Separation of lactic acid and recovery of salt-ions from fermentation broth

BACKGROUND: Fermentative lactic acid (LA) production and downstream processing require the addition of amounts of base and acid, respectively, as additives. This study tested the Amberlite resins FPA 53 and CR 5550 for separating lactic acid from inorganic salt-ions introduced by additives using water or H₂SO₄ as eluent. Furthermore, recycling of additives as acid and base was investigated. RESULTS: Using FPA 53 and 12.5 mmol L⁻¹ H₂SO₄, an almost complete separation of LA and salt-ions was achieved. The yield of LA was more than 90%, which is comparable with state-of-the-art methods. Salt-ions were concentrated by monopolar electro-dialysis and the concentrate was converted into 1.1 mol L⁻¹ NaOH and 0.8 mol L⁻¹ HCl by bipolar electro-dialysis. The NaOH solution was further concentrated to 5.3 mol L⁻¹ and used in fermentation. The LA yield obtained of 0.8 g per g saccharose is highly comparable with reference fermentation. Furthermore, it was shown that the reuse of HCl does not negatively influence downstream processing. CONCLUSION: This study presents a way to separate salt-ions and LA, and to reuse recovered salt-ions as additives. Outcomes are expected to contribute to the development of processes for the co-product free preparation of pure LA formulations to be used in poly(LA) production.