Chloride ions enhance furfural formation from D-xylose in dilute aqueous acidic solutions

Furfural production through traditional processes is accompanied by acidic waste stream production and high energy consumption. Modern furfural production process concepts will have to consider environmental concerns and energy requirements besides economics, moreover will have to be integrated within widened biorefinery concepts. In this paper, some particular aspects of the chemistry of D-xylose reaction to furfural are addressed, with the aim to clarify the reaction mechanism leading to furfural and to define new green catalytic pathways for its production. Specifically, reducing the use of mineral acids is addressed by the introduction of alternative catalysts. In this sense, chloride salts were tested in dilute acidic solutions at temperatures between 170 and 200 degrees C. Results indicate that the Cl- ions promote the formation of the 1,2-enediol from the acyclic form of xylose, and thus the subsequent acid catalyzed dehydration to furfural. For this reason the presence of Cl- ions led to significant improvements with respect to the H2SO4 case. The addition of NaCl to a 50 mM HCl aqueous solution gave 90% selectivity to furfural. Among the salts tested FeCl3 showed very interesting preliminary results, producing exceptionally high xylose reaction rates.