Max-Planck-Institut für Dynamik komplexer technischer Systeme

Motivation

Simulated moving bed (SMB) chromatography is an important technology applied, for example, to difficult separation problems in petrochemical, fine chemical, and pharmaceutical industries. The SMB process employs a series connection of several chromatographic columns. These are switched periodically against the fluid flow (Fig. 1), which 'simulates' a counter-current of liquid and solid phases. This allows for a continuous separation at often superior performance when compared to classical single-column chromatography.

Figure 1: General principle of SMB chromatography.

SMB chromatography is a maturing technology, which becomes clear when considering the many new operating modes suggested for this concept [1]. As a consequence, there is a need for methods and tools for its optimal design and its implementation within different technological environments.

Approach & Results

Equilibrium theory (e.g. [2]) is applied to derive new and straightforward design methods for different SMB configurations and operating modes.

Most existing design methods for SMB processes hold for complete separation (i.e., pure products; e.g. [3]). For SMB processes with limited purities, numerically expensive model optimizations are required for process design. Using equilibrium theory, a much faster design method was developed for systems with Langmuir isotherms [4]. The approach is based on numerically solving a simple system of nonlinear equations. It directly predicts optimum operating parameters and the concentration profiles in the SMB unit (see Fig. 2, left). The method is very useful to design, for example, flowsheet-integrated processes for the production of pure enantiomers ([5]; more details can be found here).

Figure 2: Results of equilibrium-design methods. Left – throughput of an SMB process for limited product purities. Symbols denote optimization results of a detailed model. Right – Throughput of an SMB unit with a gradient of a (here: weakly) adsorbing additive.

Another area of application are adsorbing additives, which can be applied to improve performance of conventional chromatography [6]. A design method for corresponding SMB processes has been developed [7]. Based on this, a new concept – SMB processes with gradients of adsorbing additives – was suggested, which can lead to remarkable improvements of process performance [7].

Future work

Extension of developed methods to other isotherm models,
Application to flowsheet-integrated schemes,
Experimental verifications.

References

Kaspereit, M. (2008). Advanced operating concepts for simulated moving bed processes. In Grushka, E. and Grinberg, N. (Eds.), Advances in Chromatography, Vol. 47. Taylor & Francis (in press).
M. Mazzotti, G. Storti and M. Morbidelli (1997). Optimal operation of simulated moving bed units for nonlinear chromatographic separations, J. Chromatogr. A, 769, 3–24.
H.-K. Rhee, R. Aris and N.R. Amundson (2001). First-order Partial Differential Equations. Vol's. I & II, Dover, Englewood Cliffs.
M. Kaspereit, A. Seidel-Morgenstern and A. Kienle (2007). Design of simulated moving bed processes under reduced purity requirements. J. Chromatogr. A, 1162, 2–13.
M. Kaspereit, J. García Palacios, T. Meixús Fernández and A. Kienle (2008). Systematic design of production processes for enantiomers with integration of chromatography and racemisation reactions. In: B. Braunschweig and X. Joulia (Eds.), ESCAPE 18, Elsevier, Amsterdam, pp. 97–102.
P. Forssen, R. Arnell, M. Kaspereit, A. Seidel-Morgenstern and T. Fornstedt (2008). Effects of a strongly adsorbed additive on process performance in chiral preparative chromatography. J. Chromatogr. A, 1212, pp. 89–97.
M. Kaspereit, R. Arnell, P. Forssén, A. Seidel-Morgenstern, T. Fornstedt, and A. Kienle (2008). Theoretical Analysis of Continuous Chromatography with Adsorbing Additives (oral), SPICA 2008 - 12th Intl. Symp. on Preparative and Industrial Chromatography and Allied Techniques, Zurich (Switzerland).