Ion-exchange equilibrium of N-acetyl-d-neuraminic acid on a strong anionic exchanger

N-acetyl-d-neuraminic acid (Neu5Ac) is a high value-added product widely applied in the food industry. A suitable equilibrium model is required for purification of Neu5Ac based on ion-exchange chromatography. Hence, the equilibrium uptake of Neu5Ac on a strong anion exchanger, AD-1 was investigated experimentally and theoretically. The uptake of Neu5Ac by the hydroxyl form of the resin occurred primarily by a stoichiometric exchange of Neu5Ac− and OH−. The experimental data showed that the selectivity coefficient for the exchange of Neu5Ac− with OH− was a non-constant quantity. Subsequently, the Saunders' model, which took into account the dissociation reactions of Neu5Ac and the condition of electroneutrality, was used to correlate the Neu5Ac sorption isotherms at various solution pHs and Neu5Ac concentrations. The model provided an excellent fit to the binary exchange data for Cl−/OH− and Neu5Ac−/OH−, and an approximate prediction of equilibrium in the ternary system Cl−/Neu5Ac−/OH−. This basic information combined with the general mass transfer model could lay the foundation for the prediction of dynamic behavior of fixed bed separation process afterwards.