Continuous synthesis of 5-hydroxymethylfurfural using deep eutectic solvents and its kinetic study in microreactors

•• Continuous synthesis of 5-HMF in microreactors was realized with using DESs.•• Synergistic effects of applied ionic liquids and inorganic salts were revealed.•• CrCl3 in tetraethyl ammonium chloride/ethylene glycol presented high catalytic performance.•• A complete kinetic model for 5-HMF production through glucose dehydration was established. A novel route to decompose glucose to 5-hydroxymethylfurfural (5-HMF) in microreactors with the use of deep eutectic solvents (DESs) was reported. For the catalytic mechanism, synergistic effects between quaternary ammonium ionic liquids (i.e., a component of DESs) and inorganic salts on the dehydration of glucose to 5-HMF were revealed. Under the optimal reaction conditions, CrCl3 with the tetraethyl ammonium chloride based DES was found to present the highest catalytic activity and the yield of 5-HMF reached 42% at 150 °C with only 3.64 min, which was more efficient compared with the conventional batch processing with the same or other catalytic systems. Moreover, the recycling of the CrCl3-[N2222]Cl/EG catalytic system was proven to be quite effective. Finally, a complete kinetic model was established in order to distinguish key parameters of the isomerization and its following step for the 5-HMF formation, and its predicted concentrations of glucose and 5-HMF agreed well with the experimental results. This work indicates great application potential of DESs with the combination of microreactor technology for the continuous catalytic transformation of biomass for the production of platform chemicals.