Mill Implementation of Enzymes in Pulp Manufacture, 1997 Biological Sciences Symposium Proceedings

One of the first applications of enzymes to modii pulp properties was reported by Paice and Jurasek in 1984 (1). In this work, a crude mixture of degradative enzymes, including xylanases, prepared from a wood degrading fungus was applied on a dissolving grade pulp to remove xylan. The resulting increase in alpha cellulose content was expected to allow the pulp to be derivatized to higher value products. Although no significant reductions in hemicelluloses were observed, a subsequent study by Finnish workers demonstrated that a similar enzyme treatment surprisingly reduced the requirement of chemicals needed to bleach the pulp (2). Shortly thereafter it was identified that it was the xylanase present in the crude enzyme mixture that was responsible for the prebleaching or “bleach boosting” effect (3). The first mill trial with enzymes was conducted at the Enso Gutzeit mill in Imatra Finland and was reported in 1989 (4). A reduction in chlorine chemicals for bleaching the pulp allowed the mill to lower the AOX level by over 50%. More notable was that the level of chlorinated dioxins formed was reduced below detection threshold. This was a significant achievement at a time when the pulp and paper industry was at the height of concern over dioxins in wastewaters. The positive results were tempered, however, with a loss in pulp viscosity and yield. This problem was due to the presence of cellulases which contaminated the early enzyme preparations. As a result, much of the efforts that have gone into the development of xylanases at the industrial scale have focused on the removal of cellulase contamination. A variety of ce.llulase free preparations is now available. Xylanases are produced using microbes that are either naturally free of cellulase-producing ahility or have been mutated or genetically engineered to eliminate the cellulases. The development of xylanases has permitted commercial availability of these enzymes that can function over a range of temperatures from…