The various components of crude oil have different sizes, weights and boiling
temperatures; so, the first step is to separate these components. Because they
have different boiling temperatures, they can be separated easily by a process
called fractional distillation. The steps of fractional distillation are as
follows: fractional distillation
You heat the mixture of two or more substances (liquids) with
different boiling points to a high temperature. Heating is usually done with
high pressure steam to temperatures of about 1112 degrees Fahrenheit / 600
The mixture boils, forming vapor (gases); most substances go into
the vapor phase.
The vapor enters the bottom of a long column (fractional
distillation column) that is filled with trays or plates.
The trays have many holes or bubble caps (like a loosened cap on a
soda bottle) in them to allow the vapor to pass through.
The trays increase the contact time between the vapor and the liquids
in the column.
The trays help to collect liquids that form at various heights in the
There is a temperature difference across the column (hot at the
bottom, cool at the top).
The vapor rises in the column.
As the vapor rises through the trays in the column, it cools.
When a substance in the vapor reaches a height where the temperature of
the column is equal to that substance's boiling point, it will condense
to form a liquid. (The substance with the lowest boiling point will condense
at the highest point in the column; substances with higher boiling points
will condense lower in the column.).
The trays collect the various liquid fractions.
The collected liquid fractions may:
pass to condensers, which cool them further, and then go to storage
go to other areas for further chemical processing
Fractional distillation is useful for separating a mixture of substances with
narrow differences in boiling points, and is the most important step in the
The oil refining process starts with a fractional
distillation column. On the above you can see several chemical processors that
are described in the next section.