Influence of Process Parameters on Extraction Equilibria for the Chiral Separation of Amines and Amino-Alcohols with a Chiral Crown Ether

Reactive extraction is studied as a promising chiral separation technique for commercial production scale. For chiral separation of amines and amino alcohols, a chiral crown ether was identified as a versatile enantioselective extractant. In this paper, the influence of various process conditions on the extraction performance is studied experimentally, and a predictive model is constructed based on the chemical and physical equilibria. It was found that the operational selectivity in one extraction step is mainly determined by the complexation constants between crown ether and enantiomers (which are dependent on solvent and temperature) and by the extractant concentration, whereas the distribution ratio is also strongly influenced by the pH. The model gives an excellent prediction of the operational selectivity and a good explanation for the system's responses to changes in process conditions. The model can be used as a basis for a multistage equilibrium extractor model and for conceptual process design. Under optimal process conditions, an operational selectivity >1.5 was obtained for five out of seven model compounds, with satisfying distribution ratios (D ~ 1-10).