We currently face the consequences of human-induced climate change. To reduce greenhouse gas emissions, our society has to transition from the use of fossil resources to sustainable ones. Industrial processes are often driven by thermal energy that is obtained by burning fossil fuels. However, sustainable energy is mainly generated in the form of renewable electricity. Instead of converting renewable electricity into thermal energy, it can be used directly as the driving force for the industrial process. The direct use of electricity requires changes within industry, especially in the chemical industry. One approach to more sustainable industrial syntheses are their electrification. For example, the platform chemical formaldehyde is industrially synthesized at high temperatures. Formaldehyde can also be obtained electrochemically from aqueous methanol at low temperatures. Yet, the efficiency of the electrochemical formaldehyde formation suffers from complete methanol oxidation and other side reactions that are enabled by water activation. Water activation can be avoided by using anhydrous electrolyte solutions. Only a few studies using anhydrous methanol for the electrochemical formaldehyde synthesis have been reported. These experiments were performed at laboratory scale; most lack complete experimental documentation; and used, by today’s standards, invalid reference electrodes. In this work, the electrochemical oxidation of anhydrous methanol to formaldehyde is investigated with respect to its scalability and industrial application. A suitable and reliable reference electrode was developed to enable accurate potential control under anhydrous reaction conditions. Several electrode materials were investigated in a batch cell for their activity and selectivity in the conversion of anhydrous methanol to formaldehyde. The reaction was transferred to an electrochemical flow cell to investigate its performance depending on the flow cell parameters (anode size and support, flow rate, electrode gap, and temperature) and at elevated current densities. Previously identified active electrode materials were tested under these conditions for their stability. Only platinum was stable at high current densities and reached Faraday efficiencies of up to 90%. All parameters have a significant influence on the reaction performance. In particular, the electrode gap has the largest influence on the energy requirements, which are limited by the electrolyte conductivity. A more in-depth analysis of the physical and chemical electrolyte properties allows a correlation between the electrolyte and effect on the reaction. The formaldehyde synthesis occurs via different reaction mechanisms depending on the electrolyte composition. Because of the reaction’s stable performance at elevated current densities, it has the potential to be applied industrially. Further understanding of the influences of the electrolyte composition on the reaction mechanism is required to optimize the reactor design for further scale-up.
Florian Schwarz (Wed,) studied this question.