Optimizing the Yield of a Pure Enantiomer by Integrating Chiral SMB Chromatography and Racemization. Part 2: Theory

We address the purification of the target enantiomer of a chiral compound from its racemic mixture, through simulated moving bed (SMB) chromatography either as a standalone or combined with the recycle and racemization of the undesired enantiomer. We carry out a comparative assessment of the two processes with focus on the role of the racemization kinetics, on the effect of the selectivity of the chiral stationary phase, and of the upstream symmetric synthesis of the racemate. The analysis is general thanks to the methods adopted for the optimal design of the integrated process (with racemization) and for the sizing of the SMB unit, as well as for the use of the four generalized Langmuir adsorption isotherms. In this way, we determine quantitative criteria that show that the standalone SMB process outperforms the integrated process when the performance of the racemization catalyst or the chiral stationary phase is poor and the racemic feed is inexpensive.