Hetero‐Coupling of Bio‐Based Medium‐Chain Carboxylic Acids by Kolbe Electrolysis Enables High Fuel Yield and Efficiency

Mixtures of n‐carboxylic acids (n‐CA) as derived from microbial conversion of waste biomass were converted to bio‐fuel using Kolbe electrolysis. While providing full carbon and electron balances, key parameters like electrolysis time, chain length of n‐CA, and pH were investigated for their influence on reaction efficiency. Electrolysis of n‐hexanoic acid showed the highest coulombic efficiency (CE) of 58.9±16.4 % (n=4) for liquid fuel production among individually tested n‐CA. Duration of the electrolysis was varied within a range of 0.27 to 1.02 faraday equivalents without loss of efficiency. Noteworthy, CE increased to around 70 % by hetero‐coupling when electrolysing n‐CA mixtures regardless of the applied pH. Thus, 1 L of fuel could be produced from 12.4 mol of n‐CA mixture using 5.02 kWh (<1 € L(−1)). Thus, a coupling with microbial processes producing n‐CA mixtures from different organic substrates and waste is more than promising.