Effect of Hardwood Lignin Structure on the Kraft Pulping Process, 2010 TAPPI PEERS Conference

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In an attempt to explain variations in terms of delignification behavior among different hardwood species, the kraft pulping delignification rate of E. urograndis, E. nitens, E. globulus, sweet gum, maple, red oak, birch, red alder, cottonwood and acacia was obtained and correlated with their respective lignin chemical structures. In addition, since H-factor for hardwood is calculated based on the softwood activation energy (Ea) value, a comparison between softwood/hardwood activation energy was also performed. Lignin was isolated by a modified isolation protocol, using alkaline pretreatment of the wood prior to isolation. The lignin preparations were analyzed via quantitative 13C NMR spectroscopy and the entire wood via nitrobenzene oxidation. Substantial variations have been found among the hardwood species studied. A linear correlation between the kraft delignification rate and the amount of syringyl units presented in the species was found. Activation energy values obtained for kraft pulping of hardwoods were very similar among them and almost identical to the one obtained for softwood.