Water Removal Enables High-Efficacy Synthesis of 5-Ethoxymethylfurfural and Ethyl Levulinate as Biofuel Candidates from High-Concentration Fructose

Abstract

The one-pot conversion of fructose into biofuel candidates such as 5-ethoxymethylfurfural (EMF) and ethyl levulinate (EL) avoids the energy-consuming separation of the unstable intermediate product 5-hydroxymethylfurfural (HMF), thereby representing a promising route for future biorefineries. However, this tandem reaction has an inherently low process efficiency owing to the slow reaction kinetics and facile formation of unwanted humins induced by the presence of water formed in the dehydration step. Herein, we report a water-removal strategy for the high-efficacy conversion of high-concentration fructose (10−30 wt %) to EMF and EL by the addition of silica gel as both a dewatering reagent and cocatalyst. The highest product yield of ∼87.0 mol % with a space-time yield (STY) of ∼7.7 × 10 −1 mol• L −1 •h −1 is achieved by reacting fructose in ethanol at 140 °C for 30 min under the action of 1.0 g of silica gel. A kinetic study reveals that fructose-to-HMF dehydration, HMF-to-EMF etherification, and EMF-to-EL alcoholysis are accelerated by water removal, and the promotional effect on the former two steps is more remarkable. The process efficiency, expressed as STY, improved remarkably compared to those without water removal. Such a water-removal strategy is applicable to both homo-and heterogeneously catalyzed fructose-to-EMF/EL conversions with a wide substrate scope. This provides a practical strategy for enhancing the efficiency of biofuel production in future biorefineries.