Cellulose dissolution and conversion into 5-hydroxymethylfurfural in mixed molten salt hydrate

Molten salt hydrate (MSH) is a good solvent for cellulose dissolution and an effective catalyst for cellulose conversion. In this work, a series of MSH was evaluated in terms of cellulose dissolvability, regeneration performance, and catalytic activity in cellulose conversion into 5-hydroxymethylfurfural (HMF). ZnBr₂·3H₂O–LiCl·3H₂O showed good performance on cellulose dissolution and conversion. The effects of ZnBr₂·3H₂O concentration, reaction temperature, and time on cellulose conversion into HMF in ZnBr₂·3H₂O–LiCl·3H₂O were optimized, and 48.7% HMF yield was reached at 60 wt.% ZnBr₂·3H₂O. The species of ZnBr₂·3H₂O–LiCl·3H₂O were analyzed, and the function of species concentration was correlated with the product yield from the conversion of fructose. It was found that Br⁻ and H⁺ were the active species for fructose dehydration into HMF. ZnBr₃⁻ and H⁺ catalyzed the conversion of fructose into furfural, which competed with the production of HMF. The reaction mechanism was proposed to understand the cooperate of species in MSH for cellulose conversion.