(Non-)Kolbe Chemistry Going With The Flow: The Continuous Electrolysis Of Biogenic Acids

Aiming at a circular carbon economy, electrosynthesis is gaining in importance. The conversion of bioderived materials using green electrons from renewable energy sources tackles challenges like fluctuating energy production and the integration into the already existing supply networks. Herein, we discuss concepts for transforming 150-year old Kolbe chemistry into flow processes. In a recirculation setup, levulinic acid is converted to the Kolbe product 2,7-octanedione with up to 75% yield. Single-pass setups allow for continuous production, for which conversion scales linearly with contact time. It was found that non-Kolbe electrolysis is even better suited toward continuous production because of the possibility to use lower substrate concentrations. We present an example of an n-alkyl acid converted using different flow cells including a 3D printed vessel for a semibatch non-Kolbe reaction. The electrochemically more challenging beta-hydroxy-acid is selectively converted to a drop-in oxygenate fuel, increasing the hourly production compared to the batch process by five times.