SEPARATION OF FERMENTATION PRODUCTS BY MEMBRANE TECHNIQUES - II - CONVERSION OF LACTATE TO LACTIC-ACID BY ELECTRODIALYSIS

The yield of an electrodialysis unit operating for the conversion of l actate to lactic acid (LA) is depressed by low conductivity of the lac tic acid solution. Experiments performed with a laboratory electrodial ysis unit (ED) designed to establish the limiting current density i(li m), for the whole unit and for each of the membrane/solution elements revealed high voltage drops for membranes in contact with the lactic a cid solution. By filling the LA compartment with a cation-exchange res in as the conducting turbulence promoter, it was possible to increase i(lim), from 2.7 +/- 0.3 to 18.3 +/- 2.0 mA/cm(2). With a resin suspen sion the rate of lactic acid formation was 6.0 mol.m(-2).h(-1), the cu rrent efficiency amounted to 92%, and the energy consumption was 3.3 k W.h.kg(-1). A hypothesis for the similar to 7-fold increase of i(lim) by filling the LA compartment with a grained conducting resin is prese nted.