Influence of pH on enantioselective extraction of aromatic acid enantiomers in centrifugal contactor separators: Experiments and simulation

Phenylsuccinic acid (PSA) and α-cyclohexyl-mandelic acid (α-CHMA) are dicarboxylic acid and monatomic acid, respectively, and there is effect of solution pH on multistage extraction efficiency for separation of PSA and α-CHMA enantiomers. Enantioselective liquid-liquid extraction (ELLE) of PSA and α-CHMA enantiomers with hydrophilic hydroxyphenyl-β-cyclodextrin as extractant (represented by C) was performed in a counter-current cascade of ten centrifugal contactor separators (CCSs) to investigate the influence of pH on extraction efficiency (evaluated with enantiomeric excess, ee and yield, Y) with the HP-β-CD concentration changing from 0 to 0.1 mol/L. Experimental results show that there is a significant effect of solution pH on ee and Y for multistage extraction of PSA and α-CHMA enantiomers. Single and multistage equilibrium models of ELLE were developed to investigate the effect of solution pH on ee and Y. From experiments and simulation, it is concluded that lower pH will be helpful for obtaining higher ee and Y in both exit streams and the optimal pH of 2.5 is proposed. The above results may be very helpful to optimize the extraction efficiency and realize the large-scale production of pure enantiomers.