Conversion of fructose into 5-hydroxymethylfurfural and alkyl levulinates catalyzed by sulfonic acid-functionalized carbon materials

Abstract

A series of sulfonic acid-functionalized carbon materials (C–SO₃H), including poly(p-styrenesulfonic acid)-grafted carbon nanotubes (CNT-PSSA), poly(p-styrenesulfonic acid)-grafted carbon nanofibers (CNF-PSSA), benzenesulfonic acid-grafted CMK-5 (CMK-5-BSA), and benzenesulfonic acid-grafted carbon nanotubes (CNT-BSA), have been studied for fructose dehydration to 5-hydroxymethylfurfural (HMF) and fructose alcoholysis to alkyl levulinate. A study for optimizing the reaction conditions such as the catalyst loading, the reaction time, and the temperature has been performed. Under the optimal conditions, high HMF and ethyl levulinate yields of up to 89% and 86%, respectively, are obtained. The catalytic activities of C–SO₃H for the conversions of fructose into both HMF and ethyl levulinate follow the order of their acid strength. The relationship between the catalytic activity and acid density of C–SO₃H shows a linear correspondence in the fructose dehydration to HMF. The facile separation, ease of recovery, and high thermal stability make the developed C–SO₃H efficient and environment-friendly catalytic materials for transforming biomass carbohydrate into fine chemicals.