Electrochemical\nOxidative Upgrading of Alkali-Sensitive\nFurfural and 5‑Hydroxymethylfurfural in an Anion-Exchange Membrane\nElectrolyzer with High-Concentration Products

Increasing the product concentration is important to\nthe application\nof the electrochemical oxidative upgrading of biomass-derived furfural\n(FF) and 5-hydroxymethylfurfural (HMF). However, the degradation of\nalkali-sensitive FF and HMF in a highly alkaline environment affects\nthe conversion efficiency, especially at high concentrations. Herein,\nwe perform the oxidation of FF and HMF in an anion-exchange membrane\n(AEM) electrolyzer at a batch-type and anolyte one-pass mode. The\neffect of the flow field structure on the reaction kinetics is studied.\nThe substance loss in the anolyte caused by penetration through the\nAEM and adsorption by the electrolysis system is determined. For the\nbatch-type mode, FF is added after one batch electrolysis is finished\nto avoid the presence of the concentrated reactant in the anolyte.\nResults show that the final furoic acid (FAD) concentration in the\nanolyte is accumulated to be ∼280 mM with a total yield of\n∼90% based on the anolyte and catholyte. For the anolyte one-pass\nmode, a pulsed feeding strategy is developed to minimize the retention\ntime of FF in highly alkaline media. The oxidation of 300 mM FF is\nperformed with the FAD content higher than 99% in the organic compounds\nof the anode outflow. For the oxidation of HMF, the accumulated 2,5-furandicarboxylic\nacid (FDCA) concentration of ∼270 mM with a total yield of\n∼90% and the pulsed oxidation of 165 mM HMF with the FDCA content\nhigher than 98% are realized at the batch-type and anolyte one-pass\nmode, respectively.