Environmentally Benign Approaches for Pulp Bleaching 2nd Edition

Pulp and paper production continues to increase globally, now totalling some 380 million tonnes. Growth is the most rapid in Asia, due mainly to the rapid expansion of industry in China. Asia accounts for well over a third of total world paper and paperboard production. In North America, by contrast, production is contracting. Asia accounts for almost 40% of global consumption, while the EU and North America account for about 25% each.

The industry is very capital-intensive with small profit margins, which tends to limit experimentation, development, and incorporation of new technologies into the mills. Improved environmental performance is needed as the industry is also under constant pressure to reduce environmental emissions to air and water. During the past decade, no segment of the pulping and papermaking process has received as much attention as the bleach plant. In the mid-1980s it was discovered that US chemical pulp mills using elemental chlorine and/or sodium hypochlorite as their primary bleaching agent were discharging unusually high levels of carcinogenic dioxins and furans in their effluent streams. The industry undertook a very rapid process about-face. The pace increased when further studies definitively tied the presence of these carcinogens to the use of elemental chlorine. As a result most of the bleached chemical pulp mills around the world rapidly instituted process changes away from elemental chlorine and towards combinations of chlorine dioxide, oxygen, hydrogen peroxide, ozone, peroxy acids and enzyme technologies. The focus of attention in bleaching research continues to be on the development of alternatives to chlorine-containing compounds. Most efforts have centered on the oxygen families of chemicals. Metals management development is aimed at increasing the effectiveness or selectivity of expensive chemicals.

The continuing pressure to further reduce air and water emissions is driving the development of technology to capture all mills effluents and return them to the process. Controlling the concentration and build-up of impurities in the liquor cycle is of paramount importance as more bleach plant effluents are collected for evaporation and burning. This book examines environmentally benign approaches for pulp bleaching and explores new and emerging bleaching technologies that are moving the industry towards effluent closure. * Covers environmentally friendly technologies that can help solve some of the problems associated with conventional bleaching technologies.* Information is up-to-date, authoritative and based on practical experience and pertinent research* In depth coverage of various bleaching processes, including environmental issues.