1. Crude Oil
Scientists have put forward the theory that crude oil was formed over millions of years and that this process is in fact continuing today.
The theory proposed by Engler is that coal, crude oil, and natural gas all had their origins in the vast oceans that covered most of the earth in prehistoric times.
Tiny plants and animals living close to the shore died and, over a period of time, their remains sank to the bottom of the ocean where they were covered by layers of mud and silt.
Over thousands of years these layers were converted into sedimentary rock.
As a result of the action of bacteria, heat and great pressure on the organic material, it was gradually changed into fossil fuels.

2. Crude Oil
Over time, with the disappearance of the oceans and due to massive land upheavals the oil deposits came to lie below exposed land masses. The oil and gases percolated where possible through the layers of porous rock above them. Eventually they found their way blocked by solid impervious rock. Here they collected and formed natural underground reservoirs enclosed above by a hard rock called ‘caprock’. It is precisely these non-porous rocks that geologists seek when searching for oil and gas. It is with great difficulty that this rock is drilled to reach the oil below.

3. Crude Oil

4. Fractional Distillation
Method of separating a mixture of liquids using their different boiling points
As the mixture is heated the temperature rises steadily
As the boiling point of each substance is reached that substance begins to boil off
Can then be collected by condensing it.

5. Fractional Distillation
As a particular liquid boils off the temperature remains the same
Once all that particular liquid has evaporated then the temperature begins to rise again
Until the next liquid in the mixture begins to boil off

6. Fractional Distillation
Each liquid that distils off is called a Fraction
Hence the name Fractional Distillation
A column with a large surface area improves the efficiency because
it gives a more accurate separation of temperatures
allows several cycles of evaporation/condensation
This is called a Fractionating Column or Fractionating Tower (on a large scale)

7. Boiling points differ due to
Relative Molecular Mass
Bigger mass the higher the BP
Degree of branching
More branched the lower the BP
Presence of polar groups e.g. C=O or - OH which leads to intermolecular forces increases the boiling point

8. Refinery Gas
Naphtha
Light Gasoline
Kerosene
Diesel
Gas Oil
Residue (bitumen)

9. Fractional Distillation
Vapour passes up column and as it rises its temperature drops.
At various levels up the column are trays and the largest molecules in the vapour phase at that temperature condense and collect in the tray.
They can then be tapped off.
High boiling point compounds condense near base while low boiling point compounds condense near the top
Low boiling point petroleum gases exit and have to be pressurised and cooled in order to be collected and distributed.

10. Natural Gas Liquid Petroleum Gas
Natural gas is the second most important source of alkanes after crude oil. It is a mixture consisting mostly of methane. Natural gas is an extremely important fuel both for domestic and industrial use.
Liquid Petroleum Gas
Liquefied petroleum gas is propane and butane that is liquefied under pressure.
Mercaptans
Liquid petroleum gas is odourless. Mercaptans are smelly organic sulphur compounds added to liquid petroleum gas so that leaks can be detected almost instantly by smell. (e.g ethanethiol, C2H5SH)

11. Octane Number Composition of Petrol
Petrol is not a simple compound
It is a complex mixture of many hydrocarbons
In an attempt to grade petrol researchers came up with Octane Number as a standard
Octane Number
Octane number is a measure of the tendency of a fuel to auto-ignite or cause knocking.

12. Petrol Petrol straight from Fractionating Column is not a good fuel
It pre-ignites [ignites due to compression before the spark]
Called knocking or auto-ignition or pinking
It was discovered that straight chain alkanes knock more than branched
2,2,4-trimethylpentane [iso-octane] is best
Pure 2,2,4-trimethylpentane is given an Octane Number of 100

13. Reference Hydrocarbons
2,2,4 trimethylpentane has Octane Number of 100
Straight chained Heptane has an Octane Number of 0
Fuels are compared to these and given a value e.g.
95 octane is the same as a mixture of
95% 2,2,4 trimethylpentane and 5% heptane
Good petrol has octane number of 97 or more

14. Four Stroke Petrol Engine

15. Four Stroke Petrol Engine

16. Factors affecting Octane Number
1. The shorter the chain the higher the octane number
Heptane C7H16 = 0
Hexane C6H14 = 25
Pentane C5H12 = 62
Butane C4H10 = 94

17. Factors affecting Octane Number
2. The more branched the chain the higher the octane number
E.g. C7H16
Heptane = 0
2-methylhexane = 65
2,3 dimethylpentane = 91

18. Factors affecting Octane Number
3. Cyclic compounds have a higher octane number than straight chain compounds
Hexane = 25
Cyclohexane = 83

19. Factors affecting Octane Number
4. Adding compounds such as tetraethyl lead or MTBE (methyl tertiary butyl ether)
Lead
MTBE Octane Number = 118

20. Lead in Petrol
In 1920’s it was found that adding small amounts of tetraethyl lead Pb(C2H5)4 reduced knocking significantly
Lead in atmosphere is dangerous in cities and especially to children
Banned in petrol since 2000
Pb poisons catalytic converters which reduce emissions of other pollutants

21. Processes carried out in an Oil Refinery to Improving Octane Number
Four ways to improve the Octane Number
1. Catalytic Cracking 2. Isomerisation 3. Reforming [Dehydrocyclisation] 4. Adding oxygenates

22. Processes carried out in an Oil Refinery to Improving Octane Number
Catalytic Cracking : the process involves taking long chained hydrocarbons and converting them into shorter chained hydrocarbons, some saturated and unsaturated products, which are more useful. Also produces important products for petrochemical industry
2,methyl propane
2,methyl propene
Octane

23. Processes carried out in an Oil Refinery to Improving Octane Number
Isomerisation : a straight chain alkane with a low octane number
is converted to its branched chained isomer with a
higher octane number. (using heat and catalyst)
Pentane methyl butane
Octane Number = Octane Number = 93

24. Processes carried out in an Oil Refinery to Improving Octane Number
Dehydrocyclisation : is the conversion of a straight chain alkane with low octane number into a ring compound with a higher octane number.
Hexane Cyclohexane Benzene +
3H2 + H2
Octane Number = Octane Number = Octane Number = >100

25. 3. Reforming [Dehydrocyclisation]
Using catalysts to form ring compounds
Straight-chain compounds changed to cycloalkanes
Hydrogen removed and ring compounds formed - hence dehydrocyclisation
Cycloalkanes changed to aromatic compounds
Petrol contains 3 - 4% Benzene
Benzene is carcinogenic - cause for concern

26. Processes carried out in an Oil Refinery to Improving Octane Number
4. Adding Oxygenates
Fuel containing oxygen in its molecules
(a) Methanol [CH3OH]
(b) Ethanol [C2H5OH]
(c) MTBE - Methyl Tertiary Butyl Ether
Oxygenates
Increases the octane number of the fuel
Burn cleanly - fewer pollutants e.g. less CO