XYLITOL PRODUCTION FROM BIRCH WOOD XYLAN OVER BIFUNCTIONAL RU-CONTAINING CATALYSTS BASED ON CARBON MATERIAL SIBUNIT-4®

One-pot production of xylitol from xylan seems to be more environmentally friendly and economically attractive due to the absence of intermediate stages of purification and preparation of raw materials. For this process, bifunctional catalysts containing nanodispersed ruthenium particles (0.5–3%) on the Sibunit-4 carbon support varied by different acidity (oxidized by moist-air at 400–500 °C) were synthesized and characterized. Xylan hydrolysis and xylose hydrogenation in the presence of Ru-containing carbon catalysts were considered individually. The effect of the Sibunit-4 support acidity and ruthenium content (0.5–3%) on the yield of hemicellulose hydrolysis and monosaccharide hydrogenation products, respectively, was studied. It was found that the most active catalyst in the process of xylan hydrolysis and xylose hydrogenation is the one with the support oxidized at 450 °C, providing the maximum acidity, and bearing 2 wt.% of Ru (2RuSib450). In the one-pot process of xylan hydrolysis-hydrogenation to monomers in the presence of the 2RuSib450 catalyst, the xylan hydrolysis reaction proceeds more slowly than the xylose hydrogenation reaction, with a large amounts of propylene glycol and ethylene glycol formed, indicating the low selectivity of the catalyst with respect to xylitol, the yield of which does not exceed 6 wt.%. In the one-pot process of hydrolysis-transfer hydrogenation with combination of H2SO4 and 2RuSib450 in an isopropanol-water medium, xylitol was obtained from xylan with a high yield (88 wt.%). The low amounts of H2SO4 allows the processes to be carried out in the standard stainless steel equipment instead of alloys with a high Ni content.