Aqueous Phase Conversion of Hexoses into 5-Hydroxymethylfurfural and Levulinic Acid in the Presence of Hydrochloric Acid: Mechanism and Kinetics

The kinetics of the acid-catalyzed dehydration of two common monosaccharides (glucose and fructose) to 5-hydroxymethyl-furfural (HMF) and levulinic acid is studied in this work. Reaction studies were performed in a stirred batch reactor using aqueous sugar solutions (150 g/L). The influence of reaction temperature (363–403 K) and catalyst concentration (0.05–0.25 mol/L) was also studied. The formation of the main products, as well as other minor products such as humins (in both cases) or glucose dimers and anhydroglucose (in glucose processing), is modeled considering a serial-parallel scheme reaction. The proposed model allows predicting the formation of both main and side products. Obtained results suggest that it is possible to work at total conversions of both monosaccharides, and to tune the selectivity to HMF-LA by changing the operation temperature and/or catalyst concentration. As a general trend, higher selectivities are obtained (to HMF or to LA, depending on reaction conditions) when fructose is used as a reactant. By contrast, glucose dehydration leads to a larger amount of side products such as anhydroglucose and glucose oligomers.