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

Abstract

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.