Performance analysis and optimization of enantioselective fractional extraction with a multistage equilibrium model

Chiral compounds are important products in the pharmaceutical and fine chemical industry. Fractional reactive extraction (FREX) is a promising enantiomer separation method but knowledge on translation into industrial practice is very scarce. In this work the combinations of process and product parameters that generate a specified yield and product purity have been evaluated using a multi-stage equilibrium model. The simulations demonstrated that the influence of changes in process parameters (pH, T, concentrations) can be predicted with the multistage equilibrium model for reactive extraction of phenylglycinol and phenylethylamine. A higher pH, lower temperature, higher concentrations and a higher excess of extractant all result in higher purities. Implementation of reflux results in somewhat higher product purities (or less stages), but a significant loss in capacity. Recovery of product and extractant by backextraction should be carried out by pH shift, preferably with CO2 to prevent salt formation. For separating racemic mixtures with a minimal single stage selectivity of 1.5 a multiproduct extractor should contain 50 stages, evenly distributed over the wash and strip section.