Purification of caprolactam by means of an electrodeionization technique

In this study an experimental method for purification of a system containing a 30% caprolactam aqueous solution was attempted at room temperature. The impurities in the system were removed by using the continuous electrodeionization (EDI) device, which is an ion-exchange membrane stack with 40 diluting compartments filled with mixed ion-exchange resin beads. The optimal working parameters for this technology were obtained during a 5-month test. It was shown that the conductivity of the treated caprolactam solution was considerably lower (10 µS/cm) in comparison to the feed caprolactam solution (30 µS/cm). In addition the absorption value had decreased by 20%.

The results of the tests demonstrate that continuous EDI is a plausible replacement for ion exchange in purification of a 30% caprolactam aqueous solution. From this study it was possible to determine that conductivity of the treated solution remained stable and lower than 10 µS/ cm. The reduction of the absorption value was always in excess of 20%, and impurities were lower after EDI treatment.