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Volume 86 Issue 33 | pp. 59-68
Issue Date: August 18, 2008

Cover Stories: Sustainability

Calling All Chemists

Chemists and chemical engineers will be providing the thousands of technologies needed to achieve a more sustainable world
Department: Science & Technology | Collection: Sustainability, Green Chemistry
News Channels: Environmental SCENE
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Credit: Fry Design
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Credit: Fry Design

Being Green

The 12 Principles Of Green Chemistry

Green chemistry is the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances. These principles were first published in the 1998 book "Green Chemistry: Theory & Practice," by Paul T. Anastas and John C. Warner, as a means to make the concepts of green chemistry accessible to the scientific community.

  • Prevention
    It is better to prevent waste than to treat or clean up waste after it has been created.
  • Atom Economy
    Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.
  • Less Hazardous Chemical Syntheses
    Wherever practicable, synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment.
  • Designing Safer Chemicals
    Chemical products should be designed to effect their desired function while minimizing their toxicity.
  • Safer Solvents and Auxiliaries
    The use of auxiliary substances (such as solvents and separation agents) should be made unnecessary wherever possible and innocuous when used.
  • Design for Energy Efficiency
    Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. If possible, synthetic methods should be conducted at ambient temperature and pressure.
  • Use of Renewable Feedstocks
    A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable.
  • Reduce Derivatives
    Unnecessary derivatization (use of blocking groups, protection-deprotection, temporary modification of physical-chemical processes) should be minimized or avoided if possible, because such steps require additional reagents and can generate waste..
  • Catalysis
    Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.
  • Design for Degradation
    Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment.
  • Real-time Analysis for Pollution Prevention
    Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances.
  • Inherently Safer Chemistry for Accident Prevention
    Substances and the form of a substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions, and fires.

SOURCE: American Chemical Society's Green Chemistry Institute

Something huge is going to have to give. The energy- and material-rich lifestyle that people in the developed world enjoy simply can't last, and the lifestyle that people in developing regions might aspire to will never happen, without a concerted effort by the global community to start living within the planet's means. Either we find ways to run our societies without squandering natural resources and degrading the environment, or we will foist dire consequences on ourselves for generations to come. The first option requires the world to embrace sustainability.

The concept of sustainability, which traces its roots back to the earliest days of human culture, is easy to describe: A sustainable global society is one in which people today meet their needs without compromising the ability of future generations to live equally well.

But knowing what it will take to gain some measure of sustainability is far more difficult than citing a definition because sustainability is not a final destination. Sustainability instead can be thought of as a general direction in which we all must be traveling. It is a moving target influenced by resource availability, environmental impacts, and unforeseen obstacles.

Our collective fate will come down to our ability to shift the way we produce and consume electricity and fuels and the way we design and use chemicals and the materials made from them. An ineluctable truth for the chemical enterprise is that this task will require thousands of innovations. The multiple pathways we will need to realize these innovations will have to be built by improving the efficiencies of current technologies, creating myriad new technologies, and recycling like never before.

Building those pathways will require not only accelerating the rate of innovation but also creating pragmatic social partnerships between scientists and engineers, research funding agencies, entrepreneurs, product developers, manufacturers, consumers, consumer advocates, regulators, environmental activists, and educators. Together, we will have to work through the multiple dimensions of human societies—technological, environmental, economic, political, and cultural—to ensure that food, water, medicines, electricity, fuels, and materials can be delivered wherever and whenever needed. That is what it will take to conquer the sustainability challenge, and chemists and chemical engineers are smack-dab in the middle of making it happen. It's a huge responsibility.

The late Chemistry Nobel Laureate Richard E. Smalley of Rice University, who died of leukemia at the age of 62 in October 2005, left some good advice on how to pave the way to sustainability. During his final years, Smalley developed a list of 10 challenges facing humanity, with energy standing out as paramount.

"Energy demand is the single most critical challenge facing humanity," Smalley said. "Short of a worldwide catastrophe that wipes out billions of people, science and technology will be required to find energy solutions."

Smalley made the case that solving the long-term energy-demand problem—specifically by obtaining electricity from the sun—would lead to solutions to the successive challenges on his list, including the environment, water, and food. For example, environmental problems are largely due to the way electricity and fuels are produced and used, he said. Solving the world's freshwater needs with a clean environment would in turn help solve food-production problems. Solving water and food problems would help reduce poverty worldwide, which in turn should stave off terrorism and war. Solving all these problems could lead to a reduction in disease worldwide or even to cures for still-incurable diseases, such as the leukemia that killed Smalley.

Smalley is not the only one to have formulated this sort of trickle-down set of ideas. Innumerable blue-ribbon panels, committees, working groups, and symposia have identified important "drivers" for sustainability, in addition to dozens of vital research and education topics that chemists and chemical engineers can pursue to support the global sustainability journey. Because of these events and the scientists behind them, sustainability is now in the consciousness of most chemists, chemical engineers, and indeed most scientists, which was not the case a decade ago. An important notion stemming from these efforts is that adding an environmental or sustainability layer over the traditional approach to science and technology is not a constraint, but rather it is a new and urgent challenge to creativity.

One event that has helped this shift in point of view was "Chemistry for a Sustainable Future," a National Science Foundation workshop held in May 2006 (Environ. Sci. Technol. 2007, 41, 4840). The goal of the workshop and its report, according to workshop cochair Vicki H. Grassian of the University of Iowa, was "to inspire chemists to take on sustainability challenges, questions, and issues and make advances that will positively impact society and influence fields ranging from energy and pharmaceuticals to biomaterials and agrochemicals." Grassian, whose own research involves molecular-level studies of atmospheric and environmental processes at interfaces, is a chemistry professor at Iowa and director of the university's Nanoscience & Nanotechnology Institute.

As Grassian and her colleagues discovered, sitting down and charting a chemical course toward sustainability is not an easy task.

Greengineering

The 12 Principles Of Green Engineering

Green engineering is the development and commercialization of industrial processes that are economically feasible and reduce the risk to human health and the environment. These principles, which were first outlined in 2003 in the American Chemical Society's journal Environmental Science & Technology (2003, 37, 94A) by Paul T. Anastas and Julie B. Zimmerman, add an engineering perspective to the concepts of green chemistry.

  • Inherent Rather Than Circumstantial
    Designers need to strive to ensure that all materials and energy inputs and outputs are as inherently nonhazardous as possible.
  • Prevention Instead of Treatment
    It is better to prevent waste than to treat or clean up waste after it is formed.
  • Design for Separation
    Separation and purification operations should be designed to minimize energy consumption and materials use.
  • Maximize Efficiency
    Products, processes, and systems should be designed to maximize mass, energy, space, and time efficiency.
  • Output-Pulled Versus Input-Pushed
    Products, processes, and systems should be "output-pulled" rather than "input-pushed" through the use of energy and materials. (For example, reactions can be driven by pulling out products rather than increasing inputs such as additional starting material or heat and pressure.)
  • Conserve Complexity
    Embedded entropy and complexity must be viewed as an investment when making design choices on recycle, reuse, or beneficial disposition. (For example, it might be more economically and environmentally beneficial to dispose of highly complex products such as silicon computer chips rather than to attempt to recycle or reuse the material components.)
  • Durability Rather Than Immortality
    Targeted durability, not immortality, should be a design goal.
  • Meet Need, Minimize Excess
    Design for unnecessary capacity or capability (that is, "one size fits all") should be considered a design flaw.
  • Minimize Material Diversity
    Material diversity in multicomponent products should be minimized to promote disassembly and value retention.
  • Integrate Material and Energy Flows
    Design of products, processes, and systems must include integration and interconnectivity with available energy and materials flows.
  • Design for Commercial "Afterlife"
    Products, processes, and systems should be designed for performance in a commercial "afterlife."
  • Renewable Rather Than Depleting
    Material and energy inputs should be renewable rather than depleting.

SOURCE: American Chemical Society's Green Chemistry Institute

"Sustainability is a beast that is hard for people to wrap their arms around," Grassian observes. "It's almost too big of a challenge."

Some of the experts selected to participate in the NSF workshop had difficulty seeing how their work fits into the big sustainability picture, she says. "It's hard to define sustainability in a single chemical concept or with a top 10 list, as there are hundreds of areas that chemists and chemical engineers can work in that are related to issues of sustainability," Grassian points out.

The organizers designed the workshop on four pillars that they believed play an important role in sustainability: green chemistry and engineering, energy, environmental impact, and education. The ensuing discussions led the workshop participants to identify general areas in which advances in science could significantly contribute to sustainability goals. Among these were nanoscience, catalysis, bioprocessing, analytical measurements, and computational science and data information systems.

Chemists are already off to a good start in working on these areas, Grassian says. "But we still need to sharpen our attention to sustainability. The connection between chemistry and sustainability needs to be stronger, and all scientists need to be considering how to best translate their research into sustainable solutions," she adds.

A powerful way to get this culture change going more quickly is through education, Grassian says. "Scientists need to be educated and educate others about sustainability to provide the molecular perspective that is important in evaluating the merits of chemical products and processes for their macroscale impact on society," she says. "It's something we can't ignore any longer."

The more scientists and engineers learn about how nature works and about human wants and needs, the better equipped they can become to develop innovations that are sustainable. But actually using those innovations for sustainable purposes, as Grassian points out, takes awareness. For chemistry, that awareness is embodied in green chemistry and engineering, which is best described as a conceptual framework to guide chemists and chemical engineers to design, manufacture, use, and recycle or dispose of chemical products in an economically, environmentally, and socially responsible way.

Green chemistry and engineering is based on the premise that it is better to prevent waste than to clean it up after it is created. The ideas that form the foundation of green chemistry have been around for at least a century, but the term "green chemistry" was first coined in the early 1990s at the Environmental Protection Agency by Paul T. Anastas, who is now a chemistry professor and director of the Center for Green Chemistry & Green Engineering at Yale University. Anastas also worked on green chemistry and environmental issues in the White House Office of Science & Technology Policy from 1999 to 2004, and he served as director of the American Chemical Society's Green Chemistry Institute from 2004 to 2006.

"The challenges of sustainability are among the most complex and daunting ever faced by society," Anastas says. "It may well be that only by working at the most fundamental level—the molecular level—that we can address these complex global issues in an environmentally and economically sustainable manner."

At first, green chemistry was a means for EPA to promote pollution-prevention strategies by encouraging chemical companies to use alternative chemical feedstocks, solvents, and synthetic pathways that reduce waste and improve energy efficiency. In the mid-1990s, Anastas and Polaroid's John C. Warner, now president and chief technology officer at the Warner Babcock Institute for Green Chemistry, in Woburn, Mass., codified the ideas of green chemistry and made them more broadly available to the scientific community through the "12 Principles of Green Chemistry." Warner spent 1997–07 as a chemistry professor in the University of Massachusetts system, and in 2001 he created the world's first green chemistry Ph.D. program, at the University of Massachusetts, Boston.

In 2003, Anastas and Julie B. Zimmerman, then a University of Michigan environmental engineering graduate student and now an assistant professor at Yale and assistant director of Yale's Center for Green Chemistry & Green Engineering, developed the "12 Principles of Green Engineering." These principles, the first of several sets of green engineering principles developed by various groups, embody the same underlying features as those of green chemistry, but they are written from an engineer's perspective.

The principles of green chemistry and engineering now serve a crosscutting role throughout science and engineering by prompting researchers to efficiently utilize raw materials and avoid toxic and/or hazardous reagents and solvents.

For example, one of the principles relates to atom economy, a concept made popular by Stanford University chemistry professor Barry M. Trost. Atom economy is about designing syntheses that maximize incorporation of all materials used in a process into the final product. Such syntheses produce no by-products. Some reaction types include hydrogenations, carbonylations, and hydroformylations. In one example of a carbonylation, methanol reacting with carbon monoxide produces acetic acid, a reaction with 100% atom economy.

"There are many things people can do to build a sustainable future," Warner says. "Green chemistry is the part that chemists have to do."

Society is demanding environmentally friendlier and safer materials, and industry wants to produce them, Warner notes. "We need armies of students to go into fields of chemistry, chemical engineering, and materials science," he says. "They must learn how to make more sustainable products. It's our job to manipulate molecules and be at the front end to provide alternatives. We are on the supply side of the sustainability curve."

CO2 UTILIZATION
Geoffrey W. Coates and coworkers at Cornell University devised a zinc diiminate catalyst (blue area) that stitches together CO2 and propylene oxide into a biodegradable polycarbonate (red area), the sort of tough polymer used in drinking glasses, DVDs, and lab equipment. The process, which is being commercially developed by Novomer, in Ithaca, N.Y. (C&EN, June 23, page 21), is one of many potential processes that can use CO2 as a chemical feedstock and help mitigate greenhouse gas emissions. In related work, Marco Mazzotti and coworkers at the Swiss Federal Institute of Technology, Zurich, invented a chemical method that uses ground olivine (magnesium silicate, bottom, left vial) to mineralize CO2. The magnesium carbonate product (bottom, right vial), when produced on a large scale, could be buried or used in construction materials.
Credit: H. R. Bramaz/ETH Zurich
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CO2 UTILIZATION
Geoffrey W. Coates and coworkers at Cornell University devised a zinc diiminate catalyst (blue area) that stitches together CO2 and propylene oxide into a biodegradable polycarbonate (red area), the sort of tough polymer used in drinking glasses, DVDs, and lab equipment. The process, which is being commercially developed by Novomer, in Ithaca, N.Y. (C&EN, June 23, page 21), is one of many potential processes that can use CO2 as a chemical feedstock and help mitigate greenhouse gas emissions. In related work, Marco Mazzotti and coworkers at the Swiss Federal Institute of Technology, Zurich, invented a chemical method that uses ground olivine (magnesium silicate, bottom, left vial) to mineralize CO2. The magnesium carbonate product (bottom, right vial), when produced on a large scale, could be buried or used in construction materials.
Credit: H. R. Bramaz/ETH Zurich

Green chemistry is also at the heart of the science underlying the chemical industry's 20-year-old Responsible Care program, which was created in response to the methyl isocyanate leak in 1984 that killed thousands in Bhopal, India. Yet the chemical industry did not openly embrace green chemistry when it was first articulated. For a chemical company to admit that one of its products was somehow not perfect to start with was akin to inviting additional scrutiny by consumers and regulatory agencies, even though green chemistry had its start at EPA. It's true that regulators in the past have issued rules to push companies to develop environmentally friendlier products. But the point of green chemistry is to use innovation to make regulation less relevant, Anastas and Warner point out.

"Green chemistry does not stand for the old model of regulation that industry fears," notes Porter (Bob) R. Peoples, a former carpet industry executive who became director of ACS's Green Chemistry Institute in March (C&EN, April 28, page 54). "Regulation is a means of trying to fix something that is already broken," he says. "Green chemistry and engineering is about making sure we don't create problems from the beginning. We are attempting to make regulation obsolete.

"We have already started down that path," Peoples continues, "but we can't let being perfect get in the way of being good enough and slow us down. It's better to get started, learn as we go, and make modifications along the way—to be like nature and evolve. Nature is very good at keeping what works and getting rid of what doesn't work over time. That is what we have to do as scientists and engineers to solve sustainability issues, and green chemistry is a process—a framework—for helping us to do it."

Credit: H. R. Bramaz/ETH Zurich
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Credit: H. R. Bramaz/ETH Zurich

Peoples hopes to develop greater participation by the chemistry community in the pursuit of green chemistry and engineering and sustainability. "The more perspectives we can bring to the dialogue, the more robust the solutions are going to be," he says. One of his first efforts in that regard was to attend a symposium and policy workshop entitled "Incentives & Barriers to the Adoption of Sustainable Chemistry" at the ACS national meeting in New Orleans in April.

Among the topics discussed was overcoming the lingering mind-set among some in industry that green chemistry is an academic exercise that is not practical in industry because it would be cost-prohibitive. For example, some chemical companies recently have been pushing "sustainable chemistry," which refers to a company's sustainable bottom line, as an alternative to green chemistry. But green chemistry adherents stress that green chemistry is sustainable chemistry. In fact, the many green technologies already in place are the chemical industry's resounding endorsement of green chemistry, they say.

The coveted Presidential Green Chemistry Challenge Awards, an annual program administered by EPA, has singled out some of those technologies for recognition. Since the program's inception in 1995, it has recognized 67 groundbreaking developments out of hundreds of applications. According to EPA statistics, these technologies combined will eliminate an estimated 193 million lb of hazardous chemicals and solvents, 21 billion gal of water, and 57 million lb of carbon dioxide from industrial processing in the U.S. this year.

The 67 winners have collectively made 1.1 billion lb of progress in eliminating hazardous chemicals and emissions over the 13 years of the program, notes Richard Engler, director of EPA's Green Chemistry Program. It's the result of "cleaner, cheaper, and smarter chemistry," he says.

One example from the 2008 class of award winners is a toner for printers and copiers derived from biomass-based feedstocks instead of petroleum. It was developed by Battelle Memorial Institute, the nonprofit science and technology development firm, along with toner producer Advanced Image Resources, in Alpharetta, Ga., and the Ohio Soybean Council.

In the U.S., printers and copiers consume more than 400 million lb of toner each year to make more than 3 trillion copies, according to Battelle. Traditional toners fuse so tightly to paper that they are difficult to remove during the mechanical and chemical treatment steps in paper recycling: This tenacity reduces the fiber strength and quality of recycled paper.

These toners are based on synthetic resins such as styrene acrylates and styrene butadiene. Battelle's toner uses soybean oil and soy protein along with corn sugar as chemical feedstocks to make polyester, polyamide, and polyurethane resins.

The innovation scores a sustainability point by substituting renewable resources for nonrenewable ones. It scores another point by incorporating in the toner chemical functional groups that are susceptible to degradation during the standard de-inking process. That makes the new toner significantly easier to remove from the paper fiber. The toner performs as well as traditional ones but saves significant amounts of energy during recycling and allows a higher fraction of the paper fiber to be recycled for general uses such as tissue, printing, and writing paper.

Preliminary data suggest that with a 25% U.S. market share in 2010, the new toner, which will be sold under the trade names BioRez and Rezilution, could save 9.25 trillion Btu per year in energy—the equivalent of about 1.6 million barrels of oil—and eliminate more than 360,000 tons of CO2 emissions per year.

"Green chemistry and engineering is about making sure we don't create problems from the beginning. We are attempting to make regulation obsolete."

The new toner is just one example of a smart design strategy leading to a greener technology. It is not paradigm-shifting in any sense, but it is the kind of step change that we will need by the thousands as part of the chemical enterprise's contribution to sustainability.

"No one is arguing that green chemistry alone will lead to sustainability," Anastas points out. "However, with green chemistry as an essential guide, the path toward sustainability can be traversed. Without the engagement of green chemistry, the existence of a path is not clear."

As an example, Warner estimates that of all chemical products and processes in existence, perhaps only 10% of them are already environmentally benign, meaning that their production, use, and end-of-life disposal have little environmental impact and little drag on sustainability. Maybe another 25% could be made environmentally benign relatively easily, he says.

"We still need to invent or reinvent the other 65%," Warner says. "Green chemistry is how we can do it."

But it often isn't obvious where a chemical product or process lies on the green spectrum and how well it might contribute to or detract from sustainability. Its impact on resource consumption and on the environment must be quantifiable. Researchers have been developing a host of metrics to do that, and one that is a good barometer for green chemistry is the E Factor.

The E Factor is the total amount in kilograms of solvents, reagents, and consumables used per kilogram of product produced. This metric is an abbreviated version of a complete "cradle-to-grave" life-cycle analysis, which goes beyond production of a chemical or product to include how its raw materials are procured, how the product is used, and how it is recycled or disposed of. Life-cycle analysis includes the associated costs for all phases of a product's lifetime, such as energy and transportation.

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CELLULOSE FEEDSTOCK
A challenge for those aiming to convert biomass into useful chemicals and transportation fuels is the "recalcitrance" of the plant materials—that is, the inability to quickly and economically break down plant cell walls (an atomic force micrograph of switchgrass is shown below) to get at the cellulose and hemicellulose sugars. The Department of Energy is supporting a wide range of research projects involving the high-throughput structural analysis of plant materials, identification of sugars, and genomic investigations that one day could lead to a host of easily processable genetically modified bioenergy crops.
Credit: Shi-You Ding/NREL
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CELLULOSE FEEDSTOCK
A challenge for those aiming to convert biomass into useful chemicals and transportation fuels is the "recalcitrance" of the plant materials—that is, the inability to quickly and economically break down plant cell walls (an atomic force micrograph of switchgrass is shown below) to get at the cellulose and hemicellulose sugars. The Department of Energy is supporting a wide range of research projects involving the high-throughput structural analysis of plant materials, identification of sugars, and genomic investigations that one day could lead to a host of easily processable genetically modified bioenergy crops.
Credit: Shi-You Ding/NREL

These analyses serve as accounting tools for comparing the total environmental and economic impact of products from different processing routes and under different conditions. Not only do they allow scientists to peel back the layers of their processes to see how subtle changes in solvents, water usage, raw materials, catalysts, and process equipment can make a difference, they also give executives and marketing departments leverage with stockholders and consumers.

In 1992, the E Factor was formally introduced by organic chemistry professor Roger A. Sheldon of Delft University of Technology, in the Netherlands. Sheldon, who previously had worked in the fine chemicals industry at Dutch firm DSM, developed the metric "to show students how inefficient chemical processes in the fine chemicals industry actually are," he says. Late last year, Sheldon revisited the E Factor to see how informative it has been after 15 years (Green Chem. 2007, 9, 1273).

The higher the E Factor of a chemical or a chemical process, the more waste it generates, the greater its negative environmental impact, and the less sustainable it is. Small-molecule pharmaceuticals have among the highest E Factors in the chemical industry, with 25–100 kg of additional material consumed per kilogram of product, according to Sheldon's analyses. Fine chemicals used as drug intermediates and in flavors and fragrances are not far behind at 5–50 kg of material consumed per kilogram of product. For comparison, bulk chemicals such as propylene oxide and caprolactam consume less than 5 kg of additional material inputs per kilogram of product, and petrochemicals such as polyethylene and gasoline consume less than 0.1 kg of additional material inputs.

Because the E Factor considers only the amount and not the nature of the material used or waste formed, it remains only a partial measure of the environmental impact of chemical processes. For example, 1 kg of sodium chloride doesn't have the same impact as 1 kg of a chromium salt or 1 kg of dichloromethane solvent. For that reason, Sheldon added a weighting factor for each input or waste, called Q for unfriendliness quotient, to create the Environmental Quotient (EQ) to help balance the analyses. E Factors also do not typically include water because including the amount of process water for heating and cooling, cleaning, and other needs in many cases makes the E Factor so high that meaningful comparisons between processes can't be made.

When comparing E Factors across different sectors, there are a few other considerations to keep in mind. Commercial production volumes of drugs and fine chemicals are much less than that of basic chemicals, but the difference often is offset by the fact that drugs and fine chemicals require many synthesis steps and their use in food and drugs requires their production in high purity. A commodity chemical produced on the scale of millions of pounds per year may produce more total waste, however.

Switchgrass Microfibrils
Credit: Shi-You Ding/NREL

Even at a nominal disposal cost of $1.00 per kilogram of waste, the potential annual savings of waste avoidance are significant. When high disposal costs cut too deeply into the selling price of the product, the product is not sustainable from an accountant's point of view. The bottom-line opportunity to learn how to improve a process through such an analysis is a major reason that the pharmaceutical and fine chemicals industries are leading the way in adopting green chemistry—to lower cost and make more money. They could not be competitive otherwise.

The important contribution of the E Factor and other metrics is that the chemical industry is now seriously thinking and talking about green chemistry and sustainability, Sheldon says. "Fine chemicals and pharmaceutical firms always knew that their manufacturing processes were generating substantial quantities of waste," he notes, "but putting a number to it via the concept of the E Factor really brought the message home."

That message is coming through loud and clear for senior research fellow Sa V. Ho and colleagues at Pfizer's Global Biologics unit, based in Chesterfield, Mo. These researchers turned to the E Factor to get an idea of how green the company's manufacturing processes are for making biopharmaceuticals such as monoclonal antibodies, peptide hormones, and vaccines.

TAMING SODIUM
Pure alkali metals are violently reactive and have historically been hazardous to use and store, limiting their use as reducing agents and catalysts. Researchers at SiGNa Chemistry, in New York City, have worked around the safety issue by encapsulating alkali metals in silica or alumina to form free-flowing powders (shown) that are easy to prepare and handle. The powders are being used in a range of pharmaceutical and petrochemical processes. The materials also react with water to produce hydrogen in quantities needed for fuel cells and are amenable to environmental remediation of toxic chemicals. The technology received a 2008 Presidential Green Chemistry Challenge Award.
Credit: SiGNa
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TAMING SODIUM
Pure alkali metals are violently reactive and have historically been hazardous to use and store, limiting their use as reducing agents and catalysts. Researchers at SiGNa Chemistry, in New York City, have worked around the safety issue by encapsulating alkali metals in silica or alumina to form free-flowing powders (shown) that are easy to prepare and handle. The powders are being used in a range of pharmaceutical and petrochemical processes. The materials also react with water to produce hydrogen in quantities needed for fuel cells and are amenable to environmental remediation of toxic chemicals. The technology received a 2008 Presidential Green Chemistry Challenge Award.
Credit: SiGNa

Manufacturing biopharmaceuticals using biological systems is relatively environmentally friendly compared with the production of small-molecule drugs because the processes use little if any hazardous chemicals, Ho notes. But the downside is that the processes use a lot of water in the large reactors and for purification and cleaning at the end, he says.

One current large-scale cell-culture process to make a monoclonal antibody that the team evaluated requires more than 7,600 kg of material to produce 1 kg of product. Those materials are divided up as 7,000 kg of water, 600 kg of inorganic salts and buffers (which end up in the aqueous waste), 8 kg of organic solvents (primarily alcohols), and 4 kg of consumables such as plastic tubing, filters, and chromatography resins. A typical medium-sized protein produced by genetically engineered Escherichia coli requires about 15,500 kg of material per kilogram of product, divided up as 15,000 kg of water, 400 kg of inorganic salts and buffers, up to 100 kg of organic solvents (some of it hazardous waste), and 20 kg of consumables.

Excluding water, E Factors for manufacture of therapeutic proteins currently are about five times higher than for small-molecule drugs, according to the Pfizer team's initial analysis. These values are only order-of-magnitude estimates for typical processes, Ho emphasizes, because biomanufacturing can vary widely, especially for processes that employ microbes.

Ho and colleagues also took a look at what might be possible by streamlining monoclonal antibody production. For a hypothetical highly optimized process, they found that the amount of material needed could be cut by more than half, from about 7,600 kg to about 3,300 kg.

"The take-home message is that water and some consumables usage could be reduced, perhaps significantly, if we pay attention to improving manufacturing technology," Ho says.

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SUNSHINE TO HYDROGEN
Silicon microwire arrays created by Nathan S. Lewis and coworkers at California Institute of Technology are providing more efficient and affordable means of absorbing sunlight to do useful work in solar cell applications. In this example, the arrays (top) are embedded in a polymer film (middle) and incorporated into a device (bottom ) designed to split water into hydrogen and oxygen with low energy cost and environmental impact; the hydrogen can be used as a chemical feedstock or to power fuel cells to generate clean electricity.
Credit: Courtesy of Nathan Lewis
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SUNSHINE TO HYDROGEN
Silicon microwire arrays created by Nathan S. Lewis and coworkers at California Institute of Technology are providing more efficient and affordable means of absorbing sunlight to do useful work in solar cell applications. In this example, the arrays (top) are embedded in a polymer film (middle) and incorporated into a device (bottom ) designed to split water into hydrogen and oxygen with low energy cost and environmental impact; the hydrogen can be used as a chemical feedstock or to power fuel cells to generate clean electricity.
Credit: Courtesy of Nathan Lewis

Now that the Pfizer researchers have some background data, "we can create a framework within which biologics manufacturing can be analyzed from a green technology and sustainability perspective," Ho notes. The team will continue to pursue its analysis, going deeper, for example, to look at energy usage, the development of continuous-flow reactors and nonchromatographic separations, and the impact of adopting single-use disposable equipment (C&EN, June 4, 2007, page 20) and other production platforms such as cell-free synthesis and genetically engineered crops.

Credit: Courtesy of Nathan Lewis
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Credit: Courtesy of Nathan Lewis

Beyond improving production efficiencies, green chemistry and engineering also address the environmental impact of chemistry. Everything is toxic at some level, so it can never be said that a chemical or chemical product has no toxicity. But it is a worthwhile strategy to move away from chemicals that are persistent, bioaccumulating, or endocrine-disrupting toward ones that are orders of magnitude less hazardous, be they dyes, pesticides, plastics, or pharmaceuticals.

Credit: Courtesy of Nathan Lewis
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Credit: Courtesy of Nathan Lewis

For that reason, one of the key focus areas for chemistry's contribution to sustainability is to better understand the molecular basis of toxicity and for chemists and chemical engineers to be trained in toxicology from the get-go, Anastas points out. By considering the mechanisms of action of toxicity, both in the human body and in ecosystems, green chemistry can guide scientists to design chemicals that are inherently incapable of manifesting a toxic endpoint or greatly disfavoring these toxic mechanisms, Anastas says. That will be a distinct departure from the current approach of making a chemical and then testing to see how toxic it happens to be.

One of the tough challenges standing in the way is that few if any university chemistry programs require any demonstration of knowledge regarding toxicity or the environmental impact of chemicals. Anastas and Warner both recommend that toxicology become basic training for chemists and chemical engineers, so that the next generation of graduates can tackle and render greener that remaining 65% of chemical products and processes that Warner was talking about.

"There are many things people can do to build a sustainable future. Green chemistry is the part that chemists have to do."

To get momentum heading in that direction, Anastas helped lead a first-of-its-kind event at Yale last December. The "Designing Safer Chemicals Summit," as it was called, brought together an international group representing industry, government, academia, and environmental and public health groups with a mix of expertise in toxicology, quantitative structure-activity relationships, biodegradability, and drug design. Anastas cochaired the event with toxicologist Thomas G. Osimitz, who is chief executive officer of environmental product development firm Science Strategies, in Charlottesville, Va. The summit was sponsored by ACS's Green Chemistry Institute through its financial support from the society's Petroleum Research Fund.

"Chemists, who are designing and creating new molecules, generally do not receive any training in toxicology, even though the chemicals they create ultimately may have unintended consequences on human health and the environment," Anastas notes. "Our intent with the summit and follow-up meetings is to remedy this situation by bridging the gap between chemistry and toxicology and harnessing the collective efforts of these two disciplines to design safer chemicals."

The goal is to decrease the intrinsic toxicity of chemical-based consumer products while understanding and better controlling the toxicity of secondary degradation compounds that are generated when products are at the end of their useful life. That means learning how to better recycle materials or not having to worry about them when they degrade in landfills, burn in incinerators, end up as litter, or are dumped illegally.

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CLEANER COUPLINGS
Chemistry professors Robert E. Maleczka Jr. and Milton R. Smith III of Michigan State University received a 2008 Presidential Green Chemistry Challenge Award for their work to improve C–H activation/C–C coupling reactions, one of the most common reactions in organic synthesis. The key advance is an environmentally friendlier iridium-catalyzed reaction to prepare the required boronic ester intermediate that avoids the halogenated precursor traditionally used. The boronic ester subsequently is used to create an array of compounds in one-pot palladium-catalyzed reactions under mild conditions.
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CLEANER COUPLINGS
Chemistry professors Robert E. Maleczka Jr. and Milton R. Smith III of Michigan State University received a 2008 Presidential Green Chemistry Challenge Award for their work to improve C–H activation/C–C coupling reactions, one of the most common reactions in organic synthesis. The key advance is an environmentally friendlier iridium-catalyzed reaction to prepare the required boronic ester intermediate that avoids the halogenated precursor traditionally used. The boronic ester subsequently is used to create an array of compounds in one-pot palladium-catalyzed reactions under mild conditions.

Many people today think that it may be impossible to design safer chemicals that perform their primary functions as well as or better than current gold standards, Anastas says. However, the summit participants identified currently available tools and databases that could be powerful if used in chemical design protocols. For example, EPA's Estimation Program Interface suite of computer models developed over the past two decades permits estimates of the properties and fate of chemicals in the environment. And EPA's ToxCast Program, an initiative launched in 2007, is developing computer models to rapidly forecast the potential human toxicity of chemicals.

This new way of thinking about chemicals and materials should have its greatest impact on emerging areas such as nanotechnology, says University of Oregon chemistry professor James E. Hutchison, who directs the university's Materials Science Institute. Nanomaterials such as carbon nanotubes and metal nanoparticles offer promising solutions to long-standing technological and environmental challenges in areas such as solar energy conversion, medicine, catalysis, and water purification. But because of the diminutive size of the materials, there are concerns about their toxicity, of which little is known so far. There are additional concerns about the amount of resources required to produce and purify the materials.

As nanotechnology continues to develop, Hutchison says, chemists have an opportunity to help shape an entire industry to make products greener from the beginning, before the industry exits its discovery phase and enters the large-scale production phase. For Hutchison's part, his research involves developing new processes to make gold nanoparticles that take advantage of using less toxic reagents and significantly reduce organic solvent use. The work accomplishes those goals while maintaining the high productivity and reproducibility that nanomaterials demand. And as a green chemistry advocate, Hutchison has been involved in national initiatives to ensure nanotechnology's safety is developed through coordinated research efforts that maximize applications while minimizing potential negative impacts (ACS Nano 2008, 2, 395).

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GREEN WITH ENZYMES
Researchers at the biocatalyst firm Codexis engineered three enzymes to create a more efficient synthesis of hydroxynitrile, an intermediate that forms the chiral dihydroxy acid side chain essential to the activity of atorvastatin, the active ingredient in Pfizer's blockbuster cholesterol-lowering drug, Lipitor. This reaction, which earned Codexis a 2006 Presidential Green Chemistry Challenge Award, takes place under milder conditions and requires fewer steps than the chemical synthesis it replaced. It is helping to lower atorvastatin's long-term production costs and reduce the environmental impact of its synthesis.
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GREEN WITH ENZYMES
Researchers at the biocatalyst firm Codexis engineered three enzymes to create a more efficient synthesis of hydroxynitrile, an intermediate that forms the chiral dihydroxy acid side chain essential to the activity of atorvastatin, the active ingredient in Pfizer's blockbuster cholesterol-lowering drug, Lipitor. This reaction, which earned Codexis a 2006 Presidential Green Chemistry Challenge Award, takes place under milder conditions and requires fewer steps than the chemical synthesis it replaced. It is helping to lower atorvastatin's long-term production costs and reduce the environmental impact of its synthesis.

Green nanotechnology has three take-home messages, Hutchison says. "This is a great opportunity to design and manufacture new products right the first time. There's no compromise necessary: We can have the high performance and technological advantages that we want, using less expensive, economically viable processes and materials that are greener and don't cause harm to human health and the environment. And there are real solutions that are available right now to make this happen."

By pulling together the most viable options among thousands of technological innovations that can be designed and developed with a sustainable future in mind, we can achieve the kind of sustainable society that we can be comfortable living in and be proud of having achieved. And if, as Rice's Smalley suggested, we build the path forward by first solving the energy-demand problem, the journey should be much smoother.

Bruce E. Dale, a chemical engineering professor at Michigan State University who is developing biofuels and biobased chemical feedstocks, looks at energy in a different light: "It is not the energy per se but the services that we receive from energy that we value," Dale says. "The energy services that we value are heat to keep us warm, electricity for light to let us see and to power thousands of gadgets, and mobility to transport both ourselves and our goods around." So rather than thinking of having an energy crisis, what the world really has is a heat, electricity, and mobility problem, Dale suggests (J. Agric. Food Chem. 2008, 56, 3885).

One day our descendants could look back at us and shake their heads in angst over how we took petroleum, our most readily available source of hydrocarbons, and squandered it by burning it all up and pumping the CO2 by-product into the atmosphere to wreck the planet. Or they could look back at us in awe and admiration for our creative chemical solutions to the energy-demand problem that allowed us (and them) to be warm or stay cool, see well, and get where we wanted to go.

BIOFUEL HORIZON
Randy D. Cortright, chief technical officer and cofounder of Virent Energy Systems, Madison, Wis., holds a flask of biogasoline prepared in one of the company's pilot reactors (shown). Virent's aqueous-phase reforming process employs proprietary catalysts in a low-energy process to convert aqueous solutions of sugars derived from corn and sugarcane, as well as nonfood hemicellulose sugars, into fuels and chemicals. But unlike most plant-to-biofuel processes that produce ethanol, Virent's process produces nonoxygenated hydrocarbons that are blended to make gasoline, diesel fuel, and jet fuel. The company is also developing a cellulose pretreatment process to completely convert nonfood plant materials such as switchgrass and wood into biofuels.
Credit: Virent
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BIOFUEL HORIZON
Randy D. Cortright, chief technical officer and cofounder of Virent Energy Systems, Madison, Wis., holds a flask of biogasoline prepared in one of the company's pilot reactors (shown). Virent's aqueous-phase reforming process employs proprietary catalysts in a low-energy process to convert aqueous solutions of sugars derived from corn and sugarcane, as well as nonfood hemicellulose sugars, into fuels and chemicals. But unlike most plant-to-biofuel processes that produce ethanol, Virent's process produces nonoxygenated hydrocarbons that are blended to make gasoline, diesel fuel, and jet fuel. The company is also developing a cellulose pretreatment process to completely convert nonfood plant materials such as switchgrass and wood into biofuels.
Credit: Virent

Perhaps one day a rechargeable lithium-ion battery the size of a shoe box will get us 200 miles in our hybrid-electric or fully electric cars (read about plug-in hybrids here). We could recharge our batteries from a dedicated organic thin-film solar cell on the roof of our house or apartment. We wouldn't need to buy a single drop of gas. But if we did take a long trip, an inexpensive biofuel would be available, perhaps the same type of gasoline we currently put in our cars, but made from wood chips or crop wastes. Driving a hybrid diesel? Our diesel fuel could be made from inexpensive oil derived from inedible seeds, animal fat, and bioethanol.

The electricity to power our multiple electronic devices and to control the climate of our homes might come from a solar cell farm. Or it could be generated by large stationary hydrogen- or methanol-powered fuel cells, stored temporarily in batteries or supercapacitors, and then efficiently transported via ambient-temperature superconducting power lines. In the meantime, the technologies to capture, utilize, and pack away CO2 generated during the production of the electricity and the materials needed to build the power grid will be at work preserving the atmosphere (C&EN, April 30, 2007, page 11). Perhaps some of the CO2 will be used to feed ponds of genetically modified algae that produce biofuels, plastics, or pharmaceuticals.

TAPPING THE SUN
Sandia National Laboratories' Richard B. Diver works on assembling the Counter Rotating Ring Receiver Reactor Recuperator (CR5), a solar-heated reactor that uses a ferrite (cobalt-iron oxide) thermochemical cycle to split water to form H2 and O2 or to split CO2 to form CO and O2. The reactor, which is heated to high temperature by sunlight collected and concentrated by a "solar furnace," has 14 rotating alumina rings topped by a layer of ferrite around the perimeter. The rings cycle slowly through two temperature zones, 1,500 °C and 1,100 °C, to facilitate the two reaction steps: oxide reduction to evolve O2 and ferrite reoxidation with water or CO2 to form H2 or CO. In an integrated reactor system, water and CO2 could be converted into synthesis gas (CO and H2), which in turn could be used to produce methanol, gasoline, and other liquid fuels. The prototype reactor is still 15 years or more away from commercialization, but one potential use would be to integrate CR5 units into coal-fired power plants to mitigate CO2 emissions without creating additional CO2 in the process.
Credit: Randy Montoya
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TAPPING THE SUN
Sandia National Laboratories' Richard B. Diver works on assembling the Counter Rotating Ring Receiver Reactor Recuperator (CR5), a solar-heated reactor that uses a ferrite (cobalt-iron oxide) thermochemical cycle to split water to form H2 and O2 or to split CO2 to form CO and O2. The reactor, which is heated to high temperature by sunlight collected and concentrated by a "solar furnace," has 14 rotating alumina rings topped by a layer of ferrite around the perimeter. The rings cycle slowly through two temperature zones, 1,500 °C and 1,100 °C, to facilitate the two reaction steps: oxide reduction to evolve O2 and ferrite reoxidation with water or CO2 to form H2 or CO. In an integrated reactor system, water and CO2 could be converted into synthesis gas (CO and H2), which in turn could be used to produce methanol, gasoline, and other liquid fuels. The prototype reactor is still 15 years or more away from commercialization, but one potential use would be to integrate CR5 units into coal-fired power plants to mitigate CO2 emissions without creating additional CO2 in the process.
Credit: Randy Montoya

Meanwhile, guided by green principles, chemists and chemical engineers might one day realize the ideal chemical process: Renewable feedstocks transformed via a highly selective catalyst based on a low-cost, environmentally friendly metal in continuous flow-through microreactors that permit multiple reaction steps and separation of atom-economical products without the need for a solvent (or just a single solvent such as water or CO2), with the process monitored by in-line spectroscopy. In the end, the process would generate durable and safe products, and when they wear out, they could be completely recycled or disposed of without guilt because their degradation products are completely innocuous.

This ideal sustainable scenario doesn't have to be a daydream. The means to achieve it are already available or are close at hand. But realizing it will not be possible without a commitment for change on the part of global society.

Take for example the size of houses in the U.S. The average area of a home has grown from 1,500 sq ft in 1970 to 2,500 sq ft today, even as the average U.S. household size has shrunk from 3.1 people to 2.6.

Consider further the opulence of a recently built 12,000-sq-ft single-family home in Anne Arundel County, Md., as described by the Washington Post in May. The house has seven bedrooms, six and a half baths, four fireplaces, recreation room, media room, two laundry rooms, two kitchens, and a gym—and it is certified as energy efficient by EPA's Energy Star Program for its green construction features and energy-efficient lighting and appliances. Because of the certification, the builder claims the home is good for the planet.

It's true that energy consumption for this McMansion may be lower than that of a smaller home built a generation or two ago. But in the long run, a house that large isn't sensible and can't be tenable for society, even if the owner can afford it, because it requires unsustainable amounts of wood, water, energy, and other raw materials to produce and maintain, and it would be responsible for more greenhouse gas emissions.

Scientists and engineers can design greener chemicals and create materials to be more energy efficient than ever before. But there has to be common sense in how those chemicals and materials are used. Despite best intentions, inventors often have little control over how their creations ultimately are applied, and that is one reason sustainability will always be a sticky problem requiring some level of government oversight and the moral compass of society to ensure that people do what is right.

Chemists and chemical engineers must help society move beyond the status quo in that regard and become invested in the idea of building innovation into every aspect of the economic, social, and environmental performance of chemicals and chemical products to pave the road to a sustainable future. To do that, scientists involved in the chemical enterprise have to rise to the occasion in thousands of different ways, whether by inventing a better printer toner, car battery, or drug-making process.

 

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