Formation and Involvement of Radicals in Oxygen Delignification Studied by the Autoxidation of Lignin and Carbohydrate Model Compounds

Selectivity and delignification kinetics for oxidative and nonoxidative lime pretreatment of poplar wood, part III: Long‐term

“…As a result of reactions with oxygen, lignin becomes more hydrophilic; therefore, it is easier to remove from the pulp. Oxygen reacts with phenolic structures; however, not all of these structures are reactive 13 and some lignin moieties are not degraded even for pretreatments lasting 12 weeks. An extensive list of lignin degradation products obtained in oxidative alkaline media can be found elsewhere.…”

“…This is twice the highest glucan degradation in nonoxidative pretreatment obtained for the same temperature and time (0.20 g glucan degraded/g glucan in raw biomass); thus, oxygen triggers glucan degradation, which agrees with previous research. 13 An extensive list of glucan degradation products obtained in oxidative alkaline media can be found elsewhere. 31,32 In the plots, fast-degrading glucan fractions are not evidently separable because they are very small.…”

“…Unlike the nonoxidative alkaline process, oxygen delignification attacks CAC bonds. 13 Lime pretreatment at 25 to 65 C with aeration is expected to follow a combined delignification mechanism, involving Correspondence concerning this article should be addressed to R. Sierra at rsierra@uniandes.edu.co. both oxidative and nonoxidative depolymerization of lignin.…”

Experimental Determination and Empirical Modeling of Oxalate Formation During Oxygen Delignification of Wheat Straw Kraft Pulp

“…Oxalate formation is directly related to the delignification process: a rapid initial lignin removal, followed by a slower delignification phase (Gullichsen and Paulapuro1999;Agarwal et al 1999;Tao et al 2011). Lignin can be attacked directly by the oxygen-based radicals (superoxide anion and hydroxyl radicals, et al) (Gierer et al 1997(Gierer et al , 2001) that firstly open aromatic rings to form muconic acid, which is then further oxidized to oxalate (Kempf and Dence 1980). Figure 2 shows the variation of the oxalate formation with alkali consumption for different alkali charges.…”

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

“…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). Gierer et al (2001) considered oxygen delignification as a free radical process, and it was significant for improving the selectivity of oxygen delignification process to regulate the reaction of oxygen-containing radicals with lignin. Bouchard et al (2010Bouchard et al ( , 2011 regulated reaction behavior of radicals by optimizing the oxygen delignification conditions, such as pH profile, oxygen pressure, procedure for addition of MgSO 4 , and the retention of hemicelluloses in the pulp.…”