From Biomass to Sugar Alcohols: Purification of Wheat Bran Hydrolysates Using Boronic Acid Carriers Followed by Hydrogenation of Sugars over Ru/H-ZSM-5

Abstract

Wheat bran is a lignocellulosic waste of milling industry. It contains hemicelluloses, which can be valorized into arabitol and xylitol via a few-step approach. It begins with extraction and hydrolysis of hemicelluloses to produce a solution of xylose and arabinose, along with proteins and inorganic salts. This work focuses on the purification of sugars of this hydrolysate and the subsequent catalytic production of sugar alcohols. A purification process based on the recovery of sugars by anionic extraction with a boronic acid, followed by back-extraction and a further refining step with ion exchange resins is described. After this process, a high purity sugars solution (∼90%) free of inorganic elements and proteins was obtained. The feasibility of the process was also highlighted by a successful recycling of the organic phase containing the boronic acid. The hydrogenation of purified sugars was then performed over Ru/H-ZSM-5. A high yield into pentitols of ∼70% with 100% selectivity was achieved. Importantly, the catalytic hydrogenation of sugars in the hydrolysate prior to purification did not occur. We determined that proteins caused the deactivation of the catalyst, and consequently, the inhibition of the production of sugar alcohols.