Better living through green chemistry ‐ New Scientist Friday, March 12, 2010

Better living through green chemistry 12 March 2010 by Sarah Everts

Getting greener (Image: Chris Salvo/Taxi/Getty)

COLOUR ME GREEN PASS by a chemical plant, and the plumes billowing from its smokestacks may get you thinking. What filthy concoctions are being brewed inside, and what nasty stuff is it spewing into the environment? You could be right to worry. The chemical industry relies on many ingredients that in the wrong place are harmful to the environment, human health or both. If that turns your nagging doubt into a full-blown headache, popping a pill will only make it worse: pharmaceuticals are just one of the resulting products that few of us could do without. Short of getting rid of our drugs, paints, plastics and textiles, what can be done? Quite a lot, actually. Beyond the bubbling syntheses that make the chemical products we all rely on, a different sort of chemical transformation is now taking place. Catalysed by yo-yoing oil prices, new regulations and pressure from consumers and retailers, industrial chemistry is getting cleaner. Products as diverse as the shoes we wear, the soap we wash with and the decaf we drink are starting to be manufactured in processes with a green tinge. The concept of "green chemistry" dates back to the mid-1990s, when two US chemists, Paul Anastas and John Warner, were lamenting that most strategies to combat pollution focused on cleaning up messes rather then preventing them in the first place. They set out a 12-point manifesto for a better way of working, starting with the tenet that it is better to avoid waste than to have to dispose of it. That was followed by calls for renewable starting materials, fewer harmful solvents, more efficient catalysts and minimising energy use by, for example, designing reactions that could work at ordinary, ambient temperatures. These principles might seem like common sense, but they are a step change for many industrial chemists and process engineers. Take solar panels. The energy used to make them takes away some of their sustainable-energy shine, that much is clear, but what about the materials they

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contain? Often these are toxic, come from petrochemical sources or contain scarce metals. The principles of green chemistry require all this to be taken account throughout the lifetime of a product and beyond. "We'd ask: are there toxic materials there which could cause environmental catastrophe when they are put into landfill 20 years down the road?" says Warner.

Oil decline Since 1996, the best of such thinking has been recognised by the US Environmental Protection Agency (EPA) through its Presidential Green Chemistry Challenge awards. But it is only now, with the threat that oil production will soon decline and heightened appreciation of the scarcity of other resources, that things are starting to take off. According to the American Chemistry Council, which speaks for the chemical industry, some 10 per cent of all the petroleum consumed in the US goes into making drugs, food wrappings, computer cases, cosmetics and the like. Scarce metals such as tantalum, platinum and hafnium are also frequently used in electronic components or as catalysts in conventional chemical reactions. So going green makes sound economic sense, says Buzz Cue, who introduced green chemistry to the drug manufacturer Pfizer a decade ago, and now works as an independent consultant. The improvements can help drugs companies to save $10 to 15 million per blockbuster drug per year, he says. But it's not just about the economic bottom line: pressure from consumers is increasingly a factor too. Retailers are increasingly putting pressure on suppliers to restrict or ban suspect chemicals such as those on the Substitute It Now (SIN) list drawn up by the International Chemical Secretariat (ChemSec), a pressure group based in Sweden. The UK retail pharmacist Boots, among others, has gone even further by banning chemicals outright from its own-brand products if they can have harmful effects. These include phthalates, used as plasticisers in nail polish and hairsprays, and alkylphenol ethoxylates used as emulsifiers and surfactants in products such as hand lotions. Both have been implicated as possible hormone disrupters: alkylphenol ethoxylates, for example, can degrade in the environment into chemicals that feminise fish, says Stephen Johnson of Boots. The move fits into frameworks such as the European Union's REACH (Registration, Evaluation, Authorisation and Restriction of Chemical Substances) programme, which came into force in 2007 and could restrict or even ban the use of some chemicals now on the market. It is very early days for green chemistry. "There is a lot of talk but the fact that we have a sin list means there is a way to go yet," says Nardono Nimpuno of ChemSec. "But smarter companies can see there is a market opportunity here." Even those firms that are making headway with green chemistry tend to be reticent about their achievements. For many consumers "chemical" is still a dirty word. "Let's say you've come up with this revolutionary way to make your product 10 times safer than it was before," Warner says. "The only way you can brag about that is to say that what you used to sell was 10 times as toxic." Yet some green shoots are beginning to spring up across the chemical industry, as the examples that follow show. Case Study #1: Better living through green chemistry: Pharmaceuticals Most purchases of sildenafil citrate - the generic name of Viagra - are not motivated by urges of an environmental kind. But this blockbuster drug has long been a poster-child for its manufacturer Pfizer's green credentials. When gearing up for commercial production of Viagra, Pfizer's chemists designed a new reaction strategy that radically reduced the amount of solvent required, cut out the reagents tin chloride, an environmental pollutant, and hydrogen peroxide, which is a fire and transportation hazard, and produced just a quarter of the waste of the original process (Green Chemistry, vol 6, p 43). Other companies have scored successes with drugs that have been recognised by the EPA's green chemistry awards. The chemical company BASF now makes its annual output of the painkiller ibuprofen - some 2 billion tablets - in a three-step rather than a six-step process. Of the atoms used in the synthesis, which are mostly derived from hydrocarbons, 77 per cent make it into the final product compared with 40 per cent before. The chemotherapy drug paclitaxel (marketed as Taxol) was originally made by extracting chemicals from yew tree bark. That used a lot of solvent - and killed the tree. The drug is now made by growing tree cells in a fermentation vat. The process to make atorvastatin, a mega-bucks drug used to reduce blood cholesterol marketed by Pfizer as Lipitor, now uses an enzyme that catalyses chemical reactions in water, reducing the need for potentially polluting organic solvents.

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Little blue, environmentally sound pill (Image: Garo/Phanie/Rex Features)

Such successes are possible partly because most drugs are complex molecules that must go through many purification stages to be fit for human use, says Cue. Reducing that waste "just made good business sense", he says. Since 2005, all the main drugs companies have joined a "round table" with the American Chemical Society's Green Chemistry Institute that aims to foster the development of more efficient, less polluting processes. There's a lot more to do. A life-cycle analysis is needed for most major drugs to assess the environmental impact after they are used, particularly the effect of what passes through our bodies and gets flushed down the toilet. One answer could be the powerful series of tetra-amido macrocyclic ligand (TAML) catalysts modelled on natural peroxidase enzymes, which have been developed by Terry Collins at Carnegie Mellon University in Pittsburgh, Pennsylvania (Journal of the American Chemical Society, vol 131, p 18052). Collins thinks that added at a late stage in the sewage treatment process the catalysts could break down a wide variety of chemical residues, including those from Lipitor, Prozac, the antidepressant sertraline (Zoloft), the contraceptive pill and more, before they enter the environment. Case Study #2: Better living through green chemistry: Food and drink Here's a fact you might find a tad distasteful if you drink decaf: coffee beans are often washed free of their unwanted caffeine by soaking them in solvents such as methylene chloride, a suspected carcinogen. Carbon dioxide is a cheap, non-toxic alternative. Under pressure, CO2 goes into a "supercritical" state in which it can penetrate into the nooks and crannies of a material as easily as a gas, but dissolves substances it finds there as efficiently as a liquid solvent. According to Barbara Dufrène of the European Decaffeinators Association, about 20 per cent of global decaf production now uses supercritical CO2. The beery essence of hops can be extracted in a similar way, leaving much less polluting effluent than methods such as using methylene chloride or boiling the hops in water. Over 90 per cent of hop extraction now uses supercritical CO2, says Colin Hill of hop merchant Lupofresh near Maidstone, Kent, the centre of one of England's main hop-growing regions.

Decaf? (Image: Joel Sartore/Getty)

Supercritical CO2 is now used in some 125 food and drink manufacturing plants worldwide, for processes from extracting heady essences from ginger root to drawing out pungent oil from sesame seeds. It has also been used to remove fungicide contaminants in corks, which spoil the taste of fine wine. Case Study #3: Better living through green chemistry: Packaging We know perfectly well that it's wasteful and unnecessary, yet somehow the quantity of plastic packing enveloping our purchases just keeps on growing. Derived from fossil-fuel sources that have taken millions of years to build up, these materials have a useful lifetime that can be as brief as a few hours. Several companies are now marketing alternative plastics derived from renewable sources. NatureWorks of Minnetonka, Minnesota, which is owned by the food and agricultural conglomerate Cargill, makes food containers from a polymer called Ingeo, derived from corn starch. Bacteria convert the starch into a resin that is an alternative to polyethylene terephthalate (PET), the strong, rigid plastic currently used for containers such as water bottles and yogurt pots. In future, the company says, the raw material for Ingeo could come not from fresh corn but from agricultural waste. Metabolix, a company based in Cambridge, Massachusetts, is taking a different approach. By genetically engineering plants such as tobacco, switchgrass and sugar cane, it hopes to be able to harvest usable plastic polymers known as polyhydroxyalkanoates, synthesised within the cells of the plants' leaves and stems. Bioplastics still make up less than 1 per cent of the almost quarter of a billion tonnes of plastics produced, and disposed of, globally each year. But the market is growing fast: the Bioplastics Council, an industry body, projected last year that production of bioplastics would double by 2012. Case Study #4: Better living through green chemistry: Cosmetics The creams and soaps we slather on our bodies show how rushing to replace petroleum-based chemicals with renewable alternatives might lead us astray. Most of the moisturisers, greasebusters and lathering agents contained in toiletries are derived from fossil sources. Now manufacturers have started to return to more traditional, plant-derived ingredients such as palm and coconut oil.

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Millions of years to produce something that may only be useful for a few hours (Image: Danfung Dennis/Bloomberg/Getty Images)

chemicals with renewable alternatives might lead us astray. Most of the moisturisers, greasebusters and lathering agents contained in toiletries are derived from fossil sources. Now manufacturers have started to return to more traditional, plant-derived ingredients such as palm and coconut oil. Unfortunately, while these materials are renewable, they can be far from environmentally benign, as biodiverse forests around the globe have been cleared and replaced by monocultures of oil palms. A scheme to certify palm oil as sustainable has been in operation since late 2008, but of the 40 Looking good doesn't need to cost million tonnes of palm oil produced annually, only around 1.7 million tonnes is so far covered, the Earth (Image: Jerome according to the industry-led Roundtable on Sustainable Palm Oil. Tisne/Stone/Getty) A team led by Ray Marriott, of the University of York, UK, is aiming for a more securely sustainable approach, in which the materials needed for cosmetics are made from agricultural waste. One project aims to use supercritical CO2 to extract paraffins for lipstick wax from waste wheat straw. Another innovation is the use of enzymes at room temperature to build esters, chemical compounds used to make cosmetic ingredients such as emollients, which soften skin, and emulsifiers, which bind oily and watery components into a homogeneous mix. Esters have traditionally been made using corrosive catalysts such as sulphuric acid at high temperatures. The new production technology won the Eastman Chemical Company of Kingsport, Tennessee, a green chemistry award from the EPA in 2009, but the company is still waiting for takers from the cosmetics industry to license their process. Marriott says that the cosmetics business has been slow to embrace green chemistry: they have primarily been concerned with making products that consumers want, with less regard to where the ingredients come from. One hopeful sign was the convening in November 2009 in Frankfurt, Germany, of the first of a series of "sustainable cosmetics summits" organised for representatives of the cosmetics industry by London-based consultancy Organic Monitor. Case Study #5: Better living through green chemistry: Clothing Perhaps no industry depends more on unsustainable and environmentally hazardous chemicals than the clothing trade. Growing cotton consumes vast quantities of chemical fertilisers, herbicides and pesticides. Synthetic textiles such as polyester come from petrochemicals. Dyeing both synthetic and natural fibres requires an intense chemical cocktail: giving denim jeans their typical indigo colour, for example, requires use of large quantities of sodium hydrosulphite, an environmentally antagonistic chemical that can corrode cement and damage sewage pipes. That cocktail is chased down by millions of litres of rinse water at factories that are often located in areas of the world, such as parts of India, where water is already scarce. With such problems in mind, NatureWorks is investigating the use of its corn-based Ingeo polymer to make fibres that can be woven into a textile. Unfortunately, the end product has a tendency to melt when ironed, and it is also several times the price of polyester. The Italian fashion house Gattinoni has used it to make a "bio" wedding dress, but it appears to be a long way from regular commercial production. A polymer called Sorona, made by US chemical giant DuPont, also uses corn as the source for part of its raw material - though more than 60 per cent is still derived from petroleum. If the wooden look is more your style, bamboo, beech and eucalyptus are renewably sourced textile fibres. Bamboo can grow nearly anywhere without pesticides or herbicides, and has already been used in T-shirts, ski boots and a variety of other clothing items. In one respect, however, it is no green dream: it cannot be broken down into fibres for clothing without the use of hazardous chemicals such as sodium hydroxide and carbon disulphide. A better bet might be Tencel, a wood-derived, viscose-like fabric made by the Austria-based manufacturer Lenzing in a process that uses a less corrosive solvent, N-methylmopholine oxide, than normal viscose production and recycles 99.6 per cent of it each time, dramatically reducing waste. Tencel has been used for items as diverse as chefs' outfits and surgical garments, but it is several times the price of viscose. Truly green and affordable clothes are a way off yet.

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Dye from a jeans factry runs off into the river Caledon near Maseru (Image: Robin Hammond/Panos)

Case Study #6: Better living through green chemistry: Electronics The millions of nifty electronic gadgets we buy and throw away each year are heavily dosed with chemicals. Building a microcircuit takes between 800 and 1000 steps, and requires potentially toxic chemicals such as xylene, mercury, sulphuric acid, phthalates and the carcinogenic solvent Nmethylpyrrolidone. The manufacture of a single laptop consumes some 3200 litres of water and 160 litres of fossil fuels, according to calculations by Eric Williams at Arizona State University, Tempe. The main culprit is the intricate chemical process that is used to lay down and strip off layers of material to produce a silicon microcircuit. Things could be improved, argues Jim Hutchison of the University of Oregon, Eugene, by devising processes that draw circuit features directly on the silicon, without depositing layers of chemicals most of which are eventually etched away again. He aims to do that with DNA scaffolds that guide the deposition of metal molecules along the desired circuit paths.

Silicon production could be improved (Image: Nikolaevich/The Image Bank/Getty)

Meanwhile, computer manufacturers are concentrating on removing toxic material from more mundane components. Apple says that the casings of almost all its products no longer contain brominated flame retardants, accumulations of which might disrupt the endocrine system in humans and wildlife, or the plastic polyvinyl chloride (PVC), which forms carcinogenic dioxins if incinerated. Case Study #7: Better living through green chemistry: House and home In 2005, survivors of hurricane Katrina temporarily housed in mobile homes started getting headaches and nosebleeds. The culprit was formaldehyde, a carcinogen sourced from petrochemicals that is found in the adhesives and resins that hold together many household products, including plywood, woodchip-based composites, carpets and furniture. There is an alternative. An adhesive called PureBond which contains soya proteins modified to resemble the adhesive protein mussels use to stick to rocks is now used in 40 per cent of the plywood and composite wood produced in the US, according to its manufacturer, Columbia Forest Products of Greensboro, North Carolina. A mixture of soya oil and sugar can also replace fossil-fuel-derived paint resins and solvents, halving the sometimes hazardous and always smelly volatiles that can give painters a headache. That innovation garnered Cook Chemicals and Proctor & Gamble an EPA green chemistry award in 2009. The companies claim that if the new paint formulations were universally adopted they could eliminate smog-generating emissions of volatile organic compounds equivalent to those from 7 million cars, as well as saving 900,000 barrels of crude oil per year.

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Getting stuck in (Image: Paul J. Richards/AFP/Getty Images)