Reaction Pathway Analysis of Ethyl Levulinate and 5‑Ethoxymethylfurfural from d‑Fructose Acid Hydrolysis in Ethanol

This study uses numerical modeling to provide a mechanistic discussion of the synthesis of the advanced biofuel candidates, ethyl levulinate and 5-ethoxymethylfurfural, from α/β-d-fructopyranose (d-fructose) in a condensed phase homogeneous ethanol system at 351 K catalyzed by hydrogen cations. A mechanistic comprehension is pursued by detailed measurements of reactant, intermediate, and product species temporal evolutions, as a function of H2SO4 (0.09, 0.22, and 0.32 mol/L) and d-fructose (0.14, 0.29, and 0.43 mol/L) concentrations, also considering the addition of water to the ethanol media (0, 12, and 24 mass % of water in ethanol). d-Fructose, 5-hydroxymethylfurfural, 5-ethoxymethylfurfural, ethyl levulinate, and several other intermediate species are quantified as major species fractions at 45–85% of the initial d-fructose mass. To inform the mechanistic discussion, mass-conserved chemically authentic kinetic models and empirical rate constants are derived, each assuming a first-order relationship to the hydrogen cation concentration. The optimal synthesized fractions of ethyl levulinate and 5-ethoxymethylfurfural considered as fuel components achieve a mass yield of 63% with respect to the fructose mass and a volumetric energy valorization (ΔH combustion, kcal/mL) of 215% with respect to the ethanol consumed, indicating the viability of the synthesis.