Oxygen Delignification of Southern Softwood Kraft Pulps With High Lignin Content, 2006 Engineering, Pulping, & Environmental Conference

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The selectivity of the oxygen delignification process was investigated for southern softwood Kraft pulps at high lignin content. A comparison was made between the selectivity of Kraft pulping and oxygen delignification processes over the kappa number range from 90 to 25. Kinetic data are presented reduction in kappa number, cellulose degradation rate due to random hydrolysis reactions and the selectivity coefficient. It was concluded that the Kraft pulping process was more selective than the oxygen delignification process for removing lignin from southern softwood Kraft pulps. The reason for the greater selectivity of the Kraft process compared to oxygen delignification is though to be related to the presence of hydroxyl radicals that are formed in the oxygen delignification process that are not present in the Kraft process. The hydroxyl radicals attack the carbohydrates and randomly cleave the polymeric chains, causing a significant decrease in the degree of polymerization of the carbohydrates and thus a loss of viscosity.