14.7 Green Chemistry

14.7.1 Introduction

It is well known fact that self-sufficiency in food has been achieved in India since late 20th century by using fertilizers and pesticides and exploring improved methods of farming, good quality seeds, irrigation etc. But over – exploitation of soil and excessive use of fertilizers and pesticides have resulted in the deterioration of soil, water and air.

The solution of this problem does not lie in stopping the process of development that has been set in; but to discover methods, which would help in the reduction of deterioration of the environment. Green chemistry is a way of thinking and is about utilising the existing knowledge and principles of chemistry and other sciences to reduce the adverse impact on environment.

Green chemistry is a production process that would bring about minimum pollution or deterioration to the environment. The byproducts generated during a process, if not used gainfully, add to the environmental pollution. Such processes are not only environmental unfriendly but also cost-ineffective.

The waste generation and its disposal both are economically unsound. Utilisation of existing knowledge base for reducing the chemical hazards along with the developmental activities is the foundation of green chemistry. Have you perceived the idea of green chemistry?

It is well known that organic solvents such as benzene, toluene, carbon tetrachloride etc., are highly toxic. One should be careful while using them. As you know, a chemical reaction involves reactants, attacking reagents and the medium in which the reaction takes place.

Extent of any reaction depends upon physical parameters like temperature, pressure and use of catalyst. In a chemical reaction, if reactants are fully converted into useful environmental friendly products by using an environment friendly medium then there would be no chemical pollutants introduced in the environment.

During a synthesis, care must be taken to choose starting materials that can be converted into end products with yield approximately upto 100 per cent. This can be achieved by arriving at optimum conditions of synthesis.

It may be worthwhile to carry out synthetic reactions in aqueous medium since water has high specific heat and low volatility. Water is cost effective, noninflammable and devoid of any carcinogenic effects.

 

14.7.2 Green Chemistry in day-to-day Life

(i)Dry Cleaning of Clothes

Tetra chlroroethene (Cl2C=CCl2) was earlier used as solvent for dry cleaning. The compound contaminates the ground water and is also a suspected carcinogen. The process using this compound is now being replaced by a process, where liquefied carbondioxide, with a suitable detergent is used.

Replacement of halogenated solvent by liquid CO2 will result in less harm to ground water. These days hydrogen peroxide (H2O2) is used for the purpose of bleaching clothes in the process of laundary, which gives better results and makes use of lesser amount of water.

 

(ii)Bleaching of Paper

Chlorine gas was used earlier for bleaching paper. These days, hydrogen peroxide (H2O2) with suitable catalyst, which promotes the bleaching action of hydrogen peroxide, is used.

 

(iii)Synthesis of Chemicals

Ethanal (CH3CHO) is now commercially prepared by one step oxidation of ethene in the presence of ionic catalyst in aqueous medium with a yield of 90%.

 

(iv)‘Green Solution’ to Clean Turbid Water

Powder of kernel of tamarind seeds has been found to be an effective material to make municipal and industrial waste water clean. It is non-toxic, biodegradable and costeffective material. This powder is usually discarded as agricultural waste. The present practice is to use alum to treat such water.

It has been found that alum increases toxic ions in treated water and can cause diseases. Green chemistry, in a nutshell, is a cost effective approach which involves reduction in material, energy consumption and waste generation.

 

What is our responsibility as a human being to protect our environment?

Some concepts, if followed by an individual, contribute towards a better quality of our environment and human life. Always set up a compost tin in your garden or any other place in your home and use it to produce manure for your plants to reduce the use of fertilizers.

Use a cloth bag and avoid asking for plastic carry bags when you buy groceries, vegetables or any other item. See that all newspapers, glass, aluminum and other items in your area are recycled. We might have to take little trouble to locate such dealers.

We must realize that we do not have solutions for every problem but we can concentrate on issues, which we feel strongly about and can do some thing about. We should take care to put into practice whatever we preach. Always remember environment protection begins with us.

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