Dehydration of Xylose to Furfural in Alcohol Media in the Presence of Solid Acid Catalysts

Different solid acid catalysts, which include several zeolites, zirconium oxide based catalysts, and materials that contain sulfonic acids, have been evaluated in the dehydration of xylose to furfural in alcohol media. Alcohol media were selected to reduce side reactions, many of which occur in aqueous media. Among the tested alcohols, 2-propanol provided better results and yielded a higher furfural production than ethanol and methanol. Catalyst screening evidenced that small-pore-size zeolites (H-ZSM5) or catalysts that show weak acidity (tungstated zirconia) were unable to promote the desired transformation. Kinetic studies performed for the different types of materials revealed that the nature of the acid sites influenced the catalytic performance of the different solid acids to the extent of conditioning the main reaction pathway for the transformation of xylose into furfural. Thus, whereas Lewis acids seem to promote furfural production by the direct dehydration of xylose, BrOnsted-type catalysts lead to alkyl xylosides as intermediates in the overall transformation. Although both types of catalysts provide high furfural yields in short reaction times, especially at high temperatures, commercially available -zeolite with an adequate combination of BrOnsted and Lewis acids sites seems to contain the right physicochemical properties to maximize furfural production.