Efficient fractionation of woody biomass by cooking with active oxygen species and solid alkali

The fractionation of lignocellulosic biomass via pretreatment is a critical step for its valorization. However, the efficiency of pretreatment is often limited by the robust lignin-carbohydrate complex (LCC) structure. This study employed the cooking with activated oxygen and solid-alkali (CAOSA) pretreatment, using H 2 O 2 and O 2 as the dual oxidant sources, to pretreat various types of woody biomass. The CAOSA pretreatment with H 2 O 2 and O 2 achieved over 90% removal of hemicellulose and lignin, and over 90% retention of cellulose. In addition, the enzymatic hydrolysis efficiency of various cellulose pulps was obtained around 90% after the CAOSA pretreatment. Notably, the hemicellulose was degraded into organic acids like formic acid during the CAOSA pretreatment with H 2 O 2 and O 2 , which could be served as an in-situ hydrogen source for the hydrodeoxygenation reaction of the lignin dissolved in the cooking liquor, directly producing lignin monophenols with a yield close to the theoretical yield (based on β-O-4 linkage). Mechanism studies revealed that introducing H 2 O 2 as an oxidation additive to CAOSA pretreatment promoted the generation of reactive oxygen species (ROS), thereby enhancing the cleavage of glycosidic and C-C bonds in hemicellulose, resulting in more hemicellulose degradation into small-molecular-weight acids. It also promoted cleavage of β-O-4 and C-C bonds in lignin. In-situ generated small-molecular-weight acids from hemicellulose suppressed the cleavage of lignin aromatic structures, thereby improving lignin recovery with a high delignification rate. This study provides theoretical guidance and technical support for efficient alkali-oxygen pretreatment and comprehensive utilization of woody biomass. • The incorporation of H 2 O 2 led to an enhancement in the CAOSA pretreatment efficacy • H 2 O 2 promote cleaving of C-C bonds, thereby enhance formic acid formation • The Formic acid from hemicellulose acts as an in-situ H donor for the HDO of lignin • Mechanistic studies revealed H 2 O 2 promoted the ROS activated, enhancing cleavage of lignin linkage