On the Recovery of Hemicellulose before Kraft Pulping

To assess the feasibility of implementing hemicellulose recovery stages in kraft mills, Eucalyptus globulus wood samples were subjected to aqueous treatments with hot, compressed water (autohydrolysis processing) to achieve partial dissolution of xylan. Autohydrolyzed solids were subjected to kraft pulping under selected conditions to yield a pulp of low kappa number, and to an optimized TCF bleaching sequence made up of three stages (alkaline oxygen delignification, chelating, and pressurized hydrogen peroxide), with minimized additions of pulping and bleaching chemicals. The final product had a relatively low kappa number (1.4), 641 mL/g ISO intrinsic viscosity, and 86.4% brightness.