Hill's research was spurred by a big problem in the pulp and paper industry, the release of dioxins into rivers and streams during the paper-making process. Environmental laws have called these companies into question in recent years for their current method of paper production, which entails the use of chlorine or chlorine derivatives as a bleaching agent. The chlorine is used to remove lignin, which imparts the color, texture and antioxidant properties of wood, while leaving cellulose, which gives wood its strength, intact. Chlorine and chlorine derivatives are an effective means to this end, but when chlorine reacts with lignin byproducts, the result is the creation of potentially cancerous chemicals, such as dioxins.
Hill and a team of researchers, in conjunction with several pulp and paper companies, have developed new catalysts that are not only less toxic but are also equally effective.
The new approach uses polyoxometalates, or POMs, to remove lignin from wood without damaging the cellulose. POMs take electrons from the bonds that hold lignin together, washing it out of the wood pulp altogether. Hill explained that the process involves four unit operations: bleaching, in which an oxidized form of the inorganic cluster compounds selectively recognizes and oxidizes the lignin with minimal damage to the cellulose; removal of the reduced clusters and partially oxidized lignin fragments from the cellulose; concentration and removal of salts; and wet oxidation at a high temperature in the presence of air. This last step reoxidizes the cluster back to its starting form and simultaneously mineralizes all the waste from the bleaching step, primarily partially oxidized lignin fragments, to carbon dioxide and water.
Finding a single compound that effectively performs both bleaching and mineralization without leaving fragments of lignin or destroying the catalyst is a daunting task, said Hill, and "the process is fraught with peril." Some exotic woods present different problems with processing the wood into paper. In addition, for POMs to be as cost efficient as chlorine, they must be at least 99.9 percent recyclable -- and while they have proven to be so in preliminary tests, POMs must also be able to take lignin's electrons away and later give them up to oxygen. Currently, researchers have POM varieties that can perform one task better than the other. Experimentation continues to find POMs that can do both adeptly. Thus far the principal patent for the procedure, owned jointly by Hill through Emory and Ira Weinstock of the U.S. Forest Products Laboratory, has been issued and the second and third (of three) should be issues shortly. The patent involves more than the four unit operations described above, but "we're far enough along where we've solved the little problems," Hill said.
With the little problems solved, Hill and the other researchers are beginning to look toward the incorporation and adaptation of the process by paper companies. "We need to talk to individual companies for optimum interaction," Hill said. "They don't all do things the same way. Different areas have different demands."
In recent years, however, paper companies have been under enormous pressure to get rid of the current bleaching process, and this new development may very well be the answer to their problems. Especially when the recyclability of POMs are taken into consideration, "this process is as cheap or cheaper than the existing technology," Hill said.
Changes to existing technology may not be easy or welcomed, however -- especially when the price tag on some pulping plants can be more than $1 billion. The POMs needed to bleach a ton of wood pulp are expected to cost millions compared to $60 for chlorine, and despite the one-time cost of POMs, some companies may be reluctant to incur that sort of cost. "We're going to see how we can adapt the existing plants to what we have," Hill said. "The technology is reversible. We could just work on the bleaching part and use POMs to mineralize waste. The technology is versatile and adaptable."
These qualities may indeed prove the importance of POMs to the paper industry, considering the future implications of such a procedure. "We wouldn't be polluting the environment," said Hill. While this may be the most important consideration, Hill claims there are a number of implications that could positively affect the industry. "POMs can be recycled for months, if not years," he said.
The "we" Hill speaks of involves numerous key laboratories in addition to substantial input from top research and development administrators, scientists and engineers from several pulp and paper companies. The laboratories include those of Ira Weinstock and Rajai Atalla at the U.S. Forest Products Laboratory, and Karl Houtman and Charles Hill of the Department of Chemistry Engineering at the University of Wisconsin. Several of the pulp and paper companies, including Consolidated Papers, Potlatch and Weyerhaeuser in the United States, Ahlstrom Kamyr in Sweden and Metsa-Serla Oy in Finland, have already formed a consortium to facilitate collaboration, funding of the research and the transition of the developing technology to commercialized use. The research has been funded by the U.S. Department of Agriculture and the U.S. Department of Energy.
While "each research unit has its own primary mandates," Hill said, "biannual meetings are held and everyone comes together to discuss technical specifics. Each team presents their findings, and then there is a brainstorming session." The main thrust of the Emory research is development of the multifaceted POM catalysts themselves.
Will this process, when honed, be revolutionary to the pulp and paper industry? "Absolutely," said Hill with a confident smile. Something about that smile inspires the belief that he'd sign his name to that -- on paper.
-- Danielle Service