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Atom Economy

29 Jun 2025 GS 3 Environment

What is Atom Economy?

Atom economy is a key principle of green chemistry that measures the efficiency of a chemical reaction by calculating how many of the input atoms are incorporated into the desired final product, rather than ending up as waste.

Formula:

Atom Economy (%)=(Molecular weight of desired productTotal molecular weight of all products)×100\text{Atom Economy (\%)} = \left( \frac{\text{Molecular weight of desired product}}{\text{Total molecular weight of all products}} \right) \times 100

Why it matters:

  • High atom economy means less chemical waste, better resource efficiency, and lower costs.

  • A 100% atom economy implies that all atoms from the reactants are present in the final product, with no waste generated — ideal for sustainable and green processes.

In the context of biodiesel:

Atom Economy is a fundamental concept in green chemistry, focusing on maximizing the use of all atoms in the reactants so that they end up in the desired product, minimizing waste.

  • In biodiesel production, the atom economy is 90%. This is because some atoms end up in glycerol, a by-product. However, since glycerol can be reused in cosmetics, polymers, or other industries, the process remains largely sustainable.

  • In industries producing toxic by-products, achieving high atom economy becomes even more critical to reduce hazardous waste.

  • A notable success has come from the Hyderabad campus of BITS Pilani, where chemists developed a green synthesis method for Tamoxifen (an anti-cancer drug).

    • Their method achieves 100% atom economy, meaning no atoms are wasted.

    • It is cost-effective, suitable for large-scale production, and minimizes environmental impact.

Biodiesel Production and Greener Catalysts:

In biodiesel production, a process called transesterification is used, where vegetable oil (such as from Jatropha seeds) is reacted with methanol to produce biodiesel and glycerol as a by-product.

  • Traditionally, this reaction is catalyzed by sodium hydroxide (NaOH), a liquid alkali. However:

    • It generates wastewater during the washing and separation process.

    • This wastewater contains residual alkali and impurities, requiring treatment before disposal to avoid environmental harm.

  • As a greener alternative, calcium oxide (CaO) is used:

    • It is a solid catalyst.

    • 95% of it can be recovered and reused in subsequent cycles.

    • It reduces water usage and lowers the environmental footprint of the biodiesel production process.



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