2. Crude oil
• I will be using crude oil as a recurring example during
my PowerPoint (it represent the mixture).
• It is an exceptionally valuable resource that is made
up mostly of alkanes.
• Crude oil is not renewable as it takes years to form,
this makes it ever more precious.
• It is very impure, but oil is more efficient when it is
pure.
• As there is a limited amount of oil, we need to
minimise the amount of waste. A mechanism used to
minimise waste is fractional distillation. The process
will be repeated to furthermore to decrease the
amount of waste.
3. Fractional distillation
• Fractional distillation is
the breaking down of a
mixture into its
component parts.
• This is done by boiling
the mixture and
separating the products
by their varying boiling
points.
4. Method summary
• The mixture is separated by boiling and
collecting each substance as it boils.
• Each substance is called a fraction, this is a
mixture of hydrocarbons of similar chain
length. As they are of similar chain length they
have similar properties and therefore boil at a
similar time.
5. Method stages
• The crude oil is heated in a furnace.
• A mixture of both liquid and vapour rise, and pass into a
tower that is cooler at the top than the bottom.
• The vapours pass up this tower in which there are trays
stacked at different levels, the trays contain bubble caps to
trap the vapour.
• As the vapour rises it gets cooler, once sufficiently cool the
vapour will condense into liquid and will therefore be
collected in the tray below.
• The shorter chained hydrocarbons condense in the trays
nearer to the top of the tower and vice versa. This occurs as
they have lower boiling points, and are therefore liquids in
lower temperatures.
6. Products
Name Approx boiling temperature (C) Uses
Petrol 40 Vehicle Fuel
Naptha 180 Industrial cleaners and solvents, petrol
industry
Kerosene (paraffin) 200 Used as a gas for some heaters
Diesel Oil 250 Vehicles e.g. lorries (produces less CO2
than petrol)
Lubricating Oil 280 Reduce friction between multiple parts
Fuel Oil 310 The fuel used in ships and power stations
Greases and Wax 340 Used to make things like candles
Bitumen 367 Used for road tar and roofing
7. Method flaws
• Small collections/pockets of certain length hydrocarbons may get trapped
in trays that don’t corresponded with there boiling point.
• Also some substances have overlapping boiling points (as shown in the
table) and will therefore remain mixed.
• Pollutants are created, some pollutants may induce taxes or disposal
expenses.
• There are lots of products that are less valuable that are produced.
Product Gases Petrol Naptha Kersosen
e
Gas oil Fuel oil
and wax
Approxi
mate
boiling
point/ K
310 310-450 400-490 430-523 590-620 Above
620
Chain
length
1-5 5-10 8-12 11-16 16-24 25+
Percenta
ge
Present
2 8 10 14 21 45
8. Industrial cracking
• Individual fractions all have different values, the general trend
is that the longer the fractions are the less valuable they are.
The naphtha fraction from the fractional distillation of crude
oil is in huge demand, this makes it valuable as buyers will be
competing for it. This fraction is desired for petrol and by the
chemical industry.
• Industrial cracking is used to crack larger chains into more
valuable shorter chains.
• An additional benefit of cracking is that some alkenes are
produced, alkenes are more reactive than alkanes and
therefore have some desirable uses.
• There are two sub-categories of industrial cracking. Thermal
cracking and Catalytic cracking
9. Thermal cracking
• This involves heating alkanes to a high temperature (700-1200K),and putting them
under high pressure, up to 7000kPa.
• Such high amounts of energy are required to break carbon-carbon bonds. These
bonds break in a way that one electron from the pair in the covalent bond goes to
the end carbon atom in each chain, one of chains pulls hydrogen off of the other,
consequently one of the chains needs to be double bonded to fulfil the necessary
amount of bonds, this is how the alkenes are formed.
H H H
H
R - C - C - C - C
- R Thermal
H H H H
H H
. Cracking C C
H
- - R .
R - - C C
H H
H
H H
C C
H
H
H
R
H
H
R - - - H
C C + =
H H
Free radicals-electrons=
dot
10. Catalytic cracking
• Catalytic cracking is very similar to thermal cracking, but less
energy is used (lower temperature and pressure),
temperature approx. 720K.
• As there is less energy used a catalyst is required to make the
reaction successful. The catalyst used is a Zeolite catalyst.
Zeolites have a honeycomb structure with an enormous
surface area, because of these properties it will have
particularly regular collisions.
• The products of catalytic converting are mostly branched
alkanes, such as cyclokanes and aromatic compounds.
