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Online ‘cycle to cycle’ optimizing control of simulated moving bed and Varicol processes


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

International Conference on Fundamentals of Adsorption, (FOA 9). Giardini Naxos, Sicily, Italy.

Simulated Moving Bed (SMB) and Varicol are established technologies for continuous chromatographic separation of enantiomers. Nevertheless, these processes are currently operated sub-optimally to guarantee robustness. The control group at ETH Zurich has developed a control scheme that integrates the optimization and control of the SMB unit that guarantees the fulfillment of product and process specifications and optimizes the economics of process at the same time. Besides, this controller requires only minimal information such as adsorption behavior at dilute condition and average void fraction of the columns. Recently, experimental validation of this optimizing controller is demonstrated through separation of nucleosides, a system characterized with linear isotherm. This was based on continuous online monitoring and frequent controlling (64 time in a cycle) of the SMB unit. Yet, for chiral separation, an accurate online monitoring of the SMB process remains to be the key challenge for efficient implementation of any control scheme due to a number of technical and system specific constraints. A more realistic approach would be to develop a control scheme that makes use of existing and accurate monitoring schemes currently used in the industry such as HPLC analysis over every cycle ('cycle to cycle'). This paper reports experimental validation of the 'cycle to cycle' control scheme in a laboratory scale SMB unit for the separation of a binary mixture of nucleosides exhibiting linear isotherm. The effectiveness of the 'cycle to cycle' control scheme is also shown by several simulation studies of SMB and Varicol processes under nonlinear chromatographic conditions. The results illustrate that the 'cycle to cycle' controller is able to meet the products' purity specifications and operate the process optimally with minimal information regardless of the disturbances that might take place during the operation. Besides, we also envisage presenting results of experimental implementation of the 'cycle to cycle' controller for the separation of Guaifenesin enantiomers in a laboratory SMB unit.


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M. Morari

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