Oil refining and its Products
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Petrol
and
Crude
Oil
Crude oil is separated by
fractional distillation
works because the
molecules have different
boiling/condensation
points
many of these
hydrocarbons are alkanes,
and are sorted into
fractions
each fraction has a range
of boiling points in the
distillation
narrow boiling ranges of
limited carbon number (eg
light gasoline is C5 to C7
boiling point 25C -75C)
Gasoline and gas oil fractions are sources
of petrol components
Naptha used for high grade petrol and
chemical feedstocks
Fractionation of Crude Oil
Fractions and their uses
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Refinery Gas (LPG)
Light Gasoline (Petrol)
Naphtha (Petrol)
Kerosene (Jet Fuel)
Gas Oil (Diesel Fuel)
Residue Fractions (Bitumen)
Natural Gas

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Natural gas is an extremely fuel both for
domestic and industrial use.
It is a mixture consisting mostly of methane,
CH4, (at least 85%), ethane, C2H6, (up to
10%) and small amounts of propane, C3H8,
and butane, C4H10.
Liquid Petroleum Gas (LPG)
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The gases in the refinery gas fraction are
bottled and sold for domestic use.
Propane and butane from this fraction can be
readily liquefied under pressure and are
referred to as liquid petroleum gas (LPG).
Mercaptans

Very smelly, organic sulfur compounds called
mercaptans are added to natural gas and
LPG so that leaks can be detected
Petrol Composition

Complex mixture of compounds
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Mainly Hydrocarbons
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Branched – chain alkanes
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Aromatic Compounds
Petrol in the Internal
Combustion Engine
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Vaporised
Mixed with air
Compressed
Ignited and burned
Gases produced expand
Kinetic Energy
Premature Ignition
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Problem: Auto-ignition (i.e. knocking or pinking)
Effects: a) Loss of power
b) Engine damage
Prevention: a) Additives
b) Use suitable mixtures of
high-octane compounds
Octane Rating

Measure of tendency to resist auto-ignite
or
Measure of tendency to cause knocking
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Low octane rating makes auto-ignition more
likely
Octane Rating
2,2,4-tri-methylpentane
Octane Number =100
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Heptane
Octane Number = 0
Additives
(i)
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(ii)
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Lead compounds e.g. tetra ethyl lead
Prevents reactions
Harmful environmental effects
Phased out in 2000
Oxygenates e.g. ROR orROR1 MTBE
Raise octane number
Cause less pollution
Mixture of compounds with
high octane numbers
Molecular features:
 Degree of branching – the more the better
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Chain length – the shorter the better
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Presence of rings – highly desirable
High octane numbers can be
obtained from low by:
1.
Isomerisation
2.
Dehydrocyclisation
3.
Catalytic cracking
All three methods involve the use of catalysts
Isomerisation
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Take a straight chain alkane e.g. pentane (O.N.62)
C─C─C─C─C
Heat in the presence of a catalyst
Chain breaks
Bits rejoin to form a branched compound e.g.2methylbutane (O.N.93)
C─C─C─C
│
C
Dehydrocyclisation
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Take a straight chain alkane e.g. hexane
(O.N. 25)
Catalyst causes change to a cycloalkane
(O.N. 83)
C6H14 → (CH2)6
+
H2
Catalyst causes the cycloalkane to change to
an aromatic compound e.g. benzene (O.N.
>100)
(CH2)6 → 3H2 + C6H6
Benzene
Catalytic Cracking
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Heavy oil e.g. kerosine or diesel
High temperature and catalyst
Molecule breaks into several smaller
molecules
Unsaturated products are used as feedstock
for the polymer industry
Saturated products are usually high octane
branched chain alkanes suitable for making
petrol
CH3 ─ (CH2)10 ─ CH3
↓
CH3
CH3
│
│
CH3 ─ CH ─ CH2 ─ CH ─ CH3
+
CH3
│
CH2 = C ─ CH2 ─ CH3