Greener hydrocarbons: maximizing efficiency in the electro-catalytic upgrading of n-caproic acid to renewable fuels

Abstract

The industrial-scale microbial conversion of waste carbon into medium-chain carboxylic acids (MCCAs) has become feasible, and their subsequent utilization for hydrocarbon production via the Kolbe reaction as a bioenergy source represents a highly promising route. However, controlling the concentrations of MCCAs, pH, and electrode potential during the coupling of these reactions to ensure efficient elongation and improve Kolbe reaction efficiency is crucial for reducing bioenergy production costs. Our study demonstrated that the Kolbe electrolysis of n-caproic acid exhibits a concentration threshold of 800 mM; beyond this concentration, the Faraday efficiency stabilizes, reaching a peak of 51.2%. The Kolbe electrolysis at higher substrate concentration could reduce the energy consumption required to produce the same amount of biofuel by approximately 87%. Both acidic and neutral conditions effectively promote the Kolbe reaction. In terms of electrode potential regulation, a voltage of 3.5 V generally yields better electrolysis results.