Hydrolysis of levoglucosan to 5-hydroxymethylfurfural in a biphasic system

Levoglucosan (LGA), as the main primary anhydrosugar of cellulose pyrolysis, is of great significance for future value-added chemicals production. In this study, effective conversion of LGA to 5-hydroxymethylfurfural (HMF) was investigated in a NaCl–H2O/acetone biphasic system over sulfonated resin and AlCl3. The results show that the biphasic system could efficiently inhibit the overreaction of HMF compared with pure water, leading to a significant enhancement of HMF production. HMF was obtained with the highest yield of 68.5 % at 96.5 % of LGA conversion at the optimized conditions. The use of cellobiose as substrate produced 61 % of HMF while LGA-rich bio-oil led to a sharp decease of HMF yield to 33 %. Through the respective experiments using LGA, glucose and fructose as the substrates, the reaction network was constructed for kinetic analysis, and satisfactory fitting results are observed in agreement with the experimental results, providing the best conditions for producing glucose and HMF, respectively. In addition, the mechanism of LGA conversion to HMF was calculated by DFT, which needs to overcome the highest free energy barrier of 121 kJ/mol.