Depolymerization of lignocellulosic biomass into carbohydrates remains a challenge for selective production of biofuels or biochemicals. During the dilute acid pretreatment to remove lignin, some hemicellulose also removed. Thus, hemicellulose is not efficiently utilized for biochemical productions. Solid catalysis with strong protonic acid sites is an approach to produce carbohydrates with easy separation from liquid products. Here, we report the hydrolysis of commercially available xylans (birchwood, corncob, and beechwood) into xylose at moderate to high yields (up to 95%) at mild conditions, using acid-functionalized non-porous carbon and mesoporous carbon nanoparticles (MCN). The hydrolysis of birchwood xylan, comprising of 69% of xylan at 150oC for 4 hours over functionalized non-porous carbon and MCN catalysts results in a xylose yield of 32-57% and 43-61%, respectively. The better hydrolysis performance of MCNs than non-porous carbon can be attributed to its higher adsorption capacity.

In order to understand the correlation between xylan properties and hydrolysis performance, comparative hydrolysis studies were performed using various commercially available xylans such as birchwood, corncob, and beechwood xylan over functionalized non-porous carbon and MCN catalysts. Corncob xylan, comprised of 75% xylan having low molecular weight, is soluble in water. Birchwood xylan, comprising of 69% xylan having an average of 184 xylose repeating units is only partially soluble in water. Hydrolysis of corncob xylan over non-porous carbon at 150oC for 4 hours gave a high xylose yield up to 90%. To further determinate which xylan properties contributed to the hydrolysis, beechwood xylan (comprised of 68% xylan), and a water-soluble xylan with almost the same xylose repeating units as birchwood xylan was examined. The hydrolysis of beechwood xylan over non-porous carbon catalysts gave comparable performance as the corncob xylan hydrolysis with a xylose yield of 55-84%. The results indicate that xylan solubility gives major contribution for xylan hydrolysis.

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