Deep eutectic solvent assists H-β in aldol condensation of acetovanillone and p-hydroxybenzaldehyde to prepare a high density aviation oil precursor

Abstract

An efficient deep eutectic solvent (DES) catalytic system was developed for the aldol condensation of lignin derivatives acetovanillone (AV) with p-hydroxybenzaldehyde (PHB) to prepare C16 high energy fuel precursors to solve the problems of low coverage of lignin materials, low catalyst selectivity, and compatibility with solvents. With the optimized reaction conditions of a substrate molar ratio of 1:2, 5 g ChCl/Fa (1:6), 15 wt% H-β, and 100 ℃ for 120 min, the conversion rate of AV reached 88.68%, while the selectivity and yield of C16 reached 78.5% and 69.61%, respectively. The stability of H-β in DES was found to be better than that in conventional solvents based on SEM, TEM, XRD, and TG analysis. Moreover, NH3-TPD proved that DES could effectively increase the strong acid strength of H-β, thereby enhancing reactivity. Moreover, DES increased the specific surface area of the H-β catalyst from 109.59 m2/g to 404.118 m2/g and had a significant pore-enlarging effect (from 1.529 nm to 2.157 nm), which accelerated the reaction progress. DES was also found to be less toxic to H-β, enabling it to be regenerated. Furthermore, the shape-selective catalytic mechanism of the DES-assisted H-β system was demonstrated in the feedstock pool constructed by different lignin-derived platform compounds.