It is better to prevent waste than to treat or clean up waste after it is formed – or: what Benjamin Franklin has to do with “Green Chemistry”

Benjamin Franklin, one of the Founding Fathers of the United States, was a well-known printer, author, politician, scientist and diplomat – to name only a few. Among the many great achievements that relate back to him is the creation of the first firefighting organization in Philadelphia. Now-a-days it is hard to imagine how difficult it was for Franklin to convince the Philadelphians that a group dedicated to firefighting was a good idea – isn't it? He argued that prevention of a catastrophic city-wide fire was certainly preferable to rebuilding a burned city from scratch. It was in this context Franklin noted “…an ounce of prevention is worth a pound of cure.” Finally, he succeeded: by the end of 1736, Philadelphia had its first volunteer fire department: the Union Fire Company.¹

More than 200 years later, volunteer fire departments are common practice, while the superordinate principle of “prevention” is still questioned every now and then – especially when it comes to environmental topics. Yet, in United States politics in 1990, the Pollution Prevention Act yielded a national policy focusing on the prevention of pollution at the source rather than the treatment of pollutants after formation. Coined by Paul Anastas as “Green Chemistry” and applied far beyond the United States borders, it comprises the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances.

Based on this, Paul Anastas and John Warner formulated the so-called “12 Principles of Green Chemistry” (Fig. 1) in 1998 – in a narrow interpretation, guidelines for chemists seeking to lower the ecological footprint of their products.² The first principle – It is better to prevent waste than to treat or clean up waste after it is formed – is often referred to as overarching. An example: no or less waste is achieved by higher atom economy (#2, #9), by avoidance of unnecessary auxiliary substances (#5) and energy-related waste/pollution (#6).

Fig. 1 The 12 Principles of Green Chemistry²

Prevention as often applied principle

There are numerous processes, both in industry and academia, with successful optimizations targeting for example at higher yields, fewer process steps and overall less waste. With ibuprofen for example, a commonly used nonsteroidal anti-inflammatory drug, process steps could be reduced from six to three steps by recovering and recycling the waste by-product from the manufacturing process and thus eliminating large volumes of aqueous salt waste. Implementation of process improvements in the manufacturing process for sertraline, an antidepressant of the selective serotonin reuptake inhibitor class, doubled overall product yield, significantly reduced raw material usage and eliminated the use or generation hazardous materials. An alternative route to make propylene oxide based on hydrogen peroxide eliminated most of the waste and greatly reduced water and energy use compared to the conventional process.³ These examples clearly support the first principle of Green Chemistry and show that prevention is better than treatment afterwards. But is waste prevention always better than post treatment? And what does “better” mean exactly?

To provide an answer to these questions it is important to keep in mind the overall system boundaries as well as the multi-dimensionality of environmental impacts. Waste prevention is of course desirable, but only if it is more profitable, environmentally reasonable as well as cost-efficient than waste treatment. Although often taken for granted, the answer is not always crystal clear as the following example shows:

In the synthesis of the antiepileptic drug rufinamide, a new process pathway via 2,6-difluorobenzyl chloride instead of the corresponding bromide was identified to produce less waste (lower process mass intensity) and cause a lower ozone depletion potential. However, a comprehensive life cycle assessment showed that the new (not fully optimized) route causes higher impacts in all other considered environmental categories.⁴

To judge whether waste prevention is “better”, it is not enough to simply add the amounts of generated waste as in the ‘process mass intensity’ (PMI) or E-factor. It is often also not sufficient to consider a single factor describing the “badness” of waste as in the EQ-factor.⁵ The “badness” of waste and the “betterness” of waste prevention have multiple, often contradictory dimensions. We can conclude that waste prevention is clearly better than waste treatment only if prevention is more reasonable in all environmental and economical dimensions.

Waste? Still the right metric?

After having reviewed the meaning of “better”, let us look at the definition of the most important word in the first principle: waste. In the E-factor concept introduced by Roger Sheldon in 1992 and widely applied ever since, waste is defined as everything but the desired product.⁶ But what about valuable co- and by-products? How do we clearly account for multiple desired products in highly integrated production networks? And doesn't the desired product ultimately become waste as well?

The easiest approach to waste prevention would be to not produce the product itself. While this is typically not feasible, it might be feasible to produce entirely novel products with higher quality and longer product lifetime so that lower amounts of this product are required to fulfill a certain function. Another approach is to prevent the product from becoming harmful waste, e.g. by making plastics bio-degradable. Along this line of thought, we need to rethink the concept of waste by turning existing waste into a new resource. The idea is not new: in the 1970s, Richard Buckminster Fuller stated that “…pollution is nothing but resources we are not yet harvesting”. In its simplest form, this concept is realized in the usage of waste in waste incineration for thermal energy recovery. A more sophisticated example is the utilization of carbon dioxide for the production of polymers as in the “Dream Production” project.⁷ In the purest form of this concept, also referred to as ‘cradle-to-cradle’, nothing is waste(d) and all material cycles are fully closed.⁸

Franklin’s view on it…

What goes without saying today required years of persuasion, perseverance and not least a convincing vision – worthwhile to keep in mind. At the same time it is unavoidable, even absolutely necessary to regularly question ourselves. This is the only possible way towards the future and towards celebrating the Golden Anniversary of “Green Chemistry” in 2041 and beyond. Fire departments are indispensable today – Franklin would have liked it.

The way forward…

“It is better to prevent waste than to treat or clean up waste after it is formed” – one of the most popular guidelines in process optimization. And indeed: it is easy to understand, easy to apply, and examples from industry and academia have proven it right.

We believe that the principle is still valid but we have to understand it more widely, going from a limited mass-based view of waste to more holistic thinking: (1) consider the multi-dimensional quality of waste. (2) Move from “waste per kg product” towards “waste per function delivered” and thus, we should aim at improving product quality and functionality. (3) Look at the overall life cycle: next to waste from production, we also need to consider the end-of-life waste after product consumption, including recycling of hitherto perceived wastes into valuables as well as to design for recyclability.

References

1. http://www.law.du.edu/documents/denver-university-law-review/v88-4/Kiel_ToPrinter_92611.pdf .
2. P. T. Anastas and J. C. Warner, in Green Chemistry: Theory and Practice, Oxford University Press, 1998.
3. http://www.epa.gov/greenchemistry/presidential-green-chemistry-challenge-winners .
4. D. Ott, et al. , Green Chem., 2016, 18, 1096–1116.
5. Sheldon, Chem. Soc. Rev., 2012, 41, 1437.
6. Sheldon, Chem. Ind., 1992, 903–906.
7. J. Langanke, et al. , Green Chem., 2014, 16, 1865–1870.
8. W. McDonough and M. Braungart, Cradle to cradle: Remaking the way we make things, Macmillan, USA, 2010, ISBN: 0865475873.

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