Energy-dense sustainable aviation fuel-range hydrocarbons from cyclohexanone as a biomass-derived feedstock via sequential catalytic aldol condensation and hydrodeoxygenation

Abstract

• Biomass-derivable cyclohexanone as a feedstock for high-density aviation fuel. • NbOPO 4 catalyst exhibited excellent activity for aldol condensation and alkylation. • Ni/NbOPO 4 catalyst exhibited superior hydrogenation of adducts than Pd/Al 2 O 3. • Similar results from one-pot and two-pot aldol-condensation followed hydrogenation. • Liquid compositions linked to types of coke/char deposits observed on catalyst. Climate change is the main driver for sustainable aviation fuels production as a means of decarbonising/defossilising the sector. In this work, several catalysts have been screened to produce aviation fuel (C 6 -C 16 ) component hydrocarbons from cyclohexanone, a model compound of lignin-derived bio-oils. Using a two-stage two-pot approach, up to 99 % cyclohexanone conversion was achieved in the presence of hydrogen gas. In the first stage, catalytic activities of NbOPO 4 , Al 2 O 3 , SiO 2 , and ZrO 2 -SiO 2 to promote aldol condensation were tested at 160 °C for 3 h. The NbOPO 4 exhibited the highest selectivity towards C-C coupling adducts with mainly C 12 to C 18 . In the second stage, 30 wt% Ni catalysts on three different supports and 5 wt% Pd/Al 2 O 3 were used to catalyse the hydrogenation of the first-stage adducts at 300 °C for 3 h. The 30 wt%Ni/NbOPO 4 was most effective, promoting the formation of bi-cycloalkanes, alkyl aromatic, and partially hydrogenated polyaromatic hydrocarbons. In comparison, a one-pot two-step approach was tested by sequentially reacting cyclohexanone with hydrogen gas over the two temperatures for 3 h each, using 30 wt%Ni/NbOPO 4 as catalyst. Reacting cyclohexanone with 10 wt% bio-oil samples led to significantly reduced first stage conversion, and enhanced yields of single C-C coupled oxygenates and almost no hydrocarbons in the second stage. Overall, combination of catalysts and hydrogen gas over staged reactions has effectively converted pure cyclohexanone into naphthene-rich liquid hydrocarbons and cyclohexanone/bio-oil mixed feedstocks into their oxygenated precursors. These results support potential targeted production of bio-derived sustainable alternative fuels for the defossilisation of aviation industry

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