Integrated Biphasic Electrochemical Oxidation of Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

Abstract

Production of bio-based platform chemicals and polymers via electrochemical routes enables the direct utilization of electrical energy from renewable sources. To date, the integration of electrochemical conversions in process chains remains largely unexplored and the reactions are often studied using synthetic solutions. This work demonstrates the biphasic electro-oxidation of hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) and couples the electrochemical oxidation with the biphasic dehydration of fructose to HMF. The integrated approach eradicates the intermediate HMF purification, as the HMF-rich organic product phase is fed directly into the electrochemical flow-cell reactor. Here, HMF is extracted into the aqueous phase and oxidized to FDCA on a Ni(OH)2/NiOOH catalyst in 0.1 M KOH solution at pH 13. The FDCA then remains in the aqueous phase, enabling direct recirculation of the HMF-containing organic phase. We demonstrate a FDCA yield of close to 80 % with a feed from HMF synthesis. Further, we analyze the influence of the phase ratio (V_Organic to V_Aqueous) and current density for biphasic electrochemical oxidation. By adjusting the gap width, we were able to decrease the average cell voltage from 7 down to 3 V at a current density of 30 mA cm⁻². This work presents a promising integrated process for the synthesis of green platform chemicals and provides insight into biphasic solutions in electrochemical conversions.