Display omitted •LiBr hydrate/acetone system is efficient for converting crystalline cellulose (MCC) to 5-hydroxymethylfurfural (5-HMF).•75.1% yield of 5-HMF together with 13.7% yield of glucose were obtained from MCC conversion with the addition of AlCl3.•DFT calculations indicated glucose isomerization rather than crystalline cellulose hydrolysis is the rate-determining step in cellulose conversion into 5-HMF.•Produced 5-HMF can be efficiently recovered by hyper-cross-linked polymer adsorption.•reaction system can be recycled 5 times without reducing 5-HMF selectivity. 5-hydroxymethylfurfural (5-HMF) is a crucial biomss-derived fuel precursor with versatile conversion pathways to advanced fuels. However, direct production of 5-HMF from crystalline cellulose is critical challenging due to the inefficient deconstruction of recalcitrant cellulose structure. Molten salt hydrates (MSHs) are unique in cellulose deconstruction and dissolution. In this work, a biphasic system of LiBr hydrate/acetone was established. It was found that 93.4% yield of 5-HMF can be efficiently converted from fructose without any catalysts. With the addition of AlCl3 to adjust Lewis acidity, an enhanced 5-HMF yield of 75.1% together with 13.7% of glucose were directly produced from cellulose, showing a promising carbon balance of 88.8%. A proposed mechanism for cellulose conversion was studied by density functional theory (DFT) calculations, demonstrating that the isomerization of glucose to fructose rather than crystalline cellulose hydrolysis was the rate-determining step. After reaction, the formed 5-HMF can be efficiently recycled from solvent via hyper-cross-linked polymer adsorption and the reaction system can be recycled for more than 5 times without reducing 5-HMF selectivity.