Environmental Efficiency of
Chemical Processes
Dr. Anuj Kumar Mittal, Head-R&D
PI Industries Ltd.
IGCW Convention - December 2013
Prelude
WHAT IS GREEN CHEMISTRY?
 “Green Chemistry is essentially a way of thinking rather than a new branch of
chemistry and is about utilizing a set of principles that seek to reduce the
environmental impact of chemical processes and products”
- Royal Society of Chemistry
 ‘Green Chemistry’ aims to improve the way that chemicals are both produced and
used in chemical processes in order to reduce any impact on man and the
environment.
 It is not just about industrial production. The principles involved apply equally to
the use of chemicals in for example laboratories and education.
Promotion of ‘Green Chemistry’ is one of the most important ways
in which chemistry and chemists can contribute to
sustainable development
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WHAT CONSTITUTE
ENVIRONMENTAL EFFICIENCY?
Atom Efficiency
Energy Conservation
Waste Minimization
Substitution
designing processes to maximize the amount of raw material that
is converted into the product
designing more energy efficient processes
recognizing that the best form of waste disposal is not to create
waste in the first place
using safer, more environmentally benign raw materials and
solvents or solvent free processes.
By improving resource efficiency, ‘Green Chemistry’ provides
financial benefits from lower material usage, energy and capital
expenditure costs in addition to the environmental benefits.
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Efficiency of a Chemical Process
WHAT IS AN ‘EFFICIENT’ PROCESS?

Is it high yielding ?

No. Yield alone does not characterize process efficiency

Then – what else does?

Let us look at the example below:
(NH3)2PtI2 + Ag2SO4 + 2 KCl → (NH3)2PtCl2 + 2 AgI + K2SO4

If one started with 100mg and isolated 50 mg of the main product:
 the mass yield is 50% based on the base raw material
 the theory yield is 80.5% based on the base raw material
One may call this a “good” process…
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PROCESS EFFICIENCY

Let us look closely at the “balanced equation”:
(NH3)2PtI2 + Ag2SO4 + 2 KCl → (NH3)2PtCl2 + K2SO4 + 2 AgI

Which of the reactants is the “limiting reactant”? Look at the table below (actual process
quantities)
Compound

molecular wt
milligrams
millimoles
(NH3)2PtI2
482.960
100
0.207
Ag2SO4
311.794
63
0.202
KCl
74.551
330
4.43
(NH3)2PtCl2
300.057
Used a large excess of KCl (only two equivalents were required by the reaction
stoichiometry). Should have used a bit more silver sulfate. The silver sulfate thus serves as
the limiting reagent ; theoretical yield of cisplatin was actually only 0.202 millimoles, or
60.6 mg, and our actual yield then is (50 mg/60.6 mg)*100% = 82.5% of the theoretically
possible amount of product
Is the process “efficient”?
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WHAT IS ATOM EFFICIENCY?

82.5% yield based on the limiting raw material – that is good! Or is it?

ATOM IS TOO PRECIOUS A RESOURCE TO WASTE – BARRY TROST

Professor Barry Trost, a chemist at Stanford University, felt that reliance on “yield”
as a measure of reaction efficiency represented an inappropriate measure

Reliance on yield as a measure of efficiency suggests that we are better at carrying
out chemical transformations than we in fact are.

He developed a concept called “atom economy,” looking at a chemical reaction
from the perspective of how many input atoms are incorporated in the desired
product, vs. how many are discarded as waste.
One should design a process to maximize the amount of raw
material that is converted into the product
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ATOM EFFICIENCY = ATOM ECONOMY

Look at the table below
Compound
atoms used in pdt
wt used
atoms discarded
wt discarded
(NH3)2Pt
229.151
I2
253.809
-
-
Ag2SO4
311.794
2 KCl
Cl2
70.906
K2
78.197
Totals
(NH3)2PtCl2
300.057
I2 K2 Ag2SO4
643.800
(NH3)2PtI2
Ag2SO4



We now see less than a third of the atoms in the starting materials is converted
to the product
Atom Economy for this process = 300.057/(300.057 + 643.800)*100% = 31.8%
Considering the excess KCl used in actual experiment and lower than 100%
theoretical yield, actual atom economy = (actual yield/mass of all
reactants)*100% = [50 mg/(100 mg + 63 mg + 330 mg)]*100% = 10.1%.
Conclusion: 89.9% of atoms used in the process are converted to
waste!!!
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TAKEAWAY

Waste is increasingly expensive to dispose of and is a major source of pollution
arising from the chemical industry.

Maximizing atom efficiency is linked to waste reduction. This means designing
chemical reactions so that as many atoms of starting material as possible end
up in useful product.

In an ideal process, all reactant atoms end up within the useful product
molecule. Hence, no waste is produced!

Inefficient, wasteful reactions have low atom economy

Efficient processes have high atom economy and are important for sustainable
development. They conserve natural resources and create less waste
Better Atom Economy = Lower Product Cost
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EXAMPLE


Freidel-Craft reactions using Lewis acid catalyst such as AlCl3 are very Atom
Uneconomic
New catalysts for this process such as zeolites change these reactions to more
atom economic and environmentally friendly
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WHAT IS E-FACTOR?

E-Factor is the number of kilograms of waste generated for making one kg of
the product

It is a direct indicator of the environmental efficiency of a chemical process

Obviously, E-factor calculation takes into account all the inputs and outputs in a
process – including solvents and catalysts

Solvents contribute negatively to E-factor if they are not efficiently recovered
and recycled. Hydrocarbon solvents are very high on the negative list.
Efficient Process: High Atom Economy + Low E-Factor
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Environmental Efficiency
ENERGY CONSERVATION
 Our focus should not only be on using alternative, environmentally friendly
chemicals in synthetic routes but also to increase reaction rates and lower
reaction temperatures to save energy.
 The environmental footprint is more to do with energy consumption, the climate
crisis and depleting natural resources.
 Chemists must recognize that until now there was very little thought to energy
requirements in chemical synthetic chemical processes.
 Designing more efficient methods is a necessity and if possible, synthetic methods
should be conducted at room temperature and pressure to reduce energy
requirements.
There is an urgent need to design more energy efficient processes
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WASTE MINIMIZATION
 In the last decades, 600-700 million tones of chemical materials are produced
every year (excluding fossil fuels, fertilizers and medicines) from the chemical
industries of the world. One can imagine the amount of waste that was generated
due to this.
 Green Chemistry looks very carefully on reaction efficiency, use of less toxic
solvents, minimizing the hazards of feedstocks & products and reduction of waste.
 In order to achieve Waste Minimization and Prevention, we may
 make use of catalysts instead of stoichiometric quantities,
 reduce the use of chemical derivatives and
 use renewable feedstocks
It is better to prevent than to clean or to treat afterwards
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SUBSTITUTION
 Green Chemistry must strive, wherever practical, to design safer synthetic
methods by using less toxic substances as well as the products of the synthesis.
 Less toxic materials mean lower hazards to workers in industry and research
laboratories and less pollution to the environment.
 Solvents, separation agents and auxiliary chemicals used in synthetic chemistry
must be replaced or reduced with less toxic chemicals.
 We must strive to use safer, more environmentally benign raw materials and
solvents or solvent free processes.
Replace more toxic raw materials and solvents with eco-friendly
chemicals
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SUMMARY
 Atom economy and E-Factor of a process are important criteria for process
chemists
 Atom Economic processes are more efficient than simply “high yielding” processes
 Such processes are also more environment friendly as they generate less waste
 Wherever possible, process chemists should evaluate atom economy of a reaction
and use the best option rather than look only at yields.
 Once the process is established at commercial scale it is important to continuously
review and look into possibilities of improvement w.r.t. 3R principle.
 Environmentally efficient processes are cost efficient and energy efficient too.
Atom Efficiency, Energy Conservation, Waste Minimization and
Substitution are key to achieve Environmental Efficiency in a
Chemical Process
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Thank you