The Application of Xylanase on Hardwood Kraft Pulp Bleaching and its Operating Experience

Abstract

Enzyme bleaching was introduced to the process (C-E/O-dnD) for bleaching of hardwood kraft pulp in Yonago mill in October, 1998. This is the first case in which an enzyme has been steadily applied for pulp bleaching in Japan. A thermostable xylanase from a microorganism that we isolated through screening was selected for use in this process. This microorganism, Bacillus sp. S-2113, produces two extracellular xylanases, XP1 and XP2. Expansion of the scale of enzyme production from the laboratory-scale to the mill-scale has been accomplished. It was found that hardwood kraft pulp is effective as a xylanase inducer in the case of this microorganism. The xylanase-containing culture can be applied to the bleaching process without removing the bacterial cells from the culture medium. After the enzyme bleaching process, the microorganism is killed by the bleaching chemicals used in the next step of the bleaching process. The pulp used in the culture medium is returned to the fiber line. Furthermore, because the quantity of enzyme used (the culture) is relatively low, there is no adverse influence on the quality of the pulp. One year has passed since the enzyme bleaching operation, with on-site enzyme production, was begun, and so far, this operation has been working well.The ECF bleaching sequence will start operation within the year 2000 in Yonago mill. The effects of enzyme bleaching in the ECF bleaching process are expected to be even greater then.