Effect of Zeolite Acidity and Solvent on the Conversion of Fructose to High-Value Compounds

The world is facing an imminent depletion of non-renewable fossil fuels, and the associated environmental concerns make it necessary to find sustainable alternatives. Biorefineries, using renewable biomass, are emerging as promising alternatives to traditional refineries and offer eco-friendly solutions to meet society's chemical demands.¹ However, a significant challenge in this transition is the optimization of the conversion of biomass-derived compounds, such as fructose into valuable chemicals.

This study examines the role of heterogeneous catalysts, specifically Lewis and Brønsted acid Beta zeolites, and solvents in controlling the conversion of fructose to potential platform molecules such as alpha-hydroxy acids (AHAs) and 5-hydroxymethyl furfural (HMF), or the commercially valuable difructose anhydride (DFA).

Using Sn-Beta Lewis acid catalyst to convert fructose in water results in low catalytic activity and generates undesirable by-products like furans and humins, leading predominantly to lactic acid with unsatisfactory selectivity. However, a noticeable enhancement in catalytic activity is observed with the introduction of the solvent gamma-valerolactone (GVL) in a ratio exceeding 2:8.² To achieve 61% conversion, it takes 3 hours in water compared to 15 minutes in GVL:water 9:1. In contrast, using pure GVL as a solvent the reaction shifts to the production of DFA, which is an intermediate to HMF production.³

Al-Beta, as a Brønsted acid catalyst can catalyze the dehydration reactions from carbohydrates to furans, including HMF in water, although with low catalytic activity. Again, the addition of GVL to water increased it.⁴ At 3 h only 5% of conversion is obtained in water versus 8% of conversion in GVL:water 9:1. Using pure GVL as solvent also propelled the reaction towards producing the intermediate DFA.