Breaking the concentration barrier: Formylation-driven cellulose dissolution and regeneration enables reliable production of 5-hydroxymethylfurfural from high-loading cellulose

Valorization of abundant biomass-derived cellulose into initial platform chemicals (IPCs) generally suffers from low process efficiency due to the difficulty in dissolution of recalcitrant cellulose that owns complex inter‐/intra-molecular hydrogen-bond network in structure. Herein, a coupled strategy of formylation-driven cellulose dissolution and regeneration is successfully established to break the trade-off between process efficiency and concentration barrier for reliable production of 5-hydroxymethylfurfural (HMF), an important IPC, from high-loading cellulose. This strategy initiates from the formylation of microcrystalline cellulose (MCC) in an anhydrous deep eutectic solvent (DES) composed of zinc bromide (ZnBr 2 ) and formic acid (FA), which allows the deconstruction of pristine hydrogen-bond network and re-construction to formylated cellulose (FC) with a maximum formyl substitution of 1.67. The subsequent regeneration of FC from water or ethanol causes the transformation of cellulose from type I to type II with smaller polymerization degree and crystallinity, thereby enabling the improvement of solubility and reactivity of regenerated FC (RFC) in water for the subsequent AlCl 3 -catalyzed conversion to HMF. A distinguished space-time yield of 231.1 g·L −1 ·h −1 with a high HMF yield of 63.9 mol% has been achieved from RFC (25.0  wt % in water phase) in a low-boiling biphasic 1,4-dioxane/NaCl-H 2 O solvent, which is so far the highest process efficiency achieved in cellulose-to-HMF conversion. It exemplifies an advance in high-efficient production of IPCs from renewable cellulose feedstock by breaking the concentration barrier for future biomass refinery.