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Ai Van Tran
High-consistency ozonation of hardwood kraft pulp
Keywords: brightness, hardwood, hexenuronic acid groups, kappa number, Kinetics, kraft pulp, lignin, Ozone, shrinking core model, viscosity
At present, ozone is one of the main chemicals in elemental chlorine-free (ECF) and totally chlorine-free (TCF) bleaching sequences. High consistency (HC) and medium consistency (MC) technologies are in use. This study shows that HC ozonation of hardwood kraft pulp, as expressed by the overall kappa number encompassing both hexenuronic acid groups and residual lignin, is a two-phase path. The reaction rate of the first phase is two- to three-fold higher than that of the second phase. We propose that the first phase is due to ozonation of both hexenuronic acid groups and residual lignin, whereas the second phase involves only residual lignin. The fiber width and wall thickness were relatively unchanged during ozonation. These results are in contrast to the “shrinking core kinetic model” frequently discussed in the context of HC ozonation. The development of pulp brightness and the decrease in pulp viscosity with the ozonation time are well correlated with the overall kappa number or the kappa number due to residual lignin alone.
Holzforschung, Walter de Gruyter
Print ISSN: 0018-3830
Volume: 60, 11/2006
Pages: 685 - 690