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Distillation
101
Distillation
is the process used to separate the substances composing a mixture. It involves
a change of state, that of a liquid to gas, and then the subsequent condensation
back to a liquid. Refined methods
of distillation are used in many industries, including petroleum and petro-chemical
industries.
The
Basic Distillation Process
A
simple distillation apparatus consists essentially of three parts:
Ř
a
flask, known as the “Pot”, equipped with a thermometer and with an outlet
tube from which the vapor is emitted when heated;
Ř
a
condenser that consists of two tubes of different diameters placed one within
the other and so arranged that the smaller (in which the vapor is condensed) is
held in a stream of coolant in the larger; and
Ř
a
“Receiver” is a vessel in which the condensed vapor is collected.
The
mixture of substances is placed in the flask and heated. Ideally, the substance
with the lowest boiling point vaporizes first, the temperature remaining
constant until that substance has completely distilled. The vapor is led into
the condenser where, on being cooled, it reverts back to the liquid (condenses)
and runs off into the receiver. The product so obtained is known as the
distillate. Those substances having a higher boiling point remain in the flask
and constitute the residue.
The
Fractional Distillation Process
When
the substance with the lowest boiling point has been removed, the temperature
can then be raised and the distillation process repeated with the substance
having the next lowest boiling point. The process of obtaining portions (or
fractions) in this way is one type of fractional distillation. A more efficient
method of fractional distillation involves placing a vertical tube called a
fractionating column between the flask and the condenser. This column serves to
increase the surface area on which the liquid can condense. A packing may be
added to the column to further increase this surface area. The vapors condense
in the column, then are re-evaporated as they move towards the top, effectively
distilling the vapor many times. The less volatile substances in the vapor tend
to run back down the column after they condense, concentrating themselves near
the bottom. The more volatile ones tend to re-evaporate and keep moving upward,
concentrating themselves near the top. Because of this the column can be tapped
at various levels to draw off different fractions. Fractional distillation is
commonly used in refining petroleum. Some
of the fractions obtained are gasoline, kerosene, fuel oils, lubricating oils,
and paraffins.
Fractionation
distillation is used to separate crude oil using atmospheric and vacuum
distillation towers to produce groups of hydrocarbon compounds of differing
boiling-point ranges, called fractions or cuts.
Atmospheric
Distillation
The first rough distillation cut. As
an example, crude oil is heated at atmospheric pressure.
The atmospheric distillation column separates the crude oil into lighter
products; i.e. gasoline, kerosene, naphtha, etc.
The lighter products produced in this process are further refined in the
catalytic cracking unit and/or the reforming unit.
Heavier
products that cannot be vaporized and separated in this process are distilled
further in the vacuum distillation unit.
Vacuum
Distillation
The process of
distillation employing a vacuum, which lowers the pressure on the liquid thus
allowing volatilization at a lower
temperature than under normal atmospheric pressure. The heavier cuts of crude, such as: lubricants, asphalt, residual coker feedstocks, cracking
feedstocks, etc. are fractionated in this process.
Podbielniak
analysis [POD analysis] This is a semi-automated distillation unit that
is capable of performing both atmospheric and vacuum distillations. The unit can
be configured for a wide variety of conditions and is capable of extracting
extremely narrow fractions, or cuts, from the feedstock. The pot is a small as
5L and can be as large as 20L. This unit can be used to produce quantities large
enough for pilot scale operation.
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101
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laboratory uses the methods and standards of these organizations
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For detailed information see the ASTM website at: http://www.ASTM.ORG
And The SAE [Society of Automotive Engineers]
standards.
For detailed information see the SAE website at:
http://www.SAE.ORG
the American
Petroleum Institute [API]
and/or
established industry standards.
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