Chiral separation by combining pertraction and preferential crystallization

This work describes the application of a hybrid two-step enantioselective separation process. As a first step, pertraction using supported liquid membranes provides an initial enrichment, while the following preferential crystallization delivers the enantiopure crystals as final product. Mandelic acid in water was studied as a model system. Using a suitable chiral selector, pertraction provides enrichments exceeding 10% and reaching up to 20% in the permeate phase, which was sufficient to allow for subsequent selective preferential crystallization. Based on the individual performances of pertraction and crystallization, overall yields and productivities are estimated. The calculated productivities are compared with values achievable in alternatively applicable chromatographic separation processes using chiral stationary phases. The realized hybrid pertraction-crystallization process is in its present state for the example considered still inferior to preparative chromatography. Strategies for further improvement are suggested.