Valorization of Corncob by Hydrolysis-Hydrogenation to Obtain Xylitol Under Mild Conditions

Abstract

The pretreatment of biomass represents a large energy expenditure in the production of sugar alcohols. Current research efforts are focused on integrating catalytic processes to decrease operating time and reduce energy and raw material consumption. In this work, the hydrolysis-hydrogenation of hemicellulose for xylitol production direct from corncob was studied. It was used two strategies of hydrogenation: H2 gas under pressure, and isopropanol as H2 donor. The importance of the presence of H2SO4 and 5% Ru/C catalyst in the reaction medium was analyzed. It was considered the use of H2 pressure (2 MPa) and employing isopropanol (water-isopropanol 1:3) as a source of hydrogen. The reaction products were determined by HPLC. The 5% Ru/C catalyst was active and selective for the conversion of xylose to xylitol. To promote the hydrolysis of the hemicellulose fraction of the corncob into xylose, the addition of acid was necessary. Under mild conditions (0.1% H2SO4, 413 K), xylose was detected as the main product, indicating the good selectivity of the first hemicellulose conversion step. A xylitol yield was 19% under H2 pressure while with isopropanol 7% was obtained. The intermediate purification step was eliminated because as xylose was formed it was simultaneously hydrogenated to produce xylitol in the presence of Ru catalyst. Cellulose remained intact in the solid residue and could be used to obtain other products, such as glucose, sorbitol, ethanol, or charcoal.