LACTIC-ACID RECOVERY USING 2-STAGE ELECTRODIALYSIS AND ITS MODELING

An experimental study was carried out on a two-stage process for lacti c acid recovery, which consisted of desalting electrodialysis and wate r-splitting electrodialysis. Limiting current densities were measured at various lactate concentrations in the feed solution for the determi nation of the condition for switching from constant-current mode to co nstant-voltage mode in the desalting electrodialysis. The relationship between the electrical resistance of membrane stack and the lactate c oncentration was identified. The amount of water transferred due to el ectroosmosis which caused volume change in the feed and permeate solut ion was also experimentally determined. Based on the experimental resu lts, mathematical models were developed, in which time changes in the feed and permeate volumes and the electrical resistance were considere d. Model predictions of lactate concentration, volume changes, switchi ng time and energy consumption were in good agreement with the experim ental data. The prediction of total operating time for desalting elect rodialysis showed some errors. However, it was considered to be due to the difficulties involved in determining the termination time in actu al operation. (C) 1998 Elsevier Science B.V.