Efficient Conversion of Cellulose to 5-Hydroxymethylfurfural via Coupled Dissolution–Decrystallization and Biphasic Catalytic Conversion

Abstract Effective conversion of cellulose into 5-hydroxymethylfurfural (5-HMF) remains challenging because of the recalcitrant crystalline structure of cellulose and the need for coordinated hydrolysis, isomerization, and dehydration reactions. Herein, a high-efficiency synergistic catalytic strategy integrating a LiBr·3H2O/organic solvent biphasic system and CBN@DZSM-5 solid acid was synthesized to convert microcrystalline cellulose (MCC) into 5-HMF. The process first involves the dissolution and decrystallization of MCC in LiBr·3H2O, followed by catalytic conversion with the addition of an organic phase and the prepared CBN@DZSM-5 solid acid catalyst. LiBr·3H2O effectively disrupted the hydrogen-bonding network of MCC, decreasing its crystallinity from 78.4 to 15.1% and improving substrate accessibility. Meanwhile, CBN@DZSM-5 retained the MFI zeolite framework and possessed hierarchical micro/mesoporous channels with enhanced Brønsted and Lewis acidity, enabling efficient cellulose hydrolysis, glucose isomerization, and fructose dehydration. Under optimized conditions, MCC was converted into 5-HMF with a yield of 64.3% and a cellulose conversion of 95.3% at 170 °C for 30 min. The catalyst exhibited good recyclability over five cycles and could be regenerated by calcination. The catalytic system was also applicable to various carbohydrates and lignocellulosic feedstocks with high 5-HMF yields. Finally, a possible synergistic catalytic pathway, including cellulose dissolution/hydrolysis, glucose isomerization, and fructose dehydration, was proposed.