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June 30, 2003
Volume 81, Number 26
CENEAR 81 26 pp. 30-35
ISSN 0009-2347

Presidential honors recognize innovative syntheses, process improvements, and new products that promote pollution prevention


WINE AND SONG AgraQuest's Serenade biofungicide prevents plant pathogens such as powdery mildew from reproducing, as shown by treated (left) and untreated Chardonnay grapes.
Chemists may wake up one day to find that traditional industrial chemical products and processes have all but been replaced with ones that have their roots in biotechnology. This scene could actually play out if biotech strategies increasingly become both environmentally and economically advantageous. The kind of innovative R&D that would be needed to reach this idealistic end point is already happening, as evidenced by taking a look at this year's winners of the Presidential Green Chemistry Challenge Awards.

In the eighth edition of these popular annual awards, four companies and one individual were honored last week during a ceremony held at the National Academy of Sciences in Washington, D.C. Indeed, three of the five winners were honored for their biobased developments.

The ceremony took place on the eve of the seventh annual Green Chemistry & Engineering Conference, a three-day meeting that features talks by the award winners and technical sessions on advances in green chemistry and green engineering research and education. Dignitaries representing the Environmental Protection Agency, the Commerce Department, the American Chemical Society, and the White House were on hand to welcome guests to the ceremony and congratulate the award winners.

James L. Connaughton, chairman of the White House Council on Environmental Quality, relayed a message from President George W. Bush recognizing the award winners for their innovations in chemistry. "Great environmental progress in this century will come through technology and innovation," Bush's letter stated. "Advancing environmental science helps to increase our nation's prosperity and improve the quality of life for countless individuals. ... By encouraging the development of creative strategies to prevent pollution, the Presidential Green Chemistry Challenge helps conserve our natural resources and protect our environment. I commend the honorees for applying green chemistry to achieve cleaner water, land, and skies, while benefiting our economy."

ACS Board Chair Nina I. McClelland added that "green chemistry provides a unique opportunity for the chemical enterprise to increase its significant contributions to our broader society. For decades, chemistry has been central in providing products that meet human needs, such as food, medications, consumer products, and a strong economy. Now, we are in a position, with over a decade of green chemistry science and technology development, to provide for our human needs in a more sustainable manner."

The Green Chemistry Awards highlight the innovations that are "possible and profitable when science tackles environmental issues," she said. "But innovation in the laboratory is not enough. Developing a broad consensus about the economic advantages of cleaner technologies is crucial to the adoption of green chemistry by industry."

Commerce Department Deputy Secretary Samuel W. Bodman, a chemical engineer by training, spoke on his department's role to ensure that the chemical industry remains vibrant as a major contributor to the U.S. economy. Bodman explained the missions of the National Institute of Standards & Technology, the National Oceanic & Atmospheric Administration, and the Patent & Trademark Office--all Commerce Department agencies--to couple U.S. business interests with the President's "results focused" vision for environmental protection.

"No matter where you sit, in government, in industry, or academia, there is no dispute that environmental stewardship is a very serious responsibility shared by all of us," Bodman said. "Through continued innovation and effective partnerships, like the awards we are celebrating here, we can continue to work together to clean our air, improve our health, and leave our planet a much better place for our children and their children."

The Presidential Green Chemistry Challenge Awards program was established in 1995 as a competitive effort to promote innovative chemical products and manufacturing processes that prevent pollution and are still economically viable. The awards program is administered by EPA's Green Chemistry Program in the Office of Pollution Prevention & Toxics. EPA operates the program with some 20 partners from industry, government, academia, and other organizations, including ACS and the Green Chemistry Institute.

Award nominations are solicited in five categories: small business, alternative synthetic pathways, alternative reaction conditions, designing safer chemicals, and academic. The work described in the nomination must have been carried out or demonstrated in the U.S. within the preceding five-year period. An independent panel, appointed by ACS, judges the nominations and selects the award winners.

In the small business category, AgraQuest Inc., Davis, Calif., received the Green Chemistry Award for developing Serenade, the first broad-spectrum biofungicide. Serenade's antifungal properties stem from the activity of a suite of more than 30 lipopeptides produced by Bacillus subtilis strain QST-713, which was discovered by AgraQuest scientists in soil samples taken from a California orchard.

Serenade joins the growing list of pheromone- and microbe-based pesticides that have cropped up in recent years. These include several products derived from other Bacillus species, such as B. thuringiensis (Bt) strains, which are effective insecticides.

KILLER PEPTIDE AgraQuest's biofungicide contains more than 30 lipopeptides, such as agrastatin A, produced by a strain of Bacillus subtilis. The lipopeptides form micelles that destroy fungal cells and spores to prevent plant pathogens from reproducing.

EPA considers these natural products to be inherently safer for agricultural workers and the environment since they reduce the reliance on conventional chemical pesticides and aren't harmful to nontarget plants and animals. In addition to this environmental advantage, biopesticides typically take about three years and $6 million to develop, while a chemical product can take up to 10 years and $180 million to develop, according to AgraQuest estimates.

AgraQuest's credo is "to fight microbes with microbes, without using synthetic chemicals," notes natural products chemist Denise C. Manker, director of research and new business development. Company scientists search for microorganisms in soil, plants, and animals from terrestrial and marine sources and screen them for activity against insects, nematodes, and plant pathogens such as fungi and bacteria, Manker notes. So far, AgraQuest researchers have isolated some 23,000 strains that have led to 22 potential products.

Serenade, the company's first commercial offering, is prepared by a large-scale fermentation process at a plant in Tlaxcala, Mexico. The aqueous fermentation broth containing B. subtilis cells, spores, and lipopeptides is concentrated and then spray-dried to form a powder, which is sold in bags or as an aqueous suspension.

The fungicide works on one level by forming a physical barrier on leaf surfaces to prevent attachment of the pathogens to plant cell tissues, Manker explains. On a second level, the lipopeptides form mixed micelles on plant surfaces that perforate the membranes of fungal cells and spores to prevent growth.

For efficacy studies, the lipopeptides were extracted from cultures and then separated by size-exclusion chromatography and high-performance liquid chromatography, Manker says. The individual compounds were characterized by a combination of two-dimensional nuclear magnetic resonance spectrometry, mass spectrometry, and amino acid analysis.

The B. subtilis lipopeptides are made up of a cyclic peptide portion and a fatty acid side chain, Manker says. The compounds belong to three distinct classes: iturins, plipastatins, and surfactins. The antifungal properties of some of the lipopeptides were previously known, but the QST-713 strain is the first bacterium found that produces all three classes together. Two of the plipastatins with a unique peptide portion are newly identified compounds, she adds, which AgraQuest researchers named agrastatins.

Serenade can be stored and used in the same way as a synthetic chemical pesticide, Manker says. It can be applied alone or alternated in a cycle with traditional chemical pesticides as part of an integrated pest-management program. "We created Serenade to behave in the growers' hands the way they expect a chemical product to behave," she says.

Field trials have shown that Serenade works as well as or better than chemical pesticides, while lab tests indicate that Serenade is nontoxic to trout, quail, honeybees, earthworms, and other species when used as designed. Serenade doesn't appear to increase the natural amount of B. subtilis in the soil, Manker notes, and the lipopeptides degrade within a few days to lipids and amino acids.

The low toxicity allows workers to return to fields within four hours after application and crops to be harvested even on days when the pesticide has been applied. This makes it useful for crops such as tomatoes that are harvested over several weeks and for protecting crops against late-season diseases.

Serenade is being used on commercial fruit, nut, and vegetable crops and for home and garden use in the U.S. It also is being used in the important fruit- and vegetable-producing countries of Mexico, Chile, New Zealand, and Costa Rica. Registration is pending in Europe.

After two years on the market, the biopesticide is being used on 64% of fresh-market tomato acres in the U.S. and on 12% of lettuce and 12% of premium wine grape acres in California, according to Manker. The cost of Serenade is about $30 or less per acre, depending on the rate used, which is comparable to synthetic chemical fungicides, she says.

Biopesticides currently account for only about 1% of the $28 billion worldwide pesticide market, Manker points out, but market share is growing 20 to 30% per year. That growth is expected to continue with the current boom in the organic food industry and as biopesticides become increasingly accepted by the agricultural community.

GREENCAT From left, Süd-Chemie's Hu, Robert O'Brien, and Richard Tuell look over a metal oxide catalyst prepared by the company's new wastewater-free, nitrate-free process.
Süd-Chemie Inc., in Louisville, was selected as the award winner in the alternative synthetic pathways category for its "greencat" process to prepare solid oxide catalysts. The new method is a more direct route to prepare metal oxides from metals that significantly reduces the amount of process water needed and eliminates the use of nitric acid and the nitrate waste and nitrogen oxides emissions that go along with it.

Solid oxide catalysts are widely used for chemical and refinery operations and in research for the production of next-generation clean fuels derived from biomass, coal, and natural gas, notes Günter von Au, CEO and president of Süd-Chemie. Despite many of these uses being geared toward pollution-prevention technologies, the water usage and wastes generated from nitric acid during catalyst production are a concern worldwide for catalyst producers and their customers, he says. These concerns have been growing as water resources are being more stringently controlled, emissions regulations are being tightened, and world catalyst production approaches 1 million tons annually.

For example, excess nitrates in the environment from agricultural runoff and industrial discharges can lead to heavy algal blooms that deplete oxygen in waterways and harm aquatic life. Nitrogen oxides emissions are known to contribute to acid rain and to changes in the ozone layer and greenhouse gas levels.

Current metal oxide catalyst synthesis involves oxidizing metal powder or chips with nitric acid at elevated temperature and with vigorous agitation, notes Süd-Chemie R&D Manager X. D. Hu. The resulting metal nitrate solution is treated with a base such as aqueous ammonia or sodium carbonate to precipitate a metal salt. The precipitate is washed with water repeatedly to remove soluble nitrate or other ions, he says. In the final step, it is dried and then calcined to drive off excess water and NOx, CO2, or other species from the metal's counterion, leaving the metal oxide with its incorporated additives.

Süd-Chemie's new route produces metal oxides by eliminating the nitrate formation step, Hu explains. The synthesis begins by room-temperature reaction of the metal with a mild, aqueous carboxylic acid as an activating agent and O2 from air as an oxidizing agent. A minimum amount of water is used, which yields a slurry of what is believed to be a combination of the metal oxide along with oxide hydrate and hydroxide species. Metal conversion to the metal oxide takes 24 to 48 hours, Hu says. Any unreacted metal, usually less than 1%, is occluded as part of the active catalyst or can later be removed by a magnetic separator.

The slurry is dried to evaporate residual water and to agglomerate the metal oxide particles with promoters and other additives to form the oxide catalyst. The sub-stoichiometric amount of acid used, which is regenerated during the process, is degraded to water and CO2 during a calcining stage. The calcined solid has essentially all the characteristics of a desirable catalyst: high surface area, large pore volume, high metal concentration, and crystallinity. The catalyst can be used at this stage, Hu notes, or it can be further treated to form highly crystalline material needed for specific applications.

Süd-Chemie has filed patents on the new process and has been operating a 100-lb-scale pilot plant at its site in Louisville since December 2001. In contrast to the conventional precipitation method, the catalyst precursor does not need to be washed, Hu adds, which means that the new synthesis requires only about 5% of the process water of conventional syntheses. The only emissions are water vapor and a small amount of H2, CO2, and NOx, Hu says. The NOx could be eliminated if the added catalyst promoters are nitrogen-free, he points out.

"This new process is able to achieve zero wastewater discharge, zero nitrate discharge, very low or no NOx release, and substantially reduce the consumption of water and energy," Hu says. Overall, approximately 75 tons of wastewater discharge, 2.9 tons of nitrate waste, and up to 0.8 tons of NOx emissions could be eliminated for every ton of oxide catalyst made by the new process, he notes. In addition to the environmental and cost benefits, Süd-Chemie's customers are finding that the new process provides catalysts with performance that's as good as or better than the precipitation method, he says.

CUTTING BACK Süd-Chemie's new synthesis of metal oxide catalysts (bottom route) uses a mild organic acid and O2 in place of nitric acid, which eliminates nitrate wastes and requires only 5% of the process water of the conventional precipitation process (top route).

Selected as the winner in the category of alternative reaction conditions is DuPont, which is being recognized for its development of a commercially viable fermentation pathway to produce 1,3-propanediol (PDO) from corn-derived glucose. The centerpiece of DuPont's bioprocess is an engineered Escherichia coli strain that facilitates the glucose conversion. This process is expected to be an economical and environmental advance over current petroleum-based production of PDO, making the diol more attractive as a feedstock for polymers and other chemicals.

Natural partial pathways to the diol that start with plant sugars have been known for some time, notes DuPont senior research associate Charles E. Nakamura, a biochemist and one of the project's leaders. Yeast routinely convert sugar to dihydroxyacetone phosphate and, under some conditions, on to glycerol in a two-step process, he explains. Several species of bacteria can convert glycerol to 3-hydroxypropionaldehyde and then to PDO in another two-step process.

In 1995, DuPont began a collaboration with Genencor International to engineer a single microorganism that could directly carry out the multistep glucose conversion in high yield, Nakamura notes. The researchers were charged with starting with glucose rather than glycerol since glucose is less expensive and is readily available from corn milling, he says.

A team of scientists and engineers worked for seven years to design and construct the biocatalyst, incorporating genes from baker's yeast (Saccharomyces cerevisiae) and Klebsiella pneumoniae into E. coli K12. The project required fine-tuning to steer the use of the sugar carbons toward PDO production and away from excess cell growth and undesired by-products, Nakamura says. The PDO yield is 135 g per L of fermentation broth at a rate of 3.5 g per L per hour.

"This project has revealed the power and potential of metabolic engineering to change the way chemical companies operate," Nakamura observes.

Bioprocessing is an increasingly popular strategy for chemical companies in their efforts to save on energy and production costs. Savings can stem from operating at lower temperature and at atmospheric pressure while reducing or eliminating hazardous reagents or solvents, which further leads to less waste to treat. For example, the DuPont fermentation process operates near room temperature and doesn't require a metal catalyst or organic solvent.

By comparison, one current commercial petroleum-based route to PDO involves hydroformylation of ethylene oxide to 3-hydroxypropionaldehyde, which is subsequently hydrogenated to PDO, according to an SRI International report cited by DuPont. The first step requires operating conditions of 80 °C and 1,500 pounds per square inch gauge and the use of a cobalt or rhodium catalyst in an ether solvent. The aldehyde is extracted by water and then hydrogenated in stages--for example, with a nickel catalyst at 80–120 °C and 2,200 psig. A similar petrochemical route owned by DuPont uses acrolein as a starting material. Ethylene oxide and acrolein, which must be prepared from ethylene and propylene, respectively, are listed by EPA as hazardous air pollutants.

DuPont uses PDO to make its Sorona 3GT brand of polypropylene terephthalate, a PDO-terephthalic acid copolymer, and the company may eventually build a family of polymers that use PDO as a feedstock. Demand for polypropylene terephthalate made by DuPont and others is expected to reach 2 billion lb per year by 2010. Although DuPont currently uses petroleum-derived PDO to produce Sorona, it is working on plans to build a large-scale PDO fermentation facility based on the new process. For now, DuPont is producing corn-derived PDO in a fermentation pilot plant in Decatur, Ill., operated by carbohydrate processor Tate & Lyle.

Sorona joins Cargill Dow's corn-derived polylactic acid--a 2002 Green Chemistry Challenge Award recipient--as one of the first potentially large-volume polymers that can be made at least in part from a renewable resource. Cargill Dow uses the polylactic acid in its NatureWorks brand packaging materials and Ingeo brand fibers.

CORN CHEMISTRY DuPont's engineered Escherichia coli strain efficiently converts corn-derived glucose into 1,3-propanediol, a monomer used to make the company's Sorona brand polypropylene terephthalate. A planned large-scale fermentation plant would produce 1,3-propanediol for Sorona production to make fiber for clothing and other applications.

Shaw Industries, Dalton, Ga., received the Green Chemistry Award in the category of designing safer chemicals for its EcoWorx polyolefin-based carpet tile. EcoWorx tiles are more easily recycled than traditional carpet tiles, and the company's transition to the polyolefin is replacing a major use for polyvinyl chloride and phthalate ester plasticizer.

Durable 24-inch nylon carpet tiles used in modular office settings and other commercial spaces traditionally have been made using bitumen, polyurethane, or PVC as the foundation for the backing material, notes Steven L. Bradfield, Shaw's vice president for environmental development. PVC holds the lion's share of the market, he adds.

However, carpet manufacturers have been limited in their ability to fully recycle the carpet tiles, Bradfield says, which has meant that most used carpeting is sent to a landfill or incinerated. There also have been increasing health and environmental debates surrounding chlorinated plastics and phthalate plasticizers, which are encouraging development of PVC alternatives. Shaw, the world's largest carpet manufacturer, decided to solve the recycling problem and design a nonchlorinated thermoplastic at the same time, Bradfield notes. The redesign includes a state-of-the-art polymer extrusion system that lowers energy costs as well.

The proprietary base material used in EcoWorx carpet, developed through a joint agreement with Dow Chemical, is an "interpolymer" of polyethylene and at least one longer chain -olefin, such as 1-octene, according to Shaw senior chemist Jeffrey W. Wright. The polyolefin has the flexibility needed for the carpet backing without use of a plasticizer. In addition, it has sufficiently low toxicity so that it complies with Food & Drug Administration regulations for food-contact plastics. EcoWorx has low chemical emissions, he says, which is important to help meet indoor air quality requirements.

The polymer is compounded with performance additives and 60% by weight coal fly ash from power plants as a filler, Wright notes. The filler is added to provide the bulk and loft necessary for the polyolefin to uniformly cover the tile and provide a smooth finish that will sit well on the subfloor. EcoWorx initially was made with calcium carbonate filler, an industry standard, but Shaw switched to fly ash last year. "We decided to use fly ash because it's a readily available industrial by-product, whereas calcium carbonate is a mineral resource that is mined and processed with an unnecessary environmental impact for our application," he says.

The tiles are made by adding an acrylic-based latex precoat onto the back of the nylon face fiber to form a bonding layer, Bradfield explains. A fiberglass mat is laminated to the carpet using extruded polyolefin to provide stability to the tile so it won't lose its shape. A final layer of polyolefin backing is then extruded onto the fiberglass. Most of the mass of the carpet tile stems from the polyolefin.

The EcoWorx tiles are comparable in performance to PVC-backed carpet tiles, yet with the polyolefin base they weigh 40% less and are fully recyclable, Bradfield says. The lower weight means that more carpet can be shipped in a single truckload, providing significant savings in transportation costs. This serves as a double advantage for Shaw in terms of outbound shipments for installation and inbound shipments for recycling, Bradfield points out.

Shaw is using its distribution centers and truck line to collect and transport remnants and used carpet back to the manufacturing site at no cost to customers, he says. The recovered polyolefin backing is flowing to extrusion units, while the nylon face fiber is sent to a Honeywell facility in Canada under a multiyear agreement to be depolymerized into caprolactam monomer to make new nylon. Overall, the recovery cost is less than the cost of using virgin raw materials, Bradfield notes.

But because the carpet lifetime is expected to be 10 to 15 years, significant quantities of EcoWorx backing aren't expected to return to Shaw until about 2007, Bradfield says. Eventually, new EcoWorx carpeting could contain 50% or more recycled material, he adds.

At the close of 2002, Shaw's shipments of EcoWorx tiles exceeded those of its PVC-backed tiles, Bradfield says. Carpet tiles make up only about 3% of the company's carpet businesses, but Shaw's tile sales are now more than $100 million in a $700 million North American carpet tile market that is enjoying double-digit growth. By 2005, the company expects its carpet tiles as well as its 6-foot-wide roll carpet geared toward health care facilities to be made primarily with the EcoWorx system, he notes. Long-term, Shaw is working to adapt EcoWorx to all of its carpeting, including 12-foot broadloom (wall-to-wall) carpet for contract use and, if successful, residential use.

Richard A. Gross, a chemistry professor at Polytechnic University, Brooklyn, N.Y., was selected as the Green Chemistry Award winner in the academic category for his group's research on a broad range of lipase-catalyzed polyester syntheses. These condensation or ring-opening reactions generally occur in one pot and don't require a solvent. The high selectivity of the biocatalyst streamlines the reactions by eliminating the need for protection and deprotection of reactive side groups. Overall, Gross's enzymatic approach offers environmental and cost benefits over traditional chemical-catalyzed polymerizations, and it's leading to new hydroxyl-decorated polyesters for commercial and medical applications.

"We have shown that lipases can have extraordinary activity to build and modify high-molecular-weight polymers through the formation of ester bonds," Gross says. "The mild conditions under which these reactions can be performed and the selectivity of the catalysts are particularly attractive. Polymer chemists can now consider using these enzymatic methods when they wish to find practical ways to build complex functional structures."

The natural role of lipases is to cleave C–O ester bonds in triglycerides, Gross notes. In polyester syntheses, the enzyme works in reverse, forming C–O ester bonds instead of breaking them. Immobilizing the enzymes on hydrophobic supports allows them to exhibit higher activities than free enzymes, Gross says, owing to interactions between the enzymes and the support surface. These interactions also can lead to better thermal stability, he adds.

One of the most common lipases used in biocatalysis is immobilized Candida antarctica lipase B (CALB). "This enzyme has a remarkable ability to accommodate polymeric substrates," Gross says. As director of the National Science Foundation Center for Biocatalysis & Bioprocessing of Macromolecules, he has worked with enzyme supplier Novozymes to explore the utility of immobilized CALB, particularly the company's commercial product Novozym 435, which is supported on porous polymethacrylate beads.

Gross's group has used Novozym 435 to carry out solventless condensations of polyols (three or more hydroxyl groups) as well as lactone and cyclic carbonate ring-opening polymerizations. Other syntheses include lactone polymerizations using carbohydrate and other initiators that lead to polyesters and polycarbonates with functional end groups. Also, he has shown that Novozym 435 added to the melt of high-molecular-weight polyesters catalyzes rapid transesterification reactions to form block and random copolymers.

In the case of polyol polyesters, Gross's group has demonstrated the condensation of binary, ternary, or more complex mixtures of diacids, diols, and polyols. These polymers can be produced by chemical methods, but multistep protection-deprotection is needed to avoid cross-linking between secondary alcohol groups. The reactions also normally require temperatures above 200 °C, which doesn't allow the use of monomers with thermally sensitive substituents, such as vinyl groups.

"Key to what makes this work interesting is that we are able to form monophasic liquids by simply mixing and heating polyols with diacids and diols without the need for a solvent," Gross points out. "We also have found that under these reaction conditions it isn't necessary to activate the carboxylic acids with electron-withdrawing groups."

The reactions are run under vacuum to remove the water by-product as it forms, he adds. However, the water removal can't be too efficient, he says, since a small amount of water is essential to serve as a kind of lubricant for the enzyme by forming hydrogen bonds with its functional groups, which helps to "unlock" the enzyme structure.

Thus far, Gross has focused on sorbitol or glycerol for the polyol polymerizations. In one reaction, direct condensation of adipic acid and sorbitol was carried out at 90 šC for two days using 1% by weight of CALB. The product, polysorbityladipate, is water soluble with a molecular weight of 17,000. To obtain a water-insoluble polymer, the reaction can be carried out using 1,8-octanediol to replace part of the sorbitol, which gives a terpolymer with molecular weight of 117,000. If these polymerizations had been catalyzed by a chemical system, Gross notes, the products would have been gels or insoluble because of cross-linking.

Another area of investigation in Gross's lab is rapid lactone polymerizations. Prior to 1997, lipase-catalyzed caprolactone ring opening to polycaprolactone required reaction times of four days to reach molecular weights of 2,000, he says. As Gross's group learned how water concentration is critical to molecular-weight control and began using immobilized CALB, high conversion rates were reached in as little as four hours with molecular weights near 45,000.

Some advantages of lipase catalysis over traditional chemical catalysis is that the lipases aren't oxygen sensitive and benefit from the presence of water in reactions, Gross says. In contrast, chemical catalysts are usually water sensitive and require moisture safeguards. Another benefit is that the polymerizations are metal-free. This is important in applications where metals can lead to problems in product use, such as toxicity and interference in electronic materials.

The polyesters made by Gross's group are being explored by member companies of the NSF center for potential applications. "The member companies are free to develop and patent applications for the new materials we develop," Gross says. "They are asking for samples and are coming back for more. That's a good sign."


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