Xylitol Production from Birch Wood Xylan over Bifunctional Ru-Containing Catalysts Based on Carbon Material Sibunit-4®

Objective: The study aims to investigate the one-pot production of xylitol from xylan, comparing it to traditional methods that involve xylan depolymerization to xylose followed by reduction to xylitol. The goal is to improve environmental and economic aspects by eliminating intermediate stages of purification and raw material preparation. Methods: Bifunctional catalysts containing nanodispersed ruthenium particles (0.5–3%) on Sibunit-4 carbon support with varying acidity (oxidized by a wet air mixture at 400–500°C) were synthesized and characterized. The study separately examined xylan hydrolysis and xylose hydrogenation using Ru-containing carbon catalysts. The effects of support acidity and ruthenium content on the yield of hemicellulose hydrolysis and monosaccharide hydrogenation products were studied. Results and Discussion: It was found that the most active catalyst for both xylan hydrolysis and xylose hydrogenation was 2RuSib450, which had the support oxidized at 450°C, providing the maximum acidity, and 2 wt% Ru. In the one-pot process using this catalyst, the hydrolysis reaction proceeded more slowly than xylose hydrogenation, with significant amounts of propylene glycol and ethylene glycol produced, indicating low selectivity for xylitol. The yield of xylitol did not exceed 6 wt%. However, in the one-pot process involving hydrolysis-transfer hydrogenation with a combination of H2SO4 and 2RuSib450 in an isopropanol-water medium, xylitol was obtained with a high yield of 88 wt%. The use of a small amount of H2SO4 allowed the process to be carried out in standard stainless-steel equipment, instead of requiring equipment made from alloys with high nickel content. Conclusions: The study demonstrates that the one-pot process for xylitol production from xylan using the 2RuSib450 catalyst and H2SO4 in an isopropanol-water medium can achieve high yields of xylitol (88 wt%), offering an environmentally friendly and economically attractive alternative to traditional methods. The process also benefits from using standard stainless-steel equipment, reducing the need for specialized materials.