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Oxygen was known to be an effective bleaching chemical for many years, but several obstacles prevented commercialization until 1970. The obstacles and their solutions will be discussed in this module. Oxygen delignification processes are located between the pulp mill and the traditional bleach plant. The goal of oxygen delignification is to reduce the lignent content of unbleached pulp before using more expensive bleaching chemicals.
Oxygen can reduce the Kappa number more effectively than extending the pulping process. One advantage of oxygen delignification is that the effluent, unlike that from a conventional bleach plant, is compatible with craft pulping chemical recovery processes. Oxygen delignification is an important process contributing to elemental and total chlorine-free bleaching while still economically achieving pulp brightness targets and reducing the environmental impact.