A team from Helmholtz-Centre for Environmental Research – UFZ (Leipzig, Germany) has shown the scale-up of the production of aviation drop-in fuel-like mixtures (mainly n-decane) that are obtained by Kolbe electrolysis of medium-chain carboxylic acids (n-hexanoic acid), which can be derived from biomass. A paper on their work appears in the journal Fuel.

For mobility, especially in aviation, cargo weight and volume of the energy vector are substantially more limited than in any other form of transportation. Therefore, energy vectors with high mass and volume specific energy density are needed, for which carbon-based liquid fuels are unmatched. Concurrently, there is an imperative of deriving these fuels from non-fossil sources.

… by descending order of technology readiness level (TRL), the following types of fuels incl. drop-in fuels and additives are approved for usage in international aviation: synthetic paraffinic kerosene, hydroprocessed esters and fatty acids, alcohol-to-jet synthetic paraffinic kerosene, hydroprocessed fermented sugar synthesized iso-paraffins, Fischer-Tropsch synthetic paraffinic kerosene, pyrolysis oils and others. Recently, we have shown that complex waste biomass can be converted to fuel-like mixtures using a combined microbial and electrochemical conversion process.

… The Kolbe electrolysis enables the electrochemical upgrading of MCCA [medium chain carboxylic acids] to a mixture of hydrocarbons, primarily alkanes … using the example of n-hexanoic acid (C₆) that was also used in this study.

… Here we demonstrate process feasibility in a commercially available single stack electrolysis cell, making future application of the Kolbe electrolysis possible as no further transfer from a tailor-made electrochemical cell to a commercially available one that can be numbered up is necessary.

—Rosa et al.

For their study, the researchers increased the scale to 1 L volume and 100 cm² electrode surface area within a single stack electrolysis cell allowing straightforward numbering-up. The obtained electrolysis performance was “unprecedented” at technical scale, the authors said, with a maximum n-decane production rate of 0.73 g L⁻¹h⁻¹ cm⁻², a selectivity for n-decane between 76.3% and 97.8% and Coulombic efficiencies up to 68%.

Resources

• Luis F.M. Rosa, Katharina Röhring, Falk Harnisch (2023) “Electrolysis of medium chain carboxylic acids to aviation fuel at technical scale,” Fuel, Volume 356 doi: 10.1016/j.fuel.2023.129590.