12 Principles of Green Chemistry and Green Solvents

In 1998, in a book entitled Green Chemistry: Theory and Practice, Paul Anastas and John Warner put forth 12 principles of green chemistry. Currently, the American Chemical Society(ACS) includes them on their web site, linking each principle to a practical example.

  1. Prevention It is better to prevent waste than to treat or clean up waste after it has been created.

  2. Atom Economy Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.

  3. Less Hazardous Chemical Syntheses Wherever practicable, synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment.

  4. Designing Safer Chemicals Chemical products should be designed to affect their desired function while minimizing their toxicity.

  5. Safer Solvents and Auxiliaries The use of auxiliary substances (e.g., solvents, separation agents, etc.) should be made unnecessary wherever possible and innocuous when used.

  6. Design for Energy Efficiency Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. If possible, synthetic methods should be conducted at ambient temperature and pressure.

  7. Use of Renewable Feedstocks A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable.

  8. Reduce Derivatives Unnecessary derivatization (use of blocking groups, protection/ deprotection, temporary modification of physical/chemical processes) should be minimized or avoided if possible, because such steps require additional reagents and can generate waste.

  9. Catalysis Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.

  10. Design for Degradation Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment.

  11. Real-time analysis for Pollution Prevention Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances.

  12. Inherently Safer Chemistry for Accident Prevention Substances and the form of a substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions, and fires.

It’s reassuring to see a foundation for green chemistry laid out. But at the same time, we can’t help wonder how widespread the adherence to those principles actually is. One research center that is committed to making these 12 principles as feasible as possible is the Green Chemistry Centre of Excellence at the University of York in England. (The ACS site does not link any of the principles to them perhaps because the ACS showcases only industrial and academic applications from within the United States.) With regard to principle 5, the University of York investigates the use of both supercritical and liquid carbon dioxide as a solvent.

Recall CO2‘s phase diagram. Below its triple point(518 kPa at −56.6 °C) sublimation is possible—the familiar behavior of dry ice. Above that point, CO2 liquid is possible as the molecule goes through its three states with increasing temperature. But above its critical point of 304.25 K  7.39 MPa or about 7400 kPa, it forms a supercritical fluid.CO2phase
Supercritical CO(sCO2) which exists at high pressures, has interesting hybrid properties: it acts like a gas in having high diffusion rates but also resembles a liquid in density and dissolving power, both of which are variable with slight changes in pressure.

sCO2 is non-polar, but unlike many traditional non-polar solvents it is not toxic, leaves no traces (principle 10) and can be recovered. It can extract waxes, natural products and liquid crystals.BioSolvents Also greener than conventional solvents are biological ones such as glycerin, ethanol, limonene, 2-methyl-tetrahydrofuran and the degreaser ethyl lactate. These can be generated from food waste, revealing how compost is not the only useful product that can be derived from what most people perceive as trash.

When either sCO2 or biological solvents are used as medium for reactions, they are less likely to “poison” catalysts.   When catalysts accumulate impurities or get “poisoned” , they can no longer be used to speed up reactions. So by keeping catalysts “cleaner” with the use of green solvents, they perform syntheses with less waste. There are exceptions: Ziegler catalysts are poisoned by CO2 through the formation of CO. A more important issue is that the high pressures required to generate CO2 drive up the cost. Returning to advantages, some green-solvent-assistant syntheses are also more selective when only one chiral component is desired. In fact many enzymatic reactions can operate in supercritical fluids. Such properties of the solvents help us respect green chem principle 6.

Professor James Clark, the director of U of York’s Green Chem Centre, which is the largest of about 9 green centers in Britain, is connected with India’s IGCW (Industrial Green Chemistry World) whose core objective is

to drive industry implementation of green chemistry and engineering-based technologies to sustainably address priority and pressing environmental challenges of our chemical industry.

From http://www.york.ac.uk/chemistry/staff/academic/a-c/jclark/
From http://www.york.ac.uk/chemistry/staff/academic/a-c/jclark/

Although about 85% of petroleum is used for fuel, the 15% whose distillates are used for petrochemicals, plastics, lubricants, asphalt and other products accounts for about half of the industry’s profits. Renewable sources of energy have to replace petroleum as a fuel, but we also need a sustainable source of materials for organic compounds. For this reason, the center is hoping that biorefineries will soon find their way into large industry. If we again refer to the green principles, a biorefinery uses atom economy and produces less hazardous chemical syntheses; it designs safer and more biodegradable compounds, using better solvents and makes use of renewable feedstocks.

Why There’s No Revolution Around the Corner

In the early 1980s, one of my professors was Fred H. Knelman. Born in 1919 in Winnipeg, he went on to study chemical engineering and earned a doctorate from London University. He was in England’s capital at the time of the infamous thermal inversion, the Great Smog, which in a weekend killed over 4000 people, sickened almost 100 000 and eventually went on to take 8000 more lives.

In part, that tragic event may have motivated him to teach environmental studies at Concordia for about 16 years. He wrote several books, including  “Anti nation: transition to sustainability“. Along with other intellectuals in the 1970s, he questioned the wisdom of economic growth. One of the few professors who did not own a car,  he envisioned an efficient economy that did not grow at the expense of health and the environment. sustainableWhy couldn’t technology be used to produce quality-goods rather than sheer quantity? Sure, mass production drives down the cost per item, but why not pay more for something well-made and durable but which has far less hidden costs? This sensible approach is in tune with Environment Canada’s description of sustainable development.

Sustainable development is about meeting the needs of today without compromising the needs of future generations. It is about improving the standard of living by protecting human health, conserving the environment, using resources efficiently and advancing long-term economic competitiveness. It requires the integration of environmental, economic and social priorities into policies and programs and requires action at all levels – citizens, industry, and governments.

Economic growth, it is argued, can take people out of poverty. Yet in the U.S., the world’s largest economy (soon to be overtaken by China), the fruits of growth tend to be concentrated among the wealthy. Among OECD countries, the U.S. has the 4th highest gini coefficient, which measures income inequality, a shrinking middle class and a 17% poverty rate, higher than the 11% OECD average. USIncomeDistributionIt has the 2nd highest homicide rate among those countries, the world’s highest incarceration rate, no universal medicare and college tuition that is so high that 68% of students graduate with an average of $30 000 of debt. Despite all of this, since 1972, in 10 consecutive federal elections, not more than 57.46% of eligible voters have cared enough to vote.

The other gargantuan economic engine of the world, China, is ruled by a single party with rampant corruption. Beijing’s concentration of PM 2.5 particles, small enough to get into into the lungs and bloodstream, reached 505 micrograms per cubic metre in 2014, chinaover 20 times higher than what the World Health Organisation recommends. Their own government has admitted that 19.4% of crop-growing land is contaminated with industrial waste, which also often finds its way unfiltered into major rivers.

Smaller economies that possess better social programs and environmental policies than the United States and China, respectively, are economically tied in to the big two engines and are to various degrees still enslaved to consumerism. So the rest of the countries cannot wash their hands of the problems of the largest powers.

But after 40 years of talk and print about a quiet revolution towards something sustainable, towards a world based on care and craft and not on power and money, much of our population still fantasizes about winning a lottery. breakingbad_skylerwaltmoneyIf it’s not Power Ball, it’s the aspiration of becoming a star actress, big league athlete or a Fortune 500 executive, a lust for fame and megabucks granted to one lucky winner out of myriads of dreamers. Meanwhile,  social inequalities and looming climate change are not dealt with. Why is this so?

Historian Jack A. Goldstone identifies five conditions needed for a revolution to occur.lennon

1. Part of the elite must oppose the status quo and feel alienated enough to mobilize the population.

2. There have to be widespread economic and fiscal strains.

3. The rest of the population has to feel anger at the injustice.

4. There has to be a shared narrative of resistance.

5. International relations have to be favourable to the revolution.

Not of these conditions are being met. (1) is not in the cards among our wealthy elite. Most believe that social ills can only be remedied with more raw economic growth, and they resent taxation and regulation. At the opposite end of the spectrum, those who feel economic strains cling to the American —or Chinese dream— while in many countries fiscal strains, which in part are exacerbated by catering to large corporations, are dealt with by handing debt to future generations. (2)Despite the above average poverty rate, in the United States, 42% of the population still resides in households with at least $75 000 of income.Income Distribution

(3)At best, the anger of the masses is dissipated through gargantuan sports, entertainment industries and social media, all of which advocate more spending. The rest of the frustration contributes to white collar crime, rape, theft and violence. (4) The narrative of resistance is present, but it’s neutralized by divisiveness. People blame completely different sources for their anger and propose incompatible solutions.  Finally, condition (5) cannot be a factor because in a world economy, no country can become sustainable independently.


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