A systematic design method was used to develop a pilot-scale simulated moving bed (SMB) process for the fractionation of two amino acids, tryptophan and phenylalanine. In this method, isotherms were estimated using both frontal chromatography and batch equilibrium methods, and mass-transfer parameters were estimated using frontal chromatography data. SMB experiments were then conducted using the zone flow rates and port velocity calculated from a theoretical analysis without considering mass-transfer effects (an equilibrium design). The estimated parameters were validated with computer simulation and SMB data based on the equilibrium design. A design considering mass-transfer effects (a nonequilibrium design) was then obtained from the standing wave analysis and tested experimentally. The effluent histories at the extract, raffinate, and sampling ports agreed with those from computer simulations. A sensitivity analysis shows that accurate isotherms, intraparticle diffusivities, and bed voidage are important for the SMB design, and the nonequilibrium design is more robust than the equilibrium design. Various column configurations were compared in terms of throughput and desorbent consumption.

For simulated moving bed (SMB) systems with significant mass-transfer effects, a model-based design method, which requires accurate mass-transfer parameters, was developed previously (Wu et al. Ind. Eng. Chem. Res. 1998, 37, 4023). An extended standing wave design method is developed in this study and tested using computer simulations and pilot-scale SMB experiments for the separation of phenylalanine (phe) and tryptophan (trp). In this method, propagation speeds of impurity waves are estimated from the effluent histories of SMB runs based on a design that does not consider mass-transfer effects. According to the impurity wave speeds, zone flow rates and switching time are modified to counterbalance the mass-transfer effects. The values of the individual mass-transfer parameters are not needed. High-purity (96-99%) and high-yield (96-99%) products are obtained. This method is simpler than the model-based design method and can be applied when mass-transfer parameters are either unknown or inaccurate.

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