Hetero‐Coupling of Bio‐Based Medium‐Chain Carboxylic Acids by Kolbe Electrolysis Enables High Fuel Yield and Efficiency
Katharina Neubert, Max Hell, Micjel Chávez Morejón, Falk Harnisch
Abstract
Abstract 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.