Analysis and optimization of enantioselective extraction in a multi-product environment with a multistage equilibrium model

Based on a single stage model and experimental results for enantioselective extraction of amino acids and amino alcohols, simulations are carried out for a fractional extractor using a multistage equilibrium model. A higher pH, lower temperature, higher concentrations and a higher excess of extractant all result in higher purities in both product streams, but a higher wash stream is required to realise good yield and good purity. The improved purity can be explained from a higher operational selectivity in the single stage, from lower variation of the extraction factors along the extractor, or from a combination of these effects. Application of 'reflux' results in higher product purities at a lower wash stream requirement, but a lower process capacity. It was shown that various combinations of process conditions result in the desired product specifications (99% yield and 98% enantiomeric excess for both extract and raffinate). This leads to optimization possibilities in a multi-product environment: the more stages available above the minimum number for a specific compound, the larger the process capacity for that compound. All systems for which a single stage selectivity of 1.5 was obtained can be separated in a multi-product extractor containing 50 stages, evenly distributed over the wash and strip section. (c) 2007 Elsevier B.V. All rights reserved.