Greener aromatic antioxidants for aviation and beyond†
Antioxidants (AO) inhibiting unspecific oxygen reactions are added to most susceptible industrial products, including liquid hydrocarbon-based aviation fuels. Regulatory approved jet fuel, whether synthetic or crude oil-based, requires the addition of performance antioxidants to inhibit radical-induced oxidation during storage and transport. While presently used antioxidants are petroleum-based, there have been no sustainable, less-toxic, bio-based equivalents reported so far. This study addresses the initial evaluation of carotenoid-based antioxidants as a substitution for current alkyl-phenolic antioxidants to kerosene. Inspired from natural products of Brevibacterium and Synechococcus genus synthesized analogues of candidate aromatic carotenoid cleavage products were evaluated for their effects on combustion characteristics of jet fuel, comparative radical scavenging, and endothelial cell-culture cytotoxicity. These bioinspired antioxidants show no adverse effect on jet fuel bulk properties and combustion chemistry. The radical scavenging properties of the evaluated phenolic compounds are superior to non-aromatic β-carotene cleavage products and in range with current alkyl-phenolic additives. Cytological assays demonstrated low toxicity towards human endothelial cells similar to butylated hydroxytoluene (BHT), one of the approved alkyl-phenol based additives to jet fuel, food, and cosmetics. The initial data set suggests, that the evaluated bioinspired compounds do not interfere with normal operations of jet engines and human fuel handling. Further developments towards the sustainable, biotechnological production and application of aromatic carotenoid cleavage products as antioxidants could contribute to reduced non-renewable consumption and possibly being an environmentally more compatible alternative due to their biosynthetic origin.