High yield aldose–ketose transformation for isolation and facile conversion of biomass sugar to furan

Traditional approaches to producing furfural from C5 biomass sugars have several limitations which include high reaction temperatures/pressures, significant sugar loss to side-reactions, modest furfural yields, and high purification costs. We present a novel method for converting the C5 sugar xylose to furfural at facile conditions in very high yield. In this approach, we isomerize xylose to its ketose isomer in high yield via a simultaneous-isomerization-and-reactive-extraction (SIRE) scheme, concentrate and purify xylulose by back-extraction (BE) into an acid medium, and then rapidly dehydrate the xylulose sugar to furfural at relatively low temperature (∼110 °C) with no additional catalyst. To our knowledge, production of furfural from concentrated xylulose (30 g l−1) has not been reported previously; this is likely due to the difficulty of producing relatively large quantities of high-purity xylulose in a cost-effective manner. Through simple strategies, such as addition of an aprotic solvent to the aqueous medium or in situ extraction of furfural during the dehydration, furfural yields of up to 90% were achieved. The mild process conditions associated with each of the steps in the process (SIRE, BE and dehydration), along with the ability to concentrate the incoming sugar stream and recycle process streams and catalysts, results in minimal chemical and energy inputs and have a significant favorable impact on the overall process economics.