Intensification of Hydrothermal Biomass Fractionation with the Help of Oxygen: Kinetics and Modeling

The aim of this study was to examine the influence of the oxygen atmosphere on hydrothermal fractionation of Norway spruce at 130-160 °C and 1-50 bar. The quantitative kinetics and qualitative aspects of the hemicellulose extraction were studied. The results show that the fractionation can be considerably enhanced already by low concentrations of oxygen. The ratio of lignin to hemicellulose extracted from the wood did not significantly vary with the gas atmosphere. A mathematical model was successfully developed for the extraction kinetics revealing an activation energy of 114 kJ/mol and 1/5 reaction order for the hydronium ion concentration and 1/7 reaction order for oxygen concentration. The method is easily applicable also to existing equipment and is nontoxic for obtaining extracts for use also in, for example, the alimentary and cosmetics industries, without the need for costly separation steps. Moreover, the process intensification results in increased energy, space, and time efficiency.