High Lewis acidity catalyst for direct depolymerization of microcrystalline cellulose to 5- hydroxymethylfurfural: Reaction optimization by central composite design

Abstract

In direct conversion process of cellulose to 5-hydroxymethylfurfural (5-HMF), undesirable degradation inevitably occurs in the presence of Brønsted acid. Here, a carbonaceous catalyst was synthesized by grafting phosphotungstic acid to directly depolymerize microcrystalline cellulose (MCC) to 5-HMF. This catalyst exhibits high Lewis acidity (43.10 μmol g⁻1) and low Brønsted acidity (4.15 μmol g⁻1) with pyridine as reference compound. To comprehensively analyze the factors affecting MCC depolymerization, central composite design and response surface methodology techniques, incorporating variables such as reaction time, reaction temperature, catalyst dosage and MCC dosage. The highest yield of 5-HMF, 5.88 %, was obtained after 4.90 h at 171 °C using 45 mg of catalyst and 50 mg of MCC in biphasic system consisting of 1-butyl-3-methylimidazole chloride ([BMIM]Cl) and 2-sec-butylphenol. The catalyst was easily recovered and reused five times without a significant loss of catalytic activity. This work highlights the promise of efficient biomass refining by synergizing catalysts with high Lewis acidity and low Brønsted acidity in the biphasic system.