Integrated production of second-generation ethanol, xylosaccharides and lignin-derived products from eucalyptus residues under a biorefinery approach

• Integrated use of eucalyptus sawdust yields bioethanol and valuable co-products. • Pretreatment at 160°C, 0.6% H₃PO₄, 40 min gave 15.8 g/L xylose and 87% XS recovery. • Alkaline treatment extracted lignin (61% yield), substituting 30% resin in adhesives. • Enzymatic hydrolysis reached 105–162 g/L glucose and 34 g glucose/100 g sawdust. • Ethanol yield reached 171 L/t sawdust and 73 g/L ethanol under SSF strategy. This study investigates the integrated utilization of eucalyptus sawdust for producing bioethanol and value-added co-products, such as xylose and lignin, with potential applications in various chemical industries. The sawdust underwent two pretreatment stages: an acid pretreatment with diluted phosphoric acid, followed by an alkaline treatment. The optimal acid pretreatment condition was 160°C, 0.6% phosphoric acid for 40 min, yielding a xylose concentration of 15.8 g/L and an 87% xylosaccharides recovery. The resulting solid fraction was then treated with an alkaline solution to extract lignin, recovered with a 61% yield. High enzymatic hydrolysis efficiencies of the pretreated solids were achieved, with glucose concentrations ranging from 105 to 162 g/L, resulting in glucose yields of 34 g/100 g dry sawdust. The best alkaline pretreatment condition was 14% NaOH for 60 min. The separate enzymatic hydrolysis and fermentation strategy was the most effective for ethanol production, yielding 73 g/L of ethanol and 171 L per ton of sawdust. Additionally, lignin could replace up to 30% of the phenol-formaldehyde resin used in adhesives, improving bond strength and offering a cost-effective alternative. These findings highlight the potential of eucalyptus sawdust as a sustainable resource for bioethanol production and value-added chemical products.