Biomass-derived sugars and furans: Which polymerize more during their hydrolysis?

Sugars and furans are important intermediates during the conversion of non-food lignocellulosic biomass to biofuels and chemicals. In this study, polymerization of the sugars (glucose, fructose, xylose) and furans (5-hydroxymethylfurfural, furfural) during their acid-catalyzed conversion was investigated. The potential cross-polymerization between sugars and furans was explored. Sugars and furans have very different tendencies towards polymerization. Yields of solid polymer (weight basis) during the dehydration of glucose to 5-hydroxymethylfurfural (HMF) is ca. 7% while that from HMF to levulinic acid is ca. 17% at 190 °C with Amberlyst 70 as the catalyst. Dehydration of xylose to furfural forms negligible amounts of solid polymer, while furfural polymerized almost completely. Cross-polymerization between HMF and glucose is insignificant. However, HMF does cross-polymerize with fructose and furfural, producing more insoluble polymer and soluble polymers with different structures. The cross-polymerization between furfural and xylose, if any, does not have any appreciable impact on formation of the insoluble polymer or soluble polymer. Efforts should be devoted more to stabilize the furans to diminish their polymerization during acid-catalyzed conversion of biomass/sugars/furans to value-added chemicals or biofuels