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

Abstract

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 (C6-C16) 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 NbOPO4, Al2O3, SiO2, and ZrO2-SiO2 to promote aldol condensation were tested at 160 °C for 3 h. The NbOPO4 exhibited the highest selectivity towards C-C coupling adducts with mainly C12 to C18. In the second stage, 30 wt% Ni catalysts on three different supports and 5 wt% Pd/Al2O3 were used to catalyse the hydrogenation of the first-stage adducts at 300 °C for 3 h. The 30 wt%Ni/NbOPO4 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/NbOPO4 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.