Volume 8, Number 3
Oct 1995

Polyoxometalates: They Delignify Efficiently, Don't Hurt the Cellulose, & Give Off Only H₂O & CO₂

The Forest Products Laboratory (FPL) in Madison, Wisconsin, recently responded to the APA editor's request for information on their Polyoxometalate Bleaching Program. They sent a packet of papers and short articles, with a cover letter that said the Polyoxometalate Bleaching Program is being directed by Dr. Rajai H. Atalla, head of chemistry and pulping research and professor of chemical engineering at the University of Wisconsin at Madison. It continued:

"Since 1992, FPL has been developing an innovative technology which incorporates the use of transition metal substituted polyoxometalate (POM) cluster ions for bleaching kraft pulp. POMs are highly selective and effective, stable, water soluble inorganic salts easily prepared from inexpensive, non-toxic mineral ores.

"The POM bleaching process is totally chlorine free and creates no toxic by-products, only water and carbon dioxide. In addition, the POM can be reactivated with oxygen under conditions which simultaneously oxidize the bleach mill effluents. Because the POMs can be regenerated by oxygen and reused, the process would reduce energy costs and allow for a closed mill bleaching system with complete mineralization [wet oxidation] of the organic effluent stream.

"The goal of the polyoxometalate bleaching program is to develop a highly selective, effluent-free, closed mill bleaching process which produces high quality paper. FPL has organized a consortium with industry and academia to fully develop the POM technology for future commercial implementation."

Three papers and several shorter notices were enclosed.

1. "Polyoxometalates: A New Generation," by R.H. Atalla. World Paper, June 1994, p. 28-29. POMs can oxidize lignin or residual lignin and related chromophores, while leaving the cellulose undamaged, Dr. Atalla says. Originally, the research focused on finding an oxidative bleaching system that was more selective than those in use--like the enzyme systems of fungi, but one that could be used at the high temperatures called for in an industrial setting. They realized that fungal enzymes work by using transition metal ions to catalyze the oxidation of lignin, and found that transition metal substituted polyoxometalates could do the same. In the process, the POMs are reduced, but they can be oxidized again afterward and reused.

2. "Highly Selective Oxidative Delignification of Kraft Pulp by Water Soluble Polyoxometalates," by Ira A. Weinstock, Rajai H. Atalla, Craig L. Hill, Richard S. Reiner and Carl J. Houtman. Paper given at the 8th International Symposium on Wood and Pulping Chemistry, June 6-9, 1995, Helsinki. Vol. 1, p. 369-376.

This is a technical paper, demonstrating the feasibility of using POM salts and oxygen in the commercial bleaching of chemical pulps.

3. "A New Environmentally Benign Technology and Approach to Bleaching Kraft Pulp. Polyoxometalates for Selective Delignification and Waste Mineralization," by I.A. Weinstock, R.H. Atalla, R.S. Reiner, M.A. Moen, K.E. Hammel , C.J. Houtman and C.L. Hill. Accepted for publication in the New Journal of Chemistry. 24 pp., 37 refs.

This reviews the nature, use and effects of POMs, and the research done to date by the Polyoxometalate Bleaching Conortium, which has investigators at the FPL, Emory University and the University of Wisconsin Department of Chemical Engineering, and receives support from pulp and paper companies in the Consortium.

The shorter articles included ones from the April 19 Chemical Week, p. 66; May 1995 Chemical Engineering, p. 19; April 28 Science, p. 500; and the June 1995 Environmental Solutions, p. 9. The Chemical Engineering article says the process is "cost-competitive with those that use chlorine, even apart from environmental considerations." But the Science article quotes a research director at one of the paper mills as saying that "the POMs needed to bleach a ton of wood pulp are expected to cost millions of dollars compared to at most $60 for chlorine, although the POM cost is a one-time expense." All but 0.01% of the POM is recovered after use.

For more information, contact Ms. Aasma Qazi, the Bleaching Program Coordinator at the FPL, 608/231-9442; or Dr. Atalla, at 608/231-9443.

Thanks to Marcia Watt, Preservation Officer at Emory University, for sending in a good article about Craig Hill's work on this project ("Hill Develops Environmentally Friendly Paper Making," by Danielle Service, Emory Report, Sept. 18, 1995, v. 48 # 5), and incidentally for prompting the gathering of other information, summarized above.