Multi-phase systems for the electrochemical production of 2,5-furancarboxylic acid

The future of the chemical industry aims at sustainable and flexible production methods to reduce greenhouse gas emissions. Electrified processes that use renewable electricity to convert biomass into value-added products offer significant potential through a broad range of electrochemical reactions. However, scaling these processes is challenging because reactions occur solely at the electrode surface, requiring advanced reactor designs for efficient mass transport. Additionally, variability in renewable energy generation demands greater process flexibility. Liquid multi-phase systems emerge as a promising solution for enhancing efficiency and adaptability in large-scale electrochemical applications. Optimizing fluid composition alongside electrode and reactor design is essential to address these issues. Here, I investigate two multi-phase systems: liquid-solid suspensions (particle electrodes or flow electrodes) and liquid-liquid emulsions (biphasic electrolytes). This work aims to understand the mechanisms of charge transport and electrochemical reactions in dynamic multi-phase systems and to use these insights to show the applicability of multi-phase systems for the electrochemical synthesis of FDCA (2,5-furandicarboxylic acid) from the biomass-derived compound HMF (5-hydroxymethylfurfural) approach the fundamental, mechanistic questions on microscopic scale by optical means; these include microscopic highspeed recording of particle movements, fluorescence-based analysis of reaction products and ultrasonic imaging. Moreover, I use an electrochemical flow cell to electrochemically synthesize \ac{fdca} with suspensions and emulsions. The small scale investigations reveal that particle clusters in contact with the electrode can effectively conduct electrical charge in suspensions. Furthermore, I show that the conducted charge in these clusters can trigger electrochemical reactions, thereby extending the active reaction area from the electrode surface into the bulk electrolyte solution. On a larger scale, synthesizing FDCA shows significant advantages from both suspensions and emulsions. By suspending catalyst-coated particles in the electrolyte, I can decouple the catalytic oxidation of HMF to FDCA from the electrical charging of the catalyst, resulting in a highly flexible process. Emulsions further enhance efficiency by minimizing reactant loss and eliminating the need for prior purification of HMF, thus it can be directly utilized in electrochemical synthesis. In conclusion, multi-phase systems present substantial potential for efficient and flexible FDCA production within an electrified chemical industry.