Green In 2015

Twenty years ago, the Environmental Protection Agency, in collaboration with the White House, created the Presidential Green Chemistry Challenge Awards. This year’s awards were unveiled on July 13 in a ceremony held at EPA headquarters in Washington, D.C.

As its name suggests, the program challenges chemists, chemical engineers, and the chemical industry to develop innovative technologies with demonstrable human health and environmental benefits. These include reducing the toxicity of chemical products, reducing the use or generation of hazardous substances, introducing renewable feedstocks, saving water or energy, and reducing waste even if it’s not hazardous. Preventing pollution and promoting sustainability is not enough, however. The technologies must match or improve the performance of existing products and processes and be economically viable.

“This year’s awards are a true tour de force for green chemistry, showing the fullbreadth of this field,” says Thomas M. Connelly Jr., the executive director and chief executive officer of the American Chemical Society, which helps select the award winners through its Green Chemistry Institute. “What the recipients all share is the commitment to new chemistry. Each award shows how creativity and innovation can be harnessed to provide safer and more sustainable starting materials, processing, and products.”

The following vignettes tell the stories of this year’s winners.

Skokie, Ill.-based LanzaTech takes the latter view, considering the gases assets. LanzaTech took home the Greener Synthetic Pathways Award for developing a microbial fermentation process to convert CO and CO₂ in industrial waste gas streams into fuels such as ethanol and commodity chemicals such as 2,3-butanediol.

“Our carbon-recycling platform uses ancient biology to help solve today’s climate and energy challenges,” says LanzaTech CEO Jennifer Holmgren. “We are turning harmful waste emissions from a liability to an opportunity.”

Carbon-laced waste gas streams are an unavoidable consequence of many industrial processes, such as Fischer-Tropsch synthesis of alkanes, methanol production from synthesis gas (CO + H₂), and steel and cement production. The leftover process gas typically can’t be repurposed, so it’s discarded as waste by venting it to the atmosphere or burning it to generate heat.

LanzaTech used genetic engineering tricks to alter the natural ability of gas-fermenting bacteria to alter their natural ability to feed on CO and CO₂. The microbes typically use a cascade of enzyme-mediated reaction steps to convert CO and CO₂ to acetyl-CoA, an intermediate that they use to make ethanol. LanzaTech’s new strains are capable of converting acetyl-CoA into acetic acid, 2,3-butanediol, or other chemicals in addition to ethanol.

The company’s life-cycle analysis of its process reveals that starting with steel mill off-gases reduces greenhouse gas emissions more than 70% compared with starting from natural gas, coal, or petroleum feedstocks. LanzaTech’s analysis also shows that particulate matter and emission of nitrogen oxides could be reduced by 80%.

“LanzaTech’s gas fermentation process is an excellent example of the benefits of recycling,” comments Wei Zhang, director of the Center for Green Chemistry at the University of Massachusetts, Boston. “This technology will have a huge impact on fast-growing regions, such as in China, where the balance between expanding manufacturing, resource preservation, and environmental protection is important.”

LanzaTech has scaled up its process with two 100,000-gal-per-year demonstration facilities in China that use steel mill waste gas to make ethanol. The company is also getting set to start up a 30 million-gal-per-year facility in Taiwan and is planning a 15 million-gal facility in Belgium.

Polyisobutylene is one of those industrial chemicals that you never hear about, even though it plays an important role in our everyday lives. In its chief application, polyisobutylene is an intermediate used to prepare performance-enhancing additives for lubricants and gasoline.

The polymer is typically made using solutions of a toxic and corrosive Lewis acid catalyst such as BF₃, which requires costly handling equipment and generates millions of gallons of wastewater per year. Soltex, based in Houston, landed the Greener Reaction Conditions Award for alleviating those problems by inventing a fixed-bed solid-state catalyst reactor system that replaces the catalyst solution with a BF₃-alcohol complex affixed to alumina particles.

In traditional polyisobutylene production, the acid catalyst continually feeds into the reactor and mixes with isobutylene monomer. Because of its reactivity, the catalyst needs special handling to avoid exposure to air. As the mixture leaves the reactor, the catalyst must be neutralized with a base to stop the reaction. The subsequent product separation step involves washing the polymer with copious amounts of water to remove all traces of the catalyst. Any corrosive residue that remains can be detrimental to polyisobutylene quality and stability.

In Soltex’s system, isobutylene enters the reactor and flows over the solid catalyst, allowing the polymerization to occur and the polymer to exit—no subsequent neutralization or water wash is required. Unlike the traditional process, in which the neutralized catalyst can’t be recycled, the solid catalyst can be used indefinitely until it needs to be regenerated or replaced.

Overall, the new technology dramatically saves water and energy, is safer for workers, provides a better quality product, and cuts operating costs, according to Soltex CEO Tony Massoud. The company has a pilot-scale plant operating in Pasadena, Texas, and projects that its process will lower the capital cost of building new commercial-scale polyisobutylene plants by 35%.

“Many academic labs may consider water-based reactions and separations as green chemistry practices,” comments Wei Zhang, director of the Center for Green Chemistry at the University of Massachusetts, Boston. “But it may not be the case in chemical production because removing water from the product takes a lot of energy, and wastewater treatment can be costly. Soltex’s approach is a good example of redefining specialty chemical production with environmental and economic benefits.”

Isocyanates are notorious for their bad smells. But the odors are just the tip of the iceberg: The compounds are also eye, skin, and lung irritants and potential carcinogens. Even so, the chemicals are critical to the production of polyurethane paints, coatings, adhesives, and foam insulation—some of the most useful materials ever invented.

Nanotech Industries (NTI), based in Daly City, Calif., and its commercial arm, Hybrid Coating Technologies (HCT), received the Designing Greener Chemicals Award for creating the first polyurethanes that don’t need isocyanates in the production process. The new formulation, called Green Polyurethane, instead uses cyclic carbonates and amines to replace isocyanates and polyols.

“Residual isocyanates found in incompletely cured polyurethane coatings and during the creation of polyurethane foams are known to have adverse health effects,” comments Martin J. Mulvihill, executive director of the University of California, Berkeley, Center for Green Chemistry. “They are recognized as the leading cause of occupational asthma in the U.S. and other industrialized countries, leading California to identify them as a priority substance for removal from consumer products. This new technology has the potential to make applying durable coatings and using foam insulation much safer.”

NTI/HCT developed their nonisocyanate polyurethanes by coupling a mixture of cyclic carbonates and epoxide oligomers with polyamines. The result is a new type of cross-linked polymer containing β-hydroxyurethane groups—a polyhydroxyurethane. But the kinds of polymers that can be made this way are limited by the lack of variety of cyclic carbonates. So the companies developed hydroxyalkyl urethane oligomers that contain multiple functional groups and are made in part from vegetable oil. They’re added as modifiers to the base polyurethanes to diversify the resulting polymers.

“We believe we have an obligation to continually search for safer and more renewable chemical and material solutions,” says Darin Nellis, HCT’s director of sales and marketing. “That’s why we have been working diligently to improve the safety of polyurethanes without sacrificing on quality and performance.”

Green Polyurethane paints and coatings for floors, cargo ships, and other applications have double the wear resistance, 10 to 30% better adhesion, and increased chemical resistance over conventional polyurethanes, Nellis notes. The foam has one of the highest R-values per inch—a measure of thermal resistance—of all insulation materials, and nearly double the tensile strength of conventional polyurethane foam.

The new paints and coatings are being sold directly to contractors globally, and the companies are developing a do-it-yourself floor product for sale in home improvement stores. They are also in the process of commercializing spray polyurethane foam and flexible foam.

Accessing the sugar in corn and sugarcane to make ethanol and related biobased chemicals is relatively easy. Processors extract starch from corn and use enzymes to convert it to sugar or squeeze out cane juice.

But when it comes to taking advantage of the sugar in the cellulosic parts of plants, such as in agricultural crop residues or wood chips, a little more work is involved. Processors must use a combination of acid, enzymes, and solvents to unlock the cellulose and hemicellulose biopolymers and free up the sugars. The extra cost has limited the market for cellulosic ethanol and chemicals.

Renmatix, with headquarters in King of Prussia, Pa., garnered the Small Business Award for its Plantrose process that uses supercritical water hydrolysis as a cleaner, faster, and more economical technology for processing biomass.

“Supercritical fluid processing has been a hot topic in green chemistry research, and the Renmatix technology is a great example of its application,” comments Martin J. Mulvihill, executive director of the University of California, Berkeley, Center for Green Chemistry. “The fact that the company is able to use a wide range of different plant feedstocks while avoiding costly enzymes or potentially harmful acids makes this approach very attractive.”

Under the high temperature and pressure conditions of supercritical processing—about 375 °C and 220 bar for Renmatix—water’s structured hydrogen-bonding network comes apart and its density and dielectric constant decrease. This enables the liquid to dissolve the cellulosic material. In addition, the dissociation of water produces catalytic hydronium and hydroxide ions that help dice up the cellulosic chains into sugar molecules.

In the two-step Plantrose process, the plant material and water feed into a reactor at about 200 °C, where hemicellulose solubilizes into the C₅ sugar xylose. The cellulose and lignin pass on to the supercritical water reactor, where cellulose undergoes hydrolysis to the C₆ sugar glucose. The lignin solid that remains can be burned to generate heat or electricity to run the process, or it can be chemically converted to phenolic compounds to make adhesives or thermoplastics.

“Renmatix has strived to create a process that embodies the tenets of green chemistry and engineering using nonhazardous materials with economics that can be cost-competitive with petroleum,” says Mike Simard, the company’s director of engineering. Renmatix is now operating a demonstration plant in Kennesaw, Ga., and is licensing the technology to ethanol and chemical producers to build their own plants to take advantage of different types of locally available biomass.

Blue-green algae, also known as cyanobacteria, are one of nature’s most efficient practitioners of photosynthesis. Yet developing a commercially viable process to harness the algae for converting carbon dioxide into biofuels and chemicals has remained elusive. But that could be set to change.

Algenol, based in Fort Myers, Fla., was given the Climate Change Award for developing a promising new type of photobioreactor that enables genetically enhanced strains of algae to work more efficiently.

“Carbon dioxide is an ideal carbon source for green chemistry transformations,” comments Martin J. Mulvihill, executive director of the University of California, Berkeley, Center for Green Chemistry. “In the mid-2000s, there was a proliferation of algae biofuel companies that promised to turn CO₂ into fuel using only sunlight. A decade later, there are few players in the algae biofuel space. Algenol has survived in large part because of its impressive efficiency for photosynthetically fixing carbon.”

When it comes to growing algae, one limitation has been uniform penetration of sunlight throughout large bioreactors. The algae need enough light to carry out photosynthesis. But if overexposed, the algae must work overtime to dissipate the excess energy, so photosynthesis is less efficient.

Algenol’s thin, vertical photobioreactors offer an advantage over first-generation thick, horizontal systems by providing an optimal amount of light over a greater surface area. The company’s algae are able to feed on CO₂ trapped from industrial smokestacks and divert more than 80% of the carbon they consume into the ethanol production pathway. As a bonus, the algae grow in a minimal amount of saltwater that can be taken from the ocean or brine aquifers rather than using up freshwater resources. The company also developed a process for turning waste algae into biocrude oil that can be converted into fuels and chemicals.

Algenol has achieved yields of 7,000 gal of ethanol per acre per year at a pilot facility, which dwarfs the roughly 420 gal of ethanol that can be produced per acre of corn and 860 gal per acre of sugarcane, says Paul Woods, Algenol’s founder and CEO. The company recently completed construction of a 2-acre demonstration facility containing nearly 8,000 bioreactors. Even though the facility consumes about 75 tons of CO₂ per acre per year, that’s still a drop in the bucket in terms of curbing global greenhouse gas emissions.

But the company is thinking much bigger. Woods sees a future where commercial facilities will have multiple 2,000-acre blocks of the bioreactors. “Our real goal is to consume 1 billion tons of CO₂ per year,” he says.

Condensation reactions that fuse molecules together are a common occurrence in chemistry. However, they typically are not green because they often require unsustainable use of metal catalysts and generate waste as unneeded molecule fragments such as water, ethylene, methanol, or acetic acid are discarded.

Chemistry professor Eugene Y.-X. Chen of Colorado State University got the nod for this year’s Academic Award for designing condensation reactions that use organocatalysts to upgrade the biomass-derived feedstock chemical 5-hydroxymethylfurfural (HMF) into higher value products and to make biodegradable acrylate-based polyesters in metal-free, and in some cases solvent-free, processes that are 100% atom-economical.

In one example, Chen and Dajiang Liu discovered an N-heterocyclic carbene (NHC) catalyst for upgrading HMF. In a biorefinery, HMF derived from sugar must be modified via C-C bond-forming and other reactions to make transportation fuels and commodity chemicals. Direct HMF self-condensation has been hampered because the molecule lacks a necessary hydrogen atom in the α-position to the carbonyl group and it carries a reactive hydroxyl group.

Chen and Liu found through mechanistic studies that the NHC catalyst acts to reverse the polarity of the HMF carbonyl, thereby allowing a selective condensation reaction to occur to form a new dimeric compound, 5,5´-dihydroxymethylfuroin. The furoin can subsequently be used to make diesel and jet fuel as well as fine chemicals and polymeric materials.

“The new reaction successfully integrates multiple green chemistry components, including organocatalysis, metal- and solvent-free chemistry, minimal waste, atom economy, and biodegradable products,” comments Wei Zhang, director of the Center for Green Chemistry at the University of Massachusetts, Boston. “It serves as a textbook case of green synthesis.”

On a separate front, Chen and Miao Hong became interested in expanding the versatility of acrylate-based monomers by using polycondensation reactions to make biodegradable polyesters. Acrylic monomers are typically polymerized exclusively through polyaddition reactions to make nonbiodegradable polyacrylates. And existing metal-catalyzed olefin metathesis is ineffective for polymerizing dimethacrylate monomers needed to make polyesters because they are electron-deficient and sterically hindered. Chen and Hong found an NHC catalyst that overcomes those barriers and selectively promotes polycondensation of dimethacrylates to form unsaturated polyesters.

“The new organocatalytic approach is very exciting because it promotes condensation reactions that haven’t been possible using traditional metal-based catalysis,” says Martin J. Mulvihill, executive director of the University of California, Berkeley, Center for Green Chemistry. “This work coming from Chen’s lab is a great example of how green chemistry can expand the toolbox for chemical transformations.”