Efficient separation of (R)‐(‐)‐mandelic acid biosynthesized from (R,S)‐mandelonitrile by nitrilase using ion‐exchange process

BACKGROUND: (R)‐(‐)‐Mandelic acid (R‐MA) is an important intermediate and chiral regent with broad uses. An efficient method for the separation of R‐MA from the bioreaction mixture with high yield is of great importance, thus, the main objective of this work is to investigate the recovery of R‐MA using an ion‐exchange process. RESULTS: The equilibrium isotherms for the separation of R‐MA by resin HZ202 were obtained in the pH range 5.0–9.0 and temperature range 25–35 °C. The equilibrium data are well fitted by the Langmuir isotherm. Batch kinetic experiments showed that the mobility of R‐MA^? in solution was rapid and the R‐MA^?/OH^? ion‐exchange process reached equilibrium after about 60 min. Adsorption kinetics were analyzed by a linear driving force mass‐transfer model, yielding good prediction of the kinetic behavior. In fixed bed column experiments, the breakthrough curves of R‐MA from the solution on resin HZ202 were determined at different flow rates and R‐MA was eluted with different concentrations of HCl. A favorable breakthrough curve and optimal eluant concentration were obtained. The results were used for the separation of R‐MA biosynthesized from (R,S)‐mandelonitrile with nitrilase, and separation was successfully achieved with above 90% recovery yield. CONCLUSION: Resin HZ202 presents favorable behavior for the recovery of R‐MA, in terms of capacity, kinetics, affinity, and susceptibility to regeneration. The results of this study provide an efficient method for R‐MA recovery from bioreaction mixture and could potentially be used in industry. Copyright © 2010 Society of Chemical Industry