A new leaf: Chemistry goes green

Professor Martyn Poliakoff and Dr Samantha Tang on a different branch of chemistry that promises to be less harmful to the environment

Today our lives are longer, better and richer thanks to chemistry; advances in chemistry have improved human health and made food more plentiful. However, the global population has increased dramatically and the demand for chemicals - medicines, insecticides, textiles, fertilisers - is increasing. Within a few years, current methods for making these chemicals will struggle to keep up. So, chemistry is rising to the challenge by undergoing a big revolution. We need new methods and new ideas to produce chemicals in the future and we need to start inventing now so that we are ready in time.

The problem is in two parts. Firstly, most chemicals are made directly or indirectly from petroleum. We are burning more and more of this vital resource in our cars, lorries and aircraft, so the price of oil will increase as supplies get scarcer to the point where it will probably be uneconomic to use oil as a source for many chemicals.

Secondly, many chemical processes not only make the chemical the manufacturers actually want, but also generate unwanted salts or side-products. Large quantities of oil-based solvents then have to be used to dissolve out the impurities and purify the compound. Solvents are also important for helping mix chemicals and for stopping reactions getting so hot that they explode. At the end of the production cycle, the manufacturer has to dispose of all the waste chemicals and solvents that cannot be recycled. Usually this waste is burnt or placed in landfill, both of which can cause environmental damage. This problem needs to be solved if we are to maintain our quality of life. The answer is green chemistry, a new way of designing and using chemical processes and products.

Green chemistry was born in the Nineties in the US. The idea is simple: to use chemicals, wherever possible, which are harmless to both life and the environment. Green chemistry is really a way of thinking rather than a strict set of instructions. The main ideas are collected in a set of 12 principles (see box). Several of the principles are quite obvious but, together, they provide a very useful checklist for chemists to judge how green their process is. The more principles that are obeyed, the greener the process is. If we can obey them all, we will be making chemicals far more productively than at present.

What does green chemistry mean in practice? One US pharmaceutical company needed 10kg of solvent to produce each 100mg tablet of their leading antidepressant. Redesigning their process based on green chemistry principles reduced the waste to only 4kg.

Green chemistry can also replace toxic chemicals. For example, ships need to be painted to prevent barnacles from fouling the hull and slowing the ship down. The tin compound traditionally used in the paint takes nine months to decompose in the sediment on the ocean floor and can cause reproductive damage in marine organisms. The replacement found by green chemists at the company Rohm & Haas decomposes in one hour and causes no reproductive harm.

Most importantly, some chemicals are now being made from renewable vegetable sources. Polylactic acid, a plastic which can be used for packaging for things such as sweet wrappers, can be made from agricultural waste such as stalks, leaves and wheat straw. This means that carbon dioxide from the air is captured and turned into useful chemicals.

These examples are just the start. What is holding things up is a shortage of young scientists trained in the methods of green chemistry. If you want to help, you can join in. Apply to study chemistry at university. Several UK universities are beginning to teach green chemistry so when you apply, ask what the university is doing about it.

Professor Martyn Poliakoff is a research professor in chemistry. Dr Samantha Tang is the EPSRC (energy and physical sciences rsearch council)-sponsored public awareness scientist at Nottingham University, www.nottingham.ac.uk/chemistry

The 12 principles of green chemistry

P Prevents wastes

R Renewable materials

O Omit derivatisation steps

D Degradable chemical products

U Use safe synthetic methods

C Catalytic reagents

T Temperature should be ambient

I In-process monitoring

V Very few auxiliary substances

E E-factor, maximise feed in product

L Low toxicity of chemical products

Y Yes, it is safe!

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