Electrochemical Membrane Reactor: Single-Step Separation and Ion Substitution for the Recovery of Lactic Acid from Lactate Salts

An electrochemical membrane reactor based on an in-house-prepared anion-exchange membrane was developed to achieve single-step separation and acidification (ion substitution) of lactates to lactic acid. The physicochemical and electrochemical properties of the anion-exchange membrane under standard and operating conditions reveal its suitability for the proposed reactor. Experiments using synthetic solutions of sodium and ammonium lactates of different concentrations were carried out to study the feasibility of the process. Electrochemical reactions occurring at the cathode and anode under operating conditions are proposed. It was observed that OH - formation at the cathode leads to the formation of base in the catholyte while lactate ion is transferred from the catholyte to the anolyte through the anion-exchange membrane and is acidified by the formation of H + at the anode. This process was completely optimized in terms of operating conditions such as the initial concentration of lactate in the catholyte, the applied potential gradient, the lactate flux, the recovery, the energy consumption, and the current efficiency. It was observed that ammonium lactate can be more efficiently and more rapidly separated and acidified than sodium lactate. A representative experiment with fermentation broth was also conducted for the separation and acidification of sodium lactate in the presence of polysaccharides, carbohydrates, salts, and coloring materials. It was concluded that the electrochemical membrane reactor is an efficient and simple device for the recovery and acidification of lactates from uncharged molecules such as polysaccharides, carbohydrates, and other coloring agents as these molecules are not able to cross the anion-exchange membrane in a single-step separation for producing lactic acid.