to be modified and extended.


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M. Morari

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