Integrated forest biorefineries: green liquor extraction in eucalyptus wood prior to kraft pulping

The biorefinery concept associated with pulp mills, which already have the infrastructure and logistics to handle large volumes of forest biomass, appears to be one of the best options for the valorization of lignocellulosic biomass. This work investigates alternatives to the partial recovery of the hemicelluloses present in wood, by a green liquor extraction stage prior to kraft pulping of eucalyptus chips. The aim is to obtain an extract rich in hemicelluloses suitable for use as feedstock in the production of bioethanol without modifying the quality of the cellulose pulp produced. Different green liquor charges (0–6 %), several temperatures (100–165 °C), and reaction times (30–150 min) were studied with a constant liquor-to-wood ratio of 3.5. The best results are obtained at 155–160 °C for 150 min and working with a green liquor charge of 2 %. At these conditions, 2.9–3.2 % of xylose and 3.0–3.4 % of acetic acid are obtained from wood.