How Oil Refining Works

By: Craig Freudenrich, Ph.D.

From Crude Oil

The oil refining process starts with a fractional distillation column.

The problem with crude oil is that it contains hundreds of different types of hydrocarbons all mixed together. You have to separate the different types of hydrocarbons to have anything useful. Fortunately there is an easy way to separate things, and this is what oil refining is all about.


Different hydrocarbon chain lengths all have progressively higher boiling points, so they can all be separated by distillation. This is what happens in an oil refinery - in one part of the process, crude oil is heated and the different chains are pulled out by their vaporization temperatures. Each different chain length has a different property that makes it useful in a different way.

To understand the diversity contained in crude oil, and to understand why refining crude oil is so important in our society, look through the following list of products that come from crude oil:

Petroleum gas - used for heating, cooking, making plastics

  • small alkanes (1 to 4 carbon atoms)
  • commonly known by the names methane, ethane, propane, butane
  • boiling range = less than 104 degrees Fahrenheit / 40 degrees Celsius
  • often liquified under pressure to create LPG (liquified petroleum gas)

Naphtha or Ligroin - intermediate that will be further processed to make gasoline

  • mix of 5 to 9 carbon atom alkanes
  • boiling range = 140 to 212 degrees Fahrenheit / 60 to 100 degrees Celsius

Gasoline - motor fuel

  • liquid
  • mix of alkanes and cycloalkanes (5 to 12 carbon atoms)
  • boiling range = 104 to 401 degrees Fahrenheit / 40 to 205 degrees Celsius

Kerosene - fuel for jet engines and tractors; starting material for making other products

  • liquid
  • mix of alkanes (10 to 18 carbons) and aromatics
  • boiling range = 350 to 617 degrees Fahrenheit / 175 to 325 degrees Celsius

Gas oil or Diesel distillate - used for diesel fuel and heating oil; starting material for making other products

  • liquid
  • alkanes containing 12 or more carbon atoms
  • boiling range = 482 to 662 degrees Fahrenheit / 250 to 350 degrees Celsius

Lubricating oil - used for motor oil, grease, other lubricants

  • liquid
  • long chain (20 to 50 carbon atoms) alkanes, cycloalkanes, aromatics
  • boiling range = 572 to 700 degrees Fahrenheit / 300 to 370 degrees Celsius

Heavy gas or Fuel oil - used for industrial fuel; starting material for making other products

  • liquid
  • long chain (20 to 70 carbon atoms) alkanes, cycloalkanes, aromatics
  • boiling range = 700 to 1112 degrees Fahrenheit / 370 to 600 degrees Celsius

Residuals - coke, asphalt, tar, waxes; starting material for making other products

  • solid
  • multiple-ringed compounds with 70 or more carbon atoms
  • boiling range = greater than 1112 degrees Fahrenheit / 600 degrees Celsius

You may have noticed that all of these products have different sizes and boiling ranges. Chemists take advantage of these properties when refining oil. Look at the next section to find out the details of this fascinating process.

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