Petroleum is a complex mixture of hydrocarbons and other compounds that varies in composition depending on its source. It is a thick, brown liquid found below the earth's surface. Refining petroleum involves separating it into fractions of different boiling points and removing impurities through fractional distillation. In fractional distillation, the mixture is heated and different compounds condense out of the vapor at different levels in the distillation tower based on their boiling points. Over 500 compounds can be obtained through petroleum distillation.

1. EHTISHAM UL HAQ

2. Petroleum is a complex mixture of
hydrocarbons and a number of different
compounds whose composition varies
according to its place of occurrence.

3. The word PETROLEUM is composed of two Latin
words Petra means rock and oleum means oil.
Petroleum is a dark brown, thick and viscous liquid
which occurs below the earth's surface. Petroleum
is a complex mixture of hydrocarbons and different
compounds of sulphur, oxygen and nitrogen in
small amounts. Usually it contains alkanes, alkenes,
cyclo alkanes, aromatic hydrocarbons etc.

4. The process of dividing petroleum into
fractions with different boiling range
volatilities and free from impurities is called
refining.
Petroleum is refined by fractional distillation.

5. The process of separating a mixture into a
series of fractions of different volatilities by
means of distillation is known as fractional
distillation.
In the process of fractional distillation, a
mixture of different liquids is evaporated
followed by condensation. Different liquids are
evaporated according to their boiling point and
they are collected in different chambers of
distillation tower.

6. Generally crude oil contains compounds having
boiling points upto 400 OC. In this process,
crude oil is heated to above 400OC in a pipe.
Its vapors are allowed to enter into a
fractionating tower having different
compartment to collect different volatilities.
These are now condensed to liquid and are
separated.

8. More than 500 different compounds are
obtained in the process of the distillation of
petroleum as shown in the table.

9. Gasoline which is commonly known as petrol is
a mixture of n-hexane and n-heptane. During
the process of fractional distillation, it is
obtained in the upper most portion of the
tower.

10. Octane number is a standard which
determines the knocking ability and quality of
gasoline. Higher is the octane number of a
gasoline, lower is the knocking it produces.
Octane number can be increased by the
following two methods:
Reforming
By adding TEL (tetraethyl lead)

11. Knocking is a sharp metallic sound produced in
the internal combustion engine. Knocking is
caused by the low octane number of gasoline.

12. The conversion of straight chain hydrocarbon into
branched chain hydrocarbon is called reforming of
petroleum.
By the process of reforming, the octane number of a
gasoline is improved. The process of reforming is
carried out in the presence of catalyst
n-alkanes burn in internal combustion engine with
explosion and produce knocking but branched chain
hydrocarbons burn smoothly.
Reforming is a process similar to cracking, which
converts n-alkanes into branched alkanes.
The octane number of gasoline may also be improved
by adding tetraethyl lead (TEL) Pb(C2H5)4 which is a
knock inhibitor. But the use of compounds containing
lead cause environment pollution.