Conversion of Glucose to 5-Hydroxymethylfurfural by Co-catalysis of p-Toluenesulfonic Acid (pTSA) and Chlorides: A Comparison Based on Kinetic Modeling

Hydroxymethylfurfural (HMF) has been considered as one of the most promising biomass derived precursors for producing bio-based materials. Lewis acids are usually used to facilitate the isomerization of glucose to fructose in order to improve the HMF yield. In this study, glucose was converted to HMF with p-toluenesulfonic acid (pTSA) and chlorides as Bronsted and Lewis acids catalysts in the DMSO medium at 120 °C under atmospheric pressure. Kinetic modeling of the process was investigated with consideration of glucose isomerization, dehydration of fructose, rehydration of HMF and formation of humin. NH4Cl was screened as the most efficient co-catalyst for glucose conversion with HMF yield of 47%. The developed model could be well used to simulate the process with satisfying goodness of fit. The activation energies for glucose isomerization, condensation, dehydration of fructose, and rehydration of HMF were determined to be 39.8, 18.1, 55.2, and 19.0 kJ/mol, respectively. However, because the fructose concentration was very low and the reaction rate of fructose dehydration was much higher than that of glucose isomerization, a pseudo-steady state assumption could be employed, by which the observed activation energy for a lumped reaction of glucose to HMF conversion (EHMF) was determined as 45.6 kJ/mol. The developed observed kinetic model could be well used to describe the kinetics of pTSA and chloride co-catalyzed conversion of HMF. Isomerization of glucose to fructose, condensation of glucose to form humin, dehydration of fructose to form HMF, and rehydration of HMF to LA were the major reactions in the system. To improve the HMF selectivity, efforts should be made to reduce the rate of glucose condensation to form humin