Hydrocarbons can be separated from crude oil using fractional distillation based on their different boiling points. Long chain hydrocarbons can be cracked into shorter chains through thermal or catalytic cracking. Thermal cracking uses high temperature and pressure while catalytic cracking uses lower temperature, pressure and a zeolite catalyst. Alkanes have various uses as fuels, solvents, and in biogas production where bacteria convert organic waste into methane gas. Alkenes are used to produce important polymers like polyethylene, polypropylene, and PVC.

1. USES OF
HYDROCARBONS IN
RELATIONTOTHEIR
PROPERTIES

2. Hydrocarbons
■ Oil is a mixture of HYDROCARBONS
■ Most of the compounds in crude oil consist of molecules
made up of hydrogen and carbon atoms only.
■ We can separate the different unchanged hydrocarbons
from crude oil by FRACTIONAL DISTILLATION.

3. KEY WORDS:
Boiling point:
Volatility:
Viscosity:
Flammability
:
Properties of
hydrocarbons

4. Sources of Hydrocarbons
Petroleum

5. Fractional Distillation of Petroleum

6. HEAT EVAPORATE
CONDENSE
LOW boiling points
HIGH boiling points
1. Crude oil is heated
2. Hydrocarbons
evaporate
3. Fractionating
column is hotter
at the bottom /
cooler at the top
4. Vapours condense
at their boiling
points / at
different levels.

8. Cracking
■ Short chain hydrocarbons are far more in demand than long chain hydrocarbons.
We solve this problem by ‘cracking’ long chain hydrocarbons (breaking them into
smaller hydrocarbons)

9. Types of cracking
■ Themal cracking
– High temperature and pressure
■ Catalytic cracking
– (Relatively) Low temperature and pressure
– Used in the production of petrol

10. Thermal Cracking
 In the thermal cracking long chain molecules are split apart or ‘cracked’.
 In thermal cracking, the bonds are broken using a high temperature (400 –
900oC) and a high pressure (70 atmospheres).
 An example of such a reaction is:
C8H18  C6H14 + C2H4
C C
H
H
H
H
+
ethene
C C
H
H
H
H H
C C C C C C
H
H
H
H
H
H
H
H
H
H
H
H
H
Octane
C C
H
H
H
H H
C C C C
H
H
H
H
H
H
H
H
H
hexane
Ethene
is used
to make
plastics
Heat
pressure
Used as
a fuel
This is an
example of an
alkene. It has
at least 1
double bond
and has he
formula CnH2n

11. Catalytic cracking
■
■ In catalytic cracking, the bonds are broken using a high temperature (450
oC, which is generally lower than in thermal cracking), a slight pressure
(slightly greater than 1 atmosphere), and a zeolite catalyst.
■ Catalytic cracking is cheaper and more efficient than thermal cracking as
it uses a lower temperature and pressure.
■ The zeolite catalyst favours the formation of branched alkanes and
cycloalkanes, which are widely used in motor fuels. The most important
product of catalytic cracking is 2-methylheptane, which is the major
component of petrol. It also produces aromatic hydrocarbons such as
benzene, which have a variety of uses.
Eg
C
H
H
H C
H
H
C
H
H
C
H
H
H
H
H
C
C C
C
C
C C
H
H
H
H
H
H
+ 3H2

12. A table summarising the differences between thermal and catalytic cracking can is
shown below:
Type of cracking Thermal Catalytic
Conditions High temperature (400
– 900 o
C)
High pressure (70 atm)
High temperature (450
o
C)
Slight pressure ( > 1
atm)
Zeolite catalyst
Main products High percentage of
alkenes
Motor fuels (ie
branched alkanes)
Aromatic
hydrocarbons

13. Thermal and Catalytic cracking
click play to watch the short video

14. Uses of Alkanes

15. Alkanes as Fuel
■ They're (mostly) liquid at room temp
■ are chemically stable until ignited,
■ contain enormous amounts of energy,
■ burn relatively cleanly,
■ are easy to distill and process from the raw material,
■ and they literally flow out of the ground when you drill a well in the right place..

16. Alkanes as Solvents
Eg.
• Hexane and heptane are used as solvents in the manufacture of fast drying
lacquers, glues and other adhesives.
• Petroleum jelly is oil dissolved in paraffin wax (a solid alkane)

17. Biogas production
■ What is biogas?
■ It mainly comprises of hydro-carbon which is combustible and can produce heat and energy when
burnt. Bio-gas is produced through a bio-chemical process in which certain types of bacteria
convert the biological wastes into useful bio-gas. Since the useful gas originates from biological
process, it has been termed as bio-gas.
■ Methane gas (alkane) is the main constituent of biogas.

18. Biogas production process
■ The process of bio-gas production is anaerobic in nature and takes place in two
stages. The two stages have been termed as acid formation stage and methane
formation stage. In the acid formation stage, the bio-degradable complex organic
compounds present in the waste materials are acted upon by a group of acid
forming bacteria present in the dung. Since the organic acids are the main
products in this stage, it is known as acid forming stage. In the second stage,
groups of methanogenic bacteria act upon the organic acids to produce methane
gas.
■ Raw materials for biogas production
■ Although, cattle dung has been recognized as the chief raw material for bio-gas
plants, other materials like night-soil, poultry litter and agricultural wastes can also
be used.

19. Components and process of biogas plants
■ Mixing tank - The feed material (dung) is collected in the
mixing tank. Sufficient water is added and the material
is thoroughly mixed till a homogeneous slurry is formed.
■ Inlet pipe - The substrate is discharged into the digester
through the inlet pipe/tank.
■ Digester - The slurry is fermented inside the digester
and biogas is produced through bacterial action.
■ Gas holder or gas storage dome - The biogas gets
collected in the gas holder, which holds the gas until the
time of consumption.
■ Outlet pipe - The digested slurry is discharged into the
outlet tank either through the outlet pipe or the opening
provided in the digester.
■ Gas pipeline - The gas pipeline carries the gas to the
point of utilization, such as a stove or lamp.
■ Digestate- leftover indigestible material and dead
microorganisms that can be used as fertilizer

20. Advantages of biogas production
– It is a eco-friendly fuel.
– The required raw materials for biogas production are available abundantly in
villages.
– It not only produces biogas, but also gives us nutrient rich slurry that can be
used for crop production.
– It prevents the health hazards of smoke in poorly ventilated rural households
that use dung cake and fire-wood for cooking.
– It helps to keep the environment clean, as there would be no open heap of
dung or other waste materials that attract flies, insects and infections
– Availability of biogas would reduce the use of firewood and hence trees could
be saved.

21. Uses of alkenes
■ Uses of some polymers
– Polyethylene: Plastic – Bags – Bottles – Hoses.
– Polypropylene (pp): Carpets – Cases – Cans.
– Polyvinyl chloride (PVC): Drainage tubes – plastic tubes – shoes – Hoses –
Electrical wires insulators – Floors – oil bottles.
– Polytetrafluoro ethylene (Teflon): lining cooking utensils – surgical threads.

22. References
■ https://www.youtube.com/watch?v=Kn2oYEQzNH4
■ Tindale, Ritchie et al, 2014, Chemistry for CSEC 2nd Edition, Nelson Thornes.
Chapter 14, p239-245
■ https://www.facebook.com/engrandarch/posts/fractional-distillation-of-crude-
oilcrude-oil-enters-the-fractionating-column-as/426357158059810/
■ https://www.facebook.com/engrandarch/posts/fractional-distillation-of-crude-
oilcrude-oil-enters-the-fractionating-column-as/426357158059810/
■ https://www.youtube.com/watch?v=0WhOaiMYf2A
■ https://vikaspedia.in/energy/energy-production/bio-energy/biogas