Transcript
SOME WELL-PUBLICIZEDINCIDENTS FROM THE PAST
FEW DECADES…The Cuyahoga River in Ohio became so polluted with chemicals it
caught fire.
BHOPAL GAS TRAGEDY
A PLANT ACCIDENT IN BHOPAL, INDIA,
RELEASED METHYL ISOCYANATE.
NEARLY 4000 PEOPLE DIED.
Green Chemistry is the design ofchemical products and processes that
reduce or eliminate the use and/orgeneration of hazardous substances.
GREEN CHEMISTRY IS ABOUT...
Use of Catalyst in place of Reagents
Using Non-Toxic Reagents
Waste Minimisation at Source
Use of Renewable Resources
Use of Solvent Free or RecyclableEnvironmentally Benign Solvent
systems
Improved Atom Efficiency
THE PRINCIPLES OF GREEN
CHEMISTRY 1. Prevention
It is better to prevent waste than to treat or clean up
waste after it has been created.
Chemical
Process
2. Atom Economy:
Synthetic methods should be designed to maximize
the incorporation of all materials used in the process into
the final product.
THE PRINCIPLES OF GREEN
CHEMISTRY
Let us consider some common reactions like rearrangement,
addition, substitution & elimination to find out which is more
atom economical.
O
CH2
CH2
OH
Allylphenyl Ether O-Allyl Phenol
200oC
Butadiene Ethene Cyclohexene
CH2
CH2
CH
CH
CH2
CH2
+
CH3 CH2 C OC2H5
O
+ CH3 NH2
Ethyl propionate
Mol wt 102.13
Methyl amine
Mol wt 31.05
CH3 CH2 C NHCH 3
O
N-Methyl propionate
Mol wt 87.106
+ H5C2 OH
Ethyl Alcohol
Mol wt 46.06
3. Less Hazardous Chemical Synthesis:Wherever practicable, synthetic methods should be
designed to use and generate substances that possess
little or no toxicity to people or the environment.
THE PRINCIPLES OF GREEN
CHEMISTRY
4. Designing Safer Chemicals:Chemical products should be designed to effect their
desired function while minimising their toxicity.
5. Use of Renewable Feedstock:A raw material or feedstock should be renewable rather
than depleting whenever technically and economically
practicable.
THE PRINCIPLES OF GREEN
CHEMISTRY6. Safer Solvents & Auxiliaries:
The use of auxiliary substances (e.g., solvents or
separation agents) should be made unnecessary
whenever possible and innocuous when used.
• Water should be used as a solvent
• If water is not usable then more ecofriendly solvents
like supercritical CO2 or ionic solvents
• As far as possible synthesis is carried out without
solvents
7. Designing Safer Chemicals:Chemical products should be designed to effect their
desired function while minimising their toxicity.
EXAMPLES OF GREEN CHEMISTRY
• Safer dry cleaning
Initially gasoline and kerosene were used
Chlorinated solvents are now used
Supercritical/liquid carbon dioxide (CO2)
LEAD POLLUTION HAS BEEN DECREASED BY…
• Replacing tetraethyl lead with
less toxic additives (e.g., “lead-
free” gasoline). Such as MTBE &
ETBE (ethyl tertiary butyl ether)
8. Design for Energy Efficiency:
Energy requirements of chemical processes should be
recognised for their environmental and economic impacts
and should be minimised. If possible, synthetic methods
should be conducted at ambient temperature and pressure.
This can be achieved by
• Use of proper catalyst , enzymes
• Use of micro organisms for organic synthesis
• Use of renewable materials
THE PRINCIPLES OF GREEN
CHEMISTRY
POLY LACTIC ACID (PLA) FOR PLASTICS PRODUCTION
9. Reduce Derivatives:
Unnecessary derivatization (use of blocking groups,
protection/de-protection, and temporary modification of
physical/chemical processes) should be minimised or
avoided if possible, because such steps require additional
reagents and can generate waste.
THE PRINCIPLES OF GREEN
CHEMISTRY
10. Catalysis:Catalytic reagents (as selective as possible) are superior
to stoichiometric reagents.
• Catalysts make the
reaction faster
decrease the energy requirement
minimize waste.
11. Catalysis:Catalytic reagents (as selective as possible) are superior
to stoichiometric reagents.
• Catalysts make the
reaction faster
decrease the energy requirement
can produced single desired product
minimize waste.
THE PRINCIPLES OF GREEN
CHEMISTRY
12. Designing of Degrading Products:Chemical products should be designed so that at the
end of their function they break down into innocuous
degradation products and do not persist in the
environment.
Examples:
Polyethylene, polystyrene are not biodegradable but
biodegradable polymer like polyhydroxybutyrate-
hydroxyvalarate ( PHBV )
Synthetic insecticides remains in the food grains &
vegetables & do not get degraded but natural insecticides
(chilli, neem etc.) get easily degraded after killing the
insect.
THE PRINCIPLES OF GREEN
CHEMISTRY
13. New Analytical Methods: OR Real Time
Analysis for Population Prevention:Analytical methodologies need to be further developed
to allow for real-time, in-process monitoring and control
prior to the formation of hazardous substances.
THE PRINCIPLES OF GREEN
CHEMISTRY
Analytical Substances and the form of a substance
used in a chemical process should be chosen to minimise
the potential for chemical accidents, including releases,
explosions, and fires.
14. Safer Chemicals for Accidents Prevention:
15. Safer Chemicals for Accidents Prevention:
THE PRINCIPLES OF GREEN
CHEMISTRY
Analytical Substances and the form of a substance
used in a chemical process should be chosen to minimise
the potential for chemical accidents, including releases,
explosions, and fires.
The reagents & reaction should be risk free, in the
chemical process, to minimize the chemical accidents,
explosion, fires & gas release.
1. Reaction Yield:
The reaction should have high % of yield.
Efficiency Paramenters
2. Atom Economy:
Atom economy (atom efficiency) describes
the conversion efficiency of a chemical process in terms of
all atoms involved (desired products produced).
For the reaction, atom economy should be high i.e. maximum.
2. Atom Economy:Let us consider some common reactions like
rearrangement, addition, substitution & elimination to find
out which is more atom economical.
O
CH2
CH2
OH
Allylphenyl Ether O-Allyl Phenol
200oC
2. Atom Economy:
Butadiene Ethene Cyclohexene
CH2
CH2
CH
CH
CH2
CH2
+
3. Conversion:
OR
4. Reaction Selectivity:
5. Environmental Load Factor:It should be minimum.
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