Hydrocarbons as Fuels OCR AS chemistry

OCR AS chemistry module 2

 -hydrocarbons as fuels brief word notes

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Hydrocarbons as Fuels
ALKANES: Hydrocarbons as Fuels
A Hydrocarbon is a compound of hydrogen and carbon only.
The physical states of alkanes at room temperatures and pressure change, from
gases to liquids, to solids, as the number of carbon atoms in the alkane molecule
increases.
This is the same as saying that: the volatility of alkanes decreases with the number of
carbon atoms in the alkane molecule.
Volatility is the ease with which a liquid turns to vapour
Crude Oil
Crude oil is a complex mixture of hydrocarbons
The composition of oil from different places varies considerably
Three main types present: arenes, cycloalkanes and alkanes.
Arenes are hydrocarbons containing one or more benzene rings
At a given boiling point, the densities of these decrease in, the order of arenes >
cycloalkanes > alkanes.
This provides us with a method of comparing the compositions of different oils.
The fossil deposits of crude oil and natural gas have been the primary sources of
alkanes since the 20th century.
Much of the wealth of the modern world can be ascribed to the exploitation of this
natural resource.
The vast majority provide us with heating, fuel and electricity
Smaller less significant numbers have been able to provide us with lubricants and to
provide as source of hydrocarbons for the chemical process industry.
However the burning of fossil fuels can be harmful to the environment and must be
addressed urgently.
Separating the hydrocarbons in crude oil
Firstly the crude oil is broken down into fractions
This is known as fractional distillation ­ it relies on differences in boiling points of
different molecules of the liquid
Usually each mixture contains a range of hydrocarbons and with fractional distillation
can be separated on their boiling point differences
It can be useful even if the boiling points of the hydrocarbons are low
Further distillation processes can be used to further separate the hydrocarbons into
fractions

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Hydrocarbons as Fuels
Crude oil must be vaporised
before it enters the fractional
distillation column
This is usually achieved when
crude oil is passed through
pipes in a furnace where oil is
heated to above 350 degrees
Celsius
The resulting mixture is fed
into the distillation column and
dived by a number of steel
trays.
Vapour passes up the column
through the trays while liquid
flows down the column from
the tray to tray over a "weir".…read more

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Hydrocarbons as Fuels
This enables the various fractions to be drawn from the column at approximate
points.
An individual tray will contain a mixture of hydrocarbons with quite a narrow range of
boiling points
A fractional distillation column is designed to separate crude oil into several fractions.
These include refinery gases, gasoline, naphtha, kerosene, gas oil (diesel oil), and
residue. Shown in the diagrams.
Further treatment
After distillation, the different hydrocarbon fractions are treated in a variety of ways.…read more

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Hydrocarbons as Fuels
Spillage of fuel causes grave damage to the environment which range from pollution
to immense loss of animal life…read more

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nirjala

thank you just what i was looking for :)

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