Usage of CoOOH electrodes in a flow channel reactor for the non-alkaline oxidation of 5-(hydroxymethyl)-furfural: an upscaling study†

Abstract

A major barrier for the upscaling of electrosynthetic methods is the transfer of the usually potential-controlled batch experiments to an operation in industry-typical cell designs (i.e. two-electrode flow reactors). To cross this bridge, we here present the implementation of our recently published method for the non-alkaline oxidation of 5-(hydroxymethyl)-furfural (HMF) to 2,5-furandicarboxylic acid (FDCA) in a flow channel reactor, powered by a standard laboratory power supply under cell-voltage/current control. For this purpose, the coating method for the used CoOOH catalyst was adapted to enable an electrochemical deposition in the flow channels devoid of a standard three-electrode setup. HMF oxidations were carried out in an acetate buffer (pH 5) at a current density of 1.0 mA cm⁻² and a temperature range between room temperature and 80 °C to provide a direct comparison with the previous batch experiments. The higher electrode surface area of the flow cell thereby allowed a significant reduction of the reaction time while operating under similar (albeit lower) Coulomb efficiencies. Under optimized conditions, the reactor operated at a cell voltage of ca. 2.4 V and yielded 77.1% FDCA at a Coulomb efficiency of 21.0%. Maleic acid was obtained as a side product at a yield of 9.2%.