Mechanisms of Oxidative Degradation of Carbohydrates During Oxygen Delignktcation. I. Reaction of Methyl β-D-Glucopyranoside with Photochemically Generated Hydroxyl Radicals

Modified Fenton Oxidation of Cellulose Fibers for Cellulose Nanofibrils Preparation

“…The main reason that Fenton reagents possess the ability of catalytic degradation for many organic compounds is due to the presence of HO• and HOO• with higher oxidation potentials. 34,35 Hydroxyl radicals (HO•) and hydroperoxyl radicals (HOO•) are generated from hydrogen peroxide with the catalysis of ferrous ions. As a strong oxidative agent (E 0 = 2.8 V), 38,39 HO• can cause the degradation of polysaccharides, 40 and leads to the decrease of molecular weight (M w ) as well as formation of a carboxyl group.…”

“…During Fenton oxidation, various radicals, including HO• and HOO•, would be generated, and Fe 2+ and Fe 3+ could be converted to one another. The main reason that Fenton reagents possess the ability of catalytic degradation for many organic compounds is due to the presence of HO• and HOO• with higher oxidation potentials. , …”

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.…”

“…HOO·, O 2 · -, HO· and so on, which are mainly generated from reactions between phenolic units in lignin and molecular oxygen during the process (Ericsson et al 1971;Gierer and Imsgard 1977;Gratzl 1992;Yokoyama et al 1996). Studies have shown that these active oxygen species, especially HO·, attack not only lignin, but also carbohydrates, resulting in lower pulp strength and yield (Guay et al 2000(Guay et al , 2001. To further understand the underlying fundamental chemistry in oxygen delignification in order to improve the selectivity of delignification, the mechanisms of oxidative degradation of carbohydrates and lignin have been investigated (Konishi et al 2009;Nakagawa et al 2012;Yokoyama et al 2011;Kalliola et al 2011;Rovio et al 2011;Kuitunen et al 2011).…”