"We have changed innumerable things in the practice of chemistry, but the most important thing we have changed is our minds," commented American Chemical Society President William F. Carroll, speaking last week at a ceremony honoring the winners of the 2005 Presidential Green Chemistry Challenge Awards. A few moments earlier, Carroll had recounted a story about how, during a recent discussion in China, one student's pronouncement that "pollution is inevitable with growth and progress" had stopped him cold.
"From the perspective of the chemical industry, pollution and progress are not synonymous," Carroll recalled telling the student. "Pollution is waste, and waste means cost." Carroll followed up by telling the student that the job of chemists is not to find a singular solution to a technical problem, but to challenge themselves to constantly find better solutions. "That understanding is fundamental to what we call green chemistry," Carroll said.
Green chemistry is all about more efficient production of industrial chemicals, pharmaceuticals, and consumer products. That is to say, the purpose of green chemistry is to find ways to develop ever-better chemical products and processes that require fewer reagents, less solvent, and less energy to produce, while being safer, generating less waste, and increasing profitability.
The concept of green chemistry was formally established at the Environmental Protection Agency about 15 years ago in response to the Pollution Prevention Act of 1990. The principles that guide green chemistry may seem intuitive or be viewed simply as common sense, but over the years they have become an intangible framework for the chemical community. Today, these principles are ingrained in the day-to-day operations of companies and increasingly are being incorporated into empirical research carried out at universities and national labs.
Last week, EPA presented the 10th Annual Green Chemistry Awards in conjunction with ACS, the Green Chemistry Institute, and other partners to reward noteworthy successes in green chemistry. The awards were given to five companies and an individual during a ceremony held on June 20 at the National Academy of Sciences in Washington, D.C.
The awards ceremony took place on the eve of the 9th Annual Green Chemistry & Engineering Conference, which this year was held in conjunction with the 2nd International Conference on Green & Sustainable Chemistry. Incentives and barriers to adopting greener technologies were a primary topic of discussion throughout the week of plenary sessions, technical symposia, and workshops that featured talks by the award winners.
EPA solicits Green Chemistry Award nominations in five categories: alternative synthetic pathways, alternative solvents and reaction conditions, designing safer chemicals, small business, and academic. An independent panel, appointed by ACS, judges the nominations and selects the award winners.
The Pollution Prevention Act "formally recognized what we had learned--that laws and regulations alone are not enough to solve our toughest environmental problems," noted Margaret N. Schneider, acting deputy assistant administrator of EPA's Office of Prevention, Pesticides & Toxic Substances. "What we needed was the creation of scientific and technical innovations that eliminate pollution before it's created, which we see reflected in the Presidential Green Chemistry Challenge Awards."
The results of the awards program "are pretty impressive," Schnieder added. Since it began, EPA's tracking of the impact of the winning technologies shows them to have prevented on average 140 million lb of hazardous substances from being produced each year, saved more than 55 million gal of process water per year, and prevented 57 million lb of carbon dioxide emissions per year, she noted. "In total, by our current conservative estimates, green chemistry technologies are preventing more than 3 billion lb of hazardous materials or waste per year."
There was a bit of a surprise for the alternative synthetic pathways category this year, as the selection committee named two winners. Merck was recognized for its redesign of the synthesis of aprepitant, the active ingredient in Emend, a drug used to reduce nausea and vomiting caused by cancer chemotherapy. Archer Daniels Midland and Novozymes were recognized for jointly developing an enzymatic method to produce ADM's NovaLipid line of zero- and reduced-trans-fat oils used in food processing.
Aprepitant selectively binds and blocks the neurokinin receptor NK1. This receptor normally binds substance P, a peptide neurotransmitter associated with a host of central nervous system and digestive functions.
The original Merck synthesis of aprepitant was workable, and it allowed the company to move toward commercialization. But it wasn't sustainable from a green perspective, noted R. P. (Skip) Volante, Merck's vice president of process research. For example, the synthesis was carried out in six steps and required some hazardous chemicals, such as sodium cyanide, dimethyltitanocene, and gaseous ammonia. Some steps needed cryogenic temperatures, and others generated by-products such as methane and magnesium chloride. As the drug was wending its way through clinical trials, the process research team decided that an entirely new synthesis was needed.
"At Merck, we are driven in process research by our mission statement to design elegant, practical, and efficient syntheses that are environmentally and economically viable," Volante told C&EN. "For aprepitant, we were able to use the latest technology and our fundamental understanding of chemistry to improve the synthesis and make a greener process work."
Aprepitant has a morpholine core with two substituents attached to adjacent ring carbons and a third substituent attached to the morpholine ring nitrogen. "Overall, the molecule contains three chiral centers in close proximity to one another as part of a β -amino acetal arrangement, making it a challenging synthetic target," Volante noted.
The new synthesis assembles aprepitant in only three steps by merging four compound fragments of comparable size and complexity (J. Am. Chem. Soc. 2003, 125, 2129). To begin, enantiopure trifluoromethylated phenylethanol is coupled to a racemic morpholine precursor. The desired isomer of the resulting intermediate crystallizes out of solution, leaving behind an undesired isomer.
But rather than separating and discarding the unwanted isomer, the chemists control the reaction conditions to achieve a "crystallization-induced asymmetric transformation," converting the unwanted isomer completely to the desired isomer, Volante said. In the additional two steps, a fluorophenyl group is stereoselectively attached to the morpholine ring and a triazolinone side chain is added to the ring.
The streamlined route doubles the overall yield to 76% and significantly reduces operating costs and the environmental impact, Volante pointed out. Besides eliminating several hazardous reactants, the synthesis has reduced both the amount of water used and the amount of reagents and solvents needed by 80%. Relative to the initial synthetic route, 340,000 L of waste has been eliminated per metric ton of aprepitant produced, an 85% reduction. Because the new synthesis was implemented during the first year of aprepitant production, the benefits will be realized over nearly the entire product lifetime, he said.
ADM and Novozymes put their talents together to develop NovaLipids, a new brand of zero- and reduced-trans-fat vegetable oils that are being used to make margarine, processed baked goods, and other foods. Equally important to developing NovaLipids were ADM's process scale-up expertise and Novozymes' Lipozyme immobilized lipase, noted Inmok Lee, ADM's manager of vegetable oil research. "Our interest was in developing oils suitable for making low-trans-fat versions that perform equally or even better than currently used oils," he said.
Trans fats have been identified as culprits contributing to elevated blood levels of low-density lipoprotein--the so-called bad form of cholesterol implicated in cardiovascular diseases--while decreasing the high-density "good" form of cholesterol. Food processors are under consumer pressure to reduce the amount of trans fat in foods. As an added incentive, the Food & Drug Administration has issued rules for mandatory listing of trans fat on nutritional labels beginning next January.
Food processors traditionally have partially hydrogenated the unsaturated fatty acid chains in vegetable oils using a nickel catalyst. Hydrogenation allows control over the melting characteristics of the oils, which are important to obtain the desired texture and taste of foods. But the process leads to some isomerization of the double bonds, converting cis isomers to trans isomers.
One way to avoid forming trans fats is to use fully hydrogenated oil and "interesterify" it with unhydrogenated oil, Lee explained. Interesterification typically has been a chemical process that uses sodium methoxide to cleave and randomly exchange the positions of the three fatty acid chains of the various triglycerides in oils.
Chemical interesterification avoids formation of additional trans fats, but a downside is that it produces triglycerides with a saturated fatty acid chain in the 2-position, which is not normally encountered in vegetable oil. Chemically interesterified oil also must be washed with water and sometimes acid to eliminate by-product fatty acid salts (soaps), and the oils from hydrogenation or interesterification must be bleached with citric acid and clay to remove off-color contaminants.
Lipases are generally known to hydrolyze the fatty acid ester bonds of triglycerides to form free fatty acids. But when the moisture content of the oil is kept low, Lee said, lipases can also catalyze interesterification. Low stability of the enzymes and high production costs previously had been barriers to industrial processes using lipases, however.
Novozymes in time developed a technique for immobilizing a selected lipase by spraying the enzyme along with a binder onto porous silica granules, greatly reducing the cost of immobilization. The granules are insoluble in the oil and are used as a heterogeneous catalyst for interesterification in fixed-bed reactors. ADM subsequently developed pretreatment processes to purify oils before interesterification to increase the useful life of the immobilized enzymes, Lee noted.
A bonus benefit of Lipozyme is that the enzyme is selective and interchanges the fatty acid groups only between the 1- and 3-positions of the triglycerides, he added. This leaves the fatty acid chain in the 2-position untouched, resulting in a "more natural" oil. In addition, the only postreaction processing needed is a deodorizing step.
Since July 2002, ADM has produced more than 15 million lb of lipase-interesterified oils, and the company is currently expanding the process, Lee said. "Enzymatic interesterification has provided savings in capital and operating costs for ADM, while NovaLipid products have provided food companies with a broad range of options for zero- and reduced-trans-fat products," he noted. "The benefit of enzymatic interesterification will depend upon how successful this process will be at supplanting partial hydrogenation."
One of the most important issues for paints and coatings manufacturers in recent years has been to develop new products--and new technologies to apply them--that reduce volatile organic compound (VOC) emissions to meet more stringent environmental, health, and safety regulations. The impact these changes are having on the industry is reflected in the new products developed by winners of Green Chemistry Awards in two categories.
In the alternative solvents and reaction conditions category, BASF was honored for its acrylate-based UV-cure paint primer for small automotive repairs. The primer was designed to replace infrared- or heat-cured diisocyanate-based primers in order to significantly reduce VOC emissions that are concerns for auto body repair shops, as well as to reduce repair time and costs.
Traditional primers used in automobile repairs are two-component systems consisting of a hydroxyl-containing polyacrylate solution and an aliphatic polyisocyanate, according to Bradley M. Richards, BASF's manager for coatings R&D. The components are mixed before application, and they polymerize (cure) when heated to give a high-performance acrylic urethane film to match the original finish applied by the automaker, he explained. The curing process typically takes 30 minutes or longer in a natural-gas-heated oven. Low-VOC waterborne coatings are also used in repairs, but they require long drying times as well.
BASF's new primer is a one-component urethane acrylate oligomer that, when exposed to a handheld UV lamp, cross-links to form an acrylic urethane film in just two to three minutes, Richards noted. The primer also can be cured in direct sunlight with a two- to five-minute cure time.
"One of the benefits of the oligomer is that it has a lower viscosity and a narrower molecular-weight range, so the VOCs are lower," Richards told C&EN. The UV primer contains one-third to one-half the amount of VOCs per gallon as conventional primers, he added. Also, it's more durable, and application equipment requires less frequent cleaning than with conventional primers.
The company is currently offering the primer in its R-M product line as Flash Fill VP126 and in its Glasurit product line as 151-70. The primer is part of BASF's plan for a complete ecoefficient auto refinishing coating system, including the foundation layer, primer, color base coat, and final clear coat. BASF expects its UV-cured primer to eventually be used in many of the 50,000 body shops in North America.
In addition to its Green Chemistry Award in the alternative synthetic pathways category, ADM also garnered the award in the category of designing safer chemicals for its nonvolatile Archer RC (reactive coalescent) propylene glycol monoester, an additive for latex architectural paints.
Coalescents are chemical agents that help latex particles in paints flow together to form a continuous film for a smooth finish. A primary coalescent used in the industry is 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (TMB), but it's volatile and escapes from the paint as it dries. An estimated 120 million lb of volatile coalescing agents are lost to the atmosphere in the U.S. each year, according to ADM.
"There's a need to lower VOCs in latex paints from a regulatory standpoint, so that is the first application ADM has focused on for Archer RC because it will have the biggest impact," noted Paul D. Bloom, ADM's manager of new industrial chemicals. "But there are many other possible uses for Archer RC as a nonvolatile carrier." Some examples include inks, caulks, and alkyd paints.
Archer RC is made by chemical interesterification of the fatty acid chains of triglycerides in corn oil, followed by removal of the glycerol, Bloom explained. The glycerol coproduct is a useful material for other applications, he added.
Archer RC and TMB have similar structures, except that Archer RC has a long fatty acid hydrocarbon tail, approximately 60% of which is linoleic acid, that significantly increases the molecular weight and reduces the volatility, Bloom said. Double bonds in the fatty acid chain are the "reactive" part of the coalescent, allowing the compound to oxidize and cross-link into the paint film, further reducing the chance that the compound will evaporate. Besides reducing VOC emissions, paints using Archer RC have less odor, increased scrub resistance, and better gloss than paints containing TMB, according to independent lab tests.
Metabolix, Cambridge, Mass., was selected as the award winner in the small business category for developing a fermentation process to produce polyhydroxyalkanoate (PHA) "natural plastics" from renewable feedstocks such as plant sugars or oils. These readily biodegradable polyester polymers and copolymers combine the film-barrier properties of polyesters with the mechanical performance properties of petroleum-based polyethylene and polypropylene. Metabolix is set to start making PHAs on a large scale. It will join Cargill and DuPont--former Green Chemistry Award-winning producers of NatureWorks and Sorona, respectively--as producers of biobased polymers.
"This award recognizes Metabolix' success in transforming PHA natural plastics technology from a biological curiosity to a commercial reality," noted Oliver P. Peoples, one of the company's founders and its chief scientific officer.
Some bacteria naturally synthesize PHAs for energy storage, much the way animals produce fat. In the late 1980s, Peoples and Anthony J. Sinskey, working together at Massachusetts Institute of Technology, took advantage of this biopolymerization process and used metabolic engineering techniques they developed to incorporate a series of genes from various PHA-producing bacteria into a strain of Escherichia coli. The genes in turn express enzymes that can convert sugar or oil into polymers via a multistep process within the bacterial cells. Metabolix was formed in 1992 to commercialize the technology.
The properties of PHAs range from rigid to elastic, depending on the length of side chains or type of copolymer, and they are suitable for processing into films, fibers, and molded goods using conventional polymer-processing equipment, according to James J. Barber, Metabolix' president and chief executive officer. The plastics have a long shelf life, he said, yet they quickly biodegrade in soil or water to produce CO2 and water (in aerobic environments) or CO2 and CH4 (in anaerobic environments).
The company has developed the technology with private funding and with competitive grants from the Department of Commerce's Advanced Technology Program and from the Department of Energy. Last fall, Metabolix announced a joint venture with ADM to commercialize PHAs and to construct a 50,000-ton-per-year plant based on corn sugar in the Midwest.
The key markets for PHA plastics include food packaging; disposable and single-use items, such as dinnerware and coated-paper hot-beverage cups; and agricultural and soil-stabilizing applications requiring biodegradation.
Separately, in a program sponsored by the Department of Agriculture, Metabolix is developing genetically engineered plants, such as switchgrass, a native prairie grass, that can directly produce PHAs in plant cells. The PHAs could be processed as polymers or depolymerized to form hydroxy acids for use as chemical feedstocks, and the residual plant material could be burned for energy or converted to liquid fuels. Metabolix recently formed a collaboration with BP to further develop the plant-based technology.
"The successful development of crop-based PHA natural plastics, in addition to our fermentation-based products, will provide the world with a range of agriculturally derived polymer products as alternatives to petrochemical plastics," Barber said.
Robin D. Rogers, Distinguished University Research Professor at the University of Alabama, Tuscaloosa, received the academic award in the area of alternative synthetic pathways for developing ionic liquids as recyclable solvents. The award specifically recognizes Rogers' work using ionic liquids to dissolve and process cellulose into advanced functional materials for use in textiles, sensors, and plastics.
Cellulose is an abundant and inexpensive renewable material that could replace synthetic polymers in select applications, Rogers said. Although cellulose has been widely studied, its use has been limited because it's insoluble in water and most common organic solvents. Using ionic liquids to dissolve and reconstitute cellulose could reduce volatile emissions common in cellulose processing, decrease energy requirements, and expand the potential applications for cellulose, he noted.
"If we can directly utilize the biocomplexity Mother Nature has provided with cellulose to form new materials, we could eliminate many unnecessary synthetic steps," Rogers told C&EN.
Ionic liquids typically consist of nitrogen-containing organic cations and inorganic anions, such as imidazolium salts, that are stable, nonvolatile liquids at room temperature. They are beginning to be used as industrial solvents for polymer processing, extraction and separation processes, and organic synthesis.
Rogers' group found that cellulose readily dissolves in ionic liquids with gentle heating. So far, the group has demonstrated that cellulose from wood pulp, field cotton, and other sources rapidly dissolves in 1-butyl-3-methylimidazolium chloride.
Other polymers, nanoparticles, metal-complexing agents, dyes, or biomolecules such as enzymes can be added as solutions to make functional materials, Rogers pointed out. "The ionic liquid is simply the enabler," he said.
Cellulose can be precipitated from ionic liquids by adding water, ethanol, or acetone, and the ionic liquid can be recovered for reuse. The regenerated cellulose can be formed into different architectures, ranging from beads to fibers to films.
Rogers, who is director of Alabama's Center for Green Manufacturing, is working with several colleagues at Alabama and elsewhere to license the patents on the cellulose processing and to start a company, called 525Solutions, to develop specific new products. The company is being launched under the guidance of the Alabama Institute for Manufacturing Excellence and will be led by Richard P. Swatloski, a recent Ph.D. graduate from Rogers' group who has worked on the cellulose project.