Limits of the Extended Cooking Concept and Bleachability of Resulting Pulps, 1997 Pulping Conference Proceedings

The principles of extended delignification were applied using a continuous flow reactor and the resulting pulps were compared to conventional batch pulps of a 30 kappa number for softwoods and a 20 kappa number for hardwoods. For softwoods, a kappa number 10 was achieved while maintaining a comparable viscosity of the conventional batch pulp and a kappa number 9 with a comparable pulp strength. For hardwoods, a kappa number of 6 was achieved with the continuous flow reactor while maintaining a comparable viscosity of a conventional hardwood batch pulp and a kappa number 4 with a comparable pulp strength.

The continuous flow pulps were more easily delignified in a short DE bleaching sequence with a greater delignification increase observed at lower kappa numbers. An analysis of the residual lignin showed greater degradation of the batch lignins. The quantity of phenolic hydroxyl groups was not observed to be related to the bleachability of the pulps. This implies that other factors are important for the bleachability of pulps, such as the number of condensed carbons.