Q.What is green chemistry?

Green chemistry has produced safer, cleaner alternatives to hazardous industrial chemicals and processes.

Two well-known achievements of green chemistry:

1. Dry cleaning without CCl4: Traditional dry cleaning used carbon tetrachloride (CCl4) as the solvent, which is toxic (liver-damaging), ozone-depleting, and carcinogenic. Green chemistry has replaced it with liquid/supercritical carbon dioxide (CO2) as the solvent, together with a suitable surfactant, which is non-toxic, non-flammable, and environmentally benign.

2. Chlorine-free bleaching: Traditionally, chlorine gas was used to bleach paper/textiles, producing toxic, persistent chlorinated organic by-products. Green chemistry has introduced hydrogen peroxide (H2O2) as an eco-friendly bleaching agent, since its only by-product is water, avoiding the formation of harmful chlorinated compounds.

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ZSM-5 is a shape-selective zeolite catalyst that dehydrates alcohols directly into a mixture of hydrocarbons usable as petrol, illustrating a green-chemistry route to fuel.

What is ZSM-5?

ZSM-5 (Zeolite Socony Mobil-5) is a type of synthetic zeolite — a microporous, crystalline aluminosilicate with a well-defined pore/channel structure. Because its pores are of molecular size, it acts as a shape-selective catalyst, allowing only molecules of a particular size and shape to enter, react, and diffuse out.

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Everyday green-chemistry applications include liquid-CO2 dry cleaning and H2O2 bleaching, both replacing toxic chemicals.

Green chemistry uses existing knowledge to make industrial and everyday processes environmentally benign. Examples from daily life:

1. Dry cleaning: The older solvent tetrachloroethene (Cl2C=CCl2) contaminates ground water and is a suspected carcinogen. It is now replaced by liquefied carbon dioxide with a suitable detergent - safer for health and environment. …