Closing the Gap: Towards a Fully Continuous and Self-Regulated Kolbe Electrosynthesis

In this article, we address the transition of the Kolbe electrolysis of valeric acid (VA) to n-octane as an exemplary electrosynthesis process from a batch reaction to a continuous, self-regulated process. Based on a systematic assessment of chemical boundary conditions and sustainability aspects, we propose a continuous electrosynthesis including a simple product separation and electrolyte recirculation, as well as an online-pH-controlled VA feeding. We demonstrate how essential performance parameters such as product selectivity (S) and coulombic efficiency (CE) are significantly improved by the transition from batch to a continuous process. Thus, the continuous and pH-controlled electrolysis of a 1 M valeric acid, starting pH 6.0, allowed a constantly high selectivity of around 47 % and an average Coulomb efficiency about 52 % throughout the entire experimental duration. Under otherwise identical conditions, the conventional batch operation suffered from lower and strongly decreasing performance values (S_{n-octane, 60min} =10.4 %, S_{n-octane, 240min} =1.3 %; CE_{n-octane, 60min} =7.1 %, CE_{n-octane, 240min} =0.5 %). At the same time, electrolyte recirculation significantly reduces wastes and limits the use of electrolyte components.