Efficient synthesis of high-density aviation biofuel via solvent-free aldol condensation of cyclic ketones and furanic aldehydes

Transferring lignocellulose-derived compounds to cyclic hydrocarbons via aldol condensation has great potential in synthesizing high-density biofuel. But current synthesis involves large amount of solvent that inevitably affects the production efficiency. Herein, we synthesized high-density biofuel efficiently using solvent-free condensation of cyclopentanone/cyclohexanone and furfural/5-hydroxymethylfurfural. It is found that the solvent-free reaction gives much higher conversion than the diluted one does, for example 86.7% vs 62.7% for cyclopentanone/furfural condensation, and the selectivity of condensed product is above 90.0%. The reaction rate slows down when the reactant is changed from cyclohexanone to cyclopentanone or from furfural to 5-hydroxymethylfurfural, but can be improved by simply increases the dosage of catalyst or reaction temperature. As a result, the yield over 85.0% is obtained for the condensation reactions. Subsequently, the condensed products were converted to branched cyclic hydrocarbons with selectivity of about 70–80%. Their density increases from 0.815g/ml to 0.826g/ml with the increase of carbon number, with the freezing point increasing from −24.6°C to −9.5°C. They have very low viscosity and can be used as liquid fuels alone or blended with other fuels. [Display omitted] •Aldol condensation of cyclic ketones and furanic aldehydes takes place easily.•Solvent-free reaction gives higher activity than diluted reaction.•Yield above 85% was achieved under moderate conditions.•Biofuels have density of 0.81–0.82g/ml.