Efficient conversion of cellulose into furans catalyzed by metal ions in ionic liquids

Abstract

5-Hydroxymethylfurfural (HMF) and furfural, two of the most important intermediates derived from biomass, were directly produced from the hydrolysis of microcrystalline cellulose (MCC) with metal ions in ionic liquids as catalyst under mild conditions. Various ionic liquids were tested to obtain the most efficient catalyst, 1-(4-sulfonic acid) butyl-3-methylimidazolium hydrogen sulfate (IL-1) showed the highest catalytic activity than others, and SO3H-functionalized ionic liquids exhibited better activity than non-functionalized ILs. The co-catalysis effect of Cr3+, Mn2+, Fe3+, Fe2+, Co2+ were much better than other metal ions, with a catalytic amount of these metal ions, MCC conversion increased by 10–19%, and the selectivities of products were also improved obviously. The promoting catalysis of metal nitrates were not as expected as that of chlorides and sulfates, we suggested that nitrate anion may have a negative effect on the hydrolysis of MCC. Reaction conditions were optimized and reaction mechanism was proposed to explain the improved catalysis of metal chlorides and sulfates. Also, the recycling of catalyst was put forward in our system for MCC hydrolysis and these catalysts maintained good performances even after five runs. This simple and effective catalytic system may be valuable to facilitate energy-efficient conversion of cellulose into biofuels and platform chemicals.