DYNAMIC SIMULATION OF SIMULATED-MOVING-BED CHROMATOGRAPHIC PROCESSES

The simulated-moving-bed process is a powerful tool for continuous sep aration of multi-component mixtures in which the components have diffe rent adsorption affinities. It is suitable for a broad range of prepar ative or production scale applications and allows the separation of co mponents with separation factors near unity with high resolution, yiel d and purity. Furthermore, the desorbent rates and the amount of adsor bent required by simulated-moving-bed processes are much lower than th ose for corresponding batch processes. The SMB process is subject to d ifferent parameters specifying plant size, operating conditions and pr ocess variables. Precise simulations are therefore necessary for proce ss design and evaluation of experimental results. In this paper a deta iled comparison of different modelling approaches is presented. The ai m of this project is to develop a simulation system on the basis of a flowsheeting simulator like SPEEDUP(TM) (AspenTech, Cambridge, U.S.A.) . In order to design and optimize either batch or SMB chromatographic processes it is not only necessary to describe the exact position but also the exact shape of the transient concentration fronts as a functi on of fluid velocity and complex component concentrations. In order to develop a simulation system which meets these demands and which is ac curate enough for high-purity chromatography, appropriate models for u nit operations have to be selected. Different rigorous models for batc h chromatographic separations and continuous chromatography processes in terms of either moving beds with steady-state countercurrent flow o r simulated moving beds with periodic fluid port switching have been e valuated. The results demonstrate that because of the real periodic fl ow SMB processes should be described by rigorous dynamic models with t ubular reactor units and fluid port switching. Axial dispersion and ma ss transfer resistance have to be taken into account in order to obtai n a good agreement with experimental results. The rigorous dynamic mod el which has been developed makes it possible to understand malfunctio ns of pilot plants, to optimize process conditions and to specify star tup procedures for SMB processes. (C) 1998 Elsevier Science Ltd. All r ights reserved.