Membrane Matters\nin Paired Electrolysis: Synthesis\nof 2,5-Furandicarboxylic Acid and 2‑Butanone

Paired electrolysis combines value-added oxidation and\nreduction\nreactions and thus increases electron and process efficiency. This\nwork develops a process to oxidize hydroxymethylfurfural (HMF) to\n2,5-furandicarboxylic acid (FDCA) on the anode and reduce acetoin\nto 2-butanone on the cathode in a 25 cm<sup>2</sup> flow cell. First,\nwe analyze the influence of an ion exchange membrane on the process\nand assess ion migration. We develop a stable process with a bipolar\nmembrane. We then increase the current density and the reactant concentration.\nAt 150 mA cm<sup>–2</sup>, we reach a combined yield of above\n140% and a product concentration of 1.45 mol<sub>2‑butanone</sub> L<sup>–1</sup> and 0.9 mol<sub>FDCA</sub> L<sup>–1</sup>. The space–time yields are 0.25 μmol<sub>FDCA</sub> s<sup>–1</sup> cm<sup>–2</sup> and 0.34 μmol<sub>2‑butanone</sub> s<sup>–1</sup> cm<sup>–2</sup>. We then substitute the potassium-based electrolyte with a more\ncost-effective sodium-based electrolyte. We counteract the detrimental\nincrease in cell voltage by adding Na<sub>2</sub>SO<sub>4</sub> as\na supporting electrolyte without impairing the reaction metrics. With\nthis work, we provide a structured approach for developing paired\nelectrolysis processes, showcased with the biobased products FDCA\nand 2-butanone toward the efficient electrochemical valorization of\nbiomass.