Purification of lactic acid from fermentation broths by ion-exchange resins

In this work, a novel process for lactic acid purification based on ion exchange is proposed. It consists of two stages: first, a strong cation resin was used to reduce the broth pH below the pK(a) of lactic acid (3.86) and remove the cations present in the solution; then lactic acid was separated from the other anions in the broth using a weak anion exchanger. The ion exchangers selected were Lewatit S2568H and Lewatit S3428 (Bayer, Germany). The Lewatit S2568H resin retained the cations in the broth with an apparent capacity of 1.7 equiv/L, reducing the broth pH below 3.86. It was able to decrease the pH of the broth to as low as 1.5, generating 4 bed volumes (BV) of acidified and partial demineralized broth. In the second step, the acidified broth was purified by the Lewatit S3428 resin, which retained the other anions present in the broth, producing an aqueous solution of lactic acid. This resin was able to produce 25 BV of purified lactic acid with selectivity higher than 99.9%. The final purity of lactic acid was higher than 99%.