in this issue
The 12 Misunderstandings of Green Chemistry
January 20, 2012 | By JAMES CLARK
by James Clark, professor of green chemistry, York University (York, U.K.).
The past year was another good year for green chemistry events. I was lucky enough to attend excellent events in places as far apart as Brazil, China, France, India, Korea, and the U.S. While I was in Boston, I enjoyed the benefit of a personal tour of John Warner’s new facility, the Warner Babcock Institute for Green Chemistry. Being with John at two major events (CleanTech in Boston and the extremely impressive Industrial Green Chemistry World in Mumbai) I was reminded of the continued importance of his 12 Principles of Green Chemistry and how they continue to be meaningful after almost 20 years.
Our excitement at the growth in interest must in green chemistry, however, be tempered by a determination not to allow the concept and the principles that underpin it to be undermined by basic misunderstandings of what is green and sustainable.
The term has been high-jacked in some cases by labeling an entire area as ‘green’ and thus making it more acceptable or favorable without a proper appreciation of what it really means to be green. So in the spirit perhaps more of Ebenezer Scrooge than Father Christmas I now propose the 12 Misunderstandings of Green Chemistry.
1. Hazardous chemicals must be immediately replaced.
Through EU Reach regulation and other instruments we are now identifying chemicals which are hazardous to human health and/or the environment: These should be replaced but only with alternatives that we are confident are genuinely safer - as well as being effective - across their lifecycle. There is a tendency for chemical users to demand that all ‘relisted’ chemicals be immediately replaced, but we must be careful that we don't make matters worse through hasty and ill-conceived substitution. What is clear is that we must invest more in R&D that is directed to finding genuinely greener alternatives to these unwanted chemicals.
2. Chemicals should be biodegradable.
All substances end up in the environment and when they do it is important that they don't persist or bio-accumulate. However, degradation can prevent (immediate) reuse and while the eco-system will recycle the carbon and other elements, it may be preferable to maximize the useful lifetime of complex (molecular) substances. For example, food waste is rich in interesting and useful complex molecules that can be used for other applications.
3. Water is the greenest solvent.
Water has many attractions as a solvent but it is not a good solvent for many organic compounds. It can affect the reactivity of many reagents and catalysts, and it can be difficult to work with. Its ability to dissolve small amounts of most substances means that water effluent can be difficult to treat. We do need to make more use of water as a solvent but using water does not automatically make the process green!
4. Fossil-derived (non-renewable) chemicals should be replaced by bioderived (renewable) chemicals.
Petroleum-derived chemicals are not sustainable in the long term and we must accelerate their replacement with non-food biomass-derived chemicals, however, we must not let this be an excuse for developing impractical alternatives based on scarce resources or complex, wasteful synthesis routes. Bio-derived chemicals are not automatically green; they must be processed using green chemical methods to make genuinely green and sustainable products.
5. Conventional sources of energy must be replaced by renewable sources. The most wasteful use of our diminishing fossil resources is single use burning to make energy. A more intelligent use of these increasingly precious resources is to make chemicals (see 4 above). However, we must be more holistic in our selection of alternative energy sources. Some of these are based on the large scale use of elements that have not previously been used in large quantities; we must look at the whole periodic table when making major changes to our energy and manufacturing infrastructure.
6. Involatile solvents are better than volatile ones.
Legitimate concerns about the damage to the atmosphere caused by volatile solvents have led to a general belief that all volatile organic compounds (VOCs) should be replaced and that involatile solvents are preferable. Apart from the difficulty of finding enough involatile solvents to replace the very many roles VOCs have in today’s society, we are also in danger of replacing one environmental impact with another. Involatile solvents such as ionic liquids are a useful addition to the green chemistry toolkit but due consideration must be given to all of their ‘green credentials’ including resources, preparation, separation and toxicity as well of course, as cost.
7. Catalysts are better than reagents.
The replacement of widely used hazardous reagents such as aluminum chloride and sodium chromate with catalytic alternatives rightly remains one of the great challenges in clean synthesis but we must be careful about the choice of catalyst and catalytic process. Many of the most interesting catalytic metals are also becoming scarce and the process for making some catalysts can in itself have high resource demands and produce large amounts of waste. Efficient catalyst recovery and reuse is also essential.
8. Halogenated compounds are harmful to the environment and should be replaced.
While there are some large volume halogenated compounds that need to be phased out, we must not bundle all halogenated compounds in the same ‘red’ basket. Nature turns over enormous quantities of organohalogen compounds and we need to learn from nature and avoid, as much as possible, those
compounds that it cannot deal with, such as perhalogenated compounds.
9. Bio-processes are preferable to chemoprocesses.
Nature has developed some supremely elegant processes which function in a benign environment using non-toxic species to give highly selective processes. However, we have chosen to create a society based on the engineering of resources that goes beyond natural systems and it is unreasonable to believe that we can perform all resource-to-product processes using natural organisms. We can expect an increase in the number of industrial bio-processes but chemical processes can be expected to continue to dominate for some time to come.
10. Alternatives need to be assessed by full life-cycle analysis (LCA) before they are validated.
The appreciation that if we cannot measure it we cannot improve it has been one of the most important developments in green chemistry in the past 10+ years; green chemistry metrics are now very much part of the toolkit. Part of this is the awareness that you cannot change one stage in a product life-cycle without affecting other stages and hence life-cycle awareness is important. But this needs to always extend to a full LCA which is time-consuming and dependent on the quality of input data.
11. Waste minimization should be a priority for any process optimization.
Clearly we do not want to produce something that needs to be disposed of since this is a loss of resource and causes harm to the environment. However, processes that only produce the one desired product are unrealistic. We need to fundamentally change our attitude and see what we currently refer to as waste as co-products with value either within that process or elsewhere. We can no longer afford the luxury of waste.
12. Hazardous or non-renewable chemicals in formulations should be replaced.
Almost all chemicals are ultimately used in formulations and we need to recognize this more in green chemistry. An additional complication of formulations is that changing any one component is likely to lead to a change in more than one property. While undesirable components need to be replaced we must be careful that a direct X for Y substitution - for example to make a product more “natural” or “bio” - may lead to a deterioration in performance and the need to add other components to compensate for this. We must treat formulations as a whole and find ways to simplify them, not make them more complicated.
Happy New Year!
Honorary President, Green Chemistry Network