1. Decaffeinating coffee with scCO2

2. Green
Chemistry
What is it?
Why do we need it?

3. Learning outcomes
Describe principles and discuss issues of chemical sustainability
Understand the importance of establishing international cooperation to promote the reduction of pollution levels.

4. Green Chemistry Means different things to different people.
It’s not just one thing – there are many aspects to Green Chemistry.
Lets consider some of the ‘Principles of Green Chemistry’.

5. The 12 principles Prevention Atom economy
Less hazardous chemical synthesis
Designing safer chemicals
Safer solvents and auxiliaries
Design for energy efficiency
Use of renewable feedstocks
Reduce derivatives
Catalysis
Design for degradation
Real-time analysis for pollution prevention
Inherently safer chemistry for accident prevention

6. Principles of Green Chemistry
It’s better to develop reactions with fewer waste products than to have to clean up the waste.
i.e. high atom economy
Reactants from renewable sources (e.g. plants are preferable).
Processes should rely on renewable energy resources, rather than fossil fuels.
Reactions that use fewer reactants, particularly ones that aren’t hazardous, are better.
Materials produced by chemists should be biodegradable so they don’t persist in the environment after they’ve been used.
Solvent use should be minimised, & solvents should be benign in their impact on the environment.

7. Yield vs Atom economy Yield can be calculated as:
% yield = mass (g) of product obtained x 100
theoretical yield (g)
The yield tells us how efficient a reaction is in terms of the amount of product we obtained relative to the maximum we could get from the amounts of reactants we used.
But it doesn’t take account of waste products!

8. sum of RFMs of all products
Yield vs Atom economy
Atom economy can be calculated as:
% AE = x 100
A reaction may have a high % yield but a low atom economy.
RFM desired product
sum of RFMs of all products

9. Atom economy – some examples
Calculate the % atom economy of CH2Cl2:
CH4 + 2Cl2 → CH2Cl2 + 2HCl
RFM: CH2Cl2 = 85, HCl = 36.5
% AE = x 100
AE = x 100 = 53.8 %
RFM desired product
sum of RFMs of all products 85
85 + (2 x 36.5)

10. Atom economy – some examples
CH4 + 2Cl2 → CH2Cl2 + 2HCl
An atom economy of 53.8% may be considered to be quite low. How could a chemical company maximise their profits from this chemical process?
The by-product is hydrogen chloride, which can be sold as a gas or made into hydrochloric acid. These can then be sold.

11. Atom economy – some examples
Calculate the % atom economy of ethylene oxide:
RFM: C2H4O = 44, CaCl2 = 111, H2O = 18
AE = x 100 = 37.4 %
(2 x 44)
(2 x 44) (2 x 18)

12. Atom economy – some examples
Ethylene oxide – A case of Green Chemistry
An atom economy of 37.4% is particularly poor, and this is a very wasteful process.
Nonetheless, this was the preferred method for synthesising ethylene oxide for many years.

13. Atom economy – some examples
Ethylene oxide – A case of Green Chemistry
Recently, a method of synthesising ethylene oxide from ethene and oxygen using a silver catalyst was developed.
What’s the atom economy of this reaction?
100 %

14. The role of catalysts
Catalysts have a crucial role to play in the future of Green Chemistry.
They allow the development of new reactions which require fewer starting materials and produce fewer waste products.
They can be recovered and re-used time and time again.
They allow reactions to run at lower temperatures, cutting the amount of energy required.

15. Catalysts in Action
Animation credit: Robert Raja / University of Southampton

16. The future of chemistry
We need to reconsider the way we go about all aspects of our lives.
The planet is feeling a burden.
Science has the potential to solve our problems.
Green Chemistry can play a significant role in a sustainable future.

17. Question
How does green chemistry enable chemicals and resources to be preserved?

18. Controlling air pollution
Emissions of nitrogen oxides
A three-way catalytic converter

19. Learning outcomes
• Explain the formation of carbon monoxide, oxides of nitrogen and unburnt hydrocarbons from the internal combustion engine.
• State environmental concerns relating to the toxicity of these molecules and their contribution to low-level ozone and photochemical smog.
• Outline how a catalytic converter decreases toxic emissions via adsorption, chemical reaction and desorption.
• Outline the use of infrared spectroscopy in monitoring air pollution.
© Pearson Education Ltd 2008
This document may have been altered from the original

20. POLLUTANT GASES FROM INTERNAL COMBUSTION ENGINES
POLLUTANTS
POLLUTANT GASES FROM INTERNAL COMBUSTION ENGINES
Carbon monoxide CO
Origin • incomplete combustion of hydrocarbons in petrol
because not enough oxygen was present
Effect • poisonous
• combines with haemoglobin in blood
• prevents oxygen being carried to cells
Process C8H18(g) ½O2(g) —> 8CO(g) H2O(l)

21. POLLUTANT GASES FROM INTERNAL COMBUSTION ENGINES
POLLUTANTS
POLLUTANT GASES FROM INTERNAL COMBUSTION ENGINES
Oxides of nitrogen NOx - NO, N2O and NO2
Origin • combination of atmospheric nitrogen and
oxygen under high temperature
Effect • aids formation of photochemical smog which is
irritating to eyes, nose, throat
• aids formation of low level ozone which affects plants and is irritating to eyes, nose and throat
Process sunlight breaks oxides NO2 —> NO + O
ozone is produced O + O2 —> O3

22. POLLUTANT GASES FROM INTERNAL COMBUSTION ENGINES
POLLUTANTS
POLLUTANT GASES FROM INTERNAL COMBUSTION ENGINES
Unburnt hydrocarbons CxHy
Origin • hydrocarbons that have not undergone combustion
Effect • toxic and carcinogenic (cause cancer)

23. POLLUTANTS POLLUTANT FORMATION Nitrogen combines with oxygen
N2(g) + O2(g) —> 2NO(g)
Nitrogen monoxide is oxidised
2NO(g) + O2(g) —> 2NO2(g)
Incomplete hydrocarbon combustion
C8H18(g) ½O2(g) —> 8CO(g) H2O(l)

24. POLLUTANTS POLLUTANT REMOVAL Oxidation of carbon monoxide
2CO(g) + O2(g) —> 2CO2(g)
Removal of NO and CO
2CO(g) + 2NO(g) —> N2(g) + 2CO2(g)
Aiding complete hydrocarbon combustion
C8H18(g) ½O2(g) —> 8CO2(g) H2O(l)

25. CATALYTIC CONVERTERS REMOVAL OF NOx and CO • CO is converted to CO2
• NOx are converted to N2
2NO(g) CO(g) —> N2(g) CO2(g)

26. CATALYTIC CONVERTERS REMOVAL OF NOx and CO • CO is converted to CO2
• NOx are converted to N2
2NO(g) CO(g) —> N2(g) CO2(g)
• Unburnt hydrocarbons converted to CO2 and H2O
C8H18(g) ½O2(g) —> 8CO2(g) H2O(l)

27. CATALYTIC CONVERTERS REMOVAL OF NOx and CO • CO is converted to CO2
• NOx are converted to N2
2NO(g) CO(g) —> N2(g) CO2(g)
• Unburnt hydrocarbons converted to CO2 and H2O
C8H18(g) ½O2(g) —> 8CO2(g) H2O(l)
• catalysts are rare metals - RHODIUM, PALLADIUM
• metals are finely divided for a greater surface area
- this provides more active sites

28. CATALYTIC CONVERTERS
STAGES OF OPERATION

29. CATALYTIC CONVERTERS STAGES OF OPERATION
Adsorption • NO and CO seek out active sites on the surface
• they bond with surface
• weakens the bonds in the gas molecules
• makes a subsequent reaction easier

30. CATALYTIC CONVERTERS STAGES OF OPERATION
Reaction • being held on the surface increases chance of
favourable collisions
• bonds break and re-arrange

31. CATALYTIC CONVERTERS STAGES OF OPERATION
Desorption • products are released from the active sites

32. CATALYTIC CONVERTERS STAGES OF OPERATION
Adsorption Reaction Desorption

33. CATALYTIC CONVERTERS STAGES OF OPERATION
Adsorption • NO and CO seek out active sites on the surface
• they bond with surface
• weakens the bonds in the gas molecules
• makes a subsequent reaction easier
Reaction • being held on the surface increases chance of
favourable collisions
• bonds break and re-arrange
Desorption • products are released from the active sites