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Separation of enantiomers through solvent gradient SMB chromatography


S. Abel, G. Erdem, G. Zenoni, M. Mazzotti, M. Morbidelli

AIChE Annual Meeting, Reno, USA

The SMB technology has already shown great potential for various separations, e.g. enantioseparations. It is possible to further improve SMB performance if each section is optimized independently. To this aim, an adsorption strength gradient along the unit would be needed. In section 1 of the SMB a rather weak adsorption is preferable, because all species have to be desorbed; then the adsorption strength should increase up to section 4, where all species have to be adsorbed. The adsorption strength gradient can be realized in different ways. One option is to operate the sections at different temperatures (temperature gradient mode); another one is to operate with a supercritical solvent and apply a pressure gradient. A further possibility is to use different mobile phase compositions in the different sections (solvent gradient mode). This is realized by feeding streams with a different solvent composition at the feed and desorbent inlet, respectively. In this case a step gradient between the two inlets would be generated. It is the aim of this work to develop a design method for these gradient mode operation of the SMB, and to compare the gradient and the isocratic operating mode, where temperature and mobile phase composition are constant, in terms of productivity and desorbent consumption. For design purposes a simplified model is used where mass transfer resistance and axial dispersion are neglected, i.e. the Equilibrium Theory model. This approach yields the so-called Triangle Theory, which - when properly extended to the gradient mode SMB - provides a rather accurate prediction of the optimal operating conditions for the desired separation and a qualitative and quantitative explanation of the main features of SMBs. The theoretical findings are assessed through detailed simulations and experimental investigation. For the latter, the separation of the enantiomers of the flavor keton alpha-ionone in water/methanol mobile phases, using a Nucleodex chiral column, has been considered. The advantages and drawbacks of operating the SMB in the solvent gradient mode are presented and discussed.


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% Autogenerated BibTeX entry
@InProceedings { AbeEtal:2001:IFA_388,
    author={S. Abel and G. Erdem and G. Zenoni and M. Mazzotti and M. Morbidelli},
    title={{Separation of enantiomers through solvent gradient SMB
    booktitle={AIChE Annual Meeting},
    address={Reno, USA},
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