The residue from this distillation is then ready for further processing.
NOTE: At atmospheric pressure, crude oil boils at 150, 450ƒ, 750ƒ, and 950ƒF. Each of those boiling points
produces vapors of different hydrocarbon molecules or "fractions." This is the theory behind factional
b. The residue from the first distillation undergoes a second distillation process which is performed in a
vacuum because of the extreme temperatures needed to separate the remaining fractions. If the distillation was
carried out under atmospheric pressure, the temperatures required to separate the remaining fractions would result
in hydrocarbon molecules being "racked," which is not desired at this time. The vacuum distillation produces
fractions that are used in the following petroleum products:
(1) Lubricating oils.
(3) The residue from this process is known as residuum and is processed as residual fuel oils.
(4) Depending on the desired product each of the fractions may undergo more distillations in the
The absorption process uses an absorption material to absorb unwanted compounds and allows the remaining
compounds to be separated.
a. The oil to be treated is pumped into an absorption tower.
b. The oil passes through the absorption material, which absorbs the unwanted compounds such as
c. The absorption material can be treated to remove the unwanted compounds and used again.
d. The remaining oil will go to another distillation tower for further processing.
This process is similar to absorption, but uses a liquid solvent to extract hydrocarbon compounds. Solvent
extraction is used in refining lubricating oils and other oils for specialized purposes. Solvent extraction is also
used for separating specific compounds such as bezene, toluene, and xylene from complex mixtures.
a. The solvent is mixed with the oil to be processed and is allowed to react with the oil.
b. The mixture is separated into two fractions.
(1) That portion of the oil which remains undissolved and is not removed by the selective solvent is
called raffinate and is processed as lubricating oils.