Process optimization of continuous liquid–liquid extraction in centrifugal contactor separators for separation of oxybutynin enantiomers

• OBN enantiomers separated by multistage enantioselective liquid–liquid extraction.
• Model predictions are in good agreement with the experimental results.
• By simulation and optimization, optimal process parameters are obtained.

A model for multistage enantioselective liquid–liquid extraction (ELLE) of oxybutynin (OBN) enantiomers was built on the basis of single-stage model for chiral extraction of OBN enantiomers and the law of mass conservation in a counter-current cascade of centrifugal contactor separators (CCSs). A series of experiments concerning influence of the extract phase/washing phase ratio (W/O), extractant concentration, pH value, temperature and the number of stages were conducted to verify the multistage equilibrium model. High purity and yield of enantiomer can be obtained by optimizing W/O, extractant concentration, pH value or adding more stages. The model was applied to predict the symmetrical separation of OBN enantiomers. By simulation and optimization, optimal process parameters for the symmetrical separation of OBN enantiomers, namely, pH of 5, HP-β-CD concentration of 0.1 mol/L and W/F of 5 at temperature of 278 K are obtained. With the optimal process parameters, the eeeq (equal enantiomeric excess) can be up to 97% with the number of stages (N) of 100.