Enzyme Augmentation of Kraft Pulp Bleaching with Oxygen-Based Chemicals, 1993 Environmental Conference Proceedings

Three different types of kraft pulps have been bleached with enzyme and oxygen-based chemicals. The bleaching process, here referred to as the EnZone Process, is composed of enzyme treatment in combination with, oxygen, ozone and alkaline hydrogen peroxide stages. Xylanase treatment of kraft pulps has repeatedly been demonstrated to have a very favorable effect on bleachability in subsequent stages. Here, both eucalyptus-, pine-, and pine RDH kraft pulps, delignified with a combination of xylanase and ozone stages, were found to have consistently lower kappa numbers and higher brightness at the same level of ozone charge compared to the control pulps without the enzyme stage. When the eucalyptus pulp was bleached in the sequence OXZP using 0.8% ozone, a brightness of 90.0% (ISO) was readily obtained compared to a brightness of S4.7% for the control, OZP pulp. When pine kraft- and pine RDH pulps were bleached in the sequences OXZ1EpZ2P and XEpZP respectively, brightness values of 81.0 and 85.7% were obtained compared to the brightness of the control pulps 71.3 and 763% respectively. The total oxone consumption for pine kraft pulp was 1.38%, while for RDH pulp it was O.96% based on o.d. pulp.

Brightness stability and the physical properties of the bleached pulps have been evaluated (or will be). As a reference, pulps were also bleached using the sequence DEDED to the same brightness levels. The pulps bleached with enzymes and oxygen-based chemicals have very good brightness stability, similar tensile index and slightly lower tear index compared to the reference DEDED pulps.