What is Meant by Crude Petroleum? Discuss the Principle Steps in the Refining of Crude Petroleum

Types of liquid fuels

Primary liquid fuels

Natural liquid fuels

Secondary liquid fuels

Processed liquid fuels

Petroleum

Its colour, consistency and composition vary from place to place.
It mainly contains aliphatic hydrocarbons, cycloparaffins and hydrocarbons of aromatic series.
It also contains small quantities of nitrogen, oxygen or sulphur containing compounds.
Carbon content is about 83% to 87%.

Gasoline Its composition range is C₇ C₁₂. It is a suitable fuel for automobiles and aeroplanes.
Kerosene oil It composition range is C₁₂ to C₁₅. It is good fuel for stoves and Jet engines.
Diesel oil Its composition range is C₁₅ C₁₈. It is used in diesel engines.
Methylated spirit It is obtained from sugar or starch by germination. It contains ethyl alcohol and little methyl alcohol.

Advantages and disadvantages of liquid fuel

Advantages	Disadvantages
High calorific value	Expensive
It can be stored without any loss.	Storage is a problem
Firing and fire extinguishing easy processes.	Highly inflammable and so high risk of fire.

Petroleum

Petroleum is one of the most important liquid fuels in the world. It is the single largest liquid fuel which almost meets the requirements for various purposes.

In Latin ‘Petra’ means rock and ‘Oleum’ means oil. Hence, petroleum is also known as rock oil or mineral oil.
Petroleum is a dark viscous liquid found trapped in the Earths crust.
Its colour, consistency and composition vary from place to place.
It colour varies from white to amber, to greenish brown and to black.

Composition of petroleum

Crude petroleum is made up of hundreds of different individual chemical. Petroleum consists of liquid oils, hydrocarbon, substances like naturals gas, asphalt and waxes.

The average composition of crude petroleum is given as follows : C = 83 – 87%, H = 11- 15%, S= 0.16%, O= 0.3.5%

Origin of petroleum

It can be satisfactorily explained by the following three theories:
(a) Organic theory: It is formed by the decomposition of animal and vegetable matter in the Earth’s crust.
(b) Inorganic theory: It is resulted from the action of heavy metal carbides, existing in the interior of the Earth’s crust.

(c) Radioactive theory: It is formed by the help of radio-active rays emitted from radio-active substances present under the Earth’s earth crust.

Mining of petroleum

Petroleum occurs at different depths and at different places, varying from 500 to 1500ft.
It is brought to the surface by drilling holes to various depth under the ground and sinking pipes till the drill penetrates the oil-bearing sand.
The oil may flow out by itself due to hydrostatic pressure or the oil is mechanically pumped out.
The hydraulic rotary method is a very quick method for bringing oil to the surface.

Classification of petroleum

Crude petroleum is further classified into three types based on its composition.

Paraffin base petroleum	Asphaltic base petroleum	Mixed base petroleum
It contains hydrocarbons of paraffin series [CH₄to C₃₅ H₇₂]	It contains hydrocarbons of naphthalene ring (or) naphthalene products with side chains.	It contains both paraffinic and asphaltic hydrocarbons.
The paraffins present may be straight chain or branched chain.	It contain high percentage of cyclic compounds	It is also called as Intermediate base. It is are richer in semisolid waxes.
E.g: Pennsylvanian oil.	E.g: Californian oil	E.g: Mexican oil.

Refining of petroleum or crude oil

Crude petroleum is a starting material for the formation of various petroleum products such as motor spirit, petrol, diesel, kerosene oil etc.

The crude oil obtained from the Earth is a mixture of oil and unwanted impurities like water, sulphur compound and dirt particles. After the removal of all the impurities, the crude oil is subjected to fractional distillation.

The process of removing impurities and separating out the crude oil into various fractions having different boiling points is known as refining of petroleum.

First stage

The crude oil is brought to the surface and pumped under pressure into the cylindrical tanks.
The oil floats on the top layer.
Sand and water form the lower layer.
These two lower layers are withdrawn separately.

Second stage

Addition of copper oxide in the crude oil converts sulphur into CuSO₄ which can be removed by filtration.

Third stage

Crude petroleum is washed with acid and alkali solutions in order to remove the basic and acidic impurities. It is then subjected to fractional distillation.

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