Lactic acid recovery using two-stage electrodialysis and its modelling

An experimental study was carried out on a two-stage process for lactic acid recovery, which consisted of desalting electrodialysis and water-splitting electrodialysis. Limiting current densities were measured at various lactate concentrations in the feed solution for the determination of the condition for switching from constant-current mode to constant-voltage mode in the desalting electrodialysis. The relationship between the electrical resistance of membrane stack and the lactate concentration was identified. The amount of water transferred due to electroosmosis which caused volume change in the feed and permeate solution was also experimentally determined. Based on the experimental results, mathematical models were developed, in which time changes in the feed and permeate volumes and the electrical resistance were considered. Model predictions of lactate concentration, volume changes, switching time and energy consumption were in good agreement with the experimental data. The prediction of total operating time for desalting electrodialysis showed some errors. However, it was considered to be due to the difficulties involved in determining the termination time in actual operation. (C) 1998 Elsevier Science B.V.