Hydrolytic Decomposition of Corncobs to Sugars and Derivatives Using Subcritical Water

Corncobs are a widespread and renewable by-product of corn cultivation that are typically considered waste or low-value material. Corncobs contain hemicellulose, cellulose, and lignin, which can be converted into valuable products using suitable techniques. Subcritical water is increasingly used as a green medium for the extraction of valuable components from biomass, as it has many advantageous properties (high yield, pure extracts, shorter times) compared to other organic solvents. For this reason, subcritical water was used in this study to extract valuable components from corncobs at different temperatures (150&ndash:250 &deg:C) and reaction times (10&ndash:60 min). During the decomposition of corncobs, numerous valuable products are formed in the aqueous phase depending on the temperature and reaction time. In addition to sugars and their derivatives, phenolic compounds were also formed, which are of great importance in numerous applications. It was found that at low temperatures (150&ndash:170 &deg:C) the hemicellulose in the corncobs begins to decompose and, in particular, the sugars (glucose, xylose, arabinose, and galactose) are initially formed in the aqueous phase. Higher temperatures (200 and 250 &deg:C) are more favorable for the decomposition of corncobs into valuable components. The yield of sugars increases with temperature due to the degradation of the cellulose content of the lignocellulosic biomass. At the same time, several new valuable products (furfural, 5-hydroxymethylfurfural (5-HMF), 1,3-dihydroxyacetone, levulinic acid, and formic acid as well as phenolic components) are formed through the degradation of lignin and the further degradation of sugars. The most important products are certainly the furfurals, which are central platform compounds. The highest furfural content was reached at 200 &deg:C and 60 min and accounted for almost half of all components in the aqueous phase (472.01 &plusmn: 5.64 mg/g dry extract). These biomass-derived sugars and derivatives can be used in the production of fuels, pharmaceuticals, biodegradable polymers, and surfactants.