Involvement of Oxygen-Derived Free Radicals in Chemical and Biochemical Degradation of Lignin

Hydrothermal Pretreatment of Hardwood Chips Prior to Alkaline Pulping and D0(EP)D1 Bleaching

“…Furthermore, the higher bleachability should be related to the decreased content of hemicelluloses, hexuronic acid, and transition metal ions in pulps (Liu et al 2008). Also during pulp bleaching, oxygen delignification results were much higher in regards to residual peroxide in the EP stage (Reitberger 2001). Similar results were obtained for brightness.…”

Effect of Hydroxyl Radical on the Selectivity of Delignification during Oxygen Delignification of Bamboo Pulp

“…This was because more lignin was degraded by more HO· generated by the Fenton's reaction system. Meanwhile, the rate of viscosity reduction also increased with the amount of HO· because of the poor reaction selectivity of HO·, which could not only react with lignin but also degrade carbohydrates Reitberger et al 2001;Guay et al 2000Guay et al , 2001. The selectivity of delignification was 1.8 when 10 mL of H 2 O 2 were added into the reaction system, but the selectivity of delignification dropped to 1.2 when the amount of H 2 O 2 increased to 40 mL.…”

“…Therefore, the lower selectivity is a key obstacle to oxygen delignification. To improve the selectivity of oxygen delignification, many studies have been carried out, such as optimization of process parameters (McDonough 1986;Cao et al 2006), pretreatment of unbleached pulp (Samuelson and Otjeg 1996), reinforcement of oxygen delignification with additives (Pesman et al 2010;Gaspar et al 2009), kinetics of oxygen delignification (Violette 2003;Ji 2007), cellulose protectants (Fu et al 2005;Chen and Lucia 2002), and the reaction mechanism of lignin and carbohydrates Reitberger et al 2001;Guay et al 2000;Guay et al 2001). However, our knowledge of oxygen delignification is still far from being complete.…”

Where does the Oxygen go? – Pathways and Partitioning in Autothermal Pyrolysis

“…Reactive oxygen species (ROS) become involved in both unassisted gas-phase and enzymecatalyzed oxidations. From the perspective of metal-ion catalyzed oxypulping; superoxide, hydroxyl and hydrogen radicals all play a role in the lignin-oxidation process [243]. If in a solvent, phenolate ions can reversibly lead to solvent-caged superoxide radicals, which could further form hydroperoxy in presence of metal catalyst [243].…”

“…In addition to pathways, enzymatic oxidations can be classified by general reaction conditions required. Reitberger classified enzymes as either oxygenases; those involving an oxygen-atom transfer requiring close interaction between lignified material and the enzyme, or cytochromes; involving one-electron concerted intermediate-stabilizing steps, less reliant on substrate conditions, the mode of common ligninoxidizing enzymes [243].…”