Liquid membrane technology for the separation of racemic mixtures

Many drugs and pesticides are presently used as a racemic mixture. However, the biological activity is often concentrated in one of the two enantiomers, the other enantiomer being 50% impurity. A new process has been developed to separate enantiomeric mixtures, based on the combination of a countercurrent fractionation and liquid membrane technology. Two liquids are oppositely chiralized by the addition of the R- or the S-enantiomer of a chiral selector, respectively, These liquids are miscible and are kept separated by a non-miscible liquid contained in a porous membrane. The liquid membrane should be permeable to the enantiomers to be separated and non-permeable to the chiral selector molecules. Enantioselectivities have been determined for a broad variety of racemic drugs. Different types of hollow-fiber modules have been tested and optimization of the modules has mainly been focused on the improvement of shell-side flow distribution. To proof the feasibility of the system, experiments have been performed in a bench-scale unit, in which optical purities of 99% plus for both enantiomers have been obtained.