Finding the Sweet Spot for Oxygen Delignification, 2002 International Pulp Bleaching Conference Proceedings

Y. Pu, R. Yang, L. Lucia, A.J. Ragauskas, and H. Jameel

The O-bleachability of two high kappa kraft pulps (¡Ö49) prepared via a high active alkali (HAA)/low H-factor or low active alkali(LAA)/high H-factor was examined. The response of these two pulps to OO-treatment was investigated by varying the charge of caustic and reaction temperatures. The oxygen-delignified pulps were characterized according their kappa number, viscosity, and pulp yield. SAS analysis provided mathematical relationships between the final pulp properties and OO-operating conditions. The HAA pulp exhibited an enhanced response to delignification, but the LAA pulps had improved yield and viscosity responses under the conditions employed. Indeed, the LAA pulps were able to deliver up to a 3% increase in yield and 6 cP in viscosity improvement over the HAA pulp. The fundamental lignin properties contributing to the observed oxygen delignification responses were examined by isolating the residual lignin and analyzing it by NMR and UV/Vis techniques. These studies indicated that condensed phenolics and p-hydroxyl phenols were key parameters retarding the overall lignin removal process. The presence and degradation ¦Á-carbonyl groups in lignin was inferred by UV/Vis analysis.