From Batch to Flow: Paired Electrolysis of H2 and Electrochemical Conversion of Biobased 5-HMF in a Flow Reactor

Flow reactors are an attractive process for a variety of applications in the chemical industry. This is due to advantages over batch processes, such as good scalability and constant product quality with precisely controllable reaction conditions. [1] Regarding the industrial transition towards a climate-friendly and CO2-neutral economy, electrolysis and electrosynthesis processes are a focus of current research. These make it possible to use electricity from renewable energies directly and at the same time fulfil several criteria of green chemistry [2]. However, they currently often require the use of platinum group metals (PGM) and need separators that are mostly based on perfluorinated and polyfluorinated alkyl substances (PFAS) [3]. In addition, conventional electrolysis processes used to produce green hydrogen require high overvoltage. These can be traced back to the oxygen evolution reaction (OER). Furthermore, oxygen is not a value-added product. For these reasons, there is increasing interest in coupled systems in which the sluggish OER is replaced by a thermodynamically more efficient reaction that also generates a value-added product. One possibility for this is the electrooxidation of biobased 5-HMF to the platform chemical 2,5‑furandicarboxylic acid (FDCA) [4]. A theoretical cell voltage of 0.3 V is required for the FDCAER/HER, whereas the OER/HER requires 1.23 V [5]. [6] The simultaneous production of platform chemicals and green H2 by paired electrolysis is a promising approach to enable sustainable and energy-efficient systems. Currently, this technology is still in the development stage and studies have so far focused on batch cell trials. [4,5,7] However, the use of flow reactors can further reduce overvoltage’s. This is due to factors such as better mass transport, an optimized reactor-volume/electrode ratio and minimized electrode gaps. In addition, more stable process conditions and a simplified scale-up point in favor of transferring to a flow system as early as possible