PEER-REVIEWED ARTICLE bioresources.com Reyes et al. (2016). “Pretreatment for hydrolysis,” BioResources 11(1), 612-625. 612 Evaluation of Combined Dilute Acid-Kraft and Steam Explosion-Kraft Processes as Pretreatment for Enzymatic Hydrolysis of Pinus radiata Wood Chips Pablo Reyes, a,b, * Nicole Márquez, b Eduardo Troncoso, a Carolina Parra, b Regis Teixeira Mendonça, b,c and Jaime Rodríguez b,c The combination of hemicellulose pre-hydrolysis by dilute acid or steam- explosion followed by kraft pulping was one approach evaluated in this work to generate pulps from radiata pine wood chips amenable to saccharification by enzymatic hydrolysis. Dilute acid (combined severity factor, CS = 1.67) and steam explosion (severity factor, log Ro = 4.09) treatments were able to solubilize approximately 53% and 63% of the original hemicelluloses content in wood, respectively. Extracted wood chips were subjected to kraft cooking (170 °C, 16-18% active alkali, 30% sulfidity and 1200 H-factor) to produce pulps that were further saccharified by cellulases. Lignin removal increased with increasing active alkali, affording delignification levels 28% for dilute acid and 68% for steam explosion extraction pretreatment pulps. Enzymatic digestibility of P. radiata pulps were low, and only samples pretreated by steam explosion reached glucan-to-glucose conversion near to 75%; this treatment was 31% and 37% higher than that obtained with wood chips that were pretreated by dilute acid extraction. Keywords: Dilute acid; Steam explosion; Hemicelluloses; Kraft pulping; Enzymatic hydrolysis Contact information: a: Consorcio Tecnológico BioEnercel S.A., Universidad de Concepción, Casilla 160- C Chile; b: Laboratorio de Recursos Renovables, Centro de Biotecnología, Universidad de Concepción, Casilla 160-C, Chile; c: Facultad de Ciencias Forestales, Universidad de Concepción, Casilla 160-C, Chile; * Corresponding author: preyesc@udec.cl INTRODUCTION The need to find alternatives to the fossil fuels has opened new opportunities for the use of renewable resources, such as lignocellulosic biomass (LCB), for producing biofuels, biomaterials, and chemicals. The current approach for the use of LCB in a comprehensive manner is the biorefinery, which is a facility that integrates fractionation and conversion processes for treating LCB and its components (van Heiningen 2006). Various fractionation methods for processing LCB have been developed in the past decades; these include: steam, acid, or alkali treatments (Cara et al. 2006; Al-Dajani et al. 2009; Kemppainen et al. 2012; Martin Sampedro et al. 2014); and organosolv, fungal, and combinations of these processes (Muñoz et al. 2007; Araque et al. 2008; Fissore et al. 2010). Enzymatic hydrolysis of pretreated materials is used for the production of fermentable sugars, which can be converted into bio-based fuels and chemicals. LCB pretreatments disrupt and partially open up the lignocellulose structure by removing lignin and hemicelluloses. This action is required to expose cellulose to increase its saccharification during the enzymatic hydrolysis process (Mosier et al. 2005). Cellulosic bioethanol production from sugar cane bagasse, corn, wheat, and rice straw has been extensively studied; however, it is still a challenge to produce it from forest