Hydrothermal Carbonization of Glucose, Fructose, and Xylose-Identification of Organic Products with Medium Molecular Masses

The monosaccharides glucose, fructose, and xylose were subjected to hydrothermal carbonization in aqueous solution at temperatures of 180, 220, and 250 degrees C for different operating times (30 min to 16 h). Here, 68% to 78% of the organic carbon was converted into hydrochar at 220 degrees C with glucose and fructose as feedstock, whereas hydrothermal treatment of xylose did not result in significant hydrochar formation under these conditions. The main topic of this contribution was the identification of stable organic products in the process water in the molecular mass range between 120 and 300 Da by means of GC-MS analysis using several derivatization agents. Special attention was paid to polar OH- and COOH-functionalized compounds. The overwhelming majority of identified organic compounds had cyclic structures of which a prominent group included hydroxylated benzofurans. However, the combined yield of products, which might be potential substrates for liquid biofuels, turned out very low.