(Non-)Kolbe Chemistry Going with the Flow: The Continuous Electrolysis of Biogenic Acids

Abstract

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 β-hydroxy-acid is selectively converted to a drop-in oxygenate fuel, increasing the hourly production compared to the batch process by five times.

3D Printed Reactionware for Synthetic Electrochemistry with Hydrogen Fluoride Reagents

“…3D printing, or additive manufacturing, is a rapidly maturing technology that has progressed from an engineering curiosity to become a viable, cost-effective manufacturing or prototyping technique with applications in several fields of research, [42][43][44][45][46][47] including chemical synthesis, [48][49][50][51][52][53][54][55][56] analytics, [57][58][59][60][61] and, albeit to a lesser extent, synthetic electrochemistry. [49,[62][63][64][65][66][67] As the object is built up layer by layer in a computer-controlled process, high resolution objects can be rapidly manufactured without the operator having to be familiar with the range of machining instruments and techniques normally employed. In combination with Computer Aided Design (CAD), unusual or unconventional shapes and structures can be created, including internal structures that are not easily produced by other manufacturing approaches.…”

Overcoming the Limitations of Kolbe Coupling via Waveform-Controlled Electrosynthesis

“…15 The practical conditions and broad reaction generality achieved by rAP-Kolbe reaction can finally address this longstanding challenge even on scale. Figure 2A exemplifies the realization by enlisting biomass-derived acids 1 and 30 to produce 1,19eicosadiene 4 and 2,7-octadione 12 48,49 on 200 and 300 mmol scale, respectively. No precaution to air and moisture was necessary when performing large-scale reactions.…”

Electroreforming of Biomass for Value-Added Products

“…These developments shift reliance away from expensive noble metals, potentially increasing the economic viability of electroreforming techniques. Studies of flow reactor cells [54,67,98,108], showcased the possible continual production they provide, and therefore their industrial scalability. Notably, a great advantage of the electrochemical route is the cogeneration of green hydrogen, which plays an indispensable role in decarbonization.…”

“…To support the development of electroreforming on a larger scale, Kurig et al studied the production of 2,7-octanedione from levulinic acid in a continuous flow single pass reactor [108]. Their setup involved Pt electrodes in 1 M levulinic acid and 0.1 M KOH as the supporting electrolyte.…”