Recovery of Bio-Based Fumaric Acid By Electrochemically Induced pH Shift Crystallization
Authors: Schröder Christian , Jupke Andreas 
Published: February 2024

The heterotrophic microbial production of platform chemicals is gaining increasing interest due to the growing need to replace fossil resources by renewable alternatives. Carboxylic acids such as fumaric acid are important building blocks for high-value bio-based chemicals [1]. Fumaric acid is used as an acidulant, as an antibacterial agent, and as a precursor for polymers and pharmaceuticals [2,3].
A major challenge commercializing the microbial production route is the recovery and the purification of fumaric acid after fermentation. Bio-production of fumaric acid has not yet reached industrial scale due to high additive consumption during the acid- and base-induced pH shift in the downstream process. The inevitable co-production of saline waste deteriorates process economics further and raises ecological concerns.
Therefore, we propose a new electrochemical downstream process, which reduces the use of pH adjustment agents [4]. This downstream process incorporates an electrolysis cell to adjust the pH value. During electrolysis, protons are produced at the anode and hydroxide ions are produced at the cathode by the electrochemical splitting of water. In conventional water electrolysis, protons or hydroxide ions migrate through a membrane to balance the charge in the electrolysis cell. Consequently, the pH value is constant in the electrolysis cell chambers. In pH shift electrolysis, a salt is added to the electrolyte. The salt provides additional ions to maintain electroneutrality in both electrolysis cell chambers. In this way, protons and hydroxide ions are retained in their respective chambers of the electrolysis cell and a pH difference is created between the anode and cathode. During acidification in the anode chamber, the fumaric acid salt from the fermentation is protonated. Subsequently, fumaric acid crystallizes in the electrolysis cell in high yields due to its low solubility. Afterwards, fumaric acid crystals can be easily separated from fermentation broth. Simultaneously, a base is produced at the cathode, which can be used to maintain a neutral pH in the fermentation. Consequently, saline waste production and its drawbacks are avoided.
This work presents the pH shift with an electrolysis cell and the simultaneous crystallization of fumaric acid in the anode chamber. Next, the process is analyzed using on-line and off-line analytics such as Raman spectroscopy and high-performance liquid chromatography.
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