Conversion of Xylose to Furfural Using Lewis and Brønsted Acid Catalysts in Aqueous Media

The role of molecular structure on pentose dehydration to furfural has been examined using HCl as a Brønsted acid catalyst in a single phase aqueous media. It is shown that xylulose dehydration results in a much higher furfural yield than xylose dehydration under similar reaction conditions. Furthermore, a cascade of reactions for the efficient conversion of xylose to furfural in a single pot reactor is presented whereby a Lewis acid, CrCl3, is used to isomerize xylose to xylulose, and a Brønsted acid, HCl, is employed to dehydrate xylulose to furfural. Using the combination of Lewis and Brønsted acids, a furfural yield of ∼39% is achieved compared to ∼29% using HCl alone, at a moderate reaction temperature (∼418 K) in a single aqueous phase, with an associated decrease in the residence time by a factor of 5. With this combined catalyst functionalities, a much higher yield (76%) to furfural can be obtained in a biphasic system at low temperatures and short times. Aside from increasing performance, our results indicate that the combined Lewis and Brønsted acids change the pathway for the conversion of xylose to furfural compared to carrying out the reaction in Brønsted acids alone.