Theoretical and experimental study of 5-ethoxymethylfurfural and ethyl levulinate production from cellulose

Theoretical simulations and experiments were taken to explore the mechanism of cellulose conversion into 5-ethoxymethylfurfural (EMF) and ethyl levulinate (EL) catalyzed by a mixed acid of Lewis acid and Bronsted acid. Up to 64.8 % total yield of EMF and EL can be obtained when the ratios of Lewis/Bronsted acid and water/ ethanol (v/v) were 1:2 and 3:7 respectively. The results showed that Lewis acid and water could reduce the activation energy of EMF formation from 75.6 to 47.9 kJ mol-1, and mixed acids and water/ethanol system were beneficial to the accumulation of EMF. Moreover, the results of molecular dynamics (MD) simulation indicated that Lewis acid could promote the distribution of Bronsted acid around the beta-1,4 glycosidic bond of cellobiose. The combination of DFT and frontier molecular orbital (FMO) calculation demonstrated that the breakage of the beta-1,4 glycosidic bond was the main rate-limiting step of cellulose hydrolysis. Meanwhile, the mixed acid and water/ethanol system could accelerate the hydrolysis due to the reducing energy barrier and HOMO-LUMO gap. This study gave a deep insight into the mechanism of Lewis acid with Bronsted acid on cellulose conversion into EMF and EL.