Zusammenfassung
A novel modification of simulated moving bed (SMB) chromatography, referred to as fractionation and feedback SMB (FF-SMB), has been developed recently 1). This operating regime is based on fractionating one or both outlet streams and feeding back “non-product” fractions into the unit in an alternating manner with the original feed (Figure 1). A systematic model-based optimization approach has been proposed to evaluate its superiority over the conventional SMB 2). Using the raffinate fractionation as an example, it was shown that FF-SMB outperforms SMB in terms of the maximum feed throughput and minimum desorbent consumption for both linear and nonlinear isotherms. This concept was also extended to the general case which realizes a simultaneous fractionation of both outlets 3). Quantitative performance comparison demonstrates that the double fractionation extension is the most efficient operating policy even if the two existing single fractionation modes are significantly supe
rior to the SMB process. Further evaluation of the practical applicability reveals that FF-SMB has tremendous advantages for difficult separations characterized by high product purity, low column efficiency and small adsorption selectivity.
In this presentation, we explore the potential to further improve the performance of FF-SMB by enriching the recyclates in the buffer vessels. An enrichment operation is introduced to the recyclate collected in each buffer vessel, and the resulting concentrated fraction is alternatingly fed back into the unit with the fresh mixture. Such an operation can be implemented by a continuous solvent evaporation or membrane filtration (see Figure 1). Note that a similar approach has been also adopted by the EE-SMB modification 4), where a portion of the extract stream is enriched and re-injected at the same point of the unit. In order to evaluate the effectiveness of this step, the enrichment based on evaporating solvent was used as an illustration example and the optimal performance of the recyclate-enriched scheme is compared to that of standard FF-SMB. It has been found that enriching recyclate is advantageous to FF-SMB and allows further improvements in productivity, product conc
entration and considerable savings in desorbent consumption. The benefits attainable due to the enrichment operation are particularly pronounced for difficult separation scenarios. In addition to evaluating the performance at the cyclic steady state, the transient dynamics are also examined by considering a start-up time minimization problem. A deterministic Newton-based dynamic optimization approach is employed to investigate the performance systematically.
References
1.L.C.Keßler, A.Seidel-Morgenstern, J.Chromatogr.A 1207 (2008) 55.
2.S.Li, Y.Kawajiri, J.Raisch, A.Seidel-Morgenstern, Presented at PBAST5, Singapore, 2009.
3.S.Li, Y.Kawajiri, J.Raisch, A.Seidel-Morgenstern, Presented at PREP 2009, Philadelphia, USA, 2009.
4.M.Bailly, R.-M.Nicoud, A.Philippe, O.Ludemann-Hombourger, World Patent WO2004039468 (2004).
