Refining Oil Made Simple
Name: Ken J.
Date: April 2003
A once popular TV show called "Mr. Wizard's World" aired
a program where "Mr. Wizard" (Don Herbert) showed a child how to refine
oil from crude using a very simple-looking, science fair-like rig.
Since that program, the boiler method of producing gasoline has been
altered dramatically with the advent of chemical catalysts.
Even though it is not recommended for one to do even small amounts of
gasoline refinement, could you at least tell how gasoline is currently
being made...if not tell of resources so that very small amounts could be
made for research/science fair/demonstration purposes?
Crude oil is made up of a large variety of hydrocarbons. They are usually classified by
molecular weight (how many carbons). Here is a VERY simplified example;
C=1 --> CH4 (methane)
C=2 --> C2H6 (ethane)
C=3 --> C3H8 (propane)
C=8 --> C8H18 (octane) ... and so on.
This large variety or spectrum of hydrocarbons gives rise to many different boiling point
temperatures for each molecule type. This is where the FRACTIONATING DISTILLATION COLUMN
comes into play. Chemical engineers and process engineers design huge fractionation towers
that have product outlet ports every "x number of feet", up from the bottom. They heat the
bottom of the tower and run coolant through the inside of the tower BUT NOT IN CONTACT WITH
THE OIL. The coolant line is isolated from the process line (oil line). They run the coolant
to create a temperature profile along the height of this tower. Each type of hydrocarbon has
its own specific boiling point, b.p. (methane's bp is lower than octane's b.p.). As the "mix"
moves up the column (temp. profile getting colder) the lower molecular weight molecules will
start to "dew" out and exit at each point. At the very top you will have lower molecular weight
fractions such as CH4, C2H6, etc...
Keep in mind that this is not very precise. They are many other compounds in crude oil than
just simple straight chained hydrocarbons. There is aromatic hydrocarbons, there can be some
sulphur compounds, etc...
You may ask, "OK, Fine. I want to have 1 litre of 99.999% pure hexane (C6H14)" You would have
to go to the product outlet port on the tower that is producing the highest fraction of C6H14
(which will also contain relatively high quantities of C5 and C7). Collect all of this product
and then run a separate continual fractionation of that until you get the desired purity of, in
this case, C6H14. It is this additional time and energy that explains why you might pay quite a
bit more for 99.999% product vs. 97% product.
Click here to return to the Engineering Archives
Update: June 2012