Download Chemistry: Unit F322: Chains, Energy and Resources

Chemistry: Unit F322: Chains, Energy and Resources
Fuels
Fractional Distillation is a method of separating the mixture of hydrocarbons in crude oil
according to their boiling points.
Fractions which
are more volatile,
with lower boiling
points and shorter
carbon chains, rise
to the top of the
fractionating
column and
condense where it
is cooler.
Shorter Hydrocarbon = Fewer Van
der Waals’ Forces = less energy
required to overcome forces
Longer chain
hydrocarbons
have a higher
boiling point and
so separate near
to the base of the
fractionating
column.
Longer Hydrocarbon = More Van
der Waals’ Forces = more energy
required to overcome forces
A good fuel must have three properties:
 Volatile (turns to gas easily)
 Easy to ignite
 Burns completely in air, no soot produced
There is most demand for short chain hydrocarbons because they burn most efficiently. In
order to match the demand, long chain hydrocarbons undergo a process called Catalytic
Cracking in order to convert them into shorter, more useful alkanes and alkenes.
Long chain alkane
Heat, Pressure,
AlO catalyst
shorter chain alkanes and alkenes
A catalyst is used because they speed up the rate of reaction and provide an alternative
reaction route which has lower activation energy (lower temperatures required, so less fuel
and less waste)
Petrol contains alkanes with between 4 and 12 carbon atoms. When straight
chain alkanes are compressed in the cylinder of a car engine, they pre-ignite
before the spark. This is known as knocking. Lead used to be used to
prevent this, but now, we use branched alkanes and cyclic hydrocarbons to
promote efficient combustion.
Producing Branched Hydrocarbons: Isomerisation
Unbranched, straight chain hydrocarbons are converted into branched chains under a high
temperature with a platinum catalyst.
Producing Cyclic Hydrocarbons: Reforming
+ 2H
Reforming turns straight chain alkanes into cyclic alkanes under high temperatures with a
platinum catalyst. These are used in petrol and as a feedstock for a wide range of organic
chemicals such a pharmaceuticals and dyes.
Research Octane Number is used to grade the quality of petrol. If an alkane has a high RON,
it burns efficiently. If an alkane has a low RON does not combust efficiently and tends to preignite:
Longer chains = Lower RON
Increased Branching = Higher RON
The ideal fuel is a short chain with lots of branching.
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.
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.
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.