Model-Assisted Optimization of Xylose, Arabinose, Glucose, Mannose, Galactose and Real Hemicellulose Streams Dehydration To (Hydroxymethyl)Furfural and Levulinic Acid.

Abstract

Conversion of hemicellulose streams and the constituent monosaccharides, xylose, arabinose, glucose, mannose, and galactose, was conducted to produce value-added chemicals, including furfural, hydroxymethylfurfural (HMF), levulinic acid and anhydrosugars. The study aimed at developing a kinetic model relevant for direct post-Organosolv hemicellulose conversion. Monosaccharides served as a tool to in detail describe the kinetic behavior and segregate contribution of hydrothermal decomposition and acid catalyzed dehydration at the temperature range of 120-190 °C. Catalyst free aqueous media demonstrated enhanced formation of furanics, while elevated temperatures led to significant saccharide isomerization. The introduction of sulfuric and formic acids maximized furfural yield and significantly reduced HMF concentration by facilitating its rehydration into levulinic acid (46 mol%). Formic acid additionally substantially enhanced formation of anhydrosaccharides. An excellent correlation between modeled and experimental data enabled process optimization to maximize furanic yield in two distinct hemicellulose streams. Sulfuric acid-containing hemicellulose stream achieved the highest furfural yield after 30 minutes at 238 °C, primarily due to the high Ea for pentose dehydration (150-160 kJ mol-1). Contrarily, formic acid-containing hemicellulose stream enabled maximal furfural yield at more moderate temperature and extended reaction time due to its lower Ea for the same reaction step (115-125 kJ mol-1).