Solvent extraction of lactic acid from aqueous solution

Abstract

The equilibrium distribution of lactic acid was studied in a two-phase aqueous-organic system containing various extractants with a view to the separation of lactic acid obtained as a product of lactose degradation under the effect of Lactobacillus casei (pH of the aqueous solution between 5–6 and temperature 35°C). ALIQUAT 336 containing a quaternary ammonium salt as an active component was found to be the most appropriate extractant. The effect of the experimental conditions on the distribution ratio was followed by varying the concentration of lactic acid in the aqueous solution from 0.001 to 0.033 mol l −1, pH from −0.3 to 12.5 and the concentration of extractant in the organic solution from 0.5 to 20% (vol.). On the basis of the experimental results the extraction equilibrium constant of lactic acid in the examined two-phase system was determined: K ex = 0.274. The stripping process of lactate ions from the organic phase was studied. Alkaline chlorides and carbonates were found to completely destruct the complex of lactate ions with the extractant which provided their transfer to the stripping solution. It was concluded from the obtained results that liquid-membrane extraction is the most appropriate technique for the simultaneous separation of lactate ions from the medium and their transfer and preconcentration in an aqueous solution containing alkaline chlorides or carbonates.