Coupling of simulated moving bed chromatography and fractional crystallisation for efficient enantioseparation

An optimised coupling of liquid chromatography and fractional crystallisation is suggested for efficient enantioseparation. As a first stage, a chromatographic separation, preferably simulated moving bed (SMB) chromatography, is applied to achieve an enantiomeric enrichment sufficient for a subsequent crystallisation. First results of the experimental and modelling work for the model system (+)-/(-)-mandelic acid in an aqueous solution are described. Chromatographic investigations involve the estimation of adsorption isotherms on a suitable chiral stationary phase and the simulation and optimisation of a corresponding SMB process. From the ternary phase diagram measured for the (+)-/(-)-enantiomer/ solvent system, the conditions required to crystallise a pure enantiomer from an asymmetric mixture can be derived. The productivity gains achievable from the combined process compared to the application of chromatography alone are discussed.