MECHANISMS OF OXIDATIVE DEGRADATION OF CARBOHYDRATES DURING OXYGEN DELIGNIFICATION. II. REACTION OF PHOTOCHEMICALLY GENERATED HYDROXYL RADICALS WITH METHYL Β-Cellobioside

Abstract

Reactions involving methyl b-cellobioside and several oxygen species were used to investigate cleavage of glycosidic linkages in cellulose by reaction with photochemical hydroxyl radicals. The intent is not to reproduce delignification conditions, but rather to study the specific behavior of carbohydrate models toward hydroxyl radical. Experiments show that hydroxyl radicals are responsible for the degradation of glycosidic linkages in methyl b-cellobioside by substitution reactions displacing cellobiose, D-glucose, methyl b-D-glucoside, and methanol. Once the glycosidic linkages are broken, the reducing carbohydrates undergo a series of reactions forming 67

Multistage oxygen delignification of high-kappa pine kraft pulp with peroxymonosulfuric acid (Px)

“…This suggests that the higher hemicellulose content might be a factor for the slightly higher viscosity for OO-conventional pulp at the same Kn in comparison with OPxOPxO-pulp, as they serve to protect cellulose from harmful free hydroxyl radicals that are continuously generated during oxygen delignification. (Guay et al 2002;Violette and van Heiningen 2002;van Heiningen and Violette 2003).…”

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.…”

“…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).…”

“…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.…”

Fenton Depolymerization of Cellulosic Biomass in Modified Cuprammonium Solution

“…The mechanism for the Fenton depolymerization of the dissolved cellulose presumably is that the hydroxyl radical that comes from the Fenton reaction cleaves the -1,4-linked bond. The hydroxyl radical attack takes place at the anomeric carbon, and can readily break down any encountered glycosidic linkage in cellulose (Guay et al 2002). However, besides cleaving glycosidic linkages, other reactions between hydroxyl radical and cellulose would also take place, especially for very low DP.…”