Optimization of the production of bio-jet fuel precursors from acetoin and 2-methylfuran via hydroxyalkylation/alkylation over sulfonic acid resin

Increasing carbon dioxide gas emissions in the aviation industry, together with the depletion of fossil fuel sources, are serious issues that require researchers to develop bio-jet fuel from sustainable renewable sources. A promising approach is the use of highly abundant and economic lignocellulosic waste biomass, from which furanic compounds can be derived. However, to obtain C₉-C₁₅ jet fuel-compatible products, C-C coupling strategies are mandatory to increase the chain length of the furanic platforms. Furthermore, there exists an uncovered potential for integrating fermentation-derived platforms, like acetoin, in advanced bio-jet fuel production routes. In this sense, this work explores the C-C coupling of acetoin, a fermentation-derived molecule, with 2-methylfuran (2-MF), a lignocellulose-derived molecule that can be obtained from selective hydrogenolysis of furfural, via hydroxyalkylation/alkylation (HAA). This solvent-free acid-catalyzed reaction yields oxygenated adducts incorporating one molecule of acetoin and 1-3 molecules of 2-MF (9–19 C atoms) that display high potential as bio-jet fuel precursors. However, side reactions are also present, coming from the auto-condensation of acetoin and/or 2-MF, yielding heavier or more oxygenated undesired compounds, so that selectivity appears as the key parameter in the catalyst performance. In this work, sulfonic acid-based resin Amberlyst-15 has displayed high activity and selectivity towards the most interesting di-condensed C₁₄ compound, herein denoted as Ac(MF)₂, which evidences the benefits of applying strong Brønsted acid sites allocated within a polymer matrix in high surface concentration. The optimization of the reaction conditions, assessed with the help of response surface methodology, led to over 77 % yield to Ac(MF)₂ with acetoin conversion around 90 %, under the optimized reaction conditions (60 °C, 2-MF/acetoin = 2.5 (mol), 6 h, catalysts loading 20 wt% referred to acetoin). Amberlyst-15 catalyst was tested in a 5-cycle reusability experiment, keeping an acceptable level of catalytic activity and selectivity despite evidence of fouling due to the formation of organic deposits. These results pave the way for a new route of bio-jet fuel production starting from already established biomass-derived platform molecules.