Green Chemistry
Air pollution caused by the combustion of fossil fuels:
Carbon Monoxide is
a poisonous gas,
formed by the
incomplete
combustion of
hydrocarbons. It
binds to the
haemoglobin in red
blood cells,
inhibiting the ability
to carry oxygen.
Oxides of Nitrogen are
formed under high
temperatures in the car
engine, when atmospheric
nitrogen is oxidised to
form nitrogen oxides.
They cause the formation
of low level ozone and
reacts with water to form
nitric acid, which falls as
acid rain.
Unburnt
hydrocarbons
are released in
car exhausts.
They react with
nitrogen oxides
to form low
level ozone,
which causes
breathing
difficulties.
Sustainability is the development of processes which prevent the
depletion of natural resources.
There are 5 principles of chemical sustainability:
1. Use industrial processes which will reduce or eliminate hazardous chemicals
Phasing out tetraethyl lead as a fuel additive, now using cycloalkanes
2. Minimise the production of waste materials
Cracking of distillation residues to gain chemical feedstock
3. Use renewable materials such as plant based substances
Fossil fuels being supplemented by biodiesel and bioalcohol
4. Seek alternative energy resources
Using solar, wind, tidal energy instead of consuming finite
resources
5. Ensure waste products are non toxic
Catalytic converters remove NOx, CO and Unburnt hydrocarbons from
exhaust gases from an internal combustion engine.
The 1992 Rio Declaration on Environment and Development defines the
rights of people to be involved in the development of their economies and
the responsibilities of human beings to safeguard the environment.
The Greenhouse Effect
Infrared radiation is absorbed by 3 covalent bonds:
C=O
O-H
C-H
This carbon dioxide molecule absorbs
Infrared radiation, which causes the
molecule to vibrate. The vibrating
molecule will eventually emit some of
this energy as radiation. This reemitted radiation is absorbed by other
gas molecules and at the Earth’s
surface, increasing the temperature.
Infrared Radiation
The greenhouse effect of a given gas is dependent on two things:
1. Its atmospheric concentration
2. Its ability to absorb infrared radiation
It is important to control global warming as there can be
damaging consequences:
 Rising Sea levels
 Melting polar ice caps
 Unusual weather patterns
 Increase in desertification
 Destruction of natural habitats
Scientists are trying to minimise climate change caused by the release of greenhouse gases:
 Providing Scientific Evidence that global
warming is taking place. Scientists use ice
cores from Antarctica to estimate CO2 levels
thousands of years ago – a proxy record.
Providing Information to
change opinions
 Educating Society
with information on
climate change,
through the media
(books, journals,
documentaries)
Reducing
Global
Warming
 Monitoring progress
against agreements such
as the Kyoto Protocol,
which was an
international agreement
setting targets to reduce
greenhouse gas
emissions.
 Alternative energy resources
such as solar power, wind, and
development of hydrogen fuel
cells.
Developing New Technologies
 More efficient
engines for
transport such
as lean burn
engines, hybrid
engines or
electric cars.
 Carbon Capture and
Storage – turned into
a liquid and injected
deep into the oceans
or stored in geological
formations. Waste
CO2 can be reacted
with metal oxides to
make stable
carbonates, such as
Calcium Carbonate.
The Ozone Layer
The ozone layer is in a region of the Earth’s upper atmosphere called the
stratosphere. Ozone is constantly being formed and broken down by the
action of UV radiation:
Oxygen molecules are broken down under high energy UV radiation forming two
oxygen atoms:
O2
2O
An oxygen atom then reacts with an oxygen molecule forming a molecule of ozone;
O2 + O
O3
Ozone is broken down when an ozone molecule reacts with an oxygen atom forming
two molecules of oxygen:
O3 + O
2O2
A natural state of balance is reached, where ozone is broken down at the same rate
at which it is produced;
O2 + O
O3
Chloroflourocarbons
CFCs are compounds which contain chlorine, fluorine, carbon and hydrogen only.
They were widely used because of their chemical properties:
 Low reactivity
 Volatile
 Non Toxic
Fridges
Air Conditioning
Aerosols
CFCs cause depletion of the ozone layer by free radical substitution:
Initiation - Under UV radiation, the C-Cl bond of the CFC breaks, producing a chlorine
radical.
CFCl3
Cl + CFCl2
Propagation (1) – Chlorine free radical reacts with an ozone molecule producing a
free radical and oxygen molecule.
Cl + O3
ClO
+ O2
Propagation (2) - Free radical reacts with an oxygen atom producing a chlorine free
radical and oxygen molecule.
ClO
+O
Cl
+ O2
Overall - ozone is depleted to oxygen molecules.
O3 + O
2 O2
Nitrogen Oxides, NO are a second type of free radical which deplete the ozone
layer. These come from lightning or aircraft engines. The reaction proceeds in two
propagation steps:
Propagation (1) – Nitrogen oxide free radical reacts with an ozone molecule
producing a free radical and oxygen molecule.
NO + O3
NO2 + O2
Propagation (2) - Free radical reacts with an oxygen atom producing a nitrogen
oxide free radical and oxygen molecule.
NO2
+O
NO + O2
Overall - ozone is depleted to oxygen molecules.
O3 + O
2 O2
Alternatives to CFCs have been developed:
 Hydrocarbons
o Adv: do not deplete the ozone layer
o Disadv: Contribute to global warming
 Hydrochlorofluorocarbons
o Adv: Chemically unreactive, useful in aerosols, refrigerants, air
conditioning, foam blowing
o Disadv: Found to deplete ozone and contribute to global warming
 Carbon Dioxide
o Adv: used as a blowing agent in expanded polymers. Liquid supercooled CO2 can be used as a safer solvent than chlorinated
hydrocarbons.
o Disadv: Contributes to global warming
Sustainability means meeting the demands of the population whilst
preventing the depletion of natural resources, so that future generations
are capable of meeting their own needs.
The Montreal Protocol is an agreement between 197 countries to stop the production of
CFCs and replace them with HFCs and HCFCs. International cooperation was reached to
promote the reduction of pollution levels. Pyrocol FEF should be used in fire extinguisher
rather than CFCs because it does not produce toxic or ozone depleting waste products like
other halogenated fire fighting materials.
Air pollution and the Catalytic Converter
Emissions from cars are some of the biggest air pollutants. The three main polluting
gases are:
a) Carbon Monoxide
b) Oxides of Nitrogen
c) Unburnt Hydrocarbons (Volatile Organic Compounds)
Carbon Monoxide is a
poisonous gas, formed by
the incomplete combustion
of hydrocarbons. It binds to
the haemoglobin in red
blood cells, inhibiting the
ability to carry oxygen.
Oxides of Nitrogen are formed under high
temperatures in the car engine, when
atmospheric nitrogen is oxidised to form
nitrogen oxides. They cause the formation of
low level ozone and reacts with water to
form nitric acid, which falls as acid rain.
Unburnt hydrocarbons are
released in car exhausts. They
react with nitrogen oxides to
form low level ozone, which
causes breathing difficulties.
Catalytic Converters
A catalytic converter is used to decrease the harmful emissions form an internal
combustion engine. A three way catalytic converter uses three metals as
heterogeneous catalysts, as they are in a different physical state to the reactants.
These metals are platinum, rhodium and palladium. The catalyst provides a
surface on which the reaction takes place.
 The CO and NO gas molecules diffuse over the catalytic surface. Some
molecules are held on to the metal surface by adsorption.
 Temporary bonds are formed between the catalytic surface and the gas
molecules. These bonds hold the gases in the correct orientation so that
they can react together.
 After the reaction, the CO2 and N2 products are desorbed from the
catalytic surface and diffuse away.
2CO + O2
2CO2
C7H16 + 11O2
7CO2 + 8H2O
2NO + 2CO
N + 2CO2
Catalysts and Sustainability
 Catalysts lower temperature requirements because they offer an
alternative route with lower activation energy. Less energy is required, so
less fossil fuels are burned, less CO2 produced.
 Selective catalysts mean fewer waste products are produced, because
only the desired product is formed. This increases atom economy and
promotes addition reactions.
 Enzymes are proteins with catalytic properties. They generate specific
products and operate close to room temperature and pressure.
Problems with Polymers
What is the issue?
Polymers contain non polar bonds, such as
C-H bonds, or strong bonds, like C-F bonds.
This makes them unreactive, and so they
are non-biodegradable. They cannot be
broken down by organisms in the natural
environment. They exist in the
environment for a very long time, and so
contribute to overflowing landfill sites.
Polymers must be recycled as they
are not biodegradable. However,
recycling is made very hard because
plastics are difficult to separate.
Polymers cannot be incinerated
because toxic fumes are released –
PVC is particularly hazardous
because Hydrogen chloride and
PCBs (polychlorinatedbiphenyls)
are formed.
What can chemists
do to resolve it?
Chemists are developing
new polymers which are
biodegradable and
compostable. They can be
derived from raw materials
such as starch, maize,
cellulose and lactic acid.
Polymers have identification codes (numbers 1-7)
and are separated into these groups using optical
scanning techniques, to make sorting quicker and
less labour intensive. They are then processed,
chopped, washed and the impurities are then
removed, before being melted and remoulded.
Burning polymers under controlled conditions
produces heat energy. Plastics are turned into
briquettes which are then burned to produce
electricity. Polymers can also be cracked to give
new alkenes, like synthesis gas. This can be used
as a chemical feedstock for conversion into useful
products or as a fuel in oil refineries.