The search for alternative technologies to generate and store energy, together with the need to close carbon cycles, is providing a renaissance for organic electrochemistry. This work addresses the advancement of promising methods in the context of an electrified biorefinery.As a long-term goal of most industrial chemical processes, continuous reactions are also of great interest for electrification. Therefore, general concepts for Kolbe and non-Kolbe electrolysis in flow cells were investigated using model systems. It was found that Kolbe electrolysis is particularly suitable for semi-continuous conversions due to concentrated substrate solutions. Using the dimerization of levulinic acid as an example, previous literature results were exceeded with a yield of 75%. In non-Kolbe electrolysis, various reactor designs were realized using conventional fabrication methods as well as 3D printing. The synthesis of a promising drop-in fuel mixture was then tested in the continuous flow cell, achieving a space-time-yield seven times higher than the optimized batch reaction. Lastly, 3D printing was shown to make microreactors accessible for non- Kolbe electrolysis. To make electrochemical reactions even more efficient, different reduction reactions of levulinic acid were investigated that could be coupled to Kolbe electrolysis. Direct hydrogenation, already discussed in the literature, was used here to demonstrate the suitability of screen-printed electrodes for subsequent in situ spectroscopic studies. A novel reductive valorization was demonstrated by nitrogen incorporation and cyclization to 1,5-dimethylpyrrolidone in yields up to 78%.In another study of coupling anodic and cathodic conversions, the glucose dimer cellobiose was converted to the fine chemicals cellobitol and cellobionic acid. The electrochemical synthesis of cellobitol was not demonstrated before. While the oxidation reaction had already been studied by cyclic voltammetry and the synthesis of cellobionic acid had been reported, yields of 94% were achieved for the first time by using a redox mediator. In the last part of the work, spectroelectrochemical methods were established to study the adsorption of the organic substrates on electrode surfaces and ultimately to advance the understanding of the reaction mechanisms. Using in situ ATR-SEIRAS, the competition of Kolbe electrolysis and OER was compared in aqueous and methanolic solutions. Competitive adsorption was also observed for the reductive conversions of levulinic acid, simultaneously confirming that the reactions occur within the Helmholtz layer. In addition, an in situ Raman measurement cell was developed in which low-cost screen-printed electrodes can be used for screening studies.

Dissertation, RWTH Aachen University, 2023; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2023). doi:10.18154/RWTH-2023-04090 = Dissertation, RWTH Aachen University, 2023

Published by RWTH Aachen University, Aachen