The greening of our chemical industries

Deepening concerns over the warming of our planet have made “green” and “sustainable” popular words. ‘Going green’ means taking steps to lessen harm to the environment, like adopting eco-friendly practices. Sustainability aims for changes that balance environmental concerns with economic realities.

Whatever term you use, the shared goal of minimising or eliminating environment hazards points us towards green chemistry. And this field leads us away from toxicity and pollution. The 12 Principles of Green Chemistry, introduced by Paul Anastas and John Warner in 1998, focus on basics, such as the adoption of safer solvents and reagents in chemical processes; designing energy-efficient methods that lead to safer chemicals that are as nontoxic as possible and also do not linger for too long in the environment; and preventing waste (so that you don’t have anything to clean up).

An illustration of how green chemistry can be put to work comes from the production of biodiesel. The Indian Oil Corporation, as part of a green fuels mission, produces biodiesel from non-edible oil seeds such as Jatropha (jamal ghota in Hindi and kattukkotai in Tamil). The seeds have over 30% oil content and the tree grows in lands with little rainfall and poor soils. Biodiesel is produced from a transesterification reaction, where the seed oil is reacted with methanol to yield biodiesel and the by-product glycerol, which is also commercially useful. For reducing the carbon footprint, the methanol must be derived from biomass. 

Chemical reactions are speeded up by catalysts. Biodiesel production is facilitated by an alkali. Sodium hydroxide is often used, but washing it away generates wastewater, which has to be treated before it is released into the environment. Calcium oxide is a greener alternative, because it is a solid and 95% of it can be recovered after each production cycle.

Very toxic substances are used in the manufacture of pharma products as well. In the vicinity of some of these factories, the air has a strong smell that reminds you of nail-polish: the solvent toluene is widely used in the synthesis or extraction of paracetamol and many other drugs. It is a neurotoxin. Green initiatives have led to a slow replacement of such volatile organic compounds with alternatives that are less toxic, biodegradable, and can be produced from biomass sources like sugarcane.

Another tenet of green chemistry that chemists love to work towards is the atom economy. The aim is to incorporate as many atoms present in the input mixture into the desirable product. In the biodiesel production process described above, green chemistry results in an atom economy of 90%. It is not 100% because of the atoms that are ‘taken away’ in the byproduct, glycerol. But then, in a sustainable initiative, the glycerol would itself serve as an input for making polymers, cosmetics, etc.

Attention to atom economy is even more critical in industries where the by-products are very toxic. A fine example of green chemistry’s superiority has come from chemists at the Hyderabad campus of the Birla Institute of Science-Pilani. Their green method for pharmaceutical production, of the anti-cancer drug Tamoxifen and related drug candidates, has 100% atom economy while being cost-effective and capable of making these drugs in large quantities (Tanmay Chatterjee and colleagues, Green Chem., 2023, Vol. 25, 779). Such methods hold the promise of reduced impact on our surroundings.

Jointly written with Sushil Chandani, a molecular modeler.