Synthesis of high-density biofuel with excellent low-temperature properties from lignocellulose-derived feedstock

Converting chemicals that can be derived from lignocellulose to cyclic hydrocarbons is a promising route for the synthesis of high-density biofuels. But the low-temperature properties of most synthesized fuels are not good, with high viscosity and freezing point. Herein, we presented the synthesis of cyclohexane derivatives by the alkylation of aromatic oxygenates (anisole, guaiacol and phenol) with furfural alcohol (furfuryl alcohol and 5-hydroxymethylfurfural), followed with hydrodeoxygenation. It is found that FeCl₃ exhibits relatively high activity and selectivity for the alkylation of anisole (guaiacol), and AlCl₃ is the best catalyst for phenol. The selectivity of mono-alkylation product is 71.0%, 92.4% and 84.3% for the alkylation of anisole, guaiacol and phenol with furfuryl alcohol when the reactant ratio is 10, respectively. A semi-continuous operation was adopted for the alkylation of furfuryl alcohol to improve the conversion of aromatic oxygenates. When furfuryl alcohol is replaced by 5-hydroxymethylfurfural, the selectivity reaches almost 100%, but the reaction is a little slower and longer time is needed to get full conversion. After hydrodeoxygenation by combination of Pd/C and HZSM-5, the alkylation product was converted to branched cyclohexane with density of 0.804 g/cm³ at 20 °C, kinematic viscosity of 34.4 mm²/s at − 60 °C and freezing point lower than − 80 °C, which shows great potential as additive to promote the low-temperature properties of other fuels.