Petroleum is a naturally occurring flammable liquid consisting of hydrocarbons found underground. It is extracted through oil drilling and refined into many consumer products through fractional distillation. Crude oil varies in composition but largely includes paraffins, naphthenes, and aromatics. Octane and cetane ratings indicate gasoline and diesel fuels' resistance to knocking during combustion in engines. Synthetic petrol can also be produced through processes like Fischer-Tropsch that use coal, steam, and catalysts to synthesize hydrocarbon fuels.

1. Petroleum
• Petroleum (L. petroleum, from Latin: petra rock +
oleum oil or crude oil is a naturally occurring, toxic,
flammable liquid consisting of a complex mixture of
hydrocarbons of various molecular weights, and
other organic compounds, that are found in geologic
formations beneath the Earth's surface.
• Petroleum is recovered mostly through oil drilling.
• It is refined and separated, most easily by boiling
point, into a large number of consumer products,
from gasoline and kerosene to asphalt and chemical
reagents used to make plastics and
pharmaceuticals.

2. Petroleum-composition
• Petroleum includes only crude oil, but in common
usage it includes both crude oil and natural gas.
• Both crude oil and natural gas are predominantly a
mixture of hydrocarbons.
• Under surface pressure and temperature conditions,
the lighter hydrocarbons methane, ethane, propane
and butane occur as gases,
• while the heavier ones from pentane and up are in
the form of liquids or solids.
• However, in the underground oil reservoir the
proportion which is gas or liquid varies depending on
the subsurface conditions, and on the phase diagram
of the petroleum mixture.

3. Petroleum-composition
An oil well produces predominantly crude oil, with some
natural gas dissolved in it.
Because the pressure is lower at the surface than
underground, some of the gas will come out of
solution and be recovered (or burned) as associated
gas or solution gas.
A gas well produces predominately natural gas.
However, because the underground temperature and
pressure are higher than at the surface, the gas may
contain heavier hydrocarbons such as pentane,
hexane, and heptane in the gaseous state.
Under surface conditions these will condense out of the
gas and form natural gas condensate, often shortened
to condensate.
Condensate resembles gasoline in appearance and is
similar in composition to some volatile light crude oils.

4. Petroleum-composition
• The proportion of light hydrocarbons in the
petroleum mixture is highly variable between
different oil fields and ranges from as much as
97% by weight in the lighter oils to as little as 50%
in the heavier oils and bitumens.
• The hydrocarbons in crude oil are mostly alkanes,
cycloalkanes and various aromatic hydrocarbons
while the other organic compounds contain
nitrogen, oxygen and sulfur, and trace amounts of
metals such as iron, nickel, copper and vanadium.
•

5. Petroleum-composition
Composition by weight
• The exact molecular Element Percent range
composition varies widely from
Carbon 83 to 87%
formation to formation but the
proportion of chemical Hydrogen 10 to 14%
elements vary over fairly Nitrogen 0.1 to 2%
narrow limits as follows: Oxygen 0.1 to 1.5%
Sulfur 0.5 to 6%
Metals < 0.1%
• Four different types of
hydrocarbon molecules appear Composition by weight
in crude oil. The relative Hydrocarbon Average Range
percentage of each varies from
oil to oil, determining the Paraffins 30% 15 to 60%
properties of each oil. Naphthenes 49% 30 to 60%
Aromatics 15% 3 to 30%
Asphaltics 6% remainder

6. Distillation of crude oil
• An oil refinery or
petroleum refinery is
an industrial process
plant where crude oil is
processed and refined
into more useful
petroleum products,
such as gasoline,
diesel fuel, asphalt
base, heating oil,
kerosene, and
liquefied petroleum
gas.

7. Petroleum refinery

8. • Crude oil is separated into fractions by fractional distillation. The
fractions at the top of the fractionating column have lower boiling
points than the fractions at the bottom. The heavy bottom fractions
are often cracked into lighter, more useful products. All of the
fractions are processed further in other refining units

9. • Petroleum products are usually grouped into three categories: light distillates (LPG,
gasoline, naphtha), middle distillates (kerosene, diesel), heavy distillates and
residuum (heavy fuel oil, lubricating oils, wax, asphalt). This classification is based on
the way crude oil is distilled and separated into fractions
•

10. Octane number
• An octane number is a number which reflects a fuel's resistance to
knocking .
• The octane rating is a measure of the resistance of petrol and
other fuels to auto-ignition in spark-ignition internal combustion
engines.
• The octane number of a fuel is measured in a test engine, and is
defined by comparison with the mixture of 2,2,4-trimethylpentane
(iso-octane) and heptane which would have the same anti-knocking
capacity as the fuel under test: the percentage, by volume, of 2,2,4-
trimethylpentane in that mixture is the octane number of the fuel.
• A value used to indicate the resistance of a motor fuel to knock.
Octane numbers are based on a scale on which isooctane is 100
(minimal knock) and heptane is 0 (bad knock).
•

11. Cetane Number
• Cetane number or CN is a measurement of the combustion quality
of diesel fuel during compression ignition. It is a significant
expression of diesel fuel quality among a number of other
measurements that determine overall diesel fuel quality.
• Cetane number is actually a measure of a fuel's ignition delay; the
time period between the start of injection and start of combustion
(ignition) of the fuel.
• Cetane numbers are only used for the relatively light distillate diesel
oils.
• Generally, diesel engines run well with a CN from 40 to 55. Fuels
with higher cetane number which have shorter ignition delays
provide more time for the fuel combustion process to be completed.

12. Synthetic petrol
• The petrol obtained artificially from coal as a mixture of alkanes
resembling petroleum like aliphatic hydrocarbon fuels is called
synthetic petrol.
• Two important methods for producing synthetic petrol are the
Fischer-Tropsch process and the Bergius process.
• In Bergius process, powdered coal is mixed with heavy oil and
heated with hydrogen under high pressure (200-250 atm) at about
748 K in presence of iron oxide as catalyst.
• The vapours on condensation give a liquid resembling crude oil.
This is called synthetic petroleum, which on fractional distillation
gives petrol (gasoline).

13. Synthetic petrol
• In this process, a mixture of water gas and
hydrogen under pressure (5-10 atm) is passed
over a cobalt catalyst at 450 - 475 K. The water
gas required is obtained by passing steam over
red-hot coke.
• C(red hot) + H2O(g) CO + H2 water gas
•
• The product so obtained is fractionally distilled
to obtain petrol, middle oil and heavy oil. Further
hydrogenation of the middle oil fraction then
produces petrol.