Enzimas

Chapter 12

Enzyme Processes for Pulp and Paper: A Review of Recent Developments
William R. Kenealy and Thomas W. Jeffries
Institute for Microbial and Biochemical Technology, U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, WI 53705

The pulp and paper industry is applying new, ecologically sound technology in its manufacturing processes. Many interestingenzymatic applications have been proposed in the literature. Implemented technologies tend to change the existing industrial process as little as possible. Commercial .applications include xylanases in prebleaching kraft pulps and various enzymes in recycling paper. In the future, value-added products could be built around enzyme processes. When new applications are proposed that do not fit intoexisting practices, either the process or the enzyme must be altered. The decision depends on process economics and the feasibility of changing the technology. We review here new applications of enzymes in the pulp and paper industry and how they might be changed to implement the technology on an industrial scale. Also, this review suggests how existing enzymes may be used by process engineers toimprove the efficiency of unit operations, the pulp products, or both.

This is a difficult time for the pulp and paper industry. Consumer standards are high, and manufacturing is competitive. Pulp production is

210

U.S. government work. Published 2003 American Chemical Society

211

increasingly derived from tropical regions (1). Cost reduction pressures are causing consolidation ofcompanies through mergers and acquisitions; many research and development laboratories are being downsized, closed, or directed toward short-term objectives and opportunities; and profitability is being constrainedby external factors including globalization, environmental concerns, and competition (2). Pulp and paper is a large industry that is highly capitalintensive and has been periodicallyaffected by overcapacity (1). In the United States, more than 300 kg of paper are consumed annually per capita (3). To maintain this level of supply, we need to find new ways to use our forest resources more efficiently and with fewer environmental consequences. Emerging technologies based on sustainable use of renewable resources hold promise for the rejuvenation and growth ofthe pulp and paperindustry.

Enzyme Applications in Pulp and Paper
Biotechnology has the potential to increase the quality and supply of feedstocks for pulp and paper, reduce manufacturing costs, and create novel high-value products. Novel enzyme technologies can reduce environmental problems and alter fiber properties. Because the pulp and paper industry is capital-intensive with facilities specific to the tasks(1), new technology must either reduce expenses or fit easily into the existing process design. Pulp and paper companies are reluctant to build or expand plants when the overall industry has enough capacity to satisfy market demands (1). Nevertheless, the industry has embraced enzymes for use in the paper-making process.
Environmental and Manufacturing Benefits

While the size and commoditynature of many of its products make changes difficult, the pulp and paper industry has responded to environmental and economic concerns. It implements new technology as required and when economics dictate change (4). For example, in response to environmental concerns and regulations, the industry has greatly reduced chlorinated aromatic byproducts that can be formed during pulp bleaching (5-7), firstby reducing the amount of residual lignin in pulps and second by turning to other bleaching agents (8 ). An enzyme technology based on microbial xylanases has helped to achieve this goal by reducing or even eliminating the need for chlorine in the manufacture of elemental chlorine free (ECF) and totally chlorine free (TCF) printing and writing paper grades (8-22 ). Enzymes have helped meet...