Realities and trends in enzymatic prebleaching of kraft pulp

Abstract

Use of biotechnology in pulp bleaching has attracted considerable attention and achieved interesting results in recent years. Enzymes of the hemicellulolytic type, particularly xylan-attacking enzymes, xylanases, are now used in commercial mills for pulp treatment and subsequent incorporation into bleach sequences. There are various reasons for mills to consider the use of bleaching enzymes. Some of the primary reasons are environmental (e.g. reductions in chlorine, chlorine dioxide, and hypochlorite) or economic (decreased chlorine dioxide and/or peroxide requirement), or relate to improved pulp quality (higher brightness ceiling) and improved mill flexibility.Although environmental pressures on the pulp producers were responsible for the initial interest in new technologies or biochemical solutions for eliminating chlorine-containing chemicals, which may still be the case in certain parts of the world, there is now a consumer-led demand for elemental chlorine-free (ECF) and total chlorine-free (TCF) pulps. ECF and TCF pulp production offer opportunities for enzymes, which provide a simple and cost-effective way to reduce the use of bleaching chemicals. Enzymes also offer an approach to addressing the need for the elimination of bleach plant effluent discharge. The current developments in enzymatic prebleaching are reviewed here within an engineering context.