Created in the 1990s, green chemistry promises to design and develop products (and chemical processes) to reduce or eliminate the use and synthesis of hazardous substances.

According to the CEA (The French Alternative Energies and Atomic Energy Commission), green chemistry is inspired by the concept of sustainable development . It integrates the optimization of the efficiency and energy cost of processes, the economy and recycling of raw materials and by-products from chemical reactions. Green chemistry also aims to reduce ultimate waste with, of course, the reduction of their impact on human health and the environment.

Reducing the chemical footprint first and foremost

Green chemistry - also called sustainable chemistry, ecological chemistry, or renewable chemistry - provides principles to reduce and eliminate the use or generation of substances harmful to the environment . This approach is done with new "clean" chemical processes, i.e. environmentally friendly. After the development throughout the 20th century of industrial chemistry from hydrocarbon derivatives, it must move towards more virtuous principles in order to preserve the environment as well as human health (in the face of the growing number of pathologies: cancer, diabetes, Alzheimer's disease, autism, etc.).

Moreover, one of the major challenges of this green chemistry is the reduction of the massive production of so-called CMR substances (carcinogenic, mutagenic, toxic) or endocrine disruptors .

The other major challenges of this green chemistry are:

• Reducing dependence on non-renewable energy and the carbon footprint of industries
• The problem of decomposition of landfill waste
• The desire to take advantage of certain abundant and unused resources, such as carbon dioxide.

Respect the twelve founding principles of green chemistry

The concept of green chemistry emerged in the United States in the 1990s. In 1998, Paul Anastas and John Warner, researchers at the American Environmental Protection Agency (EPA), laid the theoretical foundations of this new discipline by publishing a book setting out 12 founding principles.

1. Prevention

It is better to avoid producing waste than to have to treat or dispose of it later.

2. Economy of atoms

Implementation of synthesis methods that incorporate into the final product all the materials entering the process.

3. Design of less dangerous synthesis methods

Where possible, synthesis methods should use and produce substances that are low in toxicity (or non-toxic) to humans and have no consequences for the environment.

4. Design of safer chemicals

Development of chemical products that achieve the desired properties while being as non-toxic as possible.

5. Less polluting solvents and auxiliaries

Refrain from using synthesis auxiliaries (solvents, separating agents, etc.) or choose harmless auxiliaries when necessary. Unconventional activation methods can be used: use of water as a solvent, supercritical fluids, microwave heating, replacement with ionic liquids, etc.

6. Energy efficiency research

The energy expenditure required for chemical reactions must take into account its impact on the environment and the economy in order to be reduced to a minimum. As far as possible, synthesis operations must be carried out under ambient temperature and pressure conditions.

7. Use of renewable resources

Use a natural resource or a renewable raw material rather than fossil products, as far as technology and economics allow.

8. Reduction in the number of derivatives

Avoid, if possible, the unnecessary multiplication of derivatives which require a surplus of reactive agents and can produce waste.

9. Catalysis

Prefer catalytic solutions that are recyclable. A catalyst is a substance added to a chemical solution to carry out the chemical reaction. It accelerates the reaction rate by lowering the energy and comes out unchanged from the chemical process, which is why it is recyclable.

10. Design of products for degradation

Chemicals must be designed to break down into harmless biodegradable waste at the end of their use.

11. Real-time observation to prevent pollution

Observation methods must be improved to enable real-time monitoring and control of ongoing operations, and to control their follow-up to identify any formation of dangerous substances.

12. Fundamentally more reliable chemistry

The choice of substances and their chemical processes must anticipate the risks of accidents (dangerous emissions, explosions and fires).

The victories of green chemistry

In 2005, Japanese chemist Ryoji Noyori identified three keys to promoting the development of green chemistry: the use of carbon dioxide (CO2) in the supercritical fluid state as a "green solvent", aqueous hydrogen peroxide to purify oxidations, and hydrogen in asymmetric syntheses.

Interestingly, chemists have discovered that when CO2 molecules are kept in a transitive state (an intermediate state between liquid and gas), this gas acts as an industrial refrigerant. Applications of this so-called “transcritical” CO2 include refrigerating supermarkets, food processing plants , warehouses, ice rinks or delivery trucks.

So, if chlorofluorocarbons and hydrofluorocarbons (greenhouse gases commonly used for refrigeration) are replaced by this famous transcritical CO2, the ecological impact is reduced by around 15%.

In cosmetics , this transcritical CO2 is used in the green process of extracting odorous molecules to produce perfumes. It also allows decaffeination.

Bioengineering is also a promising technique with the realization of chemical processes inside organisms (living cells).

Polyethylene (PET), light and strong, is the most widely used plastic (water and shampoo bottles, bags, packaging). With its extremely stable molecular structure, PET is difficult to degrade. But Japanese researchers have discovered a bacterium that breaks it down and even enzymes that accelerate this decomposition process!

In California, Stanford researchers have found a way to produce plastic without using oil, using CO2 and industrial by-products or agricultural waste (fibers from carrot juice production).

Although chemistry and green seemed incompatible at first, it is clear that green chemistry has succeeded in reducing the production and use of some materials that are dangerous for both humans and the planet. But it still has a long way to go.