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

The role of molecular structure on pentose dehydration to furfural has been examined using HCl as a Bronsted 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 Bronsted acid, HCl, is employed to dehydrate xylulose to furfural. Using the combination of Lewis and Bronsted acids, a furfural yield of similar to 39% is achieved compared to similar to 29% using HCl alone, at a moderate reaction temperature (similar to 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 Bronsted acids change the pathway for the conversion of xylose to furfural compared to carrying out the reaction in Bronsted acids alone.