In-Depth Investigation of the Reaction Parameters Tuning the Ethyl Levulinate Synthesis from Fructose and Inulin

Alkyl levulinates (ALs) are strategic compounds for the development of sustainable energy transition. In this regard, the direct alcoholysis of fructose and inulin for the selective ethyl levulinate (EL) production was investigated with a One-Factor-At-a-Time (OFAT) approach employing diluted H2SO4 as catalyst to clarify the role of the main reaction parameters (substrate and acid loadings, temperature, reaction time). The OFAT investigation on fructose ethanolysis allowed to reach the EL yield of 91.5 mol%. The inulin ethanolysis was then optimized adopting the multivariate approach based on the Response Surface Methodology (RSM), which highlighted the interplay of the reaction parameters on the selective EL production. This allowed to identify the optimal conditions to reach the highest EL yield (up to 89.3 mol%) and also those which ensured the highest EL concentration, adopting a substrate loading (14 wt%) higher than the majority ones reported in the literature according to the high gravity approach, and the lowest diethyl ether (DEE) by-product yield. The DEE formation is scarcely investigated in the literature, but it can negatively influence the alcoholysis process, thus it was considered in this work. Moreover, the humin solid residue was deeply characterized to envisage its possible applications, under a circular economy perspective.